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<br />2. RESEARCH SITE AND INSTRUMENTATION. <br /> <br />The SCPP program operated in the American River Basin of the central Sierra <br />Nevada mo~ntatns in C~lifornia. A'map of the re~earch site showing the ~opog- <br />raphy, the location of instrumentation used in this paper, and the location of <br />the study area in the state of California is shown in Fig. 2. The complete net- <br />work of instrumentation used during SCPP and a thorough discussion of the SCPP <br />program is provided by Reynolds and Dennis (1986). Only instrumentation impor- <br />tant to this paper will be. described. <br /> <br />A. Dual-channel microwave radiometer <br /> <br />The dual-channel microwave radiometer is a ground-based passive instrument <br />which determines the brightness temperatures emitted by water vapor and cloud <br />liquid water. The quantity of vapor and liquid is determined by the magnitude <br />of the brightness temperature at specific microwave frequencies. The radiometer <br />operates at two frequenci~s: 20.6 GHz, sensitive primarily to water vapor, and <br />31.65 GHz, sensitive primarily to Jiquid water. The antenna beam width is 2.5 <br />degrees. The principles of microwave thermal emission from Rayleigh attenuating <br />clouds have been described by Westwater (1972). The design and operating prin- <br />ciples of the dual-channel ground-based microwave radiometer have been presented <br />by Guiraud et ale (1979) and Hogg et ale (1983). The SCPP radiometer was <br />designed by the National Oceanic and Atmospheric Administration and manufactured <br />by the Hughes Corporation. <br /> <br />Path-integrated amounts of water vapor and liquid water, expressed as depth <br />in cm and mm, respectively, were calculated from the radiometer measurements of <br />brightness temperature using statistical retrieval algorithms (Hogg et al., <br />1983). Specifics concerning retrieval algorithms and their Jse during SCPP are <br /> <br />3 <br />