Infrared cloud phase determination from MODIS and AIRS

In the hierarchy of satellite retrieved cloud properties, determination of cloud thermodynamic phase usually falls just after cloud detection and cloud height determination. Correct assignment of cloud phase is essential to the later retrieval of other cloud properties such as effective particle size, optical thickness, and water content. While near-infrared reflectance-based techniques can simplify the problem of cloud phase determination during the day, nighttime cloud phase assignment is still difficult.

Infrared-based cloud phase assessment has moved beyond simple 11 µm brightness temperature thresholding, incorporating brightness temperature differences that utilize spectral differences in the indices of refraction of water and ice. In this poster, we look at the thermodynamic phase sensitivities of several infrared brightness temperature differences to cloud height and several atmospheric profiles for the MODIS instrument. We also consider the impacts of multilayer clouds, such as cirrus overlying low-level water clouds, on the retrieval of cloud phase. We focus on the MODIS channels centered at 3.75, 8.5, and 11.0 µm. We then consider the possible advantages offered by high spectral resolution infrared instruments by focussing on the AIRS instrument.