| | 182 |
| Study Name: | | Survey Type: |
| NLDS-1998 | | Bathymetry |
| Survey Name: |
| NLDS-1998 POSTCAP Bathymetry | | Disposal Site: |
| | NLDS (1995-pres) |
| | Start Date: | 7/22/1998 | End Date: | 8/1/1999 | 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 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 |