Figure 3. Instrumentation layout on dredge Thompson

ERDC TN-DOER-I4

August 2000

The Thompson SI System. The Thompson uses the DREDGEPAK software made by Coastal

Oceanographics. This software was modified by Coastal Oceanographics starting in August 1998

to serve as a SI DSS. Additional data were collected during the 1999 dredging season and more

will be collected for the 2000 dredging season. Most of the needed hardware was already available

and installed on the dredge. The Ship Server (a 100 MHz Pentium laptop computer) was provided

by the SI work unit.

Thompson Data Acquisition. As stated earlier, primary data requirements are the corrected

three-dimensional position of the dredge cutterhead, and an indicator of production. As shown in

Figure 3, the Thompson measures horizontal position with a differential Global Positioning System

(GPS). The GPS antenna is located on the pilothouse, so the heading angle from the gyro is used

to translate the antenna position to the horizontal cutterhead position. The vertical cutterhead

position is measured with an angle sensor located on the dredge ladder. This position is corrected

using the river-stage. Although the SI specifications state that these positions should be reported

to the Class 1 survey accuracy standard of one-half foot, this has not yet been verified on the

Thompson.

Figure 3. Instrumentation layout on dredge Thompson