The Symmiktos Method

The Symmiktos Method, is a Robust and Efficient Estimation Method for Acoustic Doppler Current Estimation developed by Dr Thomas Lagö.  Sea current measurements have been of great interest for many years. Mechanical current instrument are still widely used for such applications. Electronic devices using ultrasound can measure the current at different depths, i.e. a current profile. 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, sand and other particles in the water. This is the base for the doppler signal and the measurement principle for an acoustic Doppler current meter. Due to the variance in the scattering signal, a tradeoff 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 efficient estimate of the Doppler shift consist of a bias-free estimation of the current with a low variance for various type of data. The Symmiktos method is a frequency domain method which has improved the accuracy of the Doppler estimation, compared to standard methods.