2-channels versus 3-channels configuration for MWR on altimetry missions: latest developments on the role of the 18.7 GHz channel on Wet Tropospheric Correction retrieval performances

Bruno Picard (CLS, France)

CoAuthors

Marie-Laure Frery (CLS, France); Christophe Goldstein (CNES, France); Pierre Féménias (ESA ESRIN, Italy); Rolv Midthassel (ESA ESTEC, Netherlands)

Event: 2017 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Propagation, Wind Speed and Sea State Bias

Presentation type: Type Oral

Microwave radiometers on altimetry missions are dedicated to the correction the altimeter range for the excess path delay (WTC for wet tropospheric correction) resulting from the presence of water vapor in the troposphere.

Current and past instruments are divided in two families. NASA/CNES missions (from TMR on Topex/Poseidon up to the latest generation of AMR on Jason-3) rely on 3-channels (18.7 GHz, 23.8 GHz, 34 GHz) configurations. ESA missions (from ERS-1 to Sentinel-3) rely on 2-channels (23.8 GHz, 36.5 GHz) configurations; and so does the CNES/ISRO mission (23.8 GHz, 37 GHz).

The 18.7 GHz channels brings useful information on surface characterization (temperature, roughness).
On a 2-channels configuration, historical approach (Obligis et al. 2006) used the altimeter backscattering coefficient (sig0), well-sensitive to the roughness, to compensate from the lack of this low-frequency channel.
Based on a simulation approach, Thao et al (2015) demonstrates that the benefit of using a 18.7 GHz channel is larger than using the sig0 since the brightness temperature (TB) is more sensitive to the water vapour.

Now, Obligis et al. (2009) recommended to use climatological maps of sea surface temperature and the atmospheric temperature lapse rate as additional parameters to the classical three inputs (TBs and sig0) to improve the performance of the WTC retrieval.

We will present the latest performance comparisons between a 2-channels and a 3-channels configuration.
Using the metric of SSH variance differences at cross-overs at a global scale, we will discuss the impact on the quality of the WTC retrieval of 1) the Ka-band sig0 wrt to a Ku-band sig0 2) using climatological maps for the SST wrt to L4 optimal interpolation products. Then, we will show that 2-channels configurations MWR performances are similar to 3-channels configurations, based on Jason-2, AltiKa and Sentinel-3 measurements.
Finally, we will discuss the role of the 18.7 GHz channels on some particular regions: strong oceanic currents and coastal areas.

 

Oral presentation show times:

RoomStart DateEnd Date
Symphony Ballroom IV Tue, Oct 24 2017,15:12 Tue, Oct 24 2017,15:30
Bruno Picard
CLS
France
bpicard@cls.fr