Initial evaluation of profiles of temperature, water vapor and cloud liquid water from a new microwave radiometer

Radiometrics Corporation has developed a new microwave radiometer for profiling the vertical distribution of temperature, water vapor and cloud liquid water through the depth of the troposphere. This instrument has been deployed at the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Program field site in north-central Oklahoma, USA, for an evaluation period beginning in March 2000 and extending through August 2000. Initial results of the evaluation will be presented.

The new radiometer measures at selected frequencies between 22 and 30 GHz (for water vapor profiling) and between 51 and 59 GHz (for temperature profiling). Both sets of frequencies are used for profiling cloud liquid water. Profiles are derived from the measured brightness temperatures with a retrieval based on a neural network approach (Solheim et al., 1997).

The evaluation will include a comparison of the retrieved temperature and water vapor profiles with profiles from other remote sensors and from radiosondes over a wide range of temperature, water vapor and cloud conditions. Retrieved profiles of temperature, water vapor and cloud liquid from the new radiometer will also be compared with predictions of the European Centre for Medium Range Weather Forecasting (ECMWF) model.

Although the profiles from the passive radiometer will exhibit less vertical resolution than profiles from radiosondes and some active remote sensors, this disadvantage will not be significant for many applications of the data. The high temporal resolution (10 minutes) and operation in nearly all weather conditions offer significant potential compensating advantages. To further evaluate the utility of the new profiler for addressing the scientific problems of interest to the ARM Program, profiles from it and the other profiling instruments will be input to models of longwave and shortwave radiation transfer. The resulting narrowband radiances and irradiances will be compared with measurements from collocated longwave and shortwave radiometers for clear-sky and cloudy-sky conditions.

Solheim, F. S., J. R. Godwin, E. R. Westwater, Y. Han, S. J. Keihm, K. March and R. Ware, Radiometric profiling of temperature, water vapor and cloud liquid water using various inversion methods, Radio Science, 33, 393-404, 1998.