Radiometric profiling of temperature, water vapor and cloud liquid water using various inversion methods

We have developed a tunable temperature profiler based on a highly stable synthesizer that can observe at multiple frequencies on the shoulder of the 60 GHz atmospheric oxygen feature. We are developing a similar radiometer to obtain the vertical distribution of water vapor by making observations on the pressure broadened water vapor line from 22 to 29 GHz. Information on cloud liquid water profiles is also contained in these two wavebands. Various mathematical retrieval methods for temperature, water vapor, and cloud liquid water profiles were tested based on these radiometer designs. These include neural networking, Newtonian iteration of statistically retrieved profiles, and Bayesian “most probable” retrievals. Based on realistic radiometer errors and performance, very good retrieval capability is demonstrated. The performance of the various retrieval methods are presented and compared. Examples of profile retrievals are also presented. Data were not binned into seasons to reduce computer time; better retrieval results for all methods would be expected with binning. 1. Motivation for Radiometric Atmospheric Profiling Radiosonde observations (RAOBs) are the fundamental method for atmospheric temperature, wind, and water vapor profiling, in spite of their inaccuracies, cost, sparse temporal sampling and logistical difficulties. A better technology has been sought for decades, but until now, no accurate continuous all weather technology has been demonstrated. Laser radars (LIDARS) and Fourier transform infrared spectrometers can profile temperature and water vapor, but not in the presence of cloud. Our highly stable frequency agile radiometric temperature and water vapor profilers give continuous unattended profile measurements. They also have the capability to profile cloud liquid water, a capability absent in RAOBs and all other systems except for in situ aircraft devices. Applications for this passive radiometric profiling include: weather forecasting and nowcasting; detection of aircraft icing and other aviation related meteorological hazards; determination of density profiles for artillery trajectory and sound propagation; refractivity profiles for radio ducting prediction; corrections to radio astronomy; satellite positioning and Global Positioning System (GPS) measurements; atmospheric radiation flux studies; estimation and predic-