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.
O'Mara, Greenhorne & , 20020102, Molokai Photomosaic 2000 (331-0524) - Orthorectification and Mosaicing of Color Aerial Photography Main Eight Hawaiian Islands: Greenhorne & O'Mara, Greenbelt, MD.This is part of the following larger work.
Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), National Centers for Coastal Ocean Science (NCCOS), Center for Coastal Monitoring and Assessment (CCMA), Biogeography Program, 2002, Benthic Habitats of the Main Hawaiian Islands Prepared by Visual Interpretation from Remote Sensing Imagery Collected by NOAA Year 2000: NOAA's Ocean Service, National Centers for Coastal Ocean Science (NCCOS), Silver Spring, MD.
This is a Raster data set.
Planar coordinates are encoded using Row and Column
Abscissae (x-coordinates) are specified to the nearest 1.0
Ordinates (y-coordinates) are specified to the nearest 1.0
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257.
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.
Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), National Geodetic Survey (NGS), 2000, Color Aerial Photographs Main Hawaiian Islands Collected by NOAA Year 2000: NOAA's Ocean Service, National Geodetic Survey (NGS), Silver Spring, MD.
United States Geological Survey, 200111, digital elevation models: U.S. Geological Survey, Reston, VA.
Analytical Laboratories of Hawaii, 2002, ground control points: Analytical Laboratories of Hawaii, Kailua, Hawaii.
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
Person who carried out this activity:
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.
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 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.
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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.
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(format Burned onto CD-ROM)
Project information is available online or on CD-ROM through the NCCOS Biogeography Program.
The user may utilize a variety of software to view the imagery mosaics (MrSID files), including ENVI, PCI, Arc GIS or ArcView 3.1ó or higher and the "MrSID Image Support" Extension turned on.