DE2233870C3 - Optical method for the detection of thermal contrasts - Google Patents

Description

The invention relates to an optical method for detecting thermal contrasts in the Range around 300 ° K using an atmospheric window between 3 and 5 μπι, with the Measurement used spectral range is limited by a filter arranged in front of the detector.

From the references R. A. S m ϊ t h, F. E. J ο η e s, R.P. Chasmar, The Detection and Measurement of Infra-Red Radiation Oxford, 1957, pp. 443-445 and "Applied Optics", September 1968, Vol. 7, No. 9, pages 1769 to 777 is the permeability of the Atmosphere for infrared radiation known as a function of the wavelength The permeability curves show that regions of high and low transmittance exist depending on the wavelength. For example, the curves show areas of high permeability between 1.8 and 2.5 μm and between 3.0 and 5.0 μπι and between 8 and 13 μπι. By doing The range between 3.0 and 5.0 μπι is a drop in the Curve at about 4.2 μπι. The areas of high permeability are called »optical windows« (see Der Elektronikiker, No. 3/1971, page 125).

In one from Science 1971, vol. 171, no. 3972, pp 635 to 639 known method is used for the detection of polluting constituents in the air Reflection measured from infrared radiation from a laser. In this context, in of the cited reference on the absorption of water vapor and carbon dioxide in infrared spectroscopy pointed out, behind which the polluting components may be hidden. Around The method known from Science in the atmospheric window is used to avoid influences between 8 and 13 μπι worked, which is essentially free of these influences.

The use of the atmospheric window between 8 and 13 μπι for the detection of thermal The disadvantage of contrasts is that it is difficult to correctly determine the receivers required for this window cool. In addition, this window has a very high absorption attenuation at great distances having.

In one from Applied Optics, September 1968, Vol. 7, No. 9, pages 1769 to 1777 known method for the detection of thermal contrasts is used in most of the test cases described, the spectral range between 3.7 and 5.5 μm is used (see Fig. 6 to 10.13 and 14), because in this area the infrared signal emitted by the object in question rapidly increases with increasing

me the temperature grows (see Fig. 4) and such a great sensitivity is achieved. This makes the band used in the test cases a special one Ascribed sensitivity with regard to different temperatures, i.e. its advantages

The Applied Optics reference recommends the spectral band used for the measurement to be selected according to position and width depending on the objects to be detected. It is known from this that selected spectral band by using a

limit optical filter in front of the detector. When measuring within the spectral band between 3.7 and 5.5 μπι and also in that also in this Reference discussed volume between 4 and 5.5 μπι the collapse of the permeability curve at about 4.2 μπι is also detected. This absorption band is

Cause of the interference radiation and thus has a strong Decrease in thermal contrast sensitivity to

Episode.

The object of the invention is to provide an optical method

indicate, which largely avoids this interference and thus an increase in the thermal Contrast sensitivities caused

According to the invention the object is achieved in that the partial spectral range between 33 and 4.2 μπι

μ of the atmospheric window used for measurement and filtering by means of a filter that has approximately the same decay characteristic on the long-wave side how the partial spectral range is made.

In the method according to the invention, on the one hand, a certain area of high permeability of the atmospheric window with the exclusion of the absorption band above 4.2 μπι selected, and it is on the other hand, the filtering made so that without

«O Impairment of the measurement used Spectral range from areas above 4.2 μπι originating interference radiation are suppressed. Leading to a significant increase in thermal contrast sensitivity.

■ ♦ 5 F i g. 1 shows an apparatus for practicing the method according to the invention. The / Ä detector 1 is located in the center of a spherical pinhole, whose aperture is limited by the marginal rays 5 and 6 of the objective 2 / st It is also located in the

so the center of the spherical reflection filter 3, whose Edge is also limited by the aperture of the lens;

F i g. 2 shows the structural combination of pinhole 4 and reflection filter 3;

F i g. 3 shows the arrangement of a row detector in a device according to FIG. The row detector 1, which carries the detector elements a to e and ä to S , is adjusted in the center of the spherical spherical mirror or the reflection filter that the detector element a

the element a, the detector element on the detector element b b etc. and is imaged vice versa. The various detector elements thus see each other and, since they are arranged on a common cooled carrier, their own temperature.

For this purpose 2 sheets of drawings

Claims (1)

Claim; Optical method for the detection of thermal Contrasts in the range of 300 ° K using an atmospheric window between 3 and 5μπι, the one used in the measurement Spectral range is limited by a filter arranged in front of the detector, thereby characterized in that the partial spectral range between 3.3 and 4.2 μm of the atmospheric Window is used for measurement and a filtering by means of a filter that is on the long-wave Page has approximately the same drop-off characteristic as the partial spectral range will.