Benthic Habitats of the Main Hawaiian Islands Prepared by Visual Interpretation from Remote Sensing Imagery Collected by NOAA Year 2000: Oahu (Section 2)

This project is a cooperative effort among the National Ocean Service, National Centers for Coastal Ocean Science, Center for Coastal Monitoring and Assessment; the University of Hawaii; and Analytical Laboratories of Hawaii, LLC. The goal of the work was to develop coral reef mapping methods and compare benthic habitat maps generated by photointerpreting georeferenced color aerial photography, hyperspectral and IKONOS satellite imagery. Twenty-seven distinct benthic habitat types within eleven zones were mapped directly into a GIS system using visual interpretation of orthorectified aerial photographs and hyperspectral imagery. Benthic features were mapped that covered an area of 790 km^2. In all, 204 km^2 of unconsolidated sediment, 171 km^2 of submerged vegetation, and 415 km^2 of coral reef and colonized hardbottom were mapped.

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.

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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. Please see the metadata records for each data set for complete information on the source, limitations, and proper use.

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

The purpose of this study was to determine the relative accuracy of maps generated from the photointerpretation of three sources of remotely sensed imagery. Four test areas were identified based on the diversity of the habitat types and to ensure that all benthic habitat types throughout the Hawaiian Islands were represented. A random stratified sampling method was implemented to select field sites to test the map accuracy. Each site was navigated to using a Trimble Geo Explorer 3 GPS data logger, and positional data was acquired. The three types of imagery were acquired during different days with different weather conditions. The habitat type for the portions of the test area that were not interpretable due to cloud cover, glint or water quality were classified as unknown. The accuracy assessment points that fell within polygons with the habitat type of unknown were not included in the accuracy analysis. As a result, the total number of accuracy assessment points varies between the imagery types within a single area. Two statistical analyses (Kappa and Tau test and the Z score) were performed. The Kappa and Tau statistic for the major habitat types showed that the percent overall accuracy of photointerpretation of color aerial photography, IKONOS satellite and hyperspectral imagery is 90.7%, 86.5% and 89% respectively. The Z score showed that at the 90% confidence level there was no significant difference between data gathered from the three imagery sources. At the 95% confidence level there is a significant difference in the quality between aerial photographs and IKONOS satellite imagery. The accuracy assessments tests showed that the ability to generate benthic habitat maps with an overall accuracy of 90% at the 95% confidence interval is reaching a threshold using imagery with three meter pixel size allowing for spectral enhancement of the imagery with reduced resolution.

RMS from digitized output was determined using the ESRI RMEer2 extension and shown to be less than 1m when conducted at 1:6000 scale.

NOAA supplied georeferenced imagery to Analytical Laboratories of Hawaii. Delineation of all habitat boundaries was conducted with the image scale at 1:6,000. This ensures that the level of detail produced by the photointerpreter is uniform throughout the project. Also, NOAA has shown from similar mapping efforts in the Caribbean and Florida Keys, that little additional information is gained from having the image at a smaller scale and the labor intensity increased significantly. The minimum mapping unit (MMU) for identifying habitats or features was 1 acre for visual photointerpretation. The software utilized in this project was designed to alert the photointerpreter each time a polygon was drawn smaller than the MMU. When this occurred the photointerpreter has the choice whether to include the polygon in the data set.

All three types of remotely sensed imagery were processed by NOS prior to map production. Individual color aerial photographs were georeferenced and mosaicked. The hyperspectral data composed of 72 ten nm wide bands were subsetted to three band composites that enhanced deep and shallow water features. IKONOS satellite imagery was corrected for atmospheric and water column effects. During the digitizing process, image stretches and manipulating image contrast, brightness and color balance were performed in the ArcView Image Analysis Extension to enhance features in the processed imagery.GIS topologic quality was established by executing ArcView extension routines that check for: overlapping polygons, multipart polygons, sliver polygons and void polygons. Additionally checks for adjacent polygons with the same habitat attributes were completed. All errors were identified and corrected. This file is believed to be logically consistent.