GB2445849A

GB2445849A - Guided missile dual mode seek head

Info

Publication number: GB2445849A
Application number: GB0800429A
Authority: GB
Inventors: Jochen Barth; Alfred Fendt
Original assignee: LFK Lenkflugkoerpersysteme GmbH
Current assignee: LFK Lenkflugkoerpersysteme GmbH
Priority date: 2007-01-16
Filing date: 2008-01-10
Publication date: 2008-07-23
Anticipated expiration: 2028-01-10
Also published as: FR2914055A1; DE102007002336A1; SE0702902L; DE202007018452U1; SE532100C2; GB2445849B; ITMI20072395A1; FR2914055B1; GB0800429D0

Abstract

A dual-mode seek head for a guided missile has a four-quadrant detector 12 for target acquisition by means of the laser pulses reflected by the marked target Z, and an imaging IR bolometer 16 receiving the IR radiation emitted by the target Z. The laser and IR radiation is received through a common entry window and delivered to the respective sensors. After the target marking has been carried out, signal-processing electronics 20 process exclusively the signals delivered by the IR bolometer 16 for guidance signal generation for the purpose of generating the guidance signals for the final approach phase of the guided missile. This two-stage approach enables the use of much simpler IR sensors.

Description

* 2445849

I

Seek Head for a Guided Missile The invention relates to a seek head or seeking head for enabling guided missiles to acquire and home in on a target marked by means of laser pulses, which has a detector receiving the reflected laser beams and a detector receiving the IR radiation emitted by the target, the signals of which are converted by signal-processing electronics into guidance signals controlling the target approach phase, as well as to a method for its use.

Such seek heads are known as so-called dual-mode seek heads, as presented for example by US-PS 6 111 241. A PIN photodjode is provided as a detector to receive the laser beams reflected by a target marked by means of laser pulses from a so-called laser designator with a predetermined pulse repetition frequency; and an imaging focal plane array is provided as a detector to receive the IR radiation emitted by the marked target. To evaluate the signals of these detectors, signalprocessing electronics are used which correlate these signals so that only the last laser pulse from a target region, determined by the array, is used as a target-marking signal for the guidance signal generation in order to guide the missile onto the laser spot marked on the target.

The technical outlay for this is great. Both detectors must have an equally large image field, which entails considerable difficulties for the optics of the detectors -reflected laser pulses lie in the wavelength range of 1.06 pm, and emitted IR radiation lies in the wavelength range of 3-5 pm.

Furthermore, the imaging detector must be cooled. Another disadvantage is due to the fact that the target to be hit must be marked until the end of the target approach. This allows an adversary the opportunity to initiate countermeasures against the location of the laser designator.

Although such a seek head can be operated in three different modes, i.e. as a semi-active last pulse logic seeker, as an IR seeker or as a laser-IR correlated seeker, such seek heads have not gained practical acceptance owing to the disadvantages mentioned above.

It is this which is addressed by the invention, an object of which is to provide a novel dual-mode seek head which is more suitable than previously for use in conjunction with self-propelled guided missiles.

The invention is defined in attached claim 1, with further features to be found in the dependent claims.

The invention makes it possible to operate the laser spot sensor for finding and identifying a laser-marked target and an uncooled imaging IR sensor for autonomous target homing in the final approach while determining the impact point on the target, using a common bispectral objective. This involves the use of a spectral beam-splitter mirror and relay optics in the laser sensor channel, using which the image field of the laser spot sensor can be selected substantially independently of the IR sensor while monitoring the optical aberration. Using signal_processing electronics, the guidance signals are generated as a function of the sensor signals and the operational procedure of target lock-on and tracking takes place after launch of the guided missile.

The inventive configuration of the dual-mode seek head is Particularly advantageous since, in contrast to a seek head with only a laser spot sensor, the IR sensor makes it possible to shorten the duration of the active target illumination to a minimum, i.e. until the IR sensor operating as a target tracker is locked on. Conversely, in order to achieve the operationally required detection and identification ranges, a seek head with only an imaging IR sensor would need to be produced in much more elaborate technology, say with cooled MCT or InSb sensors. A large field of view would need to be covered in order to find the target, and high geometrical resolution must be implemented for identification. This requires an expensive sensor with a very large number of pixels.

The advantage of the invention is therefore that the tasks of finding and identifying the target are allocated to the laser channel, in which they can be performed by a simple detector such as a 4-quadrant photodiode. Since the geometrical resolution of this detector outside the image centre is very small, it is readily possible to produce appropriate optics that transmit a large field of view which is advantageous for the detection process.

The laser sensor subsequently controls the line of sight so that the identified target is centred in the field of view of the two mutually aligned sensors. A passive target tracker downstream of the IR image sensor then acquires the IR target contour in the middle of the sensor, so that the active target illumination can be turned off. The IR image sensor requires only a small field of view for this task. The thermal and geometrica' resolution of the IR image sensor are sufficient to allow tracker lock-on in a reliable manner.

This moreover places less stringent requirements on the sensor and the associated image processing than identification at the same range to target.

The "monocular" structure with a jointly used bispectral objective allows a Particularly advantageous compact arrangement with easily achieved harmonisation of the optical axes, and it is also economical. In general, reflective optics are used for bispectral imaging when the spectral ranges to be imaged lie far apart (cf. e.g. US 7 049 597).

With such optics, however, it is difficult to achieve the requisite small aperture numbers in both sensor channels and the field of view size of typically about 100 in the laser channel. With currently available refractive optical materials (ZnS, ZnSe, BaF2), however, it is readily possible to produce bispectral optics which fulfil the criteria in question.

Lastly, the laser channel may also be equipped with an active laser rangefinder, which allows additional use of an integrated proximity fuze. For combat use, it is in particular advantageous that this makes it difficult, if not impossible, to determine the location of the laser designator and initiate countermeasures Besides the described dual-mode operationality, in which the two sensors sequentially generate the tracking signals which are used for aligning and holding the line of sight on the target, the following simple operational modes are naturally also possible: control only by the laser sensor with constant target illumination until impact, or purely passive combat where an operator marks the target in the image of the IR sensor and thereby locks on a target tracker.

For a better understanding of the invention, embodiments of it will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a missile mission during the target approach, Fig. 2 shows a section through a dual-mode seek head in accordance with the invention, Fig. 3 shows the construction principle of the dual-mode seek head of Fig. 2, Fig. 4 shows a schematic representation of the image

fields of the sensors of the dual-mode seek head

according to Fig. 2, and Fig. 5 shows a block diagram of the signal-processing electronics.

As shown by Fig. 1, a possible flight path of a guided missile carrying a dual-mode seek head comprises an approach path A, guided for example by inertial navigation, and a search-head_controlled final phase flight path E operating according to the principle of proportional navigation, until it strikes a target Z. The laser sensor finds and identifies the target and centres it in the field of view by controlling the line of sight, which is aligned for instance with the aid of a two-axis gimbal on which the dual-mode sensor is mounted. The IR image sensor subsequently locks on to the IR target contour at the image centre. This is followed by the changeover from the inertially guided flight path to the seek-head-guided flight path. The final phase guidance is carried out solely by means of the IR sensor, which obviates illumination of the target by the laser designator.

To this end, as shown by Figures 2 and 3, the dual-mode seek head denoted overall by the reference 10 comprises a four-quadrant detector 12, relay optics 13, a spectral beam splitter 14, and an IR sensor 16 to which a common objective 18 is allocated. The 4-quadrant detector 12 is configured as an InGaAs diode combination and operates in the wavelength range of between 1.06 pm and 1.55 pm, corresponding to the wavelength of the laser used for the target marking, while the IR sensor 16 operates at about pm.

The IR sensor is an imaging microbolorneter sensor in the form of an uncooled detector array with 160 x 120 pixels (focal plane array of the type UL 02 051 from Ulis, Grenoble), which is supplied via the spectral beam splitter 14 with the IR component of the radiation received via the objective 18 of the dual-mode seek head.

The relay optics 13 are used to magnify the image field of the detector 12, the area of which is several times less than that of the sensor 16, as represented in Fig. 4. The relay optics 13 thus shorten the overall focal length of the "laser channel" relative to the focal length of the objective 18.

The dual-mode seek head 10 furthermore comprises means (not shown here) for controlling its line of sight 15, which are known per Se.

The signal processing of the dual-mode seek head described above is represented in Figure 5, and is divided into analogue signal conditioning by the four-quadrant detector 12 and digital signal processing thereof by means of the signal-processing electronics 20. The cathodes converge at a star point in the InGaAs detector employed; this contrasts with the otherwise conventional four-quadrant detectors made of germanium or silicon, in which the anodes form the star point. Owing to the selected configuration, the four-quadrant detector 12 is operated in photovoltajc mode. A current flows through the detector diodes Al to A4 as a function of the incident radiation. The downstream amplifiers Vi to V4 have two tasks: first impedance matching, and secondly amplification of the signal level. The outputs of the amplifiers are fed to respective A/D converters Wi to W4. The output signals thereof are then evaluated in a digital signal processing unit 20, which is also supplied with the signals of the IR image sensor 16.

With its bispectral optics, the dual-mode seek head described above is distinguished by a compact design requiring little space together with a high seeking power, so that an installation space of only 70 mm in diameter and about 100 mm in overall length is needed even with a universal mount, i.e. a high degree of fitting compatibility for guided missiles above a calibre of 75 mm. The lock-on of the IR seeking mode takes place at a range to target of about 2 km to 1.5 km.

LIST OF REFERENCES

12 four-quadrant detector 13 relay optics 14 beam splitter line of sight 16 IR sensor 18 common objective signal_processing electronics A approach path Al to A4 detector diodes E final phase flight path Vi to V4 amplifiers Wi to W4 A/D converters Z target

Claims

1. A dual-mode seek head for a guided missile for acquiring and homing in on a target (Z) marked by means of laser pulses, which comprises a detecting means (12, 16) receiving the reflected laser beams and the IR radiation emitted by the target (Z), and having signal-processing electronics (20) which deliver guidance signals controlling the target approach phase after the target marking by the laser pulses, characterised in that the detecting means includes a four-quadrant detector (12) responding to the reflected laser radiation and a preferably Uncooled imaging IR bolometer (16) responding to the IR radiation emitted by the target (Z), these being supplied via a common bispectral objective (18), the arrangement being such that the guidance signals for the final target approach of the guided missile can be generated exclusively using the signals of the imaging IR bolornete.r (16) by the signal-processing electronics (20) after the laser target marking has been acquired.

2. A dual-mode seek head according to claim 1, in which the beams entering through the objective are spectrally separated using a beam splitter (14) into a laser channel and an IR channel, and in that the four-quadrant detector (12) and the beam splitter (14) are arranged lying successively along the optical axis (15) of the seeking head.

3. A dual-mode seek head according to claim 2, in which relay optics (13), which shorten the overall focal length of the laser channel relative to the focal length of the objective (18), are arranged downstream of the beam splitter (14) for the purpose of matching the image fields of the four-quadrant detector (12) and the imaging IR bolometer (16).

4. A dual-mode seek head according to any preceding claim, in which the imaging IR bolometer (16) operates at * -9 wavelengths of about 10 pm as an image-generating focal-plane array.

5. A dual-mode seek head according to any preceding claim, in which InGaAs diodes operating in the wavelength range 1.05 pm to 1.55 pm are used as the four-quadrant detector.

6. A dual-mode seek head according to any preceding claim, in which the analogue signals of the four-quadrant detector (12), which are obtained when the laser-marked target (Z) is found and identified (target signature), are delivered via AID converters as digital signals to the signal-processing electronics (20) which, after the target signature has been determined, also convert the digital signals delivered by the IR bolometer (16) into the guidance signals controlling the final target approach of the missile.

7. A dual-mode seek head according to any preceding claim, further including means for controlling its line of sight.

8. A method for acquiring and homing in on a target to be hit by a guided missile using a seek head equipped with a laser detector and an imaging IR detector (12, 16), preferably a dual-mode seek head according to any preceding claim, characterised in that the lock-on to a target (Z) marked by means of laser pulses is carried out by the following phases: -detecting the laser radiation reflected from the target (Z) by the detector (12), -pointing the line of sight at the target (Z) by controlling the line of sight with the aid of tracking signals, which the signal-processing electronics (20) generate from the signals of the detector (12), -locking on the signal_processing electronics (20) of the sensor (16) to the IR contour in a selectable region around the image centre, and -10 -keeping the line of sight on the target (Z) by controlling the line of sight with the aid of tracking signals, which the signal-processing electronics (20) generate from the signals of the detector (16)

9. A method according to claim 8, in which in order to identify a time reference in the sequence of the laser pulses, the signals received from the detector (12) have their chronological order compared with the preprogramrnable reference and the lock of the detector (16) on to an IR contour is enabled only if a match is recognised.

10. A method according to claims 8 and 9, in which a signal used for switching off the target illuminator is communicated to the target illuminator after the detector (16) has been locked on.

11. An apparatus or method substantially as described with reference to the attached drawings.