RU177419U1 - Lidar for remote measurement of temperature and humidity with minimal dead zone sounding - Google Patents

Abstract

The utility model relates to the technique of optical methods for measuring the physicochemical parameters of a substance and is intended for remote measurement of temperature and atmospheric humidity. The device contains three optical radiation receivers with smaller aperture diameters, which collect the scattered laser radiation from the “middle”, “near” and “dead” areas of the lidar. The technical result consists in the simultaneous measurement of humidity and temperature of the atmosphere with a minimum dead zone sounding. 3 ill.

Description

The utility model relates to measuring technique and is intended for remote measurement of temperature and humidity of the atmosphere, and can be used at weather stations and other atmospheric monitoring systems.

A device for measuring temperature is known (RF patent No. 129229, 2013). The disadvantage of this device is the fundamental lack of the ability to conduct remote temperature measurements.

Also known aerological radiosonde (RF patent No. 589845, 2006), containing a temperature sensor and a radio transmitter with which temperature information received as the height of the radiosonde is transmitted to a ground tracking station. The relatively high cost of a one-time measuring module of the radiosonde during regular measurements determines the high cost of operating such a system. Another disadvantage of the radiosonde system is the uncontrollability of the elevation path of the radiosonde. At average statistical speeds of the transfer of air masses in the atmosphere when ascending to a height of 15-20 kilometers, the probe may turn out to be tens or even hundreds of kilometers from the starting point, which makes it difficult to use such temperature profiles in weather forecasting tasks. At the same time, the probe rise time is 1.5–2 hours, which leads to a bias in the estimate of average temperature values due to violation of the stationarity condition.

A known lidar in which temperature measurement is associated with the restoration of the molecular density profile of the atmosphere (Shibata T., Kobuchi M, Maeda M. Measurement of density and temperature profiles in the middle atmosphere with a XeF lidar // Applied Optics. 1986. V. 25. No. 5. PP. 685-688) and its subsequent conversion to temperature, justified under the assumption of hydrostatic equilibrium of the atmosphere. The initial information for this type of lidar is the intensity of elastic scattering of the probe radiation, for which the contributions of molecular and aerosol scattering are fundamentally inseparable. The latter causes the main drawback of the method - it turns out to be workable only for the atmosphere, free from the presence of aerosol in it. Usually this is an interval of heights of 30-70 kilometers (stratosphere). In addition, the tropospheric aerosol attenuates the radiation scattered in the stratosphere, which leads to significant errors in the restoration of temperature in the stratosphere.

As a prototype, a lidar was chosen for measuring the temperature and humidity of the atmosphere (RU No. 169314 of March 15, 2017). The known device includes a laser radiation source, at the output of which there is a transmitting optical system that sends laser radiation to the atmosphere. The radiation scattered backwards enters the receiving telescope and then through the monofilament fiber to the optical scrambler, where the dependence of the focal ratio of the beam at the output of the lidar receiving telescope on the range of the scattering volume is eliminated. Further, optical radiation through a monofilament fiber is incident on a beam splitting filter. Part of the optical radiation transmitted through the beam splitting filter enters the double polychromator, which selects the corresponding optical signals of the purely rotational Raman spectrum (Raman), which at the output of the polychromator through monofilament fibers are fed to photomultiplier tubes (PMTs), which convert the optical signals into electrical ones, which are fed into a data processing unit where electrical signals are converted to digital, and then the temperature is calculated from the ratio of signal intensities to eraturno-sensitive areas purely rotational Raman spectrum by molecules of nitrogen and oxygen. Part of the optical radiation reflected from the beam splitting filter falls into a single polychromator, which selects sections of the vibrational-rotational bands of nitrogen and water vapor. The registration of sections of the vibrational-rotational bands of nitrogen and water vapor passing through a single polychromator is carried out using photoelectronic multipliers, the electrical signals from which are fed to the data processing unit, where the electrical signals are converted to digital, and then the humidity is calculated from the ratio of the intensities of the vibrational-rotational signals strips of nitrogen and water vapor.

The disadvantage of this device is the large error in measuring temperature and humidity in the "near zone" of the lidar due to the lack of a signal in the "near zone" of the lidar, i.e. large "dead zone" sensing. This is due to the fact that spectroscopic methods for measuring temperature and humidity of the atmosphere require the use of lidars with narrow fields of view (with a minimum field diaphragm). A narrow field of view of the lidar increases the "dead zone" of sounding due to less interception of scattered radiation from the "near zone" of the lidar (Fig. 1). The intensity distribution in the focal plane of a parabolic mirror with a diameter of 500 mm depending on the distance to the scattering volume, explaining the geometric mechanism of less interception of scattered radiation from the "near zone" of the lidar with a narrow field of view (a). The geometric function of the lidar for a receiving parabolic mirror with a diameter of 500 mm and a field diaphragm with a diameter of 400 μm (b)).

To solve this problem, a technical solution is proposed that allows measuring the temperature and humidity of the atmosphere at distances of 5 meters with a small error due to registration of the "near zone" of the lidar using additional optical radiation detectors.

In this regard, it is proposed to install three additional optical radiation receivers with smaller aperture diameters directly next to the transmitting optical system (beam expander) of the lidar. Three additional receivers will collect the scattered laser radiation from the “middle”, “near” and “dead” areas of the lidar. The collected radiation from four receivers is combined using monofilament fibers in one beam and sent to a beam splitting filter. Next, the radiation is selected and converted as in the prototype (RU No. 169314 of March 15, 2017).

As a result of numerous iterations using computer simulation of geometric functions for various configurations of the transceiver system, the optimal optical scheme of the lidar transceiver with one transmitting and four receiving apertures was synthesized. The parameters of the elements of the optical scheme of the transceiver and the coordinates of their relative positions are presented in table 1.

The geometric function of the multi-element lidar transceiver is shown in Figure 2 (The geometric function from 0 to 3000 m for the lidar parameters shown in Table 1 is presented in Fig. 2 (a). The geometric function from 0 to 500 m for the lidar parameters shown in table 1, is presented in Fig. 2 (b)).

Thus, the installation of additional optical radiation receivers allows measuring the temperature and humidity of the atmosphere from 5 meters with a small error due to the registration of signals from the “near” and “dead” zones of the lidar.

A block diagram of the proposed lidar is shown in FIG. 3.

Lidar for remote measurement of temperature and humidity of the atmosphere with a minimum dead zone of sounding consists of: 1 - a laser operating at a wavelength of 355 nm; 2 - transmitting optical system; 3 - receiving optical system, consisting of four receiving apertures of various diameters located directly next to the transmitting optical system; 4 - optical scramblers; 5 - beam splitting filter; 6 - double polychromator for measuring temperature; 7 - single polychromator for measuring humidity; 8, 9 - photomultiplier tubes (PMT 1, PMT 2,) for measuring temperature; 10, 11 - photomultiplier tubes (PMT 3, PMT 4) for measuring humidity; 12 is a data processing unit. All blocks and nodes of the lidar are located and fixed on one base and are in constructive unity.

The principle of operation of the proposed lidar system is as follows. The beam formed in the laser (1), through the transmitting optical system (2) is sent to the atmosphere. When propagating in the atmosphere, laser radiation undergoes scattering, including Raman scattering. The radiation scattered in the backward direction enters the receiving optical system, which consists of four receiving telescopes (3), the radiation collected by the telescopes with the help of monofilament fibers passes through the optical scramblers (4) to the beam splitting filter (5). Part of the optical radiation transmitted through the beam splitting filter (5) falls into a double polychromator (6), which selects sections of the purely rotational Raman spectrum on nitrogen and oxygen molecules. The registration of temperature-sensitive sections of the purely rotational Raman spectrum that has passed through a double polychromator is performed using photoelectronic multipliers (8, 9), the electrical signals from which are fed to the data processing unit (12), where the electrical signals are converted to digital, and then the temperature is calculated from the ratio of signal intensities of temperature-sensitive sections of the purely rotational Raman spectrum (Raman) on nitrogen and oxygen molecules. Part of the optical radiation reflected from the beam splitting filter (5) falls into a single polychromator (7), which selects sections of vibrational-rotational bands of nitrogen and water vapor. The sections of the vibrational-rotational bands of nitrogen and water vapor passed through a single polychromator are recorded using photoelectronic multipliers (10, 11), the electrical signals from which are sent to the data processing unit (12), where the electrical signals are converted to digital and then calculated humidity from the ratio of signal intensities of the vibrational-rotational bands of nitrogen and water vapor.

Claims (1)

Lidar for remote measurement of temperature and humidity of the atmosphere with a minimum dead zone of sounding, including a base, a laser source, at the output of which there is a transmitting optical system that sends laser radiation to the atmosphere, a receiving telescope, the radiation collected by the telescope is separated using a beam splitting filter, and then part of radiation transmitted through a beam splitting filter, enters a double polychromator, which selects the corresponding optical signals of a purely rotational spec Raman scattering, and part of the optical radiation reflected from the beam splitting filter falls into a single polychromator, which selects the optical signals of the vibrational-rotational bands of nitrogen and water vapor, the outputs of the double and single polychromators through monofilament fibers are optically coupled to the input of photomultiplier tubes (PMTs) that convert optical signals into electrical signals, the outputs of which are connected to a data processing unit for calculating the temperature and humidity of the atmosphere, characterized in that Three additional optical radiation detectors with smaller aperture diameters are installed directly next to the transmitting optical system (beam expander) of the lidar, which will collect the scattered laser radiation from the “middle”, “near” and “dead” zones of the lidar, the radiation from four receivers is combined using monofilament fibers in one beam and sent to a beam splitting filter.

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