The NASA-USGS-NPS EAARL Airborne Lidar Survey of the Dry Tortugas in August 2004
The geospatial distribution of 2-m resolution benthic habitat complexity within the Dry Tortugas coral reef ecosystem in the 0- to 25-m depth range has been investigated using NASA Experimental Advanced Airborne Lidar (EAARL) surveys and the Along Track Reef Imaging System (ATRIS). The NASA EAARL is a blue-green pulsed airborne laser altimeter with capabilities for cross-environment surveys of fine-scale emergent and shallow submarine topography. The USGS ATRIS is a boat-mounted instrument that acquires continuous digital still-scaled images of shallow-marine substrates. EAARL laser soundings of submarine elevations in August 2004 resulted in a 1-m resolution digital elevation model that was analyzed to create a map of the topographic complexity, or lidar rugosity, over Pulaski, Loggerhead, and Southeast Banks in the Dry Tortugas. As calculated in our study, lidar rugosity is a dimensionless number that rises from a minimum of 1.0 with substrate departure from perfect smoothness and flatness at 2-m horizontal resolution. Mean substrate lidar rugosity was calculated within narrow intervals of substrate elevation, slope, and aspect. Benthic habitat type shallower than -10 m was determined along extensive transects throughout the shallow Dry Tortugas by interpretation of voluminous, precisely geolocated, digital ATRIS images of benthic communities. Shallow topographic complexity in the Dry Tortugas increases monotonically to about 1.1 with increasing slope from 0 degrees to 17 degrees, and is highly variable about that value in the 17 degrees to 45 degree range. Sharp spikes in lidar rugosity, typically approaching maxima near 1.2, occur at roughly 24 narrow-aspect intervals, likely due to the preferred geographic orientations of high-complexity habitats. Lidar rugosity rises slightly from near unity to 1.01 with decreasing substrate elevation from 0 to -10 m, varies around that value from -10 to about -17 m, rises sharply to exceed 1.5 at -23 m, and falls to less then 1.2 at -24 m.
EAARL color-coded DEM image of Garden Key. This image shows a seamless representation of subaerial and submerged topographic data. [larger version] |
EAARL color-coded DEM image of Loggerhead Key. This image shows a seamless representation of subaerial and submerged topographic data. [larger version] |
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