A Study Of GPS Occultation Technology Application

The GPS Radio Occultation (RO) is a recent remote sensing technique whose application mainly concerns the study of climate and atmospheric conditions. The technique is based, on its simplest form, on the inversion of the excess-phase evolution measured on the GPS signal received on-board a LEO satellite, when it is occulted with respect to the transmitter. When the signals cross the atmosphere, they are delayed and their path is bent. Therefore, the overall effect is the signal reception, also below the terrestrial limb .Long-term stability, all weather capabilities and low cost of GPS receivers are significant characteristics making the GPS RO technique attractive and easily implementable in Earth's observing satellite missions.The forthcoming Indian OCEANSAT-2 satellite mission, which will be launched at the end of 2008, will carry on-board the Italian GPS receiver ROSA (Radio Occultation Sounder of the Atmosphere) devoted to RO. The ROSA raw data, downloaded both to an Indian and to an Italian ground station, will be processed by the so called ROSA-ROSSA (ROSA-Research and Operational Satellite and Software Activities) software that is composed by a chain of modular Data Generators (DG) developed by Italian universities and research centres under a contract between Italian Space Agency and Istituto Superiore Mario Boella (ISMB). The ROSA-ROSSA software will process ROSA data into atmospheric refractivity profiles and into temperature, humidity and electron density profiles.In this thesis, the attention is focused on the development of a software for validation of the Data Generators belonging to the complete processing chain. Moreover very preliminary results will be described. These results have been obtained comparing ROSA-ROSSA product at different level with correspondent product obtained by other radio occultation software (in particular the CDAAC software which processes COSMIC/FORMOSAT observations, being COSMIC a NASA-TAIWAN satellites constellation devoted to RO), given same raw data in input. The ROSA-ROSSA product is also compared with meteorological analyzes provided by European Center for Medium Range Weather Forecasting (ECMWF).In Chapter 1 we provide a general concept of GPS Radio Occultation (RO) technique. In Chapter 2, we describe Radio Occultation Technique in detail. The related RO satellite missions, the Challenging Mini-Satellite Payload (CHAMP), Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and Indian OCEANSAT-2 mission and the ROSA payload are introduced .In Chapter 3, ROSA_ROSSA Software developed by Italian universities and research centers is described. The Dataset used for comparison is described too. In chapter 4, we describe Data Comparison Software (DG_CONFRONTI) Development and show some pictures got by this software. In Chapter 5, we show the comparison results and conclude that the ROSO-ROSSA RO software has a good performance.