Land Surface Microwave Emissivities over the Globe for a Decade

Abstract

Microwave land surface emissivities have been calculated over the globe for ~10 yr between 19 and 85 GHz at 53° incidence angle for both orthogonal polarizations, using satellite observations from the Special Sensor Microwave Imager (SSM/I). Ancillary data (IR satellite observations and meteorological reanalysis) help remove the contribution from the atmosphere, clouds, and rain from the measured satellite signal and separate surface temperature from emissivity variations. The method to calculate the emissivity is general and can be applied to other sensors. The monthly mean emissivities are available for the community, with a 0.25° × 0.25° spatial resolution. The emissivities are sensitive to variations of the vegetation density, the soil moisture, the presence of standing water at the surface, or the snow behavior, and can help characterize the land surface properties. These emissivities (not illustrated in this paper) also allow for improved atmospheric retrieval over land and can help evaluate land surface emissivity models at global scales.

Interannual variability of surface water extent at the global scale, 1993–2004

“…Set, 1993Set, -2004 [37] Passive microwave emissivities between 19 and 85 GHz estimated from the SSM/I observations are the core data set used in our methodology to estimate global surface water extent. First available from 1993 to 2000, the emissivity time series have been extended to 2004 following the methodology described by Prigent et al [1997Prigent et al [ , 2006. However, intensive analyses of the emissivity times series recently revealed an issue after September 2001, as illustrated in Figure 4.…”

“…[38] The cause of this discrepancy in the emissivity data sets has its main source in the abrupt change from September 2001 observed in the ISCCP surface skin temperature derived from IR observations [Rossow and Schiffer, 1999] that are used in the emissivity calculation methodology [see equations 1 and 2 and Figure 1 in Prigent et al, 2006]. This is illustrated in Figure 4b, which shows the change in the monthly mean surface skin temperature from ISCCP after September 2001 at the global scale, for the Nile and the Amazon rivers.…”

Surface Freshwater Storage Variations in the Orinoco Floodplains Using Multi-Satellite Observations

“…(2) Passive microwave emissivities between 19 and 85 GHz, estimated from the Special Sensor Microwave/Imager (SSM/I) observations by removing the contributions of the atmosphere (water vapor, clouds, rain) and the modulation by the surface temperature [38], as well as incorporating ancillary data from the International Satellite Cloud Climatology Project (ISCCP) [39] and the National Centers for Environment Prediction (NCEP) reanalysis [40]. (3) Backscatter at 5.25 GHz from the European Remote Sensing (ERS) satellite scatterometer.…”

“…(3) Backscatter at 5.25 GHz from the European Remote Sensing (ERS) satellite scatterometer. ERS observations are averaged over each month and mapped to an equal area grid of 0.25° resolution at the equator (each pixel equals 773 km2) [23,38].…”

Estimating Confidence Intervals around Relative Humidity Profiles from Satellite Observations: Application to the SAPHIR Sounder

“…The surface emissivity is either prescribed using the 10-yr emissivity atlas of Prigent et al (2006) for the continental cases or computed within RTTOV with the Fast Emissivity Model-3 (FASTEM-3; Deblonde and English 2000) and 10-m wind speed. The 1990-2007 archive of ARSA is considered and only profiles restricted to the 308N/308S belt are kept.…”