EP0937264A1

EP0937264A1 - Single aperture thermal imager, direct view, tv sight and laser ranging system subsystems including optics, components, displays, architecture with gps (global positioning sensors)

Info

Publication number: EP0937264A1
Application number: EP98948245A
Authority: EP
Inventors: Lacy G. Cook; Darcy J. Hart; Jesus D. Lara
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1997-09-11
Filing date: 1998-09-10
Publication date: 1999-08-25
Also published as: WO1999013355A1; IL129777A0; IL129777A

Abstract

An imaging system (10) to interpret a plurality of signals has a single aperture (12) and a single telescope (14) to receive and transmit signals. The telescope (14) is aligned with the aperture (12). A plurality of sensor elements (16, 18, 20, 22, 24) is aligned with the telescope (14) to receive and transmit signals between the telescope (14) and sensor elements (16, 18, 20, 22, 24). The single telescope receives and transmits all signals regardless of the varying wavelengths for the plurality of sensing elements (16, 18, 20, 22, 24).

Description

SINGLE APERTURE THERMAL IMAGER, DIRECT VIEW, TV SIGHT

AND LASER RANGING SYSTEM

SUBSYSTEMS INCLUDING OPTICS, COMPONENTS, DISPLAYS,

ARCHITECTURE WITH GPS (GLOBAL POSITIONING SENSOR)

Background of the Invention

1 . Technical Field

The present invention relates to an imaging system and, more particularly, to a system which utilizes a single aperture and single telescope to generate a plurality of sensor functions.

2. Discussion

When sensing a target, it is desirable to have an image of the target as well as an accurate distance or range between the target and the sensor operator. Optical systems exist which provide either a visual image

(direct or TV) or thermal image, as well as a range between the target and the operator. Ordinarily, these systems include a separate visible telescope, a separate thermal imager, and if a laser is used, often a separate laser telescope. Also, each of these subsystems require its own aperture. The requirement of separate telescopes for each sensor is due to the fact that the wavelength for each of the sensors is different and thus has varying requirements. Accordingly, the optical system is large, bulky, heavy and expensive since each subsystem requires its own telescope. In addition, a major portion of the optical elements are refractive adding additional weight to the system. With this multiple aperture sensor approach, the ultimate goal of achieving a common pointing direction for all of the various subsystems is very difficult if not impossible to achieve and maintain.

Summary of the Invention Accordingly, the new and improved reflective imaging system of the present invention provides the art with a system which utilizes a single aperture as well as a single telescope to generate a plurality of images. The present invention provides a single reflective telescope capable of providing multiple wavelengths which, in turn, are utilized by various subsystems. The single telescope with a plurality of subsystems enables the system to be smaller, lightweight, and more transportable than previous designs. The present invention enables signal transmitting and receiving through the same telescope and through a single aperture. Thus, in the present invention, if a laser is used, the system enables the power of the laser to be very low. Also, the present invention may include a global positioning system which may be coupled with laser range data to generate position of a target from the transformation of the laser range data and the global positioning system data.

In the preferred embodiment of the invention, the imaging system includes a single aperture and a single telescope to receive and transmit signals. The telescope is aligned with the aperture. A plurality of sensor elements are aligned with the telescope to receive and transmit signals between the telescope and sensor elements. The single telescope receives and transmits all signals for the plurality of sensor elements regardless of the wavelengths of the sensor elements. Also, a control mechanism may be included to operate the sensor elements as desired by an operator.

Generally, the telescope is an afocal three-mirror anastigmat telescope. The plurality of sensor elements may be selected from a group including a charge couple device, high speed visible array, such as a video camera, a high speed infrared array, a laser designator, laser range finder, direct view optics, such as a binocular eye piece, or a cathode ray tube display. Also, a switching element may be included to change the optical system between a wide field of view for search and acquisition operations and a narrow field of view for identification and tracking operations.

From the subsequent description and appended claims, taken in conjunction with the accompanying drawings, other objects and advantages of the present invention will become apparent to those skilled in the art.

Brief Description of the Drawings

In the accompanying drawings:

Figure 1 is a schematic view of the present invention with a plurality of sensor elements. Figure 2 is a schematic view like that of Figure 1 of an alternative embodiment of the present invention.

Figure 3 is a schematic view like Figure 1 of an additional alternate embodiment of the present invention.

Figure 4 is a schematic block diagram of the present invention. Figure 5 is a schematic block diagram of an additional embodiment of the present invention.

Figure 6 is a schematic block diagram of an additional embodiment of the present invention.

Figure 7 is a perspective conceptual layout of an imaging system in accordance with the present invention.

Figure 8 is a perspective conceptual layout of an alternate embodiment of the present invention.

Figure 9 is a perspective view of a conceptual layout of an additional embodiment of the present invention. Figure 1 0 is a perspective view of a conceptual layout of an alternate embodiment of the present invention.

Detailed Description of the Preferred Embodiment Turning to the figures, an imaging system is illustrated and designated with the reference numeral 10. The system includes a single aperture 1 2, a reflective telescope 14, and a plurality of sensor elements 1 6, 1 8, 20, 22, 24. Also, a switching mechanism 26 is present to change the system from a wide field of view to a narrow field of view. Turning to Figure 1 , the aperture 1 2 is ordinarily large approaching an eight-inch diameter. This is useful in longwave infrared applications. Radiation passes through the aperture 1 2 into and out of the system.

The telescope 14 is preferably an afocal three-mirror anastigmat telescope. The three-mirror anastigmat telescope includes a primary mirror

28, a secondary mirror 30, and a tertiary mirror 32. The primary mirror 28 is a positive power mirror and is generally a higher order aspheric mirror. The secondary mirror 30 is positioned off-axis with respect to a central axis. The secondary mirror 30 is a negative power mirror and is generally a higher order aspheric mirror. The tertiary mirror 32 is a positive power mirror. The tertiary mirror is generally a higher order aspheric mirror.

In Figures 1 -3, radiation transmits an image of an object to be viewed to the primary mirror 28. The radiation is reflected from the primary mirror 28 to the secondary mirror 30. The secondary mirror 30 receives and reflects the radiation to the tertiary mirror 32. The radiation is then passed through an optical element such as 34 to one of the sensor elements such as 20.

The sensor element 20 is generally a charge couple device or other high speed visible array or television camera. Also, a plurality of optical elements such as lenses 36, 38 and 40 may be used to focus the radiation to the sensor 20. At the discretion of the operator, the radiation may be directed towards another optical element 42 which directs the radiation towards the direct view optical system 24. Additional optical elements 44, 46, 48 and 50, as well as fold mirrors 58 and 60, direct the radiation to the direct view optics 24 such as a binocular eyepiece.

A laser 1 8 may utilize an optical element 62 to expand the laser beam. An optical element 64 directs the laser beam towards the three- mirror anastigmat telescope. The laser beam is then aimed at the target through the aperture 1 2. An additional optical element 68 receives radiation from the three-mirror anastigmat telescope and reflects it to the forward looking infrared (FLIR) imager array and dewar. The imager may include a thermal reference source 70 as well as a telescope 72. The image may be additionally reflected to a scanning imager system 74. Referring to Figure 2, the elements which are the same as those in Figure 1 are designated with the same reference numerals. The differences between Figure 1 and Figure 2 is that the aperture 1 2 ', while being large, has a diameter of approximately six inches. Also, the forward looking infrared (FLIR) imager 1 6 ' is different from that in Figure 1 . In Figure 2, the forward looking infrared (FLIR) imager is an all-reflective imager which includes a plurality of reflective element mirrors to reflect the radiation to a staring detector array.

Figure 3 is substantially similar to Figure 2 with the same reference numerals identifying the same elements. The difference between Figure 2 and Figure 3 is that the forward looking infrared (FLIR) imager

1 6" includes a plurality of refractive elements to focus the energy onto a detector array.

Figures 4, 5 and 6 illustrate block diagrams of the systems of Figures 1 , 2, 3, respectively. Figure 4 illustrates the block diagram of system components shown in Figure 1 , showing further details of the system components along with associated system electronics. The display electronics 82 and the GPS sub-system 84 are identical to those discussed in conjunction with Figures 5 and 6. However, the thermal receiver unit 1 6 and the electronics unit 80 differs as follows. The thermal receiver unit 1 6, in addition to including an imager

90, includes a flip-flop mirror scanner 92 which operates preferably at either 30 Hz or 60 Hz, and a detector assembly 100 including a 480 x 4 detector element array 98 cooled to cryogenic temperatures by dewar assembly 1 02 and assembly controller 1 04. The detector array outputs detected signals to a digitizer 103. The digitizer 1 03 digitizes the detected signals before outputting the signals to electronics unit 80. The receiver unit also includes a point of load controller 105 which includes voltage regulators that control levels of voltages applied to the detector assembly and digitizer, and analog multiplexers that determine system status. The electronics unit 80 additionally includes a video processor

1 06 and video control 108 that process the digitized signals output from the digitizer 103 before outputting the signals to display electronics 1 32. The video processor 106 performs FLIR processing, automatic gain and level control, and global gain and level control based on inputs from the control panel. The video control 108 adds reticle and symbology to the detected video scene, as well as other functions beyond the scope of the present invention. The electronics unit 80 also includes an EMI filter 1 10" to filter unwanted spikes and noise from the supply lines. The electronics unit 80 also includes both an internal power supply 1 1 7 to provide power at various required levels to internal components of the electronic unit, and an auxiliary power supply 1 1 5 to power the display electronics, as well as the battery 1 1 6. In addition, an interface control card 1 20 controls the gain of signals input into the electronics unit to control the type of picture desired on the system display. Figure 5 illustrates a block diagram of the system shown in Figure 2 showing certain system components along with associated system electronics in greater detail. The system includes a staring thermal receiver unit 1 6', an electronics unit 80', display electronics 82' and a GPS sub- system 84'. The thermal receiver unit 1 6' differs from the unit 1 6 in that the imager 90' outputs imaged radiation directly onto a 640 x 480 element staring detector array 98' in the detector assembly 1 00'. The detector assembly 1 00' is housed within a dewar assembly 1 02' maintained at cryogenic temperatures by a cooler controller 1 04'. The detector assembly produces an output signal which is input to command and control electronics 1 05 ' that apply correction terms such as gain and level correction to the detector output. The command and control electronics outputs the signal to a forward-looking infrared (FLIR) video pre-amplifier 107'. The pre-amplifier amplifies the signal to create a more robust signal before the signal is output to the electronics unit 80'.

The electronics unit 80' differs somewhat from the electronics unit 80 in Figure 4. The electronics unit includes a non-uniformity correction (NUC) sub-system 1 1 3' that conditions the signal in a manner similar to that described above in connection with the NUC card 1 06, when the signal is input from the thermal receiver unit 1 6' to the system controller 108'. After signal levels are adjusted through the NUC subsystem 1 1 3', the signals are output through an output processor 1 1 1 '. Components within the electronics unit 80' and the thermal receiver unit 1 6' are powered by a conventional internal power supply 1 1 7 ' that provides required voltage levels to system components. The internal power supply in turn is powered by a battery 1 1 9', which is preferably a 28V D.C. battery.

Figure 6 illustrates a block diagram of the system previously described in Figure 3 showing system components and electronics in more detail. In particular, the system thermal receiver unit 1 6", as well as a system electronics unit 80", display electronics 82" and GPS system 84", are shown in more detail in association with the telescope 14. Each of the above-mentioned components are described below.

Referring to the thermal receiver unit 1 6", an imager 90" transmits radiation from an object scene passed through the telescope 1 4 onto a standard rotary polygonal mirrored scanner 92" rotated by a scanner motor 93". A scan control unit 94" controls the rotational timing of the scanner wheel 92", by controlling the speed of the scanner motor 93", as is well known in the art. The scan control unit also synchronizes a thermal reference source (TRS) 95 ", telescope focus control 96", and filter wheel 97" which contains multiple filters for filtering the detected scene based upon particular wavelength characteristics.

Still referring to the thermal receiver unit 1 6", imaged radiation is scanned by the scanner wheel 92" onto a detector array 98" housed within a detector assembly 1 00". The detector array preferably includes

240 x 4 detector element sub-arrays housed within a dewar 1 02" and cooled to cryogenic temperatures. Therefore, the detector elements detect scene energy input through the telescope optics and not peripheral forms of energy, such as energy from the warm sides of the dewar housing. Each detector element is sensitive to light in the infrared spectrum and has a detector element output coupled to the system electronics unit 80". The detector elements are controlled by a conventional detector assembly output control 104" which consists primarily of signal preamplifiers.

The electronics unit 80" is also coupled to the output control 104" and conditions the detected radiation for viewing by the display electronics 82". The electronics unit includes a non-uniformity correction (NUC) subsystem 1 06" that corrects array element signal output level non- uniformities in response to signal level adjustment commands from a system controller 1 08" and the TRS to adjust signal brightness and responsivity parameters. The NUC sub-system 106" includes an S/HMUX 1 1 0" that clocks the signals input from the detector elements for sampling and multiplexing of the outputs. The outputs are converted to digital signals by the analog to digital converter 1 1 2". The output, in turn, is transmitted to a histogram processor card 1 14". The card and other system components are powered by a conventional internal power supply

1 1 5 ", which, in turn, is powered preferably by a 28V D.C. battery 1 1 6". The histogram processor card 1 1 4" further multiplexes the digital signals input from the electronics unit 80. The signals are then reconstructed in a frame memory 1 1 7 " operatively associated with the card 1 14". The card includes a histogram 1 20" that determines scene temperature distributions and that inputs the data into a look-up table 1 22". The look-up table 1 22" compresses scene information into a display dynamic range by mapping a larger input dynamic range into a smaller output dynamic range. Once the signals are processed through the look-up table, the signals are output through a digital to analog converter

1 24" to the display electronics 82".

The display electronics 82" includes a set of console controls 1 30" that control the sensor and viewing elements of the system in a manner well known in the art. The display electronics also include conventional cathode ray tube (CRT) electronics 1 32", as well as direct viewing optics (DVO)/thermal image select controls 1 36 to allow a system user to select a particular viewing application in accordance with the preferred embodiment of the present invention.

Still referring to Figure 6, the GPS sub-system 84" includes an antenna 140 that receives GPS position-based signals, and inputs the received signals into a conventional GPS module 142". The GPS module 142" includes signal processing electronics of the type well known in the art that process and condition received GPS signals before the signals are input into the GPS navigational processor 144" with directional data from an associated compass 1 46. The processor processes the information from the GPS module 1 42" and the compass 1 46, along with distance vector information from the laser range finder, and outputs a target position signal to a system user at 1 50.

Turning to Figures 7 and 8, a conceptual layout of the system of Figure 1 and 4 is illustrated. The housing includes the system components as illustrated. In Figure 7, the binocular display optics are on the side of the housing. In Figure 8, a monocular eyepiece is positioned within the main housing.

Figure 9 illustrates a conceptual layout of the hardware package for the system of Figures 2 and 5. As can be seen, the housing includes a side portion which includes the binocular display optics. Also, the forward looking infrared receiver module is positioned at the bottom in the front of the housing.

Figure 10 is a view like that of Figure 9 with the forward looking infrared sensor optic illustrated in Figures 3 and 6.

The present system provides an optical system which may be utilized in long range thermal imaging and ranging applications. The present application may be utilized to view distant targets with a wide field of view for acquisition and then transforms the system to a narrow field of view to identify the target. With the global positioning system, the target position may be accurately defined.

One application of the present invention is a target designator. For instance, it may be desirable to locate a target while viewing the target while at the same time utilizing a laser rangefinder to determine the target's position. Through the use of a global positioning system with the laser rangefinder, the exact position of the target is determined. Also, the optical system enables the use of a single aperture as well as a single telescope to analyze radiation received from a viewed target from both a visual as well as a thermal imaging system. Thus, the present optical system would enable simultaneous visible as well as thermal imaging utilizing different wave lengths through the same telescope.

It should be understood that while the invention has been described in connection with particular examples hereof, that various modifications, alterations and variations of the disclosed preferred embodiment may be made after varying the benefits of a study of the specification, drawings and the following claims.

Claims

WHAT IS CLAIMED IS:

1. An imaging system (10) for interpreting a plurality of signals comprising: a single aperture (12); a single telescope (14) for receiving and transmitting signals, said telescope (14) aligned with said aperture (12); a plurality of sensor elements (16, 18, 20, 22, 24), said sensing elements aligned with said telescope (14) for receiving and transmitting signals between said telescope (14) and sensor elements (16, 18, 20, 22, 24), said single telescope (14) receiving and transmitting all signals for said plurality of sensing elements (16, 18, 20, 22, 24).

2. The imaging system according to Claims 1 and 6, wherein said telescope (14) is a three-mirror anastigmat telescope (28, 30, 32).

3. The imaging system according to Claims 1 and 6, wherein said plurality of sensing elements (16, 18, 20, 22, 24) are selected from the group comprising a charge couple device visible TV capability (20), an IR compatibility (16), laser designator and laser range finder (18), direct view optics (24), and a display capability (22).

4. The imaging system according to Claims 1 and 6, including reflective element (26) for changing between a wide field of view and a narrow field of view.

5. The imaging system according to Claims 1 , 6 and 7, including a global positioning system (84).

6. The imaging system according to Claim 1 , further comprising a controller (80, 82) for operating the sensor elements (16, 18, 20, 22, 24) as desired by an operator.

7. The imaging system according to Claim 6, wherein said controller including: a signal processing unit (80) that receives said plurality of electronic signals and that conditions said plurality of electronic signals for display purposes; and a system display (82) that is operative to display an image of said detected target scene based on conditioned signals output from said signal processing unit.