974-72007001/1.0 1007D Altimeter Operators Manual
Page 6 Theor
of Operation
Kongsberg Mesotech Ltd.
Port Coquitlam, BC - Canada
where R = range, Ro = reference range (1m), and a =
attenuation constant in dB/range units. The first term
compensates for the natural spreading loss proportional to the
inverse of the square of the distance, assuming a wide, flat,
bottom. The second term compensates for losses due to
energy absorption and is directly proportional to the distance,
assuming uniform water salinity, temperature, and pressure.
The sampled data set of the received signal may contain
numerous ‘returns’ of varying amplitudes due to noise or
representing actual targets. The DSP identifies those ‘returns’
that meet the following adjustable criteria as potential
candidates for the final range measurement:
a) minimum amplitude (threshold)
b) minimum pulse width
c) minimum inter-pulse gap width
d) minimum range
e) maximum range
Adjustments are made to these settings to reduce the detection
of spurious and/or low reflectance targets. The minimum
range setting can also be adjusted to eliminate nearby targets
such as vessel hulls, cables, etc. near the altimeter.
The range of candidate ‘returns’ in the sample data set is
estimated as the time the ‘return’ pulse first exceeds a
minimum amplitude threshold.
After the candidate ‘returns’ have been identified from the
sample data set, one is chosen by the DSP using a decision
rule that selects the sea bottom return. The operator can select
one of the following decision rules the 1007D uses to
determine the sea bottom return:
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