Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2000-04-26
2001-07-24
Tarcza, Thomas H. (Department: 3662)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C244S173300, C342S02500R, C342S354000
Reexamination Certificate
active
06264143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radar interferometry apparatus and to applications thereof.
2. Background of the Invention
Over the last few years, radar imaging has been enriched by the spectacular possibilities made available by combining a plurality of radar images coherently, as illustrated in particular by the following publications:
R. Golstein and H. Zebker “Interferometric radar measurement of ocean surface currents”, Nature, 328, 707-709, 1987;
C. Prati and F. Rocca “Improving slant-range resolution with multiple SAR surveys”, IEEE Trans. Aerospace Elec. Sys., 29, 135-143, 1993;
H. Zebker and R. Golstein “Topographic mapping from interferometric SAR observation”, J. Geophys. Res., 91, 4993-5001, 1986; and
D. Massonnet and T. Rabaute “Radar interferometry: limits and potential”, IEEE Trans. Geosc. and Remote Sensing, 31, 455-464, 1993.
SUMMARY OF THE INVENTION
The present invention provides radar interferometry apparatus comprising at least one emitter satellite and at least one constellation of receiver satellites, the apparatus being characterized in that the satellites are placed on orbits selected in such a manner that the receiver satellites aim at the zone of the ground that is illuminated by the emitter satellite, and such that:
the major axes thereof have the same length so that the satellites are accurately synchronous;
the focuses are separated by a distance which is the same for each of the orbits of the receiver satellites and which is greater than the distance between the focuses of the orbit of the emitter satellite, such that the eccentricity of a receiver satellite orbit is different from that of the emitter satellite orbit; and
the arguments of their perigees have values that are uniformly distributed over 360° such that during one orbital period the receiver satellites travel round an ellipse over which they are uniformly distributed, said ellipse being centered on the position that the emitter satellite would have had if its orbit had the same ascending node longitude and the same phasing as the orbits of the receiver satellites.
Preferably, the receiver satellites are permanently aimed at the ground zone illuminated by the emitter satellite, however in certain applications it is possible for the receiver satellites to aim only as a general rule or even only occasionally at the zone illuminated by the emitter satellite.
The constellation of passive receivers makes it possible to implement all radar options by using an existing radar satellite as the source. The proposed constellation is of low cost given that it is of a passive nature.
Preferably, the emitter satellite is synchronous with the receiver satellites.
Preferably, the constellation has one or more groups of three receiver satellites placed on one or more concentric elliptical orbits.
The emitter satellite can form a portion of the constellation or it can be independent thereof, depending in the implementation.
Preferably, the radar receivers are designed to record continuously the signal from the ground zone illuminated by the emitter satellite, means being provided for resynchronizing the signal as recorded in this way in the form of successive rows organized by increasing distance.
Advantageously, the emitter satellite is selected from the group of radar observation satellites such a ERS-1, ERS-2, Radarsat, and J.ERS-1.
REFERENCES:
patent: 5553816 (1996-09-01), Perrotta
D. Massonet, “Satellite Radar Interferometry”, Scientific American, vol. 276, No.2, Feb. 1997, pp. 46-53 (XPOOO696084).
H. A. Zebker et al., “Mapping the World's Topography Using Radar Interferometry: The Topsat Mission”, Proceedings of the IEEE, vol. 82, No. 12, Dec. 1, 1994, pp. 1774-1786 (XP000492720).
A. Freeman et al., “SAR Applications in the 21stCentury”, Archive Fur Elektronik Und Ubertragungstechnik, vol. 50, No. 2, Mar. 1, 1996, pp. 79-84 (XP000595503).
Centre National d'Etudes Spatiales
Mason, Kolehmainen Rathburn & Wyss
Mull Fred H.
Tarcza Thomas H.
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