Cloud Detection Techniques in NESDIS Advanced-TOVS Sounding Product Systems

The National Oceanic and Atmospheric Administration (NOAA) successfully deployed the NOAA-15 satellite into polar orbit (ascending, evening) on May 13, 1998. NOAA-15 features the first in a series of next generation atmospheric sounders referred to as Advanced TIROS Operational Vertical Sounder (ATOVS). ATOVS is comprised of the 20-channel High-resolution Infrared Radiation Sounder (HIRS), the 15-channel Advanced Microwave Sounding Unit (AMSU-A), and 5-channel Advanced Very High Resolution Radiometer (AVHRR).

The National Environmental Satellite Data and Information Service (NESDIS) recently completed a successful scientific checkout of the ATOVS sounders and operational product generation systems. A critical step in deriving these products is the identification of clouds. NESDIS has developed an extensive scientific algorithm to detect clouds using a combination of tests based on selected measurements from all the available radiometers. However, the challenge for developing methods that accurately identify clouds under all the conditions encountered globally is formidable.

The following report provides the current status of the NESDIS operational cloud detection algorithm for the NOAA-15 ATOVS system. Included are the numerous tests done, their segregation depending upon geographic, solar and seasonal constraints, and procedures to compile (and update) the datasets and coefficients used in many of the tests. Results are presented which compare the NESDIS operational cloud mask to available satellite measurements sensitive to clouds, radiosonde observations, and cloud products from satellite based and conventional data platforms. Results indicate a very good consistency between the NOAA-15 cloud mask and global cloud cover data.