RU2780672C1 - Method for determining the meteorological range of visibility in difficult weather conditions - Google Patents

Abstract

FIELD: meteorology.

SUBSTANCE: invention relates to the field of meteorology and can be used to determine the meteorological range of visibility in difficult weather conditions. Essence: to implement the method, a radiating unit, a receiving unit and a computing unit are used. Moreover, the radiating unit contains a collimating lens and an LED located in the focus of the collimating lens. The receiving unit contains a photodetector and a lens whose diameter is no less than the width of the collimated light beam, focusing the attenuated radiation on the photodetector. The intensity of the noise recorded by the photodetector is measured by the receiving unit when the LED radiation is turned off. The intensity of the unabated visible light beam generated by the LED is measured by the receiving unit near the radiating unit. The receiving unit is installed at a fixed distance from the radiating unit and the intensity of the radiation attenuated by the atmospheric layer recorded by the photodetector is measured. The meteorological visibility range is calculated taking into account the measured parameters.

EFFECT: improving the accuracy of measuring the meteorological visibility range in difficult meteorological conditions.

1 cl, 1 dwg

Description

The invention relates to the field of optics and is used to measure the meteorological range of visibility (MDV) in the atmosphere in difficult meteorological conditions (SMU).

An analogue of the proposed technical solution is "Visual method for determining the slant range by a moving observer", patent RU 2326348 C2, published 06/10/2008 Bull. No. 16. The fundamental disadvantage of this method is the impossibility of determining the slant range of visibility from the aircraft in difficult meteorological conditions, because the pilot, visually not seeing the lane, does not see the markers located on it.

The closest in technical essence to the claimed invention (prototype) is a method for measuring meteorological visibility based on measuring the attenuation of a calibrated light beam by the atmospheric layer [see, for example, I.Ya. Racimor. Oblique visibility. L.: Gidrometeoizdat, 1987, p. 6-8, 82-84; 67-71].

The disadvantage of this method is the low measurement accuracy in adverse weather conditions, due to the additional illumination of the receiver due to scattered solar radiation.

The technical result of the invention is to improve the accuracy of measuring MWP in difficult meteorological conditions.

This technical result is achieved by the fact that in the known method for measuring the meteorological visibility range, based on measuring the attenuation of a calibrated light beam by the atmospheric layer, according to the invention, the atmospheric noise intensity is additionally measured.

The essence of the invention lies in the fact that by measuring the intensity of atmospheric noise, the meteorological visibility range in adverse weather conditions is determined by the formula:

where Ф ₀ is the intensity of the unattenuated visible light beam, lm, Ф _pr is the radiation intensity recorded by the photodetector, Ф _w is the noise intensity recorded by the photodetector, r is the distance between the emitting unit and the receiver unit, m.

A known method for measuring the meteorological visibility range (MDV) is based on measuring the attenuation of a calibrated light beam by the atmospheric layer [L.T. Matveev. Course of general meteorology. Physics of the atmosphere. L .: Gidrometeoizdat, 1976, p. 165-175; 472-474. AND I. Racimor. Oblique visibility. L.: Gidrometeoizdat, 1987, p. 6-8, 82-84; 67-71]. The attenuation of the light beam is determined by the Bouguer-Lambert law:

where Ф ₀ - the intensity of the unattenuated visible light beam, lm; r is the distance between the emitter unit and the receiver unit, m; μ - coefficient of attenuation of visible radiation, 1/m.

The coefficient of transmitting radiation by the atmosphere is determined by the formula:

MDV is calculated by the Koshmieder formula [see, for example, I.Ya. Racimor. Oblique visibility. L.: Gidrometeoizdat, 1987, p. 6-8, 82-84; 67-71]:

where ε=0.05 is the average contrast sensitivity of the human eye.

This method of measuring MDR is used in all modern visibility range meters [Visibility range meter FI-3. Operation manual IKSHYU.201112.002 RE (Yu-34.12209 RE)].

The disadvantage of this method is the low accuracy of determining the meteorological range of visibility in adverse weather conditions with a low signal-to-noise ratio in the receiver. That is, additional noise exposure of the receiver by the atmosphere should be taken into account.

In reality, the radiation intensity recorded by the photodetector is equal to:

In the limit, the minimum noise intensity recorded by the photodetector Ф _w is determined by the thermal noise of the photodetector sensor.

Then:

Where do we get

Finally, the MRV, taking into account the illumination of the photodetector by the atmosphere, is calculated by the following formula, the meteorological visibility range in adverse weather conditions (MVR _cm ):

- отношение сигнал/шум приемника.where

- signal-to-noise ratio of the receiver.

If Ф _w → 0, then the proposed method for measuring MDMW _cm is reduced to the known one.

Let us show that not taking into account the noise of the receiver leads to significant errors in the measurement of the MDR, especially at a high level of noise exposure of the receiver and its low sensitivity.

Let the measurements be made by the FI-3 visibility range meter based on r=35 m. Then, according to the Koschmieder formula, at τ=0.91

According to the proposed method for calculating the MWP, taking into account atmospheric illumination in the SMU for the same value 1/τ=1.1 and a low signal-to-noise ratio of the receiver m=5, we have:

With a significant increase in the sensitivity of the receiver, for example, to the level m=20, we get:

But here, too, the measurement error of the MRV is 391 m, which is very critical when landing at the limit of the pilot's minimum.

That is, for a reliable measurement of the MDL in the SMU by a known method, the signal-to-noise ratio of the receiver must be at least m=100. To do this, a highly sensitive photodetector is used in the visibility range meter, and technically the illumination of the photodetector by the atmosphere is reduced to the minimum values.

The implementation of these requirements leads to extremely complex technical solutions in the design of visibility range meters based on the Koschmieder formula [Visibility meter FI-3. Operation manual IKSHYU.201112.002 RE (Yu-34.12209 RE)].

The method that implements the proposed technical solution is based on the use of a block diagram consisting of three blocks (Fig. 1):

1. Radiation unit (1), consisting of a non-coherent visible light source, such as an LED, and a collimating lens.

2. Receiving unit (2), consisting of a lens that focuses radiation attenuated by the atmosphere on the photodetector.

3. Computing unit (3), which determines the MPE in adverse weather conditions.

The technical result of the invention is achieved by the following sequence of actions using the main basic blocks:

1. With the LED radiation turned off, the receiving unit measures the noise intensity recorded by the photodetector Ф _w .

2. Near the emitting unit, the intensity of the unattenuated visible light beam Ф ₀ produced by the LED located at the focus of the lens collimating the beam is measured.

3. At a fixed distance r from the emitting unit, a receiving unit is installed containing a lens whose diameter is not less than the width of the collimated light beam, which focuses the radiation attenuated by the atmosphere layer on the photodetector, and the intensity of the radiation recorded by the photodetector Ф _pr is measured.

4. Signals Ф ₀ , Ф _w , Ф _pr , as well as the value of the distance r between the radiating unit and the receiver unit are fed into the computing unit, which calculates the true value of the MW _cm according to formula (7) taking into account atmospheric noise.

Note that the proposed method can be implemented at a certain slant range of visibility by the pilot from the aircraft. In this case, the emitting unit, which provides modulated visible radiation, is located at the airfield. The value Ф ₀ is also measured there. On the approach to the airfield, before the emitter is turned on on the ground, the noise intensity recorded by the photodetector Ф _w is measured. After turning on the emitter, the intensity of the radiation recorded by the photodetector f _pr is measured. In the computing unit, calculations are made of the magnitude of the slant visibility range of the MDL, _cm. In SMU, this value gives a more accurate result than the horizontal MPE measured at the aerodrome, which provides a higher reliability of landing in SMU.

Claims (1)

A method for determining the meteorological visibility range in adverse weather conditions, which consists in using an emitting unit containing a collimating lens and an LED located at the focus of the collimating lens, a receiving unit containing a photodetector and a lens whose diameter is not less than the width of the collimated light beam, focusing the attenuated radiation on the photodetector, and the computing unit, measuring by the receiving unit with the radiation of the LED turned off the noise intensity _Фw of the noise recorded by the photodetector, measuring by the receiving unit near the emitting unit the intensity Ф ₀ of the unattenuated visible light beam created by the LED, setting the receiving unit at a fixed distance r (m) from the emitting unit and measuring the intensity Ф _pr of the radiation recorded by the photodetector, calculating the meteorological visibility range according to the formula

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