MAPPING WATER DEPTH IN CHEASAPEAKE BAY, FLORIDA KEYS, AND HAWAII: A COMPARISON OF BATHYMETRIC SOUNDINGS AND LANDSAT 8 OPERATIONAL LAND IMAGER IMAGING

Rapid and accurate determination of water depth has been an elusive goal. Changes due to storms, sedimentation, and human operations require constant monitoring of water depth for scientific, commercial, and military reasons. Improvements to the Landsat program with the start of normal operations of Landsat 8 in May 2013 provide improved capability to detect water depth with moderate spatial resolution. The Landsat 8 Operational Land Imager (OLI) has two new spectral bands in the visible deep blue and shortwave infrared. Both improve the detection of shallow water, the deep blue ban directly and the shortwave infrared to eliminate cloud regions from analysis. In addition, Landsat 8 has higher radiometric resolution than previous missions, which allows much finer distinction of the color differences in shallow coastal waters. Landsat 8 collects more data than previous missions, and scenes can be freely downloaded with a 16 day revisit cycle. Multiple Landsat 8 scenes in three areas (Chesapeake Bay, Florida Keys, and Hawaii) have been compared with NOAA bathymetric soundings and lidar data to verify the accuracy of depths inferred from the Landsat OLI imagery. The accuracy of depth predictions from the Landsat imagery depends on water clarity, surface roughness of the water depending on wind generated waves, and solar elevation angle which depends on latitude and time of year. Because the 15 m panchromatic Band 8 does not add much to the other bands, Landsat imagery only supplies 30 m resolution for spatial analysis. Commercial satellites like WorldView-2 have similar multispectral capabilities and radiometric resolution with 2 m spatial resolution, and the next generation WorldView-3 will have 1.24 m resolution, bringing the possibility of high resolution bathymetric mapping from orbit.