values before producing an accurate contour plot. Analysis of the bathymetric data was 

 conducted using the Hydrographic Data Analysis System (HDAS). 



2.2 Subbottom Survey 



An X-Star Model SB-216 Full Spectrum Digital Subbottom Profiler, manufactured 

 by Precision Signal, Inc., was used to acquire subbottom profile data at CSDS. Subbottom 

 seismic profiling is a standard technique for determining changes in acoustic impedance 

 below the sediment- water interface. Acoustic impedance is the product of the density of 

 the layer and the speed of sound in the layer. The depth of penetration and degree of 

 resolution are dependent on the frequency and pulse width of the seismic signal, and the 

 characteristics of the penetrated material. 



The narrow beam (13°) transducer of the X-Star system was mounted in a towfish 

 body that trailed approximately 15 meters behind the survey vessel. During the subbottom 

 survey, the X-Star profiler generated a frequency-modulated pulse that was swept over an 

 acoustic range from 2 to 20 kHz. The pulse rate was kept at 6 pulses per second for 

 optimum performance of the output devices. At 6 pulses per second, while traveling at the 

 average vessel speed of 4-5 knots, a subbottom measurement was acquired every 34-43 cm 

 along the vessel track. 



The amplified return signal of the X-Star transducers was sent through an A/D 

 converter to an onboard Sun Sparc II Workstation for data display and archive. Data were 

 displayed on the screen in real time and ported to an Alden thermal printer for a hard copy 

 record. Data were also stored on Exabyte tapes for further processing on shore. 



Bathymetric and Subbottom Survey at the Cornfield Shoals Disposal Site, July 8, 1994 



