Orthorectification and Mosaicking of Color Aerial Photography for the Main Eight Hawaiian Islands: Lanai (318n-0506)

Habitat maps of the main Hawaiian Islands were created by visual interpretation of aerial photos and hyperspectral imagery using the Habitat Digitizer extension. Aerial photographs are valuable tools for natural resource managers and researchers since they provide an excellent record of the location and extent of habitats. However, spatial distortions in aerial photographs due to such factors as camera angle, lens characteristics, and relief displacement must be accounted for during analysis to prevent incorrect measurements of area, distance, and other spatial parameters. These distortions of scale within an image can be removed through orthorectification. During orthorectification, digital scans of aerial photos are subjected to algorithms that eliminate each source of spatial distortion. The result is a georeferenced digital mosaic of several photographs with uniform scale throughout the mosaic. Features near land are generally georeferenced with greater accuracy while the accuracy of features away from land is generally not as good. Where no land is in the original photographic frame only kinematic GPS locations and image tie points were used to georeference the images. After an orthorectified mosaic is created, photointerpreters can accurately and reliably delineate boundaries of features in the imagery as they appear on the computer monitor using a software interface such as the Habitat Digitizer.

The National Ocean Service is conducting research to digitally map biotic resources and coordinate a long-term monitoring program that can detect and predict change in U.S. coral reefs, and their associated habitats and biological communities.

514

The National Oceanic and Atmospheric Administration (NOAA) National Centers for Coastal Ocean Science(NCCOS) produced this data CD-ROM. NCCOS Biogeography Program doesnot guarantee the accuracy of the geographic features or attributes.

Project information is available online or on CD-ROM through the NCCOS Biogeography Program.;

None

None

Microsoft Windows 2000 Version 5.0(Build 2195) Service Pack 3; ESRI ArcCatalog 8.2.0.700

Average spatial accuracy of individual photomosaics is reported in Chapter 3 of Benthic Habitats of the Main Hawaiian Islands. Positional accuracy was determined by solution of Softplotter generated model (RMS less than 1) and by comparison to independent ground control data. The georegistration of these photographs is at least 95% sigma RMS of 5 meters.

Cloud Cover: 2

No color balancing was attempted since this alters color and textural signatures in the original imagery and interferes with the photointerpreter's ability to delineate habitats. As a result mosaics have visible seams between adjacent photos. This provides the photointerpreter with "true color" imagery for maximum ability to identify and delineate benthic features.

Once all of the photographs were orthorectified, the best segments of each photograph were selected for creation of the final mosaic. Segments of each photograph were selected to minimize sun glint, cloud interference, and turbidity in the final mosaic. Where possible, parts of images obscured by sunglint or clouds were replaced with cloud/glint free parts of overlapping images. As a result, most mosaics have few or no clouds or sun glint obscuring bottom features.