<title>Multiple surface channels in Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) airborne lidar</title>

In this application of LIDAR (light detection and ranging), the times of flight for signals detected from the reflection of the light pulse off the air/water `surface' interface and off the sea bottom are converted into slant range distances from which the water depth can be determined. The SHOALS system records data for three independent channels which contain surface information. Two of these, the infrared, which is effectively an interface return, and Raman, which is strictly a volume return, are used singly or in concert to ensure that these goals are met. Results from the green channel are ambiguous due to the uncertain nature of the origin of that energy, and are not used. Field test results indicate that easily detectable returns were received in both infrared and Raman channels under virtually all test conditions. The use of independent surface channels also permits operation at extremely shallow depths. Excellent delineation of tidal erosion `cuts' through nearly exposed `mud banks' was obtained in Florida Bay for use in flow modeling programs.