Patent Publication Number: US-7219853-B2

Title: Systems and methods for tracking targets with aimpoint offset

Description:
TECHNICAL FIELD 
   Embodiments of the present invention pertain to imaging systems and to target identification systems. Some embodiments pertain to missile defense systems. 
   BACKGROUND 
   Target identification and tracking systems that employ a number of tracking vehicles to track and/or destroy targets generally require high resolution imaging to identify a specific aimpoint on a target that differs from the target&#39;s centroid. It may be desirable to track an aimpoint on a target, rather than a centroid, because the lethality of the tracking vehicle can be improved, resulting in reduced cost, size, and/or weight. Some conventional target identification systems use long-wave (LW) diffraction techniques to identify and/or track a target. The resolution of these long-wave diffraction techniques is limited by aperture size and wavelength, among other things, making these techniques impractical for small tracking vehicles, such as miniature kill vehicles, to track a target&#39;s aimpoint other than a centroid. 
   Some higher resolution systems that use shorter wavelengths for imaging may have better diffraction limits for tracking a separate aimpoint, but have a limited passive acquisition range and may require external illumination to acquire targets. Some lower resolution systems that track a target&#39;s centroid do not need high resolution because they do not identify a separate aimpoint. These lower resolution systems may require the tracking vehicles to have a higher kill radius. This may result in heavier and/or more expensive tracking vehicles. 
   Thus, there are general needs for methods and target tracking systems that can track a target&#39;s aimpoint that&#39;s offset from the centroid with smaller tracking vehicles. 
   SUMMARY 
   A target identification and tracking system includes a carrier vehicle and one or more tracking vehicles. The carrier vehicle may determine an aimpoint of a target from an image of the target and may generate an offset from a tracking point to the aimpoint. The offset may be conveyed to an assigned tracking vehicle for tracking the tracking point of the target while navigating toward the aimpoint of the target. The tracking point may be the target&#39;s centroid. The carrier vehicle may employ a high-resolution LIDAR imaging system to identify the aimpoint from a target&#39;s features; while the tracking vehicle may employ a lower resolution optical imaging system for tracking the target&#39;s tracking point. The carrier vehicle may correct the offset for parallax and the offset may be revised as the tracking vehicle approaches the target. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims are directed to some of the various embodiments of the present invention. However, the detailed description presents a more complete understanding of embodiments of the present invention when considered in connection with the figures, wherein like reference numbers refer to similar items throughout the figures and: 
       FIG. 1  illustrates a target identification and tracking system in accordance with some embodiments of the present invention; 
       FIG. 2  illustrates the tracking of a target in accordance with some embodiments of the present invention; 
       FIG. 3  is a functional block diagram of a carrier vehicle in accordance with some embodiments of the present invention; 
       FIG. 4  is a functional block diagram of a tracking vehicle in accordance with some embodiments of the present invention; and 
       FIG. 5  is a flow chart of a target tracking procedure in accordance with some embodiments of the present invention. 
   

   DETAILED DESCRIPTION 
   The following description and the drawings illustrate specific embodiments of the invention sufficiently to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The scope of embodiments of the invention encompasses the full ambit of the claims and all available equivalents of those claims. Such embodiments of the invention may be referred to, individually or collectively, herein by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. 
     FIG. 1  illustrates a target identification and tracking system in accordance with some embodiments of the present invention. Target identification and tracking system  100  may include carrier vehicle  104  and a plurality of tracking vehicles  103  to track one or more targets  107 . In some embodiments, tracking vehicles may be kill vehicles, such as miniature kill vehicles, and targets  107  may be enemy missiles or warheads, although the scope of the invention is not limited in this respect. 
   In accordance with some embodiments, carrier vehicle  104  generates an offset from a tracking point from an image of target  106 , and at least one of tracking vehicles  103  (e.g., tracking vehicle  102 ) tracks the tracking point of target  106  while navigating toward an aimpoint of target  106  based on the offset. The aimpoint may be determined from the offset and the tracking point. The offset may be provided by the carrier vehicle. In some embodiments, the tracking point of a target may be a centroid of the target, although the scope of the invention is not limited in this respect. Accordingly, tracking vehicles  103  only require sufficient resolution to track a tracking point rather than an aimpoint. 
     FIG. 2  illustrates the tracking of a target in accordance with some embodiments of the present invention. Referring to  FIGS. 1 and 2  together, in accordance with some embodiments, carrier vehicle  104  may generate image  206  of target  106 , and may determine aimpoint  204  based on characteristics of image  206 . Carrier vehicle  104  may further determine offset  212  to aimpoint  204  from tracking point  202 . Carrier vehicle  104  may then convey offset  212  to tracking vehicle  102 . 
   In some embodiments, carrier vehicle  104  may correct the offset for parallax based on a position of the tracking vehicle  102  and a position of the carrier vehicle  104 . In some embodiments, the parallax correction may take into account the differing views seen by the carrier vehicle (e.g., from direction  108 ) and the assigned tracking vehicle (e.g., from direction  110 ). In these embodiments, the offset may be translated between the offset seen by the carrier vehicle to an offset that would be seen by the tracking vehicle. Carrier vehicle  104  may convey the parallax corrected offset to tracking vehicle  102 . 
   In some embodiments, offset  212  may comprise a distance and a direction from tracking point  202  to aimpoint  204 . In some embodiments, offset  212  comprises a magnitude and an angle relative to tracking point  202 . In some embodiments, tracking point  202  may be a centroid of the target  106 . In some embodiments, the centroid may be the center of mass of the target as determined from a two-dimensional image (e.g., without range of the target) generated by carrier vehicle  104 . This is described in more detail below. 
   In some embodiments, carrier vehicle  104  initially identifies a target, tracks tracking point  202 , and directs a high-resolution laser-imaging sensor (e.g., LIDAR) at the tracked target to generate image  206 . Image  206  may be a high-resolution three-dimensional (3D) image comprising a two-dimensional (2D) image of pixels with ranging information for at least some of the pixels. In these embodiments, tracking point  202  may already be known when carrier vehicle  104  generates image  206  of the target  106 . In these embodiments, carrier vehicle  104  may already be tracking target  106  when it generates the image  206  of target  106 . 
   In some embodiments, carrier vehicle  104  may track an intensity weighted centroid of target  106 , which may more closely match a natural tracking point of the target. In these embodiments the intensity of image data (e.g., pixels) may be taken into account to weight the centroid of a tracked target, although the scope of the invention is not limited in this respect. 
   In some embodiments, carrier vehicle  104  may determine aimpoint  204  by resolving the image including extracting features from the image. The features may include shape, orientation and/or size of the target, although the scope of the invention is not limited in this respect, as other features may also be used to determine the aimpoint for a particular target. 
   In some embodiments, carrier vehicle  104  and tracking vehicles  103  may use a common reference frame, such as a common inertial reference frame, which may specify the direction of the aimpoint offset in a plane perpendicular to the tracking vehicle&#39;s line-of-sight. In these embodiments, offset  212  may be provided to the tracking vehicle relative to their common reference frame. In these embodiments, tracking vehicles  103  and carrier vehicle  104  may be able to track the tracking point of the targets relative to the same reference frame, reducing errors therebetween. 
   In some embodiments, tracking vehicle  102  may revise offset  212  while navigating toward the target. Offset  212  may change with respect to the tracking point as the tracking vehicle approaches the target. A revised inertial vector for navigating to aimpoint  204  based on a revised offset may be determined to allow tracking vehicle  102  to continue in a direction toward aimpoint  204 . In some embodiments, carrier vehicle  104  may determine the revised offset and may send the revised/updated offset to tracking vehicle  102  as tracking vehicle  102  navigates toward target  106 , although the scope of the invention is not limited in this respect. 
   In some embodiments, carrier vehicle  104  may track a tracking point of each of a plurality of targets  107  and may generate an image of each of targets  107  with a high-resolution laser-imaging system. In these embodiments, carrier vehicle  104  may determine an aimpoint based on characteristics of the images for each of targets  107 , and may determine an offset to the aimpoint from a tracking point for each of the targets. In these embodiments, carrier vehicle  104  may assign one of the tracking vehicles to each of the targets (e.g., based on proximity) for possible interception and may convey an associated one of the offsets to the assigned tracking vehicle  102 . In some embodiments, carrier vehicle  104  may convey information to tracking vehicles  102  over links  112 , which may be RF links or laser/optical links, although the scope of the invention is not limited in this respect. In some embodiments, each of the assigned tracking vehicles may track the tracking point of an associated target while navigating toward the aimpoint of that target based on the associated offset. 
   In some embodiments, tracking vehicles  103  may use a passive optical imaging system to navigate toward the target. In some embodiments, the passive optical imaging system may provide sufficient resolution to determine the tracking point; however the passive optical imaging system may provide insufficient resolution to determine the aimpoint, although the scope of the invention is not limited in this respect. In this way, the imaging system may receive images from imaging direction  110  with the navigation system may direct the tracking vehicle in navigation direction  114 . 
   In some embodiments, targets  107  may be moving rapidly in space external to earth&#39;s atmosphere (i.e., in the exo-atmosphere). In some embodiments, targets  107  may be enemy missiles or enemy warheads. In some embodiments, system  100  may track and destroy one or more of targets  107 . In some embodiments, tracking vehicles  103  may comprise kinetic energy kill vehicles, miniature kill vehicles, explosive kill vehicles, space vehicles or spacecraft, guided missiles, and/or guided projectiles, although the scope of the invention is not limited in this respect. In some embodiments, tracking vehicles  103  may detonate within a predetermined kill-radius of the aimpoint of a target or at impact with the target. In other embodiments, tracking vehicles  103  may attempt to destroy a target by impact with the target. In these embodiments, the aimpoint may be a lethal spot on the target and may be determined based on the target&#39;s vulnerability as well as the potential for damage that may be inflicted by the particular type of tracking vehicle, although the scope of the invention is not limited in this respect. For example, on certain types of targets, the aimpoint may be a predetermined distance back from the front or nose of the target. 
   In some embodiments, carrier vehicle  104  may be an interceptor booster, although the scope of the invention is not limited in this respect. In some embodiments, carrier vehicle  104  may release one or more of tracking vehicles  103  after identifying one or more of targets  107 . In some embodiments, carrier vehicle  104  may release tracking vehicles  103  when within a predetermined range of targets  107 . In these embodiments, tracking vehicles  103  may be provided tracking information (e.g., the tracking points) of the targets prior to their release, although in other embodiments, the tracking information may be provided after their release. In some embodiments, tracking vehicles  103  may be released after carrier vehicle  104  processes images of the targets and determines their aimpoint. In these embodiments, tracking vehicles  103  may be provided with the offset information as well as the tracking points of the targets prior to being released, although the scope of the invention is not limited in this respect. 
     FIG. 3  is a functional block diagram of a carrier vehicle in accordance with some embodiments of the present invention. Carrier vehicle  300  may be suitable for use as carrier vehicle  104  ( FIG. 1 ), although other vehicles may also be suitable. Carrier vehicle  300  includes imaging system  304  to generate an image of a target, processing system  306  to determine an aimpoint based on characteristics of the image and to determine an offset to the aimpoint from a tracking point of the target. In these embodiments, carrier vehicle  300  may also include transmitter  310  to convey the offset to a tracking vehicle. When operating as part of system  100  ( FIG. 1 ), imaging system  304  may generate image  206  ( FIG. 2 ) of target  106  ( FIG. 1 ), processing system  306  may determine aimpoint  204  ( FIG. 2 ) based on characteristics of image  206  ( FIG. 2 ) and may determine offset  212  ( FIG. 2 ) to aimpoint  204  ( FIG. 1 ) from tracking point  202  ( FIG. 2 ). Transmitter  310  may convey offset  212  ( FIG. 2 ) to tracking vehicle  102  ( FIG. 1 ). 
   In some embodiments, processing system  306  may correct the offset for parallax based on a position of a tracking vehicle and a position of carrier vehicle  300 . Transmitter  310  may be used to convey the corrected offset to the tracking vehicle. In some embodiments, processing system  306  revises the parallax corrected offset as the tracking vehicle navigates toward the target, and transmitter  310  sends the revised offset to the tracking vehicle as it closes in on the target. 
   In some embodiments, imaging system  304  may be a high-resolution imaging system, such as a laser-radar (LIDAR) system for generating a three-dimensional (3D) image of one or more targets. In some embodiments, the three-dimensional image may comprise a two-dimensional (2D) image of pixels with ranging information for at least some of the pixels, although the scope of the invention is not limited in this respect. In some embodiments, imaging system  304  may have field-of-regard (FOR)  308  that may include the plurality of targets  103  ( FIG. 1 ). 
   In some embodiments, processing system  306  may include a feature extractor for use in determining the aimpoint of a particular target by resolving the image and extracting features from the image. The features may include shape, orientation and/or size of the target, although other features may also be used to determine the aimpoint. 
   In some embodiments, transmitter  310  may be a radio-frequency (RF) transmitter for communicating with tracking vehicles  103  ( FIG. 1 ) with antennas  314  over links  112  ( FIG. 1 ). In some embodiments, carrier vehicle  300  may also include navigation system  302  for navigating, and system controller  318  to manage and control the overall operation of carrier vehicle  300 . In some embodiments, carrier vehicle  300  may include memory  312  for use by processing system  306 . In these embodiments, processing system  306  may resolve an image of a target, the feature extractor may extract features from the image, and the resolved image and any extracted features may be compared to images and/or features stored in memory  312  to determine the aimpoint. In some embodiments, aimpoints for various target types may be stored in memory  312  and may be based on the type of target identified, although the scope of the invention is not limited in this respect. 
   Although carrier vehicle  300  is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), and combinations of various hardware and logic circuitry for performing at least the functions described herein. 
     FIG. 4  is a functional block diagram of a tracking vehicle in accordance with some embodiments of the present invention. Tracking vehicle  400  may be suitable for use as one or more of tracking vehicles  103  ( FIG. 1 ), although other tracking vehicles may also be suitable. Tracking vehicle  400  comprises sensor system  404  to generate images of a target, and navigation system  402  to navigate toward an aimpoint of a target. In some embodiments, tracking vehicle  400  may include processing system  406  to operate in conjunction with sensor system  404  to determine the tracking point of a target. In some embodiments, the aimpoint may be determined from an offset received from a carrier vehicle. 
   In some embodiments, processing system  406  may determine direction  210  ( FIG. 2 ) to the tracking point from an image of the target and may generate an inertial vector in direction  114  ( FIG. 2 ) based on offset  212  ( FIG. 2 ) for use by navigation system  402  in navigating toward aimpoint  204  ( FIG. 2 ). In some embodiments, the offset may comprise a distance and a direction from the tracking point to the aimpoint and the tracking point may comprise the centroid of the target, although the scope of the invention is not limited in this respect. 
   In some embodiments, sensor system  404  may comprise a passive optical sensor system. In some embodiments, sensor system  404  may include a passive infrared sensor to receive infrared images of a target, although the scope of the invention is not limited in this respect. In some embodiments, sensor system  404  may have sufficient resolution to identify the tracking point of a target, but may have insufficient resolution to separately identify the aimpoint of a target, although the scope of the invention is not limited in this respect. In some embodiments, sensor system  404  may have field-of-view (FOV)  408 , which may be directed toward particular one or more targets. 
   In some embodiments, tracking vehicle  400  may be substantially autonomous after being released from a carrier vehicle. In these embodiments, processing system  406  may revise the offset while navigating toward the aimpoint of a target as a range between the tracking vehicle and the target changes. The offset may need to be revised because the offset may change as the tracking vehicle approaches the target. In some embodiments, processing system  406  may revise the offset based on the target range and/or velocity, which may be provided by the carrier vehicle, although the scope of the invention is not related in this respect. 
   In some embodiments, tracking vehicle  400  may further comprise receiver  410  and one or more antennas  414  to receive communications from a carrier vehicle including offset  212  ( FIG. 2 ). In some embodiments, tracking vehicle  400  may be less autonomous after being released from a carrier vehicle. In these embodiments, receiver  410  may be used to receive one or more revised offsets from a carrier vehicle while navigating toward the aimpoint as a range between the tracking vehicle and the target changes. In some embodiments, tracking vehicle  400  may also include system controller  418  to manage and control the operations of tracking vehicle  400 . In some embodiments, tracking vehicle  400  may also comprise memory  412  to store information, such as the offset as well as other information, for use by the elements of tracking vehicle  400 . 
   Although tracking vehicle  400  is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), and combinations of various hardware and logic circuitry for performing at least the functions described herein. 
     FIG. 5  is a flow chart of a target tracking procedure in accordance with some embodiments of the present invention. Target tracking procedure  500  may be used by a target identification and tracking system to identify and track one or more targets with one or more tracking vehicles. In some embodiments, target tracking procedure  500  may be used by target identification and tracking system  100  ( FIG. 1 ) to identify and track one or more targets  107  ( FIG. 1 ) with one or more tracking vehicles  103  ( FIG. 1 ). 
   Operation  502  comprises identifying one or more targets. In some embodiments, a carrier vehicle may initially identify one or more targets from either a plurality of targets and non-targets, and/or from the background. At this point, the targets may be unresolved and their features may not be distinguishable, although the scope of the invention is not limited in this respect. In some embodiments, operation  502  may comprise the carrier vehicle tracking one or more of the identified targets. 
   Operation  504  comprises generating a high resolution image of a target. In some embodiments, operation  504  comprises generating a three-dimensional (3D) image of the one or more targets with an active laser radar imaging system. The three-dimensional (3D) image may comprise a two-dimensional (2D) image of pixels with ranging information for at least some of the pixels. In some embodiments, operation  504  comprises directing a laser-imaging sensor at a tracked target to generate the high resolution image. 
   Operation  506  comprises determining a tracking point of a target. In some embodiments, the tracking point may be a centroid and may be determined from low resolution images of the target, although the scope of the invention is not limited in this respect. In some embodiments, the tracking point of the target may be determined from the high resolution image generated in operation  504 . 
   Operation  508  comprises resolving the high resolution image to determine an aimpoint. In some embodiments, operation  508  comprises extracting features from the high resolution image including shape, orientation and/or size of the target to determine the aimpoint. 
   Operation  510  comprises generating an offset from the tracking point. The offset may comprise a distance and a direction from the tracking point to the aimpoint. 
   Operation  512  comprises assigning a tracking vehicle to the target. In some embodiments, a tracking vehicle may be assigned to a target based on its proximity to the target. In some embodiments, operation  512  may be performed at any time after a target is identified in operation  502 . In some embodiments, one or more tracking vehicles may be released from the carrier vehicle after a target is identified, although the scope of the invention is not limited in this respect. In some embodiments, the carrier vehicle may also track the targets after they are identified. 
   Operation  514  comprises correcting the offset determined in operation  510  for parallax. Operation  514  may correct the offset for parallax based on a position of the carrier vehicle and a position of an assigned tracking vehicle. 
   Operation  516  comprises sending the parallax-corrected offset to the tracking vehicle. In some embodiments, the parallax-corrected offset may be sent from the carrier vehicle to the tracking vehicle over an RF link. 
   In operation  518 , a tracking vehicle tracks a target&#39;s tracking point while it navigates toward the offset. In some embodiments, operation  518  comprises tracking a centroid of the target, which may be the tracking point. In some embodiments, the offset may be updated as the tracking vehicle approaches the target. In some embodiments, the tracking vehicle may update the offset, while in other embodiments; the carrier vehicle may update the offset and send the updated offset to the tracking vehicle. 
   In some embodiments, operation  502  through operation  516  may be performed by a carrier vehicle, while operation  518  may be performed by a tracking vehicle. Although the individual operations of procedure  500  are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. 
   Embodiments of the invention may be implemented in one or a combination of hardware, firmware and software. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by at least one processor to perform the operations described herein. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. 
   The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. 
   In the foregoing detailed description, various features are occasionally grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment.