JPH04297888A - Underwater laser radar - Google Patents

Abstract

PURPOSE:To obtain a novel measuring apparatus which can measure the temperature of seawater in addition to detection of the depth of the sea, the state of the seabed, fish schools, etc. CONSTITUTION:A light-transmitting unit 10 transmitting a pulse-shaped laser light of a prescribed wavelength into the sea, a first light-receiving unit 20 receiving a reflected light of this transmitted laser light from the sea, and a second light-receiving unit 30 receiving a Raman scattered light of the transmitted laser light from the sea and outputting a difference in a light reception level in respect to a plurality of different wavelengths set in the vicinity of a transmitted wave length, are provided. A distance calculating unit 40 calculating a distance to a target or the like based on a required time from transmission of the laser light by the light-transmitting unit to reception of the reflected light, and a temperature calculating unit 40 calculating the temperature of the sea from the difference in the light reception level outputted from the second light-receiving unit, are provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater laser radar which can be widely used for ocean research such as ocean depth, seabed condition, fish school detection, and seawater temperature observation.

0002

2. Description of the Related Art Conventionally, ultrasonic radar devices have been used to detect the depth of the ocean, the state of the seabed, and schools of fish.

0003

SUMMARY OF THE INVENTION The conventional ultrasonic radar described above is generally satisfactory in various respects such as measurement accuracy, ease of handling, reliability, time required for measurement, and cost. However, with this ultrasonic radar, it is not possible to observe seawater temperature, which is often necessary, at the same time as observing the depth of the ocean, the appearance of the seafloor, and the density of fish shadows, as in the case of observing the ecology of schools of fish. First, there is a problem in that a separate temperature observation work is required, such as by installing a temperature sensor.

[0004] If a temperature sensor such as a thermistor is used to measure the distribution of seawater temperature in the depth direction, it is necessary to hang the temperature sensor vertically downward from the ship, which requires the ship to stop. The problem is that it takes time.

[0005]

Means for Solving the Problems The underwater laser radar of the present invention has the following features: a. a light transmitting section that transmits a pulsed laser beam of a predetermined wavelength into the sea; b1. a first light receiving section that receives reflected light of the transmitted laser light from underwater; b2. a second light receiving unit that receives the Raman scattered light of the transmitted laser light from underwater and outputs received light levels for a plurality of different wavelengths set in the vicinity of the predetermined wavelength; c1. a distance calculation unit that calculates the distance to the target from which the laser beam is reflected in the sea based on the time difference between when the laser beam is transmitted by the light transmission unit and when the reflected light is received by the first light reception unit; c2. Said second
and a temperature calculation section that calculates the temperature of seawater from the difference in the light reception levels output from the light reception sections.

[0006]

[Embodiment] FIG. 1 is a block diagram showing the configuration of an underwater laser radar according to an embodiment of the present invention, in which 10 is a light transmitting section, 20 is a first light receiving section, and 30 is a second light receiving section. , 40 is a distance and temperature calculating section.

The light transmitting unit 10 includes a YAG laser 11 that generates a high-output pulsed laser beam to be transmitted into the sea, a pulse generator 12 that supplies an electric pulse signal for excitation to the YAG laser 11, and an output from the YAG laser 11. A beam splitter 13 that splits a part of the pulsed laser light that is generated, a light receiving head 14 that converts the laser light split by this beam splitter into an electrical signal, and amplifying the electrical signal output from this light receiving head. The amplifier 15 is also provided.

[0008] The first light receiving unit 20 receives from the sea a mixture of the reflected light of the laser beam sent into the sea from the light transmitting unit 10 and the Raman scattered light emitted from the seawater in the path of the laser beam. An optical filter 21 that selectively transmits only the reflected light, a light receiving head 22 that converts the reflected light that has passed through this optical filter into an electrical signal, and an amplifier 23 that amplifies the converted electrical signal. The beam splitter 24 distributes a portion of the reflected light and scattered light to the second light receiving section.

[0009] The second light receiving unit 30 receives from the sea a mixture of reflected light and Raman scattered light of the laser beam sent into the sea from the light transmitting unit 10, and detects specific first and second wavelengths. Optical filter 31 that selectively transmits only Raman scattered light
a, 31b, light receiving heads 32a, 32b that convert the scattered light transmitted through these optical filters into electrical signals, and differential amplifiers 33a, 3 that amplify the converted electrical signals.
3b, a beam splitter 34 and a reflecting mirror 35 which distribute part of the reflected light and scattered light received from the sea to the optical filters 31a and 31b.

The distance and temperature calculation unit 40 includes a sampling unit 41 that converts the analog voltage values output from the amplifiers 15, 23, 33a, and 33b into digital signals while sampling them at predetermined time intervals, and The computer 42 includes a personal computer 42 that processes the data while storing it in a built-in RAM, and a floppy disk 43 that stores the data created and edited by the personal computer 42.

The typical waveform of the laser beam emitted from the YAG laser 11 of the light transmitting section has a half width of 10 ns to 1
It has the shape of a 5 ns isolated pulse and has a wavelength of 532 nm.
The second harmonic of m is selectively radiated. The pulsed laser light transmitted through the beam splitter 13 is typically
The light enters the sea through a light transmitting lens barrel (not shown) that holds a converging lens and forms a watertight light guide path into the sea.

[0012] If there is a non-transparent target such as a school of fish in the path of the laser beam entering the sea, reflected light from such a school of fish will occur, and the light will reach the sea floor without being reflected by such a school of fish. Once it reaches the surface, light will be reflected from the ocean floor. The reflected light thus generated enters the first and second light receiving sections 20 and 30 following a path in the opposite direction to that of the incident light. In front of the first and second light receiving sections 20 and 30, there is typically a light receiving lens barrel (not shown) that holds a converging lens underwater and forms a watertight light guiding path into the sea. Placed. The lens barrel for receiving light and the lens barrel for transmitting light are typically
They are arranged adjacent to each other and substantially parallel to each other so that their respective optical axes intersect near the farthest point of the measurement range.

[0013] In addition to the above-mentioned reflected light, Raman scattered light is generated from the underwater path of the laser beam. The spectrum of this Raman scattered light (Raman spectrum) is the relative value of the wavelength expressed as the amount of deviation (cm-1) in wave number from the original laser beam sent out from the light transmitting section 10 and the level of the component of this wavelength. It is expressed in the relationship of The Raman spectrum of seawater is as shown in Figure 2, and changes depending on temperature. A part of the scattered light generated along the path of the laser beam follows a path in the opposite direction to the incident light and reaches the first and second light receiving sections 20 and 3.
0.

The reflected light and scattered light that pass through the beam splitter 24 and enter the first light receiving section 20 selectively transmit only the reflected light having a wavelength equal to the wavelength of the laser beam sent out from the light transmitting section 10. The light is guided to the light-receiving head 22 through an optical filter 21 . The light receiving head 22 is composed of an avalanche photo diode (APD), a photomultiplier tube, and the like, and converts the incident reflected light into an electrical signal with a voltage value corresponding to the level of the reflected light, and supplies the electrical signal to the sampling section 41 .

The sampling unit 41 starts operating in response to a trigger from the pulse generator 12, and
2, when the distance measurement operation mode is specified, the analog voltage value output from the amplifier 23 is converted into a digital signal while being sampled at a predetermined time interval sufficiently narrower than the half-width of the pulse. Data is supplied to the personal computer 41.

[0016] The time from when the electric signal for pumping is supplied from the pulse generator 12 to the YAG laser 11 until the laser beam is emitted varies each time the pumping is performed. Therefore, in order to determine the point of emission of the laser beam as a reference point, a part of the output of the YAG laser 11 is guided to the light receiving head 14 by the beam splitter 13, and is supplied to the sampling section 41 via the amplifier 15.

The personal computer 41 processes the digital data received from the sampling section 41 while storing it in its built-in RAM, thereby detecting the time difference between the emission of the laser beam and the appearance of the reflected light, and detecting the time difference between the emission of the laser beam and the appearance of the reflected light. The distance to the target that generated the light is converted and stored in the built-in memory or floppy disk 43.

Beam splitters 24, 34 and reflecting mirror 35
The reflected light and scattered light that have passed through the light receiving section 30 enter the optical filters 31a and 31b of the second light receiving section 30. Optical filter 31a
The transmission wavelengths of and 31b are set to different values that are shifted by a predetermined value from the wavelength of the original laser beam sent out from the light sending section 10. The setting values of these two transmission wavelengths are shown in Figure 2.
In the Raman spectrum shown in , the points where the temperature dependence of the relative level is approximately the maximum and the points where the temperature dependence is approximately the minimum are typically set at wavelengths corresponding to wave number deviations of 3200 cm-1 and 3400 cm-1. The light receiving heads 32a and 32b convert the Raman scattered light that has passed through the optical filters 31a and 31b in the previous stage into electrical signals.

The amplifiers 33a and 33b are connected to the light receiving head 32.
The electrical signals output from a and 32b are amplified and supplied to the sampling section 41. When the temperature measurement operation mode is specified by the personal computer 42, the sampling section 41 alternately samples the outputs of the amplifiers 33a and 33b, converts them into digital signals, and transfers them to the personal computer 42. The personal computer 41 calculates the seawater temperature by processing the relative value of the difference between the digital signals received from the sampling section 41 using its built-in RAM, and stores the calculated seawater temperature on the floppy disk 43. This Raman scattered light, which indicates the temperature of the seawater, is generated one after another along the path of the transmitted laser beam.
Things that occur in deeper places or farther away appear later. Therefore, the temperature distribution in the sea can be detected based on the time change of the digital data output from the sampling section 41.

The configuration in which the light transmitting section 10 and the calculating section 40 are used both for measuring the distance to a target using reflected light and for measuring the temperature of seawater using Raman scattered light has been described above. However, a dedicated light transmitting section and a calculation section are installed individually for each measurement, and a distance measurement system consisting of a light transmitting section, a light receiving section, and a calculating section for measuring distance, and a light transmitting section and a light receiving section for temperature measurement are used. It is also possible to have a configuration in which a temperature measurement system consisting of a temperature measurement section and a calculation section is installed.

[0021]

[Effects of the Invention] Since the present invention has the above-described configuration, it is often necessary to simultaneously observe the depth of the ocean, the appearance of the seabed, and the density of fish shadows, such as in the case of observing the ecology of schools of fish. It will now be possible to observe seawater temperatures while the ship is sailing, greatly improving convenience.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an underwater laser radar according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a Raman spectrum of seawater.

[Explanation of symbols]

10 Light transmitting section 11 YAG laser 12 Pulse generator 20 First light receiving section 21 Optical filter 22 Light receiving head 30 Second light receiving section 31a,b Optical filter 32a, b Light receiving head 33a,b Amplifier 40 Distance and temperature calculation section 41 Sampling section 42 PC

Claims (4)

[Claims] [Claim 1] a. a light transmitting section that transmits a pulsed laser beam of a predetermined wavelength into the sea; b1. a first light receiving section that receives reflected light of the transmitted laser light from underwater; b2. a second light receiving unit that receives the Raman scattered light of the transmitted laser light from underwater and outputs received light levels for a plurality of different wavelengths set in the vicinity of the predetermined wavelength; c1. a distance calculation unit that calculates the distance to the target from which the laser beam is reflected in the sea based on the time difference between when the laser beam is transmitted by the light transmission unit and when the reflected light is received by the first light reception unit; c2. An underwater laser radar comprising: a temperature calculation section that calculates the temperature of seawater from a difference in light reception levels output from the second light reception section. [Claim 2] a. a light transmitting unit that transmits a pulsed laser beam into the sea; b. a light receiving unit that receives reflected light of the transmitted laser light from underwater; c. The apparatus further comprises a distance calculation section that calculates the distance to the target from which the laser beam is reflected in the sea based on the time difference between when the laser beam is transmitted by the light transmission section and when the reflected light is received by the light reception section. Undersea laser radar. [Claim 3] a. a light transmitting unit that transmits a pulsed laser beam of a predetermined wavelength into the sea; b. a light receiving unit that receives the Raman scattered light of the transmitted laser light from underwater and outputs light receiving levels for a plurality of different wavelengths set in the vicinity of the predetermined wavelength; c. An underwater laser radar comprising: a temperature calculation section that calculates the temperature of seawater from the difference in the light reception level output from the light reception section. 4. The temperature calculation section calculates the temperature distribution of the seawater along the course of the laser beam from a temporal change in a difference in light reception levels output from the light reception section. 3. The underwater laser radar described in 3.