Clear-sky column water vapor retrievals using the Airborne Imaging Microwave Radiometer (AIMR)

The retrieval algorithm is based on the integrated relative humidity profiles measured by numerous dropsondes released from the National Center for Atmospheric Research ( NCAR) C-130 aircraft that operated during the 2 month Intensive Field Phase ( IFP) of INDOEX.

The highest correlations of the linear relationship between the AIMR brightness temperature measurements and the dropsonde column water vapor values are for the nadir brightness temperatures of the 37 GHz and 90 GHz AIMR channels. The column water vapor, w, given with units of kg m(-2), may be expressed in terms of the 90 GHz nadir brightness temperature, T-B, via the expression, w = -209.4 + 1.025 T-B, whereas in terms of the 37 GHz AIMR nadir brightness temperature, w = -277.8 + 1.835 T-B. These expressions are valid when AIMR brightness temperature measurements about the NCAR C-130 are made at high altitudes ( above 5 km) and when the atmospheric column is cloud-free below the aircraft.