Measurement of humidity profiles in the atmosphere by the global positioning system and radar wind profilers

Bragg backscatter of radar waves from elevated turbulent layers is very hig hly correlated with the height profile of the gradient of radio refractive index through elevated turbulent layers, as has often been documented in pa st research. However, many users need profiles of radio refractive index or the associated humidity rather than profiles of their gradients. Simple in tegration of the gradients is usually nor feasible because clutter and vari ous noise sources often severely contaminate the lower-range gates. The aut hors show that if the total integrated humidity is independently available [for example, from the Global Positioning System (GPS)] and if the surface value of humidity is known, the profiles of humidity are retrievable with g oad accuracy. This method is demonstrated with data collected in Southern C alifornia, where 7 h of 449-MHz data were recorded along with GPS data. Thr ee radiosonde balloon were launched during that period, and the profiles of humidity from the two sources are compared. Simulations are used to assess errors that result From factors such as lack of the sign of the humidity g radients. In conclusion, a humidity profile found by statistical retrieval is compared with one found by the technique proposed in this paper.