Communications: directive radio wave systems and devices (e.g. – Synthetic aperture radar
Reexamination Certificate
2001-05-04
2002-09-17
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Synthetic aperture radar
C342S191000
Reexamination Certificate
active
06452532
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO COMPACT DISC(S)
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to radar imaging methods, and in particular, to apparatus and methods for operating satellites utilizing radar and holography for imaging an orbited planet. The method of the present invention is also applicable for use in non-satellite imaging applications such as medical imaging.
2. Information Disclosure Statement
It is often desired to image a planet's surface and subsurface with high resolution in near real time. Well-known solutions for this problem include Synthetic Aperture Radar (“SAR”) using microwave imaging. Known satellite SAR focus a “flat earth” field of view (“FOV”) to a flat physical receiving antenna. Additionally, they cycle their complex imaging received signal at the rate in which the Doppler history (phase) on the physical aperture (the antenna) “fills”, i.e., when the finest phase replica is first present on the face of the antenna. At this time, known SAR convert from analog to digital (A/D) while simultaneously detecting phase, and then digitally focus and truncate series expressions of the “flat earth” geometry, in order to linearize and orthogonalize the imagery set, thereby inserting accumulating bias errors.
Unlike Doppler, which is coherent, Range is not coherent. Additionally, because prior art SAR technology uses Range for the second dimension, which is the “weak link” in its technology (limiting the finest resolution and causing the largest burden of noise), prior art SAR necessarily uses extremely wide bandwidth and is the principal cause of excessive RF power requirements at the satellite. RF propagation losses and realistic antenna beam widths force the wide bandwidth prior art SAR satellite to be limited to use at low altitudes causing associated infrequent revisit intervals, and “store and forward” imaging data is thereby forced to be downlinked at infrequent intervals, overloading the downlink capacity and limiting the overall effectiveness of prior art SAR technology. Prior art SAR technology also has very small swath widths that necessarily limit the number of available imaged areas, making prior art SAR technology unacceptable for use as a commercial service.
Known prior art interferometric imaging technology necessarily focuses outward into space because the mensurational accuracy required is too demanding for downward looking, earth oriented, fine resolution imaging using known prior art technology.
It is therefore desirable to have an improved satellite imaging system that does not have these problems found in the prior art. It would be desirable to have an improved satellite imaging system that has substantially improved gain and signal-to-noise ratio as compared to the prior art, and that further has a wide FOV swath and whose image reconstruction is decoupled from a dependence on time. It is further desirable to have an improved satellite imaging system with substantially better phase closure accuracy than heretofore possible.
Grisham, U.S. Pat. No. 3,243,706 (issued Mar. 29, 1966; hereinafter, the “ROSAE patent”), describes a satellite system having three subsystems of two pair of satellites each, and the orbits of all satellites within each subsystem are nominally circular. In one subsystem, the two pair of satellites orbit circularly in an equatorial plane. The other two subsystems have polar planes of circular orbit, with the polar planes being orthogonal to each other and also being orthogonal to the equatorial plane subsystem so that the planes of all three subsystems are mutually perpendicular. Within each subsystem, the two members of one pair of satellites are nominally 180° apart and orbit in one sense (direction), while the two members of the other pair of satellites are nominally 180° apart but orbit in the other sense (direction). While the satellite configuration of the ROSAE patent is a preferable configuration for use by the present invention, the ROSAE patent does not disclose or suggest using the microwave interferometry radiating incrementally accumulating holography (“MIRIAH”) method of the present invention in combination with the satellite configuration of the ROSAE patent.
Caputi, U.S. Pat. No. 4,325,065 (issued Apr. 13, 1982), describes a process for correcting data from a bistatic synthetic aperture radar (“SAR”) to eliminate distortions and resolution limitations due to the relative positions and motions of the radar transmitter and receiver with respect to a target.
Grisham, U.S. Pat. No. 4,602,257 (issued Jul. 22, 1986; hereinafter the “SARAH patent”) and fully incorporated herein by reference, describes a method of satellite operation utilizing a paired-satellite configuration in which one satellite illuminates the imaged field of view and the other satellite receives the reflected energy using bistatic synthetic aperture radar (“SAR”), but did not teach or suggest the use of interferometers for illumination or holography for recording the image data, and thus did not generate a large positive Gain spatial matched filter in a Fourier plane (i.e., a hologram). Instead, the SARAH patent taught use of Range/Doppler for illumination, and generated a time dependent matched filter in the Fourier plane. Because both SAR and SARAH use time referencing, image reconstruction by these prior art methods is necessarily dependent on time.
None of the known prior art references, either singly or in combination, disclose or suggest the present invention.
BRIEF SUMMARY OF THE INVENTION
The present invention is a satellite architecture used to create a narrow-bandwidth actively-illuminated interferometric Synthetic Aperture Radar (“SAR”), specifically, a bistatic SAR, whose Very Long Baseline Interferometer (“VLBI”) has a baseline between its two bistatic apertures, each on a different satellite, that is considerably longer than the diameter of the field of view (“FOV”). This is in contrast to prior art bistatic SAR where the interferometer baseline is shorter than the diameter of the FOV because both bistatic apertures were on the same satellite. The preferred embodiments of the invention use subsets of the satellite orbit configuration as described in Grisham, U.S. Pat. No. 3,243,706 (issued Mar. 29, 1966; hereinafter, the “ROSAE patent”) and fully incorporated herein by reference, whose satellite orbit structure is shown in FIG.
1
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Each of the preferred embodiments of the present invention has one or more VLBI created by pairs of satellites. The most preferred embodiments, having symmetrical configurations of three, six, and twelve satellites, are built on a foundation of Very Large Array (“VLA”) satellite VLBI triads, with each satellite of the triad being in its own nominally circular orbit, with the orbital planes of the three satellites of the triad being mutually orthogonal, and with the orbital angular velocity of each satellite preferably being five times the angular rotational velocity of the earth. For each VLA triad of satellites, VLBI pairs are formed by pairwise grouping of the satellites in the VLA, with the third satellite of the VLA being used as a control satellite to receive Michelson interferometric data from the VLBI pair to maintain phase closure, and also to receive Fizeau interferometric imaging data from the VLBI pair to be recorded in the Fourier plane of a holographic disc.
In contrast to prior art SAR technology, in which the synthetic aperture is time referenced, the present invention extends the synthetic aperture in size and in a second dimension and uses active illumination of the FOV by interferometers, thereby causing the resulting synthetic aperture to become spatially referenced. In terms of matched filter theory, the present invention's microwave interferometry radiating incrementally accumulating holography (“MIRIAH”) technology provides a two-dimensional spatial matched filter with an extraordinarily narrow passband (for finer resolution and higher
Andrea Brian
Rosae, Inc.
Tarcza Thomas H.
Walker, McKenzie & Walker PC
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