INTRUDER DETECTOR SYSTEM

Abstract: A light beam, preferably from a laser (68), is reflected from a target, which is a potential intruder. The time period for the beam to return to a light detector and the intensity of the reflected light is recorded (72). A computer analyses the measurements of distance and intensity. Intruders are detected based on changes in these measurements from those made during a "learning" period. Targets are tracked using data collected in consecutive searches of the protected area. An alarm is sounded and/or a video camera is actuated. An acoustic sensor system (53) may be included, which is able to detect intruders with sound. A sensor fusion unit (74) can determine whether propagation conditions are adequate for the operation of the laser system (70), or alternatively whether the acoustic sensor system (52) should be used instead.

Description: INTRUDER DETECTOR SYSTEM FIELD AND BACKGROUND OF THE INVENTION The present invention relates to an intruder detector system and, in particular, it concerns a system which scans an area with a laser beam and then analyzes the reflected light to determine if an intruder has entered the area. Security is becoming an increasingly complicated issue in today's world. Even one of the most basic threats, that of an intruder attempting to gain access to a building or other protected area, has become much more difficult to counter. As the technology to protect these secure areas has become more sophisticated, so have those criminal individuals who wish to subvert it. Thus, there is an increasing need for sophisticated systems to detect the presence of these intruders in protected areas. One example of an attempt to solve this problem is a method of intruder detection which is disclosed in U.S. Patent No. 4,949,074. In this method, a beam of infrared radiation is projected and the reflected radiation is measured. However, this method does not include the ability to scan a large area or to track a moving intruder. Indeed, the figures and examples in U.S. Patent No. 4,949,074 show only narrow rectangular corridors, rather than wide, irregularly shaped areas. Furthermore, the range of an infrared beam is also relatively short. Thus, the method of U.S. Patent No. 4,949,074 is highly limited in potential applications. Similarly, U.S. Patent No. 3,715,953 discloses an aerial surveillance and fire-control system which includes a laser rangefmder. However, the rangefmder is used only to aim at a target, and does not actively scan the area under surveillance. Clearly, being able to scan an entire area would enable intruder detection systems to survey much larger, wider or irregularly shaped areas. Such scanners are also called rangefmders, since they measure the distance between the object and the rangefmder itself. U.S. Patent No. 4,939,379 discloses a system for actively scanning the surface of an object and measuring its contours. However, this system is designed to be used to scan stationary objects, and has no provisions for detecting or tracking moving objects. Another example of a range finder is disclosed in U.S. Patent No. 4,788,441. This range finder includes a light source at a first location, a retroreflector attached to the target at a second location and a photoreceptor. A beam from the light source can be scanned along a path and is then reflected back by the retroreflector. The photoreceptor receives the reflected light. The distance between the light source and the retroreflector is then determined. Without the retroreflector, the device is inoperable. The range finder of U.S. Patent No. 4,788,441 is thus limited to those situations where a retroreflector can be attached to the target. However, such a limitation implies the compliance of the target, or of the individual operating the target, with being monitored. Certainly, such compliance would not be available from an intruder attempting to gain access to a protected area, since these individuals are actually attempting to avoid detection. Thus, clearly a system is required which can also scan a light beam from a light source along a path, collect the reflected light and then analyze it, without requiring a retroreflector. Such a system would be able to detect and analyze light reflected from any objects in the area to be scanned, including human beings. Another attempt to produce an effective intruder detector system is disclosed in U.S. Patent No. 5,365,218. The disclosed system includes a laser mounted on a rotation device. The laser is rotated so that the area to be protected is scanned. However, no instrumentation or method is disclosed for detecting an intruder according to such rotation of the laser. Furthermore, the highly simplistic design of the disclosed system reduces the amount of available control over the directionality of the laser beam. Thus, a more highly useful system would be able to control the horizontal and vertical direction of the laser beam. There is therefore a need for, and it would be highly useful to have, a system for detecting the presence of an intruder in a protected area, which scans the area with a light beam and then analyzes the reflected light to determine if such an individual is present. SUMMARY OF THE INVENTION According to the teachings of the present invention, there is provided an intruder detection system for detecting a presence of an intruder in an area to be protected, the system including: (a) a light source for emitting a light beam for scanning the area to be protected and for reflecting from a target, such that the light beam becomes a reflected light beam; (b) a detector for receiving the reflected light beam; and (c) an signal processor for determining an intensity of the reflected light beam and a distance of the light source from the target, and for comparing the intensity and the distance to previously stored values of the intensity and the distance, such that a change in a value of the intensity or alternatively of the distance indicates the presence of the intruder. According to another embodiment of the present invention, there is provided a method of detecting an intruder in an area to be protected, comprising the steps of: (a) scanning the area with a beam of light; (b) collecting light reflected from a target; (c) determining an intensity of the light and a distance to the target; (d) repeating steps (a) to (c) at least once to determine at least a first and a second distance, and a first and second intensity; and (e) analyzing the first distance and the second distance, and the first and the second intensity to determine if the target is the intruder. According to preferred embodiments of the present invention, the light source is a laser. Also preferably, the previously stored values of the distance and the intensity are obtained by scanning the area to be protected with the light beam. Preferably, the signal processor includes a computer and an algorithm for converting the intensity of light and the period of time required for the reflected light to return to the detector into the distance of the light source from the target. Preferably, the computer further includes an algorithm for tracking the target. According to another preferred embodiment of the present invention, the intruder detection system further includes an apparatus for visual identification of the target substantially only if the target is the intruder. Also preferably, the apparatus for visual identification is a video camera, and a movement of the video camera is controlled according to the tracking of the target. Alternately and preferably, the system further includes an alarm for being activated substantially only if the target is the intruder. According to yet another embodiment of the present invention, the intruder detection system further includes a mirror for bending the light beam and a motor for rotating the mirror, such that substantially the entirety of the area to be protected is contacted by the light beam. Alternately and preferably, the system further includes a motor for rotating the detector and the light source, such that substantially the entirety of the area to be protected is contacted by the light beam. According to still another embodiment of the present invention, there is provided a detection device for detecting a target in an area, comprising: (a) a light source for emitting a light beam; (b) a mirror for bending the light beam; (c) a motor for rotating the mirror, such that the light beam is able to contact substantially the entirety of the area and is able to reflect from the target, such that the light beam becomes a reflected light beam; (d) a detector for receiving the reflected light beam; and (e) an signal processor for determining a value selected from the group consisting of an intensity of the reflected light beam and a distance of the light source from the target. Hereinafter the term "scanning" refers to the process of moving the light beam around the area to be protected such that reflected light is received from more than one point in that area. Hereinafter the phrase "bending the light beam" refers to reflecting the light beam by a mirror such that the path of the beam is substantially changed. DESCRIPTION OF THE INVENTION The present invention is of a device and a method for detecting the presence of an intruder by scanning an area to be protected with a light beam, and then measuring both the intensity of the reflected light and the apparent distance from the device to a reflective object. Methods are disclosed for reducing the number of false alarms by evaluating any change in either the apparent distance from the device to a reflective object, or by evaluating the intensity of the reflected light, or both. These changes are calculated by first "learning" or preparing a "map" of the area to be protected, in which the area is scanned with the light beam and the values of reflected light and/or the distance from a reflective object to the detector are stored. Any deviations from the stored values for the intensity of reflected light, and/or the distance from the device to any reflective object, are calculated as a change from the "map" of values for the area to be protected. Measurement of the change of either the apparent distance from the device to a reflective object, or by evaluating the intensity of the reflected light, or both, is extremely important for a number of reasons. First, special equipment and protective clothing are available which minimize reflection of light. By reducing the amount of reflected light, an intruder could potentially evade detection by such a device as the present invention. However, such a reduction in reflected light would reduce, and therefore change, the intensity of the reflected light, as well as increasing the apparent (but not true) distance from the intruder to the device of the present invention. Thus, by measuring any changes in either apparent distance or light intensity, such attempts at evasion can be foiled. Another reason why measurement of changes is important is for reducing false alarms. As described below, such false alarms can be caused by moving reflective objects such as the branches of bushes or trees which are blown by the wind. However, the device and method of the present invention can determine if the moving reflective object is a tree branch or a human, and act accordingly, because the change in apparent distance and/or light intensity is calculated, and not just the absolute values. Finally, in preferred embodiments of the present invention, the intruder is tracked by the device of the present invention. Such tracking also requires measurement of changes, since the device must be able to calculate any deviations in intensity of reflected light or apparent distance to the reflective object, and then use these deviations to map the path of the intruder. Small non- critical targets, such as cats, and large non-critical targets, like trucks, are filtered by a size filter. Hereinafter, the term "intruder" is defined as a human who has entered a protected area. Criminal intent on the part of the intruder is neither implied nor required. Hereinafter, the term "protected area" is defined as any area to be scanned by the light source of the device of the present invention, including a bank, both the interior and the exterior of a prison, a warehouse, a factory, a private home or any other building, any area enclosed by a fence or other perimeter such as research and development parks or a portion thereof, or any mobile or semi-mobile assets. Hereinafter, the term "critical target" is any target which is not permitted in the protected area, such as an intruder. A "non-critical target" is any target whose presence is not considered important, such as a small animal. BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 illustrates one example of the intruder detection system of the present invention; FIG. 2 illustrates a second example of the embodiment of Figure 1; FIG. 3 illustrates an example of a second embodiment of the intruder detection system; FIG. 4 is a block diagram of an exemplary tracking system according to the present invention; FIG. 5 is a flowchart of an exemplary algorithm for processing the data obtained with the system of the present invention; FIG. 6 illustrates an example of an intruder detection system according to the present invention which employs an acoustic device; FIG. 7 is a block diagram of an exemplary sensor fusion unit according to the present invention; and FIGS. 8A-8C show an illustrative example of another embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is of a system for detecting a critical target in a protected area, such as intruders attempting to gain access to the protected area. As noted above, examples of such protected areas include, but are not limited to, buildings such as banks, both the exterior and the interior of prisons, private homes, research and development parks, factories and warehouses. These areas are scanned by a light beam and the reflected light is analyzed to determine if an intruder is present. According to preferred embodiments of the present invention, the analysis is performed using an algorithm which reduces false alarms. If a critical target such as an intruder is detected, an alarm or other warning mechanism may be activated, such as a video camera or other apparatus for visual identification. The principles and operation of the intruder detection system according to the present invention may be better understood with reference to the drawings and the accompanying description. It is understood that these examples are given for illustrative purposes only and are not intended to be limiting in any way. Referring now to the drawings, Figure 1 is an illustration of one example of the device of the present invention. An intruder detector system 10 includes laser range finder 12. Laser range finder 12 features light source 14, preferably of collimated light such as a laser and most preferably sending such light in timed pulses. Preferably, the laser used is a class I control laser with a beam width of 1 mrad, which allows a search path radius of 100 meters, yet is safe for operation in the vicinity of humans. Furthermore, the lifetime of such a laser ranges from about 6000 to about 9000 hours, which provides at least a year of continuous operation. The beam from light source 14 is reflected from, and bent by, a mirror 16 in order to scan an area to be protected (not shown). Mirror 16 is rotated by a motor 20 so that the rays of the scanning beam spread out in the shape of a cone, thereby enabling an area (not shown) to be scanned in a 360 degree circle described by the point of impact of the beam at ground level, which can also be termed a search path or "sweep" of light source 14. Motor 20 drives the rotation of mirror 16 by a gear 18 and a ball bearing 22, through a rotation shaft 24 which is attached at one end to mirror 16. The speed of rotation is preferably determined by a number of factors, including the need to prevent the mirror from cracking or the laser light from burning through an object. Should the device become unable to rotate in one direction, the direction of rotation is preferably reversed to prevent the laser from focusing on any one object for a long period. As an added safety measure, the laser is preferably not focusable to any one point, again to prevent any object from being damaged by the laser. During operation of intruder detection system 10, light from light source 14 is emitted from laser range finder 12 and passes through a window 26. In the embodiment illustrated, window 26 forms substantially the entirety of a case 28 which surrounds laser range finder 12 and other components of intruder detection system 10. An encoder 29 measures the shaft angular position, so that the scan angle and speed can be controlled by a control algorithm (not shown). The scanning beam is then reflected from an object or objects in the area to be protected (not shown), which are the target(s), and the reflected light is collected by a detector 30, preferably included in laser range finder 12. The object(s) can be inanimate or animate, human or animal, or even the ground itself. Once the reflected light has been collected by detector 30, the signal is fed to an signal processor 32 for analysis. Preferably, signal processor 32 includes a computer for performing the analysis (one example of one of the algorithms is described below). Preferably, an alarm is then activated if a critical target, such as an intruder, is detected (not shown). Preferably, light source 14, motor 20 and signal processor 32 are powered by one or more power sources (not shown). Examples of a power source include a stand-alone generator, electricity from the power grid and batteries. Also preferably, information such as the timing of the pulses of light from the light source and the height and angle of mirror are also given to the computer in order to detect and track the target. Preferably, the angle of mirror 16 is adjustable by adjusting a mirror elevation shaft 36 and an elevation adjustment screw 38, respectively. These adjustments permit substantially the entirety of the area to be protected to be scanned (not shown). Also preferably, intruder detection system 10 includes a protective hood 40 for protecting the device from weather elements such as rain and snow. A second example of the embodiment illustrated in Figure 1 is shown in Figure 2. In this example, intruder detection system 10 is very similar to that shown in Figure 1, with one exception. A case 41 has a smaller window 42, so that only a portion of case 41 is able to pass light. Also, case 41 rotates synchronously with mirror 16. Another embodiment of the present invention is shown in Figure 3. In this embodiment, an intruder detection system 44 has a case 46 which rotates as a whole. Case 46 rotates about a shaft 48, the rotation being driven by motor 20. A window 50 again occupies only a portion of case 46. Light is emitted from light source 14 and passes through window 50, similarly to previous examples. However, motor 20 now rotates case 46 as a whole, rather than simply rotating the mirror alone, so that substantially the entirety of the area can be scanned with the light beam. In order to facilitate this rotation, and enable an output signal to be collected from detector 30 after processing, as well as allow power to go to motor 20, laser range finder 12 and signal processor 32, a plurality of slip rings 52 is included. Each slip ring 52 enables electrical signals or power to be passed between components of intruder detection system 44, so that movement of case 46 does not impede collection of the electrical signal or the supply of power to components within case 46. As noted above, the computer or signal processor includes an algorithm for analysis of the signal from the returning reflected light. The simplest function of the algorithm is to measure either the apparent distance from the range finder to the object reflecting the light, which is the target, or the intensity of reflected light, or both. Preferably, as further described below, the algorithm also includes further analysis of the reflected light and a decision-making process for determining if there is an intruder in area or if it is a false alarm. In one embodiment of the algorithm, the light reflected from the target is analyzed and incorporated into a decision-making process for determining if the target is an intruder, in which case an alarm may be sounded or other action taken. Although the following discussion centers upon humans as critical targets, it should be noted that this is for discussion purposes only and is not meant to be limiting in any way. The laser range finder, which includes a scanning beam and a receiver for receiving the beam as described with regard to the present invention, is based upon the principle of time-of- flight measurement of short laser pulses, which is well known in the art. The range is determined by first measuring the elapsed time t between the transmission of a pulse and the reception of the reflected pulse. The range is then calculated according to the equation: R = ct/2 in which R is the range and c is the speed of light (see for example S.A. Hovamessian, Introduction to Sensor Systems, 1988, Artech House, page 235). Descriptions of complete laser range finder systems, including both hardware and the necessary processing methods for software programs, can be found in a number of prior art references (see for example H.N. Burns et al. , "System design of a pulsed laser range finder", Optical Engineering, March 1991 , Vol. 30, page 323; and P. A. Forrester and K.F. Hulme, "Review of laser range finders", Optical and Quantom Electronics, Vol. 13, 1981, page 259). Furthermore, many products which perform these functions and which could optionally be incorporated into the present invention as laser range finders include but are not limited to LD90-3™ (Riegl Laser Measurement Systems) and Controlaser 200™ (Silicon Heights Ltd.). The following algorithm is an example of an algorithm for finding the range only, although the method and device of the present invention also calculate both the intensity of received light and any changes in that intensity. The method and algorithm are performed as follows. First, the scanning beam is swept around the area to be protected, preferably in a complete circle for a complete search. Since the beam is rotated around the area in a path which can be described as at least a partial circle, if not a complete circle, the search path can be divided into separate angular samples. The number of such angular samples is N a . In order to determine if a target is a human, or alternately a non-critical target such as a animal, the search beam must be reflected from the target several times during a single search period. A high resolution is therefore required, preferably about 1-10 mrad. If a resolution of 1 mrad is obtained, then the number of separate angular samples in a search path of one complete circle is 6250, so that N a = 6250. The total number of measurements of the range, or distance from the light source to the target, is at least one, and preferably two. The measurement of the range in each angular sample is given as N r . In order to analyze the signal from the reflected light, the values of the measured range in each angular sample are collected and stored in the memory of the computer. Both the current measurement and at least one previous measurement are stored in a FIFO memory unit. These measurements are overlapped, and the resulting pattern analyzed, in order to identify the nature of the target. Preferably, the computer, or other device which runs the algorithm, "learns" the area to be protected first in order to be able to determine if a moving object is a plant or other inanimate object being moved by the wind. During the measurement of the range from the light source to the target, both the average and the standard deviation of values in all angular samples N a are considered. If the number of previous measurements, made before the current measurement, is "J", then any differences in the value of the current measurement from the previous "J" measurements are considered. Both the average value and the standard deviation (σ) are updated during the search. S(n a ) = R (n a ) - kσ{n a ) - ΔR - Examples of the actual equations employed are as above, it being understood that these examples are for illustrative purposes only and are not meant to be limiting. Furthermore, as noted above, these equations are only for determining the apparent distance, or range, from the device of the present invention to the target. In these equations, R(na) is the average of the measurement of the range in each angular sample n a from N a . The standard deviation is s^a). The limit of sensitivity, or threshold, for each angular sample n a is S(ng). k is a positive constant for multiplying with the standard deviation. ΔR mιn is a positive constant to determine the minimal range difference. The threshold is calculated during the "learning" procedure for determining the map of ranges of the area to be protected, as described previously. The equations are used as follows. The measured range stored in FIFO memory is R(n a , j, n r ). When a target enters the area to be protected, the measured range in a particular angular sample changes, which then alerts the system to the possible presence of an intruder in the area to be protected. Specifically, if the measured range in a particular angular sample is less than the measured threshold, or R(na) < S^g), then a potential target may have entered the area, thus changing the map of measured ranges in the area. These differences are entered into memory, along with the number of the sweep, the total range and the change in the measured range. The system then tests the measured data as described below, in order to decide if the target is in fact an intruder. The resolution of the laser light beam is sufficiently fine that a human target must be present in a plurality of consecutive angular samples of the search path, rather than just one angular sample. The system exploits this requirement by first checking to see if a number of consecutive samples are affected by the apparent change in the measured range. The exact number of angular samples affected depends at least partially upon the radius of the search path. However, a predefined number of consecutive angular samples should be affected if a human target has entered the area, rather than a small animal or other moving but non-critical target, or even artifacts such as system noise. If at least the predefined number of consecutive angular samples is affected, then the average measured range to the target and its width, as determined by the number of angular samples affected, is entered into the memory. Next, consecutive complete search paths, or complete sweeps of the area to be protected, are examined for the above measurements. Whether a target is moving or stationary will be revealed during consecutive sweeps, by changes in the above measurements. The system uses this information to track the target, both to determine if the target is moving, and the speed and angle of movement. If the target is moving, and meets the minimum (empirical) width requirement for a human target, the target is then tracked. The system then uses the speed and angle of movement to determine if the target is crawling, or walking upright or in a bent position. The memory records the coordinates of movement, the position during movement and the speed of the target. A video or still camera can be trained on the target to record various types of visual information. An alarm is preferably activated once the presence of a human target has been fully determined. In preferred embodiments of the present invention, the target is automatically tracked, and the path of the target is displayed to the operator by a computer screen or other display device (not shown). Such tracking enables the angular location of the target to be determined. The angular location of the target is then preferably transmitted to the tracking device. Preferably, the device of the present invention includes a video camera or other visual identification device which is slaved to the intruder detection system. Such a video camera would then automatically follow the intruder, according to the path determined by the intruder detection system, and would display visual information to an operator on a television screen, for example. The path is determined according to the angular location, such that the angular values of the target location cause the tracking unit to alter its angular position to that of the last received target angle. Such substantially constant, or alternatively intermittent, changes of angle of the tracking unit, such as of the position of the camera angle, enable the tracking unit to substantially constantly point toward the target, who is the detected intruder. Preferably, the tracking unit includes a camera, a motor for positioning the camera, and a control unit for controlling the motor, such that the angular position of the camera is substantially repeatedly altered in order to track the target and to maintain the view of the target within the viewing area of the camera. One example of a suitable product is the "Pan and Tilt Head Type 466" (Denmard). An example of such a tracking system is shown as a block diagram in Figure 4. A tracking system 53 features intruder detection system 44. The detected intruder data, and preferably the angle, are sent to an angular tracking unit 55. Angular tracking unit 55 controls the operation of a video camera 57, a display unit 59 and preferably also a spot light 61. Thus, when the presence of an intruder is detected, angular tracking unit 55 preferably causes video camera 57 to move such that video camera 57 is pointed at the intruder and such that the intruder stays within view. The visual data can then be displayed on display unit 59. Alternatively and preferably, spot light 61 is operable such that when the intruder is detected, the area around the intruder can be illuminated. In still other preferred embodiments of the present invention, the intruder detection system is able to track multiple targets. Preferably, the path of each target is shown separately to an operator, optionally on a display screen with each path marked with a different color, for example. As noted above, the presence of a human target is at least partially determined by the apparent width, or number of angular samples in which the target is present. The best values for such a width depend at least partly upon the radius of the search path and the number of angular samples within that path. Such values can be easily determined, either empirically or by calculation, for any values of the radius and the number of angular samples. The apparent width is used to eliminate such artifacts as a small moving animal. The height of the laser relative to the ground is also important, for two reasons. First, if the height is sufficiently large, small animals simply won't be detected by the reflectance of the light beam. Second, the height of the target can be specifically measured, thereby enabling the system to determine if the target is a walking or crawling human, which could be important for the positioning of such detection devices as a video camera. Figure 5 shows a flowchart of an exemplary algorithm for detecting the presence of an intruder. In step 1 A, the encoder of the present invention measures the shaft angular position of the shaft which supports the mirror, and thereby enables the angle of the light source scanning beam to be determined. In step IB, the laser range finder receives a pulse of reflected light which was emitted from the light source and then reflected from the target, such as the intruder. In step 2A, the angle of the shaft is determined by the encoder, and in step 2B, the range is determined by the laser range finder. In step 3, the range threshold is computed substantially as previously described. In step 4, the range is compared to the threshold. If the threshold is greater than the range, then the method continues to step 5. Alternatively, if the threshold is substantially not greater than the range, then the range threshold is computed again. In step 5, the data about the potential target are stored. In step 6, the data of the potential target are compared to the signature of a valid target, such as a human intruder, substantially as previously described. If the data of the potential target are substantially similar, then in step 7B, the location of the target, preferably including the angle and the range, and the scan number are stored. Otherwise, in step 7A, the data about the potential target are removed and the potential target is no longer considered to be a target. In step 8, after the location of the potential target has been determined for a plurality of times, the difference between the present scan location and the previous scan location is preferably determined. More preferably, the difference includes both the angular displacement and the range displacement of the potential target. If this difference is less than the maximal valid target displacement, then the method continues with step 9B. Otherwise, the data about the potential target are deleted and the potential target is no longer considered to be a target, in step 9 A. In the latter case, the excessively large displacement of the target may indicate the presence of a non-human target or false target. In step 9B, the method preferably continues by determining that the potential target is a valid target. In this case, the valid target location is preferably transmitted to the tracking device, substantially as previously described, as shown in step 10A. Alternatively and preferably, an alarm flag is set for the alarm device, such that the alarm device sounds an alarm, as shown in step 10B. More preferably, both steps 10A and 10B are performed. Figure 6 shows an acoustic embodiment of the intruder detection system of the present invention. An acoustic intruder detection system 52 features a transmitter 54, a receiver 56 and a signal processor 58. Transmitter 54 transmits sound waves, preferably in the ultrasonic frequency range, and more preferably in the range of from about 20 to about 40 kHz. Such transmitters are available for example from Four Square Co., Taiwan, or from Massa. The strength of the transmitted sound waves are boosted by a horn 60. The pattern of the transmitted sound waves is controlled by horn 60. This pattern is preferably omnidirectional at the azimuth, as well as at about 10 degrees on either side of the horizontal plane. The design of such a horn 60 is well known to one of ordinary skill in the art. Preferably, horn 60 features two portions as shown, each of which is substantially curved as shown, which are preferably shaped substantially symmetrically. The broadcast sound waves return after being reflected from an object or objects in the area to be protected (not shown), which are the target(s). As for Figure 1, these objects may be animate or inanimate, and if animate, human or other animal. The reflected sound waves are received by receiver 56, which preferably includes at least one, and more preferably at least 4, acoustic transducers such as microphones 62. Such acoustic transducers are available from a number of commercial suppliers, including but not limited to, "Ultrasonic Transducer ISU 4000" (Contaq), which contains both a microphone and a transmitter. According to a preferred embodiment of the present invention, the number of microphones 62 lies in the range of from about 4 to about 16. Microphones 62 are preferably dispersed about the center of acoustic intruder detection system 52. Optionally, receiver 56 could be a mechanical scanner instead of a microphone array. Also optionally, receiver 56 includes one microphone 62 attached to a receiver horn (not shown) with a pattern of sound waves which is narrow at the azimuth, which mechanically scans the azimuth. Optionally and more preferably, both transmitter 54 and receiver 56 have a narrow beam horn (not shown) which mechanically scans the azimuth. Receiver 56 preferably includes an amplifier (not shown) for amplifying the sound signal on every channel. The sound signal is converted from an analog signal to a digital signal by an A/D converter (not shown). The digital signal is then processed by signal processor 58. For an explanation of the method of processing, see for example M. Skolnik, Introduction to Radar Systems, pages 310-311 (M. Skolnik, Introduction to Radar Systems, McGraw-Hill Book Company, New York, New York, USA). Although this is an example of an electromagnetic wave multibeam receiver antenna, a similar method is used for ultrasonic waves. Signal processor 58 then calculates the angles of the received sound waves, and the amplitude of the signal in every angle. Preferably, signal processor 58 is an interferometer, so that only four microphones 62 are needed, since each pair of microphones operates in a 90 degree zone. For an explanation of the operation of an interferometer, see for example M. Skolnik, Introduction to Radar Systems, page 545 (M. Skolnik, Introduction to Radar Systems, McGraw-Hill Book Company, New York, New York, USA). Alternatively and preferably, signal processor 58 is a multi-beam array, such that from about 8 to about 16 microphones 62 are needed, as the number of microphones depends upon the number of simultaneous sound waves required, which is in turn determined by the angular resolution. For this latter embodiment, as well as for substantially any of the embodiments for angular measurements with sound waves, receiver 56 can be "stepped" in range measurement by characterizing the transmitted sound waves as pulses. Similarly to Figure 1, acoustic intruder detection system 52 "learns" the area to be protected (not shown), substantially as previously described for light beams. If no range measurement feature is included, transmitter 54 is omnidirectional and receiver 56 is multibeam, then each beam of the multibeam sound waves defines an angular sector in the azimuth. For each beam, the amplitudes of the reflected or received signal samples are stored in the memory. Next, both the average and the standard deviation are updated for every new sample, and two threshold values are calculated as well for each beam, one threshold beam being greater than the average and one threshold beam being lower than the average. For the next sample, the current amplitude is compared to these two threshold values. When a target enters the protected area, the measurement signal in the particular angle beam changes, becoming either larger or smaller than the average signal prior to the entrance of the target in the protected area. This change causes the signal to cross over one of the threshold values. Furthermore, if the signal crosses the threshold for a plurality of samples, the presence of a valid target, such as a human intruder, is detected. Acoustic intruder detection system 52 can either transmit sound waves as pulses or as continuous sound waves. Pulses can be used to determine distance by measuring the time between the transmission of the sound pulse and the reception of the reflected sound pulse, such that the time difference is used to determine the distance from the target. Furthermore, the embodiments of acoustic intruder detection system 52 can be summarized as follows. In the first embodiment, if the range measurement is not performed, then the transmitted sound waves are continuous waves. In this embodiment, the receiver cannot measure the range of the reflected sound waves. In the second embodiment, the range measurement is performed, such that the transmitted sound waves are modulated, such as pulses of sound waves. The receiver can then measure the ranges of the reflected signals. For the azimuth angle measurement according to the present invention, a number of options are possible. For example, if the transmitter is omnidirectional, the receiver can be multibeam, an interferometer or a narrow beam, mechanical scanner receiver. Alternatively, if the transmitter is a narrow beam mechanical scanner transmitter, then the receiver must also be a narrow beam, mechanical scanner receiver. As for the embodiments of Figures 1-3, a video camera and/or spotlight can be slaved to acoustic intruder detection system 52, so that when an intruder is detected, the video camera can be turned on and can follow the intruder substantially as previously described. A remote terminal can then be used to visually monitor the activity of the intruder. In addition, an audible alarm can be sounded to further alert the security staff of the presence of an intruder. More preferably, the remote terminal can include a main screen upon which the video stream data obtained from the video camera can be displayed. Preferably, the systems of Figures 1, 2 or 3 and Figure 6 are combined in order to enable both laser and acoustic detection of intruders to be performed according to the well known principle of sensor fusion, as shown as a schematic diagram in Figure 7. A sensor fusion unit 66 includes a laser sensor 68. Laser sensor 68 includes a propagation condition detector 70 for detecting the propagation conditions for the laser light beams. Propagation condition detector 70 is a software module which receives current range measurements from an intruder detection system 72, according to any of the previous embodiments of such a system as shown in Figures 1, 2 or 3. Propagation condition detector 70 could determine the propagation conditions according to any suitable method. For example, propagation condition detector 70 could compare the current range measurements to a threshold range measurement, which could be for example, the distance from intruder detection system 72 to the ground as measured when propagation conditions were suitable. The distance to the ground could be measured according to the depression angle. Such a threshold could be determined hours, days, or even longer, in advance. If the range were to be substantially shorter than the threshold distance, and preferably if the range were to be substantially shorter than the threshold distance for at least a majority of the circle defined by the laser beam, then the propagation conditions would be determined to be insufficient for intruder detection using laser intruder detection system 72. Such a determination would preferably be made by a sensor fusion module 74, which would compare the currently measured range to the threshold. If the propagation conditions are not suitable for intruder detection with laser light beams, then preferably sensor fusion module 74 would then be able to detect any intruders by using acoustic intruder detection system 52. In such a combined system, the acoustic portion can function as a good back-up system if the light detection capability is reduced, for example if fog or rain are present. Thus, the combined system could be more robust than either system alone, even though the resolution for the laser based system is typically greater. Figures 8A-8C show an illustrative example of another, relatively simple embodiment of the present invention. In this embodiment, a laser rangefinder 90 substantially as previously described, is fixed such that both the vertical and horizontal angles of a laser beam 92 are determined, since the vertical angle is perpendicular to the ground. Figure 8A shows a side view of the embodiment, with laser rangefinder 90 being attached to a support 94, which can then be anchored to the ground, for example. As shown in Figure 8B, if an intruder moves as shown by an arrow 95, the intruder must cross the path of laser beam 92. At that moment, laser rangefinder 90 measures the range to the intruder. Figure 8C shows a plurality of laser rangefmders 90 located around an area to be protected 96 such that the plurality of laser rangefmders 90 are located at the perimetry of area to be protected 96. Each laser rangefinder 90 measures the range along the horizontal line of the transmitted laser beam 92. The moment that the measured range changes, the presence of an intruder is detected. It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope of the present invention.

Claims: WHAT IS CLAIMED IS: 1. An intruder detection system for detecting a presence of an intruder in an area to be protected, the system comprising: (a) a light source for emitting a light beam for scanning the area to be protected and for reflecting from a target, such that said light beam becomes a reflected light beam; (b) a detector for receiving said reflected light beam; and (c) an signal processor for determining an intensity of said reflected light beam and a distance of said light source from said target, and for comparing said intensity and said distance to previously stored values of said intensity and said distance, such that a change in a value of said intensity or alternatively of said distance indicates the presence of the intruder. 2. The intruder detection system of claim 1, wherein said light source is a laser. 3. The intruder detection system of claim 1, wherein said previously stored values of said distance and said intensity are obtained by scanning the area to be protected with said light beam. 4. The intruder detection system of claim 1, wherein said signal processor includes a computer and an algorithm for converting a period of time required for said reflected light to return to said detector into said distance of said light source from said target. 5. The intruder detection system of claim 4, further comprising an apparatus for visual identification of said target substantially only if said target is the intruder. 6. The intruder detection system of claim 4, wherein said computer further includes an algorithm for tracking said target. 7. The intruder detection system of claim 6, wherein said apparatus for visual identification is a video camera, and a movement of said video camera is controlled according to said tracking of said target. 8. The intruder detection system of claim 4, further comprising an alarm for being activated substantially only if said target is the intruder. 9. The intruder detection system of claim 1 , further comprising a mirror for bending said light beam and a motor for rotating said mirror, such that substantially the entirety of the area to be protected is contacted by said light beam. 10. The intruder detection system of claim 1, further comprising a motor for rotating said detector and said light source, such that substantially the entirety of the area to be protected is contacted by said light beam. 11. The intruder detection system of claim 1 , further comprising: (d) a tracking unit for determining an angular location of the intruder; and (e) a video camera for being focused on the intruder and for producing a video stream of images including the intruder, said tracking unit determining an angular location of said video camera according to said angular location of the intruder. 12. The intruder detection system of claim 1 , further comprising: (d) an acoustical transmitter for transmitting a transmitted sound wave, such that said transmitted sound wave is reflected from the intruder to produce a reflected sound wave; (e) an acoustical receiver for receiving said reflected sound wave to produce a received sound wave; and (f) a signal processor for determining at least an angular location of the intruder. 13. The intruder detection system of claim 12, wherein said transmitted sound wave is a continuous wave. 14. The intruder detection system of claim 12, wherein said transmitted sound wave is a modulated wave. 15. The intruder detection system of claim 14, wherein said modulated wave is a plurality of pulses of sound waves. 16. The intruder detection system of claim 14, wherein said receiver measures a range of said reflected sound waves. 17. The intruder detection system of claim 16, wherein said range is measured according to a time difference between a transmission of said transmitted sound wave and a reception of said received sound wave. 18. The intruder detection system of claim 12, wherein said transmitter is selected from the group consisting of omnidirectional and narrow beam mechanical scan. 19. The intruder detection system of claim 18, wherein said receiver is selected from the group consisting of multibeam, interferometer, and narrow beam mechanical scanner. 20. A detection device for detecting a target in an area, comprising: (a) a light source for emitting a light beam; (b) a mirror for bending said light beam; (c) a motor for rotating said mirror, such that said light beam is able to contact substantially the entirety of the area and is able to reflect from the target, such that said light beam becomes a reflected light beam; (d) a detector for receiving said reflected light beam; and (e) an signal processor for determining a value selected from the group consisting of an intensity of said reflected light beam and a distance of said light source from said target. 21. The detection device of claim 20, wherein said signal processor compares said value to at least one previously stored value, such that a change in said value indicates the presence of the intruder. 22. The detection device of claim 20, wherein said light source is a laser. 23. The detection device of claim 21 , wherein said previously stored values of said distance and said intensity are obtained by scanning the area to be protected with said light beam. 24. The detection device of claim 20, wherein said signal processor includes a computer and an algorithm for converting a period of time required for said reflected light to return to said detector into said distance of said light source from said target. 25. The detection device of claim 24, wherein said computer further includes an algorithm for tracking said target. 26. The detection device of claim 25, further comprising a video camera, wherein a movement of said video camera is controlled according to said tracking of said target. 27. A method of detecting an intruder in an area to be protected, comprising the steps of: (a) scanning the area with a beam of light; (b) collecting light reflected from a target; (c) determining an intensity of said light and a distance to said target; (d) repeating steps (a) to (c) at least once to determine at least a first and a second distance, and a first and second intensity; and (e) analyzing said first distance and said second distance, and said first and said second intensity to determine if said target is the intruder. 28. A system for detecting an intruder at a perimeter of a protected area, the system comprising: (a) a plurality of laser rangefmders for transmitting a laser beam, said plurality of laser rangefmders being located at the perimeter of the protected area; and (b) a plurality of supports, each support supporting each of said plurality of laser rangefmders such that each of said plurality of laser rangefmders transmits said laser beam in a substantially horizontal direction.

Inventors: FRUCHT YAACOV, FRUCHT, YAACOV
Applicants: FRIEDMAN MARK M, FRUCHT YAACOV, LASER GUARD LTD, FRIEDMAN, MARK, M., FRUCHT, YAACOV, LASER GUARD LTD.
Application year: 1998
Main classification: G08B13
IPC codes: G01S15, G01S17, G01V8, G08B13, G08B15