Georegistering Aerial Photographs:

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Georegistering Aerial Photographs

• Measuring Seagrass
• Prop Scarring

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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

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Project Goals

• Obtain unregistered aerial photograph
• Obtain DOQQs
• Use basemap with known coordinate system to
  register photograph
• Use registered photograph to digitize and measure
  propscarring

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1. Aerial Photograph

• 19,600 format
• Warren Pulich Jr., Ph.D.
• International Institute for
• Sustainable Water Resources
• Texas State University
• San Marcos, Texas
• Coastal Bend Bays Estuaries Program

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2. Digital Orthophoto Quarter Quads

• Computer generated image of aerial photograph
  with features represented in true geographic
  positions
• Used as base map
• Coordinate systemNAD83
• Projection UTM
• http//www.tnris.state.tx.us/digital.htm

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DOQQs Estes Flats
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Texas Coast
Estes Flats, North Redfish Bay
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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

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1st Order Polynomial
Allows photo to be shifted or scaled, but does
not deform image
Requires at least 3 links
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2nd Order Polynomial
Allows some distortion of photo
Requires at least 6 links
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3rd Order Polynomial
Requires at least 10 links
Allows maximum distortion of photo when links are
poorly aligned
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Registered Map
2nd order transformation
13 links
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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

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

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