Other algorithm studies
Read our other algorithm studies for current, future and multi-missions.
27 January 2023
08 June 2020
Long-term observations of trends in Sea Surface Height (SSH), as well as Total Column Water Vapour (TCWV), are critical for understanding the impacts and risks of climate change. In particular, changes in SSH are of major societal importance globally, as well as regionally. The Global Climate Observing System (GCOS) has identified both SSH and TCWV as essential climate variables (ECVs).
Atmospheric water vapour increases the refraction index of air, leading to a reduction in the speed of light as compared to dry air. The accuracy of SSH estimates from radar altimetry, therefore, depends strongly on the so-called 'wet tropospheric correction' (WTC), aimed at eliminating the temporally and spatially varying impact of the atmospheric water vapour on SSH retrievals. In fact, the spatial and temporal variability of water vapour is such that an instantaneous estimation of its impact is needed to meet the SSH accuracy requirements. Consequently, the primary role of the nadir-looking Microwave Radiometer (MWR), of the Copernicus Sentinel-3 altimetry missions, is to provide the necessary water vapour observations.
In addition to WTC, TCWV is a highly important climate variable in its own right. The atmospheric water vapour feedback is believed to be the strongest feedback mechanism in climate change, approximately doubling the direct warming impact of increased CO2 forcing [Cess et al., 1990; Forster et al., 2007].
In the frame of the AMTROC study, a novel method has been implemented to derive TCWV and WTC, together with their respective uncertainties, from observations of the MWR instrument above the global ice-free oceans. The method was then applied to 10 months of continuous Sentinel-3A observations between 15 June 2016 and 15 April 2017.
Having successfully adapted the novel retrieval method to Sentinel-3 MWR observations in the first project phase, a second project phase has been initiated to allow for further bias correction and retrieval improvements, processing of the entire re-processed Sentinel-3 MWR data archive available to date, in-depth evaluation of the retrievals, and implementation of the novel method into EUMETSAT’s offline environment processing facilities.
The overall objective of this study was to contribute to enhancing the scientific quality of the Level 2 TCWV and WTC products to be derived from observations by the Microwave Radiometer (MWR) instruments onboard the Sentinel-3 series of satellites.
The primary study goal of Phase 1 was to implement a 1D-VAR method to provide accurate and robust TCWV and WTC retrievals from Sentinel-3A MWR observations, building on recent achievements such as the EMiR project, funded by the European Space Agency. The results with this new method have been compared with the Sentinel-3 operational products obtained with a semi-empirical method based on neural networks (ANN). The following results were obtained:
Further details of these results can be found in the study documents listed below.
Phase 2 of the study builds upon the outcomes of Phase 1 through the following activities: