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Innovation in the laser warning sensor field

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INNOVATION IN THE LASER WARNING SENSOR FIELD (i) F.Liberati(+) & A. Bianchi (++)

( +)

Agusta SpA - Unita di Roma, Roma, Italy

(++) Agusta SpA- Un1ta . d' & Tra1ate, I ( Varese , Italy )

Abstract

The more and more diffuse use of laser sources in the war scenario made necessary the introduction of systems capable to detect the presence of laser beams (Laser Warning Receivers). Such systems, in principle applicable not only to helicopters but to any kind of platform, .flying sailing or in land, must warn the operators and eventually activate the countermeasures fitted to decoy the potential danger related to the laser threat. In this paper we describe a novel system of reception based on a suitable arrangement of a certain number of optical fibers. The device is

Trade-offs

patent pending. between thE~

resolution regarding the incoming direction

laser beam and

of the amount of electronie handled are hardware and information to be

also shown. We also illustrate different types of proposed solutions and other -possible applications.

(t) Patent Pending

Introduction

It is well known that lasers are used very often in war scenarios and helicopters are one of the main targets because of their tactical task and their ease to movement. Just for their agility, helicopters have good chances of survival if they are warned in time about the threat. Indeed, the fact that a helicopter is

by a laser notifies imminence of an attack. most common types of threats in a battle are following: - laser rangefinders h_it the The laser the

- illuminators and designators for missile guide

- laser radars

Each of these kinds of course has characteristics: wavelength, pulse of lasers d~fferent spectral repetition rate, pulse length, intensity, kind of modulation. These parameters allow to define the kind of the laser and as a result the kind of the threat.

(2)

Requirements for a L.W.R. system Beyond these laser warning must be able parameters, a receiver system to detect the

laser incoming direction.

The more parameters are

measured by the device, the

more reliable and accurate is

the detection of the laser

beam and the subsequent

countermeasure. The field of

application of such systems,

that is a battlefield, makes

also other factors

(ruggedness, reliability,

maintenability, blind alarm

possibility) very important.

A typical L.W.R. is usually

formed by the elements shown

in the following block

diagram:

Collecting

Detect ion and

Allp

!if

I cation

Optics

Electronics

The collecting optics is

located outside the platform,

covering the solid angle

necessary to protect i t ,

catching the laser beam and

maintaining the spatial

information. According to the

utilized technologies, the

detection electronics may be

located in the electronic box

or together with the collection

optics. The first solution

allows a better defense against

electromagnetic interferences,

whereas the second one

guarantees a better light

efficiency. The electronic box

processes the detected signal,

points out the essential

parameters, identifies the type

of threat and interfaces the

presentation box. Furthermore,

it can decide the most suitable

countermeasure or leave the

decision to the operator. The

presentation box displays in a

suitable way the presence and

the type of the threat and the

countermeasures can be

Presentation

r

-Box

Electronic

1--Box

Countemeasure

-Activator

activated both automatically or by the operator.

(3)

Proposed solution

The scope of our work was to

develope a new idea regarding

the collecting optics, to

design it and to build a

prototype.

Two types of arrangements for

L.W.R. have been devised: the

first one has the sensors

outside the platform surface

and the electrical signal is

brought to the inner

electronic box via a

conventional electric cable;

in the second one the laser

beam, collected by a lens, is

brought to the inner sensor by an optical fiber.

What we propose is to replace

the external boxes, cumbersome

and fragile because of their

/

I

3 I

~

\

optics and difficult to be

assembled on any kind of

platform and in particular on

airborne ones, with a compact

head, equipped with integrated

optical fibers. The head will

end with an optical fiber

connector to make the assembly

and disassembly easier, also

without a further clamping,

directly on the platform skin.

The following figure shows a

typical configuration of an

optical fiber head. It is

possible to identify: 1 :

2 :

3 : 4: 5: I' } I

\n'

I I\ I fiber optics fiber optics field of view fiber cablehead outer cover connector of the single

---1

2 _'-,._'_/\ I I /\ /-~,

II',,

\ I \ I I \ '- ~ I I \ ' I ~ -.., t I / ' \ ~1-J _,., I I ~ \ ~ - _. j \ \

'

'

---1.23.3 I /

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The incoming laser radiation

that hits the head is

collected only by one fiber,

because the restricted

acceptance angle of the

single fiber does not allow

the radiation to enter the

other ones. The laser light

is therefore conducted through the connector to the

detector. In this

relative

way the

information regarding the

direction of the incoming beam

can be kept and the accuracy

and the resolution of the be4m

direction detection can be

determined by choosing the

appropriate acceptance angle

of the fibers. The total

number of fibers, their

position and the degree of

overlapping give the total

field of view of the head.

Normally it is convenient to

put two or more heads on the

helicopter to avoid shadowing

from one side of the external

scene. It is also possible,

using fibers made by materials

transparent in different

spect~al ranges, to see different kinds of laser. This can be done on the same heads,

using fiber bringing the

signal to detectors sensitive

to different spectral ranges,

or applying separate heads to

the helicopter.

Using special types of fibers

now available but every

expensive and not yet very

reliable, it is also possible

to cover all the range from

red (.7 microns) to far

infrared (10.6 microns), that

means to see every kind of

laser likely to be used in a

battlefield. The advantages of

such a device compared with the

previous one are obvious:

reduced weigth, costs and

dimensions, ease to assembly,

improved ruggedness and

durability, better angular

resolution, possibility to use

for communication or as a

countermeasure actuator.

The presentation to the

operator may be done on a

dedicated display, on LEDs, by

acoustic alarm or on account of

the angular accuracy, directly

on the radar display too, so

that the operator can correlate

the thread to the operational

enviroment.

Other applications

Besides the application as a

laser warning receiver, we can

foresee other utilizations for

such a sensor.

In fact the same enblock can be

used in the countermeasure

system, because through the

same fiber collecting the

incoming signal a laser jamming signal can be transmitted, that

will cover the solid angle

where the original signal came

from, disturbing therefore the

foe.

A further application of the

head is directional infrared, ultraviolet possible to as a antenna visible two-way in the or band. Finally it is use the head for in flight communications.

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Conclusions

We are sure that the new

integrated fiber optic head

shows a lot of advantages, and

for these reasons we applied

for a patent. After some

compromises between amount of

information to be handled and

angular resolution were done,

the design of a particular

configuration has

finished and finally proceeding with the construction.

been

we are

prototype

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