Sentinel-3A, launched in February 2016, is part of ESA's long-term commitment to climate monitoring from space. Its
suite of instruments for measuring surface topography includes a Microwave Radiometer (MWR) and SRAL, the first
delay-Doppler instrument to provide global coverage. SRAL promises fine spatial resolution and reduced noise levels
that should together lead to improved performance over all Earth surfaces. The Sentinel-3 Mission Performance Centre
(S3MPC) has been developing the methodology to evaluate the accuracy of retrievals, monitor any changes and develop
solutions to known problems.
The S3MPC monitors internal temperatures, path delays and the shape of the generated pulses to assess the instruments
health. The MWR records over known reference surfaces are compared with those from other spaceborne instruments.
Over the ocean the SRAL's return pulses are analysed to give range to the sea surface, wave height and signal strength
(which can be interpreted as wind speed). The metocean data are regularly contrasted with records from in situ
measurements and the output from meteorological models, which rapidly highlights the effects of any changes in
Range information is used to give surface elevation, which is assessed in three ways. First, flights over a dedicated radar
transponder provide an estimate of path delay to within ~10 mm (r.m.s.). Second, measurements are compared to GPS-levelled
surfaces near Corsica and over Lake Issyk-kul. Third, there are consistency checks between ascending and
descending passes and with other missions. Further waveform analysis techniques are being developed to improve the
retrieval of information over sea-ice, land-ice and inland waters.