Detiding shipboard-mounted ADCP data: an analysis of model data and observations using a polynomial interpolation method

Abstract

A method for determining the net non-tidal flow from shipboard-mounted acoustic Doppler current profiler (ADCP) data is applied to observations from the Gulf of the Farallones in 1991- 2. Tidal currents represent a significant portion of the total flow in the region. Both the tidal and non-tidal current fields arc characterized by spatial and temporal variability on small scales. The detiding method performs a least- squares fit to determine the spatial structure of both the amplitudes of the major tidal constituents and the magnitude of the non-tidal flow. Synthetic data is used to examine the requirements and constraints in choosing the best polynomial fitting function for each of the field's components. Arbitrarily choosing a higher-order polynomial to represent these fields may result in misrepresentation of the true flow. Results of applying this technique to vertically-averaged ADCP data from five seasonal surveys of approximately five-day duration are presented.