Klein Marine Systems, Inc. HydroChart 5000, Operation And Maintenance Manual

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CHAPTER 3 Preparation for Deployment
HydroChart 5000 Sonar Operations and Maintenance Manual P/N 11210080, Rev. 02
Following are a few available references containing information about the
calculation procedures for these offsets and errors:
• "Field Procedures for the Calibration of Shallow Water Multibeam
Echo Sounding Systems," Andre Godin, Canadian Hydrographic
Service, Halifax, Nova Scotia, Canada, 1996.
• "US Army Corps of Engineers, Engineer Manual EM-1110-2-1003,"
Hydrographic Surveying, Jan-02.
3.10.1 Static Position Offsets
It is necessary to first measure the static position offsets between the Sonar Head
Unit, the position sensor and the motion reference unit, relative to some reference.
These measurements will provide the necessary data for applying lever-arm
corrections to the final bathymetric solution. SonarPro provides an interface to
record these offsets in the Ship Geometry Setup dialog box such that they can be
recorded along with the sonar data to provide real time correction during data
acquisition. See the "SonarPro User Manual" (P/N 11210079) for more
information.
3.10.2 Latency Error
This test will provide a measurement of the latency error, or time, in the overall
system, which manifests itself as a position error in the processed data. It is
recommended that lines be run in the same direction and at different speeds over
an area with a prominent bathymetric feature. This will offset any effects due to
pitch bias. The greater the speed difference the more accurate the measurement.
The latency can be derived by measuring the along-track displacement of depth
measurements over the bottom feature.
3.10.3 Pitch Bias Test
Pitch bias is similar to roll bias, except that pitch error lies in the along-ship’s
fore-aft axis. This error occurs when the motion reference unit and the transducer
arrays are not pitch-aligned; that is, they are not mounted on the same fore-aft axis.
The resulting error changes the apparent location of a feature and is proportional to
water depth. In addition, along-track displacement error increases as water depth
increases. For the pitch bias test the survey vessel should run reciprocal lines on a
sloped bottom, preferably on the order of 10–20 degrees, for 200–300 meters. It
may be possible to use a channel feature instead of a long sloping bottom. Speed
for the test should be equal for both lines.