| 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 |