Hawaii Environmental Sensitivity Index (ESI) Maps and the Spatial Accuracy of ESI Mapping Methodology

Abstract

ABSTRACT Environmental Sensitivity Index (ESI) maps and digital databases have been generated for the Hawaiian Islands. ESI atlases integrate the most recent data available in three general categories: shoreline habitats, biological resources, and human-use resources, to provide spill responders with a synopsis of critical information. The new Hawaii atlas was prepared using standardized ESI data collection and analysis methods. For the first time, the spatial accuracy of the ESI shoreline classification method has been quantitatively measured using GPS. Shoreline classification methodology consisted of low-altitude overflights during the 2.5 hours preceding and following low-tide. Aerial classifications were then checked on the ground throughout the study area. USGS 7.5 minute basemaps were used in the field and shoreline segmentation annotation was transcribed from scanned field maps to a digital shoreline provided by the State. ESI surveys in August of 2000 resulted in nineteen shoreline classes for the Hawaiian chain. The GPS field study was conducted simultaneously with shoreline classification. During GPS surveys boundaries between ESI shoreline segments were located in the field and their position recorded with a hand held GPS. The coordinates of the segment boundary as located on the final ESI map were compared to those recorded with the GPS. Data for over 60 locations were analyzed statistically using three commonly accepted error-reporting methodologies. A Root Mean Squared (RMS) error of 33.5 meters, a Circular Error Probable (CEP) of 28 meters, and a 95% error bound of 58.2 meters were found. Error occurred unsystematically and was attributed to various factors, including inaccuracies in basemap shorelines, human error in the field and cartography, and error expected when mapping natural gradations as discreet points.