The GPS Radio Occultation ROSA-ROSSA Software: Preliminary Results

The GPS Radio Occultation (RO) is an emerging remote sensing technique for the profiling of atmospheric parameters (first of all refractivity, but also pressure, temperature, humidity and electron density). It is based on the inversion of L1 and L2 GPS signals collected on-board a Low Earth Orbit (LEO) platform, when the transmitter rises or sets beyond the Earth’s limb [1]. The relative movement of both satellites allows a “quasi” vertical atmospheric scan and the profiles extracted using this technique are characterized by a high vertical resolution (limited by Fresnel diffraction, thus varying between 500 m near the surface up to 1500 m in the higher stratosphere and ionosphere) and a high accuracy (for example < 0.5÷1% in terms of refractivity fractional error up to 30 km height). The RO technique is operatively applied for meteorological purposes (data collected by one LEO receiver placed at 700 km altitude produce 300÷400 profiles per day well distributed around the globe) since such observations can easily be assimilated into Numerical Weather Prediction models. Anyway it is very useful also for climatological purposes (the accuracy of inferred Tropopause parameters is one of the most attractive aspect of the RO technique), for gravity wave observations and for Space Weather applications. Actually, three operative satellite missions are carrying on-board GPS receivers for RO purposes: the German CHAMP satellite [2], the European METOP-1 mission [3] and the USA/Taiwan COSMIC constellation [4]. Several other missions are planned for the next future. In particular, during the 2009 Spring season, the Indian OCEANSAT-2 mission carrying on-board the Italian ROSA (Radio Occultation Sounder of the Atmosphere) GPS receiver is expected to be launched. In the framework of this opportunity, the Italian Space Agency (ASI) founded a pool of Italian Universities and Research Centers for the implementation of the overall (and state-of-the-art) RO processing chain which is called ROSA-ROSSA (ROSA-Research and Operational Satellite and Software Activities). The ROSA-ROSSA will be integrated in the operative ROSA Ground Segment by an Italian Software farm (INNOVA, located in Matera, Italy), and this ground segment will operate in Italy (at the ASI Space Geodesy Center, near Matera) and in India (at the Indian National Remote Sensing Agency, near Hyderabad) starting from the 2009 Spring season.