Device and method for the detection of buried objects

BACKGROUND OF THE INVENTION

P-0001[0001] 1. Field of the Invention

P-0002[0002] 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.

P-0003[0003] 2. Discussion of the Related Art

P-0004[0004] 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'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.

P-0005[0005] 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 <b>10</b> on which a sensor array <b>30</b> is attached to the front thereof. This sensor array <b>30</b> would be mounted to vehicle <b>10</b> be hydraulic lifts and would contain metal detectors (MD) as well as ground penetrating radar (GPR). In addition, a forward-looking infrared (FLIR) camera <b>20</b> would be mounted to the top of the vehicle <b>10</b> and aimed to cover a trapezoidal area <b>50</b> in front of the vehicle <b>10</b> and sensor array <b>30</b>. The FLIR <b>20</b> as well as sensor array <b>30</b> would detect objects <b>40</b> positioned below the ground <b>60</b>. The information from both the sensor array <b>30</b> and FLIR <b>20</b> may be combined to identify objects <b>40</b>. 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.

P-0006[0006]FIG. 2 is a top view of the CID System shown in FIG. 1 and also shows the FLIR field <b>50</b>, vehicle <b>10</b> and sensor array <b>30</b>. In addition, sensor array <b>30</b> is shown containing GPR <b>70</b> sensors and electromagnetic induction (EMI) coils <b>80</b> that act as metal detectors.

P-0007[0007] However, the CID System shown in FIGS. 1 and 2 has several drawbacks directly related to the FLIR <b>20</b>. First, the FLIR <b>20</b> is a relatively expensive and complex piece of equipment due to the lens system and IR detectors contained therein. The FLIR <b>20</b> may cost as much as 50 percent or more of the cost of the vehicle <b>10</b> itself. Thus, repair and replacement of the FLIR <b>20</b> camera is also expensive. In addition, since the FLIR <b>20</b> camera views the FLIR field <b>50</b> in front of sensor array <b>30</b>, the unification of the respective images to identify landmines located beneath ground <b>60</b> adds another layer of complexity to the system.

P-0008[0008] Still further, FIGS. 3A, 3B, and <b>3</b>C are similar to the CID System shown in FIG. 1 with the exception that difficulties due to the usage of the FLIR <b>20</b> are more clearly illustrated. In FIG. 3A, a misalignment of FLIR <b>20</b> camera by as little as one degree will create a one foot placement error in the FLIR field <b>50</b> that would result in a one foot displacement of any buried objects <b>40</b> detected. Therefore, proper calibration of the FLIR <b>20</b> camera is absolutely essential for accurate identification of buried objects <b>40</b>. Of course, in a military vehicle, such as vehicle <b>10</b>, off road usage, or simply rough roads, will necessitate the frequent realignment of the FLIR <b>20</b> camera. This may be particular the case in an active combat area.

P-0009[0009]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 <b>50</b>. 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 <b>20</b> camera would be compromised.

P-0010[0010]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 <b>40</b> buried beneath ground <b>60</b>.

P-0011[0011]FIG. 4 is an illustration of how reflected light from sky <b>65</b> may impact FLIR <b>20</b> camera. Depending upon the position of the sun and cloud patterns in sky <b>65</b>, a reflection off of object <b>90</b> may be generated by sky <b>65</b>. Depending on the weather conditions and whether the sun or moon is out, the object <b>90</b> may appear hotter or cooler to the FLIR <b>20</b> camera than would otherwise be detected relative to the ground <b>60</b>. Therefore, the accuracy of the FLIR <b>20</b> camera is also comprised by weather conditions.

P-0012[0012] 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

P-0013[0013] 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.

P-0014[0014] 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.

P-0015[0015] 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.

P-0016[0016] 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

P-0017[0017] 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.

P-0018[0018] The following represents brief descriptions of the drawings, wherein:

P-0019[0019]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;

P-0020[0020]FIG. 2 is a top of the CID System vehicle shown in FIG. 1 with its associated FLIR field;

P-0021[0021]FIG. 3A is a side view diagram showing placement error due to improper adjustment of the FLIR camera;

P-0022[0022]FIG. 3B is a side view diagram showing placement error in the FLIR camera due to an uneven road surface;

P-0023[0023]FIG. 3C is a side view diagram showing placement error in the FLIR camera due to a change in road elevation;

P-0024[0024]FIG. 4 is an illustration of how weather and cloud patterns may cause reflections that are detected by the FLIR camera; and

P-0025[0025]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;

P-0026[0026]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;

P-0027[0027]FIG. 7A is a bottom view of an example embodiment of the sensor array in the present invention;

P-0028[0028]FIG. 7B is a bottom view of an example embodiment of the sensor array in the present invention;

P-0029[0029]FIG. 7C is a bottom view of an example embodiment of the sensor array in the present invention;

P-0030[0030]FIG. 8 is a side view of an infrared (IR) sensor utilized in an example embodiment of the present invention;

P-0031[0031]FIG. 9 is a systems diagram of an example embodiment of the present invention; and

P-0032[0032]FIG. 10 is a modular flow diagram of an example embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

P-0033[0033] 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.

P-0034[0034]FIG. 5 is a side view diagram of a vehicle having a sensor array <b>30</b> with a down looking infrared (DLIR) field <b>100</b> projected in an example embodiment of the present invention. DLIR detectors <b>140</b> and <b>150</b>, further detailed in FIG. 7A through FIG. 8, are physically located on the underside of the sensor array <b>30</b>. The sensor array <b>30</b> would be permanently affixed to vehicle <b>10</b> utilizing permanent supports or hydraulic lifts (not shown). As will be discussed further in FIGS. 7A, 7B, and <b>7</b>C, the sensor array may also contain GPR <b>70</b> sensors as well as EMI coil sensors <b>80</b>. By placing DLIR detectors <b>140</b> and <b>150</b> in the sensor array <b>30</b> looking downward to generate DLIR field <b>100</b> a significant reduction in cost is realized since a FLIR <b>20</b> camera with its associated lenses is no longer required. The precise configuration of the DLIR detectors <b>140</b> and <b>150</b> 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 <b>30</b> may be connected to a processor-based system <b>130</b> and a ground positioning satellite system <b>210</b>. The DLIR detectors <b>140</b> and <b>150</b> generating the DLIR field <b>100</b> would be used to detect buried objects <b>40</b> positioned in the ground <b>60</b>

P-0035[0035]FIG. 6 is a side view diagram of a pushcart <b>110</b> having a sensor array <b>30</b> with DLIR detectors <b>140</b> in an example embodiment of the present invention. This push cart <b>110</b> 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 <b>110</b> would be grasped by handles <b>120</b> by an operator (not shown). A processor based system <b>130</b>, such as but not limited to a laptop, would be visible to the operator. A sensor array having at least DLIR detectors <b>140</b> would be positioned in front of the pushcart <b>110</b> so that the DLIR detectors <b>140</b> would be approximately 12 inches above ground <b>60</b>. As will be discussed in further detailed ahead the sensor array <b>30</b> would be utilized to detect buried objects <b>40</b> in ground <b>60</b>, such as land mines. As would be appreciated by one of ordinary skill in the art the distance between the sensor array <b>30</b> and ground <b>60</b> would vary dependent upon the nature of the sensors utilized.

P-0036[0036]FIG. 7A is a bottom view of an example embodiment of the sensor array <b>30</b> in the present invention. The sensor array <b>30</b> would contain a row of GPR <b>70</b> sensors, EMI coils <b>80</b>, and a row of DLIR detectors <b>140</b>. The sensor array <b>30</b> would be mounted as shown in FIGS. 5 and 6. All the foregoing sensors would be connected to the processor based system <b>130</b> as illustrated in FIG. 9. In addition all the foregoing sensors would be configured to look down at ground <b>60</b> as illustrated in FIGS. 5 and 6.

P-0037[0037]FIG. 7B is a bottom view of an example embodiment of the sensor array <b>30</b> in the present invention. The sensor array <b>30</b> illustrated in FIG. 7B is similar to that illustrated in FIG. 7A with the exception that a second row all DLIR detectors <b>150</b> is added to FIG. 7B. It should be noted that the DLIR detectors <b>140</b> and DLIR detectors <b>150</b> are offset from each other in order to provide a more complete image of ground <b>60</b>. All other features of FIG. 7B remain the same as that of FIG. 7A and will not be discussed further here.

P-0038[0038]FIG. 7C is a bottom view of an example embodiment of the sensor array <b>30</b> in the present invention. Sensor array <b>30</b>, shown in FIG. 7C, contains only a single row of DLIR detectors <b>140</b>. 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 <b>30</b> would, as previously discussed, be fed into a processor-based system <b>130</b> as illustrated in FIG. 9.

P-0039[0039]FIG. 8 is a side view of an individual infrared (IR) detector <b>140</b> utilized in an example embodiment of the present invention. This IR detector <b>140</b> utilizes a Fresnel lens <b>160</b> held in place with holder <b>175</b> to focus images received onto infrared detector <b>170</b> which is in turn connected to preamp <b>180</b>. In turn preamplifier <b>180</b> is connected to connection line <b>190</b> which is in turn connected to processor-based system <b>130</b> as shown in FIG. 9. The Fresnel lens <b>160</b> concentrates infrared radiation onto infrared detector <b>170</b>. The Fresnel lens <b>160</b> therefore substitutes for the complex lens system found in FLIR <b>20</b> and is substantially less expensive.

P-0040[0040]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 <b>10</b> or pushcart <b>110</b> or attached thereto. As indicated, sensor array <b>30</b> would be connected to a processor-based system <b>130</b>. In addition, a global positioning satellite system (GPSS) <b>210</b> or other well-known method of determining location is connected to processor-based system <b>130</b>. This is required in order for the vehicle <b>10</b> or pushcart <b>110</b> to precisely identify the location of any buried objects <b>40</b> detected.

P-0041[0041]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++.

P-0042[0042] Still referring to FIG. 10, an image is received by the sensor array <b>30</b> in block <b>1000</b> and passed to block <b>1010</b>. In block <b>1010</b> 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 <b>1020</b> receives the signal so that negative contrast targets can be detected and simultaneously passes the signal to a noise/clutter estimator <b>1030</b> and divider <b>1035</b>. The noise/clutter estimator <b>1030</b> 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 <b>1020</b> and the noise estimated from the noise/clutter estimator <b>1030</b>. Thereafter, the signal received from divider <b>1035</b> is compared against a predetermined threshold in block <b>1040</b>. The resulting binary threshold-exceedance map is passed to the detection merge section in block <b>1050</b>, which first dilates and then shrinks the map down to a single point at the center of the detection cluster. Thereafter, in block <b>1060</b> a mapping of the detections from the IR detector <b>140</b> coordinates (frame, row, column) to earth coordinates (north, east) is done. In block <b>1070</b>, 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.

P-0043[0043] Still referring to FIG. 10, if only IR detectors <b>140</b> are used in sensor array <b>30</b> the processing proceeds to block <b>1100</b> where an alarm is issued. However, if ground penetrating radar (GPR) and metal detectors (MD) are also used in sensor array <b>30</b>, as illustrated in FIGS. 7A and 7B, then the output from block <b>1070</b> containing the IR feature extractions and block <b>1090</b> containing the GPR and MD features are input into the multisensor fusion block <b>1080</b>. 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 <b>1100</b> where an alarm or alarms are generated solely from IR detectors <b>140</b> or in some combination of GPR <b>70</b> and EMI coils <b>80</b>.

P-0044[0044] 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.

P-0045[0045] 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 <b>140</b> in sensor array <b>30</b> depicted in FIG. 7C. Also, any processor-based system <b>130</b>, 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's <b>10</b> position on the ground may be used in substitute for the GPSS <b>210</b>. 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.