GB2126039A

GB2126039A - MTI Radar or lidar

Info

Publication number: GB2126039A
Application number: GB08224060A
Authority: GB
Inventors: Hans Spies
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-20
Filing date: 1982-08-20
Publication date: 1984-03-14

Abstract

Detector means for effecting unambiguous target discrimination on the basis of moving parts of the target or fluctuations in exhaust gas from a propulsion unit. The sensor employed emits electromagnetic waves (light in the only embodiment) which are reflected by the target. In the case of targets with moving parts the shape of the reflected pulse varies with time. This variation of pulse shape is evaluated and utilized to identify the target on the bases of certain characteristics typical of the target. The detector may be used in systems for controlling projectiles or activating warheads. <IMAGE>

Description

SPECIFICATION Detector means emitting electromagnetic radiation This invention relates to a target detector means emitting electromagnetic radiation and operating from reflected signals.

Targets which are the object of detection in this invention include helicopters with rotor blades in rotation or over-all vibration of an aircraft or of components thereof. In addition to these targets, however, there may be those where the propulstion units emit fluctuating jets of gas.

A helicopter if a quasi-static target at tree-top altitude with only the rotor blades moving, can only be detected with difficulty. This applies in particular to sensors used as detectors for guiding missiles or projectiles or for the detonation of warheads.

Present detectors used against helicopters operate with radar but radar is incapable of giving any significant unambiguous signal indicating the presence of a helicopter in the vicinity of the ground. For this reason it is necessary, in order to enable trees or houses to be differentiated, to make use, in addition, of a so-called electrostatic sensor for indicating the presence of a helicopter.

In this system the need for two different sensors is aggravated by the additional drawback of being relatively sensitive to interference and of being incapable, despite all the apparatus and cost involved, of emitting a fully significant signal indicating the presence of helicopter target.

An object of this invention is to provide a detector of the kind referred to by which a target can be detected on the basis of changing characteristics even if difficult to differentiate from surrounding features.

According to this invention there is provided a detector emitting electromagnetic waves and operating by reflection from a target and serving for detection of targets having changing characteristics, wherein the detector is responsive to moving components or fluctuating jets of exhaust gas of the target, by evaluating the pulse propagation time in accordance with the changing characteristics around the target reflection.

This invention also provides a detector means for distinguishing targets from background clutter and responsive to the characteristic moving parts or exhaust gas disturbances at the target, the detector comprising a light pulse transmitter and a receiver and means to determine range by the time of difference between transmitted and received pulses, the means further having a evaluating means to asses the form of the received pulse.

The invention thus provides an advantageous means of unambiguously discriminating a target using a detector of simple construction and on the basis of changing characteristics of the said target.

The invention is further described in greater detail with reference to the accompanying drawings, wherein: Figures 1 a, 1 b, 1 C show pulse diagrams of a detectoriccording to the invention, and Figure 2 shows a block diagram of a detector according to the invention.

In the embodiment as example the basic principle of the invention is that a laser pulse, for example, is emitted as a spike pulse and the reflected return signal is received by a receiver detector diode after a certain period in accordance with which the range is evaluated.

Since, for example, the rotor blades of a helicopter reflect less intensively than the fuselage they only appear as "shoulder" in comparison with the spike pulses. The form taken by the signal thus enables a helicopter to be clearly distinguished from a building or tree forming a static background. The radial distance of the target can then be determined in a known manner from the timing of the signal recognized as a pulse from a target.

Figures 1 a, lband 1 c show an example of the different wave forms of the pulses of static targets such as a tree by comparison with a target comprising a helicopter. Figures 1 a, 1 b and ic show also the approach of a missile to a target in the detector diagram. As the projectile or missile itself is in motion, fixed targets will be brought nearer and nearer, the pulse retaining approximately the same form even though increasing in amplitude. This is significant in the curve for the tree.The form taken by the signal of the helicopter situated near the tree and with rotating rotor blades clearly shows the "shoulders" occurring as a result of the rotor blade reflecton and the change taking place in the form of the pulse as a result of the rotor rotating and thus continually assuming a different position.

Referring to Figure 2:- A laser pulser 1 has a laser diode 2 which emits light of corresponding fast rise time and short duration in the form of spike pulses. The light from the diode 2 is conveyed via a photo-conductor 3 to the focal plane of a lens 4. The focal plane of the lens 4 also contains the receiver diode 5 for the reception of the reflected laser pulse signals.

The diode 5 is followed by an amplifier 6. A clock generator 7 operates the laser pulser 1 and a trigger 8, which in turn operates a gating generator 9 which in the example in question actuates three sampling gates 10, 11, 1 2. The outputs of the sampling gates 10, 11, 1 2, pass to a multiplexer 13. The gate generator 9 is controlled by a gate control device 1 5. The system also includes a data pre-evaluating device 14 operating in conjunction with the gate control 1 5 and a digital signal evaluating device 1 6. The digital signal evaluating device 1 6 operates in conjunction with a ground based apparatus 1 7 or serves as an output for guiding or detonation signals.

In detail the signal evaluation system operates as follows: The reflected signal passes through receiver diode 5 to the amplifier 6 and, in parellel therewith, the sampling gates 10, 11, 12. The sampling gates 10, 11, 12 are scanned in succession via the gate generator and store the momentary values of the reflected signal in an integrator. The voltage values are conveyed together with the data of the gate control 9 to the data pre-evaluating device via multiplexer 13. The signal evaluation itself then takes place in the signal evaluation device 1 6. The data preevaluating device 14 selects the reflected light pulses according to stationary signals and signals which indicate the velocity changes in addition to the approach velocity. In addition the signal evaluation is effected by reference to specific characteristics such as the pulse propagation (spread) caused by the rotating rotor blades of a helicopter or by the pulsating jet of exhaust gas from propulsion units. The signal evaluating device 1 6 processes these data as guiding and firing data. The essence of the evaluation process is to evaluate the pulse propagation caused in target reflection by the phase velocity of the rotor blades of a helicopter or by the instabilities in the flow of gas from a propulsion unit.

Claims

1. A detector emitting electromagnetic waves and operating by reflection from a target and serving for detection of targets having changing characteristics, wherein the detector-is responsive to moving components or fluctuating jets of exhaust gas of the target, by evaluating the pulse propagation time in accordance with the changing characteristics around the target reflection.

2. A detector in accordance with Claim 1, wherein frequency and phase shift of the pulse propagation time are evaluated to identify and classify moving targets and for recognition of the operating condition of the target.

3. A detector in accordance with Claim 2, wherein the phase velocity of the pulse propagation time is evaluated.

4. A detector means for distinguishing targets from background clutter and responsive to characteristic moving parts or exhaust gas disturbances at the target, the detector comprising a light pulse transmitter and a receiver and means to determine range by the time difference between transmitter and received pulses, the means further having evaluating means to asses the form of the received pulse.

5. A detector means in accordance with Claim 4, wherein the evaluating means responds to shoulders or steps in the receiver waveform each side of the main return pulse.

6. A detector means according to Claim 4 or 5, wherein the evaluating means comprises a plurality of sampling gates successively scanned to produce stoped momentary values of the reflected pulse which are fed to a data evaluating means to determine the characteristics in relation to known pulse profiles.

7. Detector means for the purposes herein set forth constructed and arranged to operate substantially as herein described with reference to the accompanying drawings.