Patent Publication Number: US-8989501-B2

Title: Method of selecting an algorithm for use in processing hyperspectral data

Description:
BACKGROUND OF THE INVENTION 
     The environment of a remote sensing system for hyperspectral imagery (HSI) is well described in “Hyperspectral Image Processing for Automatic Target Detection Applications” by Manolakis, D., Marden, D., and Shaw G. (Lincoln Laboratory Journal; Volume 14; 2003 pp. 79-82). An imaging sensor has pixels that record a measurement of hyperspectral energy. An HSI device will record the energy in an array of pixels that captures spatial information by the geometry of the array and captures spectral information by making measurements in each pixel of a number of contiguous hyperspectral bands. Further processing of the spatial and spectral information depends upon a specific application of the remote sensing system. 
     Remotely sensed HSI has proven to be valuable for wide ranging applications including environmental and land use monitoring, military surveillance and reconnaissance. HSI provides image data that contains both spatial and spectral information. These types of information can be used for remote detection and tracking tasks. Specifically, given a set of visual sensors mounted on a platform such as an unmanned aerial vehicle (UAV) or ground station, a video of HSI may be acquired and a set of algorithms may be applied to the spectral video to detect and track objects from frame to frame. 
     Spectral-based processing algorithms have been developed to classify or group similar pixels; that is, pixels with similar spectral characteristics or signatures. Processing in this manner alone is not amenable to target tracking and detection applications where the number and size of targets in a scene is typically too small to support the estimation of statistical properties necessary to classify the type of target. However, spatial processing of most HSI is compromised by the low spatial resolution of typical systems that collect HSI. As a result, remote sensing systems that collect and process HSI are typically developed as a trade-off between spectral and spatial resolution to maximize detection of both resolved and unresolved targets where a resolved target is an object imaged by more than one pixel. In this way, spectral techniques can detect unresolved targets by their signature and spatial techniques can detect resolved targets by their shape. 
     A number of search algorithms have been developed and used in the processing of HSI for the purpose of target detection. These search algorithms are typically designed to exploit statistical characteristics of candidate targets in the imagery and are typically built upon well-known statistical concepts. For example, Mahalanobis distance is a statistical measure of similarity that has been applied to hyperspectral pixel signatures. Mahalanobis distance measures a signature&#39;s similarity by testing the signature against an average and standard deviation of a known class of signatures. 
     Other known techniques include Spectral Angle Mapping (SAM), Spectral Information Divergence (SID), Zero Mean Differential Area (ZMDA) and Bhattacharyya Distance. SAM is a method for comparing a candidate target&#39;s signature to a known signature by treating each spectra as vectors and calculating the angle between the vectors. Because SAM uses only the vector direction and not the vector length, the method is insensitive to variation in illumination. SID is a method for comparing a candidate target&#39;s signature to a known signature by measuring the probabilistic discrepancy or divergence between the spectra. ZMDA normalizes the candidate target&#39;s and known signatures by their variance and computes their difference, which corresponds to the area between the two vectors. Bhattacharyya Distance is similar to Mahalanobois Distance but is used to measure the distance between a set of candidate target signatures against a known class of signatures. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention relates to a method of selecting an algorithm for use in processing hyperspectral data. The method comprises providing a set of algorithms, each having qualities for processing certain characteristics of hyperspectral data; accessing frame characteristics of the hyperspectral data; selecting at least one characteristic of the hyperspectral data; establishing a tolerance for variations in the at least one characteristic from a reference sample of the at least one characteristic; comparing the at least one characteristic in the hyperspectral data to the tolerance; and if the at least one characteristic exceeds the tolerance, selecting an algorithm from the set best associated with the at least one characteristic to process the hyperspectral data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a diagrammatic view of a method for tracking and determining a probability of detection for observed objects in HSI according to a first embodiment of the invention. 
         FIG. 2  is a diagrammatic view of a method for selecting a search algorithm according to an embodiment of the invention. 
         FIG. 3  is a diagrammatic view of a method for selecting a tolerance for a search algorithm according to an embodiment of the invention. 
         FIG. 4   a  shows a scenario where a hyperspectral imaging system according to an embodiment of the invention has detected and tracked two objects. 
         FIG. 4   b  shows a scenario where a hyperspectral imaging system according to an embodiment of the invention detects changes in tracked objects. 
     
    
    
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     In the background and the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the technology described herein. It will be evident to one skilled in the art, however, that the exemplary embodiments may be practiced without these specific details. In other instances, structures and device are shown in diagram form in order to facilitate description of the exemplary embodiments. 
     The exemplary embodiments are described with reference to the drawings. These drawings illustrate certain details of specific embodiments that implement a module, method, or computer program product described herein. However, the drawings should not be construed as imposing any limitations that may be present in the drawings. The method and computer program product may be provided on any machine-readable media for accomplishing their operations. The embodiments may be implemented using an existing computer processor, or by a special purpose computer processor incorporated for this or another purpose, or by a hardwired system. 
     As noted above, embodiments described herein may include a computer program product comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media, which can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of machine-executable instructions or data structures and that can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communication connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such a connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions comprise, for example, instructions and data, which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. 
     Embodiments will be described in the general context of method steps that may be implemented in one embodiment by a program product including machine-executable instructions, such as program code, for example, in the form of program modules executed by machines in networked environments. Generally, program modules include routines, programs, objects, components, data structures, etc. that have the technical effect of performing particular tasks or implement particular abstract data types. Machine-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the method disclosed herein. The particular sequence of such executable instructions or associated data structures represent examples of corresponding acts for implementing the functions described in such steps. 
     Embodiments may be practiced in a networked environment using logical connections to one or more remote computers having processors. Logical connections may include a local area network (LAN) and a wide area network (WAN) that are presented here by way of example and not limitation. Such networking environments are commonplace in office-wide or enterprise-wide computer networks, intranets and the internet and may use a wide variety of different communication protocols. Those skilled in the art will appreciate that such network computing environments will typically encompass many types of computer system configuration, including personal computers, hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. 
     Embodiments may also be practiced in distributed computing environments where tasks are performed by local and remote processing devices that are linked (either by hardwired links, wireless links, or by a combination of hardwired or wireless links) through a communication network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     An exemplary system for implementing the overall or portions of the exemplary embodiments might include a general purpose computing device in the form of a computer, including a processing unit, a system memory, and a system bus, that couples various system components including the system memory to the processing unit. The system memory may include read only memory (ROM) and random access memory (RAM). The computer may also include a magnetic hard disk drive for reading from and writing to a magnetic hard disk, a magnetic disk drive for reading from or writing to a removable magnetic disk, and an optical disk drive for reading from or writing to a removable optical disk such as a CD-ROM or other optical media. The drives and their associated machine-readable media provide nonvolatile storage of machine-executable instructions, data structures, program modules and other data for the computer. 
     Technical effects of the method disclosed in the embodiments include increasing the versatility and robustness of hyperspectral signature matching, especially when object detection and tracking methods are used in conjunction with the method. As well, the method improves on existing signature matching techniques by automatically selecting the best known signature matching technique in real-time. This technique can be used on any system that generates composite imagery from spectral cube arrays. 
       FIG. 1  is a diagrammatic view of a method  10  for tracking and determining a probability of detection for observed objects in HSI according to a first embodiment of the invention. Remotely sensed HSI that may include single images or a hyperspectral video feed may be input at  12  to a processor capable of processing the HSI. The processor receives the hyperspectral data at  12  and processes the data set into a set of hyperspectral image frames at  14  by performing a series of well-known image processing steps that may include but not be limited to noise filtering, corner detection, image registration, homography and frame-to-frame alignment. The processor may then select candidate targets using search algorithms at  16  from tracked objects in the hyperspectral image frames, where candidate targets and tracked objects are sets of pixels that may represent the hyperspectral image of a real-world object of interest. For example, in a system collecting HSI that is designed to search for moving targets, candidate targets may be moving objects. In this example, the processor may perform a computational search for the minimum discriminant characteristics that identify moving objects in HSI. In another example, a user of a system collecting HSI manually selects pixels on a display and identifies the corresponding signatures for further analysis. 
     The processor may then track selected candidate targets at  18  from frame to frame of the HSI. The processor may compare at  20  the selected candidate targets to reference target templates of known targets stored in a template database at  28  where reference target templates are sets of pixels that may have been previously established to represent the hyperspectral image of a real-world object of interest. 
     At  22 , the processor may make a match comparison. If a selected candidate target matches a reference target template from the template database at  28 , the processor at  24  may then determine a matching degree between the selected candidate target and a reference target template, and a probability that the selected candidate target has been detected. If the selected candidate target does not match a template, then the processor may either consider the selected candidate target to be a new reference target template at  30  or discard it at  32 . If the selected candidate target is considered a new template at  30 , then the processor may add data relating to the new target to the target template database at  28 . 
     After the determination of the matching degree and the probability of detection at  24 , the processor may compare the probability to a threshold at  26 . If the probability exceeds a threshold, the processor may take an action at  34 . Otherwise, the processor may continue to track the selected candidate target at  18 . 
     After specific reference target templates are identified from the reference target template database at  28  and compared at  20  with the candidate targets, the processor may calculate the matching degree and probability of detection at  24 . The matching degree and probability of detection may measure the probability of the selected candidate target to be a match to a specific reference target template by first comparing at  24  the top spectral signatures that appear in the selected candidate target with the top spectral signatures that define the reference target template and then matching them spatially. 
     The processor computing the method of determining the matching degree and probability of detection at  24  may first determine the set of top signatures appearing in both the selected candidate target and the reference target template. Then, the processor may calculate the distribution of those top signatures based on the number of pixels in both the selected candidate target and the reference target template. To do this, the first step is to determine the set of signatures in the reference target template that cover a certain percentage of the pixels in the reference target template and determine the percentage of each one of the signatures in the reference target template. The processor computing the method at  24  may then determine the distribution of signatures for a selected candidate target. If the distribution of pixels in each signature is similar to the distribution of signatures in the reference target template, then processor computing the method may calculate the matching degree for each one of the signatures considering the maximum and the minimum difference between similar signature pixels. The processor computing the similarity between hyperspectral pixel distributions may employ one or more measures of similarity for the computation. Similarity measures may include SAM, SID, ZMDA or Bhattacharyya Distance. The processor may employ other similarity measures depending upon the implementation. 
     Let S i ={s 1 , s 2 , . . . , s p } be the set of signatures in a target, and let x ij  be a pixel in the ij location in the two dimensional spatial representation of a hyperspectral frame. The pixel x ij  is made up of an array of subpixels such that the pixel x ij  has a set of values x b1 , x b2 , . . . , x bq  where q is the number of spectral bands in the hyperspectral imagery. Therefore, each pixel contains a subpixel value associated with each spectral band for the spatial location described by the pixel. 
     A selected candidate target referenced here for brevity as object O i  that spatially matches reference template target referenced here for brevity as target T may also spectrally match target T with confidence C if the set of R % top signatures in target T appear in a λ similar proportion in object O i . The goal is to match the object and the target spatially and spectrally, that is the shapes and the signatures of the object and target are similar. 
     Let N i  be the number of pixels in object O i  and n i1 , n i2 , . . . , n ir  with r&lt;p defining the cardinality or size of the sets of pixels in object O i  that present similar signatures s 1 , s 2 , . . . , s r . The processor computing the method at  24  considers two objects O i  and O j  a spectral match if the top R % of the spectral signatures in object O i  match the R % top signatures of object O j . The two objects O i  and O j λ-match precisely if for all the selected number of top signatures of object O i  and O j  denoted as {n i1 , n i2 , . . . , n ir } and {n j1 , n j2 , . . . , n jr } respectively: 
                        n     i   ⁢           ⁢   1         N   i       -       n     j   ⁢           ⁢   1         N   j              &lt;   λ                          n     i   ⁢           ⁢   2         N   i       -       n     j   ⁢           ⁢   2         N   j              &lt;   λ                       ⁢   ⋮                          n     i   ⁢           ⁢   r         N   i       -       n     j   ⁢           ⁢   r         N   j              &lt;   λ         
The matching degree for each signature/may be defined as:
 
 n   l ( O   i   ,O   j )=1−|max l   |x   il   −x   ijl |−min l   |x   il   −x   ijl ∥
 
The method may employ other definitions for the matching degree for each signature, l. Any definition to determine matching degree at  24  must conform to the well-known mathematical definition of a fuzzy measure.
 
     Finally, the processor computing the method at  24  may calculate a probability of detection based on the similarity between the set of signatures in the template and the set of signatures in the object. Considering N i  number of pixels in object O i  and N j  number of pixels in object O j , the processor may calculate the probability of detection at  24  based on the matching degree and the number of pixels that match each signature. The processor may calculate the probability of detection by normalizing the matching degree to the number of pixels of the object to determine a confidence level of how close the image of the selected candidate target object matches the hyperspectral image reference target template. The probability of detection, referenced as TM, is computed as: 
             TM   =           ∑   s     ⁢       η   l     *     N   i         |   s           ∑   s     ⁢     N   i       |   s             
where N i |s number of pixels in O i λ-match the signature s.
 
     At  26 , the probability of detection or TM for a selected candidate target object as a match for a target template may be compared to a threshold. As shown at  26 , the processor may calculate TM−1 and compare to threshold, ε. If the quantity TM−1 exceeds threshold, ε, the processor may take an action at  34 . Otherwise, the processor may continue to track the selected candidate target at  18 . The value of the threshold, ε, may be selected based upon the specific implementation of the matching algorithm at  22 , the search algorithm at  16  and information pertaining to the specific candidate target and reference target template in the database at  28  such as the calculated object velocity in the scene of the HSI. 
     Different levels of confidence are defined based on the value of TM. For example, in an instance, if TM is less than 0.35 the confidence level will be very low; if TM is between 0.35 and 0.60, the level of confidence will be low, if TM is between 0.60 and 0.75, the level of confidence will be medium; if TM is between 0.75 and 0.85, the level of confidence will be medium-high; and if TM is greater than 0.85, the level of confidence will be high. As the probability of a match becomes more likely, a display of the results may iterate through a series of colors mapped to these levels of TM to distinguish targets detected with a high level of confidence from targets detected with a low level of confidence. The pixels of an image of a target detected with a high level of confidence may, for example, all be colored red on a display. Other thresholds, levels of confidence and displays schemes may be used depending upon the implementation. 
     When the processor receives data at  12  and processes it into a set of hyperspectral frames at  14 , the processor may then select candidate targets at  16  from the hyperspectral frames. The processor may select and use a search algorithm for hyperspectral data for selecting the candidate targets at  16 . The dimension of the hyperspectral data may have been reduced by means of well-known dimensionality reduction techniques, including but not limited to principal components analysis, feature extraction, and entropy measurements.  FIG. 2  is a diagrammatic view of a method  100  for selecting a search algorithm for hyperspectral data according to an embodiment of the invention. To select a search algorithm for hyperspectral data, a processor computing the method at  100  may initially save characteristics of a hyperspectral frame to a database at  110 . Next, the processor may assess a characteristic of the hyperspectral frame at  112 . If the processor assesses the characteristic at  112  to be of significance for the hyperspectral frame, the processors may apply a search algorithm to the data at  116  to distinguish the candidate targets of the frame. If the processor assesses the characteristic at  112  to not be significant for the hyperspectral frame, the processor may assess a second characteristic at  114 . If the processor assesses the second characteristic at  114  to be of significance for the hyperspectral frame, the processor may apply a second spectral search algorithm at  120  to the data to distinguish the candidate targets of the frame. If the processor assesses the second characteristic at  114  to not be significant for the frame, the processor may assess a third characteristic at  118 . If the processor assesses the third characteristic at  118  to be of significance for the hyperspectral frame, the processor may apply a third search algorithm at  122  to the data to distinguish the candidate targets of the hyperspectral frame. If processor assesses the third characteristic at  118  to not be significant for the hyperspectral frame, the processor may apply a default search algorithm  124  to the data. 
     Initially, the processor may determine characteristics of a hyperspectral frame at  110 . The processor may save the hyperspectral frame characteristics at  110  such that they are available for further processing when selecting a search algorithm. Example characteristics may include an estimate of the variability of the illumination of imaged scene, the variability of pixels with similar signatures, and the number of distinct signatures in the reference target template. Other characteristics of the hyperspectral frame may be considered and these examples should not be considered limiting. 
     Based upon an assessment of the first characteristic at  112  of the hyperspectral frame, the processor may apply a search algorithm that has been proven to work well with hyperspectral data characterized by that first characteristic at  116 . If the assessment of the first characteristic at  112  of the hyperspectral frame does not indicate the first search algorithm will work well with the hyperspectral frame, the processor may access the saved frame characteristics from  110  for an assessment of a second frame characteristic at  114 . In one example, the first characteristic may be the variability of the illumination of the imaged scene of the hyperspectral frame. The processor may access the hyperspectral frame characteristics to determine the variability of the illumination of the imaged scene. The processor may make a decision to determine if the variability is high or low. The processor may use other frame characteristics as a first frame characteristic depending upon the implementation. 
     If the first hyperspectral frame characteristic is assessed to be of significance, the processor may use a first search algorithm at  116  to process the hyperspectral frame and its candidate targets. In this example, if the processor calculates high variability of the illumination of the imaged scene, a search algorithm based upon SAM may process the imaged scene for optimal results. The method may use other search algorithms based upon classification methods including but not limited to SID, Mahalanobis Distance, ZMDA and Bhattacharyya Distance, depending upon the implementation. 
     Based upon an assessment of the second characteristic at  114  of the hyperspectral frame, the processor may apply a search algorithm that is known to work well with hyperspectral data characterized by that second characteristic at  120 . If the assessment of the second characteristic at  114  of the hyperspectral frame does not indicate the second search algorithm will work well with the hyperspectral frame, the processor may access the saved frame characteristics from  110  for an assessment of a third frame characteristic at  118 . In one example, the second characteristic may be the variability of pixels with similar signatures. The processor may access the hyperspectral frame characteristics to determine the variability of pixels with similar signatures. The processor may make a decision to determine if the variability is high or low. The processor may use other frame characteristics as a second frame characteristic depending upon the implementation. 
     If the second hyperspectral frame characteristic is assessed to be of significance, the processor may use a second search algorithm at  120  to process the hyperspectral frame and its candidate targets. In this example, if the processor calculates high variability of the pixels with similar signatures, a search algorithm based upon SID may process the imaged scene for optimal results. The method may use other search algorithms based upon similarity or distance measures, including but not limited to SAM, Mahalanobis Distance, ZMDA and Bhattacharyya Distance, depending upon the implementation. 
     Based upon an assessment of the third characteristic at  118  of the hyperspectral frame, the processor may apply a search algorithm that is known to work well with hyperspectral data characterized by that third characteristic at  122 . If the assessment of the third characteristic at  118  of the hyperspectral frame does not indicate the third search algorithm will work well with the hyperspectral frame, the processor may apply a default search algorithm at  124  to process the hyperspectral frame. In one example, the third characteristic may be the number of distinct signatures in the reference target template. The processor may access the hyperspectral frame characteristics including previously tracked targets and corresponding reference target templates to determine the number of distinct signatures in the reference target template. The processor may make a decision to determine if the number of distinct signatures in the reference target template is high or low. The processor may use other frame characteristics as a third frame characteristic depending upon the implementation. 
     If the third hyperspectral frame characteristic is assessed to be of significance, the processor may use a third search algorithm at  122  to process the hyperspectral frame and its candidate targets. In this example, if the processor calculates a high number of distinct signatures in the reference target template, a search algorithm based upon Mahalanobis Distance may process the imaged scene for optimal results. The method may use other search algorithms based upon similarity or distance measures, including, but not limited to SAM, SID, ZMDA and Bhattacharyya Distance, depending upon the implementation. 
     Upon exhaustion of the frame characteristics, the processor may use a default search algorithm at  124  to process the hyperspectral frame and its candidate targets. The default search algorithm may be based upon any of SAM, SID, Mahalanobis Distance, ZMDA and Bhattacharyya Distance. The method may use other search algorithms as a default search algorithm depending upon the implementation. 
     The method at  100  may implement additional steps using other frame characteristics and their assessments. Frame characteristics may be daisy-chained into decision steps that follow the previously disclosed decision steps at  112 ,  114 , and  118 . Also, the processor may assess multiple frame characteristics to determine if a particular search algorithm is optimally deployed to process the hyperspectral frame. 
     The method at  100  may implement additional search algorithms. For example, the processor may run multiple search algorithms on the hyperspectral frame concurrently. The processor may then aggregate the results using multicriteria decision making methodologies from the concurrent processing of multiple search algorithms into a single result. 
       FIG. 3  is a diagrammatic view of a method at  200  for selecting a tolerance for a search algorithm. When processing the hyperspectral frame with a selected search algorithm at  116 ,  120 ,  122  and  124  in  FIG. 2 , the parameters or tolerances of the given algorithm may be initially set to a default value or values at  210 . The search algorithm may then process the data from the hyperspectral frame along with the default tolerances at  212 . The selected search algorithm may compute the number of hyperspectral pixels from the hyperspectral frame that are determined to match the candidate targets from the hyperspectral frame to the reference target template at  216 . If too few hyperspectral pixels match the candidate targets from the hyperspectral frame to the reference target template, the processor may relax the tolerances for the selected search algorithm at  218  and then the search algorithm may then process the hyperspectral frame again at  212  with the modified tolerances. If too many hyperspectral pixels match the candidate targets from the hyperspectral frame to the reference target template, the processor may constrict the tolerances for the selected search algorithm at  214  and then the search algorithm may then process the hyperspectral frame again at  212  with the modified tolerances. If an acceptable number of hyperspectral pixels match, the processor may save the location and signatures of the matching hyperspectral pixels at  220 . 
     The processor may repeat the steps of modifying the tolerances of the search algorithm at  214  and  218  followed by processing the hyperspectral frame with the selected search algorithm at  212  until the matching number of pixels at  216  lies within acceptable bounds. 
     The method at  10  in  FIG. 1  for tracking and determining a probability of detection for observed objects in HSI according to a first embodiment of the invention may instruct an action at  34  in  FIG. 1  based upon the probability of detection for a candidate target exceeding a threshold at  26  in  FIG. 1  based upon analysis of the spectral and spatial parameters of the candidate target relative to known templates in the reference target template database at  28 . At this point, each candidate target may have a unique identifier associated with it. If the processor computing the method at  10  of  FIG. 1  detects deviation in a candidate target based upon changes in its spectral and spatial characteristics, the processor may then autonomously mark the deviation as a significant event in that target&#39;s lifecycle. The processor may then allocate an identifier to identify the deviated target as a new object. The processor may aggregate all target events into a reviewable timeline, where a human operator has the ability to evaluate and potentially correct the processor&#39;s choice of associating new or existing identifiers to the tracked objects. 
     The processor computing the method at  10  in  FIG. 1  may create an entry in the target template database at  28  in  FIG. 1  with descriptions of both the hyperspectral and spatial information and characteristics of the candidate target at the point of target selection at  16  in  FIG. 1 . In addition to hyperspectral and spatial information, the target template database at  28  in  FIG. 1  may also store information about time as the processor tracks the candidate target in the HSI. If the processor detects a deviation in the spectral or spatial parameters at  20  in  FIG. 1  used to track a candidate target, the processor may store information in the database at  28  in  FIG. 1  that classifies the change as an event that may be used for future review. Additionally, the processor may associate either the same or a new, unique identifier to the new object whose defined parameters are appreciably different than the original target. The processor may base the decision to assign an event on a calculated confidence measurement for determining a significant deviation from the established parameters. The confidence measurement may use parameters defined in spatial, spectral or both domains to be robust to sensing errors in the hyperspectral and spatial information. 
     There are many scenarios where a candidate target&#39;s parameters may significantly deviate from its previously established parameters and trigger an event. Such scenarios may include; a tracked object becomes occluded by another object; a tracked object splits into multiple separate objects; a tracked object significantly changes its spectral characteristics, such as color, contrast, or brightness by traversing into an area covered in shadow. Other scenarios exist and these should not be considered limiting. If the processor cannot associate a candidate target before and after such an event, the processor may associate the same identifier used for the candidate target before the event to the one or more new candidate targets after the event, removing the possibility of losing or mislabeling a target. 
       FIGS. 4   a  and  4   b  demonstrate one such example scenario.  FIG. 4   a  shows an example scenario at  300  where the method for tracking and determining a probability of detection for observed objects in HSI according to an embodiment of the invention has detected and tracked two vehicles  310 ,  312  traveling on a road. The processor implementing the method at  10  in  FIG. 1  processes the received hyperspectral data at  12  in  FIG. 1  into a sequence of hyperspectral frames at  14  in  FIG. 1  to select candidate targets at  16  in  FIG. 1 . Upon a comparison of the candidate targets at  20  in  FIG. 1  with templates in the reference target template database at  28  in  FIG. 1 , the resulting calculations of degree of matching and probability of detection at  24  in  FIG. 1  are significant and trigger action at  34  in  FIG. 1 . The processor assigns each car  310 ,  312  a target identifier that may be stored in the reference target template database at  28  in  FIG. 1 . 
       FIG. 4   b  shows a scenario where the method for tracking and determining a probability of detection for observed objects in HSI according to an embodiment of the invention has detected changes in tracked objects.  FIG. 4   b  demonstrates an event whereby one of the previously identified candidate targets, a car  310  in  FIG. 4A  travels under the shadow  318  of a tree  324  thereby significantly changing the spectral characteristics of the tracked car  310  in  FIG. 4A . Additionally, a second similar car is now traveling next to the previously tracked car  310  in  FIG. 4A . The processor computing the method as  10  in  FIG. 1  may now distinguish with low confidence which car  314  or  316  is the previously tracked and identified car  310  in  FIG. 4A . The processor may take the action at  34  in  FIG. 1  to identify both cars  314  and  316  with identifiers that may be associated with the previously tracked car&#39;s identifier and log the time of the event into the database at  28  in  FIG. 1  for both objects. 
     The second of the previously identified candidate targets, a car  312  in  FIG. 4A  stops at a parking lot and a passenger  322  exits the now stopped vehicle  320 . The processor may detect and identify an event whereby the original object of the car  312  in  FIG. 4A  has split into two separately trackable objects. The processor may take the action as  34  in  FIG. 1  to identify both car  320  and person  322  with identifiers that may be associated with the car  312  in  FIG. 4A  prior to the event and to log the time of the event into the database at  28  in  FIG. 1 . 
     A benefit to storing the information about event and creating identifiers that may be associated with events is that an operator of the system may recall the event history of any target associated with any target identifier. The operator then may analyze all the objects with that identifier or associated identifiers that are being tracked along with the object&#39;s history for review. The event history may include all the data relating to all of the events where the system altered identifier&#39;s for tracked objects. Additionally, the operator could manually correct the system if the identifier that was associated with a target or targets at an event is incorrect. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.