Towfish Sensors - C-Max CM2 User Manual

CM2 Sidescan Sonar User Manual

22. TOWFISH SENSORS

Heading and Depth Sensors
The towfish heading may be different from the direction of the towfish track if there is a cross-current.
Heading information, if available, may be used to correct the apparent location of targets by compensating
for the yaw of the towfish relative to its track.
The heading sensor output also includes towfish pitch and roll. These parameters are not relevant to
processing the image but can indicate if, for some reason, the towfish is not towing correctly.
Towfish altitude measurement (bottom tracking) is standard in the CM2 towfish. Towfish depth is generally of
secondary importance and can usually be estimated by subtracting towfish altitude from water depth
measured by the ship's echo sounder. However sometimes it can be useful to have a direct measurement of
towfish depth: for example, a record of towfish depth plus altitude can provide a bathymetry trace for the
survey line.
Towfish Heading Sensor
The optional heading sensor may be already installed in the towfish when delivered or may be retrofitted in
the field.
To fit the sensor, first open the towfish to expose the towfish PCB. See the section on Replacing the Towfish
PCB for advice on opening the towfish.
Attach the Heading Sensor Extension to the towfish PCB as shown in the illustration. Then attach the
Heading Sensor itself to the extension. The heading sensor cable connects to J7 on the towfish PCB.
Fitting the Heading Sensor and Heading Sensor Extension to the Towfish PCB
Note that towfish PCBs of V.6 onwards accept full RS232 voltage levels, so they can be connected directly to
the sensor. Earlier PCBs require a converter built in to the cable, to convert from full sensor voltage to 0-5V
levels.
The heading sensor specification is in Section 15.
Note that the output of the heading sensor is "magnetic" not "true". A suitable offset may be added to correct
for local magnetic variation.
The sensor may be re-calibrated using the command available in MaxView. This procedure need only be
o
undertaken once in a new locality. After initiating the command, rotate the towfish twice through 360 over a
period of about 2 minutes, holding it approximately horizontal.
Version 3.6 (2008)
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