Applanix POS MV V5 Installation And Operation Manual page 222

POS MV V5 Installation and Operation Guide
Theory
of Operation
Default Heave Filter Parameters
The default heave filter parameters are:
• Heave bandwidth = 20 seconds
• Heave damping ratio = 0.707 (critically damped)
These default values give the best compromise between settling time and steady state heave error for a
vessel performing multibeam surveys in sea conditions up to sea state five.
On a different class of vessel in a different sea state, a different combination of heave filter parameters
may provide better results. The following guidelines assist in selecting appropriate heave filter
parameters.
Guidelines for Setting Heave Filter Parameters
The best combination of heave filter parameters will depend on the following factors:
• Survey conditions - how often does the survey vessel change speed or direction?
• The dynamic characteristics of the survey vessel, in particular the induced heave following
changes to engine throttle settings.
• Significant heave amplitudes caused by the response of the survey vessel to the sea state.
You can determine empirically the correct combination of parameters for a particular survey vessel during
trials. The following are guidelines for selecting appropriate values:
3. Select heave filter parameters according to the following criteria:
• Heave bandwidth - equal to or greater than the longest heave period
• Heave damping ratio - in the range 0.45 to 0.71
4. Calculate the maximum allowable steady state percentage error as follows:
Maximum percentage error =
Choose a heave bandwidth and damping ratio to achieve the required maximum percentage error
with the shortest settling time.
Usually, the maximum heave error is comparable with the resolution of the bathymetric sonar that
requires heave compensation. The significant amplitude will change from one day to the next with
sea state and, therefore, so will the maximum percentage error.
B-12
Maximum heave error
Significant heave amplitude
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