• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Background and review: Alternative...
 Methodology
 Analysis of data
 Results and discussion
 Conclusions and recommendations...
 Reference
 Biographical sketch














Group Title: UFLCOEL-97007
Title: Analysis of conventional aerial photography to determine shoreline position
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00091093/00001
 Material Information
Title: Analysis of conventional aerial photography to determine shoreline position
Series Title: UFLCOEL-97007
Physical Description: x, 60 leaves : ill., maps ; 28 cm.
Language: English
Creator: Kreuzkamp, August Joseph, 1970-
University of Florida -- Coastal and Oceanographic Engineering Dept
Publisher: Coastal & Oceanographic Engineering Dept., University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1997
 Subjects
Subject: Aerial photography in hydraulic engineering -- Florida -- Lee County   ( lcsh )
Coastal engineering -- Florida -- Lee County   ( lcsh )
Beach nourishment -- Florida -- Lee County   ( lcsh )
Coastal zone management -- Florida -- Lee County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis (M.E.)--University of Florida, 1997.
Bibliography: Includes bibliographical references (leaves 58-59).
Statement of Responsibility: by August Joseph Kreuzkamp III.
 Record Information
Bibliographic ID: UF00091093
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 37857027

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page i
    Acknowledgement
        Page ii
        Page iii
    Table of Contents
        Page iv
        Page v
    List of Tables
        Page vi
    List of Figures
        Page vii
        Page viii
    Abstract
        Page ix
        Page x
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Background and review: Alternative methods used to decipher the shoreline position
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Methodology
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
    Analysis of data
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
    Results and discussion
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
    Conclusions and recommendations for further study
        Page 55a
        Page 56
        Page 57
    Reference
        Page 58
        Page 59
    Biographical sketch
        Page 60
Full Text




UFL/COEL-97/007


ANALYSIS OF CONVENTIONAL AERIAL
PHOTOGRAPHY TO DETERMINE SHORELINE
POSITION






by



August Joseph Kreuzkamp III




Thesis


1997
















ANALYSIS OF CONVENTIONAL AERIAL PHOTOGRAPHY TO DETERMINE
SHORELINE POSITION








By

AUGUST JOSEPH KREUZKAMP mI


A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF
FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF
MASTER OF ENGINEERING


UNIVERSITY OF FLORIDA


1997














ACKNOWLEDGMENTS


I would like to express my gratitude to Dr. Robert G. Dean who acted as both my

advisor and supervisory committee chairman. I would also like to thank the members of

my committee, Dr. Ashish J. Mehta and Dr. D. Max Sheppard for helping me follow

through with my research.

I have really enjoyed my past two years at the University of Florida with much due

credit to the staff and students of the Coastal and Oceanographic Engineering Department.

The department has been much like a family in the classroom, outside at the beach doing

fieldwork and at the stadium cheering on the national champion Florida Gators. My

brothers and sisters include Marshall, Paul, Wally, Jie, Rob, Cindy, Pete, Mike, Bill, Mark,

Hugo, Eric, Chris, Kerry Anne, Greg, Al, Craig, Helen, Becky and Terry. I wish all of

them well in there future endeavors and hope at least some of them finish their graduate

work before my children go to college.

Friends and family have always been important to me and are to whom I attribute

my success. The boys who grew up down in the Knight's basement including Ed, Ullman,

Trev, Bri, Rich and Nick are the ones responsible for tearing my knee, giving me a

concussion and being my oldest and dearest friends. My college sailing friends including

Eric M., Barr, Wilson, Erick S., Chad, Paul, John and Heather are the ones who showed

me that nothing is as important as sailing, friendship and coubelibres. My life-long friend,








Marc Fermanian, who has shown me that the right answer is all that really counts, in every

aspect of life. My grandmother, who has been a true inspiration to me over the past many

years, has proved that perseverance and internal strength can overcome any obstacle. My

parents, who have always been there for me, deserve more praise and accolades than I

could ever give. They are truly the most giving people I have ever known.

The final thank you goes to my wife, Kristen, who will always be my best friend

and soul mate. I did this for you.















TABLE OF CONTENTS
Pag=

ACKNOWLEDGEMENTS ............................................ ............. ii

LIST OF TABLES ............................................ ........................ vi

LIST OF FIGURES ........................................................ vii

CHAPTERS

1 INTRODUCTION .................................................................... 1

2 BACKGROUND AND REVIEW: ALTERNATIVE METHODS USED
TO DECIPHER THE SHORELINE POSITION ................................. 5

Introduction .......................................... .......................... 5
Factors Limiting the Accuracy of Aerial Photography ........................... 6
Point Measurements .......................................... ................ 9
Photo Enlargements (Orthogonal Grid Matrix System) ...................... 10
Zoom Transfer Scope ........................................... .......... ... 10
Analytical Stereoplotters ....................................... ......... .. 11
Metric Mapping ............................................... ................ 13
Airborne Laser Swath Mapping ..................................... ........ 13

3 METHODOLOGY ............................................................ 15

Ground Truth .................................................................. 15
Aerial Photographs ............................................................ 19
Shoreline Location ............................................. ............... 22
Digitizing Photographs .......................................... .......... ... 26

4 ANALYSIS OF DATA ......................................... ............. 31

Calculations .................................................. .................. 31
M ethod of Analysis ................................................................. .... 33








5 RESULTS AND DISCUSSION ................................................... 38

Shoreline Position Error ..................................... ............ ... 38
Shoreline Change Error ............................................ ........... 44
Sources of Error ..................................................................... 48
Error Analysis ..................................................................... 51
Improvements .................................................. .................. 52

6 CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER
ST U D Y : ............................................................................ .. 55

Summary ..................................................... .................. 55
Recommendations for Further Study ............................................ 57

REFERENCES .................................................... ................... 58

BIOGRAPHICAL SKETCH ....................................... ......... .. 60














LIST OF TABLES


Table Page

3-1: Dates ground and aerial surveys were performed ........................... 19

3-2: Flight and equipment information .............................................. 20

4-1: Sample data set for Routine #1 ................................................. 35

4-2: Sample data set for Routine #2 ................................................. 36

4-3: Sample data set for Routine #3 .............................................. 37

5-1: Summary error results for each aerial survey by island .................... 40

5-2: Potential errors due to camera tilt ............................................ 50














LIST OF FIGURES


Figure rag

1-1: Vicinity map of Lee County, Florida ................................... 5

2-1: Comparison of orthogonal vs. tilted Images .................................. 7

2-2: Geometry of a tilted photograph showing the principal line ................ 8

2-3: Tilt displacement in the principal plane of a tilted photograph ............... 9

2-4: Correcting for tilt distortion ................... .......................... ... 11

3-1: Profile locations on Captiva Island ........................ ............. .. 17

3-2: Sample profiles taken at R-088 ........................................... 18

3-3: Tidal prediction near Estero Island, Florida 2/04/96 2/06/96 ............. 21

3-4: Tidal prediction near Estero Island, Florida 8/25/96 ........................... 22

3-5a: Aerial photograph taken August 25, 1996 at the south end of Gasparilla
Is. with evidence of runup ................ .................... ............. .. 25

3-5b: Aerial photograph taken August 25, 1996 at the north end of Lacosta Is.
with no sign of runup ............................................... ................ 25

3-6: AutoCAD display window showing a portion of the base map of
Captiva Island .............. ........................... ....................... 28

3-7: AutoCAD display window showing the composite map of Captiva
Island being assembled ............................................. ......... 29

4-1: Normal distribution curve ................................................ 33

4-2: Sample histogram ........................................... .......... .... 34

5-1: Comparison of uncorrected data sets .......................................... 39









5-2: Comparison of uncorrected data sets excluding problem areas ............. 41

5-3: Comparison of results determined by applying various computations
to all February data (including problem areas) ................................. 42

5-4: Comparison of results determined by applying various computations
to all August data (including problem areas) ...................................42

5-5: Comparison of accuracy obtained between the two aerial surveys ........ 43

5-6: Comparison of shoreline changes for the entire county .......................44

5-7: Comparison of shoreline changes for the entire county excluding
nourished areas .................. .................... .. .......... ............. 45

5-8: Comparison of shoreline changes at profiled locations excluding
nourished areas .............................................. .............. 46

5-9: Comparison of shoreline changes at profiled locations within nourished
areas ........................................ ....... ... ............. 47

5-10: Comparison of shoreline changes determined from sequential ground
surveys ............................................. .. ................. ... 51













Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering

ANALYSIS OF CONVENTIONAL AERIAL PHOTOGRAPHY TO DETERMININE
SHORELINE POSITION
By

August Joseph Kreuzkamp II

August 1997

Chairman: Dr. Robert G. Dean
Major Department: Coastal and Oceanographic Engineering

The outer coastline of Lee County, Florida, consists of a series of eight barrier

islands all of which experience episodic erosion due to storms and portions of which are

subject to long term erosional trends. With such a dynamic and valuable shoreline, the

county has participated in actions to maintain portions of the shoreline by nourishment. In

the process of maintaining the coastline, monitoring the shoreline position would be quite

expensive and time consuming by ground survey alone.

In an attempt to devise an efficient and relatively inexpensive monitoring method, a

technique was developed based on aerial photography. This technique incorporated

digitizing current aerial photography and referencing State of Florida Coastal Construction

Control Line photos to create a composite map providing a continuous shoreline for each

aerial survey performed. From this composite map, the change in shoreline position was

obtained with reference to the coordinates of each DNR monument located throughout








the county. Ground truth surveys were performed as soon before and after the aerial

photographs as possible and used later to adjust the data and evaluate the method.

Throughout the process of refining this method, several developments were made

which were found to produce more reliable data. The improvements included specifying

larger scale aerial photographs, setting visual targets over known coordinates and

coordinating the aerial survey with high tide. The best accuracy for this method was

found to be approximately 11 feet for specific areas. The results for this six month study

indicate that the average shoreline had accreted approximately 9 feet ( 3 feet) due

primarily to nourishment projects that occurred in the interim of this study. After the

nourished areas were excluded from the sampling, the average natural shoreline was found

to have eroded approximately 7 feet (3 feet). In considering these results, it is necessary

to note that the period over which these results were obtained reflects the effects of

individual storms rather than an erosional trend.

The best application for this method would be to evaluate overall annual shoreline

changes, monitor the performance of beach nourishment projects and evaluate coastal

damage due to large storms. The effectiveness of this program and the improved

reliability of its results would require the refinements already developed to be continued

and further progress to be made to minimize the remaining distortion in the photographs

which could not be avoided with the equipment used.














CHAPTER 1
INTRODUCTION



The nearshore area is very dynamic due to the large amounts of wave and current

energy that must be dissipated in a relatively small region. Relevant factors affecting

nearshore dynamics include sand grain size, incident wave direction and height, nearshore

bathymetry, and impacts of inlets and man-made structures. Particularly in regions with

unstable shorelines, it is important to document accurately the position of the shoreline at

strategic time intervals in order to identify overall trends in shoreline change and anomalies

caused by significant storms. Ground survey work has always been found to be the most

reliable in monitoring shoreline position while also being the most time consuming and

costly (Dolan et al, 1978). This has forced groups including the project sponsor (Lee

County, Florida) who work with a limited budget to consider other techniques including

aerial photography to track migrating shorelines.

Aerial photography was first utilized to determine shoreline change in coastal

regions in the late 1960s (Stafford and Langfelder, 1971). Aerial photography provides

the needed coverage and detail required for long shoreline segments at a fraction of the

time and expense associated with maps created from ground survey work. Aerial surveys

can be employed in several applications including developing sediment budgets,

monitoring beach nourishment projects, and observing the effects of coastal structures or








inlets on an immediate area. Unfortunately, the location of an object found in an aerial

photographs is somewhat misrepresented due to various distortions that exist in aerial

photography. Through the years technology has played a major role in improving the

accuracy of these shoreline positions by utilizing various equipment and techniques in an

attempt to minimize the amount of error associated with aerial photographs.

Developments in lens manufacturing has greatly reduced photographic distortions

as rectification equipment including zoom transfer scopes, space resection programs and

analytical stereoplotters. Each piece of equipment and/or software has had varied levels of

success in correcting the distortion in photographs caused by plane pitch and roll, change

in altitude, relief displacement and radial scale variations. The most effective rectification

equipment, analytical stereoplotters, can correct near-vertical or even terrestrial

(horizontal) photographs; however, the relatively high costs may be beyond the means of

various entities with shoreline monitoring responsibilities.

The project area lies in Lee County, in Southwest Florida, and consists of

approximately 40 miles of active coastline on the Gulf of Mexico. This area is comprised

of eight barrier islands which require periodic monitoring in order to document shoreline

changes associated with past and present nourishment projects as well as natural shoreline

evolution. The method of obtaining the shoreline positions for this region involved

digitizing features from uncorrected aerial photographs including the identified shoreline

based on local indicators seen in the photographs. The digitized images were next

combined into a composite map from which the shoreline position could be recalled from

any chosen reference. The acquired shoreline positions to better conform with the

shoreline positions was then adjusted determined from the ground surveys. Due to the





3


areal extent of the project area and the amount of data collected, Captiva Island was

chosen as the region of focus in the main body of this paper to show meaningful examples

with a reasonable amount of graphics and tables.














ASPARLULA
ISLAND CHARLOTE

HARBOR


LACOSTA
ISLAND


0
C.


O-ARLOTIE COUNTY
LEE COUNTY







NORTH '


CAPIVA
ISLAND


ESTERO
ISLAND


0,
0


LOVR'S


GENERAL MAP


0 4 8 MILES
i i-'-


w


LABAMA


NORTH


0


STUDY AREA /
LEE COUNTY, FLORIDA -

KEY WEST


VICINITY MAP

0 160 320 MILES



















LEE COUNTY
COVER COUNTY


FIGURE 1-1 Lee County,


MFMI


Florida














CHAPTER 2
BACKGROUND AND REVIEW: ALTERNATIVE METHODS USED TO DECIPHER
THE SHORELINE POSITION



2.1 Introduction

Aerial photography first originated in the mid-1800s using cameras mounted on

balloons and kites. With the invention of the airplane in 1902, it was not until 1913 that

the airplane was first used for aerial photography for mapping purposes. The use of aerial

photography was expanded during World War I (1914-1918) when its application for

reconnaissance was recognized and later during World War II (1939-1945) when

reasonably high quality stereo vertical (aerial) photographs were developed. Since that

time, a multitude of technological advancements in equipment and technique have been

made to advance the accuracy of aerial photography (Wolf, 1983).

While aerial photographs contain large quantities of information, they also include

a variety of distortions, which leads to their inaccuracy if left uncorrected. The distortions

include those caused by: changes in the camera's altitude, changes in tilt and pitch of the

aircraft, radial scale variations, and relief variations of the surface photographed.

Researchers attempting to determine historic erosion rates found that vertical photographs

dating as far back as the 1930's were a more reliable source for shoreline position when

compared with shoreline maps established during the same era (Crowell et al, 1991).

These researchers developed different techniques to extract the shoreline position from








vertical photographs with varying levels of success in terms of their accuracy. Ironically,

only a few authors actually discuss the errors associated with their work which

complicates matters when attempting to compare the accuracy of alternate methods

(Dolan et al., 1978; Anders and Byrnes, 1991).



2.2 Factors Limiting the Accuracy of Aerial Photography

There are several factors which limit the precision of locating points which are

photographed from a skewed or moving platform. The following are factors which cause

changes in scale between sequential photographs or within the same photograph.

Changes in camera altitude will cause an aerial photograph to have a unique scale

compared to others taken previously or subsequently after any photograph. This is very

common in smaller aircraft which are more susceptible to wind gusts. The scale of a

photograph, S is calculated by dividing the focal length of a camera, f by the altitude

flown, H.

S=f (2-1)
H

Tilt of an aircraft will create a scale variation within each photograph that is not

easy to correct due to its non-linear properties shown in Figure 2-1. Two important terms

which must be defined are the principal line and isocenter of a photograph. Referring to

Figure 2-2, vertical plane Lno is defined as the "principal plane". The intersection of the

principal plane and the plane of the tilted photograph is the principal line labeled no. The

isocenter of a tilted photograph, I, is located at the bisector of where the plane of the tilted










NO TILT




AXIS
OF
TILT


ORTHOGONAL IMAGE


WITH TILT


1"-3" (TYP.)

SAXIS
OF
TILT







TILTED IMAGE


FIGURE 2-1 Comparison of orthogonal vs. tilted images (Leatherman, 1983)



photo intersects the plane of the theoretical vertical photo shown in Figure 2-3. Based on

the geometry of Figure 2-3, Equation 2-2 represents the displacement error, dt, caused by

airplane tilt, t.


(2-2)


r2 sin tcos2 P
dtf r
f rsin tcos P


Defining the radial distance from the isocenter of the photograph to the point of interest

represented as r, camera focal length (f) tilt angle (t) and the angle measured from the

principal line to the radial line between the isocenter and the point of interest (P). Once dt

is calculated, the scale of the photograph is taken into account to convert the error to

ground dimensions (Wolf, 1983).

Objects away from the isocenter of a frame will cause an increase in radial scale

variations. Refinements in lens manufacturing have helped to minimize this effect (Clow

and Leatherman, 1984).






































FIGURE 2-2 Geometry of a tilted photograph showing the principal line (Wolf, 1983)



Different elevations in the surface photographed will cause a relief displacement.

In essence, objects rising above the average land elevation will be displaced outward from

the photo's isocenter while objects below the average grade will be displaced inward of

the photo's isocenter. Due to the fact that most of the coastal features in the project area

had low relief, radial distortion due to elevation differences is considered minimal.

















OF TILTED PHOTO


FIGURE 2-3 Tilt displacement in the principal plane of a tilted photograph (Wolf, 1983)



2.3 Point Measurements

Utilizing historical aerial photographs, Stafford and Langfelder (1971) developed a

method to determine the historical coastal erosion along the Outer Banks of North

Carolina. Shoreline positions were found by taking point measurements perpendicular to

the shore from stable reference points. Distortion due to plane tilt was minimized by

utilizing only the central portion of each photograph and by applying a unique scale to

each photograph. Stafford and Langfelder were also able to minimize the inherent change

in scale between photographs caused by altitude changes by grouping beach widths taken


NADIR








from the same photographs and then, after determining the scale for each photograph, the

beach widths could be modified. The final product became a data base of beach widths

which were compared with beach width data taken from other surveys in the same area.



2.4 Photo Enlargements (Orthogonal Grid Matrix System)

Based on the work of Stafford and Langfelder, Dolan et al (1978) were able to

document and compare continuous shoreline positions on drafted maps to determine rates

of erosion. Their method, called the orthogonal grid matrix system (OGMS), involved

using a projecting light table to superimpose photo images to the approximate scale of a

base map and manually traces the shoreline onto a USGS "T-Sheet" (topographic map).

Changing the scale of the projected images once again helped eliminate errors associated

with the change in camera altitude. Once all of the shorelines were traced onto one

common base map, beach widths were measured at 100 meter intervals. Maps were then

recreated from this data but could not reflect the same completeness as the original base

map. Although a portion of distortion was eliminated by maintaining a constant scale

throughout entire sets of photos with this method, no attempt was made to eliminate the

distortion due to plane tilt. The documented accuracy of the OGMS method was 6.3

meters (Dolan et al., 1978).



2.5 Zoom Transfer Scope

An important piece of equipment used to further reduce the amount of error in

vertical photographs is the zoom transfer scope. The zoom transfer scope (ZTS) is very

efficient in eliminating scale differences between sequential photographs by using a base










map for control The ZTS has the ability to stretch or shrink images in one direction


about the axis of tilt to reduce a portion of the distortion caused by camera tilt as


demonstrated in Figure 2-4. The reason why only a portion is corrected is due to the fact


that the ZTS is a linear adjustment device while distortion due to tilt is nonlinear as


mentioned earlier. Since zoom transfer scopes can not make the necessary scale


corrections needed to eliminate all tilt distortion, it is necessary to utilize one side of an


image at a time and superimpose the corrected points of interest onto a base map. This


process is considered to produce reasonable results but found to be time-consuming and


tedious and should be reserved for smaller-sized projects (Leatherman, 1983).


FIGURE 2-4 Correcting for tilt distortion (Leatherman, 1983)


AMS AMS
OF OF
TILT TILT
I I
I




SHRINK STRETCH

CAPABIUTIES OF A ZOOM TRANSFER SCOPE

AXIS
OF
TILT


I


TILT
CORRECTION

NECESSARY FUNCTION FOR TILT CORRECTION








2.6 Analytical Stereoplotters

An analytical stereoplotter is a very precise device which places an aerial

photograph back into its tilted position and projects a rectified image, or corrected image,

which is used to produce an orthophotograph. An orthophotograph is a corrected aerial

photograph and has the advantages of having pictorial qualities which have planimetric

correctness. In other words, information including the dimensions of images may be

extracted from such a photo as if referencing a map.

The procedure to create an orthophotograph is based on determining three

orientations, in particular, interior, relative and absolute orientations. Interior orientation

involves determining the photographic coordinate system with respect to the instrument's

image coordinate measurement system for each diapositive (a transparent positive) by

applying a least squares procedure to compute a coordinate transformation. The relative

orientation involves selecting six or more common points between two photographs and

again applying a least squares procedure to determine the orientation parameters needed

to solve for the relative coordinates for any point in the 3-D model Finally, the absolute

orientation is determined by applying a least squares procedure to two horizontal and

three vertical control points in order to determine a mathematical relationship between

model and ground coordinates. The final product of this process can be in the form of

orthophotographs, corrected maps or corrected digital images. An experienced operator

can be expected to accurately locate the shoreline position to within 5 feet (Fisher and

Overton, 1994). Although accuracy is relatively high, many factors including high cost,

size of equipment and operator time may outweigh the benefits of this technology.








2.7 Metric Mapping

Instead of utilizing expensive technical equipment, metric mapping employs the use

of more conventional computer equipment including a personal computer with moderate

storage and processing capacity and a digital scanner or digitizer. The technique first

involves scanning or digitizing an aerial photograph to convert each photo into digital

format. Each image is then rectified by applying the least squares method within a written

Fortran program. The image produced is in its best fit position whose accuracy is solely

based on the number of control points included. The methodology and theory being quite

similar to that of the stereoplotter without being as expensive and time consuming

(Leatherman, 1983).



2.8 Airborne Laser Swath Mapping

Recently, a new system has been developed which is able to obtain the shoreline

position as well as the topography of the nearby coastline. The process uses a solid state

laser ranging system mounted on the bottom of an airplane which simultaneously

references a differential GPS navigation system. During the time of operation, the laser

ranging system time-tags (with GPS time) each laser pulse in order to measure the relative

distance to a ground point below the aircraft based on the amount of time elapsed between

the time the pulse is sent and the time the return signal is received. After the flight, the

relative distances are compiled with the flight GPS coordinates to determine the ground

surface position and elevation for every point. Presently, the manufacturer is reporting the

newest equipment is able to emit 25,000 pulses per second. At this rate, it would be

possible to document the topography for hundreds of miles of coastline in only a few








hours. The accuracy for this revolutionary system is in the process of being tested at this

time; however, preliminary findings indicate a vertical error of 10 centimeters. Once this

system has been fully-developed, the amount of error in the shoreline position would be

completely due to the measuring technique alone since all of the environmental factors that

plague the accuracy of the shoreline position in photographs would be eliminated. Since

this procedure can only be used for present and future aerial surveys, aerial photography

will still be the best source for the most accurate shoreline positions of the past. Thus,

even in the future, the procedures and techniques mentioned earlier will remain valuable.














CHAPTER 3
METHODOLOGY



The method employed in this study involved analyzing the calibrated shoreline

positions determined from aerial photography and can be described as several phases. The

details of each phase with their associated procedures are included below to ensure that

all of the necessary steps can be duplicated or improved upon in future studies. The

particular phases to be discussed in this chapter include: ground truth, aerial photography,

determining shoreline locations, and digitizing photographs.



3.1 Ground Truth

In order to be able to check the geometric accuracy of aerial photography, the data

obtained from aerial photography required comparison with other reliable data that could

only be obtained from ground surveys. From the ground surveys, beach widths could be

determined and compared with the beach widths measured from aerial photography.

Beach widths were defined as the distance from a known position to a defined shoreline

elevation.

The ground truth surveys were performed as soon as practical before and after the

aerial photographs were taken. The availability of two ground surveys for each set of

photographs had two advantages. One benefit for having several sets of survey data was








storm altered topography could be accounted for immediately before or after the

photography was taken. With ground truth data available both before and after the time of

the aerial survey, it was possible to select the ground truth data which best represented the

shoreline at the time of the aerial survey or to interpolate or average results from the two

surveys. The second benefit for having a series of ground surveys gave the ability to

compare data between ground surveys since each set of ground surveys was within a fairly

short time period. By cross-referencing the data, irregularities due to human error in field

measurements would be evident.

Each ground survey consisted of a series of 46 profiles along Lee County's

coastline on the Gulf of Mexico at approximate one mile intervals. A three or four person

crew conducted the surveys with areas accessed by either boat or car depending on the

particular island. The equipment used to survey the profiles at the selected monuments

included that for standard ground surveys: level, level rod and tape. Each profile

incorporated one of the 239 Department of Natural Resources monuments which exist

along the approximately 40 mile length of shoreline within Lee County. The elevation and

location of each monument reference the National Geodetic Vertical Datum (NGVD) and

state plane coordinate system respectively. This information is provided by the Florida

Department of Natural Resources Bureau of Beaches and Coastal Systems referred to as

Monument Descriptions. Locations of the profiles taken on Captiva Island are shown in

Figure 3-1.

Beach widths were then obtained from the ground survey data by plotting cross-

sections for each of the 46 profiles and measuring the distance from the known monument













n NORTH CAM
NORTH




RED FISH PASS

A-46-2


R-Oli

GULF OF MEX/CO

R--04 "



R--O0



R-1


0 5,000 10,000 FT.


BLIND PAS,
NOTE:
MATERIAL OBTAINED FROM NOAA NAUTICAL CHART 11427 (OCT 1978)
AND NOAA NAUTICAL CHART 11425 (MAY 190)


PINE ISLAND SOUND








T CAPTIVA ISLAND


04


FIGURE 3-1 Profile locations on Captiva Island





location to the elevation of the Mean High Water Datum (MHWD). The MHWD relies


upon statistical data based on the average height of the High Water elevation over a


nineteen year period (Shalowitz, 1964). This datum, which changes slightly along a long


shoreline, is documented in 'Transformation of Historical Shorelines to Current NGVD


Position For the Florida Lower Gulf Coast" by Balsillie, Carlen and Watters (June 1987).


The range in elevation of the MHWD varies along the Lee County shoreline from +1.17


feet NGVD to +1.43 feet NGVD with the average value equal to +1.28 feet NGVD. With






18


the elevation of the MHWD known at each monument throughout the county (based on

Balsillie et al) and having the profile information from the surveys, the beach width could

be determined as shown in Figure 3-2 below. The beach widths were then later used to

calibrate and evaluate the amount of error in the computer composite map by comparing

beach widths obtained from the composite map with these ground truth beach widths.


- -6-JBH-_-_----.-


1LOW
10.0i


-L i
-^ -WH f-li.IOWA-.(. _.)
1 2.00' -- | -- -- |-- -- |- -- - -- - -
JfOatf -- -- -- -- -- -- -- -- *-- -- -- -- -- --
-1.00' s = - -- - -


4+00


2+oo
D DANCE


0 0 20 FT.
o0 40 NFT.
HOPOMWL 90"


LEGEND.:
- -- l iWY (82/0/)
----- sunwY < 1a2I7)


NOTES:
1. SA* o+oo DP IS THE LOCAIlM F EACH MOwUMIIT
I. rm LVAIUN Ram 10 sLO.V.
3. 4X OeU OUMNO linEY 2


a

I

I I
















I i


FIGURE 3-2 Sample profiles taken at R-088




Dates for the ground and aerial surveys are shown in Table 3-1. Survey number 2

was chosen to represent the ground truth for aerial survey #1 due to its timing being much

closer to the date of the photography than survey #1. Resulting beach widths for survey








numbers 3 and 4 were averaged to approximate the most accurate beach width at the time

aerial survey number 2 was performed. Certain exceptions were made in cases where the

survey crew was denied access or previously chosen monuments were destroyed or altered

by construction or erosion. Refer to Figure 3-2 for an example of how the profiles were

documented. Notice in the figure that the vertical scale is exaggerated compared to the

horizontal scale to emphasize the profile relief.



TABLE 3-1 Dates ground and aerial surveys were performed


Survey #1 11/18/95 11/19/95 & 12/02/95 12/03/95
Aerial Survey #1 2/05/96 (10:54am 11:36am)
Survey #2 2/10/96 2/12/96
Survey #3 8/16/96 8/18/96
Aerial Survey #2 8/25/96 (9:49am 10:36am)
Survey #4 8/27/96 8/28/96



3.2 Aerial Photographs

This study included collecting two sets of aerial photographs of the Gulf of Mexico

coastline of Lee County on February 5, 1996, and August 25, 1996. The specifications of

the equipment and information for the two flights are presented in Table 3-1. Under

"Camera Equipment" in Table 3-1, the "15" signifies the focal length of the lens (actually

152.28 mm) and the "23" signifies the width of the negative (actually 230.0mm). The

filter mentioned, the Minus B filter, was used while taking the photographs to reduce the

amount of blue light through the lens. This light causes a haze to develop on the film

reducing the contrast required to see detail.








TABLE 3-2 Flight and equipment information


Contractor Kucera South Kucera South
Plane Cessna 206 Cessna 206
Altitude Flown 3,000 feet 1,500 feet
Camera Equipment Ziess RMKA 15/23 Ziess RMKA 15/23
Filters Minus B, yellow filter Minus B, yellow filter
Film Type Kodak Type 2405 B/W Kodak Type 2405 B/W
Approximate Scale 1"=500' 1"=250'
Width of Negative 230.0 mm = 9 inches 230.0 mm = 9 inches
Time of Flight 10:54am 11:36am 9:49am 10:36am




The six month period between photographs was chosen to provide the greatest

amount of beach width contrast in a limited time frame. This variation in beach width is

due to the variation of the beach profile caused by the change in seasonal climate. In a six

month time period, a change in the cross-shore profile is caused by different types of wave

activity between the winter and summer months. In the winter months, storm systems

tend to be more intense and frequent which results in greater and more frequent wave

activity compared to that in the summer. The general result of this increased wave activity

is offshore sand transport which tends to form what is commonly referred to as a winter

bar.

Scheduling the time and day for the aerial surveys was initially considered to be

inconsequential With no special instructions provided to the sub-contractor for the first

aerial survey as to the phase of the tidal cycle during which the project area was to be

photographed, the aerial survey was performed near noon-time. This time is typically

preferred by aerial photographers during the winter months to avoid unnecessary shadows.

The semidiurnal tide effect in the vicinity of Estero Island during the first aerial survey is








provided in Figure 3-3 (taken from the program Xtide 0 (Version 1.5beta)). From this

figure it can be seen that the significant high tide before the first aerial survey occurred at

12:14 am, approximately 11 hours before the time the region was photographed. At the

time the region was photographed, the approximate tidal elevation for the area was 1.7

feet Mean Low Low Water Datum (MLLWD).



MHatanzas Pas, Estm-o Island, Florida
02-04 02-04 02-05 02-05 02-05 02-05 02-06
13:15 18:41 0:14 7:19 13:31 19:17 0:49
Time offist nerial survey


.-- - - - - - - -







FIGURE 3-3 Tidal prediction near Estero Island, Florida 2/04/96 2/06/96



More planning and coordination with the aerial photographer preceded the second

aerial survey was involved. Based on the detail shown in the first set of aerial photographs

(1"=500'), a larger scale was specified for the second set of aerial photographs (1"=250').

For clarification, small scale maps or photos tend to show larger portions of the earth's

surface while large scale maps or photos approach the actual size of the entity being

documented. For scheduling purposes, it was learned that it is necessary to acquire aerial

photographs in the early morning during the summer in South Florida to avoid the daily

cloud cover. This cloud cover which obstructs the detail in the photos typically appears

around mid-morning and continues throughout the rest of the day. Since the success of an








aerial survey is also weather dependent, the subcontractor was provided with a tide table

including high tides for the month and requested to start taking photographs within a time

frame of an hour (approximately) after the estimated time for high tide. The second set of

aerial photographs was taken on August 25, 1996 between 9:49am and 10:36am with the

high water tide at 9:08am at a tidal elevation of 2.9 feet MLLWD (Xtide ). Refer to

Figure 3-4 for details.



Lanzas Pass, Estero Island, Florida
08-25 08-2 08-25
4:13 10o01 17:21
Time ot second aenal survey










FIGURE 3-4 Tidal prediction near Estero Island, Florida 8/25/96



3.3 Shoreline Location

The shoreline is technically the boundary that exists between land and water. Its

position is dependent on several factors including wave and current processes, sea level

change, sediment supply, coastal geology and morphology, and human intervention

(Anders and Byrnes, 1991). One of the most important and sensitive steps in the

procedure was defining the shoreline position from the photographs. When reviewing

each set of photographs taken from the two aerial surveys, it was important to choose an

indicator which was identifiable throughout the entire 40 miles of shoreline for each set of








photographs while attempting to maintain a consistent elevation. Regardless of the

indicator's elevation, the measurements taken from the digitized image models would later

be corrected using the ground truth surveys to adjust the results.

Three choices of indicators typically exist on the beach profile which can be used

in determining the position and migration of the shoreline. The indicators are the dune line

(which is non-existent in South Florida), the High Water Line and the Water Line.

Researchers base their decision for which indicator to use on the local climate variables at

the site of interest. Both the HWL and WL can be found at the place of tonal (color)

change between wet and dry sand based on the amount of moisture content found in the

sand. McCurdy (1947) identified the High Water Line (HWL) as a perceptible feature of

the subaerial beach face which represents the highest extent of the most significant high

tide over the past day which would also include wave run-up and setup. The location of

the Water Line (WL) is where there is a contrast in tonal color in the sand dependent on

the existing wave runup and tidal elevation at the time of photography.

There are a few factors which complicate the ability of the HWL to represent a

consistent elevation along a lengthy shoreline. Variable wave runup and setup caused by

the presence of nearshore bars and shoals interfere with the amount of wave energy that

reaches the shore which in turn displaces the wet sand line above the elevation of the still

water line. The short life span of the HWL is the other factor. The identification of this

line is dependent on the percolation rates of the sand material on the beach face combined

with intense sun exposure will affect the amount of time the sand in an area will remain

wet (dark). The only advantage to using the WL over the HWL, is the WL can be

identified throughout an entire day without having any concern of the indicator fading








since it is always actively part of the swash zone at the swash terminus. Should the WL be

used as the indicator, it is important that the shoreline position be converted to a known

elevation datum.

In choosing the shoreline identifier, all the previously mentioned factors were taken

into consideration. For the first aerial survey, too much time had elapsed between the

time of the daily significant high tide and the time the photographs were taken to be able

to clearly see the High Water Line at the scale of the photographs. The only reasonable

choice was to choose the Water Line. For the second set of aerial photographs, the HWL

was easily identified with the larger scale photographs however a large variation in wave

run-up along the shoreline was noticed. Since the location of the High Water Line is

dependent on tide, wave setup and wave run-up; near-shore bathymetry will affect the

amount of wave energy that reaches the shore. The presence of ebb tidal shoals, for

example, can cause discrepancies in the High Water Line elevation as shown in Figures

3-5a and 3-5b taken at the south end of Gasparilla Island and the north end of Lacosta

Island respectively. With Boca Grande Pass separating the two photographs, just over a

mile in width, it can be seen how such changes in bathymetry can affect the wave energy

that reaches the shore. Based on this finding, the base of the swash zone, was found to be

well defined throughout and chosen as the indicator for the second set of photographs in

an attempt to maintain a constant elevation throughout the 40 miles of shoreline. Once

the shoreline positions were recorded and compared, it would be possible to calculate the

amount of shoreline advancement or recession.




























Figure 3-5a Aerial photograph taken August 25, 1996 at the south end of Gasparilla Is.
with evidence of runup


Figure 3-5b Aerial photograph taken August 25, 1996 at the north end of Lacosta Is. with
no sign of runup








3.4 Digitizing Photographs

Once the photographs were taken and the ground survey data were recorded and

processed, the next step was to determine the best method of digitizing the aerial

photographs taking into account time required and best results. Equipment used

throughout all different approaches included using a Cal Comp Digitizer tablet which was

connected to a 486 DX computer with AutoCAD Release 12 software as the user

interface. The paragraphs below describe the sequential development procedure for

photograph digitization.

The first technique was to align a series of corresponding photographs and then

digitize each set of photographs. Much attention was paid to common objects on

sequential photographs which aided in both the manual assembling of five photographs

and later the assembling of those sets of five with other sets forming entire islands using

AutoCAD. For control points, it was desired to use common objects, that had minimal

relief variations (changes in elevation which cause distortion of the object). Parking lots,

pools, tennis courts and roads were found to provide the best references. This worked

well in developed areas however in undeveloped areas some difficult choices had to be

made by selecting items including large debris on the beach or shadows of large structures

near the beach. Digitizing each set of photographs involved calibrating the digitizer tablet

in order to preserve the scale of the photographs and then recording the location of

reference points and the identified shoreline on each set of photographs to form a

computer drawing image. The sets of images were then joined together using the drawing

program with every attempt made to obtain the best fit of all the control points included in

the images. Once an entire island was assembled, visual targets that were set over DNR








monuments were used to transform the islands' shorelines from an arbitrary coordinate

system to the State plane coordinate system. After the method was applied throughout a

substantial amount of shoreline, significant errors became apparent. It seemed likely that

joining the photos together by hand into the sets was responsible for a substantial amount

of the error.

SThe next technique included digitizing photographs individually and then

assembling the digitized images of individual aerial photographs together using AutoCAD.

Control points on sequential photos were again used to guide in the assembly of the

various islands. The benefit of this method was that the images could be overlaid in the

computer program to form an image mosaic similar to using a light table. This enabled

more control points to be seen and be used in the assembling process. Once assembled

and moved into the State plane coordinate system, using the same visual targets mentioned

earlier, it became apparent that there was still a considerable amount of error in the series

of photographs, most likely due to the inherent distortions in the photographs.

The final technique minimized some of the distortion in the aerial photographs by

using a method similar to Dolan's OGMS Method. It was concluded that the State of

Florida Department of Natural Resources Coastal Construction Control Line (CCCL)

aerial photographs for Lee County (taken on 10/14/88) could be considered to be rectified

since the amount of distortion appeared minimal and had state plane coordinates inscribed

on the photos. The first step was to chose control points found in all three reference sets

(CCCL photos, Feb. '96 photos and Aug. '96 photos) having similar properties as those

mentioned earlier. After calibrating the digitizing tablet based on the state plane

coordinates displayed, the selected control points in the CCCL photographs were then









digitized creating a map of control points with known state coordinates. A map of control

points on Captiva Island can be seen in Figures 3-6 and 3-7.


430495.1401.SS7904.4901 PROFILES


R IH PASS
"ED .-


GULF
MEXof
MEXICO


PIER

- BLHMEAD


TENNIS

- ROAD


TENNIS COURTS


ROAD


FIGURE 3-6 AutoCAD display window showing a portion of the base map of
Captiva Island




Once the control points were determined, both sets of recent photographs were

digitized including the depicted shoreline position, reference points and visible targets. To

achieve greater accuracy, before the second set of aerial photographs was taken, visual

targets were placed over 16 DNR monuments throughout the county. In order to

minimize fieldwork, the monuments selected to be targeted were part of the group used in

the profile surveys. Targeting the monuments was accomplished by the combined efforts









430352.2862.B07904.4901 PROFILES


GULF

MEXICO


PROFILE LOCATION ('P,.)


. 9 IN PHOTOGRAPHS(TYP.)


FIGURE 3-7 AutoCAD display window showing the composite map of Captiva Island
being assembled




of the University of Florida Coastal and Oceanographic Engineering Department and the

Division of Natural Resources Management of Lee County. The individual digitized

images of the 9" x 9" photos for both sets of recent photographs were next imported into

the base map and placed in its best-fit location based on the control points mentioned

above. Here, a CAD application best served our needs by having the ability to change the

scale, change the alignment and shift images all with ease and minimal computer time.

Each set of images was then placed on a drawing layer inside the CAD application. This

was done to keep the two sets of recent photo images separated in order to reduce

confusion in editing later on. Figure 3-7 shows image blocks (created by digitizing aerial








photographs) being positioned in their best fit location over the base map utilizing the

control points labeled to create a composite drawing.

Once the aerial photos had been digitized and used to assemble the composite

map, reference lines were then drawn originating at the coordinates for every DNR

monument (information provided in the "Monument Descriptions") and extended past and

perpendicular to the representative shoreline. The distances from the monument locations

to the corresponding shorelines were then recorded to be compared with the beach widths

determined earlier from the ground truth profiles.

After making these comparisons, some isolated areas were found to still have

errors ranging from 40 to over 100 feet when compared with other nearby profiles. These

particular locations were then re-digitized and imported again into the composite map

utilizing additional reference points. In some cases, this provided a better fit and produced

better results. Discrepancies found in the CCCL photos and severe plane tilt could

account for the significant error which remains.














CHAPTER 4
ANALYSIS OF DATA


Once beach widths were obtained from the composite map, they required

adjustment with the ground truth corresponding beach widths to conform to a known

datum. With the shoreline indicators chosen being found to represent inconsistent

elevations, a correction had to be applied to account for difficulties including variable

tides, wave runup and setup as discussed in Chapter 3. After correcting the data using

various routines, the corrected data were compared to the ground survey data to judge the

accuracy of the method established.



4.1 Calculations

There are several ways to attempt to account for the changing elevations

associated with the shoreline position indicator. Setting up the proper instrumentation

along the entire county to measure tide, wind strength and wave characteristics at key

locations simultaneously with the photography would be both expensive; time consuming

and impractical. It was more advantageous and practical to adjust the high water line

position data based on ground truth data. Three different routines of adjusting the data

included:

1. The data were left unchanged in order to provide a control to measure
the benefits obtained by adjusting the data (refer to Table 4-1).








2. For each island, all beach widths obtained from the composite map
were shifted by a quantity X so that the average error for each
island's data reduces to zero (refer to Table 4-2). With k being the
number of profiled points on each island, Laera, being a specific beach
width determined from the aerial photographs, Lgt being the
associated beach width attained from ground truth and Lc being the
associated corrected beach width.
1k
X = I (Lar, L ,) (4-1)
k n=1


L, = Laeri. X (4-2)


3. For each island, the change in water level, Y (due to tide and run-up)
required to reduce the average error of the sample error data to zero
was calculated using equation 4-3 then used in equation 4-4 to obtain
Lc (refer to Table 4-3). This differs from procedure 2, by accounting
for a varying beach slope, S along the county shoreline and is more
consistent with the factors which vary along the shoreline.



K Laeria L,, = 0 (4-3)



L4 = Lae (4-4)
S


Once the data sets were adjusted by the above methods, all three sets of data were

then calibrated to minimize remaining errors. Calibration includes finding errors

associated with any two particular monuments and then linearly interpolating those

amounts and applying these as a correction factor to all those locations between the two.

The errors found at monuments other than those selected for calibration, would then be

used to help determine the accuracy accomplished by each of the procedures.








The two methods of data calibration included:

1. Utilizing the first and last monuments on each barrier island as the
ground truth profiles. (Calibration #1)

2. Utilizing every other monument on each island as ground truth
profiles. (Calibration #2)


4.2 Method of Analysis

In photography, most distributions of error are well represented by a normal or

Gaussian distribution (Wolf, 1983). This type of distribution is typically described as a

bell-shaped curve as shown below in Figure 4-1.


FIGURE 4-1 Normal Distribution Curve (Wolf, 1983)



Histograms are a statistical tools capable of showing the symmetry of a sample of

data, the scatter of the data and the precision of the measured values based on the overall


Size of residuals








dimensions of a plot. Relative frequency is usually chosen for such a plot to ensure fair

comparisons are being made between different size samplings. The standard deviation,

S of a sample, which is contained in the hatched area in Figure 4-1, indicates to what

degree 68 % of the data fluctuates from the mean. Also labeled in Figure 4-1 is the class

interval, Av, which is the range of error size chosen for a particular sampling. For each

size residual, the corresponding relative frequency can be determined graphically.

For each comparison made in the study, a relative frequency distribution of error

was plotted in the form of a histogram in order to highlight the merits of one procedure

over another as demonstrated in Figure 4-2. Throughout the results of this study, the

standard deviation and mean have been provided for each set of data. Using the "raw

data" in Figure 4-2 as an example, 68 % of the total sample lies within 11.8 feet from

the mean or -8.5 < (68% of the Raw Data) < +15.1 feet.


FIGURE 4-2 Sample Histogram


0











8
0


Error between Aerial Photographs and Ground Truth (Feet)
















TABLE 4-1 Calibration of Raw Data from February 1996 Survey


LEE COUNTY COASTLINE STUDY
CAPTIVA ISLAND
Raw Daa Calibration Utilizing Calibration Utilizing
DNR Ground High Water Line Error Wihout The First and Last Monument of the bland Every Other Monument of the Island
Monument Truth Position Without Correction Interpolation Calibration High Water Line Error Interpolation Calibration High Water Line Error
(Feet) Correction (Feet) Number Coefficient Position (Feet) (Feet) Number Coefficient Position (Feet) (Feet)
A-46-2 126.1 6.2 119.9 62 119.9
R-85 833.3 62 827.1 62 827.1
R-86 520.0 6.2 513.8 6.2 513.8
R-87 383.4 62 377.2 62 3772
R-s8 251.3 257.5 6.2 6.2 251.3 00 6.2 251.3 0.0
R-89 453.9 1 4.9 440.0 1 6.6 447.3
R-O0 215.1 2 3.6 211.5 2 6.9 208.2
R-91 157.5 3 2.3 155.2 3 7.3 150.2
R-92 192.2 4 1.0 1912 4 7.7 184.5
R-93 224.8 5 -0.3 225.1 5 8.1 216.7
R-94 148.3 1513 5.0 6 -1.6 154.9 6.6 6 A4 144.9 -3.4
R-95 148.3 7 -2.9 1512 7 8.8 139.5
R-96 117.7 8 -4.2 121.9 8 92 108.5
R-97 108.7 9 -5.5 1142 9 9.6 99.1
R-98 130.1 10 -6.8 136.9 10 9.9 120.2
R-9 221.8 232.1 10.3 11 4.1 240.2 1Ms 11 10.3 221.8 0.0
R-100 194.0 12 -9.4 203.4 1 7.0 187.0
R-101 277.0 13 -10.7 287.7 2 3.6 273.4
R-102 219.0 14 -12.0 231.0 3 0.3 218.7
R-103 275.0 15 -13.3 288.3 4 -3.1 278.1
R-104 256A 26.1 11.7 16 -14. 282.7 26.3 5 44 274.5 18.1
R-105 156.8 17 -15.9 172.7 6 -9.8 166.6
R-106 425.3 18 -17.2 442.5 7 -13.1 438.4
R-107 429.4 19 -18.5 447.9 8 -16.5 445.9
R-100 176.9 157.1 -198 20 -19. 1769 0.0 9 -19.8 176.9 00
R-109 374.2 -19.8 394.0 -19.8 394.0

Average Error: 2.7 Avg. 17.1 Avg. 7.3
Staannd Deviation: 12.9 S.D. 9.9 S.D. 15.2
Note: The monuments at which ground truth profiles are ocaaed are shown in bold type.




















TABLE 4-2 Calibration of Shifted Data from February 1996 Survey


LEE COUNTY COASTLINE STUDY
CAPTIVA ISLAND

Raw Data Error Correction Calibration Utilzing Calibration Utilizing
DNR around HWiWa1UM ErrorWlhou HigWeriUns Enmr Wih Ag. The Firt and Lat Monumnt of the laend Eva Oter Monummnt at the Islnd
Monument Tnruh PoonaW u Cesrodi n PodW m on Ebror Cmro Itpolaon Colaon Hiip WaaWrlUn Errr Itpoalon Cabalon HiWgl Wa Une Errr
F_____ Coecdon PIFe Avg EnrConfedon MJ 0 Numrter Coeffdet Polion (F1 Ie Number Coefident PoUlon (Feelt (F
A-46-2 126.1 12S.4 3.5 119. 3.6 119.9
R4O 81.3 1 0.6 3.5 27.1 S.5 827.1
R4- 520.0 517.3 3.5 S13.A 3 513
R47 38A.4 350.7 3.5 377.2 3.5 377.2
R14 51.3 e7e. L 2S4.8 1.5 3.5 51.3 n0 3. 51 0.0
RI4 4 5.J 451.2 1 2.2 440.0 1 3.0 447.3
RAO 215.1 212.4 2 0.0 211.5 2 4.3 208.2
R41 157.5 154. 5 -0.4 156.2 3 4.6 150.2
R-2 192.2 1.56 4 -1.7 191.2 4 5.0 114.5
R4A 224. 222.1 -3.0 225.1 5 5.4 216.7
R4M 140.L 15l.3 L 0 1a0s 3 8 -4.3 1I .6 6 L 144.9 -3.4
R4-6 14 145.6 7 6 1.2 7 12 7 .1 130.5
R4O 117.7 1150 8 -69 121.9 8 .5 104.5
R47 10 1010.0 0 -92 1142 9 6.9 90.1
R4N 130.1 127.4 10 -5a 136.9 10 72 120.2
R0 221.8 212.1 103 220.4 7.6 11 -10. 240.2 1.4 11 7.1 221.8 0.0
R-100 194.0 111.$ 12 -12.1 203.4 1 4.3 187.0
R-11 277.0 274.3 13 -13.4 257.7 2 0.9 273.4
R-102 21.0 218.3 14 -14.7 231.0 3 -2.4 218.7
R-103 27S.0 272.3 15 -16.0 21a.3 4 4-.8 271.1
R-10o 2 .4 nL1 11.7 M.4 L.0 16 -17.3 M1.7 2s. S .1 274 1&.1
R-106 15.6 154.1 17 -18. 172.7 6 -12.4 188.
R-100 465.3 422. 1 -19.9 4425 7 -15.8 481.4
R-107 429.4 42.7 18 -21.2 447.9 8 -19.1 445.9
R- R-10 3742 371.5 -225 304.0 -22.5 304.0

AvImg Br: 2.7 Avg. 0,0 AV. 17.1 Avg. 7
stenw Dwmedavsrr 12.0 s.D. 12. s.. eJ S.D. 152
Note: The monuments at which ground truth profiles are located are shown in bold type.



















TABLE 4-3 Calibration of Tide-Induced Shifted Data from February 1996 Survey


LEE COUNTY COASTLINE STUDY
CAPTIVA ISLAND

CoIrCold Date For Tnil DMi eo Cabratkon Uilizing Caibraton UWlling
DNR Tk___ Conemdm a Hi WsaUnr. Eor Wkl La.t Monument of tihem Ilad Ewry Othr Monument of the Islnd
Monument dTki dBY9ln SlopVMn HiWaterue Poidon b TidlCaoredn In up on C*raon lHiCWatrUn Eer Inulpolon Cbnmon Hih WaerUne Eror
Conedon I aehZone Condelon Tide Coeclon e(F Nunber Coelldnt Podlon (FQ Ft NHumer Coelkdint Poton (Fset i
A-4"-2 0.29 0.124 -2.1 122 3.9 119.9 3.9 119.9
R416 0.29 0.124 -2.1 81.0 3.9 127.1 3.9 827.1
R-4 029 0.124 -2.3 617.7 3.9 513.0 3.9 513.8
R-97 029 0.124 -2.3 351.1 3.9 3772 3.9 377 2
RI8 m0.29 10. -2, 3 U2 3.0 1S 0.0 3.9 291.3 0.0
R-U 029 0.126 -2.3 461.6 1 2 441. 1 4.3 447.3
R40 0.20 0.120 -2.3 212.9 2 1.1 211.7 2 4.7 209.1
R-1 029 0.110 -2.2 16.3 3 -0.3 156. 3 5.1 150.2
R4-2 029 0.133 -2.2 190.0 4 -1.0 191. 4 56 184.
R43 029 0.135 -2.2 222. 5 -3.0 225.7 5 .0 219.7
RH4 rm 0.17 -.1 151.2 2. -4.4 "15 7.3 6 .4 144. -35
IR4 0.2a 0.141 -2.1 148.2 7 -6.7 152.0 7 .8 139.4
R4 0.29 0.149 -2.0 115.7 I -7.1 122. 8 7.2 10.5
R47 029 0.151 -1.9 10A.8 -4.5 115.S 7.6 90.1
R4I 0.29 0.156 -1.9 128.2 10 -0.9 138.1 10 8.1 120.2
R4e 0.2 01Ml -1.9 20 L &a 11 -11.2 241 10.7 11 5s 2"1.9 00
R-100 0I2 0.149 -2.0 182.0 12 -12.8 204. 1 4. 187.1
R-101 0.29 0.131 *-22 274U 13 -14.0 208.8 2 1.4 273.4
R-102 0."2 0.117 -2. 211.5 14 -15.4 21.9 3 -2.2 218.7
R-10S 0 20 0.103 -2. 2722 15 -16.7 28l9 4 -6.8 277.9
R(HI 0a a0 -3. s 4. &4 19 -1.1 n.* 2M. 5 .3 274.1 17.7
R-105 0.20 0.05 -34.4 134 17 -19.5 172.9 -12.9 196.3
R-t10 0.29 0.062 -4. 421.8 18 -20.1 442.6 7 -1.5 438.2
B-107 0.20 0.079 -3.7 42.7 19 -22.2 441.0 I -20.0 446.
R-10 0 O7 3.80 -. D -2 14 -0 10 9 -21.1 1751 0.0
R-10b 0.29 0.077 -3.1 370.4 -23.0 14.0 -23.6 394.0

Average ror 0.0 Avg. 17. Avg. 7.1
Sotndd ePoIwdr 13A. S.D. 0J S.D. 1.0
Note: The moments at which ground truth profiles are located are shown in bol type.














CHAPTER 5
RESULTS AND DISCUSSION



The data produced from the various computations discussed in Chapter 4 were

published in the annual report produced for Lee County titled, "Pilot Program To Quantify

Shoreline Changes in Lee County" by Kreuzkamp and Dean (1997). This report includes

all of the ground truth and photographic data obtained from the study. In an attempt to

consolidate all of the data from the report, the following chapter will include only the most

consequential information. The following chapter includes histograms used to illustrate

the effectiveness of the various methods, the sources of error considered to affect the

results, the favorable improvements made during the study and recommendations for

further study in this area.



5.1 Shoreline Position Error

The initial beach widths recorded from the composite map were first recorded and

plotted in Figure 5-1 before being adjusted by the ground truth information. Based on the

information contained in this figure and those that follow, the success of the various

calculations and methodology could be evaluated. The most distinguishable features

found in Figure 5-1 are the difference in scatter of the data and the similarities of the mean

values between the two surveys. The standard deviation of each set of data represents the









Lee County Raw Survey Data


FIGURE 5-1 Comparison of uncorrected data sets


accuracy for any point within each sampling. The smaller standard deviation value for the

August survey is most likely due to the improvements to be mentioned in section 5.3

which helped produce more accurate data as Figure 5-1 presents. The mean values given

depict the amount each digitized shoreline would need to be shifted to conform on the

average to the true High Water Line position. Although it is curious that the mean values

resemble one another, it seems possible that the discrepancies in the tidal elevations and

shoreline indicators for the two aerial surveys could nullify the impacts of each other on

the data.

A summary table of the uncorrected data is provided in Table 5-1 to show the size

of the residuals associated with each island. Examining the standard deviations, the larger

contributors of error are: Lacosta Island, Estero Island and Lover's Key. Lacosta Island

and Lover's Key are less developed islands which results in having less available control


0

I



0


Error between Aeril Photographs and Ground Truth (Feet)








points (ie. roads, pools, tennis courts, etc.) With less control points, it becomes much

more difficult to create an accurate composite map. Adding visual targets to these areas

will help remedy the problem in future aerial surveys. The error associated with Estero

Island is probably due to a discrepancy found while digitizing the CCCL photos for that

region. After several attempts of digitizing the CCCL photos, the main road near

monument R-203 was consistently disjointed by 20+ feet on the created base map. It is

therefore possible that there may be an error in the CCCL photos. This local area of the

base map should be corrected by referencing a set of photos that were prepared at an

earlier time or another source should be employed.



TABLE 5-1 Summary error results for each aerial survey by island



Gasparilla Island -5.7 9.8 12.4 7.4
Lacosta Island -9.0 31.9 -2.8 19.9
North Captiva Island -1.3 7.4 4.4 11.4
Captiva Island 2.7 12.9 7.1 7.3
Sanibel Island 10.8 18.5 3.3 7.5
Estero Island 20.0 29.1 -2.6 14.1
Lover's Key/Bonita Beach 1.0 29.3 1.9 13.2




In an attempt to focus on the better accuracy of the method, these "problem areas"

were excluded from the data with results shown in Figure 5-2. Removing the problem

areas from the group sample slightly enhanced the difference between the mean error

values for the two surveys while it reduced the standard deviations. The change in

standard deviation appears to be the influence of having access to only a limited number of

control points within the less developed islands. The change in mean error seems to









indicate that the shoreline positions obtained within the problem areas did influence the

data, however minimal.


Error between Aerial Photographs and Ground Truth (Feet)


FIGURE 5-2 Comparison of uncorrected data sets excluding problem areas



The next question was if any of the correction routines performed on the data

resulted in significant improvements. Figures 5-3 and 5-4 focus on the various routines

applied to each complete set of data. For both surveys, the scatter and average error of

the data were reduced by comparable amounts by either shifting the data with or without

taking into account the slope of the beach face. Although the results for either method

were not dramatic, it is still felt that these techniques have merit by accounting for the

varying shoreline indicators or discrepancies caused by the shoreline being inconsistently

identified between sets of aerial photographs. After applying the two correction routines,

each set of processed data was calibrated two different ways as discussed earlier in


Lee County Raw Survey Data Excluding Problem Areas


10
6

3


























FIGURE 5-3 Comparison of results determined by applying various computations to the
February data (Including problem areas)


FIGURE 5-4 Comparison of results determined by applying various computations to the
August data (Including problem areas)









Chapter 4. Resulting errors indicated that both methods of the latter calibration produced

unreliable results shown by the inconsistent changes in the standard deviations of the data.

Based on this information, the best accuracy achieved from the aerial photography

for any individual measurement within the entire county was found to be 11 feet

(obtained by shifting the data). This was improved further by shifting the data and then

excluding the problem areas. This is shown in Figure 5-5 with the standard deviation for

the August data being 7.4 feet. This level of accuracy should be compared with the

level of accuracy achieved by other researchers using similar means. As mentioned earlier,

Dolan et al (1978) attained an accuracy of 21 feet with the OGMS method while Fisher

and Overton (1994) documented that the accuracy of digitizing directly from aerial

photographs and using USGS Topographic maps for control will have an error of 50

feet.


Lee County Shifted Survey Data Excluding Problem Areas


0

.6
0



8
o


Error between Aerial Photographs and Ground Truth (Feat)


Figure 5-5 Comparison of accuracy obtained between the two aerial surveys









5.2 Shoreline Change Error

In order to examine the reliability of using aerial photography in determining

overall shoreline change, the change in beach widths between February and August

obtained from the composite maps were compared to the changes detected by ground

truth. Figure 5-5 shows the changes that occurred for the entire county over the six

month time span based on aerial photography and ground truth. Results based on aerial

photography documented shoreline changes at every DNR monument (approximately 239

points spaced at 1/5 mile intervals) while the ground truth profiles determined the

shoreline change at 40 points spaced at approximately 1 mile intervals. The positive

mean values for both methods in Figure 5-5 are the influence of nourishment projects that

occurred between the two aerial surveys. In an attempt to investigate the natural shoreline

processes for the region, Figure 5-6 excluded known nourished areas from the


FIGURE 5-6 Comparison of shoreline changes for the entire county


Relative Frequency Distribution of Adiusted Seasonal Shoreline
Changes Throughout the Entire County

MAerial Photos
0.25 Avg.8.6 ft; S.D.=48.9 ft
2 Ground Truth
0.20 Avg.-22.7 ft; S.D.-48.9 ft

0.15

0.10



0.00

V A
Shoreline Change (Feet)










Relative Frequency Distribution of Adjusted Seasonal Shoreline
Changes Throughout the County Excluding Nourishment Sites
0.40
0.35 i Aerial Photos
Avg. -7.0 ft; S.D. 27.9 ft
0.30
05 Ground Truth
0.25 Avg.25 ft; S.D. 158 ft
it 0.20
0.15-
cc 0.10
0.05
0.00

v Shoreline Change (Feet) A

FIGURE 5-7 Comparison of shoreline changes for the entire county excluding
nourished areas




calculations. These nourished areas included the southern tip of Gasparilla Island, Captiva

Island, parts of Sanibel Island, Ft. Meyers Beach and Bonita Beach. By eliminating these

nourished regions in the county, the histogram clearly shows that the remaining

unnourished areas experienced a net shoreline recession. This recession is most likely the

influence of storm activity and not part of a seasonal trend.

To evaluate the validity of the results of Figures 5-6 and 5-7, Figure 5-8 eliminated

any composite map data that did not have corresponding ground truth data. This was

done since the ground surveying provided a different amount of coverage (one mile

spacing) compared with the aerial survey data which was analyzed at 1000 foot

increments. The standard deviation values of the two samples represented in Figure 5-8

continues to support the fact that the accuracy of the aerial photo data is still less

compared to the accuracy determined for the ground truth. Based on the average values









of the data included, it is possible to determine the accuracy of the method being applied

to analyze the average shoreline change to be 3 feet. Similarly, Stafford and Langfelder

(1971) found that although they had a large magnitude of error in some local instances,

the mean of the composite differences was very small. It was concluded by Stafford and

Langfelder that,


the composite error was concluded to be sufficiently small so as to not
have a detrimental effect on the study results expressed by mean beach
location changes as long as adequate care was taken in the measurement
process and provided that the most accurate type of aerial photograph
available in a particular area was used. (page 574)


Relative Frequency Distribution of Adiusted Seasonal Shoreline
Changes at Profile Locations Excluding Nourishment Sites
0.40 ............ .
M Aenal PhRiotos
0.35 Avg.=-0.2 ft; S.D.=28.5 ft
0 Ground Truth
0.30 Avg.=2.5 ft; S.D.=15.8 ft
0.25
0.20
0.15
E 0.10
0.05
0.00

v Shoreline Change (Fooeet) A


FIGURE 5-8 Comparison of shoreline changes at profiled locations excluding nourished areas



The last significant finding was the success in tracking nourishment projects as can

be seen in the right portion of Figure 5-6. After removing all other areas, Figure 5-9









shows the impact those projects had on the area beaches and the level of accuracy of the

data obtained from the composite map. It was detected by means of ground truth survey

that the average beach width within the designated nourished areas was increased by more

than one hundred feet in a six month span. The results from the composite map (with data

taken from profiled locations only) reflect changes of the same order with an error of 3.1

feet. This error agrees perfectly with the error determined earlier as 3 feet. It is also

important to understand that this method not only has the ability to detect shoreline

change at sites of beach construction but can easily include areas adjacent to construction

to include the natural spreading of material. These transitional areas can extend for miles

beyond the limits of a nourishment project and are important to include to insure that all of

the material within a project is accounted for during the monitoring process.


Relative Frequency Distribution of Adjusted Seasonal
Shoreline Changes at Nourished Profile Locations
0.60--
MAerial Photos
0.50 Avg.=103.1 ft
M Ground Truth
50.40 Avg.=100.0 ft


0.30

0.20

0.10

0.00
8 0
v Shoreline Change (Feet) A


FIGURE 5-9 Comparison of shoreline changes at profiled locations within nourished areas








5.3 Sources of Error

There are several sources of error in determined shoreline positions from aerial

photography. These sources include inconsistent water level elevations along any chosen

shoreline indicator, misinterpreting or inaccurately digitizing the shoreline indicator,

distorted images within the aerial photographs and small scale photographs. The

approximate magnitude of total error, afo7t, for the February and August flights were

found to be 14.7 and 7.4 feet respectively in the previous section. This section will

account for each of the contributing sources of error and attempt to quantify each one.

Although difficult to quantify, any shoreline indicator's elevation will have some

degree of fluctuation which will later be referred to as OINDICATOR This variation along

the shoreline is caused by inconsistent tide and other changing environmental factors. The

presence of inlets and large bodies of water near a region can affect the tidal elevations

along a coastline by causing the water surface elevation near an inlet to be higher or lower

than the water surface elevation a few miles alongshore from the same inlet. The degree

of wave setup and runup in the nearshore and swash regions can fluctuate depending upon

nearshore bathymetry, wave activity and wind variability. Any of these factors can alter

the elevation of a shoreline indicator from one to several feet depending upon on the

location of the study area and local climate. Based on a 1:10 slope of the beach face, the

range in horizontal discrepancies can reach over 30 feet.

The effectiveness of this entire process is dependent on the persons) identifying

and digitizing the shoreline position. The method is fairly labor intensive and requires

attention to detail. Each step of the methodology requires total consistency throughout

each set of photographs which contributes to the difficulty. A trained and careful








draftsperson or technician would be the best candidate for this type of work. Error

created by inaccurately determining the shoreline position from photographs is presently

unavoidable and would increase should a smaller scale be used. A limited study was

conducted to determine the variability of results obtained by different persons identifying

and digitizing the shoreline from aerial photographs. Based on photographs produced at a

scale of linch=250 feet, it was found that the range in error in identifying the shoreline

was 3 feet. During the same study, the range in error in digitizing established points

along the exact same image was 1 foot. The Calcomp digitizer tablet used to create the

composite map for this study has limitations in precision of 0.005 inches. At the scale of

1"=250 feet, the precision of this tablet conforms well with the study results having a

value of 1.25 feet. Should a smaller scale be used, lesser detail in the photographs

would cause a substantial increase in error due to the limitations of personnel and

equipment. Identifying and digitizing the shoreline position at a scale of 1"=500' could

have a potential error of 6 feet and 2.5 feet respectively. Since only one person

digitized the photographs for the entire study, the only relevant error is the limitation of

the digitizer with a standard deviation designated for later purposes as C Digitizer -

Aerial photographs will always have an inherent error due to distortion which has

to either be removed or circumvented, as this project attempted to accomplish. The

sources of error that cause variations in scale and distortion include: changes in the

camera's altitude, changes in tilt of the aircraft, radial scale variations and relief variations

of the surface photographed. The largest of these sources of error for this project was felt

to be the distortion due to camera tilt. This "tilt" is usually due to aircraft roll

Approximately one half of aerial photographs taken for mapping purposes are tilted








between 1 to 3 degrees (Anders and Byrnes, 1991). Even a one degree tilt can cause

non-linear scale variations throughout a photo which are difficult to correct without the

proper equipment/technology. The amount of error specific to this project that could be

expected due to camera tilt, O Roll, is shown in Table 5-2. These results apply for points

located a considerable distance off the principal line and therefore should be considered as

the maxima.




TABLE 5-2 Potential distortion in aerial photographs due to camera tilt



1 degree 26 ft 13 ft
3 degrees 80 ft 40 ft



The ground truth is the last potential source of error since a ground survey could

not be performed within a one day time frame as the aerial photography was able to

accomplish. The temporal spacing between the first two ground surveys allowed too

much natural change of the beach to occur in order to reasonably approximate the

shoreline position based on the ground truth at the time of the first aerial survey the

however the latter two surveys had only 2 weeks of time between them. Even within such

a short period of time, a sizable storm could alter the topography enough to affect the

ground survey results as shown in Figure 5-10 below. Considering the possible

differences in shoreline position at the time of flight as one-half the difference observed in

the ground surveys, the standard deviation of error, (OGT, was found to be 9.0 and 5.7






51


feet for the February and August surveys respectively. This was based on the relationship


aa = 1(mean) + SD2.
2


FIGURE 5-10 Comparison of shoreline changes determined from sequential ground surveys



5.4 Error Analysis

With only a few contributions of error capable of quantification in section 5.3,


based on the relationship shown in Equation 5-1, Roll and C Indicator could be

evaluated to assess the significance of each of these factors in the study.



Total2 =02T +02t +(O2Rol + 2Indicator) (5-1)


Relative Frequency Distribution of Shoreline Change Between
Ground Surveys

0.450 _
0.400 Changes between sunreys 1 & 2
(Avg3.7 ft,SD-17.7 ft)
S0.350
E Changes between surveys 3 & 4

0.250


c 0.150
0.100

0.000


v Shoreline Change (Fet) A








Based on the known values of error determined in section 5.3, the cumulative error

due to roll and the indicator was found to be 11.4 and 4.6 feet for the February and

August data respectively (ie. &URoi+ + Idcator = Tota rG Agizer ). After

comparing with the values of error for roll stated in Table 5-2, it would seem that the

method applied reduced to some degree the error due to plane roll. Based on the

information given and assuming the error associated with the shoreline indicator was

insignificant, it could be estimated that the resultant error would require approximately V2

degree tilt for both altitudes (scales) flown.



5.5 Improvements

Significant changes were implemented between the first and second sets of aerial

photographs which are believed to have improved the accuracy of locating the shoreline

position. It is strongly recommended that the improvements discussed in the following

paragraphs be included in subsequent aerial surveys.

Increasing the scale of the aerial photos seemed to have had a significant beneficial

influence on the accuracy of the data obtained. In this particular project, the first set of

photographs was taken at a scale of 1"=500'. This scale made it difficult to see detail

including control points, shoreline indicators and visual targets while digitizing

photographs. The second set of photographs had a larger scale of 1"=250' which helped

improve detail in the photographs and reduce distortion. Displacements of objects due to

camera tilt is inversely proportional to the scale of a photograph. Theoretically, by

increasing the scale of the photographs by a factor of two, the displacement of the

distorted object will be reduced by one half. It is believed that the larger scale is at least








partially responsible for the difference in values of standard deviation shown in Figure 5-1.

Only additional comparisons will confirm this hypothesis.

Increasing the number of visual targets set over the DNR monuments located

throughout the county helped in several ways. Visual targets were felt to be more reliable

compared to other objects that were selected as primary control points since their state

plane coordinates were already known compared to the coordinates of a tennis court that

were identified in the CCCL photos. These visual targets also aided in the importing of

images into the composite map, especially in areas where there were a limited number of

common features found in the CCCL photos and the aerial photographs recently taken.

These undeveloped areas include Lacosta Island, Lovers Key and parts of North Captiva

and Sanibel Islands. It is important that for any subsequent aerial photographs, efforts

should be made to have just as many, but preferably more, visual targets than were set for

the August 25th set.

Coordinating the time of the aerial survey with the forecasted time of high tide for

the region was believed to help photographically document a much more concise location

of the High Water Line. By providing a tide table for a one-month time frame, the

photographer was able to conform to the time frame specified while maintaining his

constraints for time of day to photograph with clear skies.

To further improve the degree of accuracy, it has been recommended by

researchers such as Anders and Byrnes (1991) among others that the error within erosion

rate studies can be minimized by extending the time between surveys. If a shoreline

change trend exists, increasing the temporal spacing results in shoreline changes which will

eventually be larger than the inherent errors of the method used. Thus, the temporal






54


spacing allows the error to be distributed throughout the associated time frame. For

example, a 5 foot error determined for a 5 year erosion study would result in one foot of

error per year.








Since initiation of the project, many different techniques have been employed to

create a composite map with the purpose of extracting the most accurate shoreline

measurements. The most significant improvements in map accuracy are believed to be due

to small changes to the flight specifications. Preliminary planning for the August survey

specified a lower flight altitude (which produces a larger scale), an increase in the number

of visual targets and flight time coordinated with the predicted high tide; all of which are

believed to have contributed to improving the results.

The method developed here would also be suitable for documenting larger

shoreline changes which occur over a shorter time span such as the result of beach

nourishment projects and the impacts of major storms. For example, the average shoreline

change for all of the nourished areas throughout the county was approximately 103 feet

determined with aerial photography while ground truth determined the change to be 100

feet. When monitoring nourishment projects, it is important to document the topography

of the beach in order to keep track of the material being deposited within the design

template and naturally spread alongshore. With the cost and time required for ground

surveying, areas adjacent to the nourishment projects are often not monitored resulting in

no possibility of evaluating volumetric conservation. Aerial surveys provide the wide

coverage needed in order to help account for all of the material placed in a region. By

combining the results from a composite map with strategically placed ground truth

profiles, a rapid, inexpensive and complete method can be used to track entire volumes of

placed material.














CHAPTER 6
CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY


6.1 Summary and Conclusions

The best accuracy for the method developed in determining shoreline position for

any one point utilizing unrectified aerial photography was 11 feet. The method

developed by Dolan et al (1980) determined an error of 20 feet on a more energetic

shoreline while Fisher and Overton (1994) documented that digitizing directly from aerial

photographs and using USGS Topographic maps for control resulted in an error of 50

feet. When evaluating average shoreline change for an entire region, the accuracy of the

composite error improved to 3 feet.

After evaluating all of the data, it was determined that the average natural

shoreline receded approximately 7 feet ( 3 feet) during the six month time frame. When

including the nourished areas, the average shoreline accreted approximately 8.6 feet ( 3

feet). This shows that the nourishment projects appear to control the net amount of beach

recession throughout the entire 40 miles of shoreline within the county. It is also

important to realize that these results are influenced by the seasonal profile changes and

storms as mentioned earlier. The best way to filter out this uncontrollable factor and other

inaccuracies is by using aerial surveys with sizable temporal spacing with special care that

both aerial surveys are performed during the same season.








Since initiation of the project, many different techniques have been employed to

create a composite map with the purpose of extracting the most accurate shoreline

measurements. The most significant improvements in map accuracy are believed to be due

to small changes to the flight specifications. Preliminary planning for the August survey

specified a lower flight altitude (which produces a larger scale), an increase in the number

of visual targets and flight time coordinated with the predicted high tide; all of which are

believed to have contributed to improving the results.

The method developed here would also be suitable for documenting larger

shoreline changes which occur over a shorter time span such as the result of beach

nourishment projects and the impacts of major storms. For example, the average shoreline

change for all of the nourished areas throughout the county was approximately 103 feet

determined with aerial photography while ground truth determined the change to be 100

feet. When monitoring nourishment projects, it is important to document the topography

of the beach in order to keep track of the material being deposited within the design

template and naturally spread alongshore. With the cost and time required for ground

surveying, areas adjacent to the nourishment projects are often not monitored resulting in

no possibility of evaluating volumetric conservation. Aerial surveys provide the wide

coverage needed in order to help account for all of the material placed in a region. By

combining the results from a composite map with strategically placed ground truth

profiles, a rapid, inexpensive and complete method can be used to track entire volumes of

placed material.








6.2 Recommendations For Further Study

A second phase of this study is recommended to further develop and automate the

process. It is recommended that the second phase concentrate on: (1) rectifying the aerial

photographs to remove distortions due to roll of the aircraft, and (2) automate digitization

of the indicator representing the Mean High Water shoreline. The use of ground truth

surveys would be continued as a means of evaluating the accuracy of the methodology

implemented. Finally, it is suggested that the second phase effort would be most effective

if focused on two areas, one developed and one in a more natural condition. This focus

on two areas of reasonable longshore extent would allow methods to be developed and

evaluated more rapidly and effectively and efforts to be concentrated on development of a

procedure for application in future.














REFERENCES


Anders, F.J. and M.R. Bymes, "Accuracy of Shoreline Change Rates as Determined from
Maps and Aerial Photographs." Shore and Beach, Vol. 57, pp. 17-26, 1991.

Balsillie, J.H., J.G. Carlen and T.M. Watters, 'Transformation of Historical Shorelines to
Current NGVD Position For the Florida Lower Gulf Coast." Florida Department of
Natural Resources; Tallahassee, Florida, 1987

Carter, W.E. and R.L. Shrestha, "Airborne Laser Swath Mapping: Instant Snapshots of
our Changing Beaches." Fourth International Conference, Remote Sensing for Marine
and Coastal Environments; Orlando, Florida, 1997.

Clow, J.B. and S.P. Leatherman, "Metric Mapping: An Automated Technique of
Shoreline Mapping." 44th American Congress of Surveying and Mapping, Falls
Church, VA, pp 309-318, 1984.

Crowell, M. and S.P. Leatherman, M.K. Buckley, "Historical Shoreline Change: Error
Analysis and Mapping Accuracy." Journal of Coastal Research, Vol. 7,
pp. 839-852, 1991.

Dolan, R., B.P. Hayden and J. Heywood, "New photogrammetric method for determining
shoreline erosion." Journal of Coastal Engineering, Vol. 2, pp. 21-39, 1978.

Dolan, R., B.P. Hayden, P. May, and S. May, "The reliability of shoreline change
measurements from aerial photographs." Shore and Beach, Vol. 48, pp. 22-29, 1980.

Fisher, J.S. and M.F. Overton, "Interpretation of Shoreline Position from Aerial
Photographs." 24th International Conference on Coastal Engineering, Vol. 2,
pp. 1998-2003, 1994.

Kreuzkamp, A.J. and R.G. Dean, "Pilot Program to Quantify Shoreline Changes in Lee
County." University of Florida, Gainesville, Florida, 1997.

Leatherman, S.P., "Shoreline mapping: a comparison of techniques." Shore and Beach,
Vol. 51, pp. 28-33, 1983.








McBeth, F.H., "A method of shoreline delineation." Photogrammetric Engineering,
Vol. 22, pp. 400-405, 1956.

Moffitt, F.H., "History of Shore Growth from Aerial Photographs." Shore and Beach,
Vol. 4, pp. 23-27, 1969.

McCurdy, P.G., Manual of Coastal Delineation from Aerial Photographs, U.S. Navy
Hydro Off. Pub. No. 592, U.S. Navy Hydrographic Office, Washington, D.C., 1947.

Stafford, D.B., J. Langfelder, "Air Photo Survey of Coastal Erosion." Photogrammetric
Engineering, Vol. 37, pp. 565-575, 1971.

Weber, J.D.,"Photographic Monitoring of Shoreline Movement." Shore and Beach,
pp.36-38, April 1970.

Wolf, P.R., Elements ofPhotogrammetry, 2nd Edition, McGraw-Hill, New York,
628 pages, 1983.














BIOGRAPHICAL SKETCH


August J. Kreuzkamp II was born in Mineola, NY on 03 November, 1970. After

moving to Connecticut in 1984, he attended and graduated from Amity Regional High

School, Woodbridge, CT, in 1988. In 1992 he graduated from Roger Williams College,

Bristol, RI, with a Bachelor of Science in Civil Engineering. After graduation, he was

employed by a coastal engineering firm, Ocean & Coastal Consultants Inc., where he first

became exposed to the coastal engineering environment. In August 1995, he and his wife

Kristen moved to Gainesville, FL, to allow August the opportunity to begin his graduate

studies at the University of Florida within the Coastal and Oceanographic Engineering

Department. In August 1997 he graduated with a Master of Engineering degree.

Currently, he is again employed at Ocean & Coastal Consultants Inc. Trumbull, CT. with

family, friends and an education that will last him a lifetime.




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