Study Name:
Survey Type:
Survey Name:
NLDS-1998 POSTCAP Bathymetry
Disposal Site:

NLDS (1995-pres)

Start Date: 7/22/1998 End Date: 8/1/1999 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 Portable Integrated Navigation and SurveyingSystem (PINSS) provided the precision

navigationrequired for all field operations. This system employs aToshiba 386 computer providing

real-time navigation andcollection of position, depth, and time data for subsequentanalysis. Vessel

speed during survey operations wasapproximately 4 to 5 knts. The PINSS system provided the

navigator and helmsman with range, bearing and offset toa selected target (i.e., begining and end

of survey lane),signal quality, time of day, and selected data from anyoperational environmental

sensors. Each fix consisted ofthe date and time, ship's position in latitude/longitude andthe local

X/Y coordinate system. PINSS logged the data atone second intervals and stored them on disk in
Attribute Accuracy Bathymetric surveys are conducted using an integratednavigation system and an ODOM DF3200

Echotrac echosounder. Accuracy limits for the echo sounder are 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, time, and

depth soundings forsubsequent analysis. Vessel positioning was determinedusing a GPS

receiver. One to 5 meter differential GPSaccuracy was achieved by applying corrections to the

GPS signals that were acquired from a modem thatrecieved corrected signals.
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 pole was marked and checkedfrequently during the

survey for any movement. The1-meter draft was corrected in the ODOM, and the speedof sound

was fixed at 1500 m/s. A Sea-Bird Electronics,Inc. Model 19-01 CTD was used to acquire vertical

profiledata of the water column at the begining middle and end ofthe survey day. This information

was used after thesurvey to adjust the bathymetric data if the CTD-measuredspeed of sound
Depth Datum Name Mean lower low water
Depth Distance Units cm