Maritime Doppler ultrasonic echo velocity correction by filtering - allowing for time constant of Doppler log in LP filter introducing difference signal for multiplication by vessel-specific coefft.

摘要

The method involves correcting (30) measurements by means of a recursive infinite impulse response low-pass filter (40) whose coeffts. are exponential functions of acquisition rate, reciprocal of a time delay of a Doppler log (20) and a constant (K) characteristic of vessel dynamics. The filtered and unfiltered signals are differenced (50) for multiplication (60) by the same constant, which may range from less than 1 for slow tankers to 10 for speedboats. The prod. is added (70) to the unfiltered signal. The differencing and multiplication may be combined in a variable-gain differential amplifier. USE/ADVANTAGE - Esp. on survey ships. Doppler log measurements are improved with avoidance or minimisation of position errors.