290

Study Name:

Survey Type:

CLDS-2000

Bathymetry

Survey Name:

CLDS-2000 HYDROGRAPHIC BASELINE Bathymetry

Disposal Site:

CLDS (1995-pres)

Start Date:

9/8/2000

End Date:

9/9/2000

Collector:

SAIC

Process Description

All data processing was conducted using the SAIC ISS2000 system. Initial navigation quality control

was done on the vessel shortly after the data was collected. Where time allowed, multibeam data

were edited onboard the vessel using the geoswath editor, which provides both plan and profile

views of each beam in its true geographic position and depth. At the end of each day, both the raw

and processed data were backed up onto 4 mm tape and shipped to the Data Processing Center in

Newport, RI. In the processing center, manual data editing was completed and reviewed by a

licensed Hydrographer. Verified tide data from the Bridgeport, CT (846-7150) station were applied to

the multibeam data during post-processing. The data collected along the three cross lines were

compared to soundings obtained from the same locations along the mainscheme survey lines as a

quality control tool. Any questionable data were noted and later evaluated by the lead Hydrographer.

Logical Consistency

Precision navigation, helmsman display, and data integration from the multitude of sensors aboard the

survey vessel were accomplished with the use of SAIC¿s Integrated Survey System 2000 (ISS-

2000). Real-time navigation, data time tagging, and data logging were controlled by the ISS-2000 in a

Windows NT 4.0 environment

Attribute Accuracy

This bathymetric survey was conducted using precision navigation, helmsman display, and data

integration from the multitude of sensors aboard the survey vessel and were accomplished with the

use of SAIC¿s Integrated Survey System 2000 (ISS-2000). Real-time navigation, data time tagging,

and data logging were controlled by the ISS-2000 in a Windows NT 4.0 environment

Horizontal Accuracy

Positioning information was recorded from multiple independent Global Positioning System (GPS)

receiver networks in the North American Datum of 1983 (NAD 83). Two, linked GPS receivers

embedded within a TSS POS/MV 320, 3-axis Inertial Motion compensation Unit (IMU) were used as

the primary source for vessel position and attitude correctors applied to the multibeam data. The

POS/MV IMU was interfaced with a Trimble Probeacon Differential Beacon Receiver to improve the

positioning data to an accuracy of +/- 5 m. Correctors broadcast from the U.S. Coast Guard

differential station in Brunswick, ME (316 kHz) were applied to the GPS satellite data. The ISS-2000

monitored horizontal dilution of precision (HDOP; quality of the signal); number of satellites, elevation

of satellites, and age of correctors to ensure the resulting bathymetric positioning errors did not

exceed five meters at the 95% confidence level. The second GPS system served as a source of

Vertical Accuracy

Because of the swath acoustic coverage provided by multibeam systems, there are several external

data sensors that must be incorporated into any multibeam survey. In addition to the position, depth,

and water column sound velocity typically required for a single-beam survey, multibeam surveys

must also have sensors to accurately measure vessel heading, heave, pitch, and roll. A RESON

8101 shallow water, multibeam system was employed for the acquisition of sounding data over the

PDS survey area. The RESON 8101 was mounted on the keel of the survey vessel, and utilizes 101

individual narrow beam (1.5°) transducers capable of yielding a total swath coverage of 150° (75°

per side). The actual width of coverage is adjustable through range scale settings with a maximum

equivalent to 7.4 times the water depth. The RESON 8101 transducer can transmit up to 12 high

frequency (240 kHz) sound pulses, or pings, per second, though that number may be reduced in

Depth Datum Name

Mean Lower Low Water (MLLW)

Depth Distance Units

centimeters