89th American Meteorological Society Annual Meeting

Monday, 12 January 2009
Evaluations of the CALIPSO Cloud Optical Depth Algorithm Through Comparisons with a GOES Derived Cloud Analysis
Hall 5 (Phoenix Convention Center)
Katie Carbonari, Northrop Grumann TASC, Chantilly, VA; and H. Kiley and R. Alliss
Poster PDF (286.5 kB)
CALIPSO (Cloud-Aerosol Lidar and Infared Pathfinder Satellite Observations) combines an active lidar instrument with passive infrared and visible imagers to probe the vertical structure and properties of thin clouds and aerosols over the globe. CALIPSO is sun-synchronous and flies in the A-train, covering the same areas of Earth w/each pass. The geometry of the orbit is such that the ground track is repeated every 16 days. Measurements are reported at 5km resolution and a full analysis of the layer (optical depth, height, thicknesses for each cloud) is performed.

The CMG (Cloud-Mask Generator) ingests GOES multi-spectral imagery (at 4km, 15minute resolution) and applies a series of single- and multi-spectral tests to detect clouds. This provides high quality information about the distribution of clouds among the lines of site between GOES satellites and the Earth's surface; however, it does not indicate cloud altitude, thickness, or fraction. We simply get a cloud/no cloud decision for each GOES pixel.

In our analysis, we compared all CMG pixels (cloud/no cloud) to each CALIPSO footprint within 15 minutes of the CALIPSO overpass for various locations in CONUS. The CALIPSO threshold for an optical depth to be “cloudy” is varied. While some disagreement is expected due to differences in spatial/temporal resolutions, preliminary results show that CALIPSO is finding many thin clouds that GOES is missing. For example, when CMG pixel is clear, 60% of CALIPSO cloud optical depth of 0.7. Further investigations into disagreements between CALIPSO and CMG will be conducted and reported on.

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