DE3007236A1 - Atmospheric emission supervision - by laser beam with intermediate reflectors preceding terminal reflector - Google Patents

Abstract

An area is supervised for atmospheric pollution, esp. for the emission of noxious substances in the environment, by a laser which radiates a coherent light across the area and by several terminal reflectors at the boundary of the area. The reflected signals are evaluated to determine the approximate source of any emission. Intermediate reflectors which are mounted across the laser path to each terminal at certain distances consist either of semi-transparent mirrors or of retroreflectors with a cross-section smaller than that of the laser beam. This results in a better resolution in depth and in a more precise location of any trouble.

Description

Device for monitoring an area for atomospheric parameters The invention relates to a device for monitoring an area atmospheric parameters, particularly on pollutant emissions, with a coherent Laser shining light over the area, one or more, on the border of the Area set up end reflectors and an evaluation circuit for determination the approximate distance of an interfering or

Emission point from the reflected signals.

Laser devices are being used more recently in the field of environmental protection Here an area is used on atmospheric parameters Azw. Disruptions, in particular monitored for pollutant emissions. Remote sensing of emission points using Laser is based on the evaluation of the scattering and absorption of the laser light sent out through the molecules of the air and molecules and particles in the pollutant clouds to be detected. So far, two different methods have been used for this purpose is based on the continuously scattered by the molecules and particles and reflected laser light with a receiving telescope and to a photodetector to guide - from the size of the backscatter picked up by the photodetector statements about the amount of pollutant particles contributing to the original reflection derived from the monitored area. However, there is a clear derivation of the particle size distribution and the particle density from the optical backscatter values are associated with difficulties.

Furthermore, the so-called end reflector method is also known which permanently installs an end reflector at the border of the area to be monitored is. This end reflector can e.g.

a suitable corner mirror, but also a natural end reflector, be like a house, a bush or a cloud.

This method provides more sensitive and sharper readings, designed however, no spatial depth resolution. However, this method works well for the detection of gas admixtures in the atmosphere along a long path in the lower atmosphere.

With the previously known end reflector systems, the spatial one is correct Depth resolution corresponds to the distance of the end reflector from the laser beam receiver; therefore it is not possible to determine the exact position of the emission point from the measurement signal of the pollutant in the path of the laser beam. This lack of depth resolution has a particularly detrimental effect if e.g.

Gas emissions occur surprisingly on a large factory site. It would be desirable to be able to localize the emission point as precisely as possible, in order to be able to take countermeasures as quickly as possible. Such measures can e.g. be necessary if the emission of the pollutant poses an acute danger, e.g. Risk of fire or poisoning.

The invention is based on the object of the end reflector method to improve working monitoring device with regard to the depth resolution, around atmospheric disturbances in the monitored area as precisely and quickly as possible to be able to localize.

This object is achieved according to the invention in that between Laser and end reflector several intermediate reflectors are provided.

The intermediate reflectors here are either partially transparent mirrors or opaque reflectors whose cross-sectional area is smaller than the cross-section of the laser beam is. If with known devices for the entire measuring section only an echo signal was generated between the laser device and the end reflector, so will according to the invention per reflector ~ ^ so for the end reflector and the intermediate reflectors, each receive an echo signal. This is how it is when a pollutant emission occurs In an area to be monitored, it is possible to measure the emission with the depth resolution of the Distance between the two reflectors closest to the resulting cloud of pollutants to locate.

For monitoring an area with a device according to the invention is preferred to use the so-called differential absorption method, in which a tunable laser is used that emits at least two different light sources Emits wavelengths, the light being of one wavelength from the pollutant absorbed, while the other row length is not absorbed. By comparison the two measured values can then be very precise as to the amount and extent of the noxious gas cloud getting closed.

Further refinements and advantages of the invention emerge from the subclaims in connection with the following description, in the two exemplary embodiments the invention will be explained in more detail with reference to the drawing. Place in the drawing represent.

FIG. 1 is a schematic view of a device for monitoring an area on pollutant emissions in a first exercise example; figure 2 shows a second embodiment of a monitoring device according to the invention.

A frequency-adjustable infrared pulse laser f, e.g. a CO2-TEA laser sends out short light impulses at certain time intervals via a beam expander 2 from a diverging and converging lens a semitransparent beam splitter 3 are fed. Part of the laser pulse is passed through the beam splitter above a collecting optics 4 passed to a reference detector 5 with this reference detector the intensity of the transmission pulse is measured. The remainder of the laser pulse is deflected by means of a reversing mirror 6 and then runs through the route between the deflection mirror 6 and one on the border of an area to be monitored arranged end reflector 7. The area to be monitored is -z * B. a factory site then several possible emission points, not shown here, approximately along the measuring section for pollutants are located. Such emission points can be, for example, chimneys, free Exhaust pipes, etc. be.

Along the measuring section are between the deflecting mirror and the end reflector several partially transparent intermediate reflectors at certain distances from one another 8, in this case the five intermediate reflectors 81 to 85. The one on the deflecting mirror 6 deflected laser pulse runs through the measuring section, at each intermediate reflector and an echo pulse is also generated at the end reflector. The reflected signals are recorded in a receiver telescope 9, which consists of a parabolic primary mirror 10 and a deflection mirror, the rear side of the Deflecting mirror 6 used for the transmission pulse is used. The reflected signals are measured in a reception detector 11.

The device works according to the so-called differential absorption method. For this purpose, the infrared pulse laser 1 emits a strongly bundled light pulse, which runs through the measuring section and here according to the existing atmospheric Parameters is weakened or absorbed. There is a Pollutant cloud 1 t as shown in FIG. 12 between the intermediate reflectors 84 and 85 is shown schematically and corresponds to the frequency of the laser light an absorption frequency of the pollutant, the laser transmission pulse is also like the echo signals from the intermediate reflector and the final refZector 7 severely weakened. In the reception detector 11, after the transmission of the end pulse normally six echo pulses from intermediate reflectors 81 to 35 and originate from the end reflector 7. -The intensity of these echo pulses is determined by the Intensity of the transmitted pulse recorded in the reference detector compared. the Intensity of the -received-echo signals except from the normal atmo- spheric Parameters also depend on the concentration and type of pollutant molecules in the Pollutant cloud 12 dependent.

A comparative measurement is used to obtain information about these variables as well carried out with a further laser pulse, but with the frequency of the laser pulse is tuned so that the laser light is not absorbed by the cloud of pollutants.

In this way one obtains the from the optical transmission of the normal distribution of the echo signal intensities determined by pure (uncontaminated) office atmosphere; the comparison with the partially absorbed echo signals in evaluation electronics gives the concentration of the pollutant cloud. Of course you can instead a frequency-tunable laser also uses two or more fixed-frequency lasers whose light has a different frequency.

As mentioned above, the intermediate reflectors are along the measuring section set up at fixed intervals; for this reason it lies between the point in time the emission of a transmission pulse and the arrival of the individual reflectors echo signals resulting from the elapsing time interval precisely fixed. The receiving part the monitoring device therefore only needs to be switched on for such moments during which an echo signal is expected. This allows interfering signals, caused by multiple reflections between the intermediate reflectors or

this and the end reflector can occur, turn off; another The possibility of suppressing such interference signals is in addition to the interval actuation of the receiving part also includes the distances between the individual intermediate reflectors vote accordingly.

In Figure 2, a modified monitoring device is shown, which with regard to the transmitting and receiving part corresponds to that in Figure 1, so that a further description is not necessary here. Instead of the partially permeable Intermediate reflectors in the device described above are in the device According to Figure 2 in the beam path of the laser along the measurement path several retroreflectors 8 'are used and in this case five retroreflectors 8'1 1 to 8-'5. As in the above embodiment, there is also an end reflector at the end of the bleed section 7 provided. The cross section of the retroreflectors is each smaller than the cross section of the laser beam so that the opaque retroreflectors are not mutually exclusive cover. The incident light emitted by the retroreflectors is directed towards the receiving part of the laser is reflected and evaluated there, as described above.

In this figure, too, it is assumed that there is a pollutant wool 12 is located between the retroreflectors 8'4 and 8 '.

5 The determination of the location and the type and concentration of the pollutant cloud takes place as in the device according to FIG. 1.

With a device for monitoring an area for atmospheric Parameters according to the invention can localize atmospheric disturbance points very precisely and also their properties are determined.

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Claims (3)

Device for monitoring an area for atmospheric parameters Claims t9 Device for monitoring an area for atmospheric conditions Parameters, especially on pollutant emissions, with a coherent light about Lasers radiating the area, one or more, placed on the border of the area End reflectors and an evaluation circuit to determine the approximate distance an emission point from the reflected signals, characterized in that Several intermediate reflectors (8, 8 ') are provided between the laser (1,6) and the end reflector (7) are 2. Apparatus according to claim 1, characterized in that the intermediate ref editors (81 to 85) are partially transparent mirrors 3. Device according to claim 1, characterized in that the intermediate reflectors retroreflectors {81 bis 85 '), the cross-section of which is smaller than the cross-section of the laser beam,