CoAuthors

Telmo Vieira (FCUP, Portugal); Clara Lázaro (FCUP, Portugal); M. Joana Fernandes (FCUP, Portugal)

Microwave radiometers (MWR) onboard satellite altimetry missions fail to provide accurate wet tropospheric correction (WTC) values over coastal regions. The retrieval errors rapidly increase for decreasing distances to the coastline due to land contamination on the MWR brightness temperatures (TBs) measurements. In this work, improved algorithms for the WTC retrieval over coastal regions are proposed, applied to the Sentinel-3 mission, based on the Sentinel-3 dual-band MWR TBs and complemented with additional parameters to account for surface effects. Methods for mitigating the effects of land contamination on input parameters, MWR TBs and Synthetic Aperture Radar Altimeter (SRAL) backscatter coefficient σ0, at Ku band, are presented. Two approaches were carried out, consisting of the usage of these modified inputs in the open-ocean retrieval algorithm, and, on a second stage, on retrieval algorithms specifically trained on coastal regions. The comparison against the WTC derived from independent coastal Global Navigation Satellite Systems (GNSS) stations shows that the combined strength of coastal retrieval algorithms with modified inputs can lead to a substantial reduction in coastal retrieval errors. The corresponding rms values are 3.1 cm between 5 and 10 km from the coast and 3.3 cm up to 5 km from the coast. For the Sentinel-3 MWR-derived operational WTC retrieval algorithm, these values are 9.2 cm between 5 and 10 km from the coast and 16.2 cm up to 5 km from the coast, which translates to rms error reductions of 6.1 cm and 12.9 cm, respectively.