Wide Coverage, fine Resolution, Geosynchronous SAR for Atmosphere and Terrain Observation
Monti Guarnieri, Andrea1; Broquetas, Antoni2; Ruiz-Rodon, Josep2; Recchia, Andrea1; Giudici, Davide3; Schulz, Detlef4; Venturini, Roberto5
1Politecnico di Milano, ITALY; 2Universitat Politècnica de Catalunya, SPAIN; 3Aresys, ITALY; 4SES, LUXEMBOURG; 5Thales Alenia Space Italy, ITALY

Geosynchronous SAR have been proposed since forty years in two quite different concepts. The first one exploits a large orbit inclination causing a figure of eight [1,2], with huge excursion north-south. Such a system gets continental coverage with twice daily revisit, but it is so demanding in power and antenna size to require near future technologies.
The second concept takes advantage of the very small orbit ellipticity of commercial geosynchronous satellites, to get the synthetic aperture, and compensate the travel path losses with very long integration time - up to 7 hours , [3].
Such a system is suited to be hosted on a Telecommunication satellite, being compatible not only for the orbit, but also capable to exploit the same antenna reflector, and a fraction of the resources in terms of power and weight. We define this concept as TLC-GEOSAT.
In [4] a dual frequency TLC-GEOSAT system was proposed. The system exploits a C band beam to get one wide coverage (thousands of km), making quick looks at coarse resolution (100 m x 100 m or more), say each 20', to sense the atmosphere, creating water-vapor maps at space-time resolutions otherwise unattainable.
Water vapor maps are major sources of information for numerical weather prediction, augmenting the value of medium scale products like ECMWF, but they can also be exploited for compensating the atmospheric artifacts in LEO SAR and GPS.
The system in [4] exploits a second frequency, in the Ku band, to generate a small beam (hundreds on km), at finer resolution in the order of tens of meters, for monitoring deformations and subsidences. This system is quite useful in hazard like fast landslides, volcanic activity, or glaciers monitoring, thanks to its twice-daily revisit.
The system here proposed is an enhancement of the dual frequency concept, where multiple fine beams are placed, time-interleaved as a sort of ScanSAR mode, to get a very wide coverage at fine resolution.

The idea is to exploit the power available in the next generation of commercial geosynchronous satellites. In the study, we will focus on the compatibility with such systems, taking care of the resources available, the strict pointing requirements (that reduces the synthetic aperture) , the data rate and the current technologies' limitations.

A full Ku+C band multibeam design is proposed, including ambiguities quantifying the quality achievable in terms of resolution, coverage, revisit for both water-vapor and deformation maps.

[1] Tomiyasu, K.; , "Synthetic aperture radar in geosynchronous orbit," Antennas and Propagation Society International Symposium, 1978 , vol.16, no., pp. 42- 45, May 1978
[2] Tomiyasu, Kiyo; Pacelli, Jean L.; , "Synthetic Aperture Radar Imaging from an Inclined Geosynchronous Orbit," Geoscience and Remote Sensing, IEEE Transactions on , vol.GE-21, no.3, pp.324-329, July 1983
[3] C. Prati, F. Rocca, D. Giancola and A. Monti Guarnieri Passive Geosynchronous SAR system reusing backscattered digital sudio broadcasting signals, in IEEE Trans. on Geosci. and Remote Sensing vol. 36, No. 6, pp. 1973-1976, Nov. 1998

[4] Andrea Monti Guarnieri, Luca Perletta, Fabio Rocca, Diego Scapin, Stefano Tebaldini, Antoni Broquetas, Josep Ruiz, "Design of a geosynchronous SAR system for water-vapour maps and deformation Estimation" in proc FRINGE 2011 (Frascati, Italy) , 19-23 Sept 2011, pp 1-5.