IMAGENEX DT101Xi, Technical Manual

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6. Data Processing
The processing of multibeam data is a specialized undertaking and cannot comprehensively be covered in
this document. The following bullet points are fundamental considerations to be made during data processing:
•
Data should be loaded with the correct sounding grid cell size (see Section 3.2.6).
•
Some packages allow for the processing of depth as elevation, but generally allow for the selection
of depth mode or elevation mode. Since DT101
Xi
and DT102
Xi
output depth, depth mode should be
selected.
•
Tide mode should be set and the tide file covering the entire time of survey and at the appropriate
interval loaded. Usually there is a tide time plot available to QC the tide data. This should be
opened and it should be verified that no tidal anomalies exist.
•
The sound velocity file(s) from the SV casts should be loaded to compensate for ray bending and
enable overall propagation calculations. Usually there is an SV time plot available to QC the SV
data. This should be opened and it should be verified that no SV anomalies exist.
•
It may be possible to set a static or dynamic draft in the processing package, that will apply a Z
offset according to draft changes. If these data is available, it should be used.
•
Various devices are usually set in the processing package that indicate the data source for things
like navigation, MRU, heading and sonar heads. This is usually where the offsets derived during
the establishment of the reference frame are set. (see Section 3.2.2).
•
Usually there is an MRU (heave, pitch and roll) time plot available to QC the MRU data. This should
be opened and it should be verified that no anomalies exist.
•
The results of the patch test are usually entered in the processing package.
•
The heave device and method to be used is usually entered in the processing package. It should
be ensured that the sign convention is correctly set (noting the heave sensor’s sign convention) as
some packages (including Hypack) apply heave in an unconventional way.
•
Once the preliminary settings are completed, the data (position and sonar) may be processed by a
combination of automatic filters and manual means. The job requirements should be consulted to
ensure compliance with specifications during processing.
Note: as previously stated, processing of data differs widely depending on the processing suite used, the
survey type, the output requirements and a host of other factors; and is therefore outwith the scope of this
document.