First year of the microwave radiometer aboard SARAL : In flight calibration, processing and validation

Marie-Laure Frery (CLS, France)


Bruno Picard (CLS, France); Estelle Obligis (CLS, France); Nathalie Steunou (CNES, France); Nicolas Picot (CNES, France)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Corrections

Presentation type: Type Oral

The AltiKa/SARAL mission has been launched on 25th of February, 2013. For the first time, an altimeter in Ka band is used to determine the ocean topography. This Ka band altimeter is combined to a two-channels microwave radiometer (23.8GHz and 37GHz) in order to correct for the excess path delay resulting from the presence of water vapour in the troposphere. The radiometer performs measurements of brightness temperatures in both bands at the location of the altimeter footprint. The wet tropospheric correction is retrieved from both brightness temperatures and altimeter backscattering coefficient to take into account the surface roughness using a statistical method based on neural networks.

Concerning the brightness temperatures, calibration during the validation phase aims at providing quantitative information on the accuracy and the precision of their measurements. In a long term point of view, it will be used to assess the stability of the instrument. 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.
We have therefore based the calibration of AltiKa radiometer on a combination of several analyses. On a long term study, comparisons to other instruments (JMR on Jason-1, AMR on Jason-2, AMSU-A on Metop02, Envisat) are performed directly over continental areas (Amazon forest, Antartica). Over ocean, coldest ocean temperatures are statistically determined and compared for several instruments. On a shorter period, the double-difference method is applied to compare coldest ocean temperatures using simulations as a common reference (using ECMWF analyses and UCL radiative transfer model).

We present here also the last results regarding the inversion algorithms and the radiometer geophysical products. A new version of these algorithms is under development to improve the performances of the inversion algorithm in the high latitudes.

Oral presentation show times:

RoomStart DateEnd Date
Ballroom Tue, Oct 28 2014,14:00 Tue, Oct 28 2014,14:15
Marie-Laure Frery