Assessment of Sentinel-3A and Sentinel-3B altimeter data in the Coastal Zone

Nadim Dayoub (National Oceanography Centre, United Kingdom)

CoAuthors

Chris Banks (National Oceanography Centre, UK); Christine Gommenginger (National Oceanography Centre, United Kingdom); Andrew Shaw (SKYMAT Ltd, UK); Helen Snaith (National Oceanography Centre, United Kingdom)

Event: 2019 Ocean Surface Topography Science Team Meeting

Session: Coastal Altimetry

Presentation type: Type Oral

The performance of satellite altimetry in the coastal zone has historically been a challenging issue. In recent years, there have been significant developments of specialised radar echo fitting (‘retracking’) algorithms to improve the quality and quantity of altimeter data closer to the coast. In addition, there have been noticeable developments to improve several geophysical corrections that must be applied to altimeter range data in coastal regions (e.g. wet tropospheric delay). Innovative technological solutions have also been used to deliver better performance near the coast. These include Ka-band altimetry with SARAL/AltiKa and its smaller radar footprint; and Delay Doppler Altimetry (DDA) also known as Synthetic Aperture Radar (SAR) altimetry. SAR mode altimetry uses unfocused along-track synthetic aperture to achieve finer spatial resolution along-track and better precision on retrieved parameters.

The SRAL altimeter currently flying on Sentinel-3A and Sentinel-3B can operate in two modes: 1) conventional Low Resolution Mode (LRM) mode corresponding to the pulse-limited altimeters from the TOPEX/Jason reference series; and 2) SAR mode. The default mode for Sentinel-3 SRAL is to operate in SAR mode globally. However, a SAR reduction technique can be applied to incoherently combine SAR mode individual echoes to recreate LRM-type waveforms, to produce what is known as Pseudo-LRM (PLRM). PLRM waveforms follow the conventional Brown model shape of LRM altimetry and can be retracked in the same manner as LRM waveforms. However, PLRM waveforms suffer from the same contamination issues close to land as conventional LRM altimetry.

This paper presents a comprehensive assessment of Sentinel-3A and Sentinel-3B data in the coastal zone. The analyses consider performance in terms of retrieved sea level, SWH and wind speed, of the evolution of these parameters as a function of distance to the coast and of the impact of geophysical corrections. Results are presented for PLRM waveforms from the Sentinel-3A and Sentinel-3B satellites retracked with the NOC implementation of the Passaro et al. (2014) Adaptive Leading-Edge Sub-waveform (ALES) coastal algorithm. The NOC-ALES Sentinel-3 PLRM results are compared with those obtained for Jason-3 LRM retracked with classical and NOC-ALES retracking. The NOC-ALES S3A and S3B PLRM data are also compared with operational Sentinel-3 SAR data to gauge the quality of SAR mode altimetry in the coastal zone compared to conventional coastal altimetry.
 

Oral presentation show times:

Room Start Date End Date
The Monroe Hub Wed, Oct 23 2019,11:15 Wed, Oct 23 2019,11:30
Nadim Dayoub
National Oceanography Centre
United Kingdom
nayoub@noc.ac.uk