In conjunction with the larger bathymetric survey conducted in February 1996 (see 

 Figure 1-2), SAIC also acquired analog sidescan sonar data along east- west lanes spaced 

 150 m apart across the southern half of PDS. Analysis of the analog sidescan records 

 acquired in close proximity to the target deployment location revealed that the seafloor 

 topography was very rough, with large boulders and features ranging from a few meters in 

 height to large rock ledges extending for distances of hundreds of meters. Nevertheless, 

 this location was chosen for the deployment of the moored array as it was the most level 

 region within the southwestern corner of PDS. As described in further detail below, the 

 final deployment site was characterized by silty sand and numerous boulders, and bordered 

 on the northeast by a large rock ledge within 100 m of the deployment site. 



2.1.3 Deployment and Recovery of Moored Instrumentation 



For all cruises, SAIC provided navigation equipment for vessel positioning during 

 deployment/recovery operations. Precision positioning data were acquired using a 

 Differential Global Positioning System (DGPS) receiver interfaced to SAIC's Portable 

 Integrated Navigation Survey System (PINSS) software. The PINSS provided helmsman 

 displays to facilitate continuous, real-time assessment of vessel position and drift in 

 relationship to target locations. 



Instrument deployments were conducted after the vessel had reached the target 

 location and determined the speed and direction of vessel drift due to winds and currents. 

 Next, the instrument array was lowered by a winch wire to approximately 2 m above the 

 seafloor while the vessel position was checked versus the target location. Release of the 

 instrument array was accomplished using either a release hook or a secondary acoustic 

 release attached to the winch wire. Both the vessel position and the exact time of release 

 were recorded by the PINSS. 



For array recovery operations, the acoustic release on the array was interrogated, 

 using an acoustic deckbox and transducer, after the vessel had been positioned in close 

 proximity to the array deployment location. Following interrogation, the array released 

 flotation that was attached to a line canister, allowing a small buoy to reach the sea 

 surface. The buoy's tether was used to raise the array from the seafloor and place it on the 

 deck of the vessel. The internally recording instrumentation was subsequently serviced and 

 electronic data were downloaded using a portable computer. 



2.1.4 Water Column Profile Measurements 



A single vertical profile of temperature, salinity (conductivity), and density was 

 acquired at the site of the moored instrumentation during the first, third, and fourth cruises 



Oceanographic Measurements at the Portland Disposal Site during Spring of 1996 



