| A new sub-bottom profiling system, the HI-DAPT II, was designed, assembled and field tested. The system is adaptable to a variety of marine acoustic sources thus suited to any aqueous environment. The system uses a digital signal processing (DSP) board with 2 channels of 16 bit analog-to-digital conversion, embedded in a PC chassis, to acquire and process sub-bottom data. Conventional post-stack processing algorithms such as frequency filtering, automatic gain control, swell filter, predictive deconvolution and spiking deconvolution have been coded to run on the DSP to enable processing of the data between successive shots. A two-channel hydrophone streamer consisting of a single hydrophone and a line array is used to collect sub-bottom data. Raw data are stored together with a time stamp and processing parameters on an magneto-optical disk. Processed data are displayed on a CRT and output to a thermal plotter. The HI-DAPT II system was field tested over a portion of the West Florida Sand Sheet, 37 km south of Panama City Florida, as part of the Coastal Benthic Boundary Layer Special Research Project. The objective of the HI-DAPT-II survey was to delineate the vertical extent of the sand sheet in the area. Three, 5 km-long, seismic lines were acquired over the lone axis of a grid as well as two tie lines. A series of tests was performed to determine the optimum processing parameters. Processed data, displayed in wiggle trace/variable area format, revealed two main reflecting horizons. The shallowest reflector is interpreted to represent an erosional cycle during the deposition of the sand sheet which occurred 10,000-7,500 ybp. The deepest, high-amplitude reflector exhibits erosional features. This reflector is interpreted to be the top of the Mio-Pliocene Intracoastal Formation. Field tests have demonstrated how this system has overcome some of the limitations of conventional subbottom profiling systems. |
