Patent Application
20140086454
A typical ground-based radar system for detecting missile or mortar launches includes, among other things, a radar transmitter, receiver, and processing electronics to both control the radar and to interpret return signals. Such radars, when in an active scanning or surveillance mode, radiate or “paint” a relatively large volume of space, looking for events. When an event of interest (such as, for example, the appearance of a rapidly-moving object in the air), the radar typically switches to a staring or small-volume scan mode to obtain more information about the potential target. This type of operation creates gaps in both time and space in the surveillance coverage when the radar is in dwell mode. In addition, since radars cannot see everything at once, there are temporal gaps in coverage due to the scanning radar's motion.
Additionally, ground-based radars have a hard time locating the launch location of small rockets. By the time the ground radar begins to track the rocket, a significant amount of time has elapsed since launch. Another basic problem is ground clutter. Typically, most radars cannot acquire a rocket in flight until it separates from (or rises above) the ground clutter. Complicating this is the fact that some recent battlefield engagements have been in urban areas, creating the need to identify the exact launch location within a few meters.
Prior attempts at using electro-optical (E/O) systems to augment radars have used a single infrared (IR) band. These approaches typically use high frame rates to determine if the alarm is real, in order to reduce false alarms. The dual band approach employed in airborne missile warning systems uses two very close mid-wavelength infrared (MWIR) bands, which produce low sun glint false alarms. Dual-band systems may also be used to discriminate concealed weapons, as in U.S. Patent Application No. US 2008/0144885 by Zucherman, et al. (directed toward detecting dangerous objects on a person using a dual IR band sensor).
A dual-band approach to ground radar augmentation has also been described in, e.g., U.S. Application Patent No. US 2011/0127328 by Warren (directed to a dual IR band radar augmentation system). However, such prior art systems tend to have unacceptably high false alarm rates and are not adaptable to active surveillance radar systems.
The following table illustrates a commonly used IR band sub-division scheme and provides a helpful reference for terms used herein. This table is reproduced from Byrnes, James, Unexploded Ordnance Detection and Mitigation, pp. 21-22, Springer (2009).
Unfortunately, there are deficiencies to the above-described conventional approaches. For example, as noted above, ground clutter and false alarms (due to sun glint or other interference) have previously limited the ability of electro-optical (E/O) systems to successfully augment ground-based active surveillance radars.
Embodiments of the presently-described E/O radar augmentation systems and methods may use two or more infrared bands to solve these problems. In one exemplary embodiment, a SWIR band may be employed to detect the launch time and bearing with the greatest sensitivity in direct and non-direct line sight viewing. A second IR sensor operating in the MWIR/LWIR band may be employed to track the rockets after burnout with the maximum range. The MWIR/LWIR band sensor may also be employed to pickup the launch position in direct line of sight. The combination of the two bands gives the maximum range for detection and tracking. The combination also reduces false alarm in the SWIR band without using time domain identification because the second sensor band(s) (e.g., MWIR/LWIR) may be used to confirm the launch detection outputs of the first (SWIR) E/O sensor.
One aspect of the present E/O radar augmentation system is the ability to run both bands at optimum sensitivity allowing target saturation, thus enabling maximum range detection. Previous designs seen in the art have required that the target not saturate the pixels so time domain analysis can be performed. Allowing the pixels to saturate in both bands gives maximum range to detection and tracking, lowering the cost and performance needs of the inventive E/O system.
One embodiment of the invention is directed to an apparatus for augmenting an active surveillance radar with a plurality of electro-optical (E/O) sensors, comprising: a first E/O sensor operating in a first infrared (IR) band having a variable range of sensitivities and an output; at least a second E/O sensor operating in a second IR band having a variable range of sensitivities and an output; a processing unit operably connected to said first E/O sensor and said second E/O sensor, said processing unit configured to: correlate the outputs of said first E/O sensor and the outputs of at least said second E/O sensor; determine a launch event from said correlation; and derive time and location information from said determination; and provide said time and location information to the active surveillance radar, wherein said first E/O sensor and said second E/O sensor are operated at optimum sensitivity to cause target saturation and enable maximum detection range in each said E/O sensor and wherein said second E/O sensor is used at least to confirm the output from said first E/O sensor.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular 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.
One exemplary embodiment of the present systems and techniques are directed to an apparatus employing two separate IR sensors: a SWIR band camera and a MWIR band camera. These two IR bands produce the best long-range detection and longest range tracking of a target missile or other projectile. Another key benefit of using two bands is lower false alarm rates allowing for maximum sensitivity of the SWIR band.
In one embodiment, depicted in
In another embodiment, one or more sensor sets may be used to cover approximately 90 degrees horizontal and less than 60 degrees vertical.
The SWIR camera (or sensor, generally) 110 may be a low noise 1280×1024 12 micrometer (μm) pixel size camera. The field of view may be selected to provide, in one embodiment, 100 degrees horizontal and 20-30 degrees vertical (1.36 milliradian [mrad] resolution). One of ordinary skill in the art will recognize that other field of view parameters may also be chosen, without limitation, and that configurations employing more than one sensor may also be used without limitation.
The SWIR sensor 110 may run at a range of speeds, in terms of frames per second (fps); in one exemplary embodiment, it runs at a 90 fps single integration time. Other embodiments may run the camera with a reduced FOV in the vertical dimension in order to speed up the frame rate to 200-400 fps. Various such trade-offs in FOV and frame rate may be made in order to tailor the images produced to a repletion rate and field of coverage appropriate to the number of sensors and the desired mission.
Since lower noise increases the system detection range, in one exemplary embodiment, the SWIR sensor 110 may have a relatively low noise floor consistent with current leading edge SWIR sensor technology. The SWIR sensor 110 may also have a double sample capability, which increases its dynamic range over single sample implementation. Such a SWIR sensor may employ the High Dynamic Range Dual Mode (HDR-DM) CTIA/SFD circuitry described in commonly-owned U.S. Pat. No. 7,492,399, issued Feb. 17, 2009 to Gulbransen et al., and incorporated herein by reference in its entirety.
With both a source follower per detector (SFD) and charge transimpedance amplifier (CTIA) modes of operation, the SWIR sensor 110 can operate with maximum detection range in bright sunlight and in the dark of night. The CTIA mode may be used primarily for night vision. The double integration time allows for maximum sensitivity without the normal image bloom caused by lack of dynamic range. The SFD mode will be used during bright sunlight allowing for maximum well depth of the pixels to handle sunlight and large dynamic range. A variable range of detection sensitivity may also be provided.
The MWIR sensor 115A-D (115B not visible) may be, in some embodiments, an off-the-shelf camera from NOVA Sensors, such as that illustrated in
Nova Sensors is a trade name of Nova Research, Inc. of Solvang, Calif.
The E/O system housing 130 may be configured for full 360-degree operation. Preferably, housing 130 is water tight, EMI tight, and designed for full military temperature operation (−40 to 71 degrees C.). In one exemplary embodiment, a full 360 degree hemispherical E/O system may contain nine cameras, namely four SWIR, four MWIR, and one LWIR uncooled sensor 120, as shown in
In one exemplary embodiment, there may be four detection modes of the E/O system for direct line of sight surveillance and at least two for non-direct line of sight, as shown in
For direct fire threats (i.e., where the sensors 310 and 320 have a direct line-of-sight to the launcher), the first warning is a possible launch alert based on the correlation of both SWIR and MWIR detection and corresponding sensor outputs. This alert provides a dual-band confirmation (or correlation) of a high-energy event consistent with a rocket or mortar ignition. The next alert would be confirmation of a moving target in both bands correlated to the ignition event, the result of determining the confirmed ignition event. This event potentially indicates detection of rocket launch or mortar motion leaving the launch tube. The last stage of sensor detection is a MWIR track correlated to the launch event providing confirmation of a ballistic threat and providing an alert to the radar system containing time and location information for the launch event.
For indirect fire threats (non-line-of-sight launch), the MWIR 320 is not expected to see the launch ignition. Since the SWIR camera 310 is very sensitive to many sources of energy, a MWIR track confirmation is needed as a false alarm filter. Upon confirmation of a MWIR track on a ballistic target, the processing unit will search the SWIR data backward in time for indications of the launch ignition. A maximum likelihood method will be used to provide the probable time of ignition for each confirmed MWIR track. The E/O sensor system 300 will then send an alert to the radar computer 370 with the MWIR track information and the SWIR ignition time. The radar may need to estimate the time differential between the ignition time and the motion time as time of motion may not be guaranteed in the non-line of sight condition.
The E/O System may use multiple methods to reduce false alarms including at least two of:
a. Dual band detection employing SWIR and MWIR flash correlation
b. Time domain profile
c. Amplitude of flash intensity
d. Number of pixels of flash
e. Movement of flash over time
f. Location in the images
The false alarm rate is inversely proportional to sensitivity of the E/O system. Simulation has shown that one false alarm per minute is achievable with the proposed E/O system.
The E/O system timing may be obtained by adding a GPS IRIG B data stream into the camera link data stream (not shown). In such a configuration, each frame may contain a time code accurate to one millisecond. The data latency within the sensors may then be used to calculate the absolute time of the image frame within one millisecond. One of ordinary skill in the relevant radar and timing arts will recognize that alternate methods of syncing the radar to the image frame may be employed, without limitation.
Once the system determines an alarm event is valid, a message with the alarm location, time, and or track data may be sent by Ethernet to the radar control computer 370 with a latency of less 50 milliseconds.
The E/O system electronic connections are shown at a high level in
In one embodiment, the first E/O sensor may operate in the SWIR (900˜1700 nm) band while the second E/O sensor operates in the MWIR (3.8-5.1 μm) band. Alternatively, the second E/O sensor may operate in the LWIR (8-12 μm) band. Images are saved continuously to accumulate, in one embodiment, five seconds of history. Alternatively, rolling image saves of shorter or longer durations may be used without limitation. The E/O system memory is thus sized according to the rolling image save duration desired. For example, for a SWIR sensor operating at 200 frames per second, five seconds=1000 frames rolling save. For a MWIR or LWIR sensor operating at 60 frames per second, five seconds=300 frames of rolling save.
Although two single-band sensors are described, those skilled in the art will realize that multiple-band sensors, or sensors configured to operate over two or more adjoining IR bands, may be used. Accordingly, the concepts, systems, and techniques described herein are not limited to any particular combination of single-band, sub-band, and/or combined band sensors.
Monitor mode 401 (
The E/O system processing unit will not go into Ignition Detection mode 402 unless both sensors have targets above a very high detection threshold in the same spatial location, shown as step 420. Here, both sensors (whether SWIR and MWIR, SWIR and LWIR, or SWIR and MWIR/LWIR combined band, without limitation) must show an ignition event to confirm. Dual band sun glint removal algorithms may also be used in this false alarm rejection mode. When both sensors positively identify a spatially correlated high-energy event, processing performs multi-frame analysis, step 424, to confirm the ignition event and sends an alert to the radar control computer containing time of ignition and line of bearing or other location coordinates of the ignition event, step 428.
High-energy events from rocket or mortar launches have patterns that can be recognized by imaging camera systems. Prior art high speed radiometry systems have attempted to identify signatures of rockets, gunfire, sunlight, etc., but these systems require very high frame rates and high dynamic ranges to prevent signal intensity (target) saturation. The concepts, systems, and techniques disclosed herein, by contrast, are capable of recognizing high-energy events consistent with rocket or mortar launch with frame rates achievable with standard (conventional) imaging sensors. Very high-energy events will achieve high threshold levels on both SWIR and MWIR/LWIR sensors, but the present system only needs to run at high enough of a frame rate to determine ignition time and the MWIR/LWIR confirms high-energy events, therefore simplifying the system design and sensor requirements as compared to the prior art.
Low energy events likely to cause false alarms with the SWIR sensor will not reach threshold levels in the MWIR/LWIR. Rocket launch events also begin from stationary locations and ignition energy expands spatially around the launch location. This behavior is easily recognized with multi-frame analysis from the pre-ignition frame over several frames.
Note the SWIR band needs to run at approximately 200 Hz to meet the ignition time detection requirements. Additionally, the 200 Hz frame rate helps reduce motion related clutter with frame subtraction analysis. The MWIR and LWIR sensors are not as sensitive to motion clutter and are used to confirm SWIR high-energy events so they could be run at approximately 60 to 120 Hz.
Referring again to
Multi-frame motion detection analysis, step 430, is similar to ignition expansion detection. Reference frame image registration and/or stabilization algorithms may be used to reduce spatial clutter and a Hough transform or equivalent may be used to identify the circular radius and origin of the high-energy event. When the origin begins to move, as in the case where a rocket moves on the launch rail or a mortar leaves the launch tube, motion detection occurs. The time of target movement is then identified from an embedded GPS time stamp in each frame in the video stream from the sensors in step 434. As noted above, this time stamp may be provided by receiving and incorporating a GPS IRIG B data stream in the sensors' output signals by conventional means.
An alert is then sent to the radar, step 438, with the time of motion. This motion will typically be observed in both SWIR and MWIR/LWIR bands. The time of motion is the essential information that the radar needs to optimize fire finder radar performance with direct fire, low quadrant elevation (QE) threats. In some cases, motion may be detected with non-rocket high-energy detections (such as explosions) with moving objects so ballistic track information, from mode 404, is needed to confirm rocket or mortar launch events.
Although rocket and mortar tracking are described, those skilled in the art will realize other projectiles may be tracked if they are distinguishable from background clutter by their IR emissions or signatures. Accordingly, the concepts, systems, and techniques described herein are not limited to tracking any particular type of projectile.
In Ballistic Track mode 404, multi-frame analysis with image registration and/or scene stabilization algorithms and frame-to-frame subtraction may be useful in identifying ballistic targets in flight, steps 440 and 444.
Direct (line-of-sight) fire detection process 400 then loops indefinitely through connector B to await the next launch event.
Process 700 begins in Monitor Mode 701, which proceeds as discussed above with respect to
Once motion is detected in Monitor Mode 701, process 700 transitions to Ballistic Track mode 702. This mode operates in similar fashion to the direct fire case for the MWIR/LWIR bands whenever the monitor mode detects a MWIR target traveling at a rate consistent with a ballistic target. Multi-frame analysis is used to confirm the MWIR/LWIR target and calculate track information, step 724. If a ballistic target is confirmed, an alert containing time and location information is sent to the radar to allow the radar to focus on the target, step 728. Ignition Detection mode 703 is then triggered in the SWIR band to look for an ignition signature.
When Ignition Detection mode 703 is triggered based on a ballistic track confirmation from the MWIR/LWIR or Radar system (steps 720-728), the search is performed in reverse time sequence using the frame buffer in step 730. Image registration and/or scene stabilization algorithms are used to reduce clutter with frame subtraction. Since this is a non-line of sight launch scenario, a broad area must be searched for the ignition source, step 734. Multi-frame subtraction is performed in reverse time order looking for broad area ignition energy near the first location of the ballistic target. A Hough transform or equivalent algorithm may be used to look for radial patterns with semi-circular ignition energy. Processing the frames in reverse order allows the method to follow the energy back an ignition source location. This method may also identify time of motion as well as launch origin location information. An alert with the ignition time and motion detection will then be sent to the radar in step 738.
As in the direct (line-of-sight) fire detection process 400, indirect fire detection process 700 then loops indefinitely through connector B to await the next launch event.
The order in which the steps of the present method are performed is purely illustrative in nature. In fact, the steps can be performed in any order or in parallel, unless otherwise indicated by the present disclosure.
Referring to
The processes described herein are not limited to use with the hardware and software of
The system may be implemented, at least in part, via a computer program product, (e.g., in a machine-readable storage device), for execution by, or to control the operation of data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). Each such program may be implemented in a high level procedural or object-oriented programming language to communicate with a computer system. However, the programs may be implemented in assembly or machine language. The language may be a compiled or an interpreted language and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. A computer program may be stored on a storage medium or device (e.g., DVD, CD-ROM, hard disk, or magnetic diskette) that is readable by a general or special purpose programmable computer for configuring and operating the computer when the storage medium or device is read by the computer to perform the processes described herein. The processes described herein may also be implemented as a machine-readable storage medium, configured with a non-transitory computer program, where upon execution, instructions in the computer program cause the computer to operate in accordance with processes 300 and 550.
The processing blocks associated with implementing the system may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as, special purpose logic circuitry (e.g., an field programmable gate array [FPGA] and/or an application-specific integrated circuit [ASIC]).
Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Other embodiments not specifically described herein are also within the scope of the following claims.
While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims. Accordingly, the appended claims encompass within their scope all such changes and modifications.
