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.
ground condition
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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 sun glint 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.
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.
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.
Photographs were scanned and orthorectified.
Elevation data was used to correct for relief displacement in the photographs.
Fixed ground features visible in the scanned photos were selected for GCPs which were then used to georeference the imagery
Aerial photographs were acquired for the main Hawaiian Islands Benthic Mapping Project in 2000 by NOAA Aircraft Operation Centers aircraft and National Geodetic Survey cameras and personnel. Approximately 1,449, color 9x9 inch photos were taken of the coastal waters of the main Hawaiian Islands at a 1:24,000 scale. Prints and diapositives were created from the original negatives. Diapositivies were then scanned at a resolution of 500 dpi using a photogrammetric quality scanner, yielding one by one meter pixels for the 1:24,000 scale photography. All scans were saved in TIFF format for the purposes of orthorectification and photointerpretation. Georeferencing/mosaicing of the TIFFs was performed using a variety of softcopy photogrammetric software including Socet Set Version 4.2.1, Autometric Softplotter, PCI OrthoEngine, and Erdas OrthoBASE. First, lens correction parameters were applied to each frame to eliminate image distortion. Airborne kinematic GPS was then used, to provide first order georegistration. Image to image tie-points were then used to further co-register the imagery, especially for photos taken over open water when ground control points were not available. Fixed ground features visible in the scanned photos were selected for ground control points (GCPs) which were then used to georeference imagery. GCPs were measured using a Differentially-corrected Global Positioning System (DGPS). We obtained points with a wide distribution throughout the imagery, especially on peninsulas and outer islands whenever possible since this results in the most accurate registration throughout each image. Only ground control points for terrestrial features were collected due to the difficulty of obtaining precise positions for submerged features. Pre-existing USGS 10-meter digital elevation models were used to correct for relief displacement
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NOAA makes no warranty regarding these data, expressed or implied, nor does the fact of distribution constitute such a warranty. NOAA and NODC cannot assume liability for any damages caused by any errors or omissions in these data, nor as a result of the failure of these data to function on a particular system.The National Oceanic and Atmospheric Administration (NOAA) National Centers for Coastal Ocean Science (NCCOS) produced this data CD-ROM. NCCOS Biogeography Program does not guarantee the accuracy of the geographic features or attributes.
Project information is available online or on CD-ROM through the NCCOS Biogeography Program.
