Source Speed Estimation using a Pilot tone in a High Frequency Acoustic Modem

In this paper, the authors propose to estimate the Doppler velocity of a moving high-frequency underwater acoustic modem source. Hermes, as this modem is known, currently uses a robust moving average estimate for Doppler compensation. A new auto-regressive approach to Doppler estimation provides better estimates. Simulation results indicate that, at a constant velocity of 2 m/s and in the presence of additive noise (with a signal-to-noise ratio of 75 dB), the Doppler velocity is estimated with an RMSE of 0.23 m/s using moving average vs. 0.00018 m/s for the auto-regressive approach. An experiment was also conducted to compare the estimated Doppler velocity obtained using the two algorithms. The setup consisted of a receiver hydrophone attached to a towing carriage that moved with a known velocity relative to a stationary acoustic source. The source transmitted 375 kHz pilot tone. The accuracy of the algorithms was compared against the true velocity values of the carriage in the presence of noise and multipath. At a constant velocity of 0.4 m/s and for a signal-to-noise and interference ratio of 6.3 dB, the RMSE was 0.6055 m/s using moving average vs. 0.0780 m/s using auto regressive approach.