An Improved Altimetry Wet Tropospheric Correction Retrieval Over Coastal Regions for the Sentinel-3 Mission

The wet tropospheric correction (WTC) retrieval over coastal regions is still nowadays a challenging task. The open-ocean retrieval algorithms, which rely on microwave radiometers (MWR) brightness temperatures (TBs) measurements, fail to provide accurate WTC values over these transition surfaces, due to the land contamination on the TBs. The retrieval errors rapidly increase with the approach of the satellite to the coastline. In this article, an improvement of the WTC retrieval over coastal regions for the Sentinel-3 mission is proposed, based on the dual-band MWR measurements, complemented with additional parameters to account for surface effects. Methods of modification of the MWR TBs and the synthetic aperture radar altimeter backscatter coefficient sigma(0), at Ku band, are presented, which aim to mitigate land contamination effects. On a first phase, these modified inputs are used in the open-ocean retrieval algorithm to compute the WTC. On a second phase, the same modified inputs are used in developed WTC retrieval algorithms specifically trained in coastal regions. The comparison against independent Global Navigation Satellite Systems derived WTC at coastal stations show that the use of coastal WTC retrieval algorithms with modified inputs is able to significantly reduce the retrieval errors over these regions, with rms values of 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.