Comparison of surface and satellite measurements of Arctic cloud properties

A number of different strategies will be used to compare cloud properties determined with surface-based sensors (radar and radiometers) to the MODIS/CERES sensor retreivals from the TERRA satellite, as well as to AVHRR retievals from the NOAA satellites. The radar and radiometers used in this study have been operating continously at the North Slope of Alaska (NSA), Department of Energy ARM site since 1998.

Different comparison strategies will be used. The most straightforward will involve comparing satellite measurements to simple layer means of cloud parameters such as crystal/droplet sizes, water contents and optical depths; this is the manner in which many ground to satellite comparisons have been made in previous studies.

In addition, calculations will be made of extinction and/or water content weighted layer averages for parameters such as equivalent droplet/crystal sizes. This strategy will clarify the response of the satellite sensors to the cloud optical depth versus the cloud water mass. Another third approach will be to define averaging layers by cumulative optical depth from cloud top; this will demonstrate how far into the cloud the different satellite radiometric measurements can penetrate.

These comparisons will take full advantage of the ability of the surface sensors to generate profiles of cloud microphysical properties, and to determine biases and limitations of the satellite-based cloud retrievals.

The extended analysis proposed in this element will more completely quantify errors in satellite retrievals and the degree to which differences in retrieved cloud properties are the result of observing system characteristics. For example, it is unrealistic to expect that particle size information in the lower portion of a thick cloud can be obtained from space. But we can identify under what conditions the lower cloud layer, and the surface below, will significantly affect retrievals and to what extent.