Sounding Better!
Correcting Multibeam Wobble in MBMAX64
By Mike Kalmbach
“Wobble” is sometimes used by Hydrographers to describe motion artifacts in multibeam
data. Figure 1 is an example. What should be a flat bottom is wobbling all over.
FIGURE 1. Multibeam wobble shown in the Sweep window of MBMAX64
Wobble can show up for a number of reasons:
Double correction for boat motion. Both the sonar and the processing software apply
corrections.
• Backward or skew mounted MRU.
• Uncompensated latency of MRU or sonar data.
These can be corrected with MBMAX64 adjustments. Other wobble sources can not – No
correction for boat motion, uncalibrated MRU and a flexible pole mount are three examples.
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Wobble adjustments are available starting in MBMAX64 version 16.1.15.
Start Wobble 64 corrections with the button at the upper right of the Sweep Window.
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Correcting Multibeam Wobble in MBMAX64
The Sweep window is a good place to start because wobble is easy to see there (Figure 1). A
tight color range and vertical exaggeration makes wobble stand out further.
CORRECTIONS
Figure 2 shows the adjustments available to correct wobble. As adjustments are made, the
Sweep window is updated to show the effect. Use the Sweep display and Wobble Magic
Number (below) to home in on the wobble fix.
FIGURE 2. Wobble Correction Options
CHOOSE STEP SIZE
This will be familiar to our Patch Test users. Step size is shown at the right and applied to the
up/down adjustment buttons.
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Coarse = 1.000
Correcting Multibeam Wobble in MBMAX64
• Medium = 0.100
• Fine = 0.010
• Very Fine = 0.001
For example, click Coarse to set 1.0 steps then click MRU, Adjust, Yaw, Down to decrease by
one degree.
MRU
The check boxes enable certain MRU special cases. For example, if the MRU is reversemounted, check Invert Pitch and Invert Roll on.
Step offset adjustments up or down, or enter values followed by the Apply button.
SONAR
Check Reverse Mount if sonar data was received backward. That can happen with bad
settings in the sonar control. Adjust sonar latency up or down if it helps.
WOBBLE MAGIC NUMBER
This number attempts to
quantify wobble error. It is
based on along-track depth
change by beam. Depth
changes are squared and the
summation is averaged to
come up with the magic
number.
The graph shows up to 256
adjustments. Try to minimize
the magic number in your analysis.
APPLY BUTTON
Click this to apply offset changes.
TEST OK BUTTON
Click this when satisfied with results.
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Correcting Multibeam Wobble in MBMAX64
RESET BUTTON
Click this to start over.
CANCEL BUTTON
Click this to exit with no changes.
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