Exploring the Scattering Signal of GMI's 166GHz Channel

Passive microwave imager channels in the 37 to 89 GHz range have long been used to detect the scattering signatures of precipitation-sized ice particles in clouds. Dual polarization plays an important role in distinguishing between brightness temperature scattering signatures and other background variability, as demonstrated by Spencer (1986), Spencer et al. (1989), Petty (1994), and others.

The new GPM Microwave Imager (GMI) is the first satellite radiometer to possess dual-polarized channels at 166 GHz. These high-frequency channels are more susceptible to emission and attenuation by cloud water and water vapor than their lower-frequency counterparts. Prior to the launch of the GMI, it was uncertain whether the 166 GHz channels would provide information about ice in clouds comparable to the more commonly used 89 GHz channels. We address this question by examining the characteristics of the 166 GHz scattering signature in cold-season precipitating cloud systems over the North Atlantic and the Great Lakes. We also compare and contrast those signatures for differing cloud systems including lake-effect snowfall, open-ocean cellular convection, and synoptic-scale precipitation cloud bands.