is determined by the distance (range) from each of the two shore stations to 

 the survey vessel and this range information is displayed on the onboard master 

 ixnit. The geographic (horizontal) position of the shore stations must be known 

 for the position of the survey vessel to be plotted by trilateration (solved by 

 using three sides of the triangle). This can be done by using an automated 

 plotter interfaced with the positioning system or by using a programable calcu- 

 lator and manually plotting the fix locations on a map or navigation chart. 



The seismic reflection records are supplemented by cores of the subbottom 

 sediment. The sediment cores are usually collected where the subbottom re- 

 flectors are within the penetration range of the cores. Cores are correlated 

 with the subbottom reflector data. Sediment data can thus be areally extrapo- 

 lated to provide a measure of continuity between cores. This, in many cases, 

 allows mapping of the general subbottom structure of the study area. 



Although not essential, side-scan sonar data collected simultaneously with 

 the seismic data are very useful. Side-scan sonar is an effective method of 

 illustrating surface geologic features and sea floor configurations such as 

 sand waves, rock outcrops, areas of scour and deposition, as well as bottom 

 hazards and potential archeological sites. In some cases it also determines 

 if a sand body is active; i.e., actively affected by waves and currents. A 

 fathometer should be used during coring operations to record water depth infor- 

 mation at core site locations. Additional informtion on sediment composition 

 between coring sites can be obtained by using a bottom grab sampler. 



2. Essential Equipment . 



In addition to the essential seismic profiling system, horizontal position- 

 ing system, and a coring device, various other types of equipment are required 

 to conduct the survey. A suitable survey vessel is needed to accommodate the 

 seismic and positioning equipment and other instruments that may be used, such 

 as side-scan sonar and a fathometer, during data collection. Radios are re- 

 quired for a communications link with the survey vessel and shore personnel 

 assigned to the positioning system shore stations. Vehicles are needed by the 

 shore personnel when periodically relocating the shore transponders used with 

 the positioning system. 



During coring operations a platform is required for the coring device, an 

 air compressor, and a crane to deploy the coring device. The coring platform 

 must be a boat large enough to accommodate the equipment- -a tug and barge 

 arrangement, or a self-propelled barge (standard or jack-up type) . A recon- 

 naissance vessel should be used to deploy buoys or floats at the core sites. 

 A small reconnaissance craft with the positioning system aboard has greater 

 maneuverability when attempting to match or duplicate range values of previous 

 position fixes. However, this is not required if a fully automated positioning 

 system with a real time plotter and steering indicator, which allows for steer- 

 ing on a direct course to the desired location, is aboard the coring platform. 



Appendix A contains a list of equipment and specifications of the various 

 components of essential equipment plus other auxiliary equipment normally used 

 with these surveys . 



