All other values are direct measurements
The USGS has developed a hydrographic survey system specifically designed to map in very shallow water. The system can acquire data in water depths of ~25cm, but in practice boat/motor draft limitations prevent surveying in water depths less than 45cm. Precise differential GPS receivers are used to measure boat position and dynamic elevation, a survey quality 200 kHz depth sounder acquires water depth measurements, and a motion sensor measures heave, pitch, and roll of the boat. A measurement is collected about every 3m along a survey line. The vertical accuracy of the system is +/- 8cm and +/- 4cm inches horizontally.
EAARL is a new airborne lidar that provides unprecedented capabilities to bays, the nearshore shoreface, benthic habitats, coastal vegetation, and sandy beaches. The EAARL sensor suite includes a rasterscanning- water penetrating full-waveform adaptive lidar, a down-looking color digital camera, a hyperspectral scanner, and an array of precision kinematic GPS receivers which provide for sub-meter georeferencing of each laser and hyper-spectral sample. EAARL has the unique real-time capability to detect, capture, and automatically adapt to each laser return backscatter over a large signal dynamic range and keyed to considerable variations in vertical complexity of the surface target. EAARL limited to water depths greater than 50 cm and can penetrate the water column to approximately 1.5 secchi disk depth. The lidar has a ground footprint of 30cm with vertical and horizontal accuracies equal to the SANDS system. The swath width is 250m which converts to a spatial coverage of approximately 1 laser shot per square meter.
The EAARL system wasa used to map shallow (less than 1.5 secchi depth) and nonturbid areas in Estero Bay and nearshore areas. The SANDS system was used in deeper areas and those which are turbid which include the Caloosahatchee River.
Bathymetric mapping has been done for the following areas: Estero Bay, Charlotte Harbor, Pine Island Sound, offshore regions of Sanibel and Captiva Islands and on the Florida West Coast the Caloosahatchee, Shark, Little Shark, Broad, Harney, Lopez, Chatham, and Turner Rivers. The offshore region between Ft. Myers and Naples, FL will be mapped during FY05.
U.S. Department of the Interior, U.S. Geological Survey
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