calibration of omni-directional fisheries sonar using split beam target positioning

The recently released scientific data format from the Simrad SX90 and SU90 fisheries sonar, the accuracy and resolution is sufficient for scientific purposes. For biomass estimation on surveys it is a necessary that the equipment is calibrated. In recent years, numerous calibration trials have been conducted on both the SX90 and SU90 fisheries sonars, where each trial has led to new discoveries and new calibration protocols. The conclusion of the calibration will be presented as two parts. First presented is a suggestion of how to perform a sonar calibration, positioning the reference target inside each acoustic beam either by the split beam method or by target amplitude interpolation between neighboring beams. Simulations are made in order to study accuracy, benefits and limitations of each positioning method. Further, the results from a full calibration is presented, along with an interpretation of calibration overall accuracy.