Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Patent
1998-01-27
2000-10-10
Issing, Gregory C.
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
342424, G01S 302
Patent
active
061306444
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and to apparatus for measuring the geoid and/or imaging the earth by processing radio signals from satellites.
Conventionally, geoid measurement or earth imaging at microwave frequencies is performed using synthetic aperture radar (SAR) of the kind found on board certain observation satellites, such as the satellite ERS-1.
In particular, by applying interferometry to SAR images, it is possible to track seismic deformations of the earth, earthquakes, volcanic eruptions, etc. . . . .
For a description of satellite radar interferometry techniques and applications thereof to imaging the earth and measuring the geoid, reference may advantageously be made to the various publications below: Didier Massonnet et al., Letters to Nature, Vol. 375, No. 6532, Jun. 15, 1995; earthquake", Didier Massonnet et al., Letters to Nature, Vol. 369, May 19, 1994; the M=6.1 Eureka Valley, Calif. earthquake of May 17, 1993", Didier Massonnet, Kurt L. Feigl, Geophysical Research Letters, Vol. 22, No. 12, pp. 1541-1544, Jun. 15, 1995; interferometry", Didier Massonnet et al., Letters to Nature, Vol. 364, No. 6433, Jul. 8, 1993; interferograms", Didier Massonnet, Kurt L. Feigl, Geophysical Research Letters, Vol. 22, No. 12, pp. 1537-1540, Jun. 15, 1995.
Reference may also be made to the following publication: ocean altimetry", Martin-Neira M, E.S.A. Journal, Vol. 17, No. 4, Jan. 1, 1993, pp. 331-355, image.
Geometers on the ground find it difficult to make use of satellite-borne SAR observation of the earth, given that in general they are not specialists in such techniques.
SUMMARY OF THE INVENTION
An object of the invention is to propose a method and apparatus for performing imaging and geoid measurement that give access to the same information as satellite-borne SAR techniques while also being very easy to use on the ground.
Comparing a reflected signal with a reference signal is a technique that is used in other applications, for example when determining radio images for the purpose of providing aircraft with assistance in landing, as proposed in DE 42 10 823.
Nevertheless, in that document, the reflected signal and the reference signal are taken from a system that is moving (an aircraft), thereby putting constraints on the time interval during which the reference radiation can be observed, thus imposing data processing that is complicated, since it is necessary to take account of the movement parameters of the receivers, and thus making precise measurement impossible.
In particular, that method does not make it possible to compare signals taken on different dates and cannot provide geodesic information concerning ground movement between two dates, and it is even less capable at providing three-dimensional information.
The invention proposes a method of geoid measurement and/or earth imaging characterized in that at least one directional antenna that is fixed relative to the ground is used to pick up a radio signal transmitted from a satellite and reflected on the ground. This signal is processed using a reference signal that corresponds to the radio signal transmitted from the satellite in order to obtain a geodesic measurement and/or an image of the zone towards which the directional antenna is pointed.
Advantageously, in particular, interferometric processing is also implemented on images taken at different dates by a single directional antenna or simultaneously by antennas situated at distinct locations.
Thus, with a minimum of instruments to be manipulated, it is possible for a geometer on the ground to make fine geodesic measurements and also measurements of the displacement field in three dimensions.
The method is advantageously associated with the various characteristics below, taken singularly or in any technically feasible combination: satellite by means of an antenna disposed in the vicinity of the directional antenna; reflected radio signal from the satellite as picked up by the directional antenna, together with a phase correction to take accoun
REFERENCES:
patent: 3171126 (1965-02-01), Wiley
patent: 3943514 (1976-03-01), Afendykiw et al.
patent: 4170776 (1979-10-01), MacDoran
Griffiths, H.D., et al., "Bistatic Radar Using Satellite-Borne Illuminators Of Opportunity," Intl. Conf. Radar 92 (Conf. Publ. No. 365), Brighton, UK, Oct. 12-13 1992, pp. 276-279.
Martin-Neira, M., "A Passive Reflectometry And Interferometry System (Paris): Application To Ocean Altimetry," E.S.A. Journal, vol. 17, No. 4, Jan. 1, 1993, pp. 331-335.
Centre National d'Etudes Spatiales
Issing Gregory C.
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