# Patent

## Title
Methods and systems for detection and identification of concealed materials

## Abstract

Methods and systems for efficiently and accurately detecting and identifying concealed materials. The system includes an analysis subsystem configured to process a number of pixelated images, the number of pixelated images obtained by repeatedly illuminating regions with a electromagnetic radiation source from a number of electromagnetic radiation sources, each repetition performed with a different wavelength. The number of pixelated images, after processing, constitute a vector of processed data at each pixel from a number of pixels. At each pixel, the vector of processed data is compared to a predetermined vector corresponding to a predetermined material, presence of the predetermined material being determined by the comparison.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional Application No. 61/555,804, filed Nov. 4, 2011 entitled METHODS AND SYSTEMS FOR DETECTION AND IDENTIFICATION OF CONCEALED MATERIALS, which is incorporated by reference herein in its entirety for all purposes.


STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This invention was made partially with U.S. Government support from the U.S. Army under contract W31P4Q-09-C-0585. The U.S. Government may have certain rights in the invention.


BACKGROUND
These teachings relate generally to methods and systems for detecting concealed materials.
Numerous conventional approaches have been taken in the field of standoff detection and identification to attempt to detect and identify materials, especially explosives, drugs, etc., concealed under clothing. Such conventional approaches that have been reported in the literature for standoff detection and identification of concealed contraband materials include: x-ray backscatter imaging, neutron excited gamma ray emission spectroscopy, terahertz reflection spectroscopy, and laser induced breakdown spectroscopy.
Problems with the x-ray backscattering imaging approach include: poor chemical selectivity for chemical identification with high potential for false positives, large size and weight of instrumentation which prevents the system from being man-portable, and human health risk from x-ray exposure.
Problems with neutron excited gamma ray spectroscopy include: limited chemical selectivity resulting from the measurement only producing elemental concentration results, limited sensitivity, and long measurement times at significant standoff distances (i.e. 1 ft. or greater), and substantial human health risks. Measurements providing only elemental analysis information would not be likely to be able to identify explosive materials such as triacetaone-triperoxide that contain only the elements C, H, and O, and identification of drugs would be very difficult.
Problems with terahertz spectroscopy include: slow measurement time, as well as substantial problems with interference from absorption of terahertz radiation by atmospheric water vapor for standoff distances greater than 10 ft. In addition, the size and weight of the equipment are too great for man-portability.
Laser induced breakdown spectroscopy (LIBS) is a trace detection method that can detect and identify small particles of explosive or other materials on the outside of a surface in a standoff mode. The primary problem with LIBS is that it cannot detect or identify materials concealed underneath a covering layer such as cloth and can only detect explosive particles on the outside surface of clothing. Explosives or other contraband materials that are well sealed in a plastic bag and concealed under clothing, where the outside surface of the clothing was not contaminated with the dust of the contraband material, could not be detected or identified with LIBS.
Further, NIR spectroscopy has been used to identify chemical compounds. In particular, Li, et al. disclose a method of analyzing NIR data, so as to identify various solid forms of chemical compounds and drug candidates. This method includes the steps of: (1) computing the second derivative spectra for collected NIR spectra; (2) applying principal component analysis (PCA) of the second derivative spectra at predetermined wavelengths either the entire wavelength region or a selected wavelength region for segregating the samples; identifying the groups and group membership from the PCA graph, and further evaluating group members by calculating Mahalanobis distances of a given group to assess qualification of the group members. However, this method is merely an initial exploratory analysis of near-infrared spectra designed to identify how many different components or materials are present in an unknown sample, and how different their spectra are.
Additional conventional methods include using NIR spectroscopy to attempt to identify components relative to a saved calibration library, via identification of absorption wavelengths, and comparison thereof to known standards. For example, an explosive device detection method and system based on differential emissivity have been disclosed. This method and system monitors the emissivity levels of target subjects in monitored zones by repeatedly scanning the pixels of an infrared photodetector array, and then processing the pixel values to determine if they correspond to at least one calibrated emissivity level associated with a concealed explosive device. The calibration techniques of that method involve attempts to eliminate the effects of clothing and other personal items, as well as environmental factors, but suffer from a concentration mainly on differences in emissivity levels caused by distance of the target from the source (IR photodetector), rather than increasing the contrast/difference in measured emissivity between the covering materials and the concealed contraband materials.
Further, such conventional methods are inaccurate, when used to attempt to identify materials concealed under clothing, covering materials, etc., due to the difficulties inherent in filtering out the wavelengths reflected from the clothing, covering materials, containment materials, etc., as well as, importantly, ambient light, sunlight, etc. Thus, to obtain accurate measurements, such conventional NIR methods generally are confined to laboratory or laboratory-like environments, not public areas, such as airports.
In view of the above, there is a need for providing a method to efficiently and accurately detect and identify concealed materials, such as explosives, drugs, or hazardous materials, concealed on a person under clothing or in a backpack, or concealed in unattended paper, plastic, cloth or leather bags (including backpacks), and a system for carrying out same.
BRIEF SUMMARY
Methods and systems for efficiently and accurately detecting and identifying concealed materials are presented below.
In one or more embodiments, the system of these teachings includes a number of electromagnetic radiation sources, each electromagnetic radiation source having substantially one wavelength from a number of wavelengths, at least some of the number of wavelengths substantially coinciding with wavelengths in an absorption spectrum of predetermined materials, a pixelated image capture device operatively disposed to receive an image of a region after illumination of the region by one electromagnetic radiation source from the number of electromagnetic radiation sources, an analysis subsystem configured to process a number of pixelated images, the number of pixelated images obtained by repeatedly illuminating regions with a electromagnetic radiation source from the number of electromagnetic radiation sources, each repetition performed with a different wavelength, the number of pixelated images, after processing, constituting a vector of processed data at each pixel from a number of pixels, and to compare, at each pixel, the vector of processed data to a predetermined vector corresponding to a predetermined material, presence of the predetermined material being determined by the comparison.
In one or more embodiments, the method of these teachings includes processing a number of pixelated images, the number of pixelated images obtained by repeatedly illuminating regions with one electromagnetic radiation source from a number of electromagnetic radiation sources, each electromagnetic radiation source having substantially one wavelength, each repetition performed with a different wavelength, the number of pixelated images, after processing, constituting a vector of processed data at each pixel from a number of pixels, and comparing, at each pixel, the vector of processed data to a predetermined vector corresponding to a predetermined material, presence of the predetermined material being determined by the comparison.
A number of other embodiments of the system and a method of these teachings are also disclosed.
For a better understanding of the present teachings, together with other and further needs thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a-1c show a background image (1a), laser image for L1 (1b) and L3 (1c);
FIG. 2 shows a histogram for ratio L1/L3;
FIGS. 3a-3c show a mapped ratio image for L1/L3 (3a), L2/L3 (3b), and L4/L3 (3c);
FIG. 4 shows an example vector in 3D vector space;
FIG. 5 shows an embodiment of the system of these teachings;
FIGS. 6a-6d show block diagram representations of the embodiments of the system of these teachings;
FIG. 7 shows a high-level block diagram of the electronics in the exemplary embodiment;
FIG. 8 shows an electrical and software block diagram of the exemplary embodiment;
FIGS. 9a-9b show a portion of a portable embodiment of the system of these teachings; and
FIGS. 10a and 10b show embodiments of the method of these teachings.



DETAILED DESCRIPTION
The following detailed description presents the currently contemplated modes of carrying out these teachings. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of these teachings.
As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise.
Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.”
In order to elucidate the present teachings, the following definitions are provided.
A “projection,” as used herein, is a measure of a portion of a number of values (sometimes referred as a vector) located along another number of values (sometimes referred to as another vector).
An “optical combiner,” as used herein is a passive device in which emission from several sources (fibers in one embodiment) is distributed to one combination fiber.
In one or more embodiments, the system of these teachings includes a number of electromagnetic radiation sources, each electromagnetic radiation source having substantially one wavelength from a number of wavelengths, at least some of the number of wavelengths substantially coinciding with wavelengths in an absorption spectrum of predetermined materials, a pixelated image capture (also referred to as a detection component) device operatively disposed to receive an image of a region after illumination of the region by one electromagnetic radiation source from the number of electromagnetic radiation sources, a analysis subsystem configured to process a number of pixelated images, the number of pixelated images obtained by repeatedly illuminating regions with a electromagnetic radiation source from the number of electromagnetic radiation sources, each repetition performed with a different wavelength, the number of pixelated images, after processing, constituting a vector of processed data at each pixel from a number of pixels, and to compare, at each pixel, the vector of processed data to a predetermined vector corresponding to a predetermined material, presence of the predetermined material being determined by the comparison.
In one instance, each one of the number of the electromagnetic radiation sources sequentially illuminates an area of interest and the number of electromagnetic radiation sources emit substantially from one location. The pixelated image capture device (also referred to as a detecting component) receives reflected/scattered electromagnetic radiation from the area of interest.
In one or more instances, the analysis subsystem (also referred to as a component) includes a background subtraction subcomponent configured for subtracting, at each pixel from the number of pixels, a background image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation, the background subtraction subcomponent producing a background subtracted value at said each pixel, a ratio intensity subcomponent configured for obtaining, at each pixel, a number of ratio values, each ratio value being a ratio of a background subtracted value at one wavelength from the number of wavelengths to a background subtracted value at a selected wavelengths from the number of wavelengths, and a projection subcomponent configured for obtaining, at each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for said predetermined materials.
In other instances, the analysis subsystem (also referred to as a component) also includes a normalizing subcomponent configured to normalize, for each pixel, the background subtracted value at each pixel respect to a difference between a value for a measure of emission from the electromagnetic radiation source used to generate the image and a measure of background electromagnetic radiation.
In one embodiment, the system of these teachings also includes a timing component providing a signal for initiation of emission from a selected one of the electromagnetic radiation sources. The timing component also provides the initiation signal for initiating detection by the pixelated image capture device
A block diagram representation of an embodiment of the system of these teachings is shown in FIG. 6a. Referring to FIG. 6a, in the embodiment shown therein, each one of a number of electromagnetic radiation sources 10, each electromagnetic radiation source having substantially one wavelength from a number of wavelengths, at least some of the number of wavelengths substantially coinciding with wavelengths in an absorption spectrum of predetermined materials, sequentially illuminates, through and optical subsystems 40, an area of interest. The number of electromagnetic radiation sources emit substantially from one location. The scattered/reflected electromagnetic radiation from the area of interest is received by the pixelated detector 50. A timing component 45 provides the initiation signal for an electromagnetic radiation source 10 and for the pixelated detector 50 and an analysis component 55, so that the pixelated detector 50 captures the scattered/reflected electromagnetic radiation resulting from elimination by the electromagnetic radiation source 10 at substantially one wavelength and the data from pixelated detector 50 is captured by the analysis subsystem 55. After the data has been collected for all the wavelengths from the number of wavelengths, the data, at each pixel, can be represented as a vector, data at each wavelength being data at one component of the vector. At each pixel, the vector of processed data is compared in the analysis subsystem 55, in one instance, by means of a projection, to a predetermined vector corresponding to a predetermined material, presence of the predetermined material being determined by the comparison.
FIG. 6c shows an embodiment of the analysis subsystem 55. Referring to FIG. 6c, in the embodiment shown therein, the analysis subsystem 55 includes a background subtraction subcomponent 60, a normalizing subcomponent 65, a ratio intensity subcomponent 70 and a projection subcomponent 75. The background subtraction subcomponent 60 is configured for subtracting, at each pixel from the number of pixels, a background image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation, the background subtraction subcomponent producing a background subtracted value at said each pixel. The normalizing subcomponent 65 is configured to normalize, for each pixel, the background subtracted value at each pixel with respect to a difference between a value for a measure of emission from the electromagnetic radiation source used to generate the image and a measure of background electromagnetic radiation. The ratio intensity subcomponent 70 is configured for obtaining, at each pixel, a number of ratio values, each ratio value being a ratio of a background subtracted normalize value at one wavelength from the number of wavelengths to a background subtracted normalize value at a selected wavelengths from the number of wavelengths. The projection subcomponent 75 is configured for obtaining, at each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for said predetermined materials (which is equivalent to the definition of a projection).
In one instance, the system of these teachings also includes an electromagnetic emission monitoring component. The timing component provides the initiation signal for initiating monitoring, using the monitoring component, of electromagnetic emission from the selected one of the electromagnetic radiation sources.
In one embodiment, emission substantially from one location for the electromagnetic radiation sources is enabled by means of an optical subsystem. In one instance, the optical subsystem has fiber optic pigtails optically coupled to each electromagnetic radiation source and an optical combiner receiving radiation from the fiber optic pigtails. In another instance, the optical subsystem includes a number of dichroic beam splitters, each dichroic beam splitter receiving electromagnetic radiation from one or more of electromagnetic radiation sources and an optical fiber receiving electromagnetic radiation from the number of dichroic beam splitters.
In one embodiment, the analysis component includes one or more processors and one or more computer usable media having computer readable code embodied therein, the computer readable code causing the one or more processors to subtract, at each pixel, a background image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation, subtraction producing a background subtracted value at said each pixel, obtain, at each pixel, a number of ratio values, each ratio value being a ratio of a background subtracted value at one wavelength to a background subtracted value at a selected wavelength from the number of wavelengths and obtain, at each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for the predetermined materials.
In one instance, the computer readable code also causes the one or more processors to normalize, for each pixel, the background subtracted value at each pixel with respect to a difference between a value for a measure of emission from one of the electromagnetic radiation sources and a measure of background electromagnetic radiation.
FIG. 6d shows an embodiment of the analysis component 55. Referring to FIG. 6d, in the embodiment shown therein, one or more processors 120 are operatively connected to a component 110 allowing receiving input from the pixelated detector 50 and to computer usable media 130 having computer readable code embodied therein, where the computer readable code causes the one or more processors to implement the method of these teachings for detecting concealed objects. In one instance, the one or more processors 120 are operatively connected by means of a computer connection component (such as a computer bus) 135.
In one embodiment, the subcomponents of FIG. 6c are configured for performing their specific function by the computer readable code, embodied in the computer usable media 130, causing the one or more processors 120 to perform the specific function.
In yet another embodiment, the system of these teachings includes a housing. In one instance, the housing has a top portion and a handle portion. The top portion has an opening at one end and a section extending away from that end. The pixelated detection component (image acquisition device) is disposed inside the house and optically disposed to receive reflected/scattered electromagnetic radiation from the area of interest through the opening. The electromagnetic radiation sources are optically disposed such that the electromagnetic radiation sources illuminate the area of interest through the opening. Weight and dimensions of the housing and components in the housing are selected to enable the housing to be handheld. The housing is operatively connected to the analysis component and to timing and power components. In one instance, the weight of the housing and components in the housing is less than 10 pounds, preferably less than 4 pounds.
FIG. 9a shows a portion of one embodiment of a portable system of these teachings including a housing. Referring to FIG. 9a, in the embodiment shown therein, the housing 140 has a top portion 150 and a handle portion 170. The top portion has an opening 160 at one end and a section extending away from that end. The pixelated detector 50 is disposed in that housing and optically disposed to receive, either through opening 160 and optic components 175 or through another opening 165, the scattered/reflected electromagnetic radiation from the area of interest. The electromagnetic radiation sources are optically disposed, either by being this post in the housing 140, as a component 6, or by being optically connected by an optical connection 185 to the housing 140, such that the electromagnetic radiation sources illuminate the area of interest through the opening. The data and timing signals can be exchanged through an electrical connector 180. A similar connector provides power signals.
FIG. 9b shows another embodiment of the housing 140. In the embodiment shown in FIG. 9b, the handle portion is embodied in the top portion 150.
The electromagnetic radiation sources 10 used in the embodiments of the system of these teachings can be any of a wide range of electromagnetic radiation sources, such as, but not limited to, light emitting diodes, lasers, laser diodes and other electromagnetic radiation sources.
The choice of wavelengths in embodiments of the system of these teachings is determined by an expeditious and efficient system design based on considerations such as what components are best suited for the application, availability of components and, in some cases, cost of components. There is no inherent limitation as to the choice of wavelengths in the embodiments of the system of these teachings.
In order to better illustrate the present teachings, an exemplary embodiment is disclosed hereinbelow. It should be noted that these teachings are not limited to this exemplary embodiment and that numerical values presented are presented for illustration purposes and not in order to limit the present teachings.
It should be noted that these teachings are not limited to the choice of electromagnetic radiation sources, wavelengths and detecting component used in the exemplary embodiment.
Although the exemplary embodiment shown hereinbelow relates to detecting explosives, it should be noted that other materials are also within the scope of these teachings.
The exemplary embodiment of the system of these teachings includes an infrared camera (an example of a detecting component or image acquisition component), a shortwave infrared (SWIR) camera in the exemplary embodiment, a set of laser sources (an example of electromagnetic radiation sources), laser diodes in the exemplary embodiment, that are used to illuminate the area under surveillance, and a reference photodetector that monitors the level of laser light launched by the source. In the exemplary embodiment, each laser diode has substantially a different emission wavelength within the spectral range about 0.9 to about 2 micron. The number of laser diodes can vary from 2 to 10 depending on the level of spectral identification required. The lasers are fired sequentially so that the illuminated area is bathed in light of only substantially one wavelength at a time. The individual laser diode signals are made to emit from substantially a common location to control the uniformity of illumination in the area under surveillance. This can be accomplished, in one instance, these teachings not be limited to only that instance, using fiber optic pigtailed laser diodes and a fiber optic combiner or, in another instance, constructing a laser module in which the laser diode beams all fed into a single fiber optic using a series of dichroic beamsplitters. One embodiment of the components of the system of these teachings that ensure that individual laser diodes emit from substantially one location is shown in FIG. 5. Referring to FIG. 5, in the exemplary embodiment shown therein, laser diodes (electromagnetic radiation sources) 10 are optically connected to optical components 15, fiber-optic pigtails in one embodiment, that provide the emitted electromagnetic radiation to a combiner component 20. A mode homogenizer 44 and a collimator 47 are subcomponents in the optical subsystem 40. A feedback photodiode (radiation monitoring component) 30 can detect the electromagnetic radiation provided by the collimator 47 or, in another embodiment, can detect the electromagnetic radiation provided to the combiner 20.
A block diagram representation of the exemplary embodiment of the system of these teachings is shown in FIG. 6b. Referring to FIG. 6b, in the exemplary embodiment shown therein, laser diodes 10 provide electromagnetic radiation through fiber pigtails 15 to a laser combiner 20. Electromagnetic radiation provided to the laser combiner 20 is monitored by the photodiode 30. The electromagnetic radiation provided by one laser diode 10 is delivered through the optical component 40 to area of interest. The optical component 40 includes a mode homogenizer 44 and a collimator 47. The electromagnetic radiation scattered/reflected from the area of interest is collected by the pixelated detection component 50 (a shortwave infrared (SWIR) camera in the exemplary embodiment). The pixelated data is provided to the analysis component 55.
An electronic trigger signal is used to t the laser diodes. A high-level block diagram of the electronics in the exemplary embodiment is shown in FIG. 7. The same trigger signal is also used to trigger the capture of an image with the SWIR camera and the capture of a reference photodetector 30 reading of the laser's launched power. The image is composed of a digital array of numbers representing the intensity of the light scatter from objects within the area of surveillance for the laser that was fired during its collection. Each member of the array is, in one instance, not a limitation of these teachings, a 14 bit reading acquired from a pixel of the camera's detector. A background image may also be collected to correct for any ambient light contribution to the acquired image. The reference photodetector signal is also digitized and stored along with the data array for that particular laser's image.
The number of members in the array depends on the type of camera being used. The camera in the exemplary embodiment has an array of 320 by 256 pixels; however cameras with larger or smaller arrays could also be used. The image data collected at each of the different wavelengths is treated as an array of numbers throughout the data processing steps used to generate the final result. The data processing steps are performed on a pixel-by-pixel basis across the collected images. This means that an operation like background subtraction is performed by subtracting a given pixel's value from the background image from the corresponding pixel of an image collected with the laser firing. Any operation generates a new array which contains the same number of elements as the array on which it was performed. The new array can be used to produce a new image by converting the value of each element of the array to a grey scale tint.
The laser wavelengths are selected so that a few of them coincide with regions of the spectrum where the material of interest, in one instance, explosives of interest, absorb electromagnetic radiation and others where the explosives have minimal absorption. Image data collected with the lasers having wavelengths where little to no absorption is observed are used to correct for the distance dependence of reflected light intensity (ie, for non collimated light intensity drops off in proportion to 1/r2 where r is the distance from the light source).
An embodiment of the method of these teachings is shown in FIG. 10a. In the embodiment shown in FIG. 10a, the method of these teachings includes sequentially illuminating, for a number of exposures, an area of interest with electromagnetic radiation, each exposure comprising electromagnetic radiation at substantially one wavelengths from a number of wavelengths (step 210, FIG. 10a), at least some of the number of wavelengths substantially coinciding with wavelengths in an absorption spectrum of predetermined materials, at least some exposures from the number of exposures being at different wavelengths. At a number of pixels, and at each exposure, reflected/scattered electromagnetic radiation from the area of interest is detected (step 220, FIG. 10a). A number of pixelated images are processed (step 230, FIG. 10a), the number of pixelated images being obtained by the sequentially illuminating. The number of pixelated images, after processing, constitutes a vector of processed data at each pixel from a number of pixels. At each pixel, the vector of processed data is compared to a predetermined vector corresponding to a predetermined material (step 240, FIG. 10a), presence of the predetermined material being determined by the comparison.
One embodiment of the processing and comparing steps is shown in FIG. 10b. In the embodiment shown in FIG. 10b, the processing and comparing steps include subtracting, at each pixel from the number of pixels, a background image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation (step 250, FIG. 10b), the subtraction producing a background subtracted value at said each pixel. For each pixel, the background subtracted value at said each pixel is normalized with respect to a difference between a value for the measure of emission and a measure of background electromagnetic radiation (step 260, FIG. 10b). At each pixel, a number of ratio values are obtained (step 270, FIG. 10b), each ratio value being a ratio of a background subtracted normalized value at one wavelength from the number of wavelengths to a background subtracted normalized value at a selected wavelengths from the number of wavelengths. At said each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for predetermined materials is obtained (the measure is a result of the projection of the vector of processed data onto the predetermined vector corresponding to a predetermined material), a presence of the predetermined materials being ascertainable from that measure.
In one instance, the steps of sequentially illuminating and detecting are performed using a handheld device. In one embodiment, sequentially illuminating and detecting are performed while scanning the area of interest with the handheld device. In another embodiment, sequentially illuminating and detecting are performed in a point-and-shoot manner.
The following describes one exemplary embodiment of the data processing steps taken to generate differential or ratio images and finally a multidimensional vector that can be used to distinguish the presence of materials, explosives in one embodiment, based on their unique optical absorption patterns.
It should be noted that other embodiments are within the scope of these teachings.
Data Processing
Data processing is used to identify those areas of the images where wavelength specific attenuation has occurred due to the presence of an explosive. This processing treats the images as a 2-dimensional data array and operates on the individual pixel elements of the arrays that make up the images to generate new 2-D arrays. The new 2-D arrays can be transformed back into images by mapping the individual pixel values, in one instance, not a limitation of these teachings, over a 256 step grey scale according to the pixel's value.
Step 1 Background Subtraction
The first step in data processing involves subtraction of background ambient light. This step involves subtracting the pixel value in the background image from the corresponding pixel value in each of the laser illuminated images. The result is a new image array for each wavelength wherein the pixel values are proportional to only the laser light being reflected back to the camera.
Step 2 Normalization for Laser Launch Energy
The output power of the laser diodes is only moderately controlled. Rather than providing a strict control over the actual power launched we simply measure the launch power at the end of the combiner fiber optic then normalize each background corrected image for the launch level of the laser with which the image was collected. Normalization involves dividing each pixel of the background corrected array with the signal value collected from the system's reference photodetector. The result is a new array with the same number of pixels as the background corrected image, but with each element of the array normalized to the laser output power.
Step 3 Calculating Differential or Ratio Intensity Image Data
The presence of an explosive in the area under surveillance would result in differences in the image data collected with laser wavelengths that coincide with absorption bands versus those that do not. Two simple ways to see these differences is to generate differential or ratio images. A differential image can be generated by subtracting the pixel value for each pixel of one image from the corresponding pixel values of another image collected under illumination at a different wavelength. It is important that this operation be done on corresponding pixels in the two images as each pixel contains data on the reflected light intensity for one specific region of the image plane. Alternatively, a ratio image can be generated by calculating the quotient of the pixel values for each pixel of one image and the corresponding pixel values from a second image taken at a different wavelength.
Difference images constructed by subtracting background-subtracted and normalized image data collected at an absorbing wavelength from data collected at a non absorbing wavelength will appear whiter in any area where an explosive is present. This is due to the lower pixel values in that area of the image where the optically attenuating explosive exists.
Similarly, ratio images constructed by taking the quotient of background subtracted and normalized image data at an absorbing wavelength and data collected at a non absorbing wavelength will appear darker in those areas of the image where explosives are present.
Step 4 Vector Treatment and Analysis of Image Data
Differential or ratio images can be generated using any unique combination of wavelength images collected by the system. The individual pixel values within the multiple image data sets generated by these treatments can be used to produce a single vector representation of the complete set of images. The vector is calculated by treating each differential or ratio image as a dimension in an n-dimensional space wherein “n” is the total number of unique difference or ratio images. The projection of the vector along each dimension is defined by the value of a pixel within the differential or ratio image data set. For example, assume the system is using three (3) wavelengths so there are three (3) unique ratio image data sets (1/2, 1/3, and 2/3) containing N×M pixels each. A 3-dimensional vector representation of any pixel within the three arrays can be then generated by setting the projection along each orthogonal dimension equal to the value of the pixel in the respective array. In other words, if you just look at one pixel within the array and treat the ratio 1/2 as the x-axis in a 3-dimensional (XYZ) space the value of X in our 3-dimensional space would be equal to that pixel's value in the 1/2 image data set. We could similarly set the value of the same pixel in the 1/3 image data set as the projection along the y-axis and the same pixel's value in the 2/3 image data set as the projection along the z-axis. The data for that pixel could then be defined as the vector—(X1/2, Y1/3, Z2/3) wherein the magnitude of the vector is with respect to the origin. This same calculation can be run on every pixel in the image data sets for as many unique combinations of wavelengths as the user wishes. In some cases it is better to not use all the possible permutations, but only a select subset. The selection of an optimal set of combinations requires experimentation with the spectral characteristics of the explosives of interest and spectrum from different potential interfering agents.
The vector that is formed by spectral results of differential or ratio imaging can then be used to determine if an unknown set of images contains any of the explosives of interest or not by comparing the pixel vectors (pixel-by-pixel). This process looks at the projection of the unknown image data vectors onto the known explosives vectors. This comparison can look at the direction and magnitude or just direction. The direction is relative to the known explosives vectors (angle between the two vectors). This is easily calculated using he expression:




  
    θ
    =
    
      arccos
      ⁡
      
        (
        
          
            k
            ·
            u
          
          
            
              
              k
              
            
            ⁢
            
              
              v
              
            
          
        
        )
      
    
  
  ,




where k·u is the dot product of the known explosive and unknown vectors and ∥v∥ denotes the magnitude of the vectors (square root sum of the squares for all the dimensions). Note: previously we defined the “metric” as simply the value of cos(θ). The result will only be zero (or nearly zero) when the two vectors have the same direction (ie, the two vector are from the same type of material).

An alternative treatment of the image data is to digitize it by setting a threshold value above which the differential or ratio is set equal to 1 and below which it is set equal to 0. Differential or ratio image data sets can be analyzed in much the same way as the non digitized data sets.
In one embodiment of the system of these teachings, the system includes one or more processors and one or more computer usable media that has computer readable code embodied therein, the computer readable code causing the one or more processors to execute at least a portion of the method of these teachings. The one or more processors and the one or more computer usable media are operatively connected.
An electrical and software block diagram of the exemplary embodiment is shown in FIG. 8. Referring to FIG. 8, in the embodiment shown there in, a timing component 45, PIC triggering system, provides the timing initiation signal (trigger) to the electromagnetic radiation source 10, a laser system, to the detection system 50, an InGaAs camera, and to the analysis subsystem 55. The detection system 50 provides the data to the analysis subsystem 55 by means of an input component 110, a frame grabber card, which communicates with the analysis subsystem 55 by means of a frame grabber DLL. An image analysis library 115 provides, in one embodiment, the predetermined vector corresponding to a predetermined material to the analysis subsystem 55.
Step 5 Presenting Results
The vector comparison results can be presented as a grey scale image like the simpler differential or ratio image data or thresh holding can be applied to highlight those areas of the image where the angle between the vectors would indicate a reason for concern (ie, presence of explosives identified). In the grey scale approach the absolute vector angular differences would be translated into a grey scale value wherein the grey scale values map the angular range of 0 and 180°. Setting the dark end of the grey scale equal to 0° would yield images with darker regions in the areas of the image where the vector differences were zero or nearly zero indicating the potential for the presence of explosives. Alternatively, a threshold comparison can be applied to the vector differences and only those pixels whose values are very close to zero assigned a value of 0 and all other pixels assigned a value of 1 (or vice versa). Images generated following this type of treatment would be sharply contrasted. Another, perhaps better way, to present the results would be to overlay the thresholded image results with a single image using red or a colored scale (blue to red) to highlight the values for the angular difference. The single image could be any one of the original images collected under a single wavelength illumination. The color scale could highlight in red those areas of greatest concern (very low or zero angular difference between the known and unknown vectors). One advantage to this approach is that the operator would see a full grey scaled image of the area under surveillance making it easier to identify the potential suspect or object holding the explosives.
In order to further better illustrate the present teachings, an exemplary embodiment of the data processing is disclosed hereinbelow.
The purpose of the process is to remove the ambient light effect and help to detect the materials, explosives in the exemplary embodiment. The example includes four (4) lasers from which three (3) ratio images are generated. A graphic showing how a vector is constructed in three-dimensional space from the projection of X, Y, and Z components is also provided. This graphic shows a simulated vector for an explosive (Ve) and a simulated vector for an unknown compound (Vu) having a sizeable angular difference between them.
Data Processing Method
1. Normalize the Laser Image with Photo Diode Reading
For each laser image, normalization is done using Equation 1,




  
    
      
        
          
            a
            i
          
          =
          
            
              
                
                  
                    L
                    i
                  
                  -
                  BK
                
                
                  
                    PIN
                    i
                  
                  -
                  
                    PIN
                    BK
                  
                
              
              ⁢
              
                
              
              ⁢
              i
            
            =
            1
          
        
        ,
        ...
        ⁢
        
          
        
        ,
        6
      
    
    
      
        (
        1
        )
      
    
  




where Li is the laser image, BK is the background image, PINt and PINBK are photo diode reading for laser and background, respectively. Here background image is the image acquired when no laser diode is turned on. The purpose of background image is to remove the effect of ambient light.

A background image and the raw laser image for L1 and L3 are shown in FIG. 1.
As we can see from the figure, the brightness of image for L1 and image for L3 is different. The PIN normalization is to eliminate such difference.
In FIG. 1 two DNT pouches are concealed under the two layers of clothes, however, from each single laser image, we cannot detect the DNT pouches.
2 Get the Ratios
After normalization in 2.1, N normalized frames are averaged to get āi. The ratio images are computed using Equation 2.




  
    
      
        
          
            r
            j
          
          =
          
            
              
                
                  
                    α
                    _
                  
                  i
                
                
                  
                    α
                    _
                  
                  k
                
              
              ⁢
              
                
              
              ⁢
              j
            
            =
            1
          
        
        ,
        ...
        ⁢
        
          
        
        ,
        
          4
          ⁢
          
            
          
          ⁢
          i
        
        ,
        
          k
          ∈
          
            [
            
              1
              ,
              ...
              ⁢
              
                
              
              ,
              6
            
            ]
          
        
      
    
    
      
        (
        2
        )
      
    
  




3 Find the Dynamic Ranges
For the ratios obtained in 2.1, the dynamic range is broad. To control the dynamic range to exclude outliers, we assume the ratio values are close to Gaussian distribution, which can be seen from the ratios's histogram as shown in FIG. 1. The mean rj and standard deviation σi of the ratio image are computed. Through our experiments, we choose [ rj−1.5*σj, rj+1.5*σj] as the dynamic range. The benefit is that this dynamic range is computed automatically from the ratio image itself and can adapt to the lighting changes.
4 Map the Ratios to Gray Scale Image
With the dynamic range ready, we can map the ratios to gray scale image as the final output. The mapping is done using equation (3).




  
    
      
        I
        =
        
          255
          *
          
            
              
                r
                j
              
              -
              
                (
                
                  
                    
                      r
                      _
                    
                    j
                  
                  -
                  
                    1.5
                    *
                    
                      σ
                      j
                    
                  
                
                )
              
            
            
              3
              *
              
                σ
                j
              
            
          
        
      
    
    
      
        (
        3
        )
      
    
  




After the mapping, the ratio computed by equation (2) is mapped to a gray scale image and can be detected by human eyes. FIG. 2 shows some ratio images for the case when a human subject conceals the DNT pouch under two layers of clothes.
5 Vectors from Multiple Laser Ratio
To fuse the information from individual ratio, we propose to form a vector feature from multiple ratios, as shown in equation (4).

v=(ri,rj,rk) i,j,kε[1, . . . ,4]  (4)

In such a way, the individual ratio becomes the component of the vector. Such a vector combines the information from multiple lasers and will have stronger detection capability than single ratio. An example vector given in equation (4) is shown in FIG. 4, where Ve is the vector from explosive region and Vu is from other regions. There is an angle 8 between the two vectors.
The principle for the vector based detection is: each individual ratio will generate values different for regions with and without explosive pouches. Therefore, the vectors composed of these ratios in explosive region will point to some specified direction with certain magnitude, while vectors without explosive pouches will point to some uncertain directions and magnitude. In such way, the region with explosive pouches will be detected.
While the above exemplary embodiment referred to the detection of explosives, these teaching are not limited only to detecting explosives and the method can be applied to other concealed materials.
For the purposes of describing and defining the present teachings, it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
The detection method of the present teachings is preferably performed at some finite distance from the material being detected, which is referred to as the “standoff distance”. The standoff distance could be in the range of from 1 cm to 100 m. In all cases, the material being detected may be concealed under some type of covering materials such as cloth, paper, plastic, or leather that has substantial optical absorption and/or light scattering properties which obscures viewing the concealed material under the covering material with light in the visible wavelength range (400-700 nm).
Elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions.
Each computer program may be implemented in any programming language, such as assembly language, machine language, a high-level procedural programming language, or an object-oriented programming language. The programming language may be a compiled or interpreted programming language.
Each computer program may be implemented in a computer program product tangibly embodied in a computer-readable storage device for execution by a computer processor. Method steps of the invention may be performed by a computer processor executing a program tangibly embodied on a computer-readable medium to perform functions of the invention by operating on input and generating output.
Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CDROM, any other optical medium, any physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, all of which are non-transitory. As stated in the USPTO 2005 Interim Guidelines for Examination of Patent Applications for Patent Subject Matter Eligibility, 1300 Off. Gaz. Pat. Office 142 (Nov. 22, 2005), “On the other hand, from a technological standpoint, a signal encoded with functional descriptive material is similar to a computer-readable memory encoded with functional descriptive material, in that they both create a functional interrelationship with a computer. In other words, a computer is able to execute the encoded functions, regardless of whether the format is a disk or a signal.”
Although these teachings has been described with respect to various embodiments, it should be realized these teachings is also capable of a wide variety of further and other embodiments within the spirit and scope of the claims.

## Claims

1. A system comprising:
a detecting component configured to detect incident electromagnetic radiation at a number of pixels;
a number of electromagnetic radiation sources; each electromagnetic radiation source emitting at substantially one wavelength from a number of wavelengths; at least some of the number of wavelengths substantially coinciding with wavelengths in an absorption spectrum of predetermined materials; each one of the number of the electromagnetic radiation sources sequentially illuminating an area of interest; the number of electromagnetic radiation sources emitting substantially from one location; the detecting component receiving reflected/scattered electromagnetic radiation from the area of interest;
a timing component configured to provide a signal for initiation of emission from a selected one of the number of electromagnetic radiation sources; the timing component also configured to provide said initiation signal for initiating detection by the detecting component; and
an analysis component configured to:
process a number of pixelated images, the number of pixelated images obtained by sequentially illuminating an area of interest, each sequential illumination being from one of the number of electromagnetic radiation sources, said one emitting at substantially one wavelength from the number of wavelengths; processing comprising subtracting, at each pixel from the number of pixels, a background image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation; the subtraction producing a background subtracted value at said each pixel; the number of pixelated images, after processing, constituting, at said each pixel from a number of pixels, a vector of processed data; each element of said vector at one pixel being one of a ratio or differential between a value pt one wavelength from the number of wavelengths and a value at another wavelength from the number of wavelengths; at said each pixel, thereby forming a vector of ratio or differential values at said each pixel; and
compare, at each pixel, the vector of processed data to a predetermined vector corresponding to a predetermined material;


presence of the predetermined material being determined by comparing.

2. The system of claim 1 wherein the analysis component further comprises:
a ratio intensity subcomponent configured for obtaining, at said each pixel, a number of ratio values, each ratio value being a ratio of a background subtracted value at one wavelength from the number of wavelengths to a background subtracted value at a selected wavelength from the number of wavelengths; and
a projection subcomponent configured for obtaining, at said each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for said predetermined materials;
a presence of said predetermined materials being ascertainable from said measure.

3. The system of claim 2 wherein the analysis component further comprises a normalizing component configured to normalize, for said each pixel, the background subtracted value at said each pixel with respect to a difference between a value for a measure of emission from one of the number of electromagnetic radiation sources and a measure of background electromagnetic radiation.

4. The system of claim 1 further comprising an electromagnetic emission monitoring component; wherein the timing component provides said initiation signal for initiating monitoring of electromagnetic emission from the selected one of the number of electromagnetic radiation sources.

5. The system of claim 1 wherein emission substantially from one location for the number of electromagnetic radiation sources is provided by use of an optical subsystem.

6. The system of claim 5 wherein the optical subsystem comprises fiber optic pigtails optically coupled to each electromagnetic radiation source from the number of electromagnetic radiation sources; and an optical combiner receiving radiation from the fiber optic pigtails.

7. The system of claim 5 wherein the optical subsystem comprises a number of dichroic beam splitters, each dichroic beam splitter receiving electromagnetic radiation from one or more of the number of electromagnetic radiation sources; and an optical fiber receiving electromagnetic radiation from the number of dichroic beam splitters.

8. The system of claim 1 further comprising:
a housing comprising:
a top portion;
a handle portion joined to said top portion;
said top portion having an opening at an upper end;
wherein the detecting component is disposed inside said housing and receives reflected/scattered electromagnetic radiation from the area of interest; and
wherein said number of electromagnetic radiation sources are optically disposed such that said number of electromagnetic radiation sources illuminate the area of interest through said opening;
wherein weights and dimensions of the housing and components in the housing being selected to enable the housing and components in the housing to be handheld.

9. The system of claim 8 wherein the detecting component receives electromagnetic radiation through said opening.

10. The system of claim 8 wherein the detecting component receives electromagnetic radiation through another opening.

11. The system of claim 8 wherein said weight is at most 10 pounds.

12. The system of claim 8 wherein said electromagnetic radiation sources are disposed inside said housing.

13. The system of claim 8 wherein said electromagnetic radiation sources are optically coupled to said housing.

14. The system of claim 8 wherein said handle portion is embodied in said top portion.

15. The system of claim 2 wherein said analysis component comprises:
at least one processor; and
at least one computer usable medium having computer readable code embodied therein, the computer readable code causing said at least one processor to:
subtract, at each pixel from the number of pixels, a background image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation; subtraction producing a background subtracted value at said each pixel;
obtain, at said each pixel, a number of ratio values, each ratio value being a ratio of a background subtracted value at one wavelength from the number of wavelengths to a background subtracted value at a selected wavelength from the number of wavelengths; and
obtain, at said each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for said predetermined materials;

said at least one processor and said at least one computer usable medium constituting the background subtraction subcomponent, the ratio intensity subcomponent and the projection subcomponent.

16. The system of claim 15 wherein the computer readable code further causes said at least one processor to:
normalize, for said each pixel, the background subtracted value at said each pixel with respect to a difference between a value for a measure of emission from one of the number of electromagnetic radiation sources and a measure of background electromagnetic radiation.

17. A method for detecting concealed objects, the method comprising:
sequentially illuminating, for a number of exposures, an area of interest with electromagnetic radiation; each exposure comprising electromagnetic radiation at substantially one wavelength from a number of wavelengths; at least some of the number of wavelengths substantially coinciding with wavelengths in an absorption spectrum of predetermined materials; at least some exposures from the number of exposures being at different wavelengths;
detecting, at a number of pixels, and at each exposure, reflected/scattered electromagnetic radiation from the area of interest;
processing a number of pixelated images, the number of pixelated images obtained by the sequentially illuminating; each sequential illumination being from one of the number of exposures; each exposure comprising electromagnetic radiation at said substantially one wavelength from the number of wavelengths; said processing comprising subtracting, at each pixel from the number of pixels, a back ground image pixel value from a pixel value for detected reflected/scattered electromagnetic radiation; the subtraction producing a background subtracted value at said each pixel; the number of pixelated images, after processing, constituting, at said each pixel from a number of pixels, a vector of processed data; each element of said vector at one pixel being one of a ratio or differential between a value at one wavelength from the number of wavelengths and a value at another wavelength from the number of wavelengths, at said each pixel, thereby forming a vector of ratio or differential values; at said each pixel, thereby forming a vector of ratio or differential values at said each pixel; and
comparing, at each pixel, the vector of processed data to a predetermined vector corresponding to a predetermined material;
presence of the predetermined material being determined by said comparing.

18. The method of claim 17 wherein processing and comparing further comprising:
obtaining, at said each pixel, a number of ratio values, each ratio value being a ratio of a background subtracted value at one wavelength from the number of wavelengths to a background subtracted value at a selected wavelength from the number of wavelengths; and
obtaining, at said each pixel, a measure of a portion of the number of ratio values located along predetermined values at the number of wavelengths for predetermined materials; a presence of said predetermined materials being ascertainable from said measure.

19. The method of claim 18 further comprising:
monitoring emission for each exposure; the monitoring providing a measure of emission for said each exposure;
normalizing, for said each pixel, the background subtracted value at said each pixel with respect to a difference between a value for the measure of emission and a measure of background electromagnetic radiation.

20. The method of claim 17 wherein sequentially illuminating and detecting are performed using a handheld device.

21. The method of claim 20 wherein sequentially illuminating and detecting are performed while scanning the area of interest with the handheld device.

22. The method of claim 20 wherein sequentially illuminating and detecting are performed in a point-and-shoot manner.