Study Name:
Survey Type:
Survey Name:
NLDS-1997 POSTCAP Bathymetry
Disposal Site:

NLDS (1995-pres)

Start Date: 9/7/1997 End Date: 9/26/1997 Collector:
Process Description Bathymetric data were processed using SAIC'sHydrographic Data Analysis System (HDAS). Data

analysisincluded depth editing, filtering, and applying adjustmentfactors as necessary. Individual

survey lanes were editedto remove sounding outliers caused by vessel cavitation,fish in the

water column, or other factors. During dataanalysis, the raw bathymetric data were collected to

MeanLower Low Water (MLLW) and sound velocity. Tidal heightcorrections from the NOAA

Ocean and Lakes LevelsDivision (OLLD) web-server(//www.olld.nos.noaa.gov/data_res.html)

via the WorldWide Web (WWW). Following corrections, the depth data points were distance-

weighted to the center of the cell, resulting in a single sounding foreach cell of the matrix. Two and

Three-dimensionalbathymetric contour plots were then generated from thedepth matrix.
Logical Consistency The SAIC Poratble Integrated Navigation and SurveyingSystem (PINSS) provided the precision

navigation requiredfor all field operations. This system employs a Toshiba 386computer providing

real-time navigation and collection ofposition, and time data for subsequent analysis. ThePINSS

provided the navigator and the helmsman withrange and bearing to selected targets, signal quality,

andtime of day. A Hewlett Packard 7475A plotter tracked thevessel's position during survey

operations relative to thestation target. A printer provided hard copy of manuallycontrolled fixes.

Each fix consisted of the date and time,ship's position in latitude/longitude and the local X/Y
Attribute Accuracy Bathymetric surveys are conducted using an integratednavigation system and an ODOM DF3200

Echotrac echosounder. Accuracy limits for the echo sounderare rated to0.01-0.05% for the

overall depth. Bathymetric data arecorrected for the speed of sound in sea water calculatedwith

an internally recorded Sea-Bird Electronics, Inc. SBE19-01 Seacat Profiler CTD. The data are also

tidecorrected during post survey processing using near realtime NOAA tide data.
Horizontal Accuracy Vessel positioning was achieved with SAIC's PortableIntegrated Navigation Survey System

(PINSS). ThisPC-based system provides real-time navigation, andcollection of position, and time.

Vessel positioning wasdetermined using a Magnavox 4200D (aboard the M/VGelberman) GPS

positioning system interfaced to thePINSS.The PINSS utilized a Toshiba 3200X PC to providereal-

time navigation as well as to collect position and timedata for subsequent analyses. One to 5-meter

accuracywas achieved by applying a differential correction to theGPS signals from a Leica 41

DGPS reciever. Vesselposition was displayed on two monitors, one for the surveynavigator and

the second for the helmsman, to aid insteering the vessel toward target station locations. Each fix

incorporated time of day, the vessel's positionin latitude/longitude and UTM coordinates, signal

quality,and station and replicate identification. All positionsreceived were displayed in North
Vertical Accuracy An ODOM DF3200 Echotrac echosounder measureddepths with a narrow-beam, 208 kHz

transducer. Accuracylimits for the echosounder are rated at 0.01 to 0.05 percentof the overall

depth (approximately 2 cm for 42 m depth atthe Mud Dump Site). The transducer was installed near

theon-board GPS receiver antenna to reduce any horizontaloffset between navigation and

bathymetry data. Inaddition, the transducer was set with a 1-meter draft toavoid surface

interference with acoustical signal. Thetransducer pole was marked and checked frequently

during the survey for any movement. The 1-meter draft wascorrected in the ODOM, and the speed

of sound was fixedat 1500 m/s. A Sea-Bird Electronics, Inc. Model 19-01CTD was used to

acquire bertical profiles of the speed ofsound in the water column at the begining and end of each

survey day. This information was used after the survey toadjust the bathymetric data if the CTD-
Depth Datum Name Mean Lower Low Water
Depth Distance Units cm