To measure the drift of the ice, the four slanted beams transmit long pulses, compared to normal current profile pings. A long transmit pulse means the ice is ensonified for the full beam width. This generates a strong, sharp and accurate echo back to the instrument which is Doppler shifted proportional to the velocity of the ice. A Nortek proprietary algorithm is used for estimating the ice tracking and the instrument gives out the ice velocity in the set coordinate system.
Figure of Merit (FOM) is a quality parameter that estimates the white noise (or Doppler noise) for each ping, and gives a snapshot of the quality of the measurement. In general, a lower FOM is better, and if the number is high it should be considered removing the velocity estimate from the series. FOM is scaled to be proportional to the standard deviation.
Updated