Currents

Ocean currents have been reported via three instruments thusfar, an FSI (Falmouth Scientific Instruments) current meter, Aanderaa current meters, and the "Workhorse" acoustic doppler current profiler.

The east and north components of the current velocity are already reported by the FSI current meter in units of cm/s and need no significant further processing. Speed and direction are derived as usual.

Current speed and direction from the Aanderaa Instruments current meter are reported in engineering units and must be calibrated. The calibration coefficients appear to always be the same. During normal processing, they are retrieved and applied against the raw sensor readings (N) of speed and direction via a simple quartic polynomial expression "A + BN + CN² + DN³". The coefficients A, B, C, and D can differ from instrument to instrument. A MATLAB implementation can be found in the appendix.

The east and north components of the current are reported in an unusual fashion. When collected by the Campbell, the two-byte values are re-ordered as least significant byte first and then reported as unsigned integers. Consequently, this process must be reversed. See Workhorse Technical Manual for details of Workhorse data formats and the appendix for a MATLAB implementation of the algorithm .