Sentinel-3A Surface Topography Mission Microwave Radiometer : in-flight calibration and performance assessment

Marie-Laure Frery (CLS, France)

CoAuthors

Bruno Picard (CLS, France); Estelle Obligis (CLS, France); Christophe Goldstein (Centre National d'Etudes Spatiales, France); Amandine Guillot (Centre National d'Etudes Spatiales, France); Nicolas Picot (Centre National d'Etudes Spatiales, France); Helge Rebhan (European Space Agency (ESTEC), Netherlands); Pierre Féménias (European Space Agency (ESRIN), Italy)

Event: 2016 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Corrections

Presentation type: Type Oral

The Sentinel-3A Surface Topography Mission has been launched on February 2016. Its objectives are to serve primarily the marine operational users but also allow the monitoring of sea ice and land ice, as well as inland water surfaces.
A two-channels microwave radiometer (23.8 and 36.5 GHz) similar to the Envisat MWR is combined to the altimeter in order to correct the altimeter range for the excess path delay resulting from the presence of water vapor in the troposphere. The radiometer performs measurements of brightness temperatures in both bands. These measurements are then interpolated at the location of the altimeter footprint.
For the retrieval of the excess path delay, the so-called wet tropospheric correction, two algorithms based on simulated parameters (brightness temperatures and altimeter backscattering coefficient) and neural networks are proposed in the Sentinel-3A products. First a classical approach, similar to Envisat’s algorithm is using both brightness temperatures and the altimeter backscattering coefficient to take into account the surface roughness. Secondly, an innovative algorithm is using additional inputs such as the sea surface temperature and temperature lapse rate to improve the retrieval over specific areas such as upwelling regions.
The retrieval of the other geophysical parameters (water vapor content, cloud liquid water content, the atmospheric attenuations of the altimeter backscatter coefficient in Ku band and C band) is performed using a classic three inputs algorithm.
We will present here a first assessment of the MWR performances over ocean as well as coastal areas, sea ice and inland water.
The in-flight calibration during the commissioning phase aims at providing quantitative information on the accuracy and the precision of the S-3A MWR measurements. On the long term, it will be used to assess its stability.
However, the main difficulty for microwave radiometry lies in the lack of references: natural targets are neither well known nor homogeneous enough and each in-flight instrument has its own calibration strategy. The strategy used for S-3A MWR is similar to the strategy employed for Envisat and AltiKa. It is based on a combination of comparisons to other instruments (AMR on Jason-2/3, AMSU-A on MetopA, AltiKa/MWR on SARAL) over Amazon forest. Over ocean, a statistical study of the coldest ocean points is performed as well as double-difference analysis using simulations as a common reference.
 

Poster show times:

RoomStart DateEnd Date
Grande Halle Thu, Nov 03 2016,11:00 Thu, Nov 03 2016,18:00
Marie-Laure Frery
CLS
France
mfrery@cls.fr