EVALUATION OF A LONGITUDINAL PROFILE DERIVED FROM AIRBORNE LIDAR: SOUTH RIVER, VA
The transport of mercury contaminated sediments in the South River poses a serious health risk to the environment and local human population. Sediment transport modeling of the river suggests that local slope is an important factor in predicting the location of short term mercury accumulation zones. A detailed longitudinal profile for the length of the river is necessary to identify these accumulation zones accurately. Acquiring a longitudinal profile of sufficient detail for 36.2 km of river through traditional field survey techniques is time and man hour intensive.
NASA Experimental Advanced Airborne Research LIDAR (EAARL) provides a means of acquiring bathymetric data for a river in a single day. EAARL utilizes a 532-nm-wavelength 1.3 ns laser pulse, with a 0.20 m diameter ground foot print at 300m, capable of penetrating 20 m below the surface of the water in ideal conditions. Post processing and filtering of the raw data set removes approximately half of the points produced (4,361,069 raw to 2,398,469 filtered points). The result of the EAARL survey is a 5 m resolution DEM and a detailed 36.2 km longitudinal profile with a 16 m point spacing. Cross sections from the EAARL DEM fit to field surveyed cross sections have RMSE values ranging from ~0.2 to ~0.6 m, providing a means to evaluate the accuracy of the bathymetry produced from the EAARL data. Evaluating the detailed longitudinal profile in terms of morphological units (pools and riffles) provides insights into the variation in river morphology that exists between the upper river (low slope) and the lower river (high slope).
Airborne LIDAR proves to be an effective means of producing a bathymetric DEM and a longitudinal channel thalweg profile.