Abstract
Ocean wind and wave parameters can be measured by in-situ sensors such as anemometers and buoys. Since the 1980s, X-band marine radar has evolved as one of the remote sensing instruments for such purposes since its sea surface images contain considerable wind and wave information. The maturity and accuracy of X-band marine radar wind and wave measurements have already enabled relevant commercial products to be used in real-world applications. The goal of this paper is to provide a comprehensive review of the state of the art algorithms for ocean wind and wave information extraction from X-band marine radar data. Wind measurements are mainly based on the dependence of radar image intensities on wind direction and speed. Wave parameters can be obtained from radar-derived wave spectra or radar image textures for non-coherent radar and from surface radial velocity for coherent radar. In this review, the principles of the methodologies are described, the performances are compared, and the pros and cons are discussed. Specifically, recent developments for wind and wave measurements are highlighted. These include the mitigation of rain effects on wind measurements and wave height estimation without external calibrations. Finally, remaining challenges and future trends are discussed.
Highlights
Ocean wind and wave information is crucial for various on- and off-shore activities such as coastal construction, ship navigation, and marine resource development
If the high-clutter direction (HCD) percentage (HCDP), which is defined as the ratio of the number of HCDs to the number of total directions for one radar image, is higher than 5%, the image is classified as a rain-contaminated radar image
It can be observed from the table that ship motion has a significant effect on the local gradients method (LGM) and optical flow motion estimation-based technique (OFM); the original Intensity Level Selection (ILS) and background noise (BGN) methods may not be applicable if portions of the radar images are blocked; the two-model-Curve Fitting (CF), texture-analysis-incorporated, and 1D spectral analysis algorithms work well under rain effects; and the OFM is calibration-free for wind speed retrieval
Summary
Ocean wind and wave information is crucial for various on- and off-shore activities such as coastal construction, ship navigation, and marine resource development (e.g., mining and oil industries). X-band marine radar has been rapidly developed as an ocean remote sensor since it can image both the spatial and temporal variations of the sea surface with high resolutions. If reliable wind and wave measurements can be obtained from such radars, the costs associated with traditional in-situ sensors such as anemometers and buoys can be significantly reduced. Since the sea surface roughness that causes the radar backscatter is induced by local winds, the dependence of the radar cross section (RCS) on wind speed [15] and the angle between radar look direction and wind direction [16] can be exploited to extract wind parameters from radar images [12].
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