FR2598238A1 - Method and device for detecting fires - Google Patents

Abstract

The present invention relates to a method and a device for detecting fires by angular scanning, from a point P dominating the area to be surveyed which surrounds it, the area being covered by a solid angle resulting from the revolution of the elevation aperture angle A delimited, for a given azimuth angle, by the two elevation angles Aa and Ab which are relative to the two extreme points to be monitored: the closest and the furthest from the said observation point.

Description

The present invention relates to a method and a device for detecting fires and in particular forest fires.

More precisely, the invention relates to a method and a device for detecting fire by angular scanning, from a dominant point of the area to be monitored which surrounds it, this being covered by a solid angle resulting from the revolution of the opening angle in bounded site, for a given bearing angle, by the two elevation angles relating to the two extreme points to be monitored: the most distant and the closest to said observation point.

To this end and according to a provision of the invention, the method essentially consists in separately measuring the radiations emitted and / or re-emitted at angles which are equal or not, the whole of which covers the opening angle in elevation. The area to be monitored is scanned at a constant angular speed.

Each toù is divided into (L) sectors and each sector is divided into (M) sub-sectors, only one sub-sector among each (M) sub-sectors must contain the signals whose value corresponds to the highest temperature.

According to another arrangement, the device implementing the method is essentially characterized by: - a converging reflecting surface, for example parabolic, set in constant angular motion so that it receives during a complete revolution of the radiation emitted and / or transmitted of the entire area to be monitored, (n) sensors sensitive to radiation characteristic of fires, stored either in a plane parallel to and near the focal plane along a straight line intended for itself in a vertical plane or outside said plane so that their projection on it is on the said straight line.

The invention will be better understood on reading the detailed description below accompanied by drawings in which - Figure (1) is a diagram showing the reflecting surface, the optical filtering means (2) and the sensors (3 ).

FIG. (2a) presents the storage details of the sensors presented on Ligure (1).

- Figure (2b) is a view along AA of Figure (2a).

- Figure (3e) shows another possibility for storing the receivers relative to the storage plane of Figure (2).

- Figure (3b) is a view along B8 of Figure (3e).

- Figure (4) is a diagram which shows a monitoring point (P) - and its opening angle in elevation (A) which is divided at several angles, each presents the viewing angle in elevation of one of sensors (n) sensors.

- Figure (5) is a diagram showing the division of the area to be monitored by an observation point into concentric sub-areas. Each is monitored by a sensor. The area to be monitored is divided into (L) sectors each is divided into (M) sub-sectors.

- Figure (6) is a block diagram of the device.

The method for detecting fires is of the type in which an angular scan of the area to be monitored is carried out from a dominant point of observation. The opening angle (A) of said scanning (FIG. 4) is the difference between the two elevation angles (Aai and (Ab) relative to the two extreme points to be monitored: the closest and the farthest from the point of observation (P).

The revolution of this angle covers the area to be monitored which has a surface whose shape depends on its topography.

For a flat area to be monitored, the solid angle that results from the revolution of the opening angle (A) covers a surface in the shape of a crown (Figure 5).

In all cases, the zone to be monitored, with a more or less crown shape, is divided into concentric Zl, Z2 ... Zn subzones.

The radiation emitted and / or re-emitted from each of these sub-areas is measured separately.

The opening angle (A) is divided into several angles Al, A2, .... AX, ... An. Each of these angles has a revolution, in solid angle which covers the corresponding sub-zone.

The scanning is carried out at a constant angular speed and at a very small opening angle in bearing so that one obtains each revolution, for each sub-area, a thermal image describing the change in the temperature of the radial band observed. by the opening angle in bearing according to its orientation.

According to one aspect of the process, the radiation to be measured is optically filtered beforehand in order to allow passage, mostly those corresponding to temperatures much higher than the ambient.

The radiations to be passed are preferably those corresponding
depending on temperatures: between 100 and 1500 c.

Electrical signals reflecting the change in temperature
of each sub-area, depending on the orientation, are produced.

Another aspect of the process is that these electrical signals are
temporally filtered so that only those whose variation
in time is fast are allowed to pass. This for
mine the radiation whose variation corresponds to the var, a-
normal plane, in temperature, of the landscape from one place to another.

Signals that have, until then, continued in space
that is, in the angle traveled, are transformed into "L"
values representative of each sweeping round.

To choose these representative values, each round is divided
in (L) sector and each sector is divided into (M) sub-sec
teurs. In each (M) subsectors belonging to a sector,
only one sub-sector is chosen to present it.

flua precisely the subsector whose signal values cor
corresponding to the highest temperature, among the (M) under
sectors, is chosen to represent the sector in question.

So, for each round, we have (L) values representing the (L)
sectors, each value represents the highest temperature
in the sector concerned.

Choosing the temperature of the hottest sub-sector
as representative of the sector in question instead of taking, for example the average temperature of each sector, leads to increase
enter the sensitivity of the detection of fires of
small areas, i.e. before the fire takes on a large size.

Indeed, the fact of dividing each sector into several sub-sectors and of comparing the temperatures of these leads to detecting fires before their surface extends over several sub-sectors. The (L) values representative of each round are compared with other (L) values relating to a previous round:
The values, with the same orientation, are thus compared two by two and an alert signal is emitted when the difference between them exceeds a certain threshold.

A signal confirming the detection of a fire can be sent either following the alert signal or following the emission, for a given orientation, of two or more alert signals during two or more successive turns.

 It is obvious that the signal confirming said detection can be used in any known way.

The device for implementing the method has a convergent reflecting surface (1) set in angular motion whose angular speed is constant.

Said surface is placed at a dominant observation point (P) and oriented so as to cover the area to be monitored, figure (4), by carrying out its angular movement.

The radiation received, for a bearing angle given by said surface corresponds to an opening angle in elevation (A). The latter consists of the difference between the two elevation angles (Aa) and (Ab) relative to the two extreme points to be monitored;
closest and furthest from the observation point.

The image formed by the received radiation, can be received
on a surface on the focal plane or on a parallel plane
and close to it.

Sensors (3) are stored on said surface along a line
do straight drawn itself in a vertical and crossing plane
the line of symmetry (4) of the reflecting surface (1) for
receive the image of a radial band from the area to be monitored.

The width of this strip is directly related to the width of the
sensors used.

On figure (2A) are presented according to a first possibility
the (n) sensors 3A1, 3A2, 3A3, ..., 3An arranged along the said straight line defined above.

Figure (2B) is a CC view of the row of sensors
shown in Figure (2A).

In figure (3A) are presented, according to a second possibility,
the (n) 381, 3B2, 3B3 ... 3Bn sensors arranged on several planes
parallel to the focal plane.

The projection of these sensors on any parallel plane
also in the focal plane are on a straight line filled
feels the conditions of that according to which the capes are arranged
teurs presented on figure (2).

Figure (3B) shows the projections of the sensors along DD on a plane parallel to the focal plane.

This second possibility can be considered in the case where the geometry of the sensors does not allow them to be stored. dals the same plan.

Each of these sensors has a sensitive surface with an elongated fo rrte. They are arranged so that their major axis follows parallel to the so-called straight line in Figures 1, 2 and 3.

The distances which separate the sensitive surfaces of these sensors, in the case where they are arranged in the same plane, or which separate their projections on a plane parallel to the focal plane, in the case where the sensors are arranged in several planes, must be minimal.

This is to minimize the area of land not covered by the sensors.

The advantage of using several sensors each covering a part of the radius to be monitored instead of using a single long sensor is to increase the sensitivity of detection to fire, in other words to decrease the ratio between the area monitored both by a sensor and that of the occupied part of a possible fire of the same surface.

According to a preferred embodiment, the detectors used are pyroelectric detectors.

An optical filtering means (2) is placed between the reflecting surface (1) and the sensors. The role of this means is to let in the majority of the radiation corresponding to erasure times between 100 and 15000C approximately.

The advantage of this optical filtering which lets in majority the corresponding radiation at higher temperatures than those characterizing the landscape is to increase the difference, felt by a given sensor and for a given orientation, between the radiation received in the case of a fire and those received normally.

Each of the sensors 31, 32, ..., 3n produces electrical signals q9es representing the temperature of the sub-zone concerned as a function of the orientation of the reflecting surface.

The electrical signals emitted by each of these sensors are amp lifted by one of the amplifiers Al, A2, ..., An.

Filters F1, F2, ..Fn each receive the electrical signals representing the temperature as a function of the orientation of the sensor concerned and let through only those whose variation over time is rapid. Indeed, the signals whose variation as a function of the orientation angle is small generally indicate the change in temperature of the landscapes from one place to another.

A sampler (5) in figure 6 divides each tower into (L) sectors (figure 5). The value of the electrical signal having each of these (L X H) sub-sectors is recorded in a memory (7) after being coded by an encoder (6). In each (M) sub-sector belonging to each of the (L) sectors, a single sub-sector is chosen to represent the sector in question (Figure 5).

A search means (8) chooses the sector whose electrical signals represent the highest temperature among each (M) sub-sectors belonging to the same sector.

The (L) sub-sectors whose values are chosen to represent the (L) sectors of a complete revolution are recorded in a memory (9).

In another memory (10) are also recorded other (L) maximum values relating to (L) sectors and relating to a previous lap.

A comparator (11) compares the (L) recorded in the memory (9) with those recorded in the memory (10); each value of the memory (9) is compared with that of the memory (10) corresponding to the same sub-sector.

The result of this comparison is transmitted after being decoded by the threshold means (13) which emits an alert signal each time the difference between two compared values exceeds a certain threshold.

The alert signals are transmitted to a decision means (14) to qualify or not qualify one or more alerts as a confirmed fire detection.

After detecting a predetermined number of alerts, one
either several from the same sector in several turns suc
the decision means emits a signal which can trigger
an alarm (15) or which can be treated with all forms of
treatment.

Several devices like the one just described can
be linked to a central unit which receives alerts or
individual red flags and who makes decisions a hundred
ralles.

Indeed, several devices can cooperate to monitor
together a surface in such a way that two or more devices
cover the same points at the same time.

The advantage of such an arrangement is that a quick decision can be made and that the location accuracy of the focus
is more returned.

The proper functioning of each observation point is tested
periodically by sending radiation for example
8itilsire to those characterizing a fire and the observation of the
reaction of the device for example by the central unit.

The method and the device, subject of this invention,
can receive any modifications coming in the field
of operations known in the art, without departing from the scope
of this patent.

Claims (1)

 R1 / Method for detecting fires in a large area  for example a forest, according to which we sweep angularly  lying, from a dominant point of observation, the area which  surrounds it, this one being covered Far the revolution of a  opening angle formed by the difference between the two  elevation angles relative to the two extreme points to be monitored  the farthest and closest to said observation point  vation, process characterized in that one measures separately  radiation emitted and / or re-emitted from the area to be monitored  at equal or non-equal angles, the whole of which covers the angle  opening on site. R2 / Method according to claim 1 characterized in that one  angularly scans at a constant angular speed the  area to watch. R3 / Method according to claim 1 characterized in that one  filters optically before taking measurements.  received to allow the majority to pass, those correspGn-  at much higher temperatures than am  biance. R4 / Method according to claim 1 characterized in that one  temporally filters the signals from the measurement of  radiation so as to favor the passage of those whose  variation over time is rapid  R5 / Method according to claims 1, 3 and 4 characterized in that  that we divide each complete scan round into (L) sectors  and each sector in (M) sub-sectors and which one chooses by  mi the (M) sub sectors of each sector the one whose  signal value represents the highest temperature  this to retain (L) maximum temperature value, for  each round, each representing one of the (L) sectors.  R6 / Method according to claim (5) characterized in that  compare at the end of each round the L value retained with  other L values relating to a previous round and that  emits an alert signal when the difference between one of  retained values and the corresponding value of the previous turn "-  laughing exceeds certain threshold.  sR7 / -Device for implementing the process defined by  Claims 1 to 6, characterized by:  - a converging reflecting surface, for example a  parabolic surface, angular movement at a  constant angular velocity so that it receives  during a full-round of emitted and / or re-emitted radiation  of the entire area to be monitored.  - (n) sensors sensitive to characteristic radiation  ques ranged fires is in a plane parallel to and  near the focal plane following a straight line drawn it  even in a vertical plane and passing through the line of  symmetry of the reflecting surface is outside the said  plan in such a way that their projection on it is found  on the said straight line. R8 / Device according to claim 7 characterized in that  said sensors each have a sensitive surface of a forum  me lying down row so that it is parallel to  the said straight line. R9 / Device according to claim 7 characterized by means  optical filter located between said surface and said  sensors to let most of the radiation through  corresponding to temperatures between about 150 and 15000C. R10 / Device according to claim 7 characterized by  temporal filtering means receiving from each sensor, the  electrical signals indicative of the temperature in function  of the orientation of said sensor and letting pass unique  those whose variation is rapid Rll / Device according to claim 7 characterized by a  sampler dividing each complete scan round into  (L) sectors and each sector in (M) sub-sectors. R12 / Device according to claim 7 characterized in that a search means (8) chooses from each (M) sub-sectors that whose signal value represents the highest temperature to represent the sector concerned.