7. Infrared Sensing

Thermal infrared radiation is a convenient tool for cloud remote sensing. Infrared emissions from cloud tops are often considered to be a proxy of the temperature there (and hence of cloud top height) regardless of day or night. Infrared brightness temperature, however, is not always a reasonable substitute for the physical temperature of clouds and could be largely misinterpreted if analyzed without care. The chapter begins with the theory of non-scattering radiative transfer, followed by simulated infrared spectra to demonstrate the impacts of clouds on satellite measurements. The ultimate goal of this chapter is to present the utility and limitations of the satellite infrared measurements of cloud properties such as cloud top temperature, particle size, and thermodynamic phase.