ACORN has two software packages for extracting wave information from the WERA radar signal.

• The basic package provided by the manufacturer, Helzel GmbH, is based on a semi-empirical method described in [1]. This provides single radar estimates of the wave frequency spectrum from which significant waveheight and dominant period are extracted. These single radar estimates are calculated at the sites and sent to the ACORN facility where they are packaged into the same NETCDF files as the currents. The option to combine these files to try to reduce the ambiguities that are present in single radar data has not yet been implemented.

• The Seaview Sensing wave measurement package, which is offered as an option by Helzel GmbH, is based on methods described in [2, 3]. The full directional spectrum and derived parameters, e.g. significant waveheight, peak period and direction, can be obtained provided the signal to noise is sufficient.  Single radar estimates can extend the coverage for waveheight and period albeit with some ambiguities. This package has not yet been implemented and these data are not yet available through the portal. This processing cannot be carried out at the radar sites and requires more data than is currently being transmitted from the sites.

ACORN has not yet implemented a SeaSonde wave measurement capability. With this system measurements can be made over an annular ring of fixed range (or small number of ranges) close to the radar sites where sufficient signal to noise is available. The CODAR software normally provides a few wave parameters at this position although methods to obtain the full directional spectrum have been developed [4, 5].

The important quality control criterion for wave measurement is the 2^nd order signal to noise level.  Other quality measures which will need to be taken into account when these data are made available through the portal are discussed in [6].

[1] Gurgel, K-W, H-H Essen and T. Schlick, 2006: An empirical method to derive ocean waves from second-order Bragg scattering: prospects and limitations. IEEE Journal of Oceanic Engineering, 31, 804-811.

[2] Green, J.J. and L.R. Wyatt, 2006: Row-action inversion of the Barrick-Weber equations. Journal of Atmospheric and Oceanic Technology, 23, 501-510.

[3] Wyatt, L. R., 2002: An evaluation of wave parameters measured using a single HF radar system. Canadian Journal of Remote Sensing, 28, 205-218.

[4] Lipa, B. and B. Nyden, 2005: Directional wave information from the SeaSonde. IEEE Journal of Oceanic Engineering, 30, 221-231.

[5] Lipa, B, Nyden, B., D. Barrick and J. Kohut, 2008: HF radar sea-echo from shallow water. Sensors, 8 4611-4635.

[6] Wyatt L.R., J.J. Green and A. Middleditch, 2011: HF radar data quality requirements for wave measurement. Coastal Engineering, 58, 327-336.

More Papers on wave measurements > Waves