SU1755124A1 - Method of measuring angular atmospheric refraction and device thereof - Google Patents

Abstract

Use: measurement of distortions of the path of propagation of optical wave beams of refractive origin, in particular, in location, geodesy, geophysics, astronomy. The invention: measures the difference of the angles of arrival of waves with different lengths when combining the optical axis of the stellar interferometer with the direction to the source of white radiation. 2 sec. f-ly, 3 ill., 3 tab. with C

Description

The invention relates to atmospheric optics and can be used to measure distortions of the path of propagation of optical wave beams of refractive origin, in particular in location, geodesy, geophysics, and astronomy.

A dispersion method for measuring angular refraction is known, in which the spectral difference of refraction (angular dispersion) is measured for two selected wavelengths of the spectrum with the formation of an interference pattern and its analysis.

A device for implementing a dispersion method for measuring angular refraction includes receiving and transmitting optoelectronic units, photodetectors, and signal processing and analysis circuits.

The disadvantage of the analogue method and the device for its implementation is the low accuracy of angular refraction measurements, reaching 2-5 at a time as required in the tenth fractions of an arc second.

This disadvantage is due to the imperfection of the methods of recording the interference pattern and devices for their realization, which have a low sensitivity to angular changes.

The analogue method can also include a method for measuring atmospheric refraction, which includes transmitting radiation through two receiving channels, forming an interference pattern, measuring the spectral dispersion of the atmosphere for two optical radiation with different wavelengths, analyzing the difference in the path of the interfering beams, fixing the interference fringes to the indicator zero, moreover, the fixation of coincidence of interference fringes is performed in antiphase.

The disadvantage of this method is the low accuracy of the coarse dispersion DGA and, as a result, the low accuracy of the determination of the refraction angle, calculated by the ratio gA kA D gA, KA 50 - 60 Di

(L

Yu

the spectral coefficient for the selected wavelengths, which is due to the low accuracy of determining the fraction of the order of interference, as well as the weak dependence of the optical path difference on the angle of arrival of the wave.

The closest to the claimed method to the technical essence is the method of measuring the angular atmospheric refraction, according to which the radiation of the white source is passed through two receiving channels with a distance B between them, modulate the path difference of the beams, reduce the beams that have passed the channels into one a beam of radiation simultaneously modulating the radiation of an auxiliary source of monochromatic radiation transmitted through a two-arm Michelson interferometer, measure the amplitude of the signals of the measuring and reference sources of radiation These are judgments of refraction.

The disadvantage of the prototype method is the narrow range of measured parameters. This drawback is due to the fact that the prototype method provides a measure of refraction only if the true direction to the radiation source is known, non-refractive.

In practical cases, it is necessary to have information about refraction without knowing the true direction to the source.

An angular refractometer is known that contains two lasers with different wavelengths and a collimator arranged in series, a receiving optical system, an image rotation element, three polarizers, a birefringent plate, a photodetector, a recording circuit, a radiation separation element, two compensators and two voltage regulators voltage comparison circuit.

The drawback of the analog device is the low accuracy of measurement of angular refraction, which is caused by the weak dependence of the path difference of interfered beams formed by the birefringent plate on the angle of arrival and the low accuracy of determining the fractions of the order of interference.

The closest in technical essence to the claimed is an astronomical refractometer containing a measuring interferometer with an oscillating mirror, mechanically connected with a piezoceramic modulator connected to a sound generator and a constant voltage generator, sequentially connected to a photodetector, synchronous detector, the second input of which connected to a sound generator, a recording device, a reference interferometer with object and translucent mirrors and series-connected phot synchronous receiver

the detector and the recorder, with the oscillating mirror made in the form of a reflective surface of the diagonal face of a triangular prism mounted on a piezoelectric modulator, one of the side faces of the prism has a reflecting surface that is an object mirror of the reference interferometer, the second input of the synchronous detector of the reference interferometer is connected to the output of the sound generator, and the photodetector and the translucent mirror of the reference interferometer are mounted on the same axis as the piezoceramic modulator.

A disadvantage of the prior art device is the fact that it can be used to measure absolute refraction only with a known true non-refractive direction to the source, or refraction with respect to the conditional direction, as well as an increment of refraction over time. This circumstance narrows the range of the measured parameters of the prototype device.

The purpose of the invention is to expand the range of measured parameters.

The goal is achieved by the fact that in the method of measuring angular atmospheric refraction, which includes transmitting radiation through two receiving channels with a distance B between them, modulating the difference in beam paths, converging beams that pass channels into one beam, generating an electrical signal, according to invented invention, path difference

beams are harmonically modulated in one of the receiving channels, they decompose the signal into the frequency spectrum and measure the amplitudes of the harmonics, which determine the modulation amplitude, select the first

and the second signal harmonics for two wavelengths AI and Kg, and the refraction angle g is found by the ratio

-1H h and A2

r kA arctg a - - arct b b -, (1)

Where

U

Ji (2) l2 (Ai) a (2)

U

J2 () li (Ai)

U

b

Jl () l2 (A2)

and

(3)

J2 (27rg) l1 (A2)

KA - spectral coefficient;

) - Bessel function of the perverts of the argument - modulation amplitude: I.2 (Ai

  amplitudes of 1st and 2nd gar11, 2 (.A2 J

monique for wavelengths AI and Aa.

A device for measuring angular atmospheric refraction, comprising a measuring interferometer in the form of a Michelson star interferometer with overlaid beams, a piezoceramic modulator, a sound generator, a generator, a constant voltage generator; two photodetectors connected to a recording device, the piezoceramic modulator being mechanically connected to one of the external mirrors of the stellar interferometer and electrically to the sound generator and the constant voltage generator, according to the claimed invention, it is equipped with a spectrodiver, mounted on the output of the stellar interferometer and a plane-parallel plate mounted in one of the arms of the interferometer can be rotated, the recording device is made in the form of a two-channel spectrometer At the same time, the photodetectors are installed behind the spectrodistator along the radiation path and are connected in parallel to the spectrum analyzer, the output of which is connected to the computing device.

The essence of the proposed technical solutions consists in measuring the difference in the angles of arrival of waves with different lengths when the optical axis of the stellar interferometer is aligned with the direction to the white light source.

The angle of arrival of the radiation is defined as the optical path difference of the interfering beams 5D1.2 divided by the base of the interferometer B - the distance between the input hatches of the optical channels. On the other hand, the definition of the optical path difference with high precision introduced modulation according to the harmonic law. Since the recorded signal is polyharmonic, it contains harmonics that are multiples of the fundamental modulating frequency and, at the same time, the signal is described through Bessel functions, whose argument is pa-, (2 l: U,

The Z () parameter is related to the amplitude of modulation or vibration displacement of the interferometer mirror and the Amplitude and is determined by the coincidence of the theoretical and measured values of the Bessel functions of different orders. To implement the method, a spectrodiver is introduced into the device, dividing the received white radiation by wavelengths for reflection and transmission through two channels, each of which has a photodetector with outputs connected to the spectrum analyzer with two inputs (channels).

To align the optical lengths of the arms of the interferometer when sighting the source, a plane-parallel plate is installed in one of the channels of the interferometer. Signal processing and calculations are carried out using a mini-computer connected to the spectrum analyzer.

The essence of the claimed technical solutions is illustrated in the drawings.

Figure 1 shows the optical scheme of the Michelson stellar interferometer (ZIM) and a diagram explaining the structure of the intensity distribution in the interference pattern 1 (5). If the source is at an angle p to the axis of the telescope, then the maximum of the picture is shifted by the value of b B sin y, the angular distance

- one

between max peaks Acr B number of maxima Qkop / bp - 57.

Figure 2 shows the optoelectronic circuit of the claimed refractometer.

In FIG. 3, the results of processing the received signals on the spectrum analyzer.

The device (refractometer) contains two optic tubes in the shoulders of the ZIM: Li, La, Ls and 1.2, U, Le, deaf mirrors ML Ma, Мз, translucent mirror М4 (beam splitter), spectrodetector FI, filter Fa, photodetectors Oi and Fa. spectrum analyzer C2, mini-computer MET, 1P piezoceramic modulator, ZN sound generator, GPN constant voltage generator, plane-parallel plate - compensator K.

From the entrance pupil of Li, La. U and L2. C. Le light falls on a mirror Mi (Ma), is reflected at an angle of 90 ° and then one of the beams passes through a plane-parallel plate K and is reflected from a deaf mirror M3. Both beams are folded onto an n / l mirror, Mz, and then the radiation is separated in wavelengths by filters FI and Fa and falls on the corresponding photomultipliers Oi and Fa. Ma's mirror is reinforced on the 1L piezo-Ceramic element. When applying to 1 S sinusoidal voltage, the mirror performs oscillatory movements with amplitude (0.2-0.5) A, depending on the amplitude of the voltage controlled by the FPG. The compensator K is installed with

rotate around an axis perpendicular to the plane of the drawing within 40-48 °. The coating of mirrors M2MzMts is external, M is internal. The thickness is equal to the thickness of the compensator K. The FI filter (spectrometer) is an interference filter; the reflected light from the spectral composition is additional to the transmitted FI, the filter F2 performs additional correction of the spectral composition of the radiation, so that fluxes of approximately the same intensity with different average wavelengths fall on the PMT Ft and Fa. The optical circuit realizes the measurement of the angle of arrival of radiation at two different wavelengths, corresponding to the average transmission wavelengths Fi and (1 - Fi) F2.

The inventive method is implemented using the described device as follows.

The interferometer is imaged at the source and its radiation is passed through two receiving channels, the interference pattern is formed in the plane of the photodetectors by rotating the plate-compensator K and the interferometer mirrors. The voltage is applied to the modulator P and harmonically modulate the optical path difference of the interfering rays at both wavelengths. The signal of one of the channels is decomposed into a spectrum using a C 2 spectrum analyzer and the amplitudes of several harmonics that are multiples of the modulating frequency are measured, including the main one, which are used to determine the amplitude of the modulation using the mini computer ME1 (amplitude of vibration of the mirror M2). After that, the 1st and 2nd harmonics of the signal are extracted at both wavelengths and they are determined from H (Ai) H (A2) and, and the angle of refraction is determined by relation (1) with regard to (2).

To simplify the computational procedure of the method, with the help of the FPG, the voltage on the piezo-ceramic modulator IP is changed, thereby changing the modulation amplitude until then. until the Bessel functions of the first and second orders h 1g are equal, which is ensured by setting the precomputed voltage U0 (AND h). The value of the spectral coefficient is calculated preliminary for the selected wavelengths in a known way.

The spectrum analyzer measures the amplitudes of the harmonics of a signal that are multiples of the fundamental frequency. The theoretical values of the arguments of the Bessel functions Zn (Zi) are calculated on the mini-computer. And besides, they calculate

a value of 20 | at which Itsl2, a no Z0 calculate the amplitude of oscillations (modulation) by the relation

Ui, 2 (4)

Implementation of the proposed technical solutions.

The appearance of the device for carrying out the method is shown in FIG. 4. The signals from the PMT were fed to the inputs of a two-channel spectrum analyzer 2034 from Brüel & Kjльr. The measurement results are shown in FIG. 3 and Table 1, and the results of the calculation of the norm D (Z) at which Z Z0 is in Table 2.

The modulation amplitude was U 0.462 µm with an error of mu 0.03 µm.

Let us estimate the effect of mu error on the accuracy of angular measurements. To do this, we write (1) in the form

, st.

f gtg-- -. (five)

Considering that dln + i (Z) / dz o

5 () + Jn -1 (2) and the ratios U "0-5 I, Z 2.65, mu 0.03 I / 2 (measurement results), we obtain from (5). mg 0.65f2mz-0.9 m z fO, 9 2 l / 1 mu (6) At the same time, the ratio

0

five

0

0

m d0 - j Jt (1 + tg2

those. m 0,2- 0,09-18

v2

 on

 At base 6 m, the error in determining the angle of arrival will be (m 50 / V) / o 3 2 10 6 angular s, and for the spectral difference m m angular c. Under these conditions, the error of the angle of refraction at Q 50 will be 0.4. This means that on the base of 0.3m, 1.

At the same time, in the method and prototype devices, even when registering 0.0007 fractions of the order of interference, the accuracy of determining the angle of dispersion will be only 0.02-0.03, i.e. The proposed technical solutions are 50-100 times more sensitive in angle than the prototype.

The refraction was measured by Q on a 6.16 km long track. The measurement results are shown in table 3.

Claims (2)

The ratios of the amplitudes of the H / I2 harmonics were determined on a spectrum analyzer, 5i, 2 are path differences calculated for 5 mini computers, Du dispersion angle, y (Ai) is the refraction angle for the green part of the spectrum, Invention 1. Method for measuring angular atmospheric refraction, which includes passing the radiation through two receiving channels with a distance B between them, modulating the difference in the course of the beams, mixing the beams that have passed the channels into one radiation beam, generating an electrical signal, in order to extend the measurement range , R the harmonicity of the beams is modulated according to a harmonic law in one of the receiving channels, the electric signal is decomposed into a frequency spectrum and the amplitudes of the harmonics are measured, which determine the modulation amplitude, the first and second harmonics of the signal for two wavelengths AI and Kg are determined, and refraction r is found by the ratio g kA B 1 arctg a -f- - arctg b -y ™ Sh Where Jl (2g #) l2 (Ai) J2 () li (Ai) Jl (2JT) i2 (A2) J2 (2) ti (A2) K A - spectral coefficient: 11.2 -2- Functions of Bessel of the first and second order from argument (2 -) 0 five 0 five 0 U is the modulation amplitude; And, 2 AI and U 1.2 A2 - amplitude of the first and second harmonics for wavelengths AI and A2 2. A device for measuring angular atmospheric refraction, containing a measuring interferometer in the form of a Michelson stellar interferometer with overlaid beams, a piezoceramic modulator, a sound generator, a constant voltage generator, two photodetectors connected to a recording device, and a piezoceramic modulator it is mechanically connected with one of the outer mirrors of the stellar interferometer and electrically with a sound generator and a constant voltage generator, characterized in that. in order to expand the measurement range, it is equipped with a spectro-divider. installed at the output of the stellar interferometer, and a plane-parallel plate installed in one of the arms of the interferometer can be rotated, the recording device is made in the form of a two-channel spectrum analyzer and a computing device, with the photodetectors installed along the spectrometer along the radiation path and connected in parallel to the spectrum analyzer. the output of which is connected to the computing device. 35 Table Table 2 tf Table 3 Wp00- ff, MttM t Db -80 ABOUT 409  I