Abstract
Sentinel-1 synthetic aperture radar (SAR) is one of the most advanced open-access satellite systems available, benefitting from its capability for earth observation under all-weather conditions. In this study, more than 280 Sentinel-1 SAR images are used to derive significant wave heights (Hs) of the sea surface using a polarization-enhanced methodology. Two study areas are selected: one is located near Hawai’i in a deep water region, and the other is in transitional water off the U.S. west coast, where the U.S. National Oceanic and Atmospheric Administration (NOAA) buoy data are available for validations. The enhanced Hs retrieval methodology utilizes dual-polarization SAR image data with strong non-Bragg radar backscattering, resulting in a better estimate of the cut-off wavelength than from those using single-polarization SAR data. The new method to derive Hs is applied to SAR images from 2017 taken from both deep water (near Hawai’i) and coastal water locations (off the U.S. West coast). The assessments of the retrieved Hs from SAR images suggest that the dual-polarization methodology can reduce the estimated Hs RMSE by 24.6% as compared to a single-polarization approach. Long-term reliability of the SAR image-derived Hs products based on the new methodology is also consolidated by large amount of in-situ buoy observations for both the coastal and deep waters.
Highlights
Synthetic aperture radar (SAR) systems are capable of observing ocean surface in high spatial resolution under all weather conditions
Our study shows that the lowest cut-off wavelength is approximately 90 m, similar to what was determined from previous studies [12,22]
The significant wave heights derived from Sentinel-1 SAR images for 2017 in deep and coastal water are shown in Figure 8, together with buoy-measured Hs
Summary
Synthetic aperture radar (SAR) systems are capable of observing ocean surface in high spatial resolution under all weather conditions. Over the past 40 years, the potential of using digitally processed SAR images of ocean surfaces has been quantitatively proven to be able to detect multiple wave parameters such as ocean wave direction, wavelength, and wave height [1,2]. Since the launch of Seasat in 1978, Almaz-1 in 1991, and ERS-1 in 1991, a large number of surface imprints of small-, meso-, and sub-synoptic-scales of oceanic and atmospheric phenomena have been investigated using SAR images to explore atmospheric and oceanic dynamics [3,4,5,6,7,8]. The C-Band (5.405 GHz) Sentinel-1 SAR is one of the most used systems that generate reliable, open-access, and continuous observations of the ocean surfaces [9,10].
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