Acoustic Doppler Current Meters (common acronym ADCM) estimates the current flow in the water by studying the Doppler frequency shift created by entrained air bubbles and particles, creating a backscatttering signal from the tonal Doppler signal transmitted. The foundation for the use of the covariance approach as the estimator for the center frequency, is based on a Gaussian assumption for the backscattered time signal. In real life applications, the signal can have a large deviation from these assumptions. Instead of using a rather "broadband random" approach, this paper proposes a tonal signal model, describing the backscattered signal, and the background to the typical Doppler signal received. Both modeled data as well as large real-life data is used to show typical behavior of the backscattering signal. Statistical tests, analyzing if the backscattering signal obeys Gaussian properties or not, is presented. Analysis of a possible Gaussian behavior is performed, quantifying when a Gaussian behavior can be expected and when this new signal model might be more appropriate. Then, an innovative signal model is presented based on a summation of multiple sinusoids, with the support from this large data set collected and the analysis. The paper also compares the results with real-life data illustrating how a tonal signal model based on "summation of sinusoids," is an interesting alternative to the classical Gaussian signal model.
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