RU1245072C - Method of laser probing of atmosphere gases - Google Patents

Description

(7 - absorption coefficient of a non-excited molecule of a test gas at a resonant transition with a wavelength of a probe pulse;

Zi and Z2 are the statistical weights of the lower and upper energy levels of the resonant transition of the studied gas molecule with a wavelength that matches the wavelength of the auxiliary laser pulse;

AR is the thickness of the sensed volume of the atmosphere;

The invention relates to methods for laser sensing of the atmosphere for remote determination of the concentration of gas components of air and can be used in meteorology and environmental protection for the operational monitoring of the concentration of water vapor and gas pollution.

An object of the invention is to increase the accuracy and sensitivity of measuring atmospheric gas concentrations.

In FIG. 1 shows a diagram of a device that implements the method; Fig. 2 is a diagram of the arrangement of energy levels of a molecule of a test gas.

The device contains a laser 1 for generating a probe pulse, which can be used as a tunable parametric CdSe laser, generating radiation with wavelengths of NaZ 8.323 μm in the absorption line of HgO and A about 8.320 μm pulse on the transmission line of H20 with a pulse duration of 100 ns, laser 2 - a pulsed CO2 laser to generate an auxiliary radiation pulse with a wavelength of Ae; - 9.214 μm in the absorption line H20 with a pulse duration of 100 NS, laser synchronization unit 3, reflector 4. dichroic. mirror 5 transmitting ant Well 6, reference signal detector 7, a receiving antenna 8, 9 on the filter region CdSe-generating laser radiation chopping cos laser detector 10 Li- Darney echo processing unit 11 lidar echoes.

The device operates as follows.

In order to determine the concentration of water vapor H20, the probe pulse of the radiation of laser 1 with a wavelength of L3 and a duration of m-100 ns, formed by the transmitting antenna 6, is sent to a given volume of the atmosphere, which is not at a distance имеющий and having a thickness of A. This

U2 and are the recorded powers of the backscattered echo signals, respectively, from the distances R and R + A R from the probe pulse sent without an auxiliary laser pulse;

Ui and u are the l-recorded powers of backscattered echo signals, respectively, from the distances R and R + Д R from the probe pulse sent simultaneously with the auxiliary pulse. 2 ill.

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the volume is located in the field of view of the receiving antenna 8. The radiation backscattered by this volume is filtered and received at a wavelength of A z. A portion of the laser radiation 1 is coupled to a reference signal detector 7 and is used to determine the range of the scattering volumes in the atmosphere.

Then, after a period of time not exceeding 1 ms, after the first probe pulse of laser 1 is emitted, two radiation pulses are simultaneously sent to the same atmosphere highlighted in FIG. 1 by a wave line: a second probe pulse from laser 1 and an auxiliary pulse from laser 2 at lengths waves, respectively, AZ and 8.3 microns and A in 92 microns. Backscattered radiation is received and filtered at an Az wavelength. The power of the echo signals at wavelength A 3 is measured. The power of the second echo signal is lower than that of the first one, which is due to an increase in the absorption of probe radiation by water vapor molecules of HCO due to the selective nature of population redistribution at the resonant transition with wavelength A in the auxiliary radiation. The power ratio of the received signals characterizes the relative spectral transparency of the atmospheric layer of the DN, which determines the desired concentration of water vapor. This ratio of received signal powers increases with increasing power of the auxiliary I1 pulse up to a power value corresponding to saturation of the population of the upper level of the resonance transition with the wavelength of the auxiliary pulse.

The method is based on the property of laser radiation to excite the energy level of a molecule, when the wavelength of this laser radiation coincides with the wavelength of the resonant transition to this energy level, and the property of the molecule

increase its ability to absorb optical radiation with a wavelength equal to the wavelength of the resonant transition of the molecule, the lower energy level of which is in an excited state.

In Fig. 2, the arrows show the transitions between the energy levels of the test gas of water vapor H20. Transition 12-13 corresponds to the wavelength I in the auxiliary laser pulse, transition 13-14 corresponds to the wavelength AZ of the probe pulse. Shown here also is a transition 15 with a wavelength of I o dl

line laser pulse

passing H20 coinciding with the absorption line of the interfering gas S02.

The duration t of the auxiliary pulse lies in the range r t 2 R / c, the power P is in the range

3 S with АЯZ 1 exp (- h с / (Я КТ) А / (ВЯ222) Р (ВЯ2),

the wavelength is located in the contour of another absorption line of the test gas at the resonant transition, the upper energy level of which coincides with the lower energy level of the resonant transition with the wavelength of the probe pulse (all notation see below).

The concentration of the test gas at a distance R is determined from the ratio

2 + Sc LI A / ()

I ((bc7Ot) g7712-T - sc 45 A7 ()

, Rn (.) - fn (u, / u,)

X - ..,

where g is the duration of the probe pulse of the laser radiation:

R is the distance from the probed volume of the atmosphere;

c is the speed of light;

S is the cross sectional area of the laser beam for the auxiliary laser pulse;

AJ is the laser line width of the auxiliary pulse;

h is Planck's constant;

I is the wavelength of the auxiliary laser pulse;

K is the constant of Boltzmann;

T is the absolute temperature of the gas;

A and B are the probabilities of spontaneous emission and absorption, respectively, at the resonance transition of the molecule

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gas with a wavelength coinciding with the wavelength of the auxiliary pulse; a is the absorption coefficient of the unexcited molecule of the test gas at the resonant transition with the wavelength of the probe pulse;

Zi and Z2 are the static weights of the lower and upper energy levels, respectively, of the resonant transition of the molecule of the gas under study with a wavelength that coincides with the wavelength of the auxiliary pulse;

AR is the thickness of the sensed volume of the atmosphere;

U2 and and 2 are the recorded powers of backscattered echo signals, respectively, from the distances R and R + ДН from the probing laser pulse sent without an auxiliary laser pulse;

Ui and and 1 are the recorded powers of the backscattered echo signals, respectively, from the distances R and R + DR from the probed laser pulse sent simultaneously with the auxiliary laser pulse;

P is the power of the auxiliary laser pulse;

.- dimensionless parameter, taking values from O to 1 over a given interval of variation of the duration of the auxiliary laser pulse r, O, 2R / c.

The expression for determining the concentration of / e is based on the dependence of / e on the relative spectral transparency of the probed region of the atmosphere for two probe pulses and takes into account the increase in the absorption coefficient due to the selective excitation of the molecule of the test gas by an auxiliary pulse. A 1 ms time shift between two probe pulses minimizes the effect of atmospheric turbulence.

The duration of the auxiliary pulse is selected within

2 R

t t -p- and power limit

It is limited by saturation of the population of the upper level of the resonance transition with the wavelength of the auxiliary pulse.

The method increases the accuracy and sensitivity of determining the concentration of atmospheric gases by increasing the absorption coefficient at the wavelength of the probe pulse by selectively exciting the molecules of the test gas with an auxiliary pulse.

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Editor T. Klyukina

Compiled by A. Gorodetsky

Tehred M. Morgenthal Corrector A. Obruchar

Order 1963 Circulation unsigned

VNIIIPI of the State Committee for Inventions and Discover at the USSR State Committee for Science and Technology 113035, Moscow, Zh-35, Rausheka nab., 4/5

Production and Publishing House Patent, Uzhhorod, 101 Gagarin St.