IMAGENEX DT101Xi, Technical Manual

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4.4.3.1. Reference Model Processing
A sounding grid should be defined (in Hypack this is done prior to commencement of the survey and is called
an MTX file) that is within the test area with a cell size of 0.3 m x 0.3 m.
Tides and sound velocity should be applied to all logged data.
MBES processing software should be used to remove outer beams that are outside of 3 times the average
water depth (or approximately 45° angle limit). Positions, attitude and bathymetric data should be thoroughly
cleaned using the manual cleaning tools (as opposed to automatic) provided in the processing package used.
In Hypack, the XYZ should be saved as one point per cell, and ‘Minimum # Points for Average’ = 3 (see
Figure 4-11)
Figure 4-11 Hypack XYZ options
4.4.3.2. Check-lines Processing
Next, the check lines should be processed. All beams should be kept (i.e. do not impose angle limits) and
only
obvious positional and bathymetric outliers should be removed. If any systematic artefacts are found in
the profiles, they should not be cleaned as they will be used to quantify variance.
The tool provided (in most MBES processing packages) is now used to compare the check-lines (with all
data) the reference model (with outer beams removed) and generate numerous statistics.
In Hypack, the same user defined Matrix file (MTX) as for the reference model is selected and the check-line
data loaded into it. The beam angle test is now run and a variety of statistics and graphics are presented
showing the comparison between the reference model and check lines.
An example of a statistical output is as follows (Figure 4-12), and shows % depth residual on the Y axis and
beam angle on the X. As can be seen, there is a 1.2% depth residual at the outer beams and approximately
0.4% residual at nadir.
Figure 4-12 Image courtesy of [Whittaker et al]