Land surface microwave emissivities derived from AMSR-E and MODIS measurements with advanced quality control

Abstract

[1] A microwave emissivity database has been developed with data from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) and with ancillary land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the same Aqua spacecraft. The primary intended application of the database is to provide surface emissivity constraints in atmospheric and surface property retrieval or assimilation. An additional application is to serve as a dynamic indicator of land surface properties relevant to climate change monitoring. The precision of the emissivity data is estimated to be significantly better than in prior databases from other sensors due to the precise collocation with high-quality MODIS LST data and due to the quality control features of our data analysis system. The accuracy of the emissivities in deserts and semiarid regions is enhanced by applying, in those regions, a version of the emissivity retrieval algorithm that accounts for the penetration of microwave radiation through dry soil with diurnally varying vertical temperature gradients. These results suggest that this penetration effect is more widespread and more significant to interpretation of passive microwave measurements than had been previously established. Emissivity coverage in areas where persistent cloudiness interferes with the availability of MODIS LST data is achieved using a classification-based method to spread emissivity data from less-cloudy areas that have similar microwave surface properties. Evaluations and analyses of the emissivity products over homogeneous snow-free areas are presented, including application to retrieval of soil temperature profiles. Spatial inhomogeneities are the largest in the vicinity of large water bodies due to the large water/land emissivity contrast and give rise to large apparent temporal variability in the retrieved emissivities when satellite footprint locations vary over time. This issue will be dealt with in the future by including a water fraction correction. Also note that current reliance on the MODIS day-night algorithm as a source of LST limits the coverage of the database in the Polar Regions. We will consider relaxing the current restrictions as part of future development.Citation: Moncet, J.-L., P. Liang, J. F. Galantowicz, A. E. Lipton, G. Uymin, C. Prigent, and C. Grassotti (2011), Land surface microwave emissivities derived from AMSR-E and MODIS measurements with advanced quality control, J. Geophys. Res., 116,

A framework for the retrieval of all-weather land surface temperature at a high spatial resolution from polar-orbiting thermal infrared and passive microwave data

“…Second, temperature retrieval from PMW measurements yields subsurface temperature, which is different from LST retrieval from TIR measurements (skin temperature). Nevertheless, subsurface temperatures can be converted to skin temperatures using the thermal diffusion equation (Gao et al, 2010;Moncet et al, 2011;Galantowicz et al, 2011). Third, the accuracies (approximately 5-6 K) of subsurface temperature retrieval from PMW measurements are worse than those (approximately 1-2 K) of LST retrieval from TIR measurements.…”

Using microwave brightness temperature diurnal cycle to improve emissivity retrievals over land

“…This assumption is supported by the variation of the discrepancy magnitude with surface type-more densely vegetated locations that are also moister showed much smaller discrepancies than arid regions. Moncet et al (2011) used the physical model proposed by Prigent et al (1999) to produce a monthly mean emissivity with consideration of microwave penetration depth effect. However, there is no available instantaneous emissivity product yet that has considered the effect of penetration depth in the retrieval.…”

The sensitivity of land emissivity estimates from AMSR-E at C and X bands to surface properties

“…These findings were in line with those obtained from forward modeling of land emissivity. AMSR-E emissivities for frequencies higher than 10.7 GHz was estimated using MODIS skin temperature product (Moncet et al, 2011a). Weng et al (2001) and Weng (2007) used a two-stream radiative transfer model for different land cover types to infer land emissivity and noted the complexity of modeling land emissivity over some surface classes like snow covered soils, sea ice and deserts.…”