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

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.

FIELD OF THE INVENTION

The present invention relates in general to electromagnetic energy collection and processing systems, and is particularly directed to a method and apparatus for generating an image of a terrestrial region of interest, by passively collecting and processing radio waves, such as, but not limited to, those illuminating the terrestrial region from a commonly available RF emission source, for example, a commercial television transmission tower.

BACKGROUND OF THE INVENTION

Conventional schemes for generating images of objects or scenes include a variety of energy illuminating and collection methodologies, such as visible and infrared light-based processes (e.g., photography), and coherent electromagnetic radiation-based processes (e.g., synthetic aperture radar (SAR) and holography). While conventional (non-coherent) light-based photography allows image capture of exterior surfaces of objects in a scene, it does not create an image of where the light cannot go (behind the exterior surface of an object, such as into the interior of a building or beneath a vegetation canopy, in the case of visible light).

Synthetic aperture radar and holography use coherent electromagnetic radiation (e.g., narrow bandwidth radar pulses in the case of SAR and coherent light in the case of holography) to construct an image. Advantageously, because it processes volume-based (rather than planar-based) differential phase information, holography is able to provide for the generation of a three-dimensional image of an object. Still, its use to date has been essentially limited to controlled, volume-constrained static environments, such as an opto-physics laboratory.

There are many terrestrial regions, such as cities, industrial areas, and the like, containing a wide variety of cultural features, such as buildings, bridges, towers, etc., as well as interior components thereof, for which images (including those captured at different times for determining the presence of environmental changes) are desired by a variety of information analysis enterprises. Curiously, many if not most of such terrestrial regions are continuously illuminated by a relatively powerful narrowband radio frequency (RF) transmitter, such as television broadcast towers, creating a condition known as ‘RF daylight’. Because of the partial transparency to such RF emissions (especially at and below VHF and UHF frequencies) of many objects, including both natural vegetation and man-made structures, these RF-daylight signals can be expected to be reflected/scattered off cultural features (including both exterior and interior surfaces) of an illuminated region.

SUMMARY OF THE INVENTION

In accordance with the present invention, advantage is taken of this ‘RF daylight’ phenomenon, to passively acquire RF reflectance or scattering coefficient parameter values of multiple points within a prescribed three-dimensional volume being illuminated by an RF transmitter. As will be described, the passive image generation system of the invention collects and processes RF energy that may be reflected-scattered from multiple points of a three-dimensional space within a region being illuminated by a coherent RF energy source, such as a television transmitter.

Pursuant to a non-limiting embodiment, the system of the invention employs a front end, RF energy collection section that contains a reference signal collector (antenna) which collects non-scattered RF energy emitted by an RF reference source illuminating the potentially cultural feature-containing terrestrial region of interest. A second, dynamic scattered image energy collector mounted on a platform, overflying the illuminated terrestrial region collects RF energy that has been scattered-reflected from various points of cultural features (such as buildings and contents thereof) within a three-dimensional volume of space containing the terrestrial region.

The reference signal collector and the scattered image energy collectors may comprise airborne or spaceborne RF energy collection platforms. Alternatively, reference signal collection and scattered energy collection may involve the use of a common RF energy collector, or respectively separate energy collectors located on the same platform. Also, the image energy collector may be located on an airborne or spaceborne platform and the reference signal collector may comprise a ground-based receiver. The scattered RF image energy collection platforms containing the scattered energy collector(s) are dynamic in plural non-coincident travel paths, to ensure that energy collected from the terrestrial region of interest will be derived by way of multiple offset views of that region, which provides the resulting aperiodic lattice additional power to resolve image ambiguities and enhance the three-dimensional imaging capability of the invention. Once captured by their respective energy receiver sections, the RF reference signal energy and the RF image energy are digitized and stored, so that they may be readily coupled to an image processing section.

The scattered image data processing section assumes that the source of RF energy illuminating the three-dimensional spatial volume of interest is located at some fixed location in space, known a priori. A respective location of a scattered RF energy collector moving along a respective travel path above and past the terrestrial region is defined by a set of collection aperture coordinates. Where the scattered RF energy collector is used to simultaneously collect non-scattered energy emitted from the reference signal source, termed a ‘self-referential’ embodiment, the received signal y(t) produced by the RF energy collector contains the direct path signal from the illumination source to the collector plus time-delayed, Lorentz-transformed RF energy that may be scattered or reflected from the illuminated location and incident upon the collection aperture.

Because the coordinates of the source of the reference signal are spatially displaced from the location of a respective illuminated point, there will be a time delay associated with the reference signal's travel path from the source to the potential scattering location, and also and a time delay associated with the reference signal's travel time from the reference signal source to the RF energy collection aperture. In addition, there is a time delay associated with the travel time of the RF energy scattered from the illuminated location to the scattered image energy collector.

To properly correlate the reference signal emanating from the illuminating source with the RF energy signal received by the moving collector, it is necessary to account for these delays, as well as the time-scaling of the signal received by the energy collector resulting from the fact its platform is moving relative to the illuminated potentially scattering location. To this end, the signal received at the dynamic collector is applied to a first Lorentz transform operator that accounts for signal propagation delay and performs a Lorentz transform of the signal from its moving frame of reference at the collection aperture location to the static frame of reference of the illuminated point in space. The output of this first Lorentz transform operator is then applied to a delay which imparts a delay associated with the reference signal's propagation time from the source to the illuminated location. The combined effect of this first Lorentz transform and delay operation serves to transform the reference signal component of the energy received at the collection aperture to the illuminated location. The transformed signal is coupled as a first input-of a correlation multiplier.

The received signal is further applied to a second Lorentz transform operator which accounts for signal propagation delay and performs a second Lorentz transform of the received signal from its moving frame of reference to the static frame of reference of the illuminated point in space. Because the ‘self referential’ embodiment of the invention provides for the collection of the scattered energy and reference illumination signals by a common energy collector, the received signal at the dynamic collection aperture also contains the reference illumination signal. In order remove this reference signal component from the desired scattered image component, the output of the second Lorentz transform operator is coupled to a reference signal suppression operator, that serves to significantly null out the reference signal component. The resultant reference-nulled signal represents the scattered component of the receive signal as transformed to the illuminated location and is coupled as a second input of the correlation multiplier.

Where the scattered energy signal and the reference signal are collected by separate energy collectors, the signal received by the scattered energy collection aperture will not contain a potentially dominant reference signal component that requires removal, as described above. In this instance, the received signal is applied only to a single Lorentz transform operator the output of which is coupled to the correlation multiplier. Moreover, where a copy of the reference signal is available, no Lorentz transform of the illuminating reference signal is necessary; instead, the reference signal need only be compensated for the signal propagation time delay and coupled to the correlation multiplier.

The correlation multiplier multiplies the reference signal transform component by the scattered signal transform component to produce a product that is integrated over a relatively long integration interval, such as one on the order of several tens of seconds to several tens of minutes, and sufficient to ensure that only scattered energy values associated with RF frequency from the reference source illuminating the scattered location will constructively combine, whereas all others will destructively cancel. This produces a scattering coefficient for the illuminated location that is representative of reference signal energy from the transmission reference signal source as scattered by that location.

The scattering coefficient information is a complex interference pattern (containing both amplitude and phase components) containing all the information necessary to recreate a three-dimensional monochromatic image of the illuminated scene. Namely, the coherent complex correlation provides scene information content that is only a function of scene scattering and collector geometry. Assuming that the scene does not change substantially over the collection period, the synthetic aperture amplitude and phase distribution may be collected and extracted sequentially rather than simultaneously.

The output of the correlation integrator may be coupled to a downstream image utility subsystem, such as a virtual reality simulator, multi-image slice display device, and the like, for generation of the three-dimensional image of the scene, and facilitate stereoscopic viewing of the image. The resolution to which the illuminated scene may be imaged (three-dimensionally) is limited by the Rayleigh wavelength (i.e., one-half the wavelength) of the illuminating reference source.

DETAILED DESCRIPTION

Before describing in detail the new and improved passive image generation scheme of the present invention, it should be observed that the scattered RF collection and processing system of the invention resides primarily in a prescribed arrangement of conventional radio wave collection subsystems and components, and associated digital processing equipment that processes digital data representative of scattered RF energy received by the radio wave collection subsystems, in order to derive pixel/voxel data representative of cultural features of a region illuminated by the RF energy illuminating a particular scene of interest.

Consequently, the configuration of the image generation system of the invention has, for the most part, been illustrated in the drawings by readily understandable block diagrams, which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with details which will be readily apparent to those skilled in the art having the benefit of the description herein. Namely, the diagrammatic illustrations to be described are primarily intended to show the major components of the invention in a convenient functional grouping, whereby the present invention may be more readily understood.

As pointed out briefly above, the passive image generation system of the present invention is operative to collect and process RF energy that may be reflected—scattered from multiple points of some prescribed portion of a three-dimensional space being illuminated by an RF energy source, such as a commercial television transmitter, as a non-limiting example, that is typically situated in proximity to a terrestrial region that can be expected to contain cultural features (e.g., buildings and contents thereof) of which an image is desired. For this purpose, as diagrammatically illustrated inFIG. 1, the image generation system of the invention includes a front end, RF energy collection section10, and a downstream RF energy processing section20.

In the system diagram ofFIG. 1, the RF energy collection section10is shown as containing a first, reference signal collector11, that is operative to collect non-scattered RF energy12emitted by an RF source13, such as a commercial television broadcast tower, that illuminates the potentially cultural feature-containing terrestrial region of interest. The RF energy collection section also includes a second, scattered image energy collector14, that is operative to collect RF energy that has been scattered—reflected from various points of cultural features (such as buildings and contents thereof)15within a three-dimensional volume of space16containing the terrestrial region of interest being illuminated by the source13.

As non-limiting examples, each of the reference signal collector11and the scattered image energy collector14may comprise respective (airborne or spaceborne) RF energy collection platforms, containing their own antenna and receiver subsystems. In an alternative configuration, both the reference signal collector and the scattered or image energy collector may involve the use of a common RF energy collector, or respectively separate energy collectors located on the same platform. As a further variation, the image energy collector14may be located on an airborne or spaceborne platform and the reference signal collector may comprise a ground-based receiver, as shown at17.

Regardless of the energy collection arrangement employed, the one or more scattered RF image energy collection platforms containing the scattered energy collector(s) are dynamic in plural non-coincident travel paths, to ensure that energy collected from the terrestrial region of interest will be derived by way of multiple offset views of that region. That is, as shown inFIG. 2, the scattered RF image energy collector14(which may include more than one image energy collector) is coupled with a platform one which overflies the illuminated region16by way of a plurality of respectively different, non-parallel ‘fly-by’ paths (three of which are shown at31,32and33, as non-limiting examples), so as to provide for the gathering of three-dimensionally scattered RF energy from cultural features in the illuminated region.

Namely, the synthetic aperture realized by the collector geometry is three-dimensional, since the travel path of the collector over the illuminated region of interest effectively follows a curved path and is not likely to be at exactly the same altitude on each pass. This provides the resulting aperiodic lattice additional power to resolve image ambiguities and enhances the three-dimensional imaging capability of the invention.

It may also be noted that the gathering of scattered energy may be carried out by multiple RF energy collection platforms traveling simultaneously or sequentially along different paths, or by a single platform sequentially traveling (and potentially repeatedly) along different paths. Once captured by their respective energy receiver sections, the RF reference signal energy and the RF image energy are digitized and stored, so that they may be readily coupled to the image processing section20.

As non-limiting examples, the coupling the stored RF energy captured and stored on board the dynamic airborne or spaceborne platform to the image processing station may be accomplished directly by providing the image processing section20on the same platform as the energy collector, such as on board an aircraft or spacecraft; it may also be accomplished by landing the platform and transferring the stored data to a terrestrially located image processing section; and it may be communication channel-downlinked (as shown by broken links21and22inFIG. 2) to the image processing station.

FIG. 3diagrammatically illustrates the overall mechanism that is carried out by the image processing section for processing RF energy data that has been collected by the front end section, so as to obtain a set of (spatially orthogonal scattering coefficient values) for the case of an arbitrary, illuminated location (pixel point pi), defined by a respective set of (three-dimensional) Cartesian coordinates (xi, yi, zi) within the volume of space16of the terrestrial region illuminated by the reference source13. In terms of the diagrammatic illustration ofFIG. 1, described above, the source13of RF energy illuminating the three-dimensional spatial volume of region16is denoted as a reference signal source so(t), which is assumed to be located at some fixed location in space, having coordinates (xo, yo, zo), known a priori.

A respective location of a scattered RF energy collector14(as it moves along a respective travel path30above and past the terrestrial region16) is defined by a set of collection aperture (a) coordinates (xa, ya, za), which may be readily provided by precision navigation instrumentation, such as a GPS-based position location subsystem. In the embodiment illustrated by the spatial diagram ofFIG. 3, the scattered RF energy collector14is also used to simultaneously collect non-scattered energy emitted from the reference signal source so(t), so as to provide what is termed as a ‘self-referential’ approach. Namely, a received signal y(t) produced by the RF energy collector14contains the direct path signal so(t) from the source13to the collector14, as well as time-delayed, Lorentz-transformed RF energy that may be scattered or reflected from the illuminated location pi, and incident upon the collection aperture (a) of the collector14.

Advantages of this self-referential embodiment include the ability to use a single energy collection location to acquire all required waveforms, the elimination of errors, such as time transfer, local oscillator offset, processing signals that have propagated through different media, and open loop differential time delay, as well as the use of less complex processing (differential Lorentz transform) and the elimination of the requirement for an absolute illumination signal reference. A disadvantage is the increase in cross-correlation noise, which requires the use of an illumination source signal suppression operator, as will be described.

The signal Y(t) may be represented in equation (1) as:y⁡(t)=⁢(goa/roa)*so(γoa⁡[t-(roa/c)]+⁢∑i⁢(goia⁢σi1/2/roi⁢ria)⁢so⁡(γia⁡[t-(roi+ria)/c])(1)

where the first term corresponds to the direct path signal from the source so(t), and the second, summation term corresponds to the scattered signal from the illuminated location pi. The components of equation (1) may be defined as follows:

c=the speed of light;

t=time as measured in the moving collection aperture (a) frame of the collector14;

goa=the gain power factor for the path from the source13to the aperture of the moving collector14;

goia=gain power factor for the path from the source13to the ith scatterer at illuminated location pito the collection aperture of the collector14;

roa=the distance from the source13to the collection aperture of the collector14;

r0i=the distance from the source13to the ith scatterer;

ria=the distance from the ith scatterer at illuminated location pito the collection aperture of the collector14;

γoa=Lorentz time scaling for the path from the source13to the collection aperture of the collector14;

γia=Lorentz time scaling for the path from the potential scatterer location pito the collection aperture of the collector14; and

σi=the scattering coefficient for the ith scatterer at illuminated location pi.

The Lorentz time scaling γoamay be defined as:
γoa=(1−roa/c)/(1−(roa/c)2)2/2(2).

The Lorentz time scaling γiamay be defined as:
γia=(1−ria/c)/(1−(ria/c)2)1/2(3)

The gain power factor goamay be expressed as:
|goa|2'λ2Gt(âoa)Gr(âoa)/16n2,  (4)

and the gain power factor goiamay be expressed as:
|goia|2=λ2Gt(âoi)Gr(âia)/64n3,  (5)

where

Gt, Grare respective gains of the transmitting antenna of the illuminating source13and the receiver antenna(s) of the collector14,

the values â are path unit vectors, and

λ is the wavelength of the RF signal transmitted by the illuminating source13.

It should be noted that, due to the differential processing mechanism of the invention, the coordinates (x0, y0, z0) used to specify the location of the reference signal source so(t) need not specify the exact location of the transmitter13. As long as the coordinates (xo, yo, zo) are reasonably proximate to the actual location of the reference signal source so(t), the processed result for the illuminated location pi(and all others) will be spatially shifted from the image produced if the coordinates of the source13were known with precision; as a consequence, the generated scene will simply be a spatially shifted image, containing the same resolvable cultural details that would be obtained were the exact location of the phase center of the transmitter's emitted RF signal known a priori.

Because the coordinates (x0, y0, z0) of the source of the reference signal so(t) are spatially displaced from he location (xi, yi, zi) of the illuminated point piof interest, there will be a time delay shown by broken lines τoiassociated with the reference signal's travel path from the source so(t) to the potential scattering location pi, and a time delay shown by broken lines τoaassociated with the reference signal's travel time from the reference signal source so(t) to the RF energy collection aperture at coordinates (xa, ya, za). In addition, broken lines τiarepresent the time delay associated with the travel time of the RF energy scattered from the illuminated location pito the received image signal coordinates (xa, ya, za) of the scattered image energy collector14.

In order to properly correlate the reference source signal so(t) emanating from the source13with the RF energy signal y(t) received by the moving collector14, it is necessary to account for these delays, as well as the time-scaling of the signal received by the energy collector14resulting from the fact its platform is moving relative to the illuminated location pi. These adjustments are shown in the correlation signal processing diagram of FIG.4.

In particular, the received signal y(t) as collected by the collector14at the RF energy collection aperture coordinates (xa, ya, za) is applied to a first processing path that includes a first Lorentz transform operator41. This first Lorentz transform operator accounts for the delay τoaand performs the first Lorentz transform γoaof the signal y(t) from its moving frame of reference at collection aperture location (xa, ya, za) to the static frame of reference of illuminated location pi.

The output of the first Lorentz transform operator41is then applied to a delay43, which imparts a delay τoiassociated with the reference signal's travel time from the source so(t) to the illuminated location pi. The combined effect of this first Lorentz transform and delay operation serves to transform the reference signal component of the-energy received by the collector14to the location pi. The output of delay43is coupled as a first input42of a correlation multiplier44.

The received signal y(t) is further applied to a second processing path that includes a second Lorentz transform operator45, which accounts for the delay τiaand performs a second Lorentz transform γiaof the received signal y(t) from its moving frame of reference at location (xa, ya, za) to the static frame of reference of location pi. Because the ‘self referential’ system ofFIG. 3provides for the collection of both the scattered energy and reference illumination signals by means of a common energy collector14, the received signal y(t) also contains the reference illumination signal so(t) (which can be expected to be a substantial or dominant portion of the received signal).

In order remove this reference signal component so(t) from the desired scattered image component of the received signal y(t), the output of the second Lorentz transform γiaoperator45is coupled to a reference signal suppression or ‘correlation discriminant’ operator47, that serves to significantly null out (e.g., reduce on the order of 30-60 dB or more) the amplitude of the reference signal component. As a non-limiting example, the reference signal suppression operator47may comprise a spectral inversion-based nulling mechanism of the type diagrammatically illustrated in FIG.5.

As shown therein, the received signal y(t) is coupled as an input to a phase locked loop tracking operator51, which produces an output representative of cos(2γoΩot). This frequency shifted signal is then multiplied in a multiplier53by the signal y(t), to produce a spectral inversion of the received signal, that places the desired information signal (containing the scattered information) at a sideband of the illuminating reference. This spectrally inverted version of the received signal is then differentially combined with the received signal y(t) in differential combiner55, which excises or nulls out the spectrally coincident reference component in the two multiplied signals, leaving only the desired scattered energy component. The resultant reference-nulled signal output by the reference signal suppression operator47, which represents the scattered component of the receive signal y(t) as transformed to the illuminated location pi, is coupled as a second input46of the correlation multiplier44.

Where the scattered energy signal and the reference signal are collected by separate energy collectors, the signal y(t) provided by the energy collector14will not contain a potentially dominant reference signal component that requires removal, as described above. In this instance, as shown inFIG. 6, the signal y(t) is applied only to the Lorentz transform operator45, the output of which is coupled to the second input46of multiplier44. Also, where a copy of the reference signal so(t) at illumination source location (xo, yo, zo) is available, no Lorentz transform of the illuminating reference signal is necessary; instead, the reference signal need only be coupled through a delay43to compensate for the travel time delay τoi, with the output of delay43being coupled to the first input42of the multiplier44as described above.

As shown inFIGS. 4 and 6, the multiplier44multiplies the reference signal transform γoabased component at its input42by the scattered signal transform γiabased component at its input46, so as to produce a product that is summed or integrated by a correlation integrator48. The integration period of integrator48is of a relatively long duration (which may be on the order of several tens of seconds to several tens of minutes, as a non-limiting example), that is sufficient to ensure that only scattered energy values associated with RF frequency from the source so(t) illuminating the location piwill constructively combine, whereas all others will destructively cancel, leaving as a valid scattering coefficient information cifor illuminated location pionly that derived from reference signal energy emanating from the transmission reference signal source13.

The scattering coefficient information obtained from the above described correlation processing is a complex interference pattern (containing both amplitude and phase components) containing all the information necessary to recreate a three-dimensional monochromatic image of the illuminated scene. Namely, the coherent complex correlation provides scene information content that is only a function of scene scattering and collector geometry. Assuming that the scene does not change substantially over the collection period (which may involve multiple passes of the image collecting platform(s)), it does not matter that the synthetic aperture amplitude and phase distribution is collected and extracted sequentially rather than simultaneously).

The output of the integrator48may be coupled to a downstream image utility subsystem49, such as but not limited to a virtual reality simulator, multi-image slice display device, and the like, for generation of the three-dimensional image of the scene, and facilitate stereoscopic viewing of the image at any perspective (within scene illumination and collection limits).

The resolution to which the illuminated scene may be imaged is limited by the Rayleigh wavelength (i.e., one-half the wavelength) of the illuminating reference source so(t). As a non-limiting example, for an illuminating frequency on the order of 50 MHz, the image feature resolution may be on the order of ten feet, while for an illuminating frequency on the order of 500 MHz, the image feature resolution may be on the order of one foot.

FIG. 7shows a reduced complexity implementation of the correlation signal processing diagram ofFIG. 4, where the differential Lorentz transform operators are replaced by a Doppler shift mechanism. In this case the Lorentz transform operator41is removed and the Lorentz transform operator45is replaced by a multiplier45M, to which the signal y(t) and the signal ejω(t)are applied, where ω(t)=Lorentz (γoa,−γia)

With respect to sensitivity of the image collection subsystem, it may be noted that the collection bandwidth should be sufficient to encompass the RF illumination source (making maximum use of its power); however, the ultimate bandwidth of the synthetic aperture (hologram) formation process is objectively zero. The correlation operation obtains a Doppler spread of the scene's cultural features as seen by the collector, and is usually much smaller the transmitted signal's bandwidth. As a non-limiting example, the Doppler spread might typically be tens of kHz at UHF, so that nearly 30 dB sensitivity improvement is immediately realized upon correlation when a television transmitter is employed as the illuminating signal source. From a functional standpoint (assuming that other system-level factors do not limit integration time), the total observation time will establish a lower bandwidth, which may be on the order of milli- or even micro-Hz. As a result, processing gain on the order of 90 dB or greater may be achieved, allowing the imaging of relatively weakly illuminated scene features, using practical implementation G/T collector components.

It may also be noted that the correlation process described above allows indefinite reduction of co-channel interference and noise biases, as such waveforms are not coherent with the transmitted signal. In addition, correlation quality improves directly with the number of samples, due to the presence of a high signal to noise plus interference reference signal, even though scattered signals received from scene features may be well below the ambient noise plus co-channel interference level. A practical implication involves imaging scene illumination points that are relatively close to the reference source relatively quickly—using a relatively low G/T collector, while scene elements at the edge of the observed region may require the coherent summation of many passes of the collector.

Because the potential collecting volume of the synthetic aperture is quite immense (e.g., tens or hundreds of miles in effective diameter), even relatively dimly illuminated regions of the scene having high co-channel interference can be imaged. The rate at which the synthetic aperture can be filled with scattered image data is proportional to the collector's G/T, which implies a trade-off between collector G/T versus the time required to form a given quality image.

As will be appreciated from the foregoing description, the passive imaging system of the present invention takes advantage of RF daylight created by commonplace RF illumination sources, such as a television broadcast tower, to passively acquire 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 and containing all the information necessary to recreate a three-dimensional monochromatic image of the illuminated scene. Thus, the 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, multi-image slice display device, and the like, for generation of the three-dimensional image of the scene, and facilitate stereoscopic viewing of the image.