Bridging the gap between cyclone wind and wave by C‐band SAR measurements

Abstract

Active microwave remote sensing of hurricane‐strength wind is a challenging task due to the saturation of col‐polarization backscattering signal under such condition. Here we take advantage of the fact that wind sea wave growth does not saturate at high wind and the intrinsic relationship among wind‐wave triplets (sea surface wind speed, significant wave height, and peak wave period) within a tropical storm to derive the wind speed. Three Sentinel‐1 (S‐1) and nine RADARSAT‐2 (R‐2) C‐band synthetic aperture radar (SAR) images acquired between 20 and 40 m/s winds are collected in this study. The S‐1 and R‐2 SAR‐derived winds are compared with those measured by coincident National Oceanic and Atmospheric Administration Stepped‐Frequency Microwave Radiometer (SFMR) and simulated by Symmetric Hurricane Estimates for Wind (SHEW) model. Validations against SFMR winds for S‐1 show Root‐Mean‐Square Error (RMSE) of 1.7 m/s with a 0.2 m/s bias at the left side of cyclone centers and RMSE of 2.9 m/s RMSE with a 0.56 bias at the backside of cyclone centers. R‐2 SAR‐derived winds against SHEW model results show a RMSE of 2.4 m/s with a 0.3 m/s bias and 2.6 m/s with a 0.35 m/s bias at the right side and the left side of cyclone centers, while the RMSE is 3.9 m/s with a 0.1 m/s bias at the backside of cyclone centers. The wave‐information‐based wind retrieval method works well at the left side and right side, but less accurately at the backside of a tropical storm when wind wave and swell are mixed.

An Empirical Algorithm to Retrieve Significant Wave Height from Sentinel-1 Synthetic Aperture Radar Imagery Collected under Cyclonic Conditions

“…These algorithms work at low-to-moderate conditions. Several typhoons and hurricanes have been captured by various C-band SARs, e.g., RADARSAT-2 [46], S-1 [1], and GF-3 [33] during their missions. Therefore, wave retrieval under cyclonic conditions is a topic of general interest in the field of SAR application.…”

“…With respect to λ and ϕ, although they are related to the ocean-wave SAR mapping mechanism [34], there is no explicit relationship with WW3-simulated SWH, according to Figure 10e,f. This can be explained by the complicated nature of the ocean wave spectrum under cyclonic conditions [46]. In fact, for instance, the right-and left-hand side of the wave spectrum are dominated by wind-sea and cross-swell, respectively.…”

“…In fact, for instance, the right-and left-hand side of the wave spectrum are dominated by wind-sea and cross-swell, respectively. complicated nature of the ocean wave spectrum under cyclonic conditions [46]. In fact, for instance, the right-and left-hand side of the wave spectrum are dominated by wind-sea and cross-swell, respectively.…”

A Wind Speed Retrieval Model for Sentinel-1A EW Mode Cross-Polarization Images

“…In this paper, the sub-bands are named sub-band 1, sub-band 2, sub-band 3, sub-band 4, and sub-band 5 with increasing distance from the sub-satellite point. Compared with VV-polarized signal, the VH-polarized signal does not saturate for wind speeds as strong as 55 m/s and is insensitive to wind direction [20,22,23]. The GRD products consist of focused SAR data that has been detected, multi-looked and projected to ground range.…”

Seismic Remote Sensing of Super Typhoon Lupit (2009) with Seismological Array Observation in NE China

“…For the sake of illustration, a typhoon moving northward in the Northern hemisphere was considered (Figure 5a,b). The winds rotate counter-clockwise (CCW) around the typhoon eye, and the highest wind speeds occur in the NE quadrant near the radius-to-maximum-wind, generating the strongest ocean waves propagating mainly in the NW direction [39,40]. When the typhoon is moving slower than the ocean waves propagate, such dominant ocean waves induced at an earlier time t1 would propagate as young swells and interfere with the wind sea around the current typhoon center at a later time t2.…”