Abstract:
A device and method for detection of buried objects ( 40 ) utilizing a down looking infrared array ( 140 ) having infrared detectors ( 170 ) positioned in a sensor array ( 30 ). This sensor array ( 30 ) may also contain ground penetrating radar ( 70 ) and EMI coils ( 80 ). All signals from the ground penetrating radar ( 70 ), EMI coils ( 80 ) and down looking infrared array ( 140 ) may be combined to generate alarms ( 1100 ). However, the down looking infrared array ( 140 ) may be utilized as a sole means of detecting buried objects ( 40 ). This device and method for detecting buried objects ( 40 ) utilizing down looking infrared array ( 140 ) reduces the cost of construction and maintenance of such a device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a system and method for detection of buried objects. More particularly, this system and method utilizes down-looking infrared (DLIR) sensors with or without ground penetrating radar (GPR) and metal detectors (MD) to locate landmines buried beneath ground level. 
     2. Discussion of the Related Art 
     Today landmines have become an enormous problem for both military forces and civilian populations. Unlike the landmines utilized during World War II and before, today&#39;s landmines may not necessarily be made of metal that can be easily detected by metal detectors. Very often these landmines may be made of plastic or other materials that are difficult to differentiate from the surrounding soil or other naturally occurring phenomena. Further, in the case of antitank mines, these mines may be buried relatively deep in the to ground, such as six inches or more. These antitank landmines are designed and positioned in the ground so that the weight of a person would not activate the mine. However, the weight of a vehicle would in most cases set off the mine. Of course, setting off such an antitank mine may also be caused by a tractor plowing a field long after the war is over. 
     Therefore, the military and other agencies have long desired a mechanism by which buried landmines may be detected and neutralized. One such mechanism is illustrated in FIG.  1  and was known as the Close-In Detection (CID) System, developed under the Mine Hunter/Killer (MH/K) advanced technology demonstration program for the United States military by TRW and subcontractors to TRW. The CID System comprises a vehicle  10  on which a sensor array  30  is attached to the front thereof. This sensor array  30  would be mounted to vehicle  10  by hydraulic lifts and would contain metal detectors (MD) as well as ground penetrating radar (GPR). In addition, a forward-looking infrared (FLIR) camera  20  would be mounted to the top of the vehicle  10  and aimed to cover a trapezoidal area  50  in front of the vehicle  10  and sensor array  30 . The FLIR  20  as well as sensor array  30  would detect objects  40  positioned below the ground  60 . The information from both the sensor array  30  and FLIR  20  may be combined to identify objects  40 . The design and operation of the CID System is further detailed in a paper presented in April, 2001 at the SPIE AeroSense Conference 4394: Detection &amp; Remediation Technologies for Mines and Minelike Targets VI, by S. Bishop et al. entitled “Improved Close-In Detection for the Mine Hunter/Killer System”, incorporated herein in its entirety by reference. 
       FIG. 2  is a top view of the CID System shown in FIG.  1  and also shows the FLIR field  50 , vehicle  10  and sensor array  30 . In addition, sensor array  30  is shown containing GPR  70  sensors and electromagnetic induction (EMI) coils  80  that act as metal detectors. 
     However, the CID System shown in  FIGS. 1 and 2  has several drawbacks directly related to the FLIR  20 . First, the FLIR  20  is a relatively expensive and complex piece of equipment due to the lens system and IR detectors contained therein. The FLIR  20  may cost as much as 50 percent or more of the cost of the vehicle  10  itself. Thus, repair and replacement of the FLIR  20  camera is also expensive. In addition, since the FLIR  20  camera views the FLIR field  50  in front of sensor array  30 , the unification of the respective images to identify landmines located beneath ground  60  adds another layer of complexity to the system. 
     Still further,  FIGS. 3A ,  3 B, and  3 C are similar to the CID System shown in  FIG. 1  with the exception that difficulties due to the usage of the FLIR  20  are more clearly illustrated. In  FIG. 3A , a misalignment of FLIR  20  camera by as little as one degree will create a one foot placement error in the FLIR field  50  that would result in a one foot displacement of any buried objects  40  detected. Therefore, proper calibration of the FLIR  20  camera is absolutely essential for accurate identification of buried objects  40 . Of course, in a military vehicle, such as vehicle  10 , off road usage, or simply rough roads, will necessitate the frequent realignment of the FLIR  20  camera. This may be particular the case in an active combat area. 
       FIG. 3B  further illustrates how a rough road having a bump as small as 2 and ¼ inches will cause a one-foot placement error in the FLIR field  50 . Of course, a similar sized pothole would also generate a similar displacement error. Since bumps and potholes are frequent occurrences even in the best road systems, the accuracy of the FLIR  20  camera would be compromised. 
       FIG. 3C  further indicates how a small rise in the road level may also generate a significant placement error. As indicated only a 4 and ½ rise can generate a one-foot placement error for objects  40  buried beneath ground  60 . 
       FIG. 4  is an illustration of how reflected light from sky  65  may impact FLIR  20  camera. Depending upon the position of the sun and cloud patterns in sky  65 , a reflection off of object  90  may be generated by sky  65 . Depending on the weather conditions and whether the sun or moon is out, the object  90  may appear hotter or cooler to the FLIR  20  camera than would otherwise be detected relative to the ground  60 . Therefore, the accuracy of the FLIR  20  camera is also comprised by weather conditions. 
     Therefore, what is needed is a device and method that will have the benefits of IR detection of landmines without the high cost of an FLIR camera. Further, these IR detectors should not require repeated or complex adjustments in order to operate properly and should not be affected by road or weather conditions. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention an embodiment is disclosed having a device for detecting buried objects. This device uses a sensor array comprised of discrete downward looking infrared detectors. A processor based system is connected to the sensor array to receive and analyze signals received from the downward looking infrared detectors and to generate alarms when the signals analyzed exceed a predetermined threshold indicative of a buried object. 
     A further embodiment of the present invention is a device to detect buried objects. This device has a sensor array having several downward looking infrared detectors, several EMI coils, and several ground penetrating radar sensors. A processor based system is connected to the sensor array to receive and analyze signals received from the downward looking infrared detectors, the EMI coils, and the ground penetrating radar sensors and to generate alarms when the signals analyzed exceed a predetermined threshold indicative of a buried object. 
     A still further embodiment of the present invention is a method of detecting buried objects. This method receives an image from several downward looking infrared detectors. The image is then passed through a two-dimensional spatial high pass filter and a signal to noise ratio for the image is determined. The signal to noise ratio is compared to a predetermined threshold. The image is dilated and then shrunk to a single point at the center of the image. The single point is mapped to earth coordinates and an alarm is issued when a buried object is detected. 
     Additional objects, features and advantages of the present invention will become apparent from the following description and the appended claims when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and a better understanding of the present invention will become apparent from the following detailed description of exemplary embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the foregoing and following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims. 
       The following represents brief descriptions of the drawings, wherein: 
         FIG. 1  is a side view of the Close-In Detection (CID) System vehicle utilizing a sensor array and a forward looking infrared (FLIR) camera; 
         FIG. 2  is a top of the CID System vehicle shown in  FIG. 1  with its associated FLIR field; 
         FIG. 3A  is a side view diagram showing placement error due to improper adjustment of the FLIR camera; 
         FIG. 3B  is a side view diagram showing placement error in the FLIR camera due to an uneven road surface; 
         FIG. 3C  is a side view diagram showing placement error in the FLIR camera due to a change in road elevation; 
         FIG. 4  is an illustration of how weather and cloud patterns may cause reflections that are detected by the FLIR camera; and 
         FIG. 5  is a side view diagram of a vehicle having a sensor array with a down looking infrared (DLIR) field projected in an example embodiment of the present invention; 
         FIG. 6  is a side view diagram of a cart having a sensor array with a DLIR in an example embodiment of the present invention; 
         FIG. 7A  is a bottom view of an example embodiment of the sensor array in the present invention; 
         FIG. 7B  is a bottom view of an example embodiment of the sensor array in the present invention; 
         FIG. 7C  is a bottom view of an example embodiment of the sensor array in the present invention; 
         FIG. 8  is a side view of an infrared (IR) sensor utilized in an example embodiment of the present invention; 
         FIG. 9  is a systems diagram of an example embodiment of the present invention; and 
         FIG. 10  is a modular flow diagram of an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference numerals and characters maybe used to designate identical, corresponding or similar components in differing figure drawings. Further, in the detailed description to follow, exemplary sizes/models/values/ranges may be given, although the present invention is not limited to the same. 
       FIG. 5  is a side view diagram of a vehicle having a sensor array  30  with a down looking infrared (DLIR) field  100  projected in an example embodiment of the present invention. DLIR detectors  140  and  150 , further detailed in FIG.  7 A through  FIG. 8 , are physically located on the undersigned of the sensor array  30 . The sensor array  30  would be permanently affixed to vehicle  10  utilizing permanent supports or hydraulic lifts (not shown). As will be discussed further in  FIGS. 7A ,  78 , and  7 C, the sensor array may also contain GPR  70  sensors as well as EMI coil sensors  80 . By placing DLIR detectors  140  and  150  in the sensor array  30  looking downward to generate DLIR field  1001  a significant reduction in cost is realized since a FLIR  20  camera with its associated lenses is no longer required. The precise configuration of the OLIR detectors  140  and  150  will be discussed further detailed in reference to FIG.  8 . As will be discussed in further detailed in reference to  FIG. 9 , the sensor array  30  may be connected to a processor-based system  130  and a ground positioning satellite system  210 . The DLIR detectors  140  and  150  generating the DLIR field  100  would be used to detect buried objects  40  positioned in the ground  60 . 
       FIG. 6  is a side view diagram of a pushcart  110  having a sensor array  30  with DLIR detectors  140  in an example embodiment of the present invention. This push cart  110  is further detailed in CAMPANA et al., “Downward Looking Infrared for Vehicle Mounted Mine Detection”, SPIE AeroSense Conference 4394: Detection &amp; Remediation Technologies for Mines and Minelike Targets VI, Apr. 16, 2001, incorporated in its entirety herein by reference. The pushcart  110  would be grasped by handles  120  by an operator (not shown). A processor based system  130 , such as but not limited to a laptop, would be visible to the operator. A sensor array having at least DLIR detectors  140  would be positioned in front of the pushcart  110  so that the DLIR detectors  140  would be approximately 12 inches above ground  60 . As will be discussed in further detailed ahead the sensor array  30  would be utilized to detect buried objects  40  in ground  60 , such as land mines. As would be appreciated by one of ordinary skill in the art the distance between the sensor array  30  and ground  60  would vary dependent upon the nature of the sensors utilized. 
       FIG. 7A  is a bottom view of an example embodiment of the sensor array  30  in the present invention. The sensor array  30  would contain a row of GPR  70  sensors, EMI coils  80 , and a row of DLIR detectors  140 . The sensor array  30  would be mounted as shown in  FIGS. 5 and 6 . All the foregoing sensors would be connected to the processor based system  130  as illustrated in FIG.  9 . In addition all the foregoing sensors would be configured to look down at ground  60  as illustrated in  FIGS. 5 and 6 . 
       FIG. 7B  is a bottom view of an example embodiment of the sensor array  30  in the present invention. The sensor array  30  illustrated in  FIG. 7B  is similar to that illustrated in  FIG. 7A  with the exception that a second row all DLIR detectors  150  is added to FIG.  7 B. It should be noted that the DLIR detectors  140  and DLIR detectors  150  are offset from each other in order to provide a more complete image of ground  60 . All other features of  FIG. 7B  remain the same as that of FIG.  7 A and will not be discussed further here. 
       FIG. 7C  is a bottom view of an example embodiment of the sensor array  30  in the present invention. Sensor array  30 , shown in  FIG. 7C , contains only a single row of DLIR detectors  140 . However, as with  FIG. 7B , multiple rows of the DLIR detectors may be implemented. As discussed in McGOVERN et al. “Analysis of IR Signatures of Surface and Buried Anti-Tank Landmines”, SPIE AeroSense Conference 4394: Detection &amp; Remediation Technologies for Mines and Minelike Targets VI, Apr. 16, 2001, incorporated by reference in its entirety herein, infrared detectors alone may be utilized to detect mines. All sensors contained in sensor array  30  would, as previously discussed, be fed into a processor-based system  130  as illustrated in FIG.  9 . 
       FIG. 8  is a side view of an individual infrared (IR) detector  140  utilized in an example embodiment of the present invention. This IR detector  140  utilizes a Fresnel lens  160  held in place with holder  175  to focus images received onto infrared detector  170  which is in turn connected to preamp  180 . In turn preamplifier  180  is connected to connection line  190  which is in turn connected to processor-based system  130  as shown in FIG.  9 . The Fresnel lens  160  concentrates infrared radiation onto infrared detector  170 . The Fresnel lens  160  therefore substitutes for the complex lens system found in FLIR  20  and is substantially less expensive. 
       FIG. 9  is a systems diagram of an example embodiment of the present invention. All components illustrated in  FIG. 9  would be contained in either vehicle  10  or pushcart  110  or attached thereto. As indicated, sensor array  30  would be connected to a processor-based system  130 . In addition, a global positioning satellite system (GPSS)  210  or other well-known method of determining location is connected to processor-based system  130 . This is required in order for the vehicle  10  or pushcart  110  to precisely identify the location of any buried objects  40  detected. 
       FIG. 10  is a modular configuration flow diagram of the software, firmware, and hardware used in the embodiments of the present invention. The blocks illustrated in  FIG. 10  represent modules, code, code segments, commands, firmware, hardware, instructions and data that are executable by a processor-based system(s) and may be written in a programming language, such as, but not limited, to C++. 
     Still referring to  FIG. 10 , an image is received by the sensor array  30  in block  1000  and passed to block  1010 . In block  1010  the image is passed through a two-dimensional spatial high pass filter. The purpose of the two-dimensional high-pass spatial filter is to optimize the mine signal in relation to sensor noise and scene clutter. The two-dimensional high-pass spatial filter is a zero-mean finite impulse response (FIR) spatial filter, implemented by summing pixels in each of three concentric windows. Thereafter, rectifier  1020  receives the signal so that negative contrast targets can be detected and simultaneously passes the signal to a noise/clutter estimator  1030  and divider  1035 . The noise/clutter estimator  1030  attempts to estimate the amount of noise contained within the signal. This is done using the average of the rectified, zero-mean filter output in the region indicated. For Gaussian noise, the rectified average is equal to the standard deviation times sqrt(2/pi). Therefore, the inverse of this scalar is used to adjust the noise estimate. The signal-to-noise ratio can be determined based on the signal received from rectifier  1020  and the noise estimated from the noise/clutter estimator  1030 . Thereafter, the signal received from divider  1035  is compared against a predetermined threshold in block  1040 . The resulting binary threshold-exceedance map is passed to the detection merge section in block  1050 , which first dilates and then shrinks the map down to a single point at the center of the detection cluster. Thereafter, in block  1060  a mapping of the detections from the IR detector  140  coordinates (frame, row, column) to earth coordinates (north, east) is done. In block  1070 , detections that fall within a specified capture radius of a prior detection are used to update the position and other metrics associated with that detection. 
     Still referring to  FIG. 10 , if only IR detectors  140  are used in sensor array  30  the processing proceeds to block  1100  where an alarm is issued. However, if ground penetrating radar (GPR) and metal detectors (MD) are also used in sensor array  30 , as illustrated in  FIGS. 7A and 7B , then the output from block  1070  containing the IR feature extractions and block  1090  containing the GPR and MD features are input into the multisensor fusion block  1080 . The fusion of data from different sensors may be accomplished as discussed in APONTE et al., “A Bayesian Approach to Multi-Sensor Fusion for Vehicle Mounted Mine Detection”, SPIE AeroSense Conference 4394: Detection &amp; Remediation Technologies for Mines and Minelike Targets VI, Apr. 16, 2001, and incorporated herein in its entirety. Thereafter, processing proceeds to block  1100  where an alarm or alarms are generated solely from IR detectors  140  or in some combination of GPR  70  and EMI coils  80 . 
     Using the embodiments of the present invention it is possible detect buried objects, such as anti-tank landmines, with a high degree of accuracy at a significantly reduced cost. By using down looking infrared detectors it is possible to eliminate the need for a costly FLIR camera and reduce clutter generated by reflections from the sky as well as placement errors due to a rough terrain. 
     While we have shown and described only a few examples herein, it is understood that numerous changes and modifications as known to those skilled in the art could be made to the present invention. An example of such a modification would include utilizing multiple rows of infrared detectors  140  in sensor array  30  depicted in FIG.  7 C. Also, any processor-based system  130 , including but not limited to, a PC, laptop or Palm computer may be used to receive and process the data and displaying the results. Further, any highly accurate means of determining the vehicle&#39;s  10  position on the ground may be used in substitute for the GPSS  210 . Therefore, we do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.