JPH02238391A - Measuring apparatus of depth of water - Google Patents

Abstract

PURPOSE:To facilitate detection of reflected light from the bottom of the water and to measure the depth of the water by one operation by a method wherein a strong scattered light from part of the water near the water surface is suppressed by an optical attenuator of which the amount of attenuation varies with time and thereby the level of the scattered light is fixed at all times. CONSTITUTION:A spread angle of a data light emitted from a pulse light generating source 1 is adjusted by a light-transmission optical system 2. The light 10 going out of the light-transmission optical system 2 is reflected partly on the water surface 11 and then enters the water 12 and strikes on the bottom 13 of the water while it is attenuated by scattering and absorption in the water 12. Part 14 of the light reflected diffusedly by the bottom 13 of the water is attenuated again in the water and then returns into the air and condensed by a light-reception optical system 3. The light condensed by the light-reception optical system 3 is controlled by a wave- shaping unit 5 measured beforehand and it is attenuated by an optical attenuator 4 of which the amount of attenuation varies with time and enters a photodetector 6. An output signal from the photodetector 6 is recorded by a waveform analyzing device 7. The signal recorded by the waveform analyzing device 7 is analyzed by a computer 8 and the depth of the water is calculated therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a water depth measuring device, and more particularly to a water depth measuring device that uses light to measure water depth over a wide range in a short period of time. [Conventional technology] Conventionally, the main method of measuring water depth has been using ultrasonic waves, but the possibility of measuring using light such as lasers has begun to be discussed, and experiments are also being conducted in other countries. In general, ft magnetic waves are severely attenuated underwater, and there is no prospect of practical use other than using blue-green light. Even this blue-green light is severely attenuated, so the scattered light in shallow water is much stronger than the light reflected at the bottom, and if the light is received as is, the reflected light from the bottom is too weak to be detected. Therefore, in conventional water depth measuring devices of this type, the photodetector is gated and set to become sensitive just before the reflected light from the water bottom returns, and the We use the time difference to distinguish between weak reflected light from the water bottom and change the sensitivity characteristics. [Issues to be solved] Conventional water depth measurement devices that use light eliminate the effects of strong scattered light underwater by gating the photodetector as described above, and eliminate the effects of weak light reflected from the bottom of the water. Although it has the advantage of being able to detect signals, if the depth of the water is unknown, it is necessary to gradually change the timing of gate application to avoid strong scattered light and find weak reflected light. The advantage of being able to take measurements in a short time compared to other methods was not fully utilized. The present invention was developed in view of the above-mentioned problems, and the purpose is to provide a water depth measuring device that can measure water depth without repeating measurement operations even when the water depth is unknown. [Means for solving the problems] In order to achieve the above object, the present invention provides a pulsed light generation source,
A light transmitting optical system that adjusts the spread angle of the light emitted from the pulsed light generation source and sends it into the water, a light receiving optical system that collects reflected light from the bottom of the water, and transmission of the light extracted from the light receiving optical system. an optical attenuator that changes the amount of light over time; a waveform shaper that supplies the optical attenuator with a control waveform signal having a Mamatsu characteristic determined based on a prior measurement result; and a light that detects the light that has passed through the optical attenuator. It consists of a detector, a waveform analyzer that records and analyzes the output signal from the photodetector, and processing means that controls these devices and performs data processing. [Example] An example of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. The light transmitting system is composed of a pulsed light generating source 1 and a light transmitting optical system 2, and the light receiving system is composed of a light receiving optical system 3, an optical attenuator 4, a waveform shaper 5, and a photodetector 6. A waveform analyzer 7 and a computer 8 as data processing means are connected to the photodetector 6, and a waveform shaper 5 is connected to the computer 8 to form a feedback system.

The data light emitted from the pulsed light source 1 is sent to the light transmission optical system 2.
The spread angle is adjusted by Light 10 emitted from the light transmitting optical system 2 enters the water 12 after being partially reflected by the water surface 11, and is attenuated by scattering and absorption in the water 12, until it reaches the water bottom 1.
It corresponds to 3. Part of the light diffusely reflected by the wooden bottom 13 l4
The light returns to the atmosphere after being attenuated again in the water, and the light receiving optical system 3
The light is focused by

The light collected by the light receiving optical system 3 is controlled by a waveform shaper 5 whose data is set based on water attenuation data measured in advance, and is attenuated by an optical attenuator 4 whose attenuation amount changes over time. and enters the photodetector 6. The output signal from the photodetector 6 is recorded by a waveform analyzer 7. The signal recorded by the waveform analysis head 7 is then analyzed by the computer 8 to calculate the water depth. Next, the operation of this embodiment will be explained focusing on the operations of the optical attenuator 4 and the waveform shaper 5. The intensity A of light propagating through water 12 with an attenuation coefficient Kw (m river) after propagating a distance L (m) is A=Ao *e
x p (1Kw*L) (where AO is the intensity of the original light.) Therefore, underwater 12 with a large attenuation coefficient
When it passes through, it attenuates rapidly. Therefore, the reflected light 14 from the water bottom 13 becomes extremely weak. On the other hand, the scattering coefficient of the underwater 12 is sufficiently small compared to the reflectance of the wooden sole 13, but some light is scattered even at a distance closer to the water surface 11, that is, where the light is strong. The intensity of the scattered light becomes stronger than the intensity of the reflected light at the water bottom 13. Furthermore, if attenuation on the return trip is taken into consideration, there may be several orders of magnitude difference in intensity between the scattered light near the tree surface 11 and the reflected light 14 from the water bottom 13. Figure 2 shows an example. Figure 2 is a graph showing the received light intensity versus time corresponding to the propagation distance of light. The vertical axis shows the intensity of light received by the detector, and the horizontal axis shows the distance corresponding to the light propagation distance. A curve 21 in the graph is an example when the attenuation coefficient is small, and a protruding portion 22 is the reflected light 14 from the water bottom 13. In reality, there is no scattered light after the light reaches the water bottom 13, but the dashed line 23 assumes scattered light when the water is deeper. Curve 24 is an example of a case where the damping coefficient is large. The received light intensity decreases rapidly for a short period of time, that is, at shallow water depths. In actual measurements, there is a limit to the dynamic range of the photodetector 6, etc., so strong scattered light near the water surface 12 should be dealt with only by processing the output signal without taking any measures to the photodetector 6, etc. Since this is difficult, countermeasures are generally taken such as placing an optical shutter or the like in front of the photodetector 6 to cut out the strong scattered light, or placing a gate on the photodetector 6. Here, it is possible to obtain a gate ratio of 104 or higher, but the timing of the gate must be selected so that the intensity of the scattered light after the gate is turned on is weaker than the reflected light from the bottom of the water. , if the water depth is unknown, use straight line 2
There are problems such as the need to detect the reflected light l4 from the water bottom while measuring by changing the gate timing time little by little as shown in 5. Before the game is turned on, that is, on the left side of the straight line 25, even if the scattered light intensity is strong, the photodetector 6 has no sensitivity, so it does not affect the measurement. Therefore, the scattered light that changes exponentially with time corresponding to the propagation distance of the light as shown in Figure 2 is passed through an optical attenuator with opposite transmission characteristics as shown in Figure 3. By doing this, the intensity of the scattered light entering the photodetector 6 is kept almost constant regardless of the time, as shown in FIG.
This makes it possible to detect reflected light 14 from the The vertical axis in FIG. 3 is the transmittance of the optical attenuator 4, and the vertical axis in FIG. 4 is the received light intensity of the photodetector 6, as in FIG. 2. As can be seen from FIG. 4, the part 27 that shows the intensity of reflected light from the water bottom 13 is the part 26 that always shows the intensity of scattered light no matter what the water depth is.
It is stronger and there is no need to change the gate timing. As shown in Fig. 2, the received light intensity varies greatly depending on the difference in attenuation coefficient, so the waveform shaper 5 adjusts the optical attenuator 4 in order to compensate for this change and obtain a substantially constant received light intensity for Makima. It emits a signal that optimizes transmittance. Regarding the waveform shaper 5 and the optical attenuator 4, in order to compensate for the saturation characteristics of the laser amplifier, a personal computer is used to control the waveform shaper 5 and the optical attenuator 4.
O4: PotaSSium Dihydrogen
Since devices using electro-optical elements such as Phosphate) have already been put into practical use, this device can be easily constructed by using them. Since the number C of the waveform shaper 5 can be set freely, it is possible to measure the intensity of scattered light in the measurement water area in advance and give it a characteristic of canceling the scattered light. Although the use of the optical attenuator 4 essentially eliminates the need for the gate of the photodetector 6, the dynamic range of the optical attenuator 4 is limited, so it is desirable to use it in combination to measure deeper water depths. ．． However, unless the water depth changes significantly, the intensity of the scattered light will not exceed the intensity of the reflected light 14 from the water bottom l3, so there is usually no need to change the timing of the gate. [Effects of the Invention] As explained above, the present invention uses an optical attenuator whose attenuation changes over time, which is controlled by a waveform shaper whose data is set based on tree attenuation data measured in advance. By suppressing strong scattered light from places close to the water and keeping the level of scattered light constant, it is easy to detect reflected light from the bottom of the water, making it possible to measure water depth with just one operation even when the water depth is unknown. This has the effect of making it possible to

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a graph showing the time change of the intensity of light entering a photodetector in the case of underwater depth measurement corresponding to the propagation distance of the light, and Fig. 3 is a graph of the A graph showing the transmittance of the attenuator as it changes over time. Figure 4 is a graph showing the time change in the intensity of light entering the photodetector after passing through the optical attenuator. 1: Pulse light source 2: Light transmitting optical system 3: Light receiving optical system 4: Optical attenuator 5: Waveform shaper 6: Photodetector 7: Waveform analysis device 8 = Computer 1O: Light for measurement 1l: Water surface 12 Diwater 13: Water bottom 14: Reflected light from the water bottom 21: Curve showing the received light intensity of scattered light when the attenuation coefficient is small 22: Curve showing the received light intensity of reflected light from the water bottom 23: When the water depth is deeper Curve 24 showing the received intensity of scattered light: Curve 25 showing the received intensity of scattered light when the attenuation coefficient is large: Gate timing time 26: Curve 27 showing the received intensity of scattered light after passing through the optical attenuator: Curve representing the received intensity of light emitted from the bottom of the water after passing through an optical attenuator Patent attorney Ki Watanabe Hiraigi Kabutsu

Claims (1)

[Claims] A pulsed light generation source, a light transmission optical system that adjusts the spread angle of the light emitted from the pulsed light generation source and sends it into the water, a light reception optical system that collects reflected light from the bottom of the water, and from the light reception optical system. an optical attenuator that changes the transmitted amount of the extracted light over time; a waveform shaper that supplies the optical attenuator with a control waveform signal having time characteristics determined based on a prior measurement result; A water depth measurement device comprising a photodetector for detection, a waveform analysis device for recording and analyzing output signals from the photodetector, and processing means for controlling these devices and processing data.