77_ 



photographs were later reconverted to NAD 27 with CORPSCON for DAMOS database 

 entry and reporting within this document. 



2.3 Bathymetric Data Collection and Processing 



An ODOM DF3200 Echotrac® Survey Fathometer with a narrow beam 208 kHz 

 transducer measured individual depths to a resolution of 3.0 cm (0.1 ft.) as described in the 

 DAMOS Navigation and Bathymetry Reference Report (Murray and Selvitelli 1996). 

 Depth values transmitted to INDAS were adjusted for transducer depth. The acoustic 

 remrns of the fathometer can reliably detect changes in depth of 20 cm or greater due to 

 the accumulation of errors introduced by the positioning system, vertical motion of the 

 survey vessel, changes in sound velocity through the water column, the slope of the 

 bottom, and tidal corrections. 



Observed tidal data were obtained through the National Oceanographic and 

 Atmospheric Administration (NOAA), Ocean and Lake Levels Division's (OLLD) 

 National Water Level Observation Network. This network is composed of 181 water level 

 stations that are located throughout the Great Lakes and coastal regions of United States 

 interest. These stations are equipped with the Next Generation Water Level Measurement 

 System tide gauges and satellite transmitters that have collected and transmitted tide data to 

 the central NOAA facility every six minutes, since 1 January 1994. 



Observed tide data are available 1 to 6 hours from the time of collection in a station 

 datum or referenced to Mean Lower Low Water (MLLW) and based on Coordinated 

 Universal Time (UTC). For the 1996 CLIS survey, data from NOAA tide station 8467150 

 in Bridgeport Harbor, Bridgeport, CT, was used for tidal calculations. The NOAA 6- 

 minute tide data was downloaded in the MLLW damm, corrected to local time, and tidal 

 differences based on the entrance to New Haven Harbor, New Haven, CT, were applied. 



During the bathymetric survey, a Seabird Instruments, Inc. SBE 26-03 Sea Gauge 

 wave and tide recorder was used to collect tidal data on-site. The tide gauge, deployed in 

 the survey area, recorded pressure values every six minutes. After conversion, the 

 pressure readings provided a constant record of tidal variations in the survey area. These 

 observed tidal data were later used to compare and verify the corrected NOAA data 

 generated from the Bridgeport Harbor station (Figure 2-2). 



A Seabird Instruments, Inc. SEACAT SBE 19-01 Conductivity, Temperature, and 

 Depth (CTD) probe was used to obtain sound velocity measurements at the start, midpoint, 

 and end of each survey day. The data collected by the CTD probe were bin-averaged to 1 

 meter depth intervals to account for any pycnoclines, rapid changes in density that create 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1996 



