Technical Note 6: FMGT fix for Kongsberg echosounders with non-zero sensor offsets for active positioning system

What are the changes?

The georeferencing of beam footprints was incorrect for Kongsberg echosounders where the active positioning system had non-zero sensor X/Y/Z offsets with respect to the vessel reference point.  These offsets are now used to adjust the georeferencing correctly.  Users can verify the positioning system offsets in the Sensor Configuration dialog in FMGT under the Settings menu.

Who does this impact?

Problems due to these offsets in previous versions would have appeared as along-track and across-track georeferencing biases in mosaic imagery and other map products like ARA or statistics.  Furthermore, large offsets in shallow water would have led to a gap in the nadir region of angular response curves used for ARA analysis.  ARA results from previous versions should be recomputed.

To  verify if  data has been impacted by this problem; create a new FMGT project, import a single .all file from the data set and have a look at the sensor offsets under the "Settings" menu by choosing the "Sensor Configuration" option.  This produces  a display that looks like the image below. If the GPS configuration offsets have a non-zero X or Y component, such as the example image, then your data will be affected by this change.  The other offsets are already accounted for correctly.