n_ 



Then future bathymetric surveys may be conducted in NAD83 using DGPS and will be 

 depth differenced to the master grid. 



For efficient survey operations at WLIS, SAIC used DGPS data in conjunction with 

 SAIC's Portable Integrated Navigation and Survey System (PINSS) to position the survey 

 vessel over the July 1996 REMOTS® camera stations. A Magnavox 4200D GPS receiver 

 and a Magnavox MX50R differential beacon receiver provided DGPS positioning data to 

 PINSS in the horizontal control of North American Datum of 1983 (NAD 83) to an 

 accuracy of ±5 m. The Coast Guard differential beacon broadcasting from Sandy Hook, 

 New Jersey (286 kHz) was selected for satellite corrections due to its close proximity to 

 WLIS. 



The target REMOTS® station locations were calculated in NAD 27, then converted 

 to NAD 83 for real-time navigation using the U.S. Army Topographic Engineering 

 Center's CORPSCON version 3.01. The acmal positions of the REMOTS® replicate 

 photographs were recorded in NAD 83 and then converted to NAD 27 with CORPSCON 

 for compatibility with bathymetric data for reporting purposes. All REMOTS® data in the 

 DAMOS Database are stored in the native NAD 83 datum. 



2.4 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 Standard Operating Procedures (Murray and Selvitelli 

 1996). Depth values transmitted to INDAS were adjusted for transducer depth. The 

 acoustic remms 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, changes in sound 

 velocity through the water colunm, the slope of the bottom, vertical motion of the survey 

 vessel, 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 (NOAA 1997, 1998). This network is composed of 181 

 water level stations that are located throughout the Great Lakes and coastal regions of the 

 United States. 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 tidal data are available 1 to 6 hours from the time of collection in a station 

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



Monitoring Cruise at the WLIS Disposal Site, September 1997 and March 1998 



