Using a micro-rain radar to assess the editing of ground - based microwave radiometer data

Kapitel i bok, 2023

A microwave radiometer measuring the radiation at 21.0 and 31.4 GHz. provides data from which it is possible to retrieve simultaneously both the integrated amount of water vapor and the cloud liquid in the atmosphere. The algorithm used for modeling the emission from the liquid water is based on the assumption that it is inversely proportional to the frequency squared. This is valid as long as the size of the liquid particles in the atmosphere is less than a few tenths of a millimeter. When independent information on the liquid water is not available the normal data reduction procedure is to screen and edit the radiometer data using its own estimates of the liquid water to decide if the quality is acceptable. Typically data acquired in presence of more than 0.7 mm of integrated liquid water are discarded. A disadvantage of this method is that the poor data quality may affect the editing process. We have installed a micro-rain radar in order to measure rain events. It transmits a frequency modulated continuous wave (FM-CW) at 24.1 GHz with a power of 50 mW, which results in an operating range of 1.4 km. The Doppler information is used in order to detect when the liquid drops are large enough to fall. Then we will have a strong indication that our radiometer data are of poor quality. We report from our first tests and evaluation of using the radar data in the radiometer data editing. We compare the results with those obtained from the standard editing and find an agreement, in terms of the number of discarded data points, when using a threshold value of 0.4 mm of liquid water.