Operation Manual
FarSounder, Inc.
F31552 (Rev. 3.8.0)
Page 46 of 69
the 3D Sonar View. Note: If this check box is not checked and there is a sea bottom, then that bottom may
show up as a large number of targets, provided the squelch is set to a low enough value.
Squelch Control
Targets on the seafloor beyond the bottom mapping limit or in the water column are detected as in-water
targets. In order to detect in-water targets, a detection threshold based on the signal level of the in-water
targets must be specified. This threshold is call the In-Water Target Squelch level and it operates similar to
the squelch level on a radio. With a high squelch level, small signals are rejected but little noise is accepted;
with a low squelch level, small signals are accepted but more noise is detected too.
Auto Squelch Check Box
With Auto Squelch checked, the software automatically determines the best detection threshold using
adaptive thresholding methods. Auto Squelch is the recommended operating mode for detection of in-water
targets.
Squelch Control Slider
Most of the time, Auto Squelch mode will perform better than manually setting the squelch level. However,
Auto Squelch may occasionally allow too much clutter to pass through the filters. In this case, the user
can still increase the squelch level manually (though they can never reduce the squelch lower than the
automatically detected level). The lowest signal level detected with Auto Squelch is indicated next to the
manual squelch slider and can be used as a reference when switching to manual squelch mode.
Like with radar, it is recommended that the squelch be set so that occasional false alarms are detected.
This will help to ensure that real targets are not missed due to squelch levels set too high.
When making squelch adjustments, typically a change of a few dB is all that is needed. Remember that
changes generally take two pings to become visible.
