Measuring rms wave height and the scalar ocean wave spectrum with HF skywave radar

Abstract

Estimates of rms wave height and the scalar ocean wave frequency spectrum were made by inverting high‐frequency (HF) skywave radar‐measured sea‐echo Doppler spectra. Whereas low‐power surface‐wave radars can make these measurements out to approximately 100 km from the radar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single ionospheric reflection. To demonstrate this capability, we used the Wide Aperture Research Faculty (WARF) HF skywave radar to measure Pacific Ocean sea backscatter near NOAA data buoy EB 20 during the passage of an at mospheric cold front. The height of the wind‐generated waves measured at the buoy doubled within a 6‐h period. Two new analysis techniques were used to derive rms wave height and the scalar ocean wave frequency spectrum from radar echoes. Estimates of rms wave height were made east and west of the front by using a power‐law relation that was derived from theoretical simulations of the sea‐echo Doppler spectrum for a wide range of wave conditions. Two of the rms wave height estimates were compared with the estimates made at EB 20 at two different times and are in agreement to within 7 and 17%, respectively. Scalar wave spectrum and rms wave height estimates were made by matching a theoretical Doppler spectrum derived in terms of a five‐parameter model of the wind‐wave spectrum to the measured Doppler spectrum. The radar and buoy estimates of the rms wave height agree within 7%. Agreement between the WARF‐derived and buoy‐derived rms wave height and wave spectra is within the combined experimental error of the buoy and the radar measurements.

HF Radar Activity in European Coastal Seas: Next Steps toward a Pan-European HF Radar Network

“…Barrick and Weber (1977) provided a solution to this scattering problem which can be written in the form of a non-linear integral equation (Lipa and Barrick, 1986;Holden and Wyatt, 1992). Wave measurements are made either by inverting this equation (Barrick, 1977;Lipa, 1977;Wyatt, 1990;Hisaki, 1996;Hashimoto and Tokuda, 1999;Green and Wyatt, 2006) or by empirical methods obtained by relating the amplitude, or integrated amplitude, of the second order spectrum (or moments thereof) to wave buoy measurements (Maresca and Georges, 1980;Wyatt, 2002;Gurgel et al, 2006;Wang et al, 2016). Note that this latter approach is sensitive to water depth and users have found it necessary to recalibrate in different situations.…”

HF Radar Instruments, Past to Present

“…Although the emphasis in this issue is on surface-wave propagation, several sky-wave phased-array radars employing very narrow beam widths have been used. Maresca and Georges (1980) describe the 2.5 km Wide Aperture Research Fac,ility (WARF) operated by SR1 International, and Georges and Harlan (1994) describe the use of military surveillance radars to obtain oceanic winds.…”

“…The same radar was used with a phased-array receiving antenna at Granite Canyon, south of Monterey, to study the effects of upwelling along the California coast (Fernandez, 1993;Shkedy et al, 1995: Fernandez et al, 1996. Maresca et al (1980) examined tidal currents in the San Francisco Bay. Building on work by the CODAR.…”

Statistical Characteristics of the Multi-Path Time Delay and Doppler Shift of a Radar Wave Propagating Through the Ionosphere

“…In physics, the received signal can be viewed as a multi-path signals superposition with different time delays, frequency shifts and incident angles ( Figure 1) [1,2]. As early as 1980s, Maresca and Georges indicated that the spectrum quality of the sea surface echo for the over-the-horizon radar is closely related to the changes in the ionosphere [3]. Given the random time-varying characteristic of the ionospheric medium, the multi-path time delay and Doppler shift effects are the main features for the HF radar wave propagating through the ionosphere [2].…”