JP2776253B2 - Laser radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a distance to an object by detecting a laser beam emitted to the air and receiving a laser beam reflected from an object or scattered in the atmosphere, and a method for measuring the concentration of trace atmospheric components. And a laser radar used to make measurements.

[0002]

2. Description of the Related Art In general, a laser beam is emitted into the atmosphere, and a laser beam reflected by an object or scattered by a trace substance such as carbon dioxide in the atmosphere is received to measure a distance to the object. To measure the concentration of trace substances in the atmosphere, to receive signals from a long distance, or to perform high-precision measurements, increase the laser light output or apply a large number of laser pulses per unit time. It is necessary to improve the S / N by increasing the number of times of measurement by firing. However, when the laser light output is increased or the frequency of emitting laser pulses is increased, the safety of the laser light for humans decreases.

For example, when a person enters the optical path while emitting a laser beam and happens to look at the laser radar, if the laser beam is strong, the intensity allowed for eye safety ( Maximum Permissible Exposure, Maximum Permi
An amount of light exceeding the sible Exposure (hereinafter abbreviated as MPE) enters the eyes. This MPE
Is generally one pulse number as the number of visible pulses increases
Since it decreases in inverse proportion to the fourth power, even if it is safe to fire one pulse, it may exceed the MPE if a plurality of pulses are seen repeatedly.

[0004] The intensity of the laser pulse or the number of laser pulses per unit time is generally designed so that even if it exceeds the MPE, it is not dangerous. The reflected laser light from a long distance is converted to a predetermined S / N
In order to receive light as described above, the laser light output is increased or the number of laser pulses per unit time is increased. As a result, when the laser light output or the number of laser pulses exceeds a predetermined value, the laser light is viewed. If received, it will exceed MPE. If there is a possibility that a person can enter any position in the optical path to be measured, an MPA is required at the exit of the device (laser radar).
As described below, it is necessary to lower the power density by lowering the laser light output or increasing the emission area.

[0005] As described above, in the conventional measuring method, the intensity of laser light or the number of repetitions that can be emitted from the viewpoint of safety is limited from the viewpoint of safety if a measure that prevents a person from entering the optical path is taken. In some cases, measurement cannot be performed or required accuracy cannot be obtained even at a short distance.

Japanese Patent Laid-Open Publication No. Sho 59-159 discloses a laser radar which prevents a powerful laser beam from damaging human eyes and skin.
No. 180472. In this conventional laser radar, first, a laser pulse A of a safe and somewhat low power level is emitted from the first light transmitting section to a person or a light receiving optical component, and it is confirmed that there is no obstacle such as a person on the optical path. The second highest power level laser pulse B
It emits light from the light-transmitting section, enabling safe measurement over long distances.

[0007]

However, in the laser radar described in the above-mentioned Japanese Patent Laid-Open Publication No. Sho 59-180472, it is high only if there is a shield on the optical path regardless of the distance R1 of the shield. Since it is determined whether or not to emit a power level laser pulse B, the distance R of the shield is determined.
No. 1 does not emit a safe level of laser light.
Generally, in a laser radar, the MPE at distance R1
With the emission of the laser light at the level shown below, an object at a distance R2 far greater than the distance R1 can be detected. Therefore, in the conventional laser radar, an opportunity to detect a target within the detectable distance R2 is missed while securing the safety of human eyes on the optical path.

In this conventional laser radar, if there is an obstacle in the optical path of the laser beam emitted from the first light transmitting unit, the second laser radar is thereafter operated until the obstruction disappears in the optical path.
Does not emit laser light. However, the shield must be in a certain limited range of azimuth (horizontal angle) or elevation angle (vertical angle), and the above-mentioned conventional laser radar can perform a wide range of measurements while ensuring safety. Since this is not the case, the opportunity for detecting the target is also missed.

Further, in the above-mentioned conventional laser radar,
When the thing that reflects the laser beam is a mixture of air and fine particles, such as clouds, fog, smoke, and sandstorms, it can be clearly distinguished from humans from the waveform of the received signal,
The mixture is recognized as a mere shield, and the emission of the high-level laser pulse B is stopped.

In addition, in the above-mentioned conventional laser radar, the only difference between the laser pulses A and B is the power level. Generally, a high-density object such as a human body or a car has a laser light reflectance of 10% or more, but a backscattering coefficient of the atmosphere is about 10 ^-6 / m. Now, the power levels of the laser pulses A and B are set to P _A and P _B , respectively.
And If this content of the conventional trace substances such as carbon dioxide in the atmosphere in the laser radar to a distance R to try measurement, and outputs a laser pulse A of first low power level P _A from the first light transmitting unit Te, by examining whether the distance to the R there is an interrupting object from the received light level, confirm the safety of a distance R, sending a laser pulse B of much greater power level P _B from P _a second thereafter The content of the trace substance in the atmosphere which is output from the optical unit and reaches the target distance R is measured. However, its power level P _A
Since the value must be low enough to be safe even at a short distance from the laser radar, the distance R cannot be made sufficiently large.

As described above, the conventional laser radar described in Japanese Patent Application Laid-Open No. Sho 59-180472 has a problem to be solved with respect to an opportunity for detecting a target and an increase in a measurement distance.

[0012]

In order to solve the above-mentioned problems, the present invention provides the following means.

A laser oscillator that oscillates a laser, emits laser light output from the laser oscillator into the atmosphere, and scatters the laser light scattered by shields in the atmosphere, trace substances in the atmosphere, and other laser light reflectors. Transmitting and receiving optical system, a light detector for converting the laser light received by the transmitting and receiving optical system into an electric signal, and a level of a light receiving signal output from the light detector and from emission to reception of the laser light A circuit for detecting the distance of the reflector based on the time of
A circuit for controlling the operation of the laser oscillator according to the light receiving signal detected by the detection circuit, and emits a laser beam for measurement after emitting low-power laser light and confirming safety to a person. In the laser radar, the control circuit, according to the light receiving signal level and the distance,
Or, only in accordance with the distance, controls the power of the laser light output from the laser oscillator , the detection circuit
Judging from the received signal level, if there is the reflector,
When the judgment is made, the laser oscillator is controlled to control the laser beam power.
It repeatedly emits and receives light to adjust the movement of the reflector.
In doing so, gradually increase the firing interval of the laser light.
Laser radar characterized by Rukoto.

A warning means for generating a warning sound or a warning signal when receiving a warning command from the control circuit;
The laser according to the above, wherein the control circuit stops the oscillation of the laser oscillator and outputs the warning command according to the light receiving signal level and the time or only the time. Radar.

The control circuit calculates from the distance and the number of the laser light pulses emitted within a predetermined time, and controls the laser oscillator with a power at which the energy of the laser light reaching the distance becomes a maximum allowable exposure amount. The laser radar according to the above or the above, wherein the laser radar is oscillated.

[0016]

[0017] A laser oscillator that performs laser oscillation,
To emit laser light output from a laser oscillator into the atmosphere
In particular, atmospheric shields, atmospheric traces and other
Transmission / reception optics to receive laser light scattered by the light reflector
System and the laser light received by the transmission / reception optical system.
A photodetector that converts the signal into a signal and the output from the photodetector
The level of the received light signal, and the
A circuit for detecting the distance of the reflector based on the time in,
According to the light receiving signal detected by the detection circuit, the laser
Circuit for controlling operation of the oscillator
Wherein the control circuit is configured to control a waveform of the light receiving signal.Acknowledge
The laser light received by the transmission / reception optical system
Places determined to be scattered light from clouds, fog, smoke, sand, storms, etc.
IfThe laser oscillatorFire the laser light from
ToA laser radar, comprising:

[0018] A laser oscillator that performs laser oscillation,
To emit laser light output from a laser oscillator into the atmosphere
In particular, atmospheric shields, atmospheric traces and other
Transmission / reception optics to receive laser light scattered by the light reflector
System and the laser light received by the transmission / reception optical system.
A photodetector that converts the signal into a signal and the output from the photodetector
The level of the received light signal, and the
A circuit for detecting the distance of the reflector based on the time at
In the laser radar having the transmission / reception optical system,
An optical scanning device that scans the direction of the emitted and received laser light,
The optical scanning according to the light receiving signal detected by the detection circuit.
A circuit for controlling the operation of the inspection device, the control circuit
Depends on the light receiving signal level and the distance, or
The optical scanning device is controlled according to only the distance,
Control the direction of the laser beam to be received and received
Laser radar.

[0019] First and second laser oscillation
Lasers and the laser output of these lasers
Not only emits light into the atmosphere, but also
Rays scattered by trace substances and other laser light reflectors
Transmission / reception optical system for receiving the light, and reception / transmission
A photodetector that converts the laser light thus emitted into an electric signal,
The level of the light receiving signal output from the photodetector and the level
The reflector based on the time from emission of laser light to reception of the laser light
A distance detecting circuit, and the detecting circuit
A circuit for controlling the operation of the laser oscillator according to a received light signal.
A laser radar having a first path and a first path.
The oscillator is ultraviolet light with a wavelength of 400 nm or less or 1400 nm.
The above-mentioned infrared light is oscillated, and the second laser oscillator is visible.
Oscillating light, the control circuit comprising: the first laser oscillator
Power at a distance where safety has been confirmed by the oscillation of
Oscillating the second laser oscillator.
Laser radar.

[0020] First and second laser oscillation
Lasers and the laser output of these lasers
Not only emits light into the atmosphere, but also
Rays scattered by trace substances and other laser light reflectors
Transmission / reception optical system for receiving the light, and reception / transmission
A photodetector that converts the laser light thus emitted into an electric signal,
The level of the light receiving signal output from the photodetector and the level
The reflector based on the time from emission of laser light to reception of the laser light
A distance detecting circuit, and the detecting circuit
A circuit for controlling the operation of the laser oscillator according to a received light signal.
A laser radar having a path,
Is the waveform of the received light signalRecognize the transmission / reception optical system
The laser light received by the cloud, fog, smoke, sand, storm, etc.
If it is determined that the scattered light isThe laser oscillator
Fire the laser light fromLaser characterized by the following:
・ Radar.

[0021]

According to the laser radar of the present invention having the above-described structure,
It is suitable for measuring the concentration of a trace substance in the atmosphere such as nitrogen dioxide (NO ₂ ). The first laser oscillator (1a) emits a laser beam for safety confirmation, and the second laser oscillator (1b) emits a laser beam for measurement. Control circuit (7)
First activates the first laser oscillator (1a), confirms that there is no obstruction up to the distance R to be measured, and that it is safe to emit the measuring laser light,
The laser oscillator (1b) is operated to emit a measuring laser beam.

First laser oscillator (1a) for safety confirmation
Outputs ultraviolet light having a wavelength of 400 nm or less or infrared light having a wavelength of 1400 nm or more. On the other hand, when the second laser oscillator (1b) for measurement uses the differential absorption method, the second laser oscillator (1b) has a molecular absorption line wavelength of a trace substance to be measured and the vicinity of the molecular absorption line wavelength, which is due to the trace substance. Outputs laser light of a wavelength with little absorption.

Generally, the MPE of a pulse of ultraviolet light having a wavelength of 400 nm or less and infrared light having a wavelength of 1400 nm or more has a wavelength of 40
It is 10,000 times or more the MPE of visible light of 0 to 770 nm. That is, ultraviolet light having a wavelength of 400 nm or less and a wavelength of 14
Infrared light having a wavelength of 00 nm or more is more than 10,000 times safer than visible light having a wavelength of 400 to 770 nm. Therefore, the ultraviolet light and the infrared light in the above wavelength range are suitable as laser light for safety confirmation. Hereinafter, ultraviolet light having a wavelength of 400 nm or less and infrared light having a wavelength of 1400 nm or more are referred to as safe wavelength light.

On the other hand, as a method for measuring the concentration of nitrogen dioxide or sulfur dioxide (SO ₂ ) in the atmosphere with a laser radar with high accuracy, a differential absorption method (Differential Absorptio) is used.
n Lidar, DIAL) has been attracting attention in recent years. In the differential absorption method, a molecular absorption line of a trace substance in the atmosphere to be measured and a wavelength near the molecular absorption line and having a small absorption are emitted at short time intervals, and light of both wavelengths is attenuated. From the difference, the concentration of the trace substance is measured. In order to perform measurement by this differential absorption method, it is necessary to emit a molecular absorption line having a wavelength specific to the trace substance to be measured as a measurement laser beam. For example, the molecular absorption line of nitrogen dioxide is 448.1 nm. Therefore, to measure the concentration of nitrogen dioxide by applying the differential absorption method, there is a high risk to the eyes, that is, M
It has to emit visible light with low PE. However, in order to measure the concentration of nitrogen dioxide over a long distance, it is necessary to emit laser light in the visible region with large power.

Therefore, when measuring the concentration of a trace substance in the atmosphere by the differential absorption method using the present invention, the power Pa _R required for confirming the safety up to the distance R to be measured is a safe wavelength. Light is transmitted to a first laser oscillator (1a)
Power required to measure the concentration of nitrogen dioxide up to the distance R by the differential absorption method.
_{At R} , laser light of a measurement wavelength that is inferior to safety but essential for the application of the differential absorption method is emitted at intervals.

The safety wavelength light is disclosed in the above-mentioned JP-A-59-180.
No. 472, which is more than 10,000 times safer than the laser beam for measurement in the visible light region in the conventional laser radar described in Japanese Patent Publication No. 472, the number of times of pulse emission repeated for security confirmation in the present invention is It is much less than in.

As described above, in the configuration of the present invention applied to the differential absorption method, the differential absorption method is applied to a laser beam having a high MPE and excellent in safety and a substance having a molecular absorption line in visible light. By properly using laser light in the wavelength range that is essential for this, we have realized a laser radar that can safely measure the concentration of trace substances such as nitrogen dioxide over long distances. Laser radar does not identify the type of shield detected by the laser beam for safety confirmation, only judges whether there is an obstacle based on the received light level, and emits a laser beam for measurement if there is an obstacle. It is normal to wait until the shield disappears, but in the present invention, in addition, the type of the shield is estimated from the waveform of the output of the photodetector (5) and estimated. If the shield is low density and widely distributed, such as cloud, fog, smoke, rain, sandstorm, yellow sand,
It is also possible to determine that it is safe even if there is a shield, and to emit the measuring laser light from the laser oscillator (1b). When the shield is a cloud, fog, smoke, rain, sandstorm, yellow sand, and the like, which is distributed at a low density and in a wide range, the output waveform of the photodetector (5) spreads on the time axis. Therefore, it can be clearly distinguished from the waveform of light reflected from a high-density body such as a human, an automobile, and a building. As described above, the type of the shield is identified from the received light waveform, and the measurement laser light is emitted even if there is a low-density object such as a cloud, so that the opportunity for measurement can be increased.

[0028]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention for explaining the embodiment. Components other than a circuit 6 for detecting the output signal level of the photodetector 5 and a control circuit 7 for stopping laser oscillation or performing strong laser oscillation in accordance with the output level of the detection ground circuit 6 are ordinary lasers. The operation is the same as that of the radar or the laser ranging device, but the operation will be described again. Light emitted from the laser oscillator 1 is emitted into space by the transmission / reception optical system 2 at a predetermined beam divergence angle. Depending on the situation, it may pass through the optical scanning device 3. The laser beam 11 striking the object 4 is reflected and condensed by the transmission / reception optical system 2 (when the optical scanning device 3 is used at the time of emission, it passes through the transmission / reception optical system 2 again and then is transmitted).
to go into). The light collected by the transmission / reception optical system 2 is converted into an electric signal by the photodetector 5. A circuit 6 for detecting the reception level and the arrival time of the electric signal output from the photodetector 5 detects the presence or absence of a light input (reflection from the object 4) at a certain level or more and the time from the laser emission to the arrival of the reflected light ( Object 4
Is measured).

When measuring the scattered light from the atmospheric trace components, the output of the photodetector 5 is received by the A / D converter / display device 8 via the detection circuit 6, where it is A / D converted. Display and memorize levels. The display on the display device 8 includes the arrival time (or a value converted into the distance) and the reflected light intensity according to the distance.

The laser radar of FIG. 1 performs the following operations in addition to the above-mentioned normal operations.

At the exit of the apparatus (laser radar), a laser beam whose output has been reduced so as to be less than or equal to the MPE of a single pulse is emitted (it is safe even if there is a person who looks in immediately before). In the case of a 10 ns Nd: YAG laser (wavelength 1.064 μm) emitted from an optical system having a diameter of 2 cm, if it is 1570 W, it will be less than or equal to the MPE immediately before the apparatus (refer to the following calculation-1).

[Calculation-1] Safe laser output level calculation immediately before the exit Safety calculation (calculation of MPE) in accordance with GIS C6802 is performed.

(Table numbers are JIS numbers.) According to Table 1, the exposure time (pulse width) is 10 ^-8 nm at a wavelength of 1064 nm.
The MPE at the time of sec is 5 × 10 ⁻² J / m ² , and an area of 3.14 × 10 ⁻⁴ m having an emission diameter of 2 cm (radius of 0.01 m).
² with respect to ^{5 × 10 -2 J / m 2} ÷ 10 -8 sec × 3.14
× 10 ^-4 m ² = 1570 W.

With this laser output, a distance measurement of several hundred meters is possible (as shown in FIG. 2, the measurable distance is about 400 m for a visibility of 1 km and about 850 m for a visibility of 5 km). FIG. 2 is a characteristic diagram showing the result of calculating the relationship between the distance to the reflecting object (horizontal axis) and the reception input level (vertical axis).

If there is a signal due to the reflected light at a detectable level, the distance to the object 4 (the time from the laser emission to the arrival of the reflected light) is measured, and the safety level at this distance (the laser that can be emitted) (Light intensity) and emits a warning sound or the like as necessary. (Because the power density of the irradiated laser decreases in inverse proportion to the square of the distance from the apparatus, when the distance to the object 4 is long, even if the laser power is increased, the power density can be kept below the safe level.) If the signal due to the reflected light was detected, but the level was low and the S / N ratio was not obtained, and the ranging accuracy was considered to be insufficient, the control circuit 7 sets the output level of the photodetector 5 to Accordingly, the laser light is increased to the safety level calculated in the item, and the measurement is performed again. Accuracy is improved by repeated ranging as needed. In that case, the laser light intensity is set to a level below the safe level even if repeated.

In the light scanning, if reflected light is detected in a certain direction, the direction is controlled so that light at a level higher than a safe level is not emitted.
The measurement is performed according to the above-mentioned item, or the scanning is performed with the direction skipped). Although it may be sufficient to measure the distance to the object 4, it is conceivable that only a laser beam having an intensity not sufficient to detect weak scattered light from atmospheric components or the like may be emitted. The measurement is temporarily suspended without emitting a strong laser.

If no signal due to reflected light is detected,
In the example of FIG. 2, it is determined that no one is within 400 m. Therefore, a laser having an output within a range up to the laser safety level at 400 m (190 kW with a beam divergence angle of 0.5 mrad, see the following calculation-2). Fire. FIG. 3 shows the distance that can be measured at that time. If it is desired to measure a distance longer than this, the laser output is further increased after confirming that there is no reflected light. If sufficient accuracy cannot be obtained due to lack of S / N, the same method as in the paragraph is applied.

[Calculation-2] A safety calculation (calculation of MPE) in accordance with JIS C 6802 at a safety level of 400 m is performed.

(Table numbers are JIS numbers.) According to Table 1, the exposure time (pulse width) is 10 ^-8 nm at a wavelength of 1064 nm.
The MPE at the time of sec is 5 × 10 ⁻² J / m ² , and when the emission diameter is 2 cm and the beam divergence angle is 0.5 mrad, it is 40.
0.02m + 0.5 × 10 ⁻³ × 400m at 0m ahead
Area spread over 0.02 m circle (radius 0.11 m) = 3.
5 for 14 × (0.11 m) ² = 0.03799 m ^{2
× 10 -2 J / m 2 ÷} 10 -8 sec × 0.03799m 2 ≒
190,000W.

In the case of measuring the scattered light from atmospheric components and the like, when the light above a certain level, that is, the reflected light from the object is received, the laser is stopped for a certain period in consideration of safety. It is necessary to restart the measurement quickly. As a method of determining the restart time, it is conceivable to emit a laser beam equal to or less than the MPE and check for the presence or absence of reflected light. There is fear. If the laser firing interval is sufficiently widened, the number of laser pulses to be fired within a certain time can be reduced, so that it is safer. , Meanwhile, the measurement is interrupted. Objects that suddenly enter the optical path during measurement are moving objects,
From a different point of view, it can be said that the possibility of staying at the same point for a long time is low. Therefore, a method of gradually increasing the laser emission interval in consideration of these factors can be considered. For example, the next laser is emitted 1 second after detecting reflected light from an object, etc., the next laser is emitted 2 seconds after detecting reflected light, and 4 seconds after detecting reflected light. , 8 seconds and 16 seconds later, the interval is doubled so that a laser beam can be emitted to a rapidly moving object immediately after the movement, and the object stops without moving. Excessive laser irradiation can be prevented from being performed on the object.

(Specific Embodiment of Apparatus) FIG. 4 is a diagram showing the configuration of another embodiment of the present invention, which is a more specific example of the embodiment of FIG. The laser beam 11 emitted from the laser oscillator 1 is attenuated to a safe level by the laser beam controller 70, adjusted to a predetermined beam divergence angle by the beam expander 21, and emitted into space. At this time, the light reflected by the optical components and the like in the middle is used as the start pulse detecting photodiode 61.
To take out as a start pulse. Since the laser radar shown in FIG. 4 is small, the optical scanning device 3 is installed together with the laser radar.
It is a structure to put on. The optical scanning device 3 includes a scanning gantry 30, a horizontal angle drive motor 31, a horizontal angle detection encoder 32,
It is provided with a vertical scanning drive motor (vertical drive motor) 33, a vertical angle detection encoder 34, and a motor drive circuit 35.

The laser light emitted into the space is reflected by the object 4 and condensed by the receiving optical system 22, and is separated by the dichroic mirror 23 which reflects the laser light and transmits visible light. The aiming optical system 24 is used when a person manually aims the object 4 and is not particularly necessary when scanning is being performed. The light reflected by the dichroic mirror 23 is
After being converted into an electric signal by the photodetector 5 and amplified by the amplifier 62, a part of the signal enters the distance counter 63. The distance counter 63 calculates a time from laser emission to reception of reflected light, that is, a distance to the object 4. Part of the output of the amplifier 62 enters the reception light level detection circuit 64 and detects the intensity of the reception light.

The CPU 76 determines whether or not the intensity of the emitted laser light is appropriate based on the distance to the object 4 and the intensity of the received light, and controls the laser light control unit 70 via the light output control unit 77. Control to optimize laser light level.
The laser oscillation is stopped as needed. Optimization means that when there is no strong reflected light, the laser light output is increased to an appropriate level in consideration of the safety level, but if there is a possibility that the laser will be emitted many times and exceeds the MPE, the laser output will be reduced. Weakening or stopping laser emission for a certain period of time. The distance measurement data is displayed on the display device 81 as it is, or is displayed on the display device 81 as distance / image data together with the output of the encoder that has detected the scanning direction. Further, the CPU 76 sends data to a computer or the like that controls the host system via the distance data output board 78.

The laser beam controller 70 is constructed by inserting an electro-optical element 72 between two polarizers 71a and 71b, as shown in FIG. Electro-optical element 72
Controls the amount of transmitted light according to the applied control voltage. The laser light control unit 70 is sometimes called an optical shutter.
Most of the energy must be lost internally to attenuate the laser light to a level that is safe at the exit.
Therefore, part of the light emitted from the polarizer 71b on the exit side is absorbed by the beam dump 73. Considering the configuration of FIG. 5 as a one-stage optical shutter, the practical limit is that the attenuation is reduced to about 1/1000 with only one stage. If a powerful laser is used, the attenuation is reduced to a safe level. Since it is necessary to drop the light, another optical shutter may be added.

FIG. 6 shows the laser light control unit 70 shown in FIG.
A fiber amplifier 74 as an example of the laser oscillator 1
FIG. 6 is a circuit block diagram showing excitation LDs 75a to 75d as an example. Even if the semiconductor laser is pulsed, there is a limit in increasing the output. Therefore, when long-distance measurement is considered, it is necessary to amplify the semiconductor laser with a fiber amplifier 74 as shown in FIG. In this case, the optimum output is obtained by adjusting the input to the pumping lasers (pumping LDs) 75a, 75b, 75c, and 75d, controlling the oscillation time, and increasing or decreasing the number of lasers to be pumped. Can be obtained.

FIG. 7 is a block diagram showing another embodiment of the present invention, which is a modification of the embodiment shown in FIG. In the embodiment shown in FIG. 7, nitrogen dioxide (NO ₂ ) which is a trace substance in the atmosphere is used.
FIG. 1 is a laser radar for measuring the density of a laser beam, comprising laser oscillators 1a and 1b, and
The embodiment differs from the embodiment in the number of laser oscillators. The laser oscillator 1a emits laser light for safety confirmation, and the laser oscillator 1b emits laser light for measurement. The control circuit 7
First, the laser oscillator 1a is operated, and it is confirmed that there is no obstruction at a distance to be measured, and that it is safe to emit the measuring laser light. Then, the laser oscillator 1b is operated to emit the measuring laser light. Fire. Other components of this embodiment operate similarly to the embodiment of FIG.

The laser oscillator 1a for safety confirmation uses ultraviolet light having a wavelength of 355 nm obtained by using the third harmonic of the YAG laser as
Output with 0mJ / pulse power. On the other hand, the measuring laser oscillator 1b has a wavelength of 448.1 nm and a wavelength of 448.1 nm by optical parametric oscillation (OPO) caused by applying the output of the YAG laser to the crystal.
6.6 nm visible light is alternately obtained at a power of several tens of mJ / pulse and output.

Generally, the MPE of ultraviolet light having a wavelength of 400 nm or less and infrared light having a wavelength of 1400 nm or more has a wavelength of 400 to 77.
10,000 of MPE for 0 nm pulsed visible light
More than double. That is, ultraviolet light having a wavelength of 400 nm or less and infrared light having a wavelength of 1400 nm or more are more than 10,000 times safer than visible light having a wavelength of 400 to 770 nm. Therefore, the ultraviolet light and the infrared light in the above wavelength range are suitable as laser light for safety confirmation.

On the other hand, as a method for measuring the concentration of nitrogen dioxide or sulfur dioxide (SO ₂ ) in the atmosphere with high accuracy by a laser radar, a differential absorption method (Differential Absorptio) is used.
n Lidar, DIAL) has been attracting attention in recent years. In the differential absorption method, a molecular absorption line of a trace substance in the atmosphere to be measured and a wavelength near the molecular absorption line and a wavelength with little absorption are emitted at short time intervals, and the attenuation rate of both wavelengths is measured. The concentration of the trace substance is determined from the difference. In order to perform measurement by this differential absorption method, it is necessary to emit a molecular absorption line having a wavelength specific to the trace substance to be measured as a measurement laser beam.
For example, the molecular absorption line of nitrogen dioxide is 448.1 nm. Therefore, to measure the concentration of nitrogen dioxide by applying the differential absorption method, there is a high risk to the eyes, that is, MP
It has to emit visible light with low E. However,
To measure the concentration of nitrogen dioxide over a long distance, it is necessary to emit laser light in the visible region with a large power.

Therefore, in the embodiment of FIG. 7, the power P required to confirm the safety up to the distance R to be measured is determined.
In a _R, a laser beam of 355nm in highly secure ultraviolet region emitted by the laser oscillator 1a, a power Pb _R required to measure the nitrogen dioxide concentration of up to a distance R by differential absorption method Thereafter, safety However, laser beams having wavelengths of 448.1 nm and 446.6 nm, which are inferior to the application of the differential absorption method, are emitted at intervals.

When the power P _MPE0 of the laser oscillator 1a which becomes the MPE at the wavelength of 355 nm at the exit of the laser radar of this embodiment is smaller than Pa _R , first, the safety up to the distance R1 is confirmed by the power of P _MPE0 , and the distance R1 When there is no obstruction between the _two , a light of 355 nm is emitted with a power P _MPE1 that becomes an MPE at a distance R1, and safety up to a distance R2 is confirmed. If R2> R, then a visible region laser beam for measurement is emitted. It is emitted from the laser oscillator 1b. If the safety confirmation distance R2 that is possible by the emission of the power P _MPE1 is smaller than the measurement distance R, 355 nm light is emitted at the power P _{MP E2} that becomes the MPE at the distance R2 and the distance R3 (R
3> R2), for example, by gradually increasing the safety confirmation distance Rn in a tapered manner, until the safety confirmation distance Rn becomes larger than the measurement distance R.
Continue safety confirmation by.

However, the 355 nm light in the ultraviolet region is 10,000 times safer than the measuring laser light in the visible light region in the conventional laser radar described in Japanese Patent Application Laid-Open No. Sho 59-180472. In addition, the number of times of pulse emission repeated for safety confirmation is significantly smaller than that in the conventional example.

As described above, in the embodiment shown in FIG. 7, the wavelength required for applying the differential absorption method to a laser beam having a high MPE and excellent in safety and a substance having a molecular absorption line in visible light. A laser radar that can measure the concentration of nitrogen dioxide safely over long distances is realized by skillfully using the laser light in the region.

In FIG. 7, the number of laser oscillators for measurement is one, and the laser oscillator 1b emits light of 448.1 nm.
Although 6.6 nm light is oscillated, it is possible to use two laser oscillators for measurement and oscillate 448.1 nm light and 446.6 nm light with independent laser oscillators.

In the embodiment shown in FIG. 7, the type of the shield detected by the laser beam for safety confirmation is not identified, and only the presence or absence of the shield is determined based on the light receiving level. It stops emitting the laser beam for measurement and waits until there is no obstruction. However, the type of obstruction is estimated from the waveform of the output of the photodetector 5, and the estimated obstruction is cloud, fog,
When it is distributed over a wide range with low density, such as smoke, rain, sandstorm, yellow sand, etc., it is determined that it is safe even if there is a shield, and the laser beam for measurement is emitted from the laser oscillator 1b. You can do it. The shield is a cloud,
When the light is distributed over a wide range at a low density, such as fog, smoke, rain, sandstorm, yellow sand, etc., the output waveform of the photodetector 5 spreads on the time axis.
It can be clearly distinguished from the waveform of light reflected from a high-density body such as a building. As described above, the type of the shield is identified from the received light waveform, and the measurement laser light is emitted even if there is a low-density object such as a cloud, so that the opportunity for measurement can be increased.

[0056]

As described above, the present invention provides a laser
This has the effect of enabling long-distance measurement and high-precision measurement while giving priority to safety in radar.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram obtained by calculating a relationship between a reception input level in a laser radar and a distance to a target object in order to know a distance that can be measured by a laser beam at a safety limit.

FIG. 3 is a characteristic diagram obtained by calculating a relationship between a reception level and a distance of a target object at the time of measurement with increased laser output when the safety of the distance range obtained in FIG. 2 is confirmed.

FIG. 4 is a block diagram showing a configuration of another embodiment of the present invention, which further embodies the embodiment of FIG. 1;

FIG. 5 is a block diagram of a laser light attenuator as an example of a laser light control unit.

FIG. 6 is a circuit block diagram illustrating a fiber amplifier that amplifies a semiconductor laser output as an example of a laser light control unit.

FIG. 7 is a block diagram showing another embodiment of the present invention in which the embodiment of FIG. 1 is modified.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 laser oscillator 2 transmission / reception optical system 3 optical scanning device 4 object 5 photodetector 6 circuit for detecting reception level and arrival time of photodetector output signal 7 stopping laser oscillation or intense laser according to detected output level Control circuit for performing oscillation 8 A / D converter / display device 11 Laser beam 21 Beam expander 22 Receiving optical system (lens, focusing telescope, etc.) 23 Dichroic mirror 24 Aiming optical system 30 Scanning gantry 31 Horizontal scanning drive Motor 32 Horizontal angle detection encoder 33 Vertical scanning drive motor 34 Vertical angle detection encoder 35 Motor drive circuit 36 Scan control CPU 61 Start pulse detection photodiode 62 Amplifier 63 Distance counter 64 Received light level detection circuit 70 Laser light control Parts 71a, 71b Polarizer 72 Electro-optical element 73 Beam dump 74 Fiber amplifier 74a Fiber loop 74b, 74c Isolator 74d, 74e Dichroic mirror coupler (mirror that separates transmission and reflection using wavelength difference) 74f, 74g Polarization coupler (transmission and reflection using difference in polarization) Separating mirror) 75a to 75d Laser for excitation (excitation LD) 76 CPU 77 Optical output control unit 78 Distance data output board 81 Display device

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G01S 7/48-7/499 G01S 17/00-17/95 G01W 1/00

Claims (7)

(57) [Claims] 1. A laser oscillator for oscillating a laser, and a laser beam output from the laser oscillator is emitted to the atmosphere and scattered by a shield in the atmosphere, a trace substance in the atmosphere, and other laser light reflectors. A transmission / reception optical system for receiving laser light, a photodetector for converting the laser light received by the transmission / reception optical system into an electric signal, and a level of a light reception signal output from the photodetector and emission of the laser light. A circuit for detecting a distance of the reflector based on a time until light reception; and a circuit for controlling operation of the laser oscillator in accordance with the light reception signal detected by the detection circuit, and emits a low-power laser beam. A laser radar that emits a laser beam for measurement after confirming safety to a person, and wherein the control circuit responds to the received light signal level and the distance or only to the distance According to the, the power of the laser light output from the laser oscillator is controlled , the detection circuit determines from the received signal level, the
Controls the laser oscillator when it is determined that there is a reflector
And repeatedly emits and receives laser light pulses.
When examining the movement of the projectile, the firing interval of the laser
Laser radar characterized by gradually increasing . Wherein when receiving the control circuits or et warning instruction,
A warning unit that generates a warning sound or a warning signal, wherein the control circuit stops the oscillation of the laser oscillator according to the light receiving signal level and the time or only the time, and issues the warning command. The laser radar according to claim 1, wherein the output is output. 3. The control circuit calculates from the distance and the number of the laser light pulses emitted within a predetermined time, and the power of the laser light reaching the distance becomes a maximum allowable exposure amount. The laser radar according to claim 1, wherein the laser oscillates. 4. A laser oscillator for performing laser oscillation, and a laser beam output from the laser oscillator is emitted into the atmosphere, and is scattered by a shield in the atmosphere, a trace substance in the atmosphere, and other laser light reflectors. A transmission / reception optical system for receiving laser light, a photodetector for converting the laser light received by the transmission / reception optical system into an electric signal, and a level of a light reception signal output from the photodetector and emission of the laser light. In a laser radar having a circuit for detecting a distance of the reflector based on a time until light reception, and a circuit for controlling operation of the laser oscillator according to the light reception signal detected by the detection circuit, the control circuit includes: Recognizing the waveform of the light receiving signal ,
The laser light received by the transmission and reception optical system is cloud, fog, smoke,
A laser radar , wherein when it is determined that the light is scattered light from sand, a storm, or the like, the laser light is emitted from the laser oscillator. 5. A laser oscillator for performing laser oscillation, and a laser beam output from the laser oscillator is emitted into the atmosphere, and is scattered by a shield in the atmosphere, a trace substance in the atmosphere, and other laser light reflectors. A transmission / reception optical system for receiving laser light, a photodetector for converting the laser light received by the transmission / reception optical system into an electric signal, and a level of a light reception signal output from the photodetector and emission of the laser light. A laser radar having a circuit for detecting the distance of the reflector based on the time until light reception; an optical scanning device for scanning the direction of laser light emitted and received by the transmission / reception optical system; A circuit for controlling the operation of the optical scanning device according to the light receiving signal, wherein the control circuit is responsive to the light receiving signal level and the distance, or only to the distance. It controls the optical scanning device, the laser radar and controlling the direction of firing and receiving laser light. 6. A first and a second laser oscillator, each of which oscillates a laser, emits laser light output from these laser oscillators to the atmosphere, shields in the atmosphere, trace substances in the atmosphere, and other lasers. A transmission / reception optical system for receiving the laser light scattered by the light reflector, a photodetector for converting the laser light received by the transmission / reception optical system into an electric signal, and a level of a light reception signal output from the photodetector A circuit for detecting the distance of the reflector based on the time from emission of the laser light to light reception, and a circuit for controlling the operation of the laser oscillator in accordance with the light reception signal detected by the detection circuit. In the radar, the first laser oscillator emits ultraviolet light having a wavelength of 400 nm or less or infrared light having a wavelength of 1400 nm or more, the second laser oscillator emits visible light, A laser radar, wherein the control circuit oscillates the second laser oscillator with safe power at a distance where safety is confirmed by the oscillation of the first laser oscillator. 7. A first and a second laser oscillator, each of which oscillates a laser, emits laser light output from these laser oscillators to the atmosphere, shields in the atmosphere, trace substances in the atmosphere, and other lasers. A transmission / reception optical system for receiving the laser light scattered by the light reflector, a photodetector for converting the laser light received by the transmission / reception optical system to an electric signal, and a level of a light reception signal output from the photodetector A circuit for detecting the distance of the reflector based on the time from emission of the laser light to light reception, and a circuit for controlling the operation of the laser oscillator according to the light reception signal detected by the detection circuit. In the radar, the control circuit recognizes a waveform of the light receiving signal, and
The laser light received by the transmission and reception optical system is cloud, fog, smoke,
A laser radar , wherein when it is determined that the light is scattered light from sand, a storm, or the like, the laser light is emitted from the laser oscillator.