Evaluation of modeled microwave land surface emissivities with satellite-based estimates C. Prigent and F. Aires (Estellus + Observatoire de Paris ) P. Liang and J.-L. Moncet (AER) T. Tian (NASA) S. Boukabara (NOAA)

The use of modeled emissivity planed for the next generation of GPM algorithms. On going model developments, with evaluation mostly at local scales, with CRTM. In the current GPM algorithm, use of satellite-derived emissivity information (TELSEM classification). Global evaluation of the CRTM modeled emissivity with the TELSEM emissivity direct comparison of the emissivities comparison of emissivities in the Tb space (use of the modeled and TELSEM emissivities in a radiative transfer code and comparison with AMSR-E Tbs)

I - Direct comparison of the emissivities Modeled emissivity: CRTM V2.0 with the Microwave Land Emissivity Model (MLEM), fed by the NASA Land Information System (LIS). LIS-CRTM run at 0.25°x0.25°, at 30mn intervals, with output every 3h, from July 2004 to June 2009 Satellite-derived emissivity: TELSEM, anchored to SSM/I-derived emissivity with the frequency, angular and polarization dependence estimated from AMSU/SSMI/TMI.

Emissivities for January CRTM TELSEM 89GHz H 89GHz V 19GHz H 19GHz V

LIS/CRTM - TELSEM Dense forest Grassland Deserts Snow and Ice

II - Comparisons in the Tb space with AMSR-E LIS-CRTM and TELSEM used in a radiative transfer code and comparison with AMSR-E observations MonoRTM and 1° 6-hourly NCEP GFS analysis Four weeks in 2008 (one week in January, April, July, October) Clouds filtered out

Tbs at 18.70 GHz for July (midnight) V polarization H polarization TELSEM LIS-CRTM AMSR-E

Correlations between the Tbs, for all frequencies and polarization

Tbs differences (Sim-AMSR) at 18 and 89 GHz (nighttime) CRTM TELSEM Snow Ice Desert Grassland Dense forest

Tbs differences (Sim-AMSR) at 18 and 89 GHz CRTM TELSEM CRTM TELSEM Desert Grassland Mid-night Mid-day

Conclusions Rather good agreement between the modeled (CRTM) and satellite-derived emissivity estimates for vegetated areas Over deserts and snow, significant differences, partly due to the model inputs The ECMWF land surface emissivity model has also been tested. The results are much worse. The comparison in the Tb space shows a better agreement with the satellite-derived emissivities. Ideas to improve the emissivity modeling, especially over desert regions. Joint work between modelers and remote sensing experts to be continued