Doc. P/N:
WSP-009-008
Version: V1.3
Issue Date:
April 2014
64
9.11 Why is my WASSP System not tracking the Seafloor?
Any source of noise mentioned in the answer to 9.9 and 9.10 above can cause the seafloor detection
to fail if it is bad enough. In some cases bad noise can cause the tracking to fail and it could take a
number of pings for the WASSP system to re-acquire the seafloor. In some instances noted below and
in bad cases of noise, it may not be possible to automatically resume seafloor tracking.
►
Power
If too much power is being used for the depth of water you are operating in, the seafloor tracking signal
could be noisy especially if there is enough power to cause signal distortion as the tracking algorithm may
track the rings produced by this. Conversely, too low a power level may result in the signal levels from the
seafloor being below the noise floor of the system and thus they will be ignored as noise. This will tend to
cause the surface noise to be considered as a bottom detection candidate.
►
Depth
The WASSP system can acquire a seafloor profile swath 3.5 times the nadir depth but this requires the acqui-
sition depth to be at least twice that of the maximum depth on that swath. WASSP takes this into account
and when the Range Dial reads 100m the system acquires to 210m. If the acquisition depth (i.e. range dial)
is in manual mode or the system fails to track down with the seafloor then you may need to manually in-
crease the system range to allow it to re-acquire the seafloor.
►
Fish
Occasionally a very large dense school of fish can be detected as a mountain on the seafloor. This should
be easy to determine with a second pass over the area at a later time. This function also allows wrecks to
show on the contour display as these are often similar in density to fish schools.
►
GPS Position
If there is no position input, the WASSP system will not output depth data and will cease to map the sea-
floor.
►
Minimisation
The seafloor tracking is affected by the Minimisation level; ensure this is set appropriately as described in the
Installation Manual on page 49.
9.12 Why doesn’t the seafloor line up when I go over it again?
There are several factors which can cause this to show on your WASSP display however remember that
if the vessel is operating in a high sea state, your motion sensor may not be able to fully compensate
for the vessel’s movement:
►
GPS Time Lag
The standard Furuno SC-50 and SC-30 Heading sensors have a
1.2 second delay
on GPS data. Ensure that
any GPS delay is entered into the Sensor Tab of the Ship Setup as this will cause large errors in depth (see
“Sensor” on page 49).
►
Motion Compensation
To make good use of motion compensation we must ensure that the WASSP transducer and any motion
sensors are securely mounted and do not move at all. The dynamic and static accuracy of the motion sen-
sor effectively determines the differences you can expect when you pass over the same area again.
►
Sea State
Motion Compensation is a complex process and makes some assumptions – the bigger the sea state and
the smaller the boat the less reliable the seafloor data will be as there is more reliance on the accuracy of
measurements and the input from the motion sensors.
►
Cornering
Motion compensation is costly to do to the nth degree. Most low end motion sensors have poor perfor-
mance on corners due to the centripetal acceleration forces caused by the turn affecting the delicate
balance of the sensor. Thus, seafloor detections collected while the boat is turning are likely to be of lesser
quality than those collected in a straight line.
