An algorithm for improving the retrieval of cloud liquid water and water vapor using effective radiating temperature of clouds

摘要

An algorithm is discussed which can significantly lower the rms errors in integrated cloud liquid water and water vapor retrieval from radiometric brightness temperature. This algorithm makes use of the effective radiating temperature of the atmosphere which is estimated from surface temperature, cloud base temperature, and cloud base height. The surface temperature is easily measured, while the cloud base temperature and the cloud base height may be measured by use of a pyrometer and a ceilometer, respectively. The effective radiating temperature T/sub eff/ is estimated at two separate frequencies corresponding to the two frequencies used to measure radiometric brightness temperature, and these estimates are then used to modify the brightness temperatures. For a data base compiled at University Park, Pennsylvania, the estimates of effective radiating temperature reduced the rms error in retrieving cloud liquid water content from 37 to 21 /spl mu/m, and reduced the rms error in retrieving water vapor under cloudy conditions from 0.20 to 0.11 cm. The reduction in the uncertainty in retrieved liquid water content was consistent with that achieved by Han and Thomson (1) for tropical conditions. Han and Thomson used measurements of cloud base height and cloud base temperature, along with a climatological mean effective radiating temperature to improve their retrievals.