Clouds cover about 2/3 of Earth’s surface. They play a crucial role in regulating Earth’s energy budget. Clouds reflect part of the sunlight back to space (i.e., albedo effect), which reduces the solar energy available to Earth’s surface. At the same time, clouds also act like greenhouse gases—they block the emission of heat to space and inhibit the ability of the planet to release its absorbed solar energy (i.e., greenhouse effect). The net radiative effect of clouds on the climate depends on the global distribution of clouds and their optical and microphysical properties. Satellite-based, long-term, global cloud observation is the key to understanding the role of clouds in the current climate system and how clouds will change with global warming.

In this talk, I will provide an overview of the remote sensing of global cloud properties using a NASA satellite sensor—MODIS (Moderate Resolution Imaging Spectroradiometer). In the first part, I will explain the fundamental physics behind the retrieval of two key cloud parameters, cloud optical thickness and cloud particle effective radius, from MODIS cloud reflection measurements. In the second part of this talk, I will present our recent studies on several key issues in MODIS cloud retrieval algorithm. Topics will include: i) an assessment of the uncertainties in MODIS ice cloud products due to the complex and variable nature of ice crystals; ii) an investigation of the influence of cloud vertical structure on cloud particle effective radius retrieval; and iii) a study on the 3-D radiative transfer effect on MODIS cloud particle effective radius retrieval.

Location: Physics Bldg., Room 401