JPH11248838A - Laser radar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser radar apparatus, for weather observation, by which an aerosol in the troposphere and an aerosol in the stratosphere can be measured without a changeover. SOLUTION: In a laser radar, a laser is emitted to the sky, and the distribution of an aerosol floating in the air is measured on the basis of backscattered light from the air. In the laser radar, a transmitting telescope 2 which transmits a laser beam in the vertical direction, a receiving telescope 3, for troposphere measurement, which is adjacnet to the transmitting telescope 2 and a receiving telescope 4, for stratosphere measurement, which is installed in a position at a distance from the receiving telescope 3 are arranged side by side in a row. An aerosol in the stratosphere is measured on the basis of the measured result of an aerosol in the troposphere only when the aersol in the stratosphere can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a meteorological system which emits a high-power pulse laser to the sky and remotely senses the concentration distribution of fine particles (aerosol) floating in the atmosphere from the intensity of backscattered light from the atmosphere. The present invention relates to an observation laser radar device.

[0002]

2. Description of the Related Art The measurement target of a laser radar for weather observation is:
There are so-called tropospheric aerosols that are relatively low (about 100 m to 10 km) and stratospheric aerosols that are relatively high (about 10 km to 35 km). The former changes drastically every day, and constant changes are seen throughout the day. Determining the aerosol distribution in the troposphere is effective for capturing the structure of the flow of the atmosphere, and is known to be very effective for remote sensing such as inversion of the atmosphere. When a clear inversion layer exists, the lower atmosphere becomes stagnant, and it is possible to accurately predict conditions that require attention in terms of pollution.
On the other hand, stratospheric aerosols are very stable compared to the troposphere. It is known that volcanic ash, once lifted into the stratosphere by a large explosion of a volcano, circulates around the earth quickly and stays in the stratosphere for a long time. The amount is by no means large, but attention has been paid to long-term fluctuations in global weather and its close relationship with the ozone hole.

Therefore, aerosol measurements in the troposphere and stratosphere are performed in different measurement cycles. Also, the reception strengths are greatly different. The intensity received by the laser radar receiving telescope is exponentially inversely proportional to the distance from the scattering object. Furthermore, the suspended concentration of scatterers such as aerosols is more contaminated and higher in low altitudes, while it is very clean and low in the stratosphere. In the troposphere measurement, a high concentration aerosol in the low sky is measured from a short distance, so that a very strong pulse light is detected immediately after the laser is emitted. It is not desirable for a high-sensitivity photodetector to have excessively strong light incident thereon. However, to measure from a short distance,
Naturally, the field of view of the laser beam and the receiving optical system must overlap from low altitude, and the receiving optical system must be as close to the laser beam as possible. The detector used for measuring the tropospheric aerosol is used in an analog detection system that can be used even with relatively strong light input.

On the other hand, in the measurement of the stratosphere, the reflected light that returns is very weak and becomes an optical signal of the number of photons. In order to measure such weak light, a photomultiplier tube is cooled, and a photocurrent counting method is used in which a dark current is reduced and a pulse current based on photons is measured. In the measurement, counting of photons by long-term integration is indispensable, with the background light at night being negligible. In this high-sensitivity detection method, it is necessary to be able to count the signal even if one photon is incident, and the most problematic is the presence of a dark current that determines that there is a signal even without a photon incident. As described above, when measuring the troposphere with a laser radar, it is known that a large pulse is inevitably incident on the detector immediately after launch, and it is known that dark light increases immediately after such light enters . Therefore, in order to simultaneously measure the troposphere and the stratosphere, special consideration has conventionally been required to prevent excessive light input to the high-sensitivity detector for measuring the stratosphere.

Next, a method for measuring a tropospheric aerosol and a stratospheric aerosol by a conventional technique will be specifically described. As described above, in the measurement of the tropospheric aerosol, it is necessary to measure from a low altitude, so the transmitting optical system and the receiving optical system are brought close to each other, and in some cases, the beam area of the transmitting and receiving optical system starts to overlap from low altitude by coaxial method It is necessary to arrange them. However, in such an arrangement, during measurement of the stratospheric aerosol, excessive light is incident on the corresponding detector, and high-sensitivity detection cannot be performed. For this 2
There are two methods.

In the first method, the rising position of the transmitting beam is moved from the time of the troposphere measurement to the time of the stratospheric measurement so that the overlapping of the transmitting beam and the receiving beam occurs at a high altitude for the first time. We can protect container. FIG. 6 shows a block diagram of the first prior art. In the figure, 1 is a laser device, 2 is a transmission telescope, 3 is a second transmission telescope, 4 is a reception telescope, 5 is a photomultiplier tube for analog detection, 6 is a photomultiplier tube for photon counting, and 7 is an AD converter. , 8 is a laser radar signal processor, 9 is a photoelectron counting counter, and 10 is a photoelectron detection signal processor. The transmission optical systems 2 and 3 are switched and used for each measurement in the troposphere and stratosphere. In the measurement of the troposphere, the receiving telescope 4
Is used so that measurement can be performed even at low altitude using the transmission telescope 3 as close as possible to the altitude. At this time, the received signal is measured by the photomultiplier tube 5, the AD converter 7, and the laser radar signal processor 8. At this time, the photomultiplier tube 6 for photoelectron counting is shielded from light by the shutter 11 for protection.
On the other hand, in the measurement of the stratosphere, the transmission telescope 2 is switched, and the transmission and reception beams are not overlapped at a low altitude to prevent an excessive input. At the time of stratospheric measurement, the shutter 11 is opened, and a photomultiplier 6 for photoelectron counting, a counter 9 for photoelectron counting, and a signal processor 10 are used to count while returning photons from a certain altitude while resolving the distance. .

The second method is a method in which the detector for measuring the stratosphere is shielded from light by a shutter for a predetermined time after the laser is transmitted without changing the layout of the transmission / reception optical system. FIG. 7 shows a block diagram of the second prior art. In FIG. 7, 1 is a laser device, 2 is a transmission telescope, 4 is a reception telescope, 5 is a photomultiplier tube for analog measurement, 6 is a photomultiplier tube for photoelectron counting,
7 is an AD converter, 8 is a laser radar signal processor, 9
Is a photoelectron counting counter, and 10 is a signal processor. From this arrangement, the measurement of the troposphere is the same as in the first prior art of FIG. The receiving optical system divides the received light beam into two and makes the light beams enter the photomultiplier tubes 5 and 6, thereby enabling simultaneous observation. However, in order to protect the photomultiplier tube 6 for photoelectron counting from excessive input, a high-speed chopper 12 is provided immediately before. The laser controller 11 monitors the rotation of the chopper, and emits a laser just at the timing when the chopper is closed. As a result, excessive input from low altitude is prevented. Photoelectron counting counter 9, signal processor 1
The configuration of 0 is the same as the first prior art.

[0008]

However, the first method has a complicated mechanism for changing the starting position of the laser.
It is impossible to measure the troposphere and stratosphere simultaneously. In the second method, the operation and control of a high-speed shutter are complicated, and high-speed on / off control is not easy with a mechanical shutter.

An object of the present invention is to provide a meteorological observation laser radar apparatus capable of stably and automatically measuring both the troposphere and the stratosphere receiving system without switching mechanism for a long period of time.

[0010]

According to the present invention, in a laser radar for emitting a laser to the sky and measuring a distribution of aerosol floating in the atmosphere from backscattered light from the atmosphere, a laser beam is directed vertically. A transmitting telescope to send out,
A laser radar device characterized by arranging a receiving telescope for tropospheric measurement adjacent thereto and a receiving telescope for stratospheric measurement installed at a more distant position in a line.

According to the present invention, there is provided a laser radar for measuring a distribution of an aerosol floating in the atmosphere from a backscattered light from the atmosphere by emitting a laser to the sky. A laser radar apparatus having a receiving system and simultaneously performing stratospheric measurement only in the atmospheric state where stratospheric measurement can be performed based on the result of steady-state tropospheric measurement is obtained.

As described above, since the tropospheric aerosol changes greatly in a daily cycle, it is necessary to constantly measure it at regular time intervals. On the other hand, the stratospheric aerosol may be measured once a day with sufficient time. To measure stratospheric aerosols, there must be no clouds in the troposphere, and clear skies without clouds at night are essential. In the present invention, the conditions under which the measurement of the stratospheric aerosol is possible are determined from the measurement results of the tropospheric aerosol which are constantly measured, and the stratosphere measurement by the integrated measurement is automatically performed for the time during which the required SN ratio can be obtained within the time. By doing so, stable automatic observation can be performed stably.

[0013]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, 1 is a laser device, 2 is a transmitting telescope, 3 is a first receiving telescope for measuring the troposphere, 4 is a second receiving telescope for measuring the stratosphere, 5 is a photomultiplier tube for analog detection, and 6 is a photomultiplier tube. Photomultiplier tube for photon counting, 7 is A
A D converter, 8 is a laser radar signal processor, 9 is a photoelectron counting counter, and 10 is a photoelectron detection signal processor.

It is clear from the above description that the troposphere and the stratosphere can be measured simultaneously with such a layout. In addition, the optical system has no moving parts, and enables stable measurement. In addition, measurements of the tropospheric aerosol are measured continuously at regular intervals and diurnal changes are recorded. Further, since the laser echo level of the cloud is very high as compared with the atmospheric aerosol, the laser radar signal processing unit 8 can easily identify whether or not the cloud exists in the sky. The laser radar signal processing unit 8 determines a situation where the measurement of the stratospheric aerosol is possible from the measurement result of the measured tropospheric aerosol, and performs the photon counting photomultiplier tube 6 and the counter 9 so as to measure the stratospheric aerosol only at that time. , And sends a control signal to the photoelectron detection signal processing unit 10. Specifically, the background level at night is sufficiently lowered, and the situation where the laser reaches the stratosphere without being disturbed by the clouds in a clear cloudless sky is judged from the laser echo signal, and the necessary SN in the meantime is determined. A count measurement is made for the time when the ratio is obtained. Normally, measurement can be performed if a time of about one hour is secured per day. With such a configuration, it is possible for the first time to automatically and continuously operate the tropospheric aerosol and the stratospheric aerosol.

FIG. 2 shows the relationship between the tropospheric aerosol measurement and the stratospheric aerosol measurement for the emitted laser. In the tropospheric aerosol measurement, the transmitted and received beams begin to overlap at a and completely enter the field of view at b. Also, regarding the stratospheric aerosol measurement, the transmitting and receiving beams start to overlap at c, and d
To completely enter the light receiving field of view.

FIG. 3 is a diagram showing 1 / R ² curves of the signal intensities SIG1 and SIG2 and the echo signal intensities obtained from the first receiving telescope 3 and the second receiving telescope 4 in the relationship shown in FIG. FIG. 4 shows S obtained corresponding to FIG.
It is a figure showing an IG1 signal and a SIG2 signal.

FIG. 5 is a diagram for explaining a case where the presence or absence of a cloud is determined based on the SIG1 signal. A cloud presence / absence determination level having a threshold higher than the 1 / R ² curve by a predetermined amount is set and exceeds the threshold. When there is a signal level, the laser radar signal processing unit 8 determines that there is a cloud, and stops the operation of each element of the SIG2 measurement system. Therefore, the SIG2 measuring system counts the number of photoelectrons and obtains a SIG2 signal in order to measure SIG2 only at night when it is determined that there is no cloud.

[0018]

As described above, according to the present invention, a meteorological laser radar apparatus capable of measuring a tropospheric aerosol and a stratospheric aerosol without switching can be obtained. In addition, the presence or absence of clouds is determined from the measurement results of the tropospheric aerosol, and if the presence of clouds is determined, the operation of the stratospheric aerosol measurement system is stopped to protect the photomultiplier from excessive input. An observation laser radar device is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between tropospheric aerosol measurement and stratospheric aerosol measurement for a radiation laser in the embodiment of FIG. 1;

FIG. 3 is a diagram showing signal strengths and echo signals obtained from a first receiving telescope and a second receiving telescope in the relationship shown in FIG. 2;

FIG. 4 is a view showing various signals obtained corresponding to FIG. 3;

FIG. 5 is a diagram for explaining an operation for determining the presence or absence of a cloud based on a measurement result of a tropospheric aerosol.

FIG. 6 is a diagram showing a conventional laser radar device.

FIG. 7 is a diagram showing another conventional laser radar device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser apparatus 2 Transmission telescope 3 First reception telescope 4 Second reception telescope 5 Photomultiplier tube for analog detection 6 Photomultiplier tube for photon counting 7 Analog-digital converter 8 Laser radar signal processor 9 Counter 10 Photoelectron detection signal Processor

Claims (6)

[Claims] 1. A laser radar for measuring a distribution of aerosol floating in the air from a backscattered light from the air by emitting a laser to the sky, and a transmitting telescope for vertically transmitting a laser beam and a troposphere adjacent thereto. A laser radar device, comprising: a measuring receiving telescope and a stratospheric measuring receiving telescope installed at a more distant position arranged in a line. 2. A laser radar which emits a laser to the sky and measures a distribution of aerosol floating in the atmosphere from backscattered light from the atmosphere, comprising a receiving system for tropospheric measurement and a receiving system for stratospheric measurement, A laser radar apparatus which simultaneously performs stratospheric measurement only in an atmospheric state where stratospheric measurement can be performed based on a result of steadily measuring the troposphere. 3. The laser radar device according to claim 2, wherein an atmospheric state in which stratospheric measurement is possible is performed by determining the presence or absence of a cloud in the troposphere. 4. The method according to claim 1, wherein the receiving operation of the stratospheric measurement receiving system is substantially stopped when the reception level of the receiving output of the troposphere measuring receiving system becomes higher than a predetermined threshold value. 2 laser radar device. 5. The laser radar apparatus according to claim 4, wherein said threshold value is set at a level higher than an echo signal level of a laser emitted above. 6. The laser radar device according to claim 2, wherein the troposphere measurement receiving system is installed closer to the laser emission position than the stratospheric measurement receiving system.