Abstract:
In a sensor-fuzed munition system and method, the munition is provided with an additional laser designator mode of operation. In the laser designator mode, the munition has the option of initiating a target strike additionally based on whether laser designator energy is detected as being present on the target. This additional mode of operation is preferably achieved using the existing laser receiver of the rangefinder hardware, with minimal additional hardware and software systems for detecting and processing the additional laser designator signal energy. In this manner, collateral damage and false-target firings are decreased to near-zero probability.

Description:
BACKGROUND OF THE INVENTION 
   Sensor-fuzed munitions are a class of air-to-ground “smart weapons” that use the body dynamics of a projectile, or “munition”, to continuously translate the instantaneous sensor field of view to thoroughly search the suspected target area. A munition is placed in motion over a region of interest. Such motion may be induced in a number of different ways, for example, by ejecting the munition from a propulsion vehicle such as a missile, by dropping the munition from an aircraft, or by launching the munition from a ground-based launch system canister such as a wide-area munition (WAM) launch system, for example, of the type disclosed in United States Patent No. 6,820,531, incorporated herein by reference. Other systems and methods for munition extraction are disclosed in United States Patent No. 6,666,145, incorporated herein by reference. The munitions can be dispensed individually, or a plurality of munitions, i.e. “submunitions”, can be scattered from a common delivery vehicle in a cluster pattern to blanket a target area. During flight of each munition, on-board “sensors” scan for targets within the region of interest and, if a target is located, that information is used to “fuze”, or activate, a warhead on the munition when the warhead is aimed at the target; hence the name “sensor-fuzed” munition. 
   Upon dispensing, the munition is at a given altitude and is caused to spin. As it descends from that altitude, over the region of interest, on-board sensors and corresponding processors are activated and instructed to search along the circumference of a conical scan pattern for “target-like” objects that meet the sensor algorithm criteria. The offset angle of the scan beam of the scanning instruments to the line of flight remains approximately the same during the flight. Revolution of the munition at a constant offset angle about a vertical trajectory axis, combined with the continuous descent of the munition, causes the radius of the search pattern at the intersection of the scan cone and the ground to continuously decrease, such that the scanning operation of the region of interest follows an inward spiral pattern; Deceleration technology and spin-inducing technology can be employed to arrest the ballistic path of the munition. Such technology includes a Samara wing, as disclosed in U.S. Pat. Nos. 4,583,703 and 4,635,553, incorporated herein by reference. Other deceleration and spin-inducing technologies include a parachute systems and hinged-mass systems that include an offset mass that cause the munition to spin at the offset angle about the axis of the direction of fall or simply inducing the dynamics by the action of dispense without any other decelerator or cone inducing mechanism as is done in the USAF Sensor Fuzed Weapon and the US Army Hornet. 
   On-board sensor systems for conventional sensor-fuzed munitions include a dual-mode infrared sensor and a laser rangefinder. The infrared sensor is a passive sensor that receives infrared energy from the background and target-like objects located in the field of view. The collected infrared data is used to search for targets that algorithmically match defined infrared signature parameters. The laser rangefinder provides a height profile to the target algorithm for improved aim point selection and greater lethality. The laser rangefinder is an active sensor including a laser transmitter that emits a laser pulse for each successive incremental foot of observation in the direction of the scan. A reflection of the transmitted pulse is received at a laser receiver and the time-of-flight of the, as reflected by the ground or the target, is measured. Processors coupled to the sensors analyze received sensor data to determine whether a target is present within the scanned region. A decision is reached by the processors, based on the sensor data and the algorithm applied, whether to trigger a stand-off warhead on the munition, such as an explosively formed penetrator (EFP), to strike the targeted object with a high-speed projectile. 
   Conventional applications of sensor-fuzed munition technology include the USAF Sensor Fuzed Weapon (SFW), the US Army “Hornet” off-route mine, the US Army Sense And Destroy (SADARM) 155 mm artillery projectile, the German “Smart 155” 155 mm projectile and the Swedish/French “BONUS” 155 mm projectile. While these applications have proven effective in searching for and attacking enemy target vehicles, uncertainty in the application of the detection criteria of the conventional sensor-fuzed munition to military targets and civilian vehicles is still very high. This target uncertainty is undesirable in modern warfare where minimization of collateral damage and decrease in the likelihood of engagement of an other-than-intended target(s) are of utmost concern. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a sensor-fuzed munition system and method in which the munition is provided with an additional “laser designator” mode of operation. In the laser designator mode, the munition has the option of initiating a target strike additionally based on whether laser designator energy is detected as being present on the target. This additional mode of operation is preferably achieved using the existing laser receiver of the rangefinder hardware, with minimal additional hardware and software systems for detecting and processing the additional laser designator signal energy. In this manner, collateral damage and false-target firings are decreased to near-zero probability. 
   In a first aspect, the present invention is directed to an autonomous munition. The munition includes a rangefinder and an illumination module. The rangefinder includes a laser transmitter that transmits a first laser energy to the ground and eventually scans over and illuminates a remote target. A laser receiver receives a reflected portion of the first laser energy as reflected by the ground and eventually the remote target within a scanned field of view of the laser receiver. It also receives a reflected portion of a second laser designator energy as reflected by the remote target within the scanned field of view of the laser receiver. A range module determines a range of the remote target from the reflected portion of the first laser energy. An illumination module determines whether the reflected portion of the second laser energy is present within the scanned field of view of the laser receiver. 
   In one embodiment, the laser transmitter and laser receiver comprise a rangefinder for determining the range of the munition with respect to the target. In another embodiment, the illumination module comprises a filter circuit that passes energy within an expected frequency band of the second laser energy. In another embodiment, the second laser energy is modulated and the illumination module includes a circuit that discriminates the second laser energy to determine whether the defined modulation in the second laser energy is present. The second laser energy may be amplitude modulated, phase modulated, or frequency modulated. 
   In another embodiment, the second laser energy is sourced from a ground location. In another embodiment, the scanned field of view of the laser receiver translates in an inward-spiral scan pattern during operation of the munition. The inward-spiral scan pattern has an inter-scan spacing between adjacent spiral scan segments. The second laser energy is incident at the remote target and illuminates a spot of a width that is larger than the inter-scan spacing. 
   In another embodiment, the munition further includes a warhead that is activated in response to whether the reflected portion of the second laser energy is present within the scanned field of view of the laser receiver. 
   In another embodiment, the munition further includes a passive infrared receiver that receives infrared energy emitted by the remote target within a scanned field of view of the infrared receiver. 
   In another aspect, the present invention is directed to a method for engaging a munition with a target. First laser energy is transmitted within a transmission field of view. A reflected signal is received including a reflected portion of the first laser energy as reflected by a remote target within a receiver field of view. The remote target is illuminated with a second laser energy. It is determined whether the reflected signal further includes a reflected portion of the second laser energy as reflected by the remote target within the receiver field of view. 
   In one embodiment, the target is engaged as a result of the step of determining that the second laser energy is within the receiver field of view. In another embodiment, engaging the target comprises engaging the target when it is determined that the reflected signal includes the second laser energy. In another embodiment, engaging the target comprises engaging the target with a warhead. 
   In another embodiment, the method further comprises modulating the second laser energy for illuminating the remote target. In another embodiment, determining comprises discriminating the second laser energy using a bandpass filter that is centered at a frequency equal to that of a modulation frequency of the second laser energy. In another embodiment, the method further comprises amplitude-modulating, phase-modulating, or frequency-modulating the second laser energy. 
   In another embodiment, the receiver field of view translates in an inward-spiral scan pattern during operation of the munition. The inward-spiral scan pattern has an inter-scan spacing between adjacent spiral scan segments. In this case, illuminating comprises illuminating the remote target with the second laser energy of a spot size of a width that is larger than the inter-scan spacing. 
   In another embodiment, the method further comprises receiving an infrared signal at a passive infrared receiver including infrared energy emitted by the remote target within a scanned field of view of the infrared receiver. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
       FIG. 1  is an exemplary illustration of operation of the systems and methods of the present invention. 
       FIG. 2  is a close-up view of a munition in flight, in accordance with the present invention. 
       FIG. 3  is an exemplary illustration of the respective fields of view of the passive infrared sensor, the laser rangefinder receiver and the laser rangefinder transmitter of the munition of  FIG. 2 . 
       FIG. 4A  is a conceptual illustration of the inward-spiral scan pattern of the munition of  FIG. 2 .  FIG. 4B  is a close-up view of the scan pattern of  FIG. 4A , illustrating the size of the transmitted designator beam at the target relative to the interscan spacing distance and relative to the field of view of the laser rangefinder receiver, in accordance with the present invention. 
       FIG. 5  is a graph of signal energy as a function of frequency at the laser rangefinder receiver, illustrating the electronic bandwidth of the transmitted and received laser rangefinder energy, in accordance with the present invention. 
       FIG. 6  is a system block diagram of the laser designator transmitter, the laser rangefinder transmitter, the laser rangefinder receiver, and related processor in accordance with the present invention. 
       FIG. 7A  is a block diagram of an embodiment of the designator beam detection module, in accordance with the present invention.  FIG. 7B  is a block diagram of an alternative embodiment of the designator beam detection module, in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  is an exemplary illustration of operation of the systems and methods of the present invention.  FIG. 2  is a close-up view of a munition in flight during the operation illustrated in  FIG. 1 , in accordance with the present invention. Referring to  FIG. 1 , a plurality of submunitions  22  are dispensed and given independent and autonomous flight from a delivery vehicle over a battlefield known to include enemy targets  24 . The submunitions  22  are extracted from the delivery vehicle, for example, according to the techniques disclosed in U.S. Pat. No. 6,666,145, incorporated herein by reference above. The submunitions  22  are scattered across the battlefield as shown. Upon extraction, deceleration and stabilizer mechanisms  62  on each submunition  22  are activated to control the trajectory and velocity of the submunition  22 , and to induce a spin of the submunition body about a trajectory axis  96  at a constant offset angle θ. 
   The submunitions  22  each include an infrared scanner  32 . In one embodiment, the infrared scanner  32  comprises a dual-mode passive infrared scanner unit consisting of a set of optics that image the approximately 40 milliradian by 40 milliradian field of view onto a detector array in the focal plane. The target detector element is sensitive to infra-red energy emitted from the target at approximately 3 to 5 microns wavelength and is surrounded by a four segment guard band detector that is sensitive to infra-red emissions between 1 and 2 microns. The timing of the initiation and duration of signals received in these two channels as well as the ratio of their signal levels are used to discriminate between targets and false targets such as fires and hot fragments in the field of view. The infrared scanner  32  includes an infrared sensor element  34  (see  FIG. 2 ) that converts infrared energy to electrical energy which is digitized and provided as a stream of data to a resident processor or processors located within the submunition  22  housing. Algorithms running on the processor perform target detection and classification operations and reach engagement decisions based on target presence within the scanned region, according to known techniques, in response to the received and collected infrared signatures. 
   The submunitions  22  each further include a laser rangefinder  36 . In one embodiment, the laser rangefinder  36  comprises separate laser transmitter and laser receiver optical trains. The laser rangefinder  36  includes a laser rangefinder transmitter  38  (see  FIG. 2 ) that emits a pulsed transmitted rangefinder beam  44  in the direction of the field of view of the passive infrared sensor  32  consisting of a pulse generator driving a laser diode at the focal plane of the transmit aperture lens that images the diode onto a spot that is 2 milliradians by 10 milliradians in the far field and a laser rangefinder receiver  40  that receives the reflected rangefinder beam  46 , as reflected by the target, ground, or nearby structures and is collected via a larger laser receiver aperture lens that focuses the received laser pulse onto an avalanche photodiode detector mounted on the receive focal plane and a suitable time counting circuit that measures the elapsed time from pulse generation to pulse detection. The received laser energy is converted to data that is analyzed by the on-board processors to determine the slant range of the submunition  22  with respect to ground-based objects under scan by the passive infrared scanner  32 , based on the time-of-flight of the transmitted and received rangefinder beam pulse  44 ,  46 . The progression of the set of scanned pulses along the ground and then up onto and over the target provides a height profile of the target that can be further employed by the processors in conjunction with the infrared signatures to enhance accuracy in target detection and classification. 
   Upgrading the capability of the conventional sensor-fuzed munition to include both the conventional passive infrared sensor system and the recently added laser rangefinder system has improved the system target detection rate. However, while false-target detection rate and collateral damage rate are indeed improved by the addition of the laser rangefinder, even further improvement is provided by the systems and methods of the present invention, as will now be described in detail. 
   Referring to  FIGS. 1 and 2 , the systems and methods of the present invention improve on the conventional sensor-fuzed munition capability by taking advantage of additional, dormant, bandwidth capabilities of the existing laser rangefinder receiver  40  (see  FIG. 2 ) to add an additional mode of operation referenced to herein as “laser-designatormode”. To accomplish this, an additional beam of energy, referred to herein as “designator beam”  48 , is used to illuminate the target  24  with electromagnetic energy, for example energy at a laser wavelength. The laser designator beam  48  is generated by a laser designator transmitter  28  and is directed by ground-based personnel, or alternatively, may be directed by air-based personnel, or ground-based, air-based, or space-based automated systems. The transmitted designator beam  48  is incident on the target at designator spot  60 . The beam is reflected by the target  24  at spot  60  and a portion of the reflected designator beam  50  is oriented toward the scanning submunition  22 , and received by the laser rangefinder receiver  40  (see  FIG. 2 ). In one embodiment, the reflected designator beam  50  is received by the same laser rangefinder receiver  40  as the reflected rangefinder beam  46 . Alternatively, a separate laser energy receiver that is independent of the laser range finder receiver  40  may be used to receive the reflected designator beam  50 . 
   The laser energy received at the laser rangefinder receiver  40  is processed and analyzed to determine the presence of the reflected designator beam  50  at the target. The presence or absence of the reflected designator beam  50  energy in the received energy is then used to reach a determination as to whether to fuze the warhead of the munition. In this manner, the dispensing platform, or other suitable platform, has detected and selected the intended target for engagement by the munition and this platform is and can remain in position to provide continuous direct line-of-sight contact with the intended target during the time of flight of the munition to the target. This situation has already been successfully exploited for a class of precision-guided weapons referred to as laser-guided or laser-designated munitions. In the previously deployed laser-guided or laser-designated weapons, a seeker, usually a gimbaled seeker, in the nose of the munition, searches for the laser-illuminated-and-coded spot on the ground or target, and once found, locks on to that laser reflected signal to guide the munition to strike the target. A similar principle is applied in the present invention; however, the present invention must accommodate the inward-spiral scan pattern of the sensor-fuzed munition. Typical scan rates for the inward spiral scan are in the range of 12,000 to 22,000 feet per second. With this inward-spiral scan pattern, the sensor-fuzed munition may scan over the laser-illuminated spot only a single time, for a very brief period of time. At 22,000 feet per second, the scan passes through a 1-foot spot in less than 50 microseconds. Based on that single, brief, detection, the system must recognize the laser designator and enable the sensor to detect and trigger on that target in the same time frame that the sensor fuzed scan operation normally allows, for example on the order of about 50 microseconds. By recognizing the reflected designator beam, and by integrating this additional information with the information received by the conventional sensor-fuzed operation, the munition can be optionally programmed to engage only the selected, laser-designated, target, and no other, thus satisfying the need for reduced collateral damage and avoiding engagement with unintended targets in complex environments. 
   A designator beam  48  having a spot configuration  60  incident at the target  24  that will be detected and recognized by the laser rangefinder receiver of the sensor-fuzed munition is critical. The designator spot  60  must be provided in a manner and time coincidence such that that its presence can be used to enable the munition to lethally engage the target  24  so designated. The laser rangefinder  36  is configured to detect and recognize the designator spot  60  and decision logic is incorporated into the sensor processor system that enables the munition  22  to appropriately respond to the designator spot  60 . Existing detection processes can optionally be modified to engage only the designated target when laser-designator mode is selected, and, for example, to revert to the conventional mode of operation to autonomously detect and engage targets when the laser-designator mode is not selected. Existing laser receivers of the rangefinder systems are designed to detect the short, high-intensity laser pulses that are generated by the resident laser rangefinder transmitter and to measure the time-of-flight of the pulses in order to estimate the instantaneous slant range to the ground or target while the submunition is scanning an arc of the region of interest at a rotational velocity of roughly 60 to 90 radians per second. This rotational velocity is given by the sine of the offset angle between the sensor and the vertical times the number of scan cycles per second. In the typical cases, the rotation rate is 30 cycles per second times a 30 degree offset angle giving 94 radians per second. In another embodiment, the offset angle is 20 degrees yielding 64 radians per second. The instantaneous field of view of the laser rangefinder receiver is on the order of a foot, so that the dwell time on any laser designator beam spot is on the order of 50 microseconds. Hence, the convenience of a laser designator that is continuously seen and tracked within the laser receiver field of view, such as that enjoyed by conventional laser-guided systems, is not available to the present sensor-fuzed munition application. 
     FIG. 3  is an exemplary illustration of the respective fields of view of the passive infrared sensor  34 , the laser rangefinder receiver  40  and the laser rangefinder transmitter  38  of the munition  22  of  FIG. 2 . At any instant in time, the field of view of the passive infrared target detection sensor  52  is on the order of 10 milliradians by 10 milliradians, the field of view of the laser rangefinder receiver  54  is on the order of 5 milliradians by 2 milliradians, and the field of view of the laser rangefinder transmitter  56  is on the order of 5 milliradians by 0.5 milliradians. Assuming a standoff range of approximately 200 feet, the projected image of the passive infrared sensor  52  in the region of interest is on the order of 2 ft by 2 ft, the projected image of the laser rangefinder receiver  54  in the region of interest is on the order of 1 ft by 0.4 ft, and the projected image of the laser rangefinder transmitter  56  in the region of interest is on the order of 1 ft by 0.1 ft. Therefore, at any given instant in time, the region under scan by the laser rangefinder  36  is relatively narrow, relative to the region under scan by the passive infrared system  32 . 
     FIG. 4A  is a conceptual illustration of the inward-spiral scan pattern of the munition of  FIG. 2 .  FIG. 4B  is a close-up view of the scan pattern of  FIG. 4A , illustrating the size of the transmitted designator beam at the target relative to the interscan spacing distance and relative to the field of view of the laser rangefinder receiver, in accordance with the present invention. As described above, during flight of the munition, the munition is spinning about its vertical axis at an offset angle θ, as described above. At the same time, the munition is continuously losing altitude. Therefore, the projected images of the sensor infrared and laser receivers sweep the region of interest in an inward spiral pattern  64 , as shown in  FIG. 4A  (also see the scan pattern of the projected image of the passive infrared sensor  52  in the region of interest in  FIG. 2 ). At each complete revolution of the munition  22 , the successive projected images of the laser rangefinder receiver at adjacent segments of the spiral may actually overlap, as shown; however, due to the relatively narrow profile of the projected image of the laser rangefinder receiver  54 , subsequent sweeps at adjacent spiral segments are spaced apart from each other as shown. This phenomenon is referred to as “interscan spacing”, and is represented by the distance  58  between adjacent spiral arc segments of the scans at each revolution. 
   Interscan spacing  58  of the laser rangefinder receiver field of view  54  is an important consideration in the present invention. For example, if the laser designator beam  48  illuminates a spot  60  on the target  24  that is small relative to the interscan spacing  58 , the spot  60  may fall entirely between adjacent scan segments, and will not be detected by the scanning system. Therefore, in order to ensure that the laser rangefinder receiver  40  will detect the reflected designator beam  50  from the spot  60  of the laser designator beam, the beam spot  60  should be large enough to subtend the anticipated maximum interscan spacing  58 . If the spot is also circular, its extent in the direction of scan also ensures an adequate dwell time of the field of view of the laser rangefinder receiver  54  within the designator beam spot  60 , and therefore greatly reduces the possibility of missing the scanning and detecting of a properly applied laser designator beam. For the example given above, an illuminated designator spot  60  at the target of a size at least 1.5 m in width would be sufficient to secure detection at the laser rangefinder receiver of the reflected designator beam. It will be noted by those skilled in the art that spreading the same total amount of laser energy over a larger spot size will diminish its intensity and reduce the return signal level. Hence a tradeoff of spot size versus spot intensity must be made. 
   In defining the spot  60  characteristics of the laser designator transmitter  28  at the target such that the there is high assurance of the spot  60  being “seen”, and instantly recognized, by the rangefinder laser receiver  40  and associated processor, the characteristics of the scanning rangefinder laser sensor and processor are to be considered. The laser rangefinder transmitter  38  generates a rangefinder beam  44  at a wavelength on the order of 900-940 nanometers (near-IR). Also, the laser receiver scan rate is on the order of 60 radians per second (or 60 milliradians per millisecond) and its slant range varies from 15 to 100 meters. The laser rangefinder transmitter sends out roughly 10 nanosecond-duration pulses roughly every 50 microseconds and the laser rangefinder receiver scans for laser pulse returns during the first 700 nanoseconds (or 0.7 microseconds) of each inter-pulse interval. That leaves the remaining 49.3 microseconds (98.6% of the time) for the laser rangefinder receiver system to detect and recognize the designator laser beam spot on the target. The relationship between the angular scan rate and the translational velocity, which translational velocity can range between horizontal and vertical orientations, results in an interscan spacing  58  of the projected image of the laser rangefinder receiver  54  of approximately 1 to 1.5 meters. That interscan spacing  58  and the size of the laser rangefinder receiver instantaneous field of view (0.15 to 1 meter) require that, for this example, the laser designator spot be at least 1.5 meters in cross-scan width to insure that the receiver field of view  54  passes through the designator spot  60  at least once during its scan search. 
   The spot  60  of the laser designator beam  48  is directed to the desired target  24  and, preferably, to the desired aim-point on that target, so as to ensure that the sensor-fuzed munition will detect and recognize the laser designator beam  48  in time to attack the target during that scan. At the shortest anticipated range of the submunition, for example at about 15 meters, the 10-milliradian field-of-view of the laser rangefinder receiver  54  scanning at a rotational velocity of 60 milliradians per second will “dwell” on the spot  60  for about 1.6 milliseconds. At the longest anticipated range of the submunition at about 100 meters, the laser rangefinder receiver field-of-view will dwell on the spot  60  for about 0.7 milliseconds. In view of this, the laser designator transmitter  28  should be configured to continuously illuminate the target  24  with the laser designator beam  48  of an appropriate size so that the spot  60  can be detected at the instant the laser rangefinder receiver field of view  54  scans over the spot  60 . 
   In addition, it is preferred that the reflected energy of the laser designator beam  48  is distinguishable from the solar-illuminated background. This can be accomplished by amplitude-modulating the laser transmitter at a frequency in the range of about 50-100 kHz, in order to provide a sufficient number of cycles (&gt;&gt;10) to be detected and recognized by this laser designator receiver channel. The desired amplitude modulation may be accomplished by causing the voltage of the drive signal to the laser diode to be varied by a sinusoidal function whose frequency is between 50 and 100 kHz. In alternative embodiments, the laser designator beam  48  is phase-modulated or frequency-modulated in order to discern the designator beam from background noise. When this amplitude modulated continuous wave (AMCW) signal is detected at the laser rangefinder receiver in the avalanche photodiode detector, the detected signal is passed though several filters in parallel as shown below in  FIG. 6 . The AMCW laser designator reflected signal is passed through a band pass filter that is matched to the AMCW modulation rate of the laser designator (50 to 100 kHz). The pulsed laser rangefinder signal is passed through the 1 MHz to 40 MHz band pass filter that feeds the compute range module. 
     FIG. 5  is a graph of signal energy as a function of frequency at the laser rangefinder receiver, illustrating the electronic bandwidth of the transmitted and received laser rangefinder energy. The laser designator AMCW signal is centered around the 50 kHz while the energy of the laser rangefinder pulsed signals is within the 1 MHz to 40 MHz bandpass. 
     FIG. 6  is a system block diagram of the laser designator transmitter, the laser rangefinder transmitter, the laser rangefinder receiver, and the related processor in accordance with the present invention. In  FIG. 6 , a laser designator  28 , which is situated on a separate platform from the munition, generates a continuous designator laser beam  48 . The beam  48  is modulated by modulator  94 , which, in one embodiment, provides amplitude modulation of the beam, as described above, and is directed at the target  24  to generate a beam spot  60  at the target  24 . At the same time, the laser rangefinder transmitter  38  of the sensor-fuzed munition generates a rangefinder beam  44  that is scanning the region of interest below the munition during its flight. The rangefinder beam  44  is pulsed by pulse generator  92  so that time-of-flight of the pulse can be measured for the purpose of range determination. The reflected rangefinder beam  46  is sensed by the laser rangefinder receiver and processed. A portion of the reflected energy of the designator laser beam  50  is also received by the laser rangefinder receiver  40 . The two received laser signals are nominally at the same optical wavelength (about 900 to 940 nanometers in this embodiment) and hence are passed through the same receive optics and detected in the same avalanche photodiode detector and converted to electrical signals. These two sets of electrical signals are each presented to two parallel bandpass filters which each pass one signal and not the other. The 50 kHz bandpass filter located in the designator beam detection module  72  passes the designator laser signal  50  component of received signal  68  to the true/false (“T/F”) processor  76  and rejects the reflected rangefinder beam component  46 , while the 1 MHz to 40 MHz bandpass filter located in the compute range module  70  rejects the designator laser signal component  50  and passes the reflected rangefinder beam component  46  along to the compute range module  70 . 
   A compute range module (CRM)  70  processes the received signal  68 , and computes the range  74  of the munition relative to the target, or relative to the ground surrounding the target, depending on the positioning of the field-of-view of the laser transmitter  38  and receiver  40  relative to the target  24 . The determination of range  74  by the CRM is based on the time-of-flight (each additional 2 nanoseconds of elapsed time equals 1 foot of range) of the transmitted, reflected, and received rangefinder laser signal pulse  44 ,  46 , and is computed according to conventional techniques. 
   A designator beam detection module  72  that uses standard constant false alarm rate techniques also processes the received signal  68 , and determines whether a reflected designator beam  50  is present in the energy received at the laser rangefinder receiver  40 . In one embodiment, the determination results in a true (laser designator beam is present) or false (laser designator beam is not present) reading  76 . 
   The range information  74  and the true/false reading  76  are provided to the system processor  78  which generates an outcome  80  based on the information provided. In one embodiment, when operating in laser designator mode, a true reading  76  by the designator beam detection module  72  is required before the warhead can be fired. In another embodiment, when operating in laser designator mode, a true reading  76  by the designator beam detection module  72  results in a firing of the warhead, irrespective of the readings by the other sensor or sensors. In another embodiment, when operating in laser designator mode, a true reading  76  by the designator beam detection module  72  results in the firing of the warhead only if readings by the other sensor or sensors confirm that such a firing should take place. In another embodiment, a false reading  76  by the designator beam detection module  72  results in deactivation of the firing of the warhead, irrespective of the readings by the other sensor or sensors. In another embodiment, a false reading  76  by the designator beam detection module  72  is taken into consideration by the processors, but a firing of the warhead can still occur if readings by the other sensor or sensors confirm that such a firing should take place. The processor  78  can be programmed to initiate any of a number of possible outcomes  80 , including and beyond those exemplary embodiments mentioned above, in view of the detection or non-detection of the presence of the laser designator beam on the anticipated target. The determination of the presence, or not, of the laser designator beam on the target can be combined with the results of other sensors, including whether certain criteria concerning the target are met by the data collected by the passive infrared sensors on the munition, and whether certain criteria are met by the data collected by the active rangefinder  40  of the munition. Any logic combination can be conceived regarding these, and other, criteria in formulating a decision regarding engagement by the munition. 
   In another mode of operation, the laser designator can be directed by the host platform to the preferred engagement location of the target, and, when engagement occurs, the munition can be fired at the designator spot on the target. 
     FIG. 7A  is a block diagram of an embodiment of the designator beam detection module  72 , in accordance with the present invention. A bandpass filter  82  receives the signal  68  generated by the laser rangefinder receiver  40  (see  FIG. 6 ). The bandpass filter  82  is configured to pass a narrow band of received energy around the modulation frequency of the laser designator beam  48 , as modulated by the modulator  94 . The resulting amplitude-modulated signal, if present, is provided to the full-wave rectifier  84  that performs an absolute-value function on the signal. The rectified signal is integrated at integrator  86 , which integrates for the period of time that the laser rangefinder receiver dwells in the illuminated spot of the target provided by the designator beam. The resulting DC signal is compared to a threshold voltage at comparator  90 . The output of the comparator  90  is the true/false reading  76 . 
     FIG. 7B  is a block diagram of an alternative embodiment of the designator beam detection module  72 , in accordance with the present invention. As in the embodiment of  FIG. 7A , the input signal  68  is bandpass filtered at filter  82 , rectified at rectifier  84  and integrated at the first integrator  86 A. The integration period of the first integrator  86 A is equal to the dwell time of the laser signal  56  in the field of view of the receiver  54 . The output of the first integrator  86 A is applied to a positive terminal of comparator  90 . A constant false alarm rate (CFAR) threshold is achieved by further applying the output of the first integrator  86 A to an amplifier  98 , having a gain of K, and then integrating the amplified output for a much longer time period at the second integrator  86 B. In one embodiment, the integration period for the second integrator  86 B is approximately the time elapsed during one circular scan of the system, in other words, the time for the inter-scan spacing  58 . The output of the second integrator  86 B is applied to a negative terminal of the comparator  90 . The output of the comparator  90  is the true/false reading  76 . The false alarm rate in this embodiment is therefore controlled by the gain K of the amplifier  98 . 
   Other systems and methods for determining the presence of reflected designator beam energy  50  in the signal received by the laser rangefinder receiver  40  are equally applicable to the present invention, including systems that detect phase-modulation or frequency-modulation in the laser designator beam, for those systems incorporating such modulation. 
   The addition of a laser designator mode capability to the sensor-fuzed munition provides the greatest flexibility with regard to the Rules of Engagement in effect at the time of its use. The sensor-fuzed munition can optionally operate in the standard mode that employs infrared target detection and laser rangefinding capabilities, without the need for external designation by a designator beam, or, alternatively, to require laser designation when it is available and appropriate. In this manner, a desired level of fire control can be achieved and avoidance of unintended or collateral damage can be further realized. 
   While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made herein without departing from the spirit and scope of the invention as defined by the appended claims. 
   In other embodiments of the present invention, the munitions or submunitions can be dispensed from different types of delivery vehicles, for example by the missile-based system illustrated above in conjunction with  FIG. 1 , or alternatively, from manned aircraft, unmanned aircraft (UAVs), or ground-based launch systems. Cluster bomb units (CBUs) which release a plurality of sub-modules that are each decelerated by parachute, for example BLU-108 sub-modules, each sub-module containing a plurality of submunition projectiles, may also be deployed. The designator beam for illuminating the target can optionally be provided from a ground-based location, as shown, or, alternatively may be provided by other ground-based, air-based, or space-based locations. The designator beam may be manually directed at the target as shown in  FIG. 1 , or, alternatively, may be automatically directed using automated systems. 
   In another embodiment, multiple laser designator beams  48  at multiple wavelengths, from one, or multiple platforms can be used to relay information about the target to the laser rangefinder receiver  40  on the munition  22 . In this case, the different designator beams can be distinguished using different modulation frequencies that are resolved at multiple band pass filters in the designator beam detection module  72 . The ability to differentiate between the multiple designator beams is determined by the dwell time of the receiver beam on the reflected source, or the number of cycles of modulation that are received in the band pass filter.