Abstract
Synthetic Aperture Radar (SAR) in wave mode is a powerful tool for monitoring sea states in terms of long-period ocean swells of a specific wave directional partition. Since 2016, SARs aboard Sentinel-1A/B operating in wave mode have provided ocean swell spectra dataset as Level-2 Ocean products on a continuous and global basis over open oceans. Furthermore, Level-3 swell products are processed by Copernicus Marine Environment Monitoring Services (CMEMS) taking the benefit of the unique “fireworks” analysis. In this paper, swell wave heights from Sentinel-1A/B wave mode during the period from June 2016 to June 2020 are evaluated. The reference data include the collocated in situ measurements from directional wave buoys and WaveWatch III (WW3) hindcasts. Assessment results show systematic overestimation of approximately 0.2 m in terms of the partitioned swell heights for Sentinel-1A/B Level-2 products compared to the directional buoy observations in eastern Pacific and the western Atlantic. Based on the reliable SAR-WW3 collocations after quality-controls, empirical corrections have been proposed for Sentinel-1 Level-2 swell heights. Independent comparisons against WW3 hindcasts and buoy observations demonstrate the validity of our postprocessing correction for both Level-2 and Level-3 swell heights by eliminating the biases and reducing the root mean square errors. The consistency between CMEMS Level-3 swells and buoy in situ is also examined and discussed by case studies.
Highlights
Swells are long-period ocean waves, which are generated by remote storms and are weakly affected by the local wind
Munk et al [13], used to locate the storm sources responsible for swell observations at buoy stations, has been revisited with remote sensing data. This technique has been employed to propagate the observed Envisat ASAR swells across the ocean basin, which is referred to as “fireworks” from their visual view when represented on a world map or regional view [14,15,16], and used to study the swell dissipation across oceans [17,18], to characterize the time and space structures of swells [19]
The accuracy of the Synthetic Aperture Radar (SAR)-derived partitioned swell wave height products from the Sentinel-1A/B satellites operating in wave mode has been assessed over the period from June 2016 and June 2020 by comparison against moored buoys observations and WW3 modeling
Summary
Swells are long-period ocean waves, which are generated by remote storms and are weakly affected by the local wind. Munk et al [13], used to locate the storm sources responsible for swell observations at buoy stations, has been revisited with remote sensing data This technique has been employed to propagate the observed Envisat ASAR swells across the ocean basin, which is referred to as “fireworks” from their visual view when represented on a world map or regional view [14,15,16], and used to study the swell dissipation across oceans [17,18], to characterize the time and space structures of swells [19]. SAR ocean wave acquisitions have proven to benefit the numerical wave model community to propose new modeling developments [17,21] or for assimilation in operational systems, e.g., [22] In this context, the detailed statistical knowledge of quality assessments on the Sentinel-1A/B (S-1A/B) SAR swell height products
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