The Italian Space Agency ROSA receiver: update on data analysis and future outlook

ROSA is a dual-frequency GPS receiver developed for space applications and tailored for GPS radio occultation studies and is currently flying on-board three satellites: the Indian OCEANSAT-2, the Argentinean SAC-D and the Indian/French MEGHA-TROPIQUES. Availability of ROSA data is seen as an opportunity by the scientific community to cover the 2013-2016 gap that will be left by the decommissioning of the Taiwan/US COSMIC-FORMOSAT3 constellation. This paper will provide an overview of signal ROSA quality in the neutral and ionized terrestrial atmosphere, in view of the delivery of ROSA observations to the user community. In particular, in this contribution a quality check comparative analysis between ROSA data collected on-board SAC-D and OCEANSAT-2 is shown. This deep analysis compares observability performances of the same instrument on-board two different satellite missions, putting in evidence the goodness of ROSA instrument on board the Argentinean platform against the unsatisfactory L2 performances the instrument showed on-board OCEANSAT-2. Causes of these non-satisfactory performances should be probably searched in the critical position of the ROSA antenna on-board the platform, and in the corresponding strong local multipath effects which create serious difficulties in the acquisition and tracking of the L2 signal. On the contrary, the quality of both rising and setting raw data acquired on-board SAC-D is completely different, demonstrating the criticality of having a good accommodation for the occultation antennas. A very limited (and “physiological”) number of data gaps is observed and impact heights of L1 and L2 start tracking are in line with all the others Radio Occultation sounders currently flying. An attempt of inverting data observed on-board the Argentinean mission was made using a non optimized inversion tool developed in Italy and preliminary results will be shown. Results of ROSA on MEGHA-Tropique platform are of the same level of the SAC-D results, i.e. good acquisition and tracking on both L1 and L2. The effectiveness of ROSA receiver in sounding the ionosphere will be demonstrated comparing electron density profiles (Ne) retrieved applying the Onion Peeling algorithm to OCEANSAT-- -derived TECs and SAC-D-derived TECs, against collocated products derived by the CDAAC COSMIC/FORMOSAT3 Radio-Occultation observations. These aspects are very important since the next few years will be characterized by high solar activity and, without the US/TAIWAN constellation, the number of ionospheric occultation products will be necessarily reduced. Finally, some ideas related the ROSA receiver hardware and on-board software updates will also be discussed.