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Remote Sens. 2019, 11(1), 71; https://doi.org/10.3390/rs11010071

Group Line Energy in Phase-Resolved Ocean Surface Wave Orbital Velocity Reconstructions from X-band Doppler Radar Measurements of the Sea Surface

1
Marine Meteorology Division, Naval Research Laboratory, Monterey, CA 93943, USA
2
Department of Coastal and Marine Systems Science, Coastal Carolina University, Conway, SC 29528, USA
*
Author to whom correspondence should be addressed.
Received: 2 November 2018 / Revised: 15 December 2018 / Accepted: 24 December 2018 / Published: 2 January 2019
(This article belongs to the Special Issue Sea Surface Roughness Observed by High Resolution Radar)
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Abstract

The wavenumber-frequency spectra of many radar measurements of the sea surface contain a linear feature at frequencies lower than the first order dispersion relationship commonly referred to as the “group line”. Plant and Farquharson, showed numerically that the group line is at least partially caused by wave interference-induced breaking of steep short gravity waves. This paper uses two wave retrieval techniques, proper orthogonal decomposition (POD) and FFT-based dispersion curve filtering, to examine two X-band radar datasets, and compare wave orbital velocity reconstructions to ground truth wave buoy measurements within the field of view of the radar. POD allows group line energy to be retained in the reconstruction, while dispersion curve filtering removes all energy not associated with the first order dispersion relationship. Results show that when group line energy is higher or comparable to dispersion curve energy, the inclusion of this group line energy in phase-resolved orbital velocity reconstructions increases the accuracy of the reconstruction. This increased accuracy is demonstrated by higher correlations between POD reconstructed time series with buoy ground truth measurements than dispersion curve filtered reconstructions. When energy lying on the dispersion relationship is much higher than the group line energy, the FFT and POD reconstruction methods perform comparably. View Full-Text
Keywords: Doppler radar; radar; sea surface roughness; air-sea interaction; proper orthogonal decomposition; ocean surface waves; dispersion curve filtering; marine X-band radar; phase-resolved wave fields Doppler radar; radar; sea surface roughness; air-sea interaction; proper orthogonal decomposition; ocean surface waves; dispersion curve filtering; marine X-band radar; phase-resolved wave fields
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Kammerer, A.J.; Hackett, E.E. Group Line Energy in Phase-Resolved Ocean Surface Wave Orbital Velocity Reconstructions from X-band Doppler Radar Measurements of the Sea Surface. Remote Sens. 2019, 11, 71.

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