Improving Sentinel-3 Altimetry Data With GPD+ Wet Tropospheric Corrections

• Type: Article in International Scientific Journal
• Date: 2024

Authors

Fernandes, MJ (Author) FCUP; Vieira, T (Author) Other; Clara Lazaro (Author) FCUP; Vasconcellos, B (Author) Other; Aguiar, P (Author) Other

Journal

The Journal is awaiting validation by the Administrative Services.

Title: EARTH AND SPACE SCIENCE

Vol. 11

ISSN: 2333-5084

Indexing

ISI Web of Knowledge - 0 Citations

Scopus - 0 Citations

Other information

Authenticus ID: P-013-C81

DOI: 10.1029/2024ea003536

Abstract (EN): The provision of accurate wet tropospheric corrections (WTC), accounting for the delay of the radar pulses caused mostly by the atmospheric water vapor in the altimeter-range observations, is pivotal for the full exploitation of altimeter-derived surface heights. The WTC is best retrieved by measurements from Microwave Radiometers (MWR) on board the same altimeter mission. However, these instruments fail to provide valid WTC over land and ice and under rainy conditions. The GNSS-derived Path Delay Plus (GPD+) algorithm has been designed to provide WTC over these surfaces where the onboard MWR WTC is invalid. This study focuses on the estimation of enhanced GPD+ WTC for the Copernicus Sentinel-3A and Sentinel-3B satellites, for the latest Baseline Collection 005.02 (BC005.2), spanning the period since the beginning of the missions until March 2023. GPD+ corrections are being provided operationally since 2022 and have been adopted as the default WTC in the calculation of the sea level anomaly (SLA). Compared to previous versions, the BC005.2 GPD+ WTC features improved data combination procedures, possesses a larger percentage of points estimated from observations, a better intermission alignment and reduced systematic differences among ascending and descending passes. Overall, GPD+ WTC are consistent, calibrated corrections, valid over all points present in the Non Time Critical marine product, allowing to recover, on average, about 17% of the altimeter observations with valid SLA, which otherwise, most of them would be rejected. Impacts of these WTC are most significant over coastal and inland water regions, at high latitudes and during rain events. Satellite radar altimetry is a powerful technique to measure the Earth's topography during day and night, in all weather conditions. It uses radar pulses to measure the distance between the satellite and the surface beneath the satellite, from which the height of the mean sea level, rivers and lakes, for example, can be obtained. The atmosphere affects the propagation by delaying the signal and increasing the measured trajectory. The effect of the atmospheric water vapor is particularly difficult to model, since it is highly variable. This study concerns with a method to estimate the so-called wet tropospheric correction, which accounts for the water vapor effects in the altimeter measurements. Over open ocean, the correction is usually based on the measurements from a dedicated instrument collocated on the same satellite, which fails to provide valid information over non-water surfaces. The method, called GNSS-derived Path Delay Plus (GPD+), aims to fill the gaps left by the previous instrumental correction. The study describes the latest version of the GPD+ wet tropospheric corrections for the Copernicus Sentinel-3 altimeter products. It is demonstrated that these corrections can extend the altimeter observations to important regions such as coastal regions, rivers and lakes and high latitudes. New GPD+ wet tropospheric corrections have been produced for Sentinel-3, for the latest Baseline Collection (BC) 005.02 These corrections are consistent, calibrated, valid over all surface types, improving data coverage mainly over coastal and polar regions GPD+ are improved wet tropospheric corrections with respect to the Sentinel-3 onboard radiometer and to the European Centre for Medium Range Weather Forecasts (ECMWF) operational model

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 19