Currents
The basic current data provided by either type of radar is a radial current – i.e. the component of the true current along the direction from the radar site to the measurement position. This is obtained from the frequency shift of the first order peaks in the Doppler spectrum from the Doppler shift predicted by linear wave theory. Files with this information are generated at the individual sites and sent to the ACORN facility together with some additional quality control and assessment data. These are then packaged into NETCDF files and sent on to the IMOS archive for access through the data portal.
In the case of SeaSonde data the radials from the pair of sites are combined using CODAR software to provide ~1-hour averaged vector currents at the facility and these too are transferred as NETCDF files to IMOS.
A similar procedure for the WERA data is carried out by eMII using their own matlab code. A number of quality control measures are recommended in the literature [1, 2, 3] and on manufacturer’s websites, when carrying out this procedure and the values currently in use are shown in the table below.
When the full data files have been collected from the WERA radar sites they are reprocessed using ACORN-developed software.
[1] Lipa, B. J., and D. E. Barrick, Least-square methods for the extraction of surface currents from CODAR crossed-loop data: Application at ARSLOE, IEEE J. Oceanic Eng., 0E-8(4), 226-253, 1983.
[2] Gurgel K-W. and G. Antonischki, Measurement of surface current fields by HF radar, IGARSS’97 conference proceedings, 1820-1822, 1997.
[2] Chapman, R.D., L. K. Shay, H . C. Graber, B . Edson, A. Karachintsev, C. L. Trump, and D. B. Ross: On the accuracy of HF radar surface current measurements: Intercomparisons with ship-based sensors. Journal of Geophysical Research, 102, 18,737-18,748, 1997.
