Patent Publication Number: US-2007103671-A1

Title: Passive-optical locator

Description:
BACKGROUND  
      During some military operations, one or more soldiers locate targets to be fired upon by indirect fire systems or air support (for example) and transmit a geographic location for the target to a fire control center or an integrated tactical network. The fire control center or an integrated tactical network then deploys a strike on the target using the target geographic location. Target designators are used by military personnel to determine the geographical coordinates of a target. One type of target designator is designed so that an operator is able to shine a laser at the target and to receive light scattered and/or reflected from the target in order to determine the geographical coordinates of the target.  
      However, such lasers are typically detectable by enemy sensors, which detect the laser light and set off alarms. In some cases, once the enemy realizes the target geographic location is being determined, the target is moved and/or hidden and/or hardened. Additionally, the enemy can sometimes trace the optical beam back to the operator of the target designator. In this case, the operator can become a target of the enemy.  
      Moreover, the divergence of the laser beam used in such target designators limits the range of such target designators. If the range is too large, the spot size of the laser becomes too large for range determination. Thus, the operator must be within 10,000 meters for ranging, and 5000 meters for designation of the target, which can place the operator in tactical danger. Timing, coordination and lethality are of the essence for combined arms operations, particularly for non-organic fire support/air operations. It is highly desirable for the combat team to engage targets at the farthest practical range possible.  
      Moreover, there are safety issues associated with target designators that use lasers in this way. If the operator or other soldiers near the target designator look directly into the laser, their retina can be burned and/or their vision otherwise impaired.  
     SUMMARY  
      A first aspect of the present invention provides a passive-optical locator including a passive-optical range-finder to generate information indicative of a distance to a target and a sensor to generate information indicative of an azimuth and an elevation of an optical axis of the passive optical range-finder. The passive-optical locator uses information indicative of a geographic location associated with the passive-optical locator, the information indicative of the distance to the target, and the information indicative of the azimuth and the elevation of the optical axis the information to determine information indicative of an absolute geographic location associated with the target.  
      A second aspect of the present invention provides a method to determine geographic location of a target. The method includes receiving information indicative of a distance between a target and a passive-optical locator, receiving information indicative of an azimuth and an elevation of a direction to the target, receiving information indicative of the geographic location of the passive-optical locator, and generating an absolute geographic location of the target.  
      A third aspect of the present invention provides a passive-optical locator including a passive-optical range-finder to generate information indicative of a distance to a target and a sensor to generate information indicative of an azimuth and an elevation of an optical axis of the passive optical range-finder and a communication interface. The communication interface communicates at least a portion of: the information indicative of a geographic location associated with the passive-optical locator, the information indicative of the distance to the target, and the information indicative of the azimuth and the elevation of the optical axis to a remote device for processing that generates information indicative of an absolute geographic location associated with the target therefrom.  
      A fourth aspect of the present invention provides a passive-optical locator, the system including means for receiving information indicative of a distance to a target from a passive-optical locator, means for receiving information indicative of an azimuth and an elevation of a direction to the target, means for receiving information indicative of the geographic location of the passive-optical locator, and means for generating an absolute geographic location of the target.  
    
    
     DRAWINGS  
       FIG. 1  is a block diagram of a first embodiment of a system that uses a passive-optical locator.  
       FIG. 2  is a block diagram of an embodiment of a passive-optical range-finder.  
       FIG. 3  is a flowchart of one embodiment of a method of determining an absolute geographic location of a target.  
       FIG. 4  and  5 A- 5 B illustrate the calibration of components of the system of Figure and trigonometric relationships used therein.  
       FIG. 6  is a block diagram of a second embodiment of a passive-optical locator.  
       FIG. 7  is a block diagram of a third embodiment of a passive-optical locator. 
    
    
      The various described features are not drawn to scale but are drawn to emphasize features relevant to the subject matter described. Reference characters denote like elements throughout the figures and text.  
     DETAILED DESCRIPTION  
      In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the claimed invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the claimed invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the claimed invention. The following detailed description is, therefore, not to be taken in a limiting sense.  
       FIG. 1  is a block diagram of a one embodiment of a system  100  that uses a passive-optical locator  32 . In the embodiment shown in  FIG. 1 , the passive-optical locator  32  is deployed in a military application in which the passive-optical locator  32  operates as a laser-free passive-optical locator. The passive-optical locator  32  includes a passive-optical range-finder  85 , a global positioning system/gyroscope (GPS/GYRO) device  62 , a processor  90 , a memory  91 , and a display  75 . The GPS/GYRO device  62  comprises one or more gyroscopic devices  73  integrated with a global positioning system (GPS)  60 . The various components of the passive-optical locator  32  are communicatively coupled to one another as needed using appropriate interfaces (for example, using buses, traces, cables, wires, ports, transceivers and the like).  
      The processor  90  executes software and/or firmware that causes the processor  90  to perform at least some of the processing described here as being performed by the passive-optical locator  32 . At least a portion of such software and/or firmware executed by the processor  90  and any related data structures are stored in memory  91  during execution. Memory  91  comprises any suitable memory now known or later developed such as, for example, random access memory (RAM), read only memory (ROM), and/or registers within the processor  90 . In one implementation, the processor  90  comprises a microprocessor or microcontroller. Moreover, although the processor  90  and memory  91  are shown as separate elements in  FIG. 1 , in one implementation, the processor  90  and memory  91  are implemented in a single device (for example, a single integrated-circuit device). The software and/or firmware executed by the processor  90  comprises a plurality of program instructions that are stored or otherwise embodied on a storage medium (not shown in  FIG. 1 ) from which at least a portion of such program instructions are read for execution by the processor  90 . In one implementation, the processor  90  comprises processor support chips and/or system support chips such as ASICs.  
      The passive-optical range-finder  85  generates information indicative of a distance R from the passive-optical locator  32  to a target  50 . This information is also referred to here as “distance information.” The passive-optical range-finder  85  generates the distance in a passive optical manner in which the target  50  is not illuminated with a laser. The passive-optical range-finder  85 , in one implementation of the embodiment shown in  FIG. 1 , comprises an image-coincidence range finder of the type shown in  FIG. 2 . In other embodiments, the passive-optical range-finder  85  is implemented in other ways, for example, using a passive auto-ranging range-finder, a tilted image plane sensor range-finder, a depth-of-focus range-finder, Charged Coupled Devices (CCD), Active Pixel Sensors (APS), and night vision capability with technologies like an infra-red imaging viewer, or a light intensification imaging viewer. One example of a commercially available passive-optical image coincidence range-finder is the Commercial-Off-The-Shelf (COTS) RANGING  200  rangefinder, which is available from CABELAS. One example of an infra-red imaging viewer is the COTS T14FLIR THERMAL IMAGING HAND HELD VIEWER-GOGGLE AND WEAPON SIGHT, which is available from Imaging1.com. In one implementation, the distance information generated by the passive-optical range-finder  85  is used to generate a distance between the passive-optical locator  32  and the target  50 . The designation, ranging and range accuracy are limited by the quality and capability of the optics and the accuracy of the coordinate system and its transforms. As used herein, the passive-optical range-finder  85  is referred to as being “focused” or “in focus” when the passive-optical range-finder  85  is optically configured or otherwise adjusted so as to measure properly the distance between the passive-optical range-finder  85  and the target  50 .  
      The one or more gyroscopic devices  73  in the GPS/GYRO device  62  generate information indicative of an azimuth θ and an elevation φ of an optical axis  35  of the passive-optical range-finder  85 . Such information is also referred to here as “azimuth and elevation information.” In  FIG. 1 , only one such gyroscopic device  73  is shown though it is to be understood that one or more gyroscopic devices  73  are used in various implementations of such an embodiment. In one implementation of such an embodiment, gyroscopic device  73  comprises an inertial navigation system that generates the azimuth and elevation information.  
      The GPS  60  in the GPS/GYRO device  62  generates or otherwise outputs information indicative of an absolute geographic location associated with the passive-optical locator  32 . Such information is also referred to here as “GPS information.” In one implementation of such an embodiment, the GPS information associated with the passive-optical locator  32  includes the latitude Lat L , the longitude Long L , and the attitude Alt L  of the passive-optical locator  32 . The GPS  60  includes various GPS implementations such as Differential GPS (DGPS). Although the gyroscopic device  73  and the GPS  60  are shown in  FIG. 1  as a single, integrated device, in other implementations the GPS  60  and the gyroscopic device  73  are implemented using two more separate devices. The software and/or firmware executing on the processor  90  processes the GPS information, the distance information, and the azimuth and elevation information in order to determine information indicative of an absolute geographic location associated with the target  50  (also referred to here as the “target location information”). The target location information is defined by a latitude Lat T , a longitude Long T , and a altitude Alt T  of the target  50  and is generated using one or more trigonometric relationships between the distance between the passive-optical range-finder  85  and the target  50 , the azimuth θ and the elevation φ of the optical axis  35  of the passive-optical range-finder  85 , and the absolute geographic location of the passive-optical locator  32 . In one implementation, such trigonometric relationships are established and/or corrected using the calibration techniques described below in connection with  FIGS. 4 and 5 A- 5 B. In one implementation of the embodiment of the passive-optical locator  32  of  FIG. 1 , the processor  90  outputs the target location information associated with the target  50  on the display  75 . The display  75  provides a visual indication of the absolute location of the target  50  for the operator of the passive-optical locator  32 . In one implementation of such an embodiment, the display  75  shows the values for the target latitude Lat T , target longitude Long T  and target altitude Alt T . In another implementation, the display  75  shows the values for the azimuth θ and the elevation φ from the passive-optical locator  32 , as well as, the target latitude Lat T , a target longitude Long T  and a target altitude Alt T . In other implementations, information indicative of the absolute location of the target  50  is displayed in other ways.  
      In the embodiment shown in  FIG. 1 , the passive-optical locator  32  comprises a communication interface (CI)  33  that communicates at least a portion of the information indicative of the absolute location of the target  50  from the passive-optical locator  32  to a remote device  20  over a communication link  71 . The communication link  71  comprises one or more of a wireless communication link (for example, a radio-frequency (RF) communication link) and/or a wired communication link (for example, an optical fiber or copper wire communication link). For applications of such an embodiment in which secure communication is desired, one or more appropriate protocols for automation, encryption, frequency hopping, and spread-spectrum concealment are used in communicating such information from the passive-optical locator  32  and the remote device  20 . In one implementation of such an embodiment, the target location information is communicated from the passive-optical locator  32  to the remote device  20  by having the operator read such the target location information off the display  75  and describe the target (for example, “Dismounted troops in the open at this grid coordinate”). The operator announces the target location information and the target description into a microphone coupled to the communication interface  33  so that the voice of the operator is communicated over the communication link  71  to the remote device  20 . In another implementation, the target location information is communicated in digital form from the processor  90  over the communication link  71 . In such an implementation, a processor  21  included in the remote device  20  executes software to process such target location information.  
      In an alternative embodiment, the target location information is not generated at the passive-optical locator  32  and, instead, the distance information, azimuth and elevation information, and GPS information is communicated from the passive-optical locator  32  to the remote device  20  and the remote device  20  generates the absolute geographic location associated with the target  50  using such distance information, azimuth and elevation information, and GPS information (for example, using software executing on the processor  21  of the remote device  20 ).  
      In the embodiment shown in  FIG. 1 , the remote device  20  is part of an integrated tactical network. The integrated tactical network comprises a wide area network (WAN) used for communications, command, control and intelligence functions for military operations. The integrated tactical network integrates the indirect fire control centers and forward air controllers to direct fire missions and air strikes. As shown in  FIG. 1 , the remote device  20  is part of an integrated tactical network. The remote device  20  communicates the target location information for the target  50  to a fire control center  25  over a communication link  72 . A target description is also communicated. The fire control center  25  is operable to deploy a weapon (not shown) on a trajectory  26  towards the target  50 . In one implementation, the passive-optical locator  32  is packaged in a bipod/shoulder unit that can be carried by a soldier. In another implementation, the passive-optical locator  32  is packaged in a tripod unit that can be carried by a soldier. In yet another implementation, the passive-optical locator  32  is mounted on a vehicle.  
      The communication link  72  comprises one or more of a wireless communication link (for example, a radio-frequency (RF) communication link) and/or a wired communication link (for example, an optical fiber or copper wire communication link). For applications of such an embodiment in which secure communication is desired, one or more appropriate protocols for automation, encryption, frequency hopping, and spread-spectrum concealment are used in communicating such information from the remote device  20  to the fire control center  25 .  
      Although a military application is described here in connection with  FIG. 1 , it is to be understood that the passive-optical locator  32  can be used in other applications, including commercial applications. Generally, the target  50  is an object to be located at an absolute geographic location. In one exemplary usage scenario, the object to be located is a person stranded on a side of a mountain. In this usage scenario, a person in a search and rescue party uses the passive-optical range-finder  85  of the passive-optical locator  32  to focus on an image of the stranded person and the target location information of the stranded person is communicated to a rescue helicopter. Other applications include geographical surveying, civil engineering and navigation.  
       FIG. 2  is a block diagram of one embodiment of a passive-optical range-finder  85 . The embodiment of the passive-optical range-finder  85  shown in  FIG. 2  is described here as being used in the system  100  of  FIG. 1  (though it is to be understood that the passive-optical range-finder  85  can be used in other embodiments).  
      The particular embodiment of the passive-optical range-finder  85  shown in  FIG. 2  comprises an implementation of an image-coincidence range finder. The passive-optical range-finder  85  comprises focusing optics (not shown) and relative components  86 . In this embodiment, the relative components  86  include a self contained base  89 , a first mirror  87  and a second mirror  88 . The first mirror  87  and the second mirror  88  are at opposing ends of the self contained base  89 . While passive optical range-finder  85  is focused, the first mirror  87  and the second mirror  88  are rotated. The rotation is about a vertical axis formed at the point where the first mirror  87  and the second mirror  88  intersect with the self contained base  89 . A mechanical adjustment system (not shown) is operable to ensure that angle β between the first mirror  87  and the self contained base  89  always equals the angle β between the second mirror  88  and the self contained base  89 .  
      When the focusing optics of the passive-optical range-finder  85  focus the light  65  that is reflected, emitted and/or scattered from the target  50 , the first mirror  87  and the second mirror  88  each reflect at least a portion of the light  65 . The first mirror  87  reflects light  65  as light  66  towards the focal plane  98  of the passive-optical range-finder  85 . The second mirror  88  reflects light  65  as light  67  towards the focal plane  98  of the passive-optical range-finder  85 . The angle of incidence of the light  65  is 90°−α for both the first mirror  87  and the second mirror  88 , where α is the angle formed between the first mirror  87  and the light  66  and the second mirror  88  and the light  67 . As the image  53  of the target  50  is focused in the focal plane  98 , the first mirror  87  and the second mirror  88  are rotated into the angular position in which the light  66  is coincident with light  67  in the focal plane  98 . When target  50  is “focused” (also referred to here as being “in focus”) in the focal plane  98 , the target image  53  from light  66  is coincident with the target image  53  from light  67 .  
      One or more relative-position sensors  97  in the passive-optical range-finder  85  generate relative-position sensor data about the relative angle β between the self contained base  89  and the first mirror  87  and the second mirror  88 . When the target  50  is focused, the relative-position sensor data about the relative angle β is output by the passive-optical range-finder  85  to the processor  90  (shown in  FIG. 1 ). In such an embodiment, the software and/or firmware executing on the processor  90  generates calculates the distance between the passive-optical range-finder  85  and the target  50  using one or more trigonometric relationships between the length of the self contained base  89  and the relative angle β between the self contained base  89  and the first mirror  87  and the second mirror  88 . In one implementation, such trigonometric relationships are established and/or corrected using the calibration techniques described below in connection with  FIGS. 4 and 5 A- 5 B. In other embodiments, the passive-optical range-finder  85  comprises a separate, integrated processor that performs the trigonometric and/or calibration processing and outputs data that encodes or otherwise contains the distance between the passive-optical range-finder  85  and the target  50 .  
      In military or self-contained-base rangefinders, the first mirror  87  and the second mirror  88  are penta-prisms or penta-mirrors and only one of the first mirror  87  and the second mirror  88  rotates so that the two images from the first mirror  87  and the second mirror  88  overlap. An implementation of a self-contained-base rangefinder is described in pages in pages 238-242 of “Optical System Design,” written by Rudolf Kingslake and published in 1983 by Academic Press, Inc.  
       FIG. 3  is a flowchart of one embodiment of a method  300  of determining an absolute geographic location of a target. The embodiment of method  300  is described as being implemented using the passive-optical locator  32  of  FIG. 1 . In such an embodiment, at least a portion of the processing of method  300  is performed by software executing on the processor  90  of the passive-optical locator  32  and/or the GPS/GYRO device  62  or the passive-optical range-finder  85 .  
      When an operator of the passive-optical range-finder  85  has aligned the optical axis  35  of the passive-optical range-finder  85  along a line of sight  54  to the target  50  (checked in block  302 ) and the operator has focused the passive-optical range-finder  85  (checked in block  304 ), the information indicative of the distance between the passive-optical locator  32  and the target  50  (that is, the distance information) is generated (block  306 ). For example, in one implementation, the passive-optical locator  32  comprises a button or other switch that the operator actuates in order to signal to software executing on the processor  90  that the operator has aligned the optical axis  35  of the passive-optical range-finder  85  along a line of sight  54  to the target  50  and has focused the passive-optical range-finder  85 . When this happens, the passive-optical range-finder  85  generates the distance information (for example, as described above in connection with  FIG. 2 ) and outputs such distance information to the software executing on the processor  90 .  
      Software executing on the processor  90  then receives information indicative of an azimuth θ and an elevation φ of an optical axis  35  of the passive-optical range-finder  85  and information indicative of the absolute geographic location of the passive-optical locator  32  from the GPS/GYRO device  60  (blocks  308  and  310 ). The software executing on the processor  90  then uses one or more trigonometric relationships between the distance between the passive-optical range-finder  85  and the target  50 , the azimuth θ θ and the elevation φ of the optical axis  35  of the passive-optical range-finder  85 , and the absolute geographic location of the passive-optical locator  32  to generate information indicative of an absolute geographic location of the target  50  (block  312 ). The software executing on the processor  90  of the passive-optical locator  32  then displays the absolute geographic location of the target  50  on the display  75  (block  314 ) and/or communicates the absolute geographic location to the remote device  20  over the communication link  71  (block  316 ).  
      In order for the distance information about the target  50  to be accurate, the passive optical range-finder  85  must be calibrated. In order for the azimuth and elevation information to be accurate, the gyroscopic device  73  must be calibrated. Likewise, in order for the GPS information to be accurate, the global positioning system  60  must be calibrated.  FIG. 3  illustrates one approach to calibrating the global positioning system  60 , the gyroscopic device  73 , and the passive-optical range-finder  85  of  FIG. 1  that makes use of the image-coincidence range finder shown in  FIG. 2 . When the global positioning system  60 , the gyroscopic device  73 , and the passive-optical range-finder  85  are all calibrated, the passive-optical locator  32  is operable to determine accurately an azimuth θ θ, an elevation φ and a distance R to a target  50  when the target  50  is focused on an image plane  98  (shown in  FIG. 2 ) of the passive-optical locator  32 . Then the processor  90  accurately determines the absolute location information for the target geographic location  52  of a target  50 .  
      A calibration benchmark  70  is positioned at a calibration geographic location  22  defined by a benchmark latitude Lat BM , benchmark longitude Long BM , and benchmark altitude Alt BM . The calibration geographic location  22  is at the origin of the coordinate system defined by the vectors X c , Y c , and Z c . In the field, the passive-optical locator  32  is located at geographic location  40  defined by a passive-optical locator latitude Lat L , passive-optical locator longitude Long L , and passive-optical locator attitude Alt L . The geographic location  40  is at the origin of the coordinate system defined by the vectors X L , Y L , and Z L .  
      As defined herein, altitude is the height above or below sea level where a positive altitude is above sea level. As defined herein, elevation φ is the angle subtended by a line, such as unit vector  95 , and a locally absolute horizon in the plane defined by X L  and Y L . The tail of unit vector  95  is at the origin of the coordinate system defined by the vectors X L , Y L , and Z L  and unit vector  95  points toward the target  50  positioned at the absolute target geographic location  52 . Unit vector  95  is equal in direction to range vector  94 . Range vector  94  has the length R equal to the distance between the passive-optical locator  32  and the target  50 .  
      The locally absolute horizon at a given geographic location includes the points in the plane tangential to the earth&#39;s surface as the distance away from the geographic location becomes much larger than other dimensions under consideration as shown in  FIGS. 5A and 5B . Except for the special cases when the geographic location is at one of the earth&#39;s poles, the locally absolute horizon contains the cardinal direction vectors north, south, east and west. The zenith and nadir of the geographic location are perpendicular to this tangential plane, the zenith being directly above the given geographic location and the nadir being directly below the given geographic location.  
      In accordance with one implementation of the passive-optical locator  32 ,  FIGS. 5A and 5B  are a top view and a side view, respectively, of the azimuth θ, elevation φ to the target  50  from the passive optical range-finder  32  with respect the locally absolute horizon  36 .  
      In  FIG. 5A , the top view of the passive-optical locator  32  shows the locally absolute horizon  36  in the plane defined by X L  and Y L . The passive-optical locator  32  is located at the geographic location  40  where X L  and Y L  intersect and optical axis  35  is pointed towards the target  50 . The azimuth θ is defined as the angle subtended by the north direction and a line on the locally absolute horizon. A 90° azimuth is the east direction, and a 270° azimuth is the west direction. In  FIG. 5A , the optical axis  35  is seen projected onto the locally absolute horizon  36  and the azimuth θ is about 225°.  
      In  FIG. 5B , the side-view of the passive-optical locator  32  shows the cross-sectional view of the locally absolute horizon  36 . The optical axis  35  is seen at an elevation φ of about 45° from the locally absolute horizon  36 . The zenith of the passive-optical locator  32  is defined by Z L .  
      As shown  FIG. 4 , the azimuth θ is between the north direction X L  and a line that is the projection of vector  95  onto the plane defined by X L -Y L . The line of sight  54  is along the vector  94  shown connecting the geographic location  40  to the target geographic location  50 . The geographic location  40  is a distance R from the target geographic location  50 . Thus as illustrated, the target  50  is at an azimuth θ, an elevation φ and a distance R from the passive-optical locator  32 .  
      The calibration benchmark  70  includes a graduated range  24 , which includes an exemplary plurality of calibration targets C 1 , C 2 , C 3  and C 4(. . . ) . More than four calibrations targets are typically implemented in a calibration benchmark. Calibration targets C 1 , C 2 , C 3  and C 4  provide reference points from the calibration geographic location  22 . Each calibration target C 1 , C 2 , C 3  and C 4  is at a known distance, a known azimuth and a known elevation from the calibration geographic location  22 . In one implementation of the calibration process of the passive-optical locator  32 , the passive-optical locator  32  is positioned at the calibration geographic location  22  and sequentially aimed at each of the calibration targets C 1 , C 2 , C 3  and C 4 .  
      While the passive-optical locator  32  is located at the calibration geographic location  22  and the passive-optical range-finder  85  is focused on the calibration target C 1 , information is obtained for correlation with the reference point of calibration target C 1 . The obtained information includes: distance information about calibration target C 1 ; azimuth and elevation information about calibration target C 1  which includes azimuth and elevation information about the optical axis  35  when the passive-optical range-finder  85  is focused on target C 1 ; and information indicative of the geographic location of the passive-optical locator  32 .  
      When focused on the calibration target C 1 , the passive-optical range-finder  85  generates distance information about calibration target C 1 . The gyroscopic device  73  generates the azimuth and elevation information about calibration target C 1 . The global positioning system  60  generates GPS information for the passive-optical locator  32 . If the generated information indicates the known distance r 1  to the calibration target C 1 , the known azimuth θ 1 ,of the calibration target C 1 , the known elevation φ 1 , of calibration target C 1 , and the benchmark latitude Lat BM , benchmark longitude Long BM , and benchmark altitude Alt BM  of the calibration geographic location  22 , the passive-optical locator  32  is calibrated for that calibration target C 1 .  
      In one implementation of the calibration process, during the next stage of calibration, the passive-optical range-finder  85  is focused on the calibration target C 2 . The obtained information then includes: distance information about calibration target C 2 ; azimuth and elevation information about calibration target C 2  which includes a azimuth and elevation information about the optical axis  35  when the passive-optical range-finder  85  is focused on target C 2 . The information indicative of the geographic location of the passive-optical locator  32  has not changed since the passive-optical locator  32  has not moved from the calibration geographic location  22 .  
      When focused on the calibration target C 2 , the passive-optical range-finder  85  generates the distance information about calibration target C 2 . The gyroscopic device  73  generates azimuth and elevation information about calibration target C 2 . If the respective information indicates the known distance r 2  to the calibration target C 2 , the known azimuth θ 2  of the calibration target C 2 , and the known elevation φ 2  of calibration target C 2  the passive-optical locator  32  is calibrated to the second calibration target C 2 . In one implementation of the calibration process, during the next stage of calibration, the passive-optical range-finder is focused on the calibration target C 3 . The process is repeated for all the remaining calibration targets C 3 -C 4 . If there are no differences between the known and measured distances, azimuths and elevations and geographic locations, the passive-optical locator  32  is calibrated.  
      When the passive-optical range-finder  85  is calibrated with the calibration benchmark  70  and is focused on the target  50 , the passive optical range-finder  85  generates accurate distance information for the target  50 .  
      When the global positioning system  60  is calibrated with the calibration benchmark  20 , the global positioning system  60  generates accurate GPS information indicative of a passive-optical locator latitude Lat L , a passive-optical locator longitude Long L  and a passive-optical locator altitude Alt L  for any position of the passive-optical locator  32 . Global positioning systems are known by those of skill in the art and are not described herein.  
      When the gyroscopic device  73  is calibrated with the calibration benchmark  20  and co-located with the global positioning system  60 , the gyroscopic device  73  generates accurate azimuth and elevation information for the optical axis  35 . The azimuth and elevation information includes an optical axis azimuth θ OA  and an optical axis elevation φ OA  ( FIGS. 5A and 5B ). The elevation φ OA  can be negative or positive. Inertial navigation systems are known by those of skill in the art and are not described herein. In one implementation of the passive-optical locator, the gyroscopic device  73  in the passive-optical locator  32  recognizes, tracks and stores all movements of the passive-optical locator subsequent to the calibration process as the passive-optical locator is transported to other geographic locations. This information may be stored with the gyroscopic device  73  or downloaded into the integrated tactical network for maintenance record keeping. In one implementation of such an embodiment of a gyroscopic device  73 , the gyroscopic device  73  includes an accelerometer  74  ( FIG. 7 ).  
      In another implementation of the passive-optical range-finder  85 , the global positioning system  60 , the gyroscopic device  73 , and the passive-optical range-finder  85  are calibrated when they are manufactured and the calibration is maintained by the manufacturer of each of the global positioning system  60 , the gyroscopic device  73 , and the passive-optical range-finder  85 .  
       FIG. 6  is a block diagram of a second embodiment of a passive-optical locator  30 . In the embodiment shown in  FIG. 6 , the global positioning system  60  and one or more gyroscopic devices  73  are located external to the passive-optical locator  30 . The passive-optical locator  30  includes a passive-optical range-finder  85 , a processor  90 , memory  91 , a GPS interface  33 A, a gryo interface  33 B and a communication interface  33 C. In  FIG. 6 , only one such gyroscopic device  73  is shown though it is to be understood that one or more gyroscopic devices  73  are used in various implementation of such an embodiment. In this implementation of the passive-optical locator  30 , the one or more gyroscopic devices  73  located external to the passive-optical locator  30  are physically attached to the passive-optical locator  30  and the one or more gyroscopic devices  73  are each calibrated for alignment to the optical axis  35  of the passive-optical range-finder  85  before the passive-optical locator  30  is implemented.  
      The global positioning system  60  communicates with the passive-optical locator  30  via the GPS interface  33 A. The GPS interface  33 A communicates data from the global positioning system  60  to the processor  90 . The one or more gyroscopic devices  73  communicate with the passive-optical locator  30  via gyro interface  33 B. The gyro interface  33 B communicates data from the one or more gyroscopic devices  73  to the processor  90 . The passive-optical locator  30  in conjunction with the externally-located global positioning system  60  and one or more gyroscopic devices  73  attached to the passive-optical locator  30  performs the same functions as the passive-optical locator  32  of  FIG. 1 .  
      The various components of the passive-optical locator  30  are communicatively coupled to one another as needed using appropriate interfaces (for example, using buses, traces, cables, wires, ports, and the like). In one implementation of the embodiment shown in  FIG. 6 , the GPS interface  33 A, the gyro interface  33 B and the communication interface  33 C comprise one communication interface. Other implementations of such an embodiment are implemented in other ways. In one implementation of the embodiment shown in  FIG. 6 , the one or more gyroscopic devices  73  are strapped onto an aiming barrel of the passive-optical locator  30  prior to a calibration alignment of the one or more gyroscopic devices  73  to the optical axis  35 .  
       FIG. 7  is a block diagram of a third embodiment of a passive-optical locator  31 . In this embodiment of the passive-optical locator  31 , the one or more gyroscopic devices  73  are co-located with one or more accelerometers  74  in the passive-optical locator  31  and the global positioning system  60  is external to the passive-optical locator  31 . The global positioning system  60  is communicatively coupled to the rest of the passive-optical locator  31  via a GPS interface  33 A. The one or more accelerometers  74  are communicatively coupled to the processor  90 .  
      The one or more accelerometers  74  are operable to sense linear motion of the passive-optical locator  31 . The one or more accelerometers  74  are also operable to monitor for shock or vibrations of the passive-optical locator  31  that could negatively impact the operation of the passive-optical locator  31 . In one implementation of the passive-optical locator  31 , the processor  90  transmits a warning to the operator if the one or more accelerometers  74  sense a potentially damaging impact on the passive-optical locator  31 . In another implementation of the passive-optical locator  31 , the operator of the passive-optical locator  31  carries the global positioning system  60  in a backpack while operating the passive-optical locator  31 . The passive-optical locator  31  in conjunction with the externally-located global positioning system  60  performs the same functions as the passive-optical locator  32  of  FIG. 1 .  
      Other methods of range-finding are operable with the various passive-optical locators  30 ,  31  and  32 . In one implementation of the passive-optical locator, the range-finder includes an imaging devices such as charge-coupled-devices (CCD) or active pixel sensors (APS). In such an implementation, the CCD or APS images the target  50 , the processor  90  receives data from the CCD and processes the data to determine the apparent size of the target  50  at the specific magnification of the passive-optical locator. Then the processor  90  searches databases of sized-images stored in memory  91  and determines if a dimensional fit correlates with the image sensed at the CCD. If there is a fit, the processor  90  provides the distance R to the target  50  to the operator of the passive-optical locator.  
      Both APS and CCD technologies input entire frame images to processing electronics so the process is very fast. The operator views the image of the Field-Of-View (FOV) in the display  75  ( FIG. 1 ). In this implementation, the target  50  is not necessarily an object, but may be a Field-Of-View that can be focused upon. An automated routine would search for the sharpest pixel delineation.  
      Available detectors arrays in CCDs and APSs are capable of detecting a broadband spectrum including visible light, the near infrared (NIR), and near ultraviolet. In one implementation of this embodiment, the passive-optical locator includes a plurality of detector arrays that in combination cover all of the above spectral ranges. CCD detectors include Intensified CCD (ICCD), Electron Multiplying CCD (EMCCD), and other associated technologies, such as light intensification and infra-red imagery. Light intensification and infra-red imagery allow for night vision.  
      The automated imaging function provided by imaging devices allows for integration of the passive-optical locator in a robotic system. A robotic system that includes a passive-optical locator is capable of indirect fire and air control, forward observation/spotting and optical surveillance for robotic maneuver teams, long-term staring forward observation/spotting for indirect fire and air control and optical surveillance missions.  
      One implementation of the passive-optical locator includes a warning capabiliy to warn the operator, the fire control center and/or the integrated tactical network if the passive-optical locator has sent or is ready to send a fire request that will provide an impact that endangers the location of the passive-optical locator.  
      The various components of the passive-optical locator  31  are communicatively coupled to one another as needed using appropriate interfaces (for example, using buses, traces, cables, wires, ports, transceivers and the like). In one implementation of the embodiment shown in  FIG. 7 , the GPS interface  33 A and the communication interface  33 C comprise one communication interface. Other implementations of such an embodiment are implemented in other ways.  
      The methods and techniques described here may be implemented in digital electronic circuitry, or with a programmable processor (for example, a special-purpose processor or a general-purpose processor such as a computer) firmware, software, or in combinations of them. Apparatus embodying these techniques may include appropriate input and output devices, a programmable processor, and a storage medium tangibly embodying program instructions for execution by the programmable processor. A process embodying these techniques may be performed by a programmable processor executing a program of instructions to perform desired functions by operating on input data and generating appropriate output. The techniques may advantageously be implemented in one or more programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and DVD disks. Any of the foregoing may be supplemented by, or incorporated in, specially-designed application-specific integrated circuits (ASICs).  
      A number of embodiments of the invention defined by the following claims have been described. Nevertheless, it will be understood that various modifications to the described embodiments may be made without departing from the spirit and scope of the claimed invention. Accordingly, other embodiments are within the scope of the following claims.