The Roles of the S3MPC: Monitoring, Validation and Evolution of Sentinel-3 Altimetry Observations

Abstract

The Sentinel-3 Mission Performance Centre (S3MPC) is tasked by the European Space Agency (ESA) to monitor the health of the Copernicus Sentinel-3 satellites and ensure a high data quality to the users. This paper deals exclusively with the effort devoted to the altimeter and microwave radiometer, both components of the Surface Topography Mission (STM). The altimeters on Sentinel-3A and -3B are the first to operate in delay-Doppler or SAR mode over all Earth surfaces, which enables better spatial resolution of the signal in the along-track direction and improved noise reduction through multi-looking, whilst the radiometer is a two-channel nadir-viewing system. There are regular routine assessments of the instruments through investigation of telemetered housekeeping data, calibrations over selected sites and comparisons of geophysical retrievals with models, in situ data and other satellite systems. These are performed both to monitor the daily production, assessing the uncertainties and errors on the estimates, and also to characterize the long-term performance for climate science applications. This is critical because an undetected drift in performance could be misconstrued as a climate variation. As the data are used by the Copernicus Services (e.g., CMEMS, Global Land Monitoring Services) and by the research community over open ocean, coastal waters, sea ice, land ice, rivers and lakes, the validation activities encompass all these domains, with regular reports openly available. The S3MPC is also in charge of preparing improvements to the processing, and of the development and tuning of algorithms to improve their accuracy. This paper is thus the first refereed publication to bring together the analysis of SAR altimetry across all these different domains to highlight the benefits and existing challenges.

Sentinel-3 Microwave Radiometers: Instrument Description, Calibration and Geophysical Products Performances

“…We notice an average bias of −0.55 cm between S3A and Jason-3 and close to zero (−0.06 cm) for AltiKa. These results are consistent with the multi-mission monitoring of D_Tropo (MWR-ECMWF difference) presented in [15] or [22]. The bin averaged values present a V-shape, with lower differences in the equatorial band and higher differences in the highest latitudes.…”

“…During phase E2, there have been a full hand-over to Sentinel-3 Mission Performance Center (MPC) team for the ramp-up and routine operational phases. S3MPC is in charge of the monitoring of the health of the instruments and the quality of the data for the users [15].…”

“…Four analyses per day are used, and bilinear interpolation in space and time is performed to compute a model correction co-located to the measurements. Details on this comparison can be obtained in the S3 MPC related paper [15] or the cyclic reports available online on ESA website [22].…”

Sensitivity of Altimeter Wave Height Assessment to Data Selection

“…This yields a sharper waveform than for LRM, with both a steeper leading edge and trailing edge (see Figure 1b). The data from Sentinel-3A are also processed without the Doppler information to yield pseudo-LRM (PLRM) waveforms to which conventional trackers can be applied in order to permit an understanding of the relative differences between LRM and DDA processing (an overview of the performance of Sentinel-3A is given in Quartly et al [15]).…”

Validation of Sentinel-3A Based Lake Level over US and Canada

“…The best performance was obtained with a modified version of the Multiple Waveform Persistent Peak (MWaPP) retracker [12]. Reference [21] did several evaluations to quantify the performance of Sentinel-3A and 3B for inland water for example, demonstrated an accuracy of 1.5 cm over lake Issyk-Kyl and showed the consistency of the water surface height between the Sentinel-3A and 3B over Lake Lagoda in Russia.…”