JP3156690B2 - Laser radar device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environment measuring laser radar device used for observing the atmosphere, seawater, and the like.

[0002]

2. Description of the Related Art In an environment measuring laser radar device generally used for observing the atmosphere, seawater, or the like, the signal level with respect to the distance rapidly attenuates when the distance is equal to or more than the minus square of the distance.
Since the range of the level of the received signal to be measured covers at least 5 to 6 digits or more, a very wide dynamic range is required for the photodetection system. However, a normal photodetector system cannot cover such a wide dynamic range by itself.

[0003] In order to make up for this drawback, several systems have conventionally been considered. As an example, there is a method as shown in FIGS. FIGS. 7 and 8 show a conventional general Mie scattering measurement laser radar apparatus. The main components are, as shown in FIG. 7, a transmission optical unit 11 including a laser generation unit 100, a reception optical unit 12 for receiving scattered light, a light detection unit 13 for detecting received light, a transmission optical unit 11, and A control / signal processing unit 14 that controls the light detection unit 13. In detail, as shown in FIG.
1 includes a laser generation unit 100, mirrors 210 to 214, and an expander 220.
Telescope 300, field stop 310, collimating lens 32
0, a mirror 330, and the light detection unit 13 includes a short-distance measurement light detector 401 and a long-distance measurement light detector 40.
2. The control / signal processing unit 14 is constituted by a partial transmission mirror 410, and includes a computer unit 500, an AD conversion unit 51
0, a timing pulse generator 520.

[0004] In this laser radar device, the laser output from the laser generator is mirror 210-214,
The scattered light transmitted to the sky via the expander 220 and scattered by the atmosphere is received by the receiving optical unit and input to the light detecting unit. The partially transmitting mirror 410 has a high transmittance (for example, 95%) and a low reflectance (for example, 5%) with respect to the wavelength of the laser light. The received light transmitted through the partially transmitting mirror 410 is incident on the photodetector 402 for long distance measurement.
Here, since the level of the signal light is high, measurement can be performed up to a long distance. However, at a short distance, the photodetector 402 is saturated and accurate measurement cannot be performed. Therefore, the short distance measurement is performed by the short distance measurement light detector 401. Here, since the level of the signal light is low, long distance measurement cannot be performed. However, since the short distance level is relatively low, saturation does not occur, and accurate measurement can be performed.

[0005]

However, this method has the following problems. First, the configuration of the photodetector 13 is complicated because two photodetectors are required. This point is particularly important not only in the measurement system of one wavelength shown in FIG. 8, but also in an apparatus capable of measuring multiple wavelengths or an apparatus which simultaneously measures two polarized lights. The second problem is that
The point is that the linearity of the photodetector 402 for long distance measurement may be reduced. That is, in this method, since a very strong signal is input to the long-distance measurement photodetector 402 at a short distance, not only the output at a short distance is saturated but also the amplifier used for the photodetector 402. In some cases, a signal at a long distance with a low signal level may be distorted.

As another method for increasing the dynamic range, there is a conventional method as follows. This is a method in which a photomultiplier tube with a gate is used as a photodetector. In the case of long-distance measurement, the applied voltage of the photomultiplier is temporally controlled in order to attenuate a strong signal at a short distance, and a short distance (that is, a fixed time from the start of AD conversion).
For example, a portion of 5 μs) is not amplified, and a voltage gate is applied so as to amplify only a long-distance portion. In the case of short distance measurement, adjust the gate timing etc. so that amplification is performed in the entire range of measurement,
An optical attenuator or the like is inserted before the photodetector to adjust the output of the photodetector so as not to be saturated. This method has a problem that the gate control function is required for the photodetector and the control system, and the configuration becomes complicated. When an avalanche photodiode generally used as a photodetector is used, a gate function cannot be added, so that this method cannot be applied.

In view of the above circumstances, an object of the present invention is to provide a laser radar device which has a large dynamic range, is small in size, and realizes low cost.

[0008]

A laser radar device according to claim 1, further comprising a transmission optical unit having a laser generating unit for emitting a laser beam to a measuring object, wherein the laser scattered by the measuring object is scattered. in the laser radar apparatus for receiving light, said transmitting optical unit is configured to fire the different laser beams intensity Rutotomoni, wherein
One laser output from the laser generator is
And control the intensity of the laser beam
An optical path branching section is provided .

In this laser radar device, since the intensities of the plurality of laser beams are different, for example, two types of laser beams are emitted, and a laser beam of low intensity is used for a short-distance measurement system, and a laser beam of high intensity is used. It can be used for long distance measurement systems. Since the laser beam for the short distance measurement system has a small beam intensity and the light detector is not saturated by the scattered light due to the atmosphere due to the short distance, the light detector can be shared with the long distance measurement system.

The transmission optical unit is provided with an optical path branching unit that branches one laser output by the laser generation unit into a plurality of laser beams and controls the intensity of the laser beams. It is characterized by being.

In this laser radar device, since the optical path branching unit splits one laser into a plurality of laser beams, it is not necessary to provide two laser generating units to emit a plurality of laser beams. The plurality of laser beams whose intensity is controlled by the optical path branching unit are used for a short-distance measurement system, a long-distance measurement system, and the like as described above. Here, the optical path branching unit may divide one laser into a plurality of lasers at the same time, or may selectively switch one laser to a plurality of laser beams. Note that controlling the intensity means that a plurality of laser beams are each set to a predetermined intensity.

Further, the plurality of lasers emitted to the object to be measured are
The laser beam is characterized in that each optical axis is separated .

In this laser radar device, for example, if the optical axis of the telescope for receiving scattered light and the optical axis of the laser beam for the short-distance measurement system are arranged substantially the same, the scattered light due to the short-range atmosphere will be reduced. It can be placed in the viewing angle of the telescope, and can measure near-field atmosphere. Further, when the optical axis of the laser beam for the long-distance measurement system is arranged far from the optical axis of the telescope, the scattered light due to the short-range atmosphere having high intensity can be excluded from the viewing angle of the telescope, and the medium- and long-range atmosphere Can be measured.

[0014] The optical path branching unit may be configured to emit a laser beam.
The optical path branching section is configured to be selectively launched.
Control the emission of the plurality of laser beams by time
Switch, and in synchronization with this switch, the received scattering
It has a control / signal processing unit that processes light data separately.
You.

In this laser radar device, the optical path branching portion can branch the laser into a plurality of laser beams, but is configured such that some of the beams are selectively emitted. You. The switching is controlled by the control / signal processing unit based on time, so that different measurement distances are measured while being distinguished by time. For example, when measuring a short distance, the control / signal processing unit controls the optical path branching unit to emit a short-distance measurement system laser beam, and processes the input scattered light data as a short-distance data. When measuring a long distance, the optical path branching unit is controlled to emit a long-distance measurement system laser beam, and the input scattered light data is processed as a long-distance data.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a laser radar device according to the present embodiment.
The main components are a laser generator 100, a laser generator 1
00, a receiving optical unit 12 for receiving scattered light, a light detecting unit 13 for detecting received light, a control / signal processing unit 1 for controlling the transmitting optical unit 11 and the light detecting unit 13.
4 is provided. Next, a more detailed description will be given with reference to FIG. The thing shown in FIG. 2 is a time chart of a Mie scattering laser radar device for performing Mie scattering measurement of the atmosphere. In this laser radar device, the transmission optical unit 1
Reference numeral 1 denotes a laser generator 100, mirrors 210-214, an expander 220, a partially transmitting mirror 230, and a shutter A
The receiving optical unit 12 includes a telescope 300, a field stop 310, a collimating lens 320, and a mirror 330.
3 includes a photodetector 400, and the control / signal processing unit 14 includes a computer unit 500, an AD conversion unit 510,
Timing pulse generator 520, shutter controller 530
It consists of. In the transmission optical unit 11,
Partially transmitting mirror 230, shutter A240, shutter B
241 constitutes the optical path branching unit 15.

The laser generator 100 uses a pulse YAG laser having a wavelength of 532 nm. Main specifications are laser output 200mJ, repetition cycle 10Hz, pulse width 7
ns. The laser generator 100 can control ON / OFF of laser emission by computer control. The transmission optical unit 11 includes a plurality of folding mirrors 210-214,
Expander 220 for expanding the laser beam diameter, partially transmitting mirror 230, shutter A240, shutter B241
Consists of The spread angle of the laser beam emitted from the expander 220 is about 0.5 mrad.

Here, the characteristic configuration of this embodiment is a partially transmitting mirror 230, two shutters A240 and a shutter B241. Partially transparent mirror 230
Is about 1 of energy for 532 nm laser light.
Transmits 0%, reflects about 90%, and transmits 2
The beam is separated into two beams, that is, a short distance measurement system transmission beam and a long distance measurement system transmission beam. Here, the two transmission beams are both launched toward the sky. The optical axis of the short-range measurement system transmission beam is substantially coaxial with the optical axis of the telescope 300. The optical axis of the transmission beam of the telemetry system is telescope 300
Are parallel to the optical axis of a certain distance from each other (here, about 60 cm)
is seperated. The shutter A240 is installed on the optical path of the short range measurement system transmission beam, and transmits or blocks the transmission beam. The shutter B 241 is provided on the optical path of the transmission beam for the long distance measurement system, and transmits or blocks the transmission beam. The opening and closing of the shutter A240 and the shutter B241 can be controlled by computer control.

The receiving optical section 12 includes a telescope 300, a field stop 310, a collimating lens 320, and a mirror 330. The telescope 300 is a Cassegrain type having an effective diameter of 40 cm and a focal length of 150 cm, and collects atmospheric scattered light. The collimating lens 320 is a lens for converting the signal light into substantially parallel light and guiding the signal light to the light detection unit 13. The reception viewing angle must always be set slightly larger than the transmission laser beam divergence angle. In this case, the reception viewing angle is adjusted to about 1 mrad using the field stop 310. The light detection unit 13 includes a light detector 400 using a photomultiplier tube. The signal light (atmospheric scattered light) is converted into an electric signal by the photodetector 400.

The control / signal processing unit 14 is a unit for performing control and signal processing of the entire embodiment. Computer section 500, AD conversion section 510, timing pulse generation section 5
20 and a shutter control unit 530. In response to a command from the computer unit 500, the laser emission of the laser generation unit 100 is performed by the shutter A2 through the shutter control unit 530.
The opening and closing of the shutter 40 and the shutter B 241 are controlled. The signal output from the photodetector 400 is converted into a digital signal by the AD converter 510, and the digital signal is subjected to data processing, display, storage, and the like in the computer unit 500. Timing pulse generator 52
The laser pulse emission timing for each shot and the AD conversion start timing in the AD converter 510 are controlled by a repetitive 10 Hz trigger pulse generated from 0.

Next, the operation of the laser radar device will be described with reference to FIGS. First, the measurement sequence will be described. Laser emission repeats ON and OFF as shown in the time chart of FIG. While laser emission is ON, laser pulses are emitted continuously at a repetition cycle of 10 Hz. The ON / OFF time is set according to the content of the measurement. Typical values are about 3 minutes for ON and about 7 minutes for OFF. After turning on the laser emission, after a certain warm-up time (about 30 seconds), the shutter A240 is opened, and the laser light is emitted from the short distance measurement system. Immediately after that, the AD conversion of the short distance measurement starts. That is, the analog signal output from the photodetector 400 is converted into a digital signal by the AD converter 510. A
The D conversion time (or the number of times of averaging) is set by the computer unit 500. This value is set according to the content of the measurement.
A short time of about a second (100 times at 10 Hz) is sufficient.

After the measurement of the short distance is completed, the shutter A 240 is closed and the shutter B 241 is simultaneously opened. Immediately thereafter, the AD conversion of the long distance measurement starts. That is, the analog signal output from the same photodetector 400 as in the short distance measurement is converted into a digital signal. The AD conversion time (or the number of times of averaging) at the time of long-distance measurement is set depending on the content of the measurement, but is usually 100 seconds (1 at 10 Hz).
000 times). After the end of the long distance measurement, the shutter B 241 is also closed, and then the laser emission is turned off. In both the short distance measurement and the long distance measurement, since the average value is finally processed, the time lag of about 100 seconds between the two measurements can be practically ignored. Usually, the above sequence is repeated, for example, every 10 minutes. The sequence is controlled by the computer unit 500.

FIG. 4 is a schematic diagram of a signal waveform. The feature of the short distance measurement system is a fairly short distance (point A, for example, 100 m).
This is the point that the signal from is obtained. This is because the optical axis of the short-distance measurement system transmission beam is arranged close to the optical axis of the telescope 300, and thus the atmospheric scattered light from a short distance is transmitted to the telescope 30.
This is because it is within the viewing angle of 0. Further, since the intensity of the transmission beam is set small, the signal level does not saturate at a short distance. However, since the signal level is low as a whole, a certain distance (point C, for example, 5 km)
You can only get a signal up to On the other hand, the features of the long distance measurement system are as follows: from a medium distance (point B, for example, 3 km) to a long distance (point D,
For example, a signal up to 20 km) can be obtained. Since the optical axis of the telemetry transmission beam is located away from the optical axis of the telescope 300, atmospheric scattered light from a short distance does not enter the viewing angle of the telescope 300, and the intensity of the atmospheric scattered light is reduced. The signal level is low from a strong short distance to point B. For this reason, signal distortion at a long distance due to excessive input can be avoided.

As described above, according to the laser radar apparatus according to the present embodiment, short-distance measurement and long-distance measurement can be performed with a simple photodetector configuration, so that the laser radar apparatus is simple and has a wide dynamic range for measurement. Can be configured. In particular, the present invention is more effective in a laser radar device that requires the use of a plurality of photodetectors, such as measurement of the degree of depolarization and simultaneous measurement of multiple wavelengths (not limited to three wavelengths).

The laser radar device may have the following configuration. First, in the above description, the light detection unit is configured with one photodetector 400, but another configuration may be used. For example, when measuring the polarization dependence of signal light and determining the degree of depolarization, a polarization beam splitter is inserted before the photodetector, and signal lights of different polarizations are separately separated by two photodetectors. You only need to measure it. In this case, it is natural that two channels of AD converters are necessary, but the operation and effect of this device are the same as those of the above-described embodiment, and do not depend on the configuration of the photodetector.

The same effect can be obtained with the measurement sequence described with reference to FIG. For example, the long distance measurement may be performed first, and then the short distance measurement may be performed. Generally, the long distance measurement time is longer than the short distance measurement time, but depending on the content of the measurement, both may be the same or vice versa. Also, there is a sequence in which when the long distance measurement time is considerably long, the long distance measurement time is divided into two and the short distance measurement is performed between them. Such a sequence can be easily handled by changing the software of the computer section 500.

Further, in the above-described embodiment, the expander 220 shown in FIG. 2 is used, but this may not be necessary depending on the conditions such as the laser used. Further, the arrangement and number of the mirrors for turning back as shown in FIG. 2 are not necessarily the same as those in FIG. 2 because they are determined from conditions such as the overall size in an actual apparatus. This is irrelevant to the essence of the present invention.

The laser radar device according to the present invention is not limited to the Mie scattering laser radar device, but a laser radar device other than the Mie scattering laser radar device, that is, a differential absorption laser radar device or a Raman scattering laser radar device. It can also be used for most environmental measurement laser radar devices. It is also effective not only in analog measurement but also in photon counting measurement.

Next, a second embodiment of the present invention will be described.
This will be described with reference to FIG. The main configuration of this embodiment is the same as that shown in FIG. In the first embodiment, as the optical path branching unit 15, the transmission optical unit 11 is provided with the partially transmitting mirror 230 and the two shutters 240 and 241 inserted in the respective optical paths, but in the present embodiment, Instead, a low-reflection mirror 250 with a beam damper having a drive mechanism (reflectance 10%) and the mirror control unit 54
Set 0. Other configurations are almost the same as those of the first embodiment. When guiding the transmission beam to the short distance observation system, the low reflection mirror 250 is driven and inserted into the optical path. When guiding the transmission beam to the long-distance observation system, remove it from the optical path. The insertion and removal of the low-reflection mirror 250 is performed by a command from the computer unit 500, and the same effects as in the first embodiment can be obtained. In the case of short-distance measurement, since it is necessary to absorb a strong laser beam at the portion of the low-reflection mirror 250 with a beam damper, the low-reflection mirror 250 with a beam damper is
A beam damper for absorbing the transmitted laser light is provided.

Next, a third embodiment of the present invention will be described.
This will be described with reference to FIG. The main configuration of this embodiment is the same as that shown in FIG. FIG. 6 shows a transmission optical unit in a laser radar device capable of simultaneously measuring three wavelengths. In the present embodiment, a multi-wavelength partially transmitting mirror 231, a shutter A240, and a shutter B241 are provided as the optical path branching unit 15. The laser generator 100 simultaneously emits three wavelengths of the pulse YAG laser (a fundamental wave, a second harmonic, and a third harmonic). The transmission optical unit 11 converts the laser light into a dichroic mirror 260-2.
63, the light is once separated into each wavelength, and the beam diameter is expanded by the expanders 221 to 223 for each wavelength, and then the light is combined again. The transmission optical unit 11 is the same as the first embodiment except that the expander portion and the partial transmission mirror 231 correspond to multiple wavelengths corresponding to multiple wavelengths, and the same sequence as the first embodiment. The same effect can be obtained by operating with. In this case, although not shown in the figure, a dichroic mirror for wavelength separation and three light detectors corresponding to three wavelengths are required in the light detection unit, and the control / signal processing unit is required. It is needless to say that an AD converter corresponding to three channels is required.

Further, as a modification of the third embodiment, a laser radar apparatus which measures the depolarization degree of three wavelengths simultaneously may be used. In this case, a polarization beam splitter for each wavelength and a total of six photodetectors are required in the photodetection unit. The number of photodetectors is half that in the case where the conventional method shown in FIG. 8 is adopted.

[0032]

As described above, according to the present invention, short-distance measurement and long-distance measurement can be performed with a simple photodetector configuration, so that a laser radar device having a simple and wide dynamic range for measurement can be configured. In particular, the present invention is more effective in a laser radar device that requires the use of a plurality of photodetectors, such as measurement of the degree of depolarization and simultaneous measurement of multiple wavelengths (not limited to three wavelengths). Furthermore, the present invention can be used for most environment measuring laser radar devices such as a laser radar device other than the Mie scattering laser radar device as in the above embodiment, that is, a differential absorption laser radar device and a Raman scattering laser radar device. It is also effective not only in analog measurement but also in photon counting measurement.

[Brief description of the drawings]

FIG. 1 is a block diagram of a laser radar device shown as a first embodiment of the present invention.

FIG. 2 is a schematic diagram of the laser radar device.

FIG. 3 is a sequence diagram showing an operation of the laser radar device.

FIG. 4 is a schematic diagram showing a signal waveform of scattered light received by the laser radar device.

FIG. 5 is a schematic diagram of a laser radar device shown as a second embodiment of the present invention.

FIG. 6 is a schematic diagram of a laser radar device shown as a third embodiment of the present invention.

FIG. 7 is a block diagram of a conventional laser radar device.

FIG. 8 is a schematic diagram showing the laser radar device.

[Explanation of symbols]

 11 transmission optical unit 15 optical path branching unit 100 laser generation unit

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

Claims (3)

(57) [Claims] 1. A laser radar device comprising a laser generating unit for emitting a laser beam to a measurement target and receiving a scattered light of the laser scattered by the measurement target, wherein the transmission optical unit is is configured to fire the different laser beams intensity Rutotomoni, the laser generating unit
Splits one laser output into multiple laser beams
Optical path branching for controlling the intensity of the laser beam
The laser radar apparatus characterized by parts is provided. 2. The laser radar device according to claim 1, wherein
The plurality of laser beams emitted to the object to be measured are each
A laser radar device , wherein the optical axes are separated . 3. The laser radar device according to claim 1, wherein
The optical path branching unit selectively emits a laser beam.
And controlling the optical path branching unit to emit the plurality of laser beams.
The shots are switched according to time and synchronized with this switch.
Control to distinguish and process the received scattered light data
A laser radar device having a signal processing unit ;