Image formation by passive collection and processing of radio frequency signals illuminating and scattered by cultural features of terrestrial region

• US 20040058643A1
• Filed: 09/17/2003
• Published: 03/25/2004
• Est. Priority Date: 11/15/2000
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Martin, Gayle Patrick, Shipley, John W.
• Granted Patent: US 6,917,784 B2
• Time in Patent Office: Days
• US Class Current: 455/3.02
• CPC Class Codes: G01S 13/9058 Bistatic or multistatic SAR

Abstract

An imaging system uses ‘RF daylight’ created by an RF illumination source, such as a television broadcast tower, to passively generate RF scattering coefficients for multiple points within a prescribed three-dimensional volume being illuminated by the RF transmitter. The scattering coefficients provide a complex interference pattern having amplitude and phase components that contain all information necessary to recreate a three-dimensional monochromatic image of the illuminated scene. Coherent complex correlation provides scene information content that is only a function of scene scattering and collector geometry. The scene information may be coupled to an image utility subsystem, such as a virtual reality simulator, for generation of a three-dimensional image of the illuminated scene.

Claims

1. A method of generating an image of a terrestrial region upon which electromagnetic energy from an electromagnetic energy source is incident comprising the steps of:

(a) passively collecting electromagnetic energy emitted by said electromagnetic energy source by way of at least one first energy collector;

(b) passively collecting, by at least one second energy collector moving among a plurality of distributed energy collection locations, electromagnetic energy emitted by said electromagnetic energy source and scattered by features of said terrestrial region of interest;

(c) processing a reference signal representative of electromagnetic energy collected in step (a), in accordance with information representative of the collection geometry of said at least one first energy collector and the geolocation of said electromagnetic energy source, so as to derive a time- and location-corrected reference signal;

(d) correlating the time- and location-corrected reference signal derived in step (c) with an image signal representative of electromagnetic energy collected by said at least one moving second energy collector in step (b), so as to derive composite amplitude and phase values of scattering components for plural locations of said terrestrial region as received by said at least one moving second energy collector as a function of spatial position; and

(e) processing said composite scattering components derived in step (d) to produce said multidimensional image of said terrestrial region of interest.

2. A method according to claim 1, wherein said electromagnetic energy source comprises a television signal transmitter, and step (b) comprises passively collecting electromagnetic energy emitted by said television signal transmitter, and scattered by features of said terrestrial region of interest, by means of an airborne or spaceborne electromagnetic energy collection platform moving among said plurality of distributed energy collection locations.

3. A system for deriving image information representative of cultural features of a terrestrial region illuminated by an RF transmitter comprising:

a reference signal collection subsystem which is operative to collect non-scattered RF energy emitted by said RF transmitter illuminating said terrestrial region;

a dynamic scattered image energy subsystem which is operative to travel past said terrestrial region, and collect from plural non-coincident viewing paths of said terrestrial region, RF energy scattered from points of cultural features within a three-dimensional volume of space containing said terrestrial region; and

a collected signal processing subsystem, which is operative to process information representative of said non-scattered RF energy as collected by said reference signal collection subsystem, to derive a coherent reference signal corresponding to that transmitted by said RF transmitter illuminating said terrestrial region, time- and location-corrected as necessary to points within said three-dimensional volume of space, and to correlate said coherent reference signal with a scattered RF energy signal representative of electromagnetic energy collected by said dynamic scattered image energy subsystem, time- and location-corrected as necessary to said points within said three-dimensional volume of space, so as to derive composite amplitude and phase values of scattering components for said points of said three-dimensional space.

4. A system according to claim 3, further including an image generator subsystem, which is operative to process said composite amplitude and phase values of scattering components for said points of said three-dimensional space to produce a multidimensional image of cultural features of said terrestrial region.

5. A system according to claim 3, wherein said reference signal collection subsystem and said dynamic scattered image energy subsystem are configured to employ a common RF energy collector that simultaneously collects said non-scattered RF energy emitted by said RF transmitter illuminating said terrestrial region, and RF energy scattered from points of cultural features within said three-dimensional volume of space containing said terrestrial region.

6. A system according to claim 3, wherein said reference signal collection subsystem and said dynamic scattered image energy subsystem employ respectively separate RF energy collectors that simultaneously collect said non-scattered RF energy emitted by said RF transmitter illuminating said terrestrial region, and RF energy scattered from points of cultural features within said three-dimensional volume of space containing said terrestrial region.

7. A system according to claim 5, wherein said collected signal processing subsystem includes:

a coherent reference signal processing section having a first Lorentz transform operator that accounts for signal propagation delay from said transmitter to said reference signal collection subsystem, and performs a Lorentz transform of an RF energy signal received thereby to a static frame of reference of a respective point in said three-dimensional space, and a delay associated with said reference signal'"'"'s propagation time from said transmitter to said respective point, so as to effectively transform a reference signal component of RF energy received at the collection aperture of said reference signal collection subsystem to said respective point, and

a dynamic scattered signal processing section having a second Lorentz transform operator which accounts for signal propagation delay and performs a second Lorentz transform of RF energy received by said dynamic scattered image energy subsystem from its moving frame of reference to the static frame of reference of said respective point in said three-dimensional space.

8. A system according to claim 7, wherein said dynamic scattered signal processing section includes a reference signal suppression operator coupled to remove a reference signal component from the scattered image component of RF energy received by said dynamic scattered image energy subsystem.

9. A system according to claim 8, wherein said collected signal processing subsystem includes a correlator, which is operative to correlate the output of said dynamic scattered signal processing section with the output of said coherent reference signal processing section, to derive composite amplitude and phase values of scattering components for said points of said three-dimensional space.

10. A system according to claim 9, further including an image generator subsystem, which is operative to process said composite amplitude and phase values of scattering components for said points of said three-dimensional space to produce a multidimensional image of cultural features of said terrestrial region.

11. A method for passively deriving image information representative of cultural features of a region illuminated by an RF transmitter comprising:

(a) providing a coherent reference signal representative of RF energy emitted by said RF transmitter illuminating said terrestrial region;

(b) collecting, from a plurality of mutually offset travel paths offset from said terrestrial region, RF energy scattered, as a result of illumination by RF energy emitted by said RF transmitter, from points that are capable of defining cultural features within a three-dimensional volume of space containing said terrestrial region; and

(c) correlating said coherent reference signal, time- and location-corrected as necessary to said points within said three-dimensional volume of space, with a scattered RF energy signal representative of electromagnetic energy collected by said dynamic scattered image energy subsystem, time- and location-corrected as necessary to said points within said three-dimensional volume of space, so as to derive composite amplitude and phase values of scattering components for said points of said three-dimensional space.

12. A method according to claim 11, further including the step (d) of processing said composite amplitude and phase values of scattering components for said points of said three-dimensional space to produce a multidimensional image of cultural features of said terrestrial region.

13. A method according to claim 11, wherein steps (a) and (b) include employing a common RF energy collector to simultaneously collect non-scattered RF energy emitted by said RF transmitter illuminating said terrestrial region, and RF energy scattered from said points of cultural features within said three-dimensional volume of space containing said terrestrial region.

14. A method according to claim 11, wherein steps (a) and (b) include employing respectively separate RF energy collectors to collect RF energy emitted by said RF transmitter illuminating said terrestrial region, and RF energy scattered from said points of cultural features within said three-dimensional volume of space containing said terrestrial region.

15. A method according to claim 13, wherein step (c) comprises:

(c1) processing said coherent reference signal in accordance with a first Lorentz transform that accounts for signal propagation delay from said transmitter to a collector for said reference signal and performs a Lorentz transform of an RF energy signal received thereby to a static frame of reference of a respective point in said three-dimensional space, and providing a delay associated with said reference signal'"'"'s propagation time from said transmitter to said respective point, so as to effectively transform a reference signal component of RF energy received by said collector to said respective point, and

(c2) processing said scattered RF energy signal in accordance with a second Lorentz transform operator which accounts for signal propagation delay and performs a second Lorentz transform of RF energy received by a collector for said scattered RF energy signal from its moving frame of reference to the static frame of reference of said respective point in said three-dimensional space.

16. A method according to claim 15, wherein step (c2) includes processing said scattered RF energy signal in accordance with a reference signal suppression operator that is operative to remove a reference signal component from said scattered RF energy signal.