Bad-weather calibration of split-beam echo sounder systems

A condition for standard-target calibration is stability of the sonar platform and target rig. This condition cannot always be met, nor need it be when the transducer has a split-beam function. Since the position of the target can be known even when it is moving, the beam pattern can thus be removed from the measurement, allowing direct sensing of the target's backscattering cross section whenever the target is in the beam. The calibration can therefore be performed when the target is off-axis or moving