Abstract:
The hyperspectral detector systems and methods disclosed herein include capturing a context image and a single-column spectral image that falls within the context image. The context and spectral images are then combined to form a fused image. Using the fused image, the spectral image is panned over the scene and within the context image to capture spectral signatures within the scene. The spectral signatures are compared to reference spectral signatures, and the locations of the one or more spectral signatures within the context image are marked. The systems and methods obviate the need to store and process large amounts of spectral data and allow for real-time display of the fused context image and spectral image, along with the marked locations of matched spectral signatures.

Description:
This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/881,671 filed on Sep. 24, 2013 the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to hyperspectral imaging, and in particular relates to hyperspectral detector systems and methods that use context-image fusion. 
     The entire disclosure of any publication or patent document mentioned herein is incorporated by reference. 
     BACKGROUND 
     Hyperspectral imaging involves imaging multiple (e.g., dozens or hundreds of) narrow spectral bands over a spectral range to produce a composite image wherein each pixel in the scene being captured includes contiguous spectral data of the scene. An aspect of hyperspectral imaging combines a conventional two-dimensional (2D) spatial image with a third dimension of contiguous spectral bands, essentially performing spectrometry on each individual pixel of the 2D spatial image. 
     Conventional hyperspectral imaging involves generating a hyper-cube of data for the scene being imaged. A hyper-cube is in essence a three-dimensional (3D) image, where two of the dimensions are spatial and one dimension is contiguous spectral data. Depending on the device used to generate the data, the acquisition time for a single hyper-cube image from most hyperspectral systems can be on the order of tens of seconds before useful context-sensitive information can be extracted. 
     Due to the 3D nature of the data, hyper-cubes can be quite large, with their size depending on the spatial and spectral resolution of the image. While this amount of data collection is necessary for many hyperspectral applications, it is not necessary for all of them. In spectral detection applications, more often than not, the vast majority of the data collected is not needed. 
     One type of hyperspectral imaging system looks for specific pre-determined spectral signatures in a given area and is called a hyperspectral detector or HSD. In essence, HSDs are “Go/No-Go” sensors that verify the presence or absence of the particular spectral signatures that cannot be readily detected by visual methods or other means. It is often preferred that the information from the HSD be available in real-time so that users can take action in real-time rather than having to wait for the computation to be completed. Furthermore, for mobile or hand-held HSDs, computing power of the HSD may be limited. 
     SUMMARY 
     An aspect of the disclosure is a method of performing hyperspectral detection of a scene. The method includes: capturing a digital context image of at least a portion of the scene over a field of regard; capturing a spectral image of the scene over an instantaneous field of view that falls within the field of regard, and wherein the instantaneous field of view is less than half of the field of regard; fusing the context image and the spectral image to form a fused image; panning the spectral image over the scene and within the field of regard to capture one or more spectral signatures within the scene; and comparing the one or more spectral signatures to one or more reference spectral signatures and marking one or more locations of the one or more spectral signatures within the context image. 
     Another aspect of the disclosure is a method of performing hyperspectral detection of a scene. The method includes capturing a digital context image of at least a portion of the scene over a field of regard; capturing a spectral image of the scene over an instantaneous field of view with a single column of pixels of a first sensor, wherein the instantaneous field of view falls within the field of regard; fusing the context image and the spectral image to form a fused image; panning the spectral image over the scene to capture one or more spectral signatures within the scene; comparing the one or more spectral signatures to one or more reference spectral signatures and marking one or more locations of the one or more spectral signatures within the context image; and displaying on a display in real-time the fused image and the one or more marked locations. 
     Another aspect of the disclosure is a hyperspectral detection system for spectrally analyzing a scene. The system includes a context camera operably arranged to capture a digital context image of at least a portion of the scene over a field of regard. The system also includes an imaging spectrometer operably arranged to capture a spectral image of the scene over an instantaneous field of view that falls within the field of regard and that is less than half of the field of regard. The system also includes means for panning the spectral image over the scene and within the field of regard to capture one or more spectral signatures within the scene. The system further includes a processor that receives and fuses the context image and the spectral image to form a fused image. The processor is configured to compare the one or more spectral signatures to one or more reference spectral signatures and to mark one or more locations of the one or more spectral signatures within the context image. 
     Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which: 
         FIG. 1  is a schematic diagram of an example hyperspectral detection system according to the disclosure; 
         FIG. 2  is a front-on view of an example scene to be analyzed by the hyperspectral detector system of  FIG. 1 ; 
         FIG. 3A  is a front-on view of an example hyperspectral detection system that shows the context camera and the imaging spectrometer supported by a support member; 
         FIG. 3B  shows the example hyperspectral detection system supported by a support device shown as a tripod by way of example; 
         FIGS. 4A through 4C  are similar to  FIG. 1  and show an example of how the hyperspectral detector system disclosed herein can be used to analyze the scene of  FIG. 2 ; 
         FIGS. 5A through 5C  correspond to  FIGS. 4A through 4C , respectively, and show the scene of  FIG. 2  as viewed by the hyperspectral detection system as the scene is panned; 
         FIG. 6  illustrates an example embodiment of the hyperspectral detection system wherein the imaging lenses for the context camera and the imaging spectrometer are replaced with a single lens; 
         FIGS. 7A through 7C  are side, front and back views of an example hand-held hyperspectral detection system; 
         FIGS. 8A and 8B  are front-elevated and back-elevated views, respectively, of an example handheld hyperspectral detection system that employs a smart phone; and 
         FIG. 9  is a close-up view of an example context camera that includes a spectrally dispersive element that allows the context camera to also serve as the imaging spectrometer. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure. 
     The claims as set forth below are incorporated into and constitute part of this Detailed Description. 
     The entire disclosure of any publication or patent document mentioned herein is incorporated by reference. 
     Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation. 
       FIG. 1  is a schematic diagram of an example hyperspectral detection (HSD) system  10  according to the disclosure. The HSD system  10  is shown arranged relative to a scene  12  to be spectrally analyzed, which is discussed in greater detail below. Cartesian coordinates are shown for the sake of reference.  FIG. 2  is a front-on view of an example scene  12 , i.e., looking in the z-direction. 
     The HSD system  10  includes a context camera  20  that includes a housing  22  that operably supports a context-camera lens  24  and an image sensor  26 . In an example, context camera  20  is a conventional visible-wavelength digital camera, while in another example the context camera is an infrared (IR)-wavelength camera or a combination of a visible (VIS) and near-IR (NIR) camera (e.g., VIS and/or near-IR (NIR) and/or short-wavelength IR (SWIR) and/or mid-wavelength IR (MWIR) and/or long-wavelength IR (LWIR)). In an example, lens  24  has zoom capability. In an example embodiment, context camera  20  is image-stabilized using one or more image-stabilization techniques known in the art. Also in an example embodiment, lens  24  includes autofocusing capability using one or more autofocusing techniques known in the art. 
     In an example, image sensor  26  comprises an array of pixels  27  (see corresponding close-up inset) wherein the pixel array has a size of equal to or greater than 1,280×1,024 pixels. In an example, pixels  27  have a width W 27  in the range from 3 μm to 5 μm. In an example, context camera  20  is a cell-phone camera, a tablet camera or a smartphone camera. 
     The context camera  20  has a field of view that is referred to herein as a “field of regard” FoR. The context camera  20  captures a digital context image of a portion of scene  12  over the field of regard FoR and generates in response a digital context-image signal SC. The digital context image is a generally recognizable 2D spatial image that provides spatial (visual) context of at least a portion of scene  12 . 
     The HSD system  10  also includes an imaging spectrometer  40  that in an example includes a housing  42  that operably supports an imaging lens  44  and an image sensor  46  having pixels  47  (see corresponding close-up inset). In an example, pixels  47  have a width W 47  in the range from 10 μm to 25 μm (e.g., from about 2× to about 8× the size of pixels  27 ). In an example, sensor  46  has multiple rows and columns of pixels  27  that allows for spectral imaging over a portion (i.e., a sub-region) of the digital context image. In an example, imaging lens  44  has zoom capability. In an example, imaging spectrometer  40  is dispersion-based. In an example, sensor  46  is capable of analyzing 512 spatial pixels 47×80 spectral pixels, with a size of 15 microns/pixel, and a spectral range of 0.9 μm to 1.7 μm at 10 nm (spectral)/pixel. In an example embodiment, imaging spectrometer  40  is compact, e.g., has a volume of less than about 12 cubic inches, to facilitate portability of HSD system  10 . In an example embodiment, imaging spectrometer  40  is image-stabilized using one or more image-stabilization techniques known in the art. Also in an example embodiment, lens  44  includes autofocusing capability using one or more autofocusing techniques known in the art. 
     The imaging spectrometer  40  has an instantaneous field of view iFoV that is substantially narrower than a field of regard FoR of context camera  20 .  FIG. 1  shows a width W S  of the spectrometer instantaneous field of view iFOV in scene  12 , along with the corresponding width W′ S  of the corresponding spectrometer (spectral) image formed at image sensor  46 .  FIG. 1  also shows a width W R  of the field of regard FoR in scene  12 , as well as the corresponding width W′ R  of the corresponding context-camera image formed at image sensor  26 . The widths W S  and W′ S  are related by the magnification M 44  of imaging lens  44 , i.e., W′ S =M 44 ·W S . Likewise, the widths W R  and W′ R  are related by the magnification M 24  of imaging lens  24 , i.e., W′ R =M 24 ·W R . In the case where M 44 =M 24 , it follows that W′ S /W′ R =W S /W R . 
     The imaging spectrometer  40  captures a digital spectral image of a narrow portion of scene  12  over the instantaneous field of view iFoV and generates in response a digital spectral-image signal SS that includes one spatial dimension (e.g., a column of pixels) and one spectral dimension (i.e., the spectral data for each pixel in the column of pixels). In example embodiments, imaging spectrometer  40  operates over one or more of the visible and IR wavelengths, e.g., one or more of VIS, NIR, SWIR, MWIR and LWIR. 
     The instantaneous field of view iFoV is substantially narrower than field of regard FoR. In an example, the instantaneous field of view iFoV is less than half of the field of regard FoR. The width W′ S  of the spectral image is define by the number N C47  of columns of pixels  47  multiplied by the width W 47  of a single pixel  47  of sensor  46 , i.e., W′ S =(N C47 )·(W 47 ). The minimum width of W′ S  is when N C47 =1, i.e., W′ S =W 47 . Likewise, the width W′ R  of the context image is defined by the number N C27  of columns of pixels  27  multiplied by the width W 27  of a single pixel  27  of sensor  26 , i.e., W′ R =(N C27 )·(W 27 ). Note that the minimum value of the ratio W′ S /W′ R  (and thus the minimum value of W S /W R ) is W 47 /W R . 
     In various examples, W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.5 or W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.25 or W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.15 or W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.10 or W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.5 or W 47 /W R ≦[W′ S /W′ R ]&lt;0.1 or W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.05 or W 47 /W′ R ≦[W′ S /W′ R ]&lt;0.1. In an example embodiment, instantaneous field of view iFoV is defined by a single column of pixels  47  of image sensor  46 , so that W′ S /W′ R =W 47 /W′ R . In other example embodiments, instantaneous field of view iFoV is defined by a portion of the available row and column pixels  47  of image sensor  46 . 
       FIG. 3A  is a front-on view of an example configuration of HSD system  10  wherein context camera  20  and imaging spectrometer  40  are operably supported by a support member  50  so that each can rotate about respective axes A1 and A2 shown oriented in the y-direction. Also in an example, support member  50  is rotatable about an axis A3 oriented in the same direction as axes A1 and A2. In an example, support member  50  is attached to or includes a post  52  to facilitate rotation about axis A3. In an example, post  52  is sized and otherwise configured to be hand-held (e.g., to have a hand grip) so that that HSD system  10  can be hand-held by a user (see  FIGS. 7A through 7C , introduced and discussed below). Thus, in an example, post  52  defines a handle. 
     In another example illustrated in  FIG. 3B , post  52  is used to mount HSD system  10  to a support device  54 , such as a gimbaled device or a tripod (as shown). In an example, post  52  includes a switch  53  that can be used to activate HSD system  10 , e.g., to capture a context image  100  and/or a spectral image  110  (see  FIG. 5A ), to provide input to a computer, etc. 
     The support device  54  serves to facilitate the relative alignment of context camera  20  and imaging spectrometer  40  so that select pixels of context-camera image sensor  26  are co-located with pixels  47  of imaging-spectrometer sensor  46 . 
     With reference again to  FIG. 1 , HSD system  10  also includes a computer  60  operably connected to context camera  20  and imaging spectrometer  40 . The computer  60  is configured to receive context-image signals SC and spectral-image signals SS and to process these signals (and, when needed, to fuse spectral image  110  with context image  100 ) to perform context-based hyperspectral detection, as described in greater detail below. The HSD system  10  also includes a display  70  operably connected to computer  60 . The display  70  can be used to display context image  100 , spectral image  110  or both images to together when viewing at least a portion of scene  12 , as discussed below. In an example, display  70  has touch-screen capability that can be used to control computer  60 . 
     The computer  60  includes a processor  62  and a memory unit (“memory”)  64 . In an example, memory  64  includes stored spectral data (reference spectral data) to which the measured spectra can be compared. 
     The computer  60  is configured to execute instructions stored in firmware and/or software to process spectral-image signals SS and context-image signals SC. The computer  60  is programmable to perform the functions described herein, including the operation of HSD system  10  and the aforementioned signal processing of spectral-image signals SS and context-image signals SC. As used herein, the term “computer” is not limited to just those integrated circuits referred to in the art as computers but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application-specific integrated circuits and other programmable circuits, and these terms are used interchangeably herein. 
     Software in the form of instructions embodied in a computer-readable medium may implement or aid in the performance of the operations of HSD system  10  disclosed herein, including the aforementioned signal processing. The software may be operably installed in computer  60  and in particular in processor  62  and memory  64 . Software functionalities may involve programming, including executable code, and such functionalities may be used to implement the methods disclosed herein. Such software code is executable by the general-purpose computer, e.g., by processor  62 . 
     In an example, the software causes processor  62  to fuse or otherwise combine a 2D context image  100  with a 1D spectral image  110 . In particular, the pixels of context-camera image sensor  26  and imaging-spectrometer sensor  46  can be given respective grid coordinates that the software can use to process context image  100  and spectral image  110 . For example, the pixels of context-camera image sensor  26  can be given grid coordinates C1H through C1280H by (x) C1V through C1,024V, and the imaging-spectrometer sensor  46  can be given coordinates S1V through S512V (where V=vertical, H=horizontal). The imaging spectrometer  40  and context camera  20  are aligned so that the context-camera image-sensor pixels C1V×C640H and C2V×C640H are co-located with spectrometer pixel row S1V, and C1023V×C640H and C1024V×C640H are co-located with spectrometer pixel row S512V. 
     In operation, the code and possibly the associated data records are stored within a general-purpose computer platform within processor  62  and/or in memory  64 . At other times, however, the software may be stored at other locations and/or transported for loading into the appropriate general-purpose computer systems. Hence, the embodiments discussed herein can involve one or more software products in the form of one or more modules of code carried by at least one machine-readable medium. Execution of such code by processor  62  of computer  60  enables the platform to implement the catalog and/or software downloading functions in essentially the manner performed in the embodiments discussed and illustrated herein. 
     The computer  60  and/or processor  62  may each employ a computer-readable medium or machine-readable medium (e.g., memory  64 ), which refers to any medium that participates in providing instructions to the processor for execution, including, for example, determining the spectral content of select items in scene  12 , as discussed in greater detail below. The memory  64  constitutes a computer-readable medium. Such a medium may take many forms, including but not limited to non-volatile media, volatile media and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as any of the storage devices in any computer(s) operating as one of the server platforms discussed above. Volatile media include dynamic memory, such as the main memory of such a computer platform. Physical transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise a bus within a computer system. 
     In an example, computer  60  includes input means (e.g., the aforementioned touch-screen capability for display  70 ) such as a keyboard, buttons, etc. (see buttons  210 ,  FIG. 7C , which is introduced and discussed below) that allow a user to provide input to the computer. Example inputs to HSD system  10  via computer  60  include software control settings such as image acquisition speed or shutter speed, selection of spectral data stored in memory  64  (e.g., selection from a spectral library), on/off selection for recording a context image and/or a spectral image, and on/off selection for illumination (not shown). 
     In an example embodiment, HSD system  10  includes a power supply  80 , such as a battery pack, so that the HSD system can be portable. 
     Examples of how spectral-image signals SS and context-image signals SC are processed are described in greater detail below. The HSD system  10  is operable to capture still images as well as video images. 
     The HSD system  10  can have other components that are not shown that provide additional functionality and information, such as GPS coordinates, geographic-information-system (GIS) data, compass heading, inclinometer heading, etc. As noted above, these devices/functions may also reside in computer  60  or other parts of HSD system  10 . 
     In an example, computer  60  is contained in context camera  20 , e.g., as processor  62  and memory  64  therein. For example, in the case where context camera  20  comprises a smartphone camera or a tablet camera, computer  60  can include the smartphone computing elements and the functionality of these devices, such as those mentioned immediately above (see  FIG. 9 , introduced and discussed below). 
     In conventional HSD systems, the spectral image data is captured by a stationary sensor platform that systematically step-scans a small instantaneous field of view (iFoV) (e.g., a single column of pixels) over the much wider field of regard (FoR). The duration of the scan can be from one to tens of seconds, depending on the particular application, the conditions, and the nature of the scene being analyzed. The spectrometer sensor and the scene must remain stationary and undisturbed relative to each other for the duration of the scan to capture coherent, accurate spatial context information, which is usually not available until the scan is complete. 
     The HSD system  10  operates in a simpler and more efficient manner. Rather than collecting all the spectral data for each pixel  47  of imaging-spectrometer sensor  46  for scene  12 , spectral data is collected for only a small region of the scene, e.g., a single column of pixels  47  or a small number of columns of pixels  47 , wherein, in an example, the number of pixel columns is defined by the user. The spectral data for the small region of scene  12  is then displayed as a spectral image  110  in real-time along with context image  100 , i.e., the spectral image is fused with the context image and displayed on display  70 . 
       FIGS. 4A through 4C  are similar to  FIG. 1  and show an example of how HSD system  10  can be used to analyze scene  12 .  FIG. 4A  shows context-camera field of regard FoR being directed to the “+x” end of scene  12 . In this position, context camera  20  captures a context image of an end portion of scene  12 . The imaging spectrometer is arranged (e.g., rotated) so that its instantaneous field of view iFoV is roughly in the center of field of regard FoR at the location of scene  12 . Other positions of instantaneous field of view iFoV are possible, and a center position is shown as one convenient example position. 
       FIGS. 4B and 4C  show context camera  20  and imaging spectrometer  40  being scanned together over scene  12 , with  FIG. 4B  showing the center of the scene being analyzed, and  FIG. 4C  showing the “−x” end of the scene being analyzed. Note that by scanning context camera  20  and imaging spectrometer  40  together, instantaneous field of view iFoV maintains its position within field of regard FoR. However, context camera  20  and imaging spectrometer  40  need not be scanned together in this manner. In an example, the relative position of instantaneous field of view iFoV can change within field of regard FoR, e.g., by moving (rotating) imaging spectrometer  40  at a different rate than context camera  20 . In another example, context camera  20  can be fixed and imaging spectrometer  40  moved (e.g., rotated) to scan over some or all of field of regard FoR. 
     In examples, the scanning of scene  12  by context camera  20  and imaging spectrometer  40  can be performed manually or automatically, e.g., under the control of computer  60 . Because context camera  20  is used, it is not necessary to wait for imaging spectrometer  40  to complete an entire scan of field of regard FoR before presenting useable data (spectral recognition fused with spatial context) to the user, e.g., via display  70 . Because the feedback is in real-time (e.g., &gt;15 frames/second), the user has the ability to position instantaneous field of view iFoV anywhere within field of regard FoR, and can also change the position of the field of regard relative to scene  12 . The user can start and stop anywhere in scene  12  and can instantly reposition anywhere within the scene, including looking into “blind-spots” or otherwise inaccessible areas. 
       FIGS. 5A through 5C  correspond to  FIGS. 4A through 4C , respectively, and show scene  12  as viewed by HSD system  10 .  FIGS. 5A through 5C  each includes a context-camera image  100  defined by field of regard FoR and the corresponding spectral image  110  in the form of a vertical stripe superimposed with the corresponding context-camera image. The spectral image  110  is stippled for clarity and represents the hyperspectrally sensitive portion of scene  12 . The combination of context image  100  and spectral image  110  defines a fused image  114 . 
       FIG. 5A  shows fused image  114  at the +x side of scene  12 . This represents the initial position of HSD system  10  for scanning and analyzing scene  12 .  FIG. 5A  also shows the width W′ R  of context image  100  and the width W′ S  of spectral image  110 . Note how in  FIG. 5A  context image  100  covers only an end portion of scene  12 , and how spectral image  110  only covers a portion of context image  100  at the left edge of the scene. 
     In an example of the operation of HSD system  10 , the system is powered up and initialized. This can include initializing context camera  20 , including initiating automated adjustment of the focus and light intensity levels. The initialization process can also include initializing imaging spectrometer  40 , including initiating the automated adjustment of focus and light intensity levels and performing a spectral calibration. 
     Once the initialization is completed, the user can direct HSD system  10  toward a select portion (e.g., a target area) of scene  12 . The user can then position spectral image  110  within context image  100 , i.e., within field of regard FoR, to define the configuration of fused image  114 . As noted above,  FIG. 5A  represents an example initial position of context image  100  and spectral image  110  for fused image  114  relative to scene  12 . 
     At this point, the user activates imaging spectrometer  40  (e.g., via switch  53 ) and moves context camera  20  and the imaging spectrometer (e.g., in synchrony) to pan scene  12  to identify spectral signatures of interest, e.g., by comparing detected spectra to reference spectra stored in memory  64 . The movement (scanning) of fused image  114  is indicated by arrows AR1 and AR2 that show the movement of context image  100  and spectral image  110 . 
       FIG. 5B  shows context image  100  and spectral image  110  after having scanned over the left-half of scene  12  so that the context image and the spectral image are about centered in the scene. A tag  120  has been placed on a lamp  13 , which contains an incandescent bulb (not shown) that burns hot and thus has a strong spectral signal over the IR spectrum that matches a stored spectral signature in the spectral library maintained in memory  64 . The tag  120  serves to mark the position of the spectral signature within context image  100 . 
     If a spectral signature of interest (i.e., a spectral match) is found during the scanning of fused image  114 , then the corresponding area of context image  100  is identified as a region of interest RoI, as shown as a dotted-line box in  FIG. 5B . For example, the corresponding context-image pixels  27  are highlighted and the spatial, color and intensity geometry of the surrounding context-image pixels are highlighted e.g., to define region of interest RoI on context-camera display  70 . The region of interest RoI can be tracked while it remains within field of regard FoR. 
     As context camera  20  and imaging spectrometer  40  continue to move and scan fused image  114  over scene  12 , tag  120  remains in place. Moreover, context image  100  is updated with new tags to mark new spectral matches as they are identified.  FIG. 5C  shows fused image  114  at the right side of scene  12  after having scanned the scene. Two new spectral signatures associated with a tea cup  14  and a teapot  16  are each identified and marked with respective tags  120 . Note that the two new tags  120  are black diamonds, which represent a different spectral signature than the star tag  120  that identifies the spectral signature associated with lamp  13 . 
     In an example embodiment, spectral matches are continuously tracked and the associated pixels  27  of context image  100  highlighted while they remain within field of regard FoR. For example, a spectral-match tag  120  at lamp  13  can be used to indicate a spectrally matching fingerprint on the lamp. 
     The result of the scan of scene  12  as performed by HSD system  10  is spectral identification information (and optionally geometry-tracking information) about the scene. The information can be embodied in one or more still images or in a video image. 
     At this point, the user can display a still version or video version of fused image  114  complete with spectral tags  120  and optionally with geometry tags  122 . The user also can relocate within scene  12  from a different perspective, angle or distance, can return to earlier scanned portions of the scene to rescan and/or can relocate to another scene within field of regard FoR. 
     The type of scanning performed by HSD system  10  is not the same as, and nor should it be confused with, the so-called “push-broom” hyperspectral imaging method. The push-broom method generates a continuous 2D spatial×1D spectral hyper-cube of the scene line by line (similar to a strip-chart) by scanning in one direction across the scene. While the scanning method disclosed herein requires moving context camera  20  and imaging spectrometer  40  relative to scene  12  to spatially and contextually locate a spectrally matching region within the scene, it is not necessary to move across the entire scene, nor in any pre-determined fashion, to acquire and display contextually useful data to the user. 
     As noted above, conventional hyperspectral imaging performs spectral analysis on each and every pixel of the imaging spectrometer within a given 2D image. A 3D hyper-cube of data is generated for each image, with two spatial dimensions and one spectral dimension. As an example of conventional hyperspectral imaging, for a moderate-resolution image, there could be 640×480 spatial increments (pixels) and 100 spectral increments (bands), for a total of 30,720,000 data points. After capture and storage of that data cube (approximately 20 seconds @ 30 camera frames/second), contextual analysis of the scene by the user can begin. 
     The HSD system  10  and associated methods disclosed herein obviate the need for generating the second (horizontal) spatial dimension to access contextually usable data. Using the above hyper-cube resolution as a baseline, the elimination of the generation of the second spatial dimension has at least the following advantages. First, it reduces the number of data points required for contextual analysis from 30,720,000 to 48,000, which is a 640× improvement. Second, it reduces the time required for the user to gain access to contextually useful information from &gt;20 seconds to &lt;0.03 seconds, which represents a 600× improvement. Third, it reduces the complexity and increases the compactness of HSD system  10 , to the point where the HSD system can be hand-held. 
       FIG. 6  illustrates an example embodiment of HSD system  10  wherein imaging lenses  24  and  44  for context camera  20  and imaging spectrometer  40 , respectively, are replaced with a single lens  144  that is used for both the context camera and the imaging spectrometer. This allows for context image  100  and spectral image  110  to be captured using a common (i.e., the same) lens. In the example shown, a dichroic mirror  146  and a regular mirror  148  are employed to direct light from scene  12  to imaging spectrometer  40 . In another example embodiment, additional optical components  149  in the form of lenses, one or more aperture stops, etc., are positioned between lens  144  and either context camera  20  or imaging spectrometer  40  (as shown, by way of example) to correct for imaging at the different wavelengths and to otherwise define the imaging optics for the context camera or the imaging spectrometer. The embodiment of  FIG. 6  allows for a single light-collection optical system in the form of lens  144 , which simplifies HSD system  10 . In an example, lens  144  has zoom capability. In an example, lens  144  is image-stabilized using one or more image-stabilization techniques known in the art. Also in an example embodiment, lens  144  includes autofocusing capability using one or more autofocusing techniques known in the art. 
       FIG. 6  also illustrates an example embodiment of HSD system  10  that includes an illumination source  160  for illuminating at least a portion of scene  12  with illumination light  162 . The light  162  may be selected to have wavelengths specifically intended for use by imaging spectrometer  40  or by context camera  20 , or both. 
     If active illumination by illumination source  160  is necessary or desirable, only the narrow region being spectrally scanned needs to be stably illuminated, and only for the duration of a camera frame. The entire scene  12  need not be illuminated for the entire scan of the scene. This results in a significant gain in illumination intensity (based on area reduction and/or pulse duration) for the same illumination source, resulting in a corresponding increase in the signal-to-noise ratio and system sensitivity. 
     The HSD systems and methods disclosed herein have a number of advantages over prior art HSD systems and methods. Because of the simplified data collection and processing, the HSD system can be portable and can be configured as a hand-held device. Further, the system user has the flexibility to rapidly and easily scan any portion or sub-portion of a scene that they want to analyze at their discretion, in real-time. Because of the context feedback provided by context image  100 , the user has the ability to make immediate adjustments to the spatial scan parameters on-the-fly during a scan. 
     By eliminating the need to generate a complete spectral scan for every pixel in the 2D context image  100 , by spectrally scanning only a very narrow portion of the 2D context image and by seeking only a good spectral match to stored spectral signature(s), the acquisition speed, analysis, and presentation of context-sensitive information occurs in real-time (&gt;15 frames per second). 
     Because context image  100  provides the spatial context information of scene  12  being analyzed, it is not necessary to have equally high spatial resolution for spectral image  110 . This allows for larger pixels to be used for sensor  46  of imaging spectrometer  40 , with a corresponding improvement in the signal-to-noise ratio and decrease in hardware costs, thereby making HSD system  10  more sensitive in the spectral domain and more cost effective. 
       FIGS. 7A through 7C  show a side view, a front-on view and a back view, respectively, of an example hand-held HSD system  10 . The hand-held HSD system  10  includes a housing  200  having a front end  202 , a back end  204 , and a handle  52  attached to the housing. The housing  200  includes an interior  206  configured to contain the main elements of HSD system  10  as described above. The context camera  20  and imaging spectrometer  40  optically communicate through housing front end  202 . In addition, optional illumination source  160  also communicates through housing front end  202 . The housing back end  204  includes display  70  as well as various buttons  210  that provide input to HSD system  10 , turn the system on and off, direct/rotate context camera  20  and imaging spectrometer  40 , etc. The handle  52  allows a user to hold HSD system  10  and point it at scene  12  while conveniently viewing fused image  114  on display  70 . 
       FIGS. 8A and 8B  are front-elevated and rear-elevated views, respectively, of another example hand-held HSD system  10 . The hand-held HSD system  10  utilizes a smart phone  250  whose digital camera serves as context camera  20  and whose display serves as display  70 . The smart phone  250  is supported by support member  50 , which is attached to the back end of imaging spectrometer  40  supported by handle  52 .  FIGS. 8A and 8B  show a context-camera optical axis AC and an imaging-spectrometer optical axis AS. In an example, computing components (not shown) of smart phone  250  are used as computer  60 . 
       FIG. 9  is a close-up view of context camera  20  illustrating an embodiment wherein context-camera image sensor  26 , which is made up of pixels  27 , can also collect spectral data, thereby eliminating the need for a separate imaging spectrometer. In the embodiment of  FIG. 9 , context camera  20  includes a spectrally dispersive element  270  adjacent to image sensor  26 . The spectrally dispersive element  270  serves to disperse light  280  from scene  12  over a range of pixels  27 S and is used to define the spectral data, while the remaining pixels  27 C are used for context camera  20  in the usual fashion. The context-camera image  100  will be missing context data from those pixels  27 S used to capture spectral data. Thus, in the embodiment of  FIG. 9 , context camera  20  includes a built-in imaging spectrometer  40 . 
     It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations, provided they come within the scope of the appended claims and the equivalents thereto.