JPH083530B2 - Water depth measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water depth measuring device, and more particularly to a water depth measuring device adapted to measure a wide range of water depth in a short time using light.

[Prior Art] Conventionally, the measurement of water depth has mainly been performed using ultrasonic waves, but the possibility of measurement using light such as laser has begun to be discussed, and experiments are being conducted in other countries.

Generally violently electromagnetic wave attenuation in water than those using blue-green light has not passed since prospect of practical use. Even this blue-green light is heavily attenuated, so the scattered light in shallow water is much stronger than the light reflected at the bottom of the water, and if received as it is, the reflected light from the bottom of the water is too weak to be detected. Therefore, in this type of conventional water depth measuring device, the photodetector is set so that the gate has a gate and the photodetector has sensitivity immediately before the reflected light from the bottom returns, and strong scattered light from the water The weak reflected light from the bottom of the water is distinguished by changing the sensitivity characteristic by utilizing the time difference.

[Problems to be solved] A conventional water depth measuring device uses a light detector as described above to eliminate the influence of strong scattered light in water and eliminates the weakness of reflected light from the bottom of the water. Although it has the advantage of being able to detect signals, if the water depth is unknown, it is necessary to avoid strong scattered light by gradually changing the timing of applying the gate and to find weak reflected light. In comparison, the advantage of being able to measure in a short time has not been fully utilized.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a water depth measuring device capable of measuring the water depth without repeating the measurement operation 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 transmission optical system for adjusting the divergence angle of light emitted from the pulsed light generation source and transmitting the light into water, and a light transmission system from the bottom of the water. A light receiving optical system for collecting reflected light, an optical attenuator that changes the amount of light transmitted from the light receiving optical system with time, based on water attenuation data obtained by previously receiving scattered light from water A waveform shaping device that supplies a control waveform signal having the time characteristic determined by the above to the optical attenuator, a photodetector that detects light transmitted through the optical attenuator, and an output signal from the photodetector is recorded and analyzed. And a computer for controlling the waveform shaper by calculating so that the product of the attenuation by water and the attenuation by the optical attenuator becomes constant.

[Embodiment] An embodiment 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 transmission system is composed of a pulsed light generation source 1 and a light transmission optical system 2,
The light receiving system includes a light receiving optical system 3, an optical attenuator 4, a waveform shaper 5,
It is composed of a photodetector 6. A waveform analyzer 7 and a computer 8 as a data processing means are connected to the photodetector 6, and the waveform shaper 5 is connected to the computer 8 to form a feedback system.

The divergence angle of the laser light emitted from the pulsed light generation source 1 is adjusted by the light transmission optical system 2. A part of the light 10 emitted from the light transmitting optical system 2 is reflected by the water surface 11 and then enters the water 12. The light 10 impinges on the water bottom 13 while being attenuated by scattering and absorption in the water 12. A part 14 of the light diffusely reflected by the water bottom 13 is attenuated again in water and then returned to the atmosphere to be condensed by the light receiving optical system 3.

The light condensed by the light receiving optical system 3 is controlled by the waveform shaper 5 in which data is set based on the attenuation data of water measured by previously receiving scattered light from water, and the amount of attenuation changes with time. It is attenuated by the changing optical attenuator 4 and enters the photodetector 6. The output signal from the photodetector 6 is recorded by the waveform analyzer 7.

Then, the signal recorded by the waveform analysis device 7 is calculated by the computer 8
And calculate the water depth.

Next, the operation of this embodiment will be described focusing on the operations of the optical attenuator 4 and the waveform shaper 5.

The light propagating through the water 12 with the attenuation coefficient Kw (m ^-1 ) is at the distance L
(M) The light intensity A after propagating is A = A ₀ * exp (−Kw * L) (where A ₀ is the original light intensity). When it passes through a large underwater 12, it decays 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 water bottom 13, but there is light scattered at a distance closer to the water surface 11, that is, even where the light is strong. The intensity of the light becomes stronger than the intensity of the reflected light at the bottom 13. Further considering the attenuation on the return path, the scattered light near the water surface 11 and the reflected light 14 from the water bottom 13
There may be several orders of magnitude difference. FIG. 2 shows an example thereof. FIG. 2 is a graph showing the received light intensity with respect to time corresponding to the light propagation distance. The vertical axis represents the received light intensity of the detector, and the horizontal axis represents the time corresponding to the light propagation distance. The curve 21 in the graph is an example in the case where the attenuation coefficient is small, and the protruding portion 22 is the reflected light 14 from the water bottom 13. Actually bottom
There is no scattered light after the light reaches 13, but it is shown by the broken line 23 assuming the scattered light when the water depth is deeper. curve
24 is an example when the damping coefficient is large. The received light intensity sharply decreases in a short time, that is, in a shallow water depth.

Since the dynamic range of the photodetector 6 etc. is limited in actual measurement, it is not possible to deal with the strong scattered light near the water surface 11 only by processing the output signal without taking any measures for the photodetector 6 etc. Since it is difficult, the photodetector 6 is generally used.
In order to prevent the strong scattered light from being placed in front of the optical shutter, or to take a gate on the photodetector 6, measures are taken.

Here, it is possible to obtain a gate ratio of 10 ⁴ or more, but it is necessary to select the timing of the gate and measure so that the intensity of scattered light after the gate is ON is weaker than the reflected light from the bottom of the water. If the water depth is unknown, there is a problem that the reflected light 14 from the water bottom must be detected while measuring the gate timing time as shown by the straight line 25 little by little. Before the gate is turned on, that is, on the left side of the straight line 25, there is no sensitivity of the photodetector 6 even if the scattered light intensity is strong, so the measurement is not affected. Therefore, as shown in FIG. 2, the scattered light that changes exponentially with time corresponding to the propagation distance of the light as shown in FIG. 2 is passed through an optical attenuator having a transmission characteristic opposite to this. Thus, as shown in FIG. 4, the intensity of scattered light entering the photodetector 6 is made substantially constant regardless of time, and the reflected light 14 from the water bottom 13 can be detected regardless of the water depth.

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. As can be seen from FIG. 4, a portion 27 showing the intensity of reflected light from the bottom 13 of the water.
Is the part that always shows the scattered light intensity regardless of the water depth
It's stronger than 26, and you don't need to change the gate timing.

As shown in FIG. 2, the received light intensity changes greatly depending on the difference in the attenuation coefficient, so this change is compensated and the waveform shaper 5 transmits the light through the optical attenuator 4 so as to obtain a substantially constant received light intensity with respect to time. It gives a signal to optimize the rate. The waveform shaper 5 and the optical attenuator 4 are controlled by a personal computer in order to compensate the saturation characteristics of the laser amplifier, and potassium phosphate [KDP (KH ₂ PO ₄ : Potassiu
m Dihydrogen Phosphate)] and other devices using electro-optical elements have already been put to practical use, and this device can be used to easily configure this device. Since the signal of the waveform shaper 5 can be freely set, it is possible to measure the intensity of scattered light in the measurement water area in advance and have a characteristic of canceling the scattered light.

The use of the optical attenuator 4 virtually eliminates the need for the gate of the photodetector 6, but the dynamic range of the optical attenuator 4 is limited, so that it is desirable to use it together for deeper water depth measurement. . However, unless the water depth changes significantly, the intensity of scattered light does not exceed the intensity of reflected light 14 from the water bottom 13, so the timing of the gate usually does not need to be changed.

[Effects of the Invention] As described above, the present invention uses an optical attenuator that is controlled by a waveform shaper in which data is set based on attenuation data of water measured in advance and whose attenuation amount changes with time.
By suppressing the strong scattered light from near the water surface and keeping the scattered light level constant, it is easy to detect the reflected light from the bottom of the water, and even if the water depth is unknown, the water depth can be measured with a single operation. The effect is that you will be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a graph showing the time variation of the intensity of light entering a photodetector in the case of water depth measurement, and FIG. FIG. 4 is a graph showing the transmittance of the attenuator which changes with time, and FIG. 4 is a graph showing the time change of the intensity of the light entering the photodetector after passing through the optical attenuator. 1: Pulsed light source, 2: Light-transmitting optical system 3: Light-receiving optical system, 4: Optical attenuator 5: Waveform shaper, 6: Photodetector 7: Waveform analyzer, 8: Calculator 10: Light for measurement , 11: Water surface 12: Underwater, 13: Water bottom 14: Reflected light from the water bottom 21: Curve indicating the received light intensity of scattered light when the attenuation coefficient is small 22: Curve indicating the received light intensity of the reflected light from the water bottom 23: Water depth Curve 24 showing the received light intensity of scattered light when the depth is deeper: Curve 25 showing the received light intensity of scattered light when the attenuation coefficient is large 25: Gate timing time 26: Received light intensity of scattered light after passing through the optical attenuator Curve 27: Curve showing the received light intensity of the reflected light from the water bottom after passing through the optical attenuator

Claims (1)

[Claims] 1. A pulsed light generation source, a light transmission optical system that adjusts a spread angle of light emitted from the pulsed light generation source and sends the light into water, and a light reception optical system for collecting reflected light from the bottom of the water. An optical attenuator that changes the amount of light transmitted from the light receiving optical system with time, a control waveform signal having a time characteristic determined based on water attenuation data previously obtained by receiving scattered light from water, A waveform shaper to be supplied to the optical attenuator, a photodetector for detecting light transmitted through the optical attenuator, a waveform analyzer for recording and analyzing an output signal from the photodetector, attenuation by water and an optical attenuator A water depth measuring device comprising: a computer that controls the waveform shaper by performing a calculation so that the product of attenuation due to is constant.