Abstract:
An imaging device is provided which may include a plurality of imaging lenses. Each imaging lens may be placed adjacent to a dispersive element. The imaging lenses and dispersive element(s) may be placed adjacent to a focal plane array to allow light from a light emitting event traveling through the imaging lenses to be simultaneously received by the focal plane array. One of the optical channels provides continuous broadband imagery without interfering with the operation of the dispersive optical channels. No moving parts are required in this small compact system, and no reconfiguration during operation is necessary to enable any of the functions, they are all simultaneous. Information related to the light received by the focal plane array may be transmitted to a processor for processing to determine whether the light emitting event is of interest and to determine an event type. Broadband imagery provided may be used for situational awareness, targeting, and surveillance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to imaging devices, and more particularly to devices for detecting and identifying light emitting events. 
     Prior art imaging devices may comprise a rotating spectral separation element or subassembly installed in the collimated space of an imaging lens that is focused on a focal plane array and then may use spectro-tomographic image processing techniques to extract hyperspectral image data. Prior art imaging devices also may comprise a spectral separation element or subassembly placed in front of the imaging lens of a single channel imaging system comprised of an imaging lens focused on a focal plane array. The prior art imaging devices may receive light from a light-emitting event occurring within a scene. The emitted light travels through the spectral separation element or subassembly while the spectral separation element or subassembly is either in a fixed position or is rotating and is then received by the focal plane array. The focal plane array transmits information related to the received light to a processor. Thereafter, if the spectral separation element or subassembly is rotated to a second angular position, and the emitted light travels through the spectral separation element or subassembly and is received by the focal plane array, the focal plane array then transmits this information related to the received light to the processor and spectro-tomographic image proceesing is used to extract spatially organized spectral information. This process of spectral separation, reception and transmission is continued until the light-emitting event may be identified by the processor based on the transmitted information. 
     There are several shortcomings to the prior art. While the systems described are collecting this spectral information, they cannot collect broadband image information. Another problem is that in order to locate the source of a light-emitting event within the sensors&#39; field of view in the case where the spectral separation element or subassembly rotates, the spectral separation element or subassembly must rotate enough to generate an arc in the light spectrum received by the focal plane array that is collected over several frames of the focal plane array in order to locate the position of the light-emitting event. This process takes-time-and requires that several frames of focal plane array imagery be processed. In order to perform this location function on short time events, the spectral separation element or subassembly must rotate at high rates, the focal plane array must operate at high frame rates that is transmitted to the processor at high rates that drives the required capability of the processor to a higher level. Another problem associated with the prior art imaging devices is that the prior art imaging devices must be stable for proper operation. 
     Accordingly, there is a need in the art for an improved imaging device. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides for an improved imaging device. In particular, the device may comprise of one or more dispersive elements, a plurality of imaging lens, focal plane array, processor and an output. These components in combination with each other provides for multiple frames of the light-emitting event simultaneously on the focal plane array. 
     The device may have at least one dispersive element or have a respective number of dispersive elements as there are imaging lenses. The dispersive elements may be placed adjacent to the imaging lenses. The imaging lenses may be placed adjacently to the focal plane array. The focal plane array may comprise a plurality of detectors which define a respective number of sets of detectors as there are imaging lenses. For example, if there are a first imaging lens, a second imaging lens and a third imaging lens, then light which travels through these lenses may be received by respective first set of detectors, second set of detectors and third set of detectors, all of which are elements of one focal plane array. 
     The dispersive elements split the light into a plurality of wavelength bands. These split wavelength bands provide a spectral profile of the light emitting event. Each dispersive element may split the light differently in that the first, second and third imaging lens may split the light into less number of wavelength bands compared to each successive dispersive element. Once the dispersive elements split the light into the plurality of wavelength bands, the imaging lenses focus the split light onto the focal plane array. Hence, the focal plane array may receive different spectral profiles of the light emitting event at different resolutions. 
     In use, the light travels through all the imaging lenses simultaneously. The light also travels through the first, second and third imaging lenses and may be respectively received by the first, second and third sets of detectors. The detectors transmit information regarding the light traveling through each respective first, second and third imaging lenses to a processor for processing. The processor then communicates the processed information to the output to indicate to a user whether the light emitting event is of interest. If the light emitting event is of interest then the output may also indicate the type of event. 
     In an aspect of the present invention, the focal plane array may receive the light passing through the plurality of imaging lenses, as discussed above. The information may be transmitted to the processor for processing. The processor may correlate the information received and transmitted by each set of detectors because the dispersive element, imaging lens and focal plane array are in a fixed relationship to each other. In other words, the light traveling through the first, second and third imaging lenses may always be received by respective first, second and third sets of detectors. Once the information is correlated, then the processor may build the spectral profile of the event and may compare such spectral profile with known spectral profiles of events of interest. 
     One lens may be used to collect broadband imagery just as a normal video camera would, adding additional functionality to the system. This broadband imaging channel is used to locate the source of the light emitting event as well as to provide continuous imagery to the processor that may be used for situational awareness, broadband targeting and surveillance. 
     All spectral and/or broadband information is contained in one frame of image data produced by the focal plane array, making image processing more streamlined and the time required to collect all of the necessary data minimal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawings in which: 
         FIG. 1  illustrates light emitting events being detected and identified via an imaging device; 
         FIG. 2  is an exploded view of a first embodiment of the imaging device; 
         FIG. 3  is a top view of a focal plane array of the  FIG. 2  imaging device illustrating that dispersive elements may orient dispersed light at different angular directions; 
         FIG. 4  illustrates a second embodiment of the imaging device; 
         FIG. 5  is a-top view of a focal-plane array of the  FIG. 4  imaging device; and 
         FIG. 6  is a flow chart illustrating steps for detecting and identifying the light-emitting event. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The drawings referred to herein are for the purpose of illustrating the preferred embodiments of the present invention and not for the purposes of limiting the same. For example, certain portions of the detailed description make reference to detecting and identifying a single light emitting event  10   a  within a scene  12 . However, it is also contemplated within the scope of the present invention that the aspects of the present invention described herein may detect and identify two simultaneous light emitting events  10   a  within the scene  12 . 
     An imaging device  14  (see  FIGS. 1 ,  2  and  4 ) may be provided. The imaging device  14  may be for the purpose of detecting-and identifying the light emitting event  10   a.  The light emitting event  10   a  may occur within the scene  12 . Also, other light emitting events  10   b  may also occur within the scene  12 . For example, as shown in  FIG. 1 , light emitting events  10   a,    10   b  may occur simultaneously within the scene  12 . Light emitting event  10   a  shown in  FIG. 1  is a firing of a rocket, and light emitting  10   b  shown in  FIG. 1  is a sun reflection off of a surface of a pond. By way of example and not limitation, the event  10   a  may be a man-made event such as a fire, small firearms flash, large firearms flash, laser, rocket propelled grenade, anti tank guided missile or a munition&#39;s explosion. Flashes determined to be not of interest are termed “clutter.” The event  10   b  may also be a natural event  10   b  such as a bolt of lightning, camp fire, sun glint (e.g., reflection from pond surface), natural fire, etc. 
     The device  14  may initially distinguish events  10   a, b  occurring within the scene  12  as being those events of interest  10   a  and those events not of interest  10   b.  If the event  10   a  is of interest, then further event identification is desired. For example, in military applications, the device  14  may be utilized in hostile environments where hostile events  10   a  such as firing of an anti tank guided missile may occur. In these types of hostile environments, whether certain emitted lights are from hostile events  10   a  such as firing of an anti tank guided missile (i.e., events of interest) or whether it is from non hostile events  10   b  (i.e., events not of interest) may be necessary for military personnel. Hence, the device  14  may detect a flash of light  26  (see  FIG. 2 ) emitted from the scene  12  and be able to distinguish whether the light flash is from a hostile source (i.e., event of interest)  10   a  or a non hostile source (i.e., event not of interest)  10   b.    
     Referring now to  FIG. 2 , the device  14  may comprise a focal plane array  16 . The device  14  may also have at least two imaging lens  18  adjacent to the focal plane array  16 .  FIG. 2  illustrates the device having four imaging lens  18   a - d.  The device  14  may also have at least one dispersive element  20  adjacent to the imaging lens  18 .  FIG. 2  illustrates the device  14  having three dispersive elements  20   a, b, c  adjacent to the imaging lens  18   a, b, c,  respectively. These dispersive elements  20   a, b, c  may be an optical transmission grating or a prism. Element  22  may be a non dispersive element (i.e., flat). Accordingly, every imaging lens  18   a - d  may not have a dispersive lens  20  adjacent thereto. These component parts  16 ,  18 ,  20 ,  22  of the device  14  may be aligned with respect to optical paths  24   a, b, c, d  of the light from the light emitting event  10   a, b.  These component parts  16 ,  18 ,  20 ,  22  may also each define a channel of the device  14 . 
     The events  10   a, b  within the scene may emit light  26 . Such light may be collimated, as shown in  FIGS. 2 and 4 . For example, the emitted light  26  may be a flash of light from a firearm muzzle. The emitted light  26  may travel along the optical paths  24   a, b, c, d  shown in  FIG. 2 . In particular, the emitted light  26  which may be collimated at the entrance aperture of the described sensor will travel through the dispersive elements  20   a, b, c,  imaging lens  18   a, b, c, d  and be received onto the focal plane array  16 . As stated above, at least one of the imaging lenses  18  may not have a dispersive element  20  adjacent thereto.  FIG. 2  illustrates imaging lens  18   d  not having a dispersive element  20  adjacent thereto. Rather, the element  22  may be flat such that there is no dispersion of the light  26  passing through the element  22 . As such, non-dispersed light travels through imaging lens  18   d.    
     The dispersive element  20  may be a prism, optical transmission grating or the like so as to separate the light  26  traveling therethrough into different wavelength bands. More particularly, the light  26  may be split into many narrow, adjacent wavelength bands. The separated light  26  then travels through the imaging lens  18   a - c  which may focus the separated light  26  onto the focal plane array  16 . The dispersive elements  20   a - c  may also direct the separated light toward different directions. For example, as shown in  FIG. 3 , the dispersive elements  20   a - c  may direct the separated light vertically, horizontally or diagonally. 
     The focal plane array  16  may receive the imaged and/or dispersed light. Imaged and dispersed light refers to the light  26  traveling along optical paths  24   a, b, c.  Imaged light refers to light traveling along optical paths  24   d.  The focal plane array  16  may measure the energy in each wavelength band via a plurality of detectors  28 . The focal plane array  16  may comprise the plurality of detectors  28  (i.e., spectral bins). The detectors  28  may be placed adjacently next to each other. The detectors  28  when assembled may have a square or rectangular configuration as shown in  FIGS. 2 and 3 . The focal plane array  16  may be sized and configured to receive the imaged and/or dispersed light to measure the energy in each band. 
     Each detectors  28  may have a saturation point and noise. The saturation point of each detector  28  may be characterized as the maximum amount of energy measurable by the detector  28 . For example, if energy received by the detector  28  is greater than the saturation point, then the energy above the detector&#39;s saturation point would not be measured by the detector  28 . On the other hand, the detector noise may affect performance of the device because if sufficient energy is not received by the detector  28  then the energy received by the detector may not be differentiable from the detector noise. 
     Accordingly, the detectors  28  may be configured or selected such that its saturation point and detector noise matches the expected use of the device  14 . In other words, if the device  14  is expected to be used in combat with light emitting events occurring approximately two hundred (200) yards away, the detectors  28  may be configured and selected such that expected light emitting events two hundred (200) yards away does not saturate the detectors  28  and the device  14  is able to differentiate between detector noise and the energy received by the detector  28 . 
     Moreover, the dispersive elements  20   a - c  may have different spectral spreading characteristics such that at least some of the detectors  28  of a plurality of detectors may not receive energy above its saturation point and the energy received by the detector  28  may be sufficiently great such that the received energy is differentiable from the detector noise. To this end, the three dispersive elements  20   a, b, c  may each have a different spectral spreading characteristic. The dispersive elements  20   a, b, c  may have different spectral spreading performances ranging from a low amount of spectral spreading to a high amount of spectral spreading. Dispersive elements  20  with the high amount of spectral spreading divides the light into smaller wavelength bands (i.e., less energy in each band) compared to dispersive elements with the low amount of spectral spreading (i.e., more energy in each band). The dispersive elements  20  with the high amount of spectral spreading may be referred to herein as high dispersive elements. Also, the dispersive elements  20  with the low amount of spectral spreading may be referred to herein as low dispersive elements. Also, dispersive elements  20  with spectral spreading characteristics between the low and high dispersive elements may be referred to herein as medium dispersive elements. Dispersive element  20   a  may be a high dispersive element. Dispersive element  20   b  may be a medium dispersive element. Lastly, dispersive element  20   c  may be a low dispersive element. 
     The light traveling through each dispersive element  20   a, b, c  may also travel through respective imaging lens  18   a, b, c  and may be received by detectors  28  of the focal plane array. A set of detectors  28  may be associated with respective imaging lens  18  and dispersive element  20 . In particular, a first set of detectors  30  may be associated with imaging lens  18   a  and dispersive element  20   a.  A second set of detectors  32  may be associated with imaging lens  18   b  and dispersive element  20   b.  A third set of detectors  34  may be associated with imaging lens  18   c  and dispersive element  20   c.  A fourth set of detectors  36  may be associated with imaging lens  18   d  and element  22 . 
     This arrangement of having dispersive elements  20   a, b, c  having low, medium and high spectral spreading characteristics may ensure that at least one of a first, second or third set of detectors  28 ,  32 ,  34  does not receive energy greater than its saturation point and the received energy is differentiable from the detector noise. For example, a light emitting event may occur two hundred (200) yards away. However, the light when dispersed through the low dispersing element  20   c  may disperse the light into wavebands having energy greater than the saturation point. As such, the third set of detectors  34  may not be able to provide accurate information about the dispersed and imaged light through the dispersive element  20   c  and imaging lens  18   c.  However, since the dispersive elements  20   a  and  20   b  divides the light into more wavebands, less energy is contained within each waveband to thus make it more likely that the energy contained in those wavebands do not exceed the saturation points of the first or second set of detectors  30 ,  32 . 
     Conversely, if the light emitting event  10  is very faint or far away then the dispersed and imaged light via the dispersive element  20   a  and imaging lens  18   a  may divide the energy into wavebands having miniscule amounts of energy which are not differentiable from the detector noise of the first set of detectors  30 . However, since the dispersive elements  20   b  and  c  divides the light energy into fewer wavebands compared dispersive element  20   a,  more energy may be contained within each wavelength band compared to the light dispersed via dispersive element  20   a  such that sufficient amounts of energy may be contained in each waveband so as to be differentiable from the detector noise of the second and third sets of detectors  32 ,  34 . 
     The dispersive element  20 , imaging lens  18  and focal plane array  16  may produce a spectral profile of the detected light. In particular, each detector  28  may receive the separated wavelength bands and convert the received energy into information (i.e., spectral profile of detected light) which may be communicated to a processor  38 . The communicated information may be processed via the processor  38  to detect whether the light emitting event is of interest  10   a  or not  10   b.  Once the event  10   a, b  is determined to be of interest  10   a,  the processor may further identify the type of light emitting event  10  by comparing the spectral profile of the detected light with known spectral profiles of light emitting events of interest  10   a.    
     The detectors  28  may be arranged in rows and columns. Each detector  28  may be assigned a unique address such as row X, column Y. The detectors  28  may define the first set of detectors  30  which may receive light traveling through the imaging lens  18   a.  The detectors  28  may further define the second set of detectors  32  which may receive light traveling through imaging lens  18   b.  The detectors  28  may further define third, fourth, etc sets of detectors  34 ,  36  which may receive light traveling through third, fourth, etc imaging lens  18   c, d.  As shown in  FIG. 3 , the dispersive elements  20   a, b, c  may split the light into many different wavebands at different rotational angles (e.g., horizontally, vertically, diagonally). Since the collimated light  26  raveling through the imaging lens  18   a, b, c, d  and/or dispersive elements  20   a, b, c, d  is split into wavebands received into known sets of detectors  30 ,  32 ,  34 ,  36 , the first, second, third and fourth sets of detectors  30 ,  32 ,  34 ,  36  may be correlated with each other. The correlation between the sets of detectors  30 ,  32 ,  34 ,  36  and the various directions of the dispersive elements  20   a, b, c  may provide position information of the event. In other words, the processor  38  may receive the information of the light  26  received by the detectors  28 , correlate the information and calculate the event position which may be displayed on the output  40 . 
     In another aspect of the present invention, referring now to  FIGS. 4 and 5 , the device  14  may comprise a plurality of channels  42   a, b.  The channels  42   a  and  42   b  may comprise a first and second set of detectors  46 ,  44  adjacent to imaging lenses  18   a, b,  respectively. At least one of the channels  42   a  or  42   b  may have dispersive element  20   a  adjacent to imaging lens  18   a.  At least one of the channels  42   a  or  42   b  may be characterized as a broadband channel.  FIG. 4  illustrates a device  14  with one broadband channel  42   b  and another channel  42   a  with dispersive element  20   a,  imaging lens  18   a  and first set of detectors  46  adjacent to each other. As shown in  FIG. 5 , the dispersive element  20   a  may disperse the light  26  vertically. It is also contemplated within the scope of the present invention that the dispersive element  20   a  may disperse the light horizontally or diagonally. 
     The light may travel through the imaging lens  18   b  and be received by the second set of detectors  44 . The second set of detectors  44  may also transmit information related to the light received by the second set of detectors to the processor which may determine the existence of an event. In particular, the transmitted information may be processed with a frame subtraction image processing method to determine whether a light emitting event occurred. The light may also travel through the imaging lens  18   a  and be received by the first set of detectors  46 . The first set of detectors  46  may also transmit information related to the light received by the first set of detectors to the processor. The processor may process specific detectors of the first set of detectors based on the information related to the light received by the second set of detectors to determine whether the light emitting event is of interest or not. 
     The device may have a broadband channel, a channel with a low dispersive element and a channel with a high dispersive element. In use, the light may travel through all three channels. However, initially, the light traveling through the broadband channel is received and processed by the processor to determine whether an event has recently occurred (step  100 ) as shown in  FIG. 6 . If an event has recently occurred then the processor may process the information related to the light passing through the low dispersive element by calculating a ratio between the different bands to determine whether the light emitting event is of interest or not. (step  102 ). If the event is of interest, then the processor may process the information related to the light passing through the high dispersive element to determine the type of event. In particular, the spectral profile of the detected light may be compared to known spectral profiles of events of interest (step  104 ). 
     This description of the various embodiments of the present invention is presented to illustrate the preferred embodiments of the present invention, and other inventive concepts may be otherwise variously embodied and employed. The appended claims are intended to be construed to include such variations except insofar as limited by the prior art.