Water body temperature profile coherent measurement system and method based on Brillouin scattering

Abstract

The invention belongs to the technical field of laser radars, and particularly discloses a water body temperature profile coherent measurement system based on Brillouin scattering. Comprising a laser seed source, a first coupler, a pulse modulation and amplification module, an acousto-optic modulator, a sinusoidal signal generator, a collimator, a transmitter-telescope, a water body, a receiving telescope, a second coupler, a photoelectric detector, an AD acquisition card, a computer and a connection relation thereof. The invention further discloses a water body temperature profile coherent measurement method based on Brillouin scattering. The heterodyne detection technology is utilized, the system works under the conditions of wide pulse width and low peak power, and water body profile temperature information can be obtained with high sensitivity and high range resolution through coherent detection and a fast Fourier transform algorithm.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a water body temperature profile coherent measurement system and method based on Brillouin scattering with high sensitivity and high distance resolution. Background Art

[0002] LiDAR ocean profile temperature detection technology is an active optical detection technology and the only technology that is expected to obtain ocean profile information on a large scale. Its working principle is to use a laser transceiver system to collect seawater scattering signals containing Brillouin scattering information, and then analyze and calculate these measurement data to obtain the Brillouin scattering spectrum information of the ocean profile water body, and then obtain real-time ocean profile temperature information with high distance resolution and high temperature accuracy.

[0003] The current ocean temperature measurement technology is divided into active detection and passive detection. Passive detection has a large measurement range, but can only measure sea surface temperature information and lacks ocean profile information. The active detection technology of ocean temperature profile based on lidar adopts direct detection technology, that is, the Brillouin spectrum information is converted into light intensity information through edge detection technology, or the Brillouin spectrum information is directly collected through Fabry-Perot interferometer or photomultiplier tube array. The Brillouin scattering information of the ocean profile is very weak. Both edge detection technology and Brillouin spectrum direct measurement technology have high requirements for laser echo energy, so the peak power of the laser emission system needs to be very high. This places very stringent requirements on the output power of the laser emission system.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problems existing in the background technology: how to use lidar technology to achieve high-distance resolution and high-precision water body profile temperature measurement while reducing the peak power of the laser emission system. To this end, a water body temperature profile coherent measurement system and method based on Brillouin scattering is provided.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A water body temperature profile coherent measurement system based on Brillouin scattering, comprising a laser seed source, wherein the output end of the laser seed source is connected to the input end of a first coupler, the output end 1 of the first coupler is connected to the input end 1 of an acousto-optic modulator, and the output end 2 of the first coupler is connected to the input end of a pulse modulation and amplification module;

[0008] The output end of the pulse modulation and amplification module is connected to the input end of the collimator, the output end of the collimator is connected to the input end of the transmitting telescope, the output end of the transmitting telescope emits the laser beam in parallel in the water body, the scattered light is received by the receiving telescope, and the output end of the receiving telescope is connected to the input end 1 of the second coupler;

[0009] The output end of the acousto-optic modulator is connected to the second input end of the second coupler;

[0010] The output end of the second coupler is connected to the input end of the photodetector, the output end of the photodetector is connected to the input end of the AD acquisition card, and the output end of the AD acquisition card is connected to the input end of the computer.

[0011] The following is a technical solution further defined by the system in the present invention, which also includes a sine signal generator, the output end of the sine signal generator is connected to the second input end of the acousto-optic modulator for providing a driving signal.

[0012] The following is a technical solution further defined by the system in the present invention, wherein the laser seed source is a 532nm single longitudinal mode optical fiber continuous seed source.

[0013] The following is a technical solution further defined by the system in the present invention, wherein the first coupler is a 1:99 optical coupler; wherein 1% of the light enters the acousto-optic modulator and is used as local oscillator signal light; and 99% of the light enters the pulse modulation and amplification module and the collimator, and is finally emitted through the transmitting telescope.

[0014] A water body temperature profile coherent measurement method based on Brillouin scattering, using the above-mentioned water body temperature profile coherent measurement system based on Brillouin scattering, comprises the following steps:

[0015] Step 1: The laser output from the laser seed source is divided into two parts after passing through the first coupler: most of the laser passes through the pulse modulation and amplification module, is amplified into pulse light after pulse modulation, and then is emitted by the transmitting telescope after passing through the collimator; a small part of the laser passes through the acousto-optic modulator and is frequency-shifted as the local oscillator signal light;

[0016] Step 2: The receiving telescope receives the target echo signal light, and sends the target echo signal light to the second coupler through the optical fiber, and the local oscillator signal light is also sent to the second coupler;

[0017] Step 3: The coherent light output by the second coupler passes through the photodetector and is collected by the AD acquisition card. The output signal of the AD acquisition card enters the computer. The emitted laser is a pulsed laser. Due to the continuous scattering of the water body, the scattered light received by the receiving telescope is continuous light, and the local oscillator signal light is also continuous light. Therefore, the light entering the second coupler is continuous light.

[0018] Step 4: In the computer, the coherent signal output by the photodetector is segmented according to the time sequence and the pulse width of the emitted pulse light. Different segments represent different distance information. Each segment of the coherent signal is subjected to fast Fourier transform to obtain the coherent signal spectrum. The two frequency peaks of the spectrum are located at the driving frequency f of the acousto-optic modulator. aom and the other at the Brillouin frequency shift f brillouin and the AOM driving frequency f aom The difference frequency, that is, f 6rillouin -f aom The sum of the two frequencies gives the Brillouin frequency shift f brillouin .

[0019] Step 5: Fix the water salinity, that is, the water salinity is known, and the Brillouin frequency shift f brillouin The water temperature T is calculated.

[0020] The following is a technical solution further defined in the method of the present invention, wherein the Brillouin frequency shift f brillouin Substitute into Fry's formula to calculate the water temperature T:

[0021] T(S,v B )=t0+t1(ν B -7.5)+t2(v B -7.5) 2 +t3(ν B -7.5) 3 +t4(v B -7.5) 6 +S[t6+t6(v B -7.5)+t7(v B -7.5) 2 +t8(v B -7.5) 3 ],

[0022] Among them, S is the salinity of the water body, T is the temperature of the water body, and v B =f brilloiin is the Brillouin frequency shift, and t0, t1, t2, t3, t4, t6, t7, and t8 are all parameters.

[0023] Compared with the prior art, the present invention has the following technical effects:

[0024] The system provided by the present invention can coherently amplify weak scattered signals containing Brillouin spectrum information through a specific signal processing method, greatly improving the sensitivity; the Brillouin scattering spectrum is obtained through spectrum analysis, and then the temperature information is calculated according to the empirical formula. By processing the coherent signal in sections, the system can obtain high-distance resolution and high-precision water temperature profile measurements;

[0025] The local oscillator light and the output pulse of the present invention originate from the same seed and have coherence, thus ensuring the continuity of the coherent signal;

[0026] The system of the present invention adopts coherent detection technology, thereby effectively amplifying the echo signal and having a higher signal-to-noise ratio and sensitivity;

[0027] The system of the present invention can obtain a complete Brillouin spectrum, and then use the Fry empirical formula to infer the temperature;

[0028] The present invention divides the coherent signal into time segments and has high distance resolution and high precision.

[0029] The present invention is further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a system overall structure block diagram of the present invention.

[0032] Figure numerals: 1. laser seed source; 2. first coupler; 3. pulse modulation and amplification module; 4. acousto-optic modulator; 5. sinusoidal signal generator; 6. collimator; 7. transmitting telescope; 8. water body; 9. receiving telescope; 10. second coupler; 11. photodetector; 12. AD acquisition card; 13. computer. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0034] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0035] In the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connection" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0036] The basic principle of the present invention is to split the laser into two parts through the first coupler, and most of the light passes through the pulse modulation and amplification module, is amplified into pulse light through pulse modulation, and finally emitted through the emission optical path system through the collimator. A small part is frequency-shifted by the acousto-optic modulator as the local oscillator signal light for coherent detection; the echo signal light and the local oscillator signal light enter the second coupler for coherence, and the coherent light is converted into an electrical signal through the photoelectric detector, and is collected and converted into a digital signal by the AD acquisition card. The AD acquisition card is connected to a computer, and the collected digital signal is fast Fourier transformed to obtain the radio frequency spectrum.

[0037] like Figure 1 As shown, this embodiment provides a water body temperature profile coherent measurement system based on Brillouin scattering, which is mainly composed of a laser seed source, a first coupler, a pulse modulation and amplification module, an acousto-optic modulator, a sinusoidal signal generator, a collimator, a transmitting telescope, a water body, a receiving telescope, a second coupler, a photoelectric detector, an AD acquisition card, a computer, etc.

[0038] The output beam of the laser seed source is divided into two parts through the first coupler: most of the laser is emitted by the transmitting telescope after passing through the pulse modulation and amplification module and the collimator, and the beam is emitted parallel to the water body, and the generated scattered light is received by the receiving telescope; the remaining small part of the laser is frequency-shifted by the acousto-optic modulator and used as the local oscillator signal light for coherent detection. The output end of the sine signal generator is connected to the second input end of the acousto-optic modulator to provide a driving signal.

[0039] The two input ports of the second coupler are connected to the output port of the receiving telescope and the output port of the acousto-optic modulator, respectively. The output port of the second coupler is connected to the input port of the photodetector, and the output port of the balanced detector is connected to the input port of the AD acquisition card. The output signal of the AD acquisition card enters the computer. In the computer, the coherent signal output by the detector is segmented according to the time series and the pulse width of the emitted pulse light as the standard. Different segments represent different distance information. Each segment of the coherent signal is subjected to fast Fourier transformation to obtain the coherent signal spectrum. The two frequency peaks of the spectrum, one is located at the driving frequency f of the acousto-optic modulator 4, and the other is located at the driving frequency f of the acousto-optic modulator 4. aom At the Brillouin frequency shift f brillouinand AOM 4 driving frequency f aom The difference frequency, that is, f brillouin -f aom The sum of the two frequencies gives the Brillouin frequency shift f brillouin , and then use Fry's empirical formula to deduce the water temperature.

[0040] The specific devices used in this embodiment are: the laser seed source is a 532nm single longitudinal mode fiber continuous seed source; the first coupler is a 1:99 optical coupler: 1% of the light is frequency-shifted by an acousto-optic modulator and used as local oscillator signal light; 99% of the light is pulse modulated and amplified by a module and a collimator, and then emitted as a laser through a transmitting telescope.

[0041] A water body temperature profile coherent measurement method based on Brillouin scattering, using the above-mentioned water body temperature profile coherent measurement system based on Brillouin scattering, comprises the following steps:

[0042] 1. The laser output from the laser seed source is divided into two parts through the first coupler: 99% of the laser passes through the pulse modulation and amplification module, is amplified into pulse light after pulse modulation, and then is emitted by the transmitting telescope after passing through the collimator; 1% of the laser is used as the local oscillator signal light after frequency shifting by the acousto-optic modulator.

[0043] 2. The receiving telescope receives the target echo signal light, and outputs the target echo signal light to enter the first input port of the second coupler through the optical fiber. The second input port of the second coupler is connected to the output port of the acousto-optic modulator to receive the local oscillator signal light. The output signal of the second coupler enters the photodetector, and the coherent signal obtained by the photodetector is connected to the AD acquisition card. The output signal of the AD acquisition card enters the computer. In the computer, the output coherent signal is subjected to fast Fourier transform to obtain the coherent signal spectrum, and the peak frequency f on the center frequency side of the spectrum is obtained. aom , the peak frequency on the other side is f brillouin -f aom The sum of the two frequencies gives the Brillouin frequency shift f brillouin .

[0044] 3. Shift the Brillouin frequency f brillouin Substitute into Fry's empirical formula: T(S,v B )=t0+t1(v B -7.5)+t2(v B -7.5) 2 +t3(v B -7.5) 3 +t4(ν B -7.5) 6 +S[t5+t6(v B -7.5)+t7(v B -7.5)2 +t8(ν B -7.5) 3 ], where S is the salinity of the water body, in units of 1‰; T is the temperature of the water body, in degrees Celsius; ν B =f brillouin is the Brillouin frequency shift in GHz; t0 = 23.5, t1 = 65.5, t2 = 75, t3 = 252, t4 = 1100, t5 = -0.402, t6 = -0.287, t7 = -0.902, t8 = -5.5. Fixed water salinity, the Brillouin frequency shift f brillouin The water temperature T is deduced.

[0045] The system provided by the present invention utilizes heterodyne detection technology. The system operates under wide pulse width and low peak power. Through coherent detection and fast Fourier transform algorithm, the water body profile temperature information can be obtained with high sensitivity and high distance resolution.

[0046] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, all equivalent changes made according to the shape, structure and principle of the present invention without departing from the content of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A water body temperature profile coherent measurement system based on Brillouin scattering, characterized in that: It includes a laser seed source, wherein the output end of the laser seed source is connected to the input end of the first coupler, the output end 1 of the first coupler is connected to the input end 1 of the acousto-optic modulator, and the output end 2 of the first coupler is connected to the input end of the pulse modulation and amplification module; The output end of the pulse modulation and amplification module is connected to the input end of the collimator, the output end of the collimator is connected to the input end of the transmitting telescope, the output end of the transmitting telescope emits the laser beam in parallel in the water body, the scattered light is received by the receiving telescope, and the output end of the receiving telescope is connected to the input end 1 of the second coupler; The output end of the acousto-optic modulator is connected to the second input end of the second coupler; The output end of the second coupler is connected to the input end of the photodetector, the output end of the photodetector is connected to the input end of the AD acquisition card, and the output end of the AD acquisition card is connected to the input end of the computer.

2. The water body temperature profile coherent measurement system based on Brillouin scattering as claimed in claim 1, characterized in that: It also includes a sinusoidal signal generator, the output end of which is connected to the second input end of the acousto-optic modulator for providing a driving signal.

3. The water body temperature profile coherent measurement system based on Brillouin scattering as claimed in claim 1, characterized in that: The laser seed source is a 532nm single longitudinal mode optical fiber continuous seed source.

4. The water body temperature profile coherent measurement system based on Brillouin scattering as claimed in claim 1, characterized in that: The first coupler is a 1:99 optical coupler, wherein 1% of the light enters the acousto-optic modulator and is used as local oscillator signal light; 99% of the light enters the pulse modulation and amplification module and the collimator, and is finally emitted through the transmitting telescope.

5. A coherent measurement method of water body temperature profile based on Brillouin scattering, characterized in that: The water body temperature profile coherent measurement system based on Brillouin scattering according to any one of claims 1 to 4 comprises the following steps: Step 1: The laser output from the laser seed source is divided into two parts after passing through the first coupler: one part of the laser passes through the pulse modulation and amplification module, is amplified into pulse light after pulse modulation, and then is emitted by the transmitting telescope after passing through the collimator; the other part of the laser passes through the acousto-optic modulator and is used as the local oscillator signal light after frequency shifting; Step 2: The receiving telescope receives the target echo signal light, and sends the target echo signal light to the second coupler through the optical fiber, and the local oscillator signal light is also sent to the second coupler; Step 3: The coherent light output by the second coupler passes through the photodetector and is collected by the AD acquisition card, and the output signal of the AD acquisition card enters the computer; Step 4: In the computer, the output coherent signal is subjected to fast Fourier transform to obtain the coherent signal spectrum, and the peak frequency on the side of the spectrum center frequency is obtained as f aom , the peak frequency on the other side is f brillouin -f aom , the two frequencies are added to get the Brillouin frequency shift f brillouin ; Step 5: Fix the water salinity and calculate the Brillouin frequency shift f brillouin The water temperature T is calculated.

6. The method for coherently measuring the water temperature profile based on Brillouin scattering according to claim 5, characterized in that: The Brillouin frequency shift f brilkiuin Substitute into Fry's formula to calculate the water temperature T: T(S,v B )=t0+v1(v B -7.5)+t2(v B -7.5) 2 +t3(v B -7.5) 3 +t4(v B -7.5) 6 +S[t5+t6(v8-7.5)+t7(v B -7.5) 2 +t8(v B -7.5) 3 ], Among them, S is the salinity of the water body, T is the temperature of the water body, and v B =f brillouin is the Brillouin frequency shift, t0, t1, t2, t3, t4, t5, t6, t7, and t8 are all parameters.

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