Modifying and Implementing an Inversion Algorithm for Shallow Water Wave Characteristics from a Broad-Beam HF Radar Network

Within the U.S., coastal ocean current mapping with HF radar has matured to the point where it is now considered an essential component of regional ocean observing systems. A Mid-Atlantic HF radar network now provides high-resolution coverage within five localized networks, which are linked together to cover the full range of the Mid-Atlantic coast. While the primary focus of these networks has been on offshore current mapping observations, a long-term objective has been to develop and evaluate nearshore waves and currents. The wave measurements are obtained from the HF radar either by using empirically derived algorithms or by inverting a nonlinear integral equation describing the relationship between the power spectrum of the radar backscatter and the ocean wave directional spectrum. Several mathematical models for extracting the significant wave height from the radar backscatter have been devised [1, 2].

Here, a shallow water correction for Barrick’s equation [3] is implemented following the methodology outlined in Lipa, et al. [4]. The study takes place outside the New York / New Jersey Harbor in a series of three experiments taking place between December 2005 and February 2008 (instruments were deployed for a total of 154 days). The CODAR sites are located at Breezy Point, NY (25 MHz) and Sandy Hook, NJ (3 co-located radars, 5, 13, and 25 MHz). The corrected wave characteristics extracted from the HF radars were then compared to several in situ wave measurements. Each experiment contained at least three in-situ instruments (a combination of NDBC buoy 44025, a NORTEK AWAC, Teledyne RDI ADCP 600 or 1200, or a Sontek ADP). Initial analysis has shown a significant improvement in the estimation of wave characteristics. Works Cited:

[1] D. E. Barrick, "The ocean waveheight nondirectional spectrum from inversion of the HF sea-echo Doppler spectrum," Remote Sensing of Environment, vol. 6, pp. 201-227, 1977.

[2] D. E. Barrick, "Extraction of Wave Parameters from Measured HF Radar Sea-Echo Doppler Spectra," Radio Science, vol. 12, pp. 415-424, 1977.

[3] B. J. Lipa and D. E. Barrick, "Extraction of sea state from HF radar sea echo: mathematical theory and modeling," Radio Science, vol. 21, pp. 81-100, 1986.

[4] B. J. Lipa, B. Nyden, D. E. Barrick, and J. Kohut, "HF radar sea-echo from shallow water," Sensors, vol. 8, pp. 4611-4635, 2008.