Generation Mechanism of Acoustic Doppler Velocity Measurement Bias

A Doppler velocimetry logger (DVL) is a sonar attached to a vehicle that, when underway, transmits a pulse signal at regular intervals and measures the Doppler frequency of the seafloor echo to determine the vehicle's velocity relative to the Earth. The velocity measurement bias of DVL refers to the deviation of the average measurement velocity from the true value and is a quantitative measure of accuracy, which can be used to evaluate the performance of a DVL. DVL designers must tradeoff velocity measurement bias and requirements, such as size and power. To date, the DVL measurement bias has received little attention, and the underlying physical mechanism has yet to be completely elucidated. In this article, the DVL echo is modeled by a linear time-varying channel. An analytical expression for the DVL seafloor echo Doppler spectrum is established by analyzing echo statistical properties. The physical mechanism of the bias has been analyzed by this analytical expression. Then, an analytical equation for predicting the bias is proposed. Compared with the bias prediction method proposed by Taudien and Bilén (2018), the equation proposed in this article has equivalent predictive power, but with clear physical meaning, and provides a means to predict bias.