Kongsberg Simrad ST90, Reference Manual

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Details
Minimum Threshold
Some echoes are stronger than others. If you have noise problems, or you are bothered
with for example smaller fish (different species), jellyfish or plankton, you can use the
Minimum Threshold
function to adjust the sensitivity. The target strength (TS) for a
single target must exceed this threshold (in dB) to be accepted.
Use this function to define a "filter" value.
Follow 40 Log
Select this option to let the threshold follow the minimum level defined on the
Colour
Scale
page for the corresponding channel.
Minimum Echo Length
/
Maximum Echo Length
These settings only apply to CW operation.
The echo from a single target will normally have a similar (or slightly longer) length
than the length of the transmitted signal. This is due to the physical properties of
the target.
Some single targets are so close in range that they are overlapping. These will give
you a longer echo than the length of the transmitted pulse. It is important that such
multiple targets are excluded. By using the echo length values, you can define the
maximum and minimum length of the echo compared to the transmitted pulse. If the
echo is too long or too short, it will be excluded.
Example
If you set
Minimum Echo Length
to 0.8, all echoes shorter than 0.8 times
the length of the transmitted pulse will be deleted.
If you set
Maximum Echo Length
to 1.8, all echoes longer than 1.8 times
the length of the transmitted pulse will be deleted.
Maximum CW Phase Deviation
This setting only applies to CW operation.
Several single targets occurring at the same range will give you echoes in different
parts of the beam’s cross section. All samples in an echo from a single target will
normally have similar phase value (angles) as the samples arrives from the same
location. Echoes from multiple targets or random noise will show great variation
in phase.
To remove the bad targets, the angle (phase) between the samples in the echo are
measured. If the angle is too large, the echoes are deleted.
Functions and dialog boxes