Utilizing Orthogonal Coprime Signals for Improving Broadband Acoustic Doppler Current Profilers

Abstract

Broadband acoustic Doppler current profilers (BBADCPs) are instruments that are widely used for measuring ocean currents. The ambiguity velocity of the conventional method used in BBADCPs must accommodate all possible measurement velocities. Unfortunately, allowing a high-ambiguity velocity results in a high measurement deviation in conventional BBADCPs. We propose a method to break through the limitation imposed by the ambiguity velocity to improve BBADCPs. Our proposed method involves designing an orthogonal coprime signal to replace the conventional transmit signal in BBADCPs. The proposed orthogonal coprime signal consists of two orthogonal subsignals, whose ambiguity velocities are designed to be low and coprime. Utilizing the coprime property, we then employ the robust Chinese remainder theorem to resolve the velocity ambiguity from the two independent measurements made via the two orthogonal subsignals. Simulations show that our proposed method decreases the standard deviation of measurement velocity by nearly three times, compared to the conventional method used in BBADCPs. Our simulations also show that the proposed method can yield a 12-dB improvement of signal-to-noise ratio over the conventional method. This can help increase the profiling range significantly.