Characteristics of summertime microwave land emissivity over the conterminous United States

Abstract

This study examines the microwave land emissivity, a key value that can be derived from microwave measurements. At microwave frequencies the atmosphere is semitransparent. Consequently, a satellite radiance measurement contains a large fraction of energy from the Earth's surface. Microwave radiometers have been in space beginning in the early 1970s, and have shown great utility in retrieving atmospheric variables such as total precipitable water, cloud liquid water, and rain over the ocean where the emissivity is well known. These retrievals cannot be performed over land, due to the poor characterization of the underlying land surface; specifically the land surface temperature and surface emissivity. This research characterizes microwave surface emissivity and its associated error over the summertime Conterminous United States (CONUS) during 2000 - 2002 for use with various remote sensing applications and data assimilation systems. It is found that the microwave emissivity errors are dominated by the error in the land surface temperature. The microwave emissivity error is generally better than two percent within a natural summertime variability of five percent.