Abstract:
Methods and apparatus for early detection and identification of a threat such as individuals carrying hidden explosive materials, land mines on roads, etc. are disclosed. Methods comprise transmitting radar signals in the direction of a potential threat, measuring the energy in reflected signals, dynamically generating a threat threshold value from signals received from multiple areas and comparing the energy in the reflected signals corresponding to different areas to the generated threat threshold value. The threat threshold value may be generated by averaging the weighted reflected energy measured from different areas during a single scan of a region including the different areas. The contribution to the threshold from different areas is weighted in some embodiments as a function of the distance from the transmitter and/or receiver to the particular area. Analysis of areas and treating different areas as segments facilitates accurate analysis and display of threat information.

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 10/229,761 filed Aug. 28, 2002 now U.S. Pat. No. 6,720,905. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of threat detection and, more specifically, to a system and method for identifying potential threats and displaying information indicating the position of the potential threats both indoors and outdoors. 
     BACKGROUND OF THE INVENTION 
     The suicide or homicide bomber has been identified as the one threat that is virtually unstoppable. The thinking of the bomber defies all societal norms. With that being said, the logical solution to the problem would be the development of a means for detecting the bomber at a safe distance from a potential target. To date, there are no known concealed weapons or explosive detection systems available that purport to detect a concealed weapon (or weapons) or explosive devices from a distance of more than 20 yards. Reference is made to an article in the July 2002 Discover Magazine entitled “Beyond X-ray Vision” by Ivan Amato for a recent survey of the current state of the technology. Attention is also called to an article in the fall 1998 The Bridge published by the National Academy of Sciences entitled “Preventing Aircraft Bombings” by Lyle Malotky and Sandra Hyland for additional background information on the problem to be solved. 
     Almost every known detection system is electromagnetic based and requires an individual to pass through a fixed passageway. When metallic objects pass through the passageway, a warning signal is activated because a change in magnetic flux is detected. This type of system either detects or does not detect a metal object and makes no determination relative to the amount of metal present. Keys, jewelry, watches, and metal-framed eyeglasses may all trigger such a system. 
     U.S. Pat. No. 6,359,582 describes a weapons detector and method utilizing Radar in conjunction with stored spectral signatures. The system is said to be capable of measuring the self-resonant frequencies of weaponry. It is claimed that accuracies of greater than 98% can be obtained at distances, preferably between 4-15 yards. It is also claimed to be capable of detecting metal and non-metal weapons on a human body, in purses, briefcases and under clothing and discerning from objects such as belt buckles, coins, keys, calculators and cellular phones. This system has the disadvantage of relying on the presence of unique spectral signatures, which must be pre-stored or learned by a computer employing artificial intelligence techniques. 
     Another patent, U.S. Pat. No. 6,243,036, titled Signal Processing for Object Detection System describes another concealed weapon detection system. The patent describes detecting concealed weapons by calculating the difference of a pair of differences between levels of different polarized reflected energy in the time domain, and by using signal processing methods and apparatus to improve the reliability of the detection process. This technique which relies on differences between levels of different polarized reflected energy is difficult and potentially costly to implement. 
     Information at http://www.nlectc.org/virlib/InfoDetail.asp?intinfoID=201 and http://www.rl.af.mil/div/IFB/tefchtrans/datasheets/CWD-LPR.html, indicates that Lockheed Martin, under contract to the Air Force Research Laboratories and the National Institute of Justice, is in the process of developing a dual-mode (millimeter wave/infrared) camera to detect weapons concealed on an individual. The information indicates that the system will operate at a range of 10 to 40 feet, without the control or cooperation of the individual under surveillance. The described system develops images from the returned Radar energy. The image information is processed using algorithms to automatically detect and recognize concealed weapons. The detection and position information from the Radar sensor would be linked to a second sensor IR or visual camera to display the subject to authorities. 
     In addition to the above discussed detection systems, there are several new initiatives being pursued under the auspices of the Small Business Innovation Research (SBIR) program in the Concealed Weapons Detection arena. The DARPA SBIR, Topic SB022-033 entitled Personnel and Vehicular Monitoring and Tracking at a Distance seeks to “develop 3D biometric technologies as part of a multi-modal system to detect, track and recognize humans . . . at a distance to support early warning, force protection, and operations against terrorist, criminal and other human based threats.” The particular focus of this work is 3D imaging. The Army Research Office (ARO) SBIR Topic A02-061, Terahertz Interferometric Imaging Systems (TIIS) for Detection of Weapons and Explosives seeks to “develop and demonstrate a terahertz-frequency imaging array with sufficient spatial and spectral resolution to enable the rapid and effective detection of concealed weapons and explosives. The envisioned sensing system will provide real-time imaging with adequate sensitivity for the short-range remote interrogation of objects and persons that might be concealing either weapons or explosives” with a parallel focus on collecting “signature information for a set of expected targets and concealment materials.” The Army Research Lab (ARL) SBIR, Topic A02-037, Explosive Detection System, is focused on chemical signatures of explosives. Such development programs further highlight the need for improved concealed weapon detection systems. The Air Force SBIR, Topic AF03-123 entitled Hidden Threat Detection Techniques seeks to “capitalize on emerging non-contact nondestructive evaluation detection techniques as well as revolutionary concepts for sensors and detectors and tailor them to specific applications for personnel protection.” 
     In view of the above discussion, it is apparent that there is a need for new or improved systems and methods for rapidly evaluating the threat potential of an individual amongst other individuals at a relatively long distance both indoors and outdoors. It is desirable that at least some systems or methods be capable of being implemented without the need for complex signal processing thereby reducing implementation costs relative to many of the known systems. It is also desirable that the methods and/or apparatus provide an integrated, threat-driven solution to the threat detection problem discussed above. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to systems and methods for detecting and displaying information, e.g., location information, about possible threats. Threats may include, for example, individuals carrying concealed weapons, mines placed along a road or various other types of weapons. A visual representation of a region examined for threats is displayed with different areas of the region, e.g., cells, being highlighted and/or displayed differently as a function of a threat assessment made with regard to each particular area of the displayed region. Friend and foe information may be combined on the display so that areas detected to have a signal indicative of a possible threat can be designated with a friend indicator in cases where a friend identification signal has been received from the area. 
     An exemplary embodiment of a system of the present invention uses Radar to pan an environment for potential targets, measures the difference between the Radar signal level returned or reflected and exploits the difference between normal background areas and threat areas resulting from, e.g., the presence of weapons or other hardware, to present to an operator a visual representation of the examined area with potential threats highlighted using visual markers such as distinctive coloring, particular shapes, or other visual indicia of information, e.g., a potential threat, associated with the different areas which are examined. 
     In one particular exemplary embodiment, the region to be examined is divided into segments, e.g., cells, corresponding to different physical areas. The distance of the cells from the combined receiver/transmitter unit used in various exemplary embodiments of the present invention is taken into consideration when assessing the amount of detected energy returned from signals transmitted into a particular area. In various embodiments, a threat threshold is determined as a function of a weighted average of detected energy measurements corresponding to multiple areas of a region scanned during an analysis period. In generating the weighted average, energy measurements corresponding to different areas are adjusted, e.g., normalized, as a function of distance to the area from which the signals are received and the expected decrease in power as the distance increases. The weighted energy measurements are averaged to form a value which is used in generating the threat threshold for the corresponding analysis period. The weighted energy measurement corresponding to a particular area, e.g., cell, is compared to the generated threshold and a threat is declared when the returned energy for an area exceeds the dynamically generated threshold level. The threat threshold level is normally generated to be higher than the weighted energy average, e.g., by a fixed or user adjustable amount, to reduce the risk of threats being declared erroneously. 
     The method and apparatus of the present invention can be mounted on mobile devices or positioned at fixed locations. The mobile mounted embodiments can be used by trucks and/or other vehicles to identify possible roadside threats or threats which may exist in the vehicle&#39;s direction of travel. Such threats include, e.g., above ground mines, improvised explosive devices and/or other types of weapons. 
     In cases where hidden weapons on individuals is the primary concern the display may limit the visual display of information to areas, e.g., cells of a scanned region, where a human presence is detected, e.g., through the use of thermal or other information. Such an embodiment reduces clutter on the display and helps a user focus on potential threats. 
     Numerous additional features, embodiments and benefits of the methods and apparatus of the present invention are discussed below in the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary system and various signals passed between the system components in accordance with the present invention. 
         FIGS. 2   a ,  2   b  illustrate the appearance of the image display on the monitor, in the video image view, through the target acquisition process including superimposing threshold and signal strength variations on the video image for an outdoor application.  FIG. 2   c  illustrates the appearance of the image display on the monitor, in the video image view, through the target acquisition process including superimposing threshold and signal strength variations on the video image for an indoor application. 
         FIG. 3 , which comprises the combination of  FIGS. 3   a  through  3   c , is a flow chart illustrating steps performed by a System Signal Processor in accordance with the method of the present invention. 
         FIG. 4  illustrates a typical set of parameters used to implement a system in accordance with the invention. 
         FIG. 5  illustrates the appearance of the image display on the monitor, in the perspective view, through the target acquisition process including superimposing rectangles on populated cells, displaying on cells symbols identifying a friend or a foe, and the use of different colors corresponding to areas found to correspond to different threats and/or other differences in information associated with the particular cells. 
         FIG. 6 , which comprises the combination of  FIGS. 6A ,  6 B, and  6 C is a flow chart illustrating steps performed by a System Signal Processor in accordance with the method of the present invention in which the data is presented in the video image view. 
         FIG. 7 , which comprises the combination of  FIGS. 6A ,  7 B, and  7 C is a flow chart illustrating steps performed by a System Signal Processor in accordance with the method of the present invention in which the data is presented in the perspective view. 
         FIG. 8  illustrates various steps which are performed in an exemplary embodiment to dynamically generate a threat threshold to be used in analyzing different cells of a scene in an attempt to detect the presence of a threat. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the exemplary concealed weapon/explosive detection System  111  may advantageously be positioned more than 100 yards from the Scene  109  to be monitored. The system  111  includes various components  101 ,  102 ,  103 ,  104 ,  105 ,  106 ,  108 ,  133  coupled together to permit the communication and/or transmission of signals and/or control information between the elements as shown in FIG.  1  through the use of arrows. The Operator/Observer  129  interacts through Control Pad  108  to direct System Signal Processor (SSP)  106  to control each of the operator selectable options of the System  111 . The Operator/Observer  129  observes the Scene  109  by using the Monitor  102 . The Control Pad  108  allows the Operator to interact with each of the elements of the System  111  through commands to the SSP  106 . System  111  can, and in various embodiments does, implement an automated scanning process, without the need for a human operator. Also, the entire System  111  can, and in various embodiments is, fixed mounted while in other embodiments it is mounted on a vehicle or other movable platform. 
     The SSP  106 , among its other functions, advantageously processes the information received from each of the System  111  sensors (Radar  101 , Video Imaging Device  103 , “Friend or Foe” Transmitter/Receiver  105 ,) to provide near real time representation of the Scene  109  and all its calculated and determined informational tags (signal strength, distance, direction, etc). 
     In the preferred implementation of the subject system and method the Operator/Observer  129  advantageously decides the angular limits of the Scene  109  to be evaluated by viewing the Scene  109  on the Monitor  102  as presented by the Video Imaging Device  103  and inputting control instructions via Control Pad  108 . Using the Control Pad  108 , the Operator/Observer  129  causes the SSP  106  to zoom or frame-size Video Imaging Device  103  to set the angular limits of the depicted portion of Scene  109 . For the purpose of this description, some activities are described as occurring sequentially, but the preferred embodiment and utilization of the subject system will beneficially exploit many of the features and scene presentations through actual or essentially simultaneous activities of the individual components. 
     Referring to  FIGS. 1 and 2 , the Radar  101  rapidly and continuously pans over the Scene  109  as directed by SSP  106 . The SSP Radar instructions would advantageously include the lateral start and stop points to pan the selected portion of Scene  109 . The Radar  101  includes a receiver  151  and a transmitter  153 . The receiver can measure received signal values, e.g., energy values. The Video Imaging Device  103  presents a wide-angle representation of the horizontal angular width of the selected portion of Scene  109  in response to the instructions of SSP  106 , which in turn is responsive to inputs from Control Pad  108 . Alternatively, the camera and monitor could utilize the infrared band, or other non-visual portion of the frequency spectrum, for use in low-light or nighttime conditions, as an example. The Radar  101 , the Video Imaging Device  103 , the “Friend or Foe” Transmitter/Receiver  105 , and the Laser Designator  104  simultaneously “view” the Scene  109 . SSP  106  advantageously causes the center of the video image presented on the Monitor  102  to correspond to the center of the scan of the Radar  101 . However, the SSP  106  may either slave the Radar to scan the scene depicted on Monitor  102 , as directed by Operator/Observer  129 , or the Video Imaging Device  103  could be slaved to show the area being panned by the Radar  101 , wherein the Operator/Observer  129  may advantageously direct the Radar  101 &#39;s scanning area through manipulation of Control Pad  108 , and thence SSP  106  directing Radar  101 . The Radar  101  transmits its signal incrementally toward individual targets of the Scene  109  as it pans over the Scene  109 , and the Radar Signal Processor  133  measures the amount of the transmitted signal that is reflected from the Scene  109  and detected by Radar  101 . The Radar Signal Processor  133  sends the detected signal data to SSP  106 . 
       FIGS. 2   a ,  2   b ,  2   c  illustrate the appearance of the image display as it may appear on monitor  102  at different points during the target acquisition process. The SSP  106  may advantageously calculate the average of the detected signals from Scene  109 , hereinafter the Average Detected Signals  204  (of FIG.  2 ). Said average may be an average, e.g. of signal power or some other signal value such as a detected signal amplitude or intensity, which is a function of the detected returned signal. The average detected Radar return signal is calculated by utilizing the reflected signal data at each incremental pointing angle of Radar  101  or at least a plurality, e.g., majority of the pointing angles, from the leftmost to the rightmost extreme of the portion of Scene  109  being scanned. Since, in the exemplary embodiment, the Radar  101  pans over the Scene  109  at a uniform rate, the SSP  106  samples the detected reflected signal data across the scene and calculates and re-adjusts the Average Detected Signals  204  for every Radar  101  pan over the Scene  109 . The SSP  106  next calculates a threshold at a pre-determined amount above the Average Detected Signals. Alternatively, the threshold could be arbitrarily selected by the user/operator. Also, a user-selected reference line could be implemented in place of Average Detected Signals  204 . The SSP  106  causes the Monitor  102  to depict the Average Detected Signals  204  and the value of the threshold  201  on Monitor  102 . The pre-determined amount above the Average Detected Signals  204  may be user selectable. A level of 10 times (10 dB) the Average Detected Signals is a beneficial nominal amount and is an exemplary value that can be used. 
     The SSP  106  causes Monitor  102  to simultaneously depict the detected signals as a varying continuum  206  superimposed on the pictured Scene  210  as well as the Average Detected Signals  204  and the threshold  201 . 
       FIG. 2   a  represents the pictured Scene  210 , which may be a portion of Scene  109  of  FIG. 1 , as it is presented on the Monitor  102  to the Operator/Observer  129  and which also represents the area scanned by Radar  101 . At any given time, the Scene  210  includes candidate, or potential threats  203 . The reflected signal data is advantageously represented on the vertical axis  212  as a level relative to the Average Detected Signals in dB. (A level higher by 3 dB represents twice as much signal; a level higher by 10 dB represents ten times as much signal). SSP  106  causes Monitor  102  to superimpose the detected signal  206  over the Individuals  203  by synching the aiming direction of Radar  101  with the associated position on horizontal axis  211  on the Monitor  102 . The horizontal axis  211  is the angular limit of pictured Scene  210  as selected by the Operator/Observer  129 . Whenever the detected signal  204  exceeds the threshold  201 , the SSP  106  notes the Radar  101  aiming direction (the Noted Position  208  in  FIG. 2   b ) within the scanned Scene  210 . In  FIG. 2B , by way of example, the detected signals  204  data reaches a peak at the Noted Position  208  at which the threat appears, and is superimposed on the image of the threatening Individual at the Noted Position  208 .  FIG. 2   b  further depicts a “picture in picture” image which is displayed by SSP  106  on Monitor  102 , for each noted position, and is thereby presented to the Operator/Observer  129  on Monitor  102 . The Individual at Noted Position  208  appears in the inset box  207  (“picture in picture”) and the Noted Position  208  is marked on the pictured Scene  210  as directed by SSP  106 . SSP  106  may also advantageously activate a visual, aural, or other alarm (not shown) at this time. 
     SSP  106  also uses the Noted Position  208  to cause the “Friend or Foe” Transmitter/Receiver  105  ( FIG. 1 ) to transmit an interrogation signal in that direction. If the Individual  128  is equipped with a correctly configured “Friend or Foe” Transponder  107 , e.g., one equipped with the proper response codes, the response is transmitted by “Friend or Foe” Transponder  107  to “Friend or Foe” Transmitter/Receiver  105 , which will send a message indicating “Friend” to SSP  106 . SSP  106  will thereupon cause Monitor  102  to superimpose the “Friend” response on the Monitor  102  at a position in the picture corresponding to the Noted Position  208 . Further, the “picture in picture” could then be deactivated by SSP  106  via another Monitor  102  instruction. If the Individual is not so equipped, the SSP  106  does not receive the transponder message indicating “Friend”, and thereupon directs the Laser Designator  104  to be pointed at and to illuminate the Individual  128  by aiming in correspondence to the Noted Position  208  and activating the laser beam. Alternatively, an illuminating beam of a wavelength not visible to the naked eye could be used instead of a laser, so that a viewer wearing special eye pieces, or viewing a specialized monitor screen, could see the target of the illumination, but the subject of the illumination would not know that he was being so targeted. By virtue of an advantageous embodiment of the Radar  101 , the distance to the target is obtained simultaneously with the resultant reflected energy from the target and that distance is passed to SSP  106 , and SSP  106  causes Monitor  102  to display the distance measurement at the Noted Position  208 , which would effectively label the target on the Monitor  102 , as depicted in  FIGS. 2   b  and  2   c.    
     The Radar  101  continues to pan over the Scene  109  and the Radar  101  will re-detect and constantly update the location of a detected signal in excess of the threshold, and will automatically note the position of this signal, which will be different than the original Noted Position  208 , if the target has moved. The Video Imaging Device  103  and Monitor  102  continue to present the wide-angle view of the Scene  210  and Laser Designator  104 , “Friend or Foe” Transmitter/Receiver  105  are directed by SSP  106  to aim at the new Noted Position  208 , continuously refreshing the data and image presentation at each new Noted Position  208 , effectively “following” the targeted Individual  128  who caused the threshold to be exceeded. The pan rate of the Radar  101  over the Scene  109  is rapid enough to allow the light of the Laser Designator  104  to appear to the Operator/Observer  129  to be stationary on each designated Individual  128  (visual persistence). If other Individuals  128  are determined to be threats (additional signal returns from a position more than a prescribed amount from the first Noted Position  208 , advantageously two feet, exceed the threshold) the SSP  106  will create an additional “picture in picture” of the additional Noted Position (not shown) on the Monitor  102 , marking each threat by Laser Designator  104 , and noting on Monitor  102  the Distance and video image markers at each new Noted Position. 
     The reflected detected signal that results from the illumination of the potential threatening individual by the narrow beam Radar is likely to be greatest when there are metal objects present. The more metal objects, the greater the signal reflected. Metal objects with corners, like nails that are used to augment the killing power of an explosive device, provide a greater signal. Metal objects that are spherical like bearings or cylindrical-like bullets, also reflect greater signals. The present invention does not require pre-stored or learned signatures. The present invention establishes a reference signal threshold (Average Detected Signals) in real time from the pictured Scene  210  and relies on the fact that the aforementioned metal or other reflective objects are likely to reflect sufficient energy to exceed that threshold whereas a few incidental metal objects carried by an innocent individual is not likely to exceed the threshold. The use of the video imaging system permits the operator to distinguish between individuals carrying weapons in the open from those carrying concealed weapons and/or explosives. 
     The narrow beam Radar provides range to the target and velocity of the target. Several techniques well known to those skilled in the art can, and in various embodiments are, used to augment the signal return. Examples of such techniques include circular polarization and multi-frequency transmissions. In addition, a high range resolution mode of operation (short pulse or other means), could provide additional discrimination data within the populated cell. The Radar beam should be narrow enough to be able to isolate an individual from other individuals, but wide enough to encompass the whole individual. Dependent upon scenarios presented by the user community, the parameter specifications for the Radar will be determined. The signal strength returned from the target is proportional to the size of the antenna, the frequency of the Radar, the power transmitted as well as the distance to the target and the reflectance of the target. Various features of the present invention are directed to one or more of the following long range detection of the threat, minimal signal processing, self-calibration, no requirement that the system be re-trained for each new weapon or configuration, low cost, light weight and simplicity of operation (including both manual and automatic modes). 
       FIG. 3  which comprises the combination of  FIGS. 3   a ,  3   b  and  3   c , illustrates the System Signal Processor (SSP) process flow of the invention. Referring to  FIG. 3   a , the SSP  106  receives input from the operator at step  301 , and in response to the input, controls the camera aiming direction and the size of the photographed scene (zoom) in step  302 . The SSP then causes the Radar scan limits to be in accordance with the camera&#39;s aiming direction and zoom setting in step  303 . In steps  304  and  305 , the SSP  106  causes the Radar  101  to pan according to the scan limits and transmit a continuous signal, and causes the Monitor  102  to display the picture as photographed by the camera  103 . The SSP  106  receives the detected signal data from the Radar  101  in step  306 . 
     Referring to  FIG. 3   b , the SSP  106  next calculates the average of the received detected levels and the threshold in step  307 , and in steps  308  and  309  causes the average and the threshold to be superimposed on the Monitor  102 , advantageously as straight horizontal lines. In step  310 , the SSP  106  causes the detected levels to be superimposed on the Monitor  102 , corresponding to the Radar aiming direction at the time of each detected level, advantageously as a curved line or as a plurality of short connected lines. In step  323 , the SSP  106  checks to see if new operator input had been received, and if so, returns to step  301 . If not, it proceeds to step  311 , wherein it determines if the detected level exceeded the threshold. If not, it returns to step  307 . If so, it proceeds to step  312 . 
     Referring to  FIG. 3   c , in step  312 , the SSP  106  causes the “Friend or Foe” transmitter  105  to transmit an interrogation signal in the direction that the Radar  101  was presently aimed corresponding to the Noted Position, and in step  313  the SSP  106  receives the response signal (if any) from the transmitter  101 . In step  314 , the SSP determines whether there was a pre-determined “Friend” response, and if so, classifies the target as “Friend” and proceeds to step  315 , where the SSP superimposes the “Friend” response on the Monitor at the Noted Position corresponding to the time of the threshold being exceeded and then returns to step  307 . 
     If the pre-determined “Friend” response is not detected in step  314 , the SSP  106  next causes the laser  104  to illuminate in the Radar aiming direction corresponding to the Noted Position at step  316 . The SSP  106  obtains the distance to the object in the Radar aiming direction in step  317 , and in step  318  superimpose that distance on the Monitor  102  at the Noted Position. Next, in step  319  the SSP frames the image at approximately the size of a human at the Noted Position and in step  320  inserts that framed image as a “picture in picture” in a corner of the Monitor  102 . Simultaneously, the SSP  106  marks the Noted Position on the primary display of the Monitor  102  at step  321 . Then in step  322  the SSP  106  updates the Noted Position information. In step  322 , if another detected signal exceeds the threshold near the Noted Position, the SSP  106  would replace the old Noted Position with the subsequent Noted Position. If the next Noted Position is not near the first Noted Position, then the SSP  106  would treat that next Noted Position as an additional Noted Position on the Monitor  102 , including using an additional picture in picture for that Noted Position. From step  322  the SSP  106  returns to step  307 . 
       FIG. 4  illustrates an exemplary set  400  of design parameters. Parameters  413  and corresponding exemplary values  414  are illustrated in the left and right columns, respectively. The exemplary values were selected with practical considerations in mind. Such considerations include the availability of components, acceptable operating frequencies, an antenna size that is manageable, beamwidths that are narrow enough to pinpoint the target, power levels that are safe, etc. The frequency, 95 Ghz  401 , f, is selected from the historical possibilities that were initially determined by analysis to be least affected by atmospheric conditions. The frequency should be high enough for the resultant antenna size to be small enough to be portable and narrow-beamed to encompass a man-size target. In other embodiments for fixed installation, i.e., not portable, or different design distances, different frequencies can be chosen. Since this class of frequencies has been used extensively, components are widely available. The wavelength,  402 , λ, is calculated from the frequency. The antenna gain  403 , G, is derived from size of the antenna  409 , which is based on the beamwidth  408 , α, selected to encompass the target. The antenna efficiency factor  410 , η, is based on the electric field distribution over the antenna and the total radiation efficiency associated with various losses, including spillover, ohmic heating, phase nonuniformity, blockage, surface roughness, etc. and is typically equal to 55 percent. The Radar receiver bandwidth  404 , B, is advantageously selected to be 475 MHz or 0.5 per cent and is a design parameter. It is defined as the frequency spread around the center frequency where the receiver response to an input no more than half that at the peak center frequency. Noise  FIG. 405 , N F , is a measure of the sensitivity of the Radar Receiver and is a design parameter. For an inexpensive receiver a Noise Figure of 5 dB is assumed. The Losses  406 , L T , is defined as the loss between the transmitter and antenna, receiver and antenna and other unexplained losses. A good “catch-all” value that has empirical basis is 4 dB. The Peak Transmitted Power  407 , P T , advantageously at 0.1 watt is selected to be as low as practicable to minimize unnecessary exposure of the innocent population and is a design parameter. The distance to the target  411  is advantageously selected to be 100 meters and is a design parameter, which in conjunction with the height of the anticipated target  412  of 2 meters drives much of the Radar design. 
     The calculation of the signal strength and the signal strength dependencies as set forth below describe how the exemplary set of design parameters of  FIG. 4  determine the performance of the system and how some of the design parameters are determined from the exemplary system requirements. The energy reflected from a target competes with background noise from many sources. The Radar Range Equation rearranged to calculate Signal to Noise Ratio 
           P   T     ⁢     G   2     ⁢     λ   2     ⁢   σ           (     4   ⁢           ⁢   π     )     3     ⁢     R   4     ⁢     KT   0     ⁢     BN   F     ⁢     L   T           
 
explains the ability of Radar to detect a target. The signal to noise ratio is directly proportional to the Transmitted Power  407 , P T , the square of the Antenna Gain  403 , G, the square of the Wavelength  402 , λ, and the Radar Cross Section of the target, σ, and inversely proportional to the fourth power of the Distance to the target  411 , R, the Bandwidth of the Receiver  404 , B, the Noise  FIG. 405 , N F , and miscellaneous Losses  406 , L T . The calculation of the Signal to Noise Ratio for an embodiment of the subject invention as beneficially described by the result of substituting the parameters of  FIG. 4  in the above described Radar Range Equation is 3.6 dB or 2.3 times more than the noise present in the system. Since the target for the subject invention is an individual, the length of the arc at a distance to the target should encompass the height of an individual. Assuming an exemplary 2 meter tall individual, the calculation determines the resultant angle or beamwidth to be 1.15 degrees, for an exemplary distance to the individual of 100 meters. The beamwidth determines the diameter of the antenna at the exemplary frequency of 95 GHz to be 0.193 meters based on the relationship understood by those skilled in the art to be Diameter, D, equals a constant factor, typically 1.22, times the speed of light, c, and divided by the product of the beamwidth and the frequency, f, beneficially represented as 
       D   =       1.22   ⁢     (   c   )           (   f   )     ⁢     (   Beamwidth   )             
 
The Gain of the antenna, G, given the exemplary frequency of 95 GHz, a Diameter, D, of 0.193 meters, is determined based on the relationship understood by those skilled in the art to be equal to an antenna efficiency factor, η, typically 55%, times the product of the parameter pi, π, the antenna diameter, D, times the frequency, f, divided by the speed of light, c, all to the second power beneficially represented as
 
 G =η(π Df/c ) 2 
 
It should be noted that a pointing accuracy of one-tenth the beamwidth is a reasonable expectation.
 
     Additional exemplary embodiments of the invention will now be discussed in which a region to be examined for possible threats is treated as being comprised of a plurality of cells, e.g., cells having different range and azimuth relationships to the transmitter, receiver and/or a combined receiver transmitter commonly used in various embodiments of the invention to implement Radar  101 . In these additional embodiments the average detected Radar return signal for each cell is beneficially calculated by utilizing the reflected signals from each populated range-azimuth cell, as modified by a range attenuation factor corresponding to the particular cell from which the signals are received. In this manner, range is taken into consideration when processing signals from different cells with weighting being used to perform what may be described as a normalization process so that returned energy from different cells can be used in generating a threshold suitable for detecting a threat in any of the cells being examined. As will be discussed below, in several cell embodiments, the SSP  106  sums the modified detected reflected signal data, e.g., weighted measured energy values for different cells or a beneficially selected subset of the cells in the scene being examined, and calculates and re-adjusts an Average Detected Signal, e.g., average energy value generated by the weighted measured energy values, for every Radar  101  cycle over the Scene  109 . The subset of cells in the scene may be, e.g., human populated cells and/or cells populated by items believed to pose a potential threat such as land mines or other military equipment. In the cell embodiments, as will be discussed further below, the SSP  106  calculates a threat threshold from the weighted detected energy values, e.g., by adding user selected or pre-determined offset amount to the average energy value determined from the range adjusted detected energy values corresponding to one or more cells. Alternatively, the threat threshold could be arbitrarily selected by the user/operator  129 . 
     Assuming  FIG. 2   b  corresponds to a multi-cell implementation, by way of example, the populated range-azimuth cell corresponding to Noted Position  208  has a returned detected signal energy level which exceeds the generated threat threshold thereby providing a way to detect the cell in which the exemplary threat appears. 
     In some embodiments, the operator selectively aims the Radar  101  and/or camera  103  at a person who appears on the monitor  102  and the SSP  106  then causes the Radar  101  to transmit in the direction of that person. The SSP  106  receives the detected signal data from the Radar  101  and performs a threat analysis with the results being superimposed on the displayed image on the monitor  102  which includes the visual image of the person and corresponding region at which the radar  101  or camera  103  were pointed. 
       FIGS. 2   a  and  2   b  illustrates the appearance of an exemplary image display on the monitor of an outdoor scene, at the completion of a target acquisition process which includes superimposing a cross-hair  214  on the video image as shown in  FIGS. 2   a  and  2   b .  FIG. 2   c  illustrates the appearance of an exemplary image display  221  on the monitor of an indoor scene that may be generated in accordance with the invention. The view provided in exemplary images of  FIGS. 2   a    2   b  and  2   c  shall hereinafter be referred to as a video image view. 
     In another embodiment of the invention, an alternative visual display format for displaying information about a scanned region is used. In this alternative format, shown in  FIG. 5 , a perspective view, e.g., “bird&#39;s-eye” view is used. With the perspective view presentation, the scene  109  is subdivided into cells, each cell corresponding to a different distance and/or angle, e.g., azimuth, from the transmitter and/or signal detector included in Radar  101 . Those range azimuth cells which are populated are highlighted as an array of rectangles, e.g. a rectangle with grid lines. Each populated range azimuth cell is further classified, and color-coded and/or symbolically-coded to allow the operator  129  to quickly distinguish between targets and identify threats. 
       FIG. 5  illustrates a radar  509  covering a field of view  511 , either indoor or outdoor, and displaying information collected on a screen display  501 , subdivided into range azimuth cells  503 ,  505 ,  507 . Each area of the rectangular portion of visual display  501  corresponds to a different area, e.g., cell, of a scanned region. The radar may be coordinated with a camera aiming direction and zoom setting. The radar may pan within its controlled setting automatically. The radar may also be selectively controlled and aimed by an operator to point at a specific target, e.g. a suspected terrorist. The bottom of the screen display  513  corresponds to the minimum range of radar coverage used for evaluation and presentation, while the top of the screen display  515  corresponds to the maximum range of radar coverage used for evaluation and presentation. Some of the range azimuth cells of screen display  501  may be populated, assuming the radar has acquired targets within its designated coverage area.  FIG. 5  includes such exemplary populated range azimuth cells,  505 ,  507 ,  503 . Each populated range azimuth cell appears on screen display  501  as an array of rectangles, the location of each array of rectangles on the screen in relation to the minimum range  513 , maximum range  515 , and azimuth with respect to the radar field of view  511  definition, can be used to determine the position of the populated range azimuth cell, e.g. acquired target. Each identified populated range azimuth cell displayed in the threat arena, has been highlighted, in accordance with the invention, with a symbolic code and/or color for identification. In the particular example, display of populated cells is limited to cells populated with at least one human being. However, in mine detection and/or other applications displayed populated cells may include cells populated with a device such as a weapon which may pose a security threat. 
     Exemplary rectangle  505  shown with grid lines and with no symbolic overlay, represents a bystander. Rectangle  507  shown with a smiley face superimposed on the grid lines represents an identified friend, rectangles  507  are colored green in some embodiments. Rectangle  503  shown with shaded diamonds superimposed on the grid lines represents a terrorist; rectangles  503  are colored red in some embodiments to distinguish them through the use of color from other cells. The  FIG. 5  illustration may, and sometimes is, superimposed on an image of the region being examined provided by a camera or by a stored map whose location registration is obtained e.g., by Global Positioning Satellite system tags, by a forward observer designation, by reference to known landmarks, or some other known technique. 
     Each of the various exemplary cell based detection methods of the present invention can support a “video image” view and a “perspective” view.  FIGS. 6 and 7  may be used to illustrate the steps performed by a System Signal Processor  106  in accordance with various method of the present invention.  FIG. 6  comprises the combination of  FIGS. 6A ,  6 B, and  6 C.  FIG. 7  comprises the combination of  FIGS. 6A ,  7 B and  7 C. Both embodiments use the exemplary set of threat threshold determination steps shown in FIG.  8 . 
     In the embodiment of the process flow of  FIGS. 6 and 7 , the previously described two different innovative representations, video image view and perspective view, of the threat environment are both possible with the user being able to switch between information presentation formats through the use of user input, e.g., entry of a command or pressing a button. 
     Regardless of the information display format, the SSP  106  calculates the returned energy content of the Scene  109  for the various cells. In various embodiments, the SSP  106  beneficially causes the Monitor  102  to display the previously described rectangles corresponding to the locations of the populated range-azimuth cells. The rectangular grids may be, and often are, superimposed on a camera image of the area being examined. The cell or cells corresponding to an individual whose returned signal is determined to be indicative of an individual who is wearing or carrying explosives or weapons, i.e., a threatening individual, would be advantageously color-coded red or by other means symbolically delineated. In some embodiments, the populated range-azimuth cells corresponding to non-threatening individuals would be advantageously color-coded green or by other means symbolically delineated. A populated range-azimuth cell whose return exceeded the established threshold but returned a Friend indication in response to an interrogation system would be advantageously color-coded green or by other means symbolically delineated, including an indication that the cell corresponds to an ally. 
     The flow chart in  FIG. 6  will be described with reference to the video image display option wherein image areas corresponding to cells have grids superimposed thereon. Referring to  FIG. 6A , the SSP  106  receives input from the operator in step  601 , and in response to the input, controls the camera aiming direction, and the size of the photographed scene (zoom) in step  602 . The SSP  106  then causes the Radar scan limits to be in accordance with the camera&#39;s aiming direction and zoom settings in step  603 . Thus, the region being scanned corresponds to the camera viewing area and the area into which radar signals are transmitted. In step  604  and  605 , the SSP  106  causes the radar  101  to pan according to the scan limits and transmit a continuous signal; the SSP  106  also causes the monitor  102  to display the picture as photographed by the camera  103 . In step  608 , the SSP  106  causes the radar  101  to transmit at each image in the field of view. In step  607 , the operator may also selectively aim the radar  101  at a person to be monitored, in which case the SSP  106  in step  609  causes the radar  101  to transmit in the direction of the selected person. In step  606 , the SSP  106  receives the detected signal from the radar  101  which may come from: the radar pan of step  604 , the radar directed at the images within the field of view of step  608 , or the radar directed by operator targeting a person of step  609 . The SSP  106  coordinates the transmitted signal with the received signal so as to be able to correlate received levels with specific range-azimuth cells, e.g., different areas of a scanned region. 
     Referring to  FIG. 6B , the SSP  106  next dynamically calculates the average of the received detected levels for each of the populated range-azimuth cells and the threat threshold in step  610 . The threat threshold may be generated by averaging the detected energy corresponding to different cells after weighting the measured energy corresponding to the different cells as a function of the distance the radar signal traveled before reaching the detector of Radar  101 . 
     Referring now briefly to  FIG. 8 , an exemplary set of steps which can be used to implement the threat threshold determination step  610  are shown. The threat determination step starts in node  612 . Then, in step  614  a signal characteristic, e.g., energy, in the detected reflected signals corresponding to each cell is measured to produce a measured signal value. This results in a measured signal value, e.g., a detected energy measurement value, for each cell. Next, in step  616  the detected energy measurement value corresponding to each of the cells is modified according to the distance of the cell to which a measurement value corresponds from the receiver (detector), transmitter and/or combined receiver/transmitter. This modification may be performed by multiplying an energy measurement value by a factor which is determined as a function of distance. Such a factor can be described as a distance factor since it is a function of the distance to the cell of interest. For example, measurements corresponding to cells furthest away may be multiplied by a maximum factor which is greater than one while closer cells are multiplied by smaller factors. The closest cells are multiplied by the smallest factors to take into consideration that the signals from these near cells should be the strongest since they have to travel the shortest distance. In this manner, detected energy values from different cells can be normalized for comparison purposes by taking into consideration the effect of the distance on the detected amount of energy. The energy measurement value modification process performed in step  616  produces a set of modified measured detected energy values, e.g., one per cell. 
     From step  616  operation proceeds to step  618  wherein a threat reference threshold is generated from the modified measured detected energy values corresponding to one or more cells. It should be noted that in steps  616  and  618  all values need not be used. For example, exceptionally high or low values may be discarded and/or values corresponding to cells with known unusual radar characteristics may also be discarded. Thus, the threat threshold may be generated from a particular subset of the values corresponding to the cells which have been scanned, e.g., values corresponding to populated cells. In step  618 , in the exemplary embodiment, the modified measured detected energy values are averaged to generate an average detected modified energy value to which a user selected or pre-selected offset is added to generate the threat threshold used to analyze the cells during the particular scan period. With the threat threshold determined, the threat threshold determination processing stops as indicated in node  620 . 
     Referring once again to  FIG. 6 , with the threat threshold having been determined in step  610 , operation proceeds to step  611 . In step  611 , the SSP  106  checks to see if new operator input had been received, and if so, returns to step  601 . If there has not been new operator input, operation proceeds to step  612 , wherein the SSP  106  determines if the detected level has exceeded the threshold. If the detected level has not exceeded the threshold, the SSP  106  takes no declarative action in step  623 , returns to step  610 , and continues to calculate the average of the detected levels for each populated range-azimuth cell and the threshold. If the detected level has exceeded the threshold, operation proceeds to step  613 . 
     Referring to  FIG. 6C , in step  613 , the SSP  106  causes the “Friend or Foe” transmitter to transmit an interrogation signal in the direction of the suspect terrorist, e.g., the direction of the populated range-azimuth cell that has exceeded the threshold, and in step  614  the SSP  106  receives the response signal, if any. In step  615 , the SSP  106  determines whether there was a pre-determined “Friend” response, and if so, classifies the target as “Friend” and proceeds to step  622 , where the SSP  106  superimposes the “Friend” marker on the Monitor  102  at the Noted Position corresponding to the time of the threshold being exceeded and then returns to step  610 . 
     If the pre-determined “Friend” response is not detected in step  615 , the SSP  106  superimposes a cross-hair on the terrorist image on the monitor  102  in step  616 . Next, in step  617  the SSP  106  causes the laser designator  104  to illuminate the cross-hair marked terrorist. In step  618  the SSP  106  superimposes distance on the Monitor  102  at the Noted Position. Next, the SSP  106  frames the image at approximately the size of a human at the Noted Position and in step  619  inserts that framed image as a “picture in picture” in a corner of the Monitor  102 . Simultaneously, the SSP  106  marks the Noted Position on the primary display of the Monitor  102  at step  621 . From step  621  the SSP  106  returns to step  610 . 
       FIG. 7  shows the steps associated with generating the perspective view illustrated in FIG.  5 .  FIG. 7  comprises the combination of  FIGS. 6A ,  7 B and  7 C. Accordingly, the initial processing is as already described in regard to  FIG. 6  but with the processing proceeding from step  606  of  FIG. 6A  to step  610  of FIG.  7 B. Referring to  FIG. 7B , the SSP  106  dynamically calculates the threat threshold in step  610  from the average energy of the received detected returned signal for some or all of the range-azimuth cells, e.g., the populated cells, as modified to reflect the effect of different cell distances on the returned energy from various cells. In step  725  the SSP  106  positions the aforementioned rectangles on the monitor  102  corresponding to the location in the scene of the populated cells. In step  711 , the SSP  106  checks to see if new operator input had been received, and if so, returns to step  601 . If new operator input has not been received, operation proceeds to step  712 , wherein the SSP  106  determines if the detected level for each range-azimuth cell exceeded the threshold. If not, it colors the corresponding rectangle “green” in step  724  and returns to step  710  and continues to calculate the average of the detected levels for each populated range-azimuth cell and the threshold. If yes, it proceeds to step  713 . 
     Referring to  FIG. 7C , in step  713 , the SSP  106  causes the “Friend or Foe” transmitter to transmit an interrogation signal at the suspect terrorist. Proceeding to step  714 , the SSP  106  interprets the received response, if any, to the “Friend or Foe” interrogation signal. In step  715 , the SSP  106  determines whether there was a pre-determined “Friend” response, and if so, classifies the target as “Friend” and proceeds to step  728 . In step  728  the SSP  106  identifies the cell as a “Friend” on the perspective display by coloring the cell green and superimposing the “Friend” marker on the cell located at the Noted Position corresponding to the populated range-azimuth cell that had exceeded the threshold, yet returned an acceptable “Friend” identification response signal. From step  728  operation returns to step  710 , where the monitoring process continues. 
     If the pre-determined “Friend” response is not detected in step  715 , the SSP  106  next changes the color of the populated cell to red in step  726  and superimposes the “Terrorist” marker on the cell. The SSP  106  next causes the laser designator  104  to illuminate the red designated terrorist by directing the laser designator  104  in the Radar aiming direction corresponding to the Noted Position at step  729 . Next, in step  730 , the SSP  106  superimposes distance on the view at the noted position. 
     While the initial embodiments have been particularly shown and described with reference to the specific application of homicide bomber detection, it will be understood by those skilled in the art that other embodiments and/or various changes in form and detail, including tradeoffs of Radar design parameter selection, may be made therein without departing from the spirit and scope of the invention and that other applications are addressable with the spirit and scope of the invention. Other applications include perimeter security, side-attack mines (off-route mine detection), through-the-car window vehicle check-point occupant threat assessment and personnel detection and warning for perimeter, ambush and casualty detection. In various implementations, different visual identifiers may be used for different types of detected threats, e.g., mines may be indicated on a display differently from a human who is determined to be armed. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail, including tradeoffs of Radar design parameter selection, may be made therein without departing from the spirit and scope of the invention.