1. Georegistering Aerial Photographs:
Measuring Seagrass
Prop Scarring

2. Seagrass
Submerged flowering plant found in shallow marine or estuarine waters
Provides habitat for many commercially important animals
Disturbed by brown tide, low water quality, dredging, and propeller scarring

3. Project Goals: Obtain unregistered aerial photograph Obtain DOQQ’s
Use basemap with known coordinate system to register photograph
Use registered photograph to digitize and measure propscarring

4. 1. Aerial Photograph 1:9,600 format Warren Pulich Jr., Ph.D.
International Institute for
Sustainable Water Resources
Texas State University
San Marcos, Texas
Coastal Bend Bays & Estuaries Program

5. 2. Digital Orthophoto Quarter Quads
Computer generated image of aerial photograph with features represented in true geographic positions
Used as base map
Coordinate system:NAD83
Projection: UTM

6. DOQQ’s: Estes Flats

7. Texas Coast
Estes Flats,
North Redfish Bay

8. Registering Aerial Photos
Add unregistered aerial photo to basemap
Use Georeferencing tools to align aerial photo with basemap
Fit to display
Add control points
Choose transformation order

9. 1st Order Polynomial
Allows photo to be shifted or scaled, but does not deform image
Requires at least 3 links

10. 2nd Order Polynomial Allows some distortion of photo
Requires at least 6 links

11. 3rd Order Polynomial Requires at least 10 links
Allows maximum distortion of photo when links are poorly aligned

12. Registered Map
2nd order transformation
13 links

13. Measuring PropScars ArcCatalog: Create New Feature Class
Use editor and sketch tool to trace along each prop scar
Open attribute table of New Line feature class and sum total length of new lines

14. Digitized Propeller Scars
Total length of prop scarring =
6,456 meters
Average length of each prop scar =
122 meters

15. Conclusions Higher resolution photo needed for measuring smaller scars
Thanks. Questions?