The Symmiktos method: a robust and accurate estimation method for acoustic Doppler current estimation

Electronic devices, using ultrasound, can measure sea currents at different depths. The current at different depths, or cells, is directly proportional to the Doppler shift in that cell. When the burst or ping is transmitted toward the surface, scattering occurs from entrained air bubbles and other particles in the water. This is the basis for the Doppler signal and the measurement principle for an acoustic Doppler current meter. Due to the variance in the scattering signal, a trade-off between burst length, cell size and measurement time has to be made. Bias in the Doppler estimate is often a drawback when trying to decrease the variance. Traditional estimators are based on a Gaussian assumption about the scattered signals distribution, or rather the Doppler shift distribution. A robust and accurate estimate of the Doppler shift consists of a bias-free estimation of the current with a low variance for various types of data. The Symmiktos method is an estimation method that has improved the accuracy of the Doppler calculation, compared to standard methods. This paper contains a description of the background to acoustic Doppler current meters, the scattering signal, the traditional assumptions for a Doppler estimate, as well as suggestions for the improvement of models for the estimation. An introduction to the Symmiktos method, and the models that are the foundation for this new estimation method is also presented