Study On Some Problems In Atmospheric Inversion By GPS Occultation Amplitude Observations

GPS/LEO occultation technique in probing the Earth's atmospheric profiles is one of the most potential topics in atmospheric science. It has advantages with high accuracy, high resolution, all-weather condition, low consuming, globally coverage, self-adjustment, free of observer to climb sounding point. Recently, the GPS/LEO occultation phase inversion algorithm has been widely noticed and rapidly developed. The achievements from MicroLab1, CHAMP, SAC-C etc. have been successfully applied in weather prediction, climate analysis and global change researches. The further study of amplitude inversion in association with phase inversion is attractive for quantity assessment of phase inversion by GPS occultation observation, for mechanism study and correction method of minus departure in low troposphere by GPS occultation data inversion, and for tiny construction probing of ionosphere. It might be another purpose of our research to further analyze the applications of GPS occultation amplitude inversion in atmospheric scientific researches, national economy, and national defence.Under the assumptions of geometric optics and thin phase screen the retrieval algorithms of amplitude in GPS/LEO occultation technique were listed in this paper, respectively. A processing software construction of amplitude inversion by GPS occultation is independently developed in Shanghai Astronomical Observatory. Geometric and physical decay sources producing observed signal amplitude variations were sorted according to their physical mechanisms. In dealing with the upper singularity point of Abel inversion transfer, a zenith compensation term is introduced, which makes simple and stable in Abel inversion process. Using CHAMP observational data samples, the profiles of atmospheric bending, refractivity, pressure, and temperature were retrieved in turn by the series of signal noise ratio. The results were compared and discussed with that from phase process. The influences of both geometric and physical sources on the atmospheric retrievals were analyzed briefly. Within height range of 5-30km, in both bending angle and refractivity the relative bias between profiles of phase and amplitude inversions is below 4%, in temperature the bias is about 2-3oC. From the results in our study we believe that amplitude inversion is a noticeable research field in GPS/LEO occultation technique.