FIELD PERFORMANCE OF A SPINNING-REFLECTOR MICROWAVE RADIOMETER

In the winter of 1986, two microwave radiometers were operated side by side at a high-altitude weather observation site in the central Sierr a Nevada for the purpose of comparing measurements in a variety of amb ient weather conditions. The instruments continuously recorded measure ments of vertically integrated water vapor and liquid water during sto rms affecting the area. One radiometer was designed with a spinning re flector to shed precipitation particles, while the other radiometer's reflector was fixed. Temporal records of the data show periods of wet weather contamination for the fixed reflector radiometer. The absence (presence) of these contaminated periods is mainly explained by the di fference in the design of the radiometers. These contaminated periods led to larger standard deviation in the data from the fixed-reflector radiometer and lower correlation coefficients between the two instrume nts. Correlation coefficients of 0.83 for the liquid and 0.68 for the vapor values were found for the radiometer-radiometer comparisons. Whe n some of the points suspected of contamination were removed, the cor- relation coefficients improved to 0.87 and 0.71 for the liquid and vap or values, respectively. The standard deviations were 0.1 mm and 0. 12 cm for the liquid and vapor channels, respectively, of the spinning r eflector radiometer. For the fixed-reflector design radiometer, a stan dard deviation of 0.1 mm for the liquid and 0.26 cm for the vapor was found. Comparison of radiometer vapor and rawinsonde precipitable wate r resulted in a correlation coefficient of 0.97 for the spinning-refle ctor radiometer and 0.8 for the fixed-reflector radiometer.