While it is generally acknowledged that a key to improving climate prediction is the improved treatment of clouds, there still remains a need for accurate measurements of global cloud properties. In particular, vertically integrated ice cloud mass (or ice water path, IWP) and particle size (such as mass median diameter Dme). Global scale measurements of the global distributions of IWP and Dme are needed currently available to assess the treatment of ice clouds by climate models. Recent satellite programs have been proposed to address these issues using observations in the infrared and far-infrared wavelengths. The paper will review ice cloud remote sensing techniques that have been recently developed for application to high-spectral resolution measurements in the 4-700 micron region. Applications to narrowband observations at these wavelengths will also be discussed.

In addition, the paper introduces the Cloud Infrared Radiometer for UnESS (CIRRUS), a novel far-IR radiometer that uses new High Temperature Superconducting detectors in a dewar assembly with an integrated cryocooler. The radiometer, proposed to fly on the International Space Station, makes observations in four spectral channels in the far-infrared (15, 22, 28, and 45 cm-1 or 667, 450, 350 and 220 microns) that are combined with existing infrared observations from geostationary platforms to retrieve IWP and Dme. The scientific goal of CIRRUS is to provide an improved characterization of ice clouds that contributes significantly to our understanding of the global water cycle, and thus climate predictability.