2.0 METHODS 



2.1 Bathymetry and Navigation 



The SAIC Integrated Navigation and Data Acquisition System (INDAS) provided the 

 precision navigation required for all field operations. A complete description of this system 

 can be found in DAMOS Contribution No. 48 (SAIC 1985). Quality assurance and quality 

 control procedures utilized throughout this survey are described in the QA/QC plan for the 

 DAMOS Program (SAIC 1990b). The INDAS system uses a Hewlett-Packard 9920 series 

 computer to collect position, depth, and time data for real-time navigation and for subsequent 

 data analysis. A Del Norte Trisponder® System determined positions to an accuracy of ±3 

 meters. Shore stations for the present survey were established in Connecticut at known 

 benchmarks at the Millstone Point nuclear power plant and the New London Lighthouse 

 (Figure 1-1). The continued use of these shore station locations allows accurate comparisons 

 of past and present surveys. 



An Odom DF3200 Echotrac® Survey Recorder with a narrow-beam 208 kHz 

 transducer recorded depth to a resolution of 3.0 cm (0.1 feet). However, the acoustic 

 records could reliably detect changes in depth on the order of only 20 cm or more due to the 

 accumulation of errors introduced by the positioning system, tidal corrections, the calibration 

 of the fathometer (speed of sound through the water column), the slope of the bottom, and 

 the vertical motion of the vessel. The speed of sound used in depth calculations was 

 determined from water temperature and salinity data measured by a Seabird SEACAT SBE 

 19-01 CTD (Conductivity, Temperature, and Depth) probe (see Section 2.4 below). During 

 analysis, raw bathymetric data were corrected for speed of sound in sea water and 

 standardized to Mean Low Water by compensating for transducer depth and changes in tidal 

 height during the survey. A detailed discussion of the bathymetric analysis technique is 

 given in DAMOS Contribution No. 60 (SAIC 1989). 



The bathymetric survey conducted at NLON on 25 and 27 June 1991 encompassed a 

 1600 x 1600 m grid with 25 m lane spacing, centered at coordinates 41° 16.235' N and 

 72° 04. 492' W (Figure 1-2). This was the same grid used for the bathymetric survey in 

 June- July 1990, permitting depth differences to be calculated relative to the 1990 survey. 



2.2 REMOTS® Sediment-Profile Photography 



REMOTS® sediment-profile photographic surveys of the New London Disposal Site 

 have been carried out since June 1984. REMOTS® photography has been used to detect and 

 map the distribution of thin (1-20 cm) dredged material layers. This capability complements 

 the precision bathymetric surveys which can measure bottom elevation changes greater than 

 20 cm. In addition, REMOTS® is used to map benthic disturbance gradients, and monitor 



Monitoring Cruise at the New London Disposal Site, June 1991 



