Kongsberg 1007D, Operator'S Manual

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974-72007001/1.0 1007D Altimeter Operators Manual
Page 40 1007D Altimeter Altitude Detection Algorithm
Kongsberg Mesotech Ltd.
Port Coquitlam, BC - Canada
If the algorithm is set to PEAK RETURN, the return just validated is saved as a
potential altitude and the search for further returns continues after
F . In order to help
distinguish between distinct returns, the software first looks for an 'absence' of return
signal where the level solidly drops below the threshold level for a specified distance.
This distance is controlled by the minimum gap parameter. The signal cannot be above
the threshold anywhere in the gap. As shown in the figure, the gap will probably not be
right after the width test - the program will continue to search for the gap until one is
found
F to G .
After the gap is found, the program resumes looking for another return after the point
G, using the same threshold value and width checking as for the first return. A buffer
of up to 30 potential altitudes can be built up in the PEAK RETURN mode.
Once all potential returns have been found to the end of the ping, the program then
chooses the altitude value from the return that has the highest amplitude. Referring to
the figure above, a second return was found at
H with an amplitude N - the program
would then use the altitude H with amplitude N .
Care must be used when employing the PEAK RETURN mode. This mode is not
appropriate when the desired altitude is the first return and it has an amplitude less
than later returns or when the gain is increased so that normal sonar background noise
becomes a level higher than the threshold (especially near the end of the ping with the
increase in TVG. This noise will probably can easily be detected and returned as
altitude in the PEAK RETURN mode.
The additional maximum range parameter can be set to limit the maximum range at
which the search for returns in the data will stop. When this value is less than the range
setting, no sonar samples beyond that range will be evaluated as possible returns. This
may be useful in some situations when there are unwanted targets (real targets or
noise) at ranges much larger than the actual altitude being measured.