Kongsberg 1007D, Operator'S Manual

Page: 45 / 49

1007D Altimeter Operators Manual 974-72007001/1.0
1007D Altimeter Altitude Detection Algorithm Page 39
Kongsberg Mesotech Ltd.
Port Coquitlam, BC - Canada
The altitude extraction software starts processing the sonar data from range (time) 0.
At the start of the ping, at point
A , there is a large transmit pulse which will be ignored
by the altitude detection software. The software starts looking for a target return
starting after the end of the transmit pulse is over and also after a user-specified
minimum range parameter. If the user specifies a minimum range less than the range
corresponding to the transmit pulse length, then the pulse length value will be used as
the minimum range. Otherwise the user value is employed. This parameter can also be
used to eliminate unwanted returns from objects near to the altimeter (e.g. hulls, chains
etc.) by setting the value beyond the range of these objects. However, care must be
taken to not set the value too high so as to miss desirable returns.
A user-specified threshold parameter is used to set the level above which the sonar
data will be detected as returns. This is usually set high enough so that small unwanted
targets and noise (such as at
B ) do not become detected as returns.
Return samples are then evaluated proceeding to longer ranges. There may be low-
level returns and noise that are ignored because they are below the threshold. At some
point
C the signal rises above the threshold at the start of a potential return value. This
return is qualified to meet a minimum width as determined by a user-specified
minimum width parameter. After point
C is detected, the program evaluates the sample
data in the width interval following the first sample over the threshold (over the
interval
C to E ). Provision is included so that some samples may actually fall below
(low) the threshold D , but the majority of samples over the width must be greater
(high) than the threshold. If the majority is greater, then the return is flagged as a valid
return and its peak value
M is recorded as well as the range C . If the tested return is
not valid, then the search for a return resumes at the first sample after C .
If the return is valid and the profiling algorithm parameter is set to FIRST RETURN
then profile detection terminates and the value
C is taken as the altitude and M is taken
as the amplitude.