328

Study Name:

Survey Type:

CCBDS-2001

Bathymetry

Survey Name:

CCBDS-2001 INTERIM Bathymetry

Disposal Site:

CCBDS (1982-pres)

Start Date:

8/18/2001

End Date:

8/21/2001

Collector:

SAIC

Process Description

Bathymetric data were processed using HYPACK processing module. Data processing included

depth editing, filtering, and applying adjustment factors as necessary. Individual survey lanes were

edited to remove sounding outliers caused by vessel cavitation, fish in the water column, or other

factors. During data analysis, the raw bathymetric data were collected to Mean Lower Low Water

(MLLW) and sound velocity. Tidal height corrections from the NOAA Ocean and Lakes Levels

Division (OLLD) web-server (//www.olld.nos.noaa.gov/data_res.html) via the WorldWide Web

(WWW). Following the corrections, the depth data points were distance-weighted to the center of

the cell, resulting in a single sounding for each cell of the matrix. Two and Three-dimensional

Logical Consistency

Coastal Oceanographic¿s HYPACK provided the integration platform for precision navigation required

for all field operations. This system employs a Toshiba Satellite computer providing real-time

navigation and collection of position, depth, and time data for subsequent analysis. Vessel speed

during survey operations was approximately 4 to 5 knots. The HYPACK system provided the

navigator and helmsman with range, bearing and offset to a selected target (i.e., beginning and end

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

sensors (i.e., water depth data from the fathometer). Each fix consisted of the date and time, ship's

position in latitude/longitude and the local X/Y coordinate system. HYPACK logged the data at one-

Attribute Accuracy

Bathymetric surveys are conducted using an integrated navigation system and an ODOM Hydrotrac

echosounder. Accuracy limits for the echo sounder are rated to 0.01-0.05% for the overall depth.

Bathymetric data are corrected for the speed of sound in sea water calculated with an internally

recorded Sea-Bird Electronics, Inc. SBE 19-01 Seacat Profiler CTD. The data are also tide corrected

during post survey processing using near real time NOAA tide data.

Horizontal Accuracy

A Trimble DSMPro DGPS receiver provided differentially-corrected Global Positioning System (DGPS)

data in conjunction with Coastal Oceanographic¿s HYPACK® navigation and survey software to

provide real-time navigation to an accuracy of 1-3 meters.

Vertical Accuracy

An ODOM Hydrotrac echosounder measured depths with a narrow-beam, 208 kHz transducer.

Accuracy limits for the echosounder are rated at 0.01 to 0.05 percent of the overall depth . The

transducer was installed near the on-board GPS receiver antenna to reduce any horizontal offset

between navigation and bathymetry data. In addition, the transducer pole was marked and checked

frequently during the survey for any movement. The 1-meter draft was corrected in the ODOM, and

the speed of sound was fixed at 1500 m/s. A Sea-Bird Electronics, Inc. Model 19-01 CTD was used

to acquire vertical profile data of the water column at the beginning middle and end of the survey

day. This information was used after the survey to adjust the bathymetric data if the CTD-measured

Depth Datum Name

Mean lower low water (MLLW)

Depth Distance Units

centimeters

Use Constraints

This data was collected and processed for a specific U.S. Army Corps of Engineers activity and

indicates the general existing conditions at the time of collection. As such, the data are only valid for

their intended use, content, time, and accuracy specifications. The user is responsible for the

results of any application of the data for other than the intended purpose.