| | 175 |
| Study Name: | | Survey Type: |
| NLDS-1997 | | Bathymetry |
| Survey Name: |
| NLDS-1997 MASTERdGPS Bathymetry | | Disposal Site: |
| | NLDS (1995-pres) |
| | Start Date: | 9/7/1997 | End Date: | 9/26/1997 | Collector: | | SAIC |
| 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 |