Cloud parameters from a combination of infrared and microwave measurements

Clouds are both absorbers of outgoing longwave radiation and reflectors of incoming solar radiation. Due to their crucial role, the knowledge of the horizontal and vertical distribution and the optical properties of globally distributed clouds are of fundamental importance to the understanding of the radiation and heat balance, weather and climate of the earth and the atmosphere. Measurements of radiation from space can play a big role in helping us to understand how radiation depends on cloud properties. They can also help us to identify which are the most critical cloud properties to measure. The goodness of satellite-based measurements is that they offer the only practical way of making cloud measurements over the entire global. The improvement of spatial resolution and spectral characterisations allow us to apply sophisticated retrieval procedures, which will provide new cloud products with enhanced accuracy. Since clouds are practically opaque in the infrared sounding frequencies and since the majority of the clouds are transparent in the microwave regions, it would appear that a proper combination of infrared and microwave measurements could be useful and significant data to determine the cloud coverage, the vertical cloud structure and the composition in all weather conditions. First of all the paper explores the performance of a cloud detection scheme for the Atmospheric Infrared Sounder (AIRS) data, then the improvements in retrieval cloud parameters, using high spectral resolution AIRS sounder data. together with the Advanced Microwave Sounding Unit (AMSU-A) and the Humidity Sounder for Brazil (HSB) on the Aqua mission, represents the most advanced sounding system ever deployed in space. AIRS measures simultaneously in more than 2300 spectral channels in the range of 0.4 to 1.7 μm and 3.4 to 15.4 μm. AIRS measurements are at 13.5 km resolution in infrared bands and at 2.3 km in four visible and near-infrared bands. AMSU has 42 km FOVs and is a temperature sounder (15 channels in the range of 50 to 89 GHz). HSB has 15 km FOVs and is a moisture sounder (4 channels in the range of 150 to 183MHz). AMSU and HSB are co-aligned with AIRS.