Interference-sensitive coastal SAR altimetry retracking strategy for measuring significant wave height

Benefits of fully focused SAR altimetry to coastal wave height estimates: A case study in the North Sea

“…Coastal SWH observations from satellite altimetry are often discarded or are of bad quality due to coastal interference that originates from strongly reflective targets such as sandbanks, sheltered bays, or calm waters close to the shoreline. Schlembach et al (2022) showed that the correlation of SWH data of the operational baseline product of S3 with in-situ data from buoys amounts to less than 0.20 for closer than 20 km from the coast. Tailored retracking algorithms have been developed to account for the coastal interference, such as ALES (Passaro et al, 2015), Brown-Peaky (Peng and Deng, 2018) for the conventional low resolution mode (LRM) altimetry, and SAMOSA+ (Dinardo et al, 2018), SAMOSA++ (Dinardo et al, 2020), ALES + SAR (Passaro et al, 2021), RiwiSAR-SWH (Gou and Tourian, 2021), CORS (Garcia et al, 2022), or CORALv1 (Schlembach et al, 2022) for UF-SAR altimetry.…”

“…Schlembach et al (2022) showed that the correlation of SWH data of the operational baseline product of S3 with in-situ data from buoys amounts to less than 0.20 for closer than 20 km from the coast. Tailored retracking algorithms have been developed to account for the coastal interference, such as ALES (Passaro et al, 2015), Brown-Peaky (Peng and Deng, 2018) for the conventional low resolution mode (LRM) altimetry, and SAMOSA+ (Dinardo et al, 2018), SAMOSA++ (Dinardo et al, 2020), ALES + SAR (Passaro et al, 2021), RiwiSAR-SWH (Gou and Tourian, 2021), CORS (Garcia et al, 2022), or CORALv1 (Schlembach et al, 2022) for UF-SAR altimetry. The enhanced coastal processing algorithms allow the derivation of relevant wave-related statistics in the coastal zone, e.g.…”

“…They investigated the global attenuation of SWH from offshore at 30 km to >3 km off the coast and found the wave heights are globally, on average, 22% smaller than offshore while using the conventional LRM altimetry with a lower posting rate of 1 Hz (and the ALES retracker (Passaro et al, 2015)). The estimation of SWH in the coastal zone with a distance-to-coast (dist-to-coast) of <5 km remains challenging, as the quality of the estimates deteriorates (Schlembach et al, 2022). Nevertheless, the need to approach the coastline even closer is specified by the current draft of the mission requirement documents of the Copernicus Sentinel-3 Next Generation Topography (S3NG-T) team, which has defined the requirement to give SSH and SWH estimates up to 3 km and, as an enhanced target, up to 0.5 km off the coastline (European Space Agency and Noordwijk, The Netherlands, 2022).…”

Validity assessment of SAMOSA retracking for fully-focused SAR altimeter waveforms

“…On the other hand, each fully-focused along-track sample is still a statistically independent speckle noise realisation (Egido and Smith, 2017) and the superimposed and highly problematic coastal clutter (e.g. discussed in Vignudelli et al, 2011;Passaro et al, 2018;Schlembach et al, 2022) is nonetheless resolved with several meters. Hence, less waveforms are affected by this clutter in FF-SAR, and therefore, more useful ocean samples are available for retracking, with potential benefits for altimetry data quality.…”

Signal Processing and Waveform Re-Tracking for SAR Altimeters on High Mobility Platforms with Vertical Movement and Antenna Mis-Pointing

“…Unfocused SAR (UF-SAR) retracking methods (e.g., the physical SAMOSA model) have been utilized to retrack fully-focused SAR (FF-SAR) waveforms in [27], ultimately improving data quality for SAR altimetry in coastal regions. A novel coastal retracking algorithm for SAR altimetry was presented in [28] that employed an adaptive interference masking scheme to mitigate interfering signals from reflective coastal targets, significantly increasing the number of valid records in the coastal zone without compromising the quality of the estimated significant wave height.…”