GPS and Ground-Based Microwave Radiometer IPWV: A Case Study at Cagliari Astronomical Station, Italy

Rosa Pacione, Ermanno Fionda, Cecilia Sciarretta, Francesco Vespe and Riccardo Ferrara

Abstract:	Since January 1999 in the framework of the European Community Project MAGIC, at Centro di Geodesia Spaziale (CGS) of the Italian Space Agency (ASI), GPS zenith tropospheric total delays (ZTD) are routinely produced and monitored for all the Italian GPS permanent stations. The GPS signals are analyzed with the GIPSY-OASIS II software, using the Precise Point Positioning strategy. During 1999, at the Astronomical Station (SAC) building located in Cagliari (Italy), a ground-based dual-channel microwave radiometer (WVR-1100), managed by Fondazione Ugo Bordoni (FUB), was collocated with a permanent GPS receiver, in the framework of the Sardinia Radio Telescope Project (1999 SRT Project). The SRT Project is performed by ASI and Istituto di Radio Astronomia (IRA), Consiglio Nazionale delle Ricerche (CNR), Bologna(Italy). The aim of the SRT Project is to set up a large radio telescope near the Cagliari City, for many radio astronomy purposes. Cagliari is located along the South cost of Italian Sardinian Island in the middle of the Mediterranean Sea. The WVR-1100 measure atmospheric sky brightness temperatures at 23.8 and 31,4 GHz. Zenith integrated precipitable water vapor (IPWV) values have been estimated by using suitable retrieval technique based on radiometric optical depth. From GPS, zenith IPWV values have also been obtained exploiting the well know linear relationship between zenith wet delay (ZWD) and water vapor content. Zenith hydrostatic delay (ZHD) has been calculated by the Saastamoinen model. Furthermore during 1999, radiosondes (RAOB) have been launched four times a daily from the Cagliari-Elmas airport, approximately 15 km away from the GPS and WVR-1100 site. By using RAOB profiles, IPWV have been calculated at 00, 06, 12, and 18 UT for each day. IPWV concurrent values derived by these different tools and independent retrieval techniques have been compared. The analysis is performed for various time bases: year, seasons, and months, allowing indications on statistical parameters as standard deviation and bias differences. Fairly good agreement has been found. However, discrepancies have been pointed out when the comparison has involved no-electromagnetic observations as RAOB data.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1149 - 1158
Cite this article:	Pacione, Rosa, Fionda, Ermanno, Sciarretta, Cecilia, Vespe, Francesco, Ferrara, Riccardo, "GPS and Ground-Based Microwave Radiometer IPWV: A Case Study at Cagliari Astronomical Station, Italy," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1149-1158.
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