Wednesday, 17 January 2007
A theoretical study of the uncertainties in the remote sensing of ice cloud optical thickness and effective size using high spectral resolution satellite observations
217D (Henry B. Gonzalez Convention Center)
Covering approximately 20% of the globe and 30-40% of the tropics, ice cloud plays a significant role in the climate system. It is well recognized that cloud optical thickness and effective size are two of the most important parameters determining the sign of ice cloud radiative forcing. At present, the global remote sensing of these two parameters depends primarily on satellite measurements from visible and near-infrared spectral regions and therefore is limited to the daytime. Because of the capability of providing high-vertical-resolution atmospheric profile that is crucial for the thermal-infrared remote sensing of ice clouds, the high-spectral-resolution satellite-based sensors, e.g., Atmospheric Infrared Sounder (AIRS), the Infrared Atmospheric Sounding Interferometer (IASI), the Cross-Track Infrared Sounder (CrIS), and the Hyperspectral Environmental Suite (HES), provide an unprecedented opportunity for the study of ice cloud optical thickness and effective size during both daytime and nighttime. Some attempts have already been made to retrieve the two parameters using high-spectral-resolution satellite measurements. However, little effort has been directed towards understanding the uncertainties in the retrieval caused by the errors and uncertainties from the atmospheric profile, surface properties, cloud top properties, cloud thermodynamic phase, ice crystal scattering properties, horizontal and vertical inhomogeneity of cloud, radiative transfer model as well as instrument noise. The objective of this study is to estimate the impact of these uncertainties on the remote sensing of ice cloud optical thickness and effective size using high-spectral-resolution satellite measurements.