A seawater salinity and turbidity measurement system and method based on optical carrier radio frequency

Abstract

The application discloses a seawater salt turbidity measurement system and method based on optical carrier radio frequency, and mainly relates to the technical field of marine environmental sensors. The seawater salt turbidity measurement system comprises the following steps: emitting a double-channel radio frequency signal with a fixed frequency difference through an adjustable signal source, generating an optical carrier radio frequency signal through an electro-optical modulator and a laser modulator, entering a seawater sensing chamber through a collimating emission light path, converting the transmitted optical carrier radio frequency into a radio frequency signal through a coupling receiving light path and a photoelectric detector, reflecting the salt turbidity information of seawater on the radio frequency characteristics of the radio frequency signal, performing frequency mixing measurement on the radio frequency signal based on a double-mixing measurement method, and obtaining a seawater measurement signal. The seawater salt turbidity measurement method comprises the following steps: extracting group delay data and phase noise data of the seawater measurement signal, constructing a seawater turbidity calculation model and a system salt turbidity decoupling model, and calculating the salt turbidity of seawater based on the group delay data and the phase noise data.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of marine environment sensors, mainly to the technical field of optical sensing of seawater salinity and turbidity, and particularly to a seawater salinity and turbidity measurement system and method based on optical carrier radio frequency. BACKGROUND

[0002] The existing methods for measuring seawater salinity based on conductivity and optical refractive index have good application effects in low turbidity and stable environments, but in complex sea areas, especially in high turbidity sea areas, the conductivity and optical refractive index of seawater are unstable, and the measurement results are easily affected by impurities such as suspended particles and silt in seawater, making it difficult to meet the high-precision measurement requirements of seawater salinity, and the stability of the seawater salinity measurement system cannot be guaranteed.

[0003] Therefore, there is an urgent need for a seawater salinity and turbidity measurement system and method that can effectively work in complex marine environments and has high precision and high reliability. SUMMARY

[0004] The main purpose of the present application is to provide a seawater salinity and turbidity measurement system and method based on optical carrier radio frequency, to solve the problem of insufficient measurement accuracy and stability of seawater salinity measurement in complex marine environments, especially under conditions of high turbidity and dynamic changes, and to improve the accuracy and stability of seawater salinity measurement.

[0005] To achieve the above-mentioned purpose, the present application provides a seawater salinity and turbidity measurement system based on optical carrier radio frequency, comprising: a tunable signal source, an electro-optic modulator, a laser, a collimated emission light path, a seawater sensing chamber, a coupled reception light path, a photoelectric detector and a radio frequency receiving module, the tunable signal source, the electro-optic modulator, the collimated emission light path, the seawater sensing chamber and the photoelectric detector are connected in sequence to form a detection link;

[0006] The tunable signal source is used to emit a double-channel radio frequency signal with a fixed frequency difference;

[0007] The electro-optic modulator is connected to the laser, and is used to modulate the radio frequency signal onto the light signal emitted by the laser through the electro-optic effect to generate an optical carrier radio frequency signal;

[0008] The collimated emission light path is connected to the electro-optic modulator and the seawater sensing chamber, and is used to irradiate the optical carrier radio frequency signal into the seawater sensing chamber;

[0009] The seawater sensing chamber is used for optical measurement of seawater;

[0010] The coupled reception light path is connected to the seawater sensing chamber and the photoelectric detector, and is used for combining the optical power of the same wavelength;

[0011] The photoelectric detector is used for converting the optical carrier radio frequency signal into a radio frequency signal;

[0012] The radio frequency receiving module is used for mixing frequency measurement of the radio frequency signals emitted by the tunable signal source and the photoelectric detector.

[0013] Further, the tunable signal source emits a double channel, and the first radio frequency signal and the second radio frequency signal have frequencies f1 and f2 respectively, the frequency difference of the first radio frequency signal and the second radio frequency signal is fixed, the fixed frequency difference is Δf = |f1-f2|, and the phase difference value of the first radio frequency signal and the second radio frequency signal is

[0014] A 50:50 power divider is arranged in the tunable signal source, the first radio frequency signal is equally divided into a first radio frequency first channel signal and a first radio frequency second channel signal through the 50:50 power divider, and the second radio frequency signal is equally divided into a second radio frequency first channel signal and a second radio frequency second channel signal, the first radio frequency second channel signal enters the detection link to perform optical measurement on seawater in the seawater sensing chamber, and a seawater measurement radio frequency signal is obtained.

[0015] Further, the radio frequency receiving module is integrated with a mixing frequency measurement module, the mixing frequency measurement module is used for mixing frequency measurement of the radio frequency signals emitted by the tunable signal source and the photoelectric detector based on a double mixing frequency measurement method, and a seawater measurement signal is obtained, which comprises:

[0016] First mixing frequency, the first radio frequency first channel signal and the second radio frequency first channel signal are mixed through the left mixer of the mixing frequency measurement module, and a background mixing frequency signal is obtained, which is equivalent to a reference mixing frequency signal; the seawater measurement radio frequency signal and the second radio frequency second channel signal are mixed through the right mixer of the mixing frequency measurement module, and a measurement mixing frequency signal is obtained, the measurement mixing frequency signal carries depth information of group delay and phase noise caused by different salt turbidity of seawater;

[0017] Second mixing frequency, the background mixing frequency signal and the measurement mixing frequency signal are mixed through the mixing frequency measurement module, and a seawater measurement signal is obtained, the seawater measurement signal carries depth information of group delay and phase noise caused by different salt turbidity of seawater.

[0018] The application also provides a seawater salt turbidity measurement method based on an optical carrier radio frequency, which comprises:

[0019] S1. obtaining a seawater measurement signal based on a seawater salt turbidity measurement system, and extracting group delay data and phase noise data caused by different salt turbidity of seawater in the seawater measurement signal;

[0020] S2. performing data processing on the group delay data and the phase noise data, and calculating an integral area value of a phase noise spectrum;

[0021] S3. Construct a mathematical model of seawater turbidity, calculate the seawater turbidity based on the integral area value of the phase noise spectrum;

[0022] S4. Construct a system salt turbidity decoupling model, calculate the seawater salinity based on the integral area value of the phase noise spectrum and the group delay data.

[0023] Further, based on the double-mixing method, the to-be-demodulated phase frequency characteristic signal of the seawater measurement signal is extracted, and the phase noise data is extracted according to the to-be-demodulated phase frequency characteristic signal The extraction formula of the phase noise is:

[0024]

[0025] Among them, is the phase noise data The value at the frequency offset f, P phase (f) is the phase noise data The phase noise power spectrum density at the frequency offset f, P carrier is the carrier power;

[0026] Under the condition of the same bandwidth of the optical carrier radio frequency signal, the phase noise spectrum corresponding to different turbidity is extracted, the phase noise spectrum is subjected to smoothing and noise reduction processing and integral processing, the integral area value of the phase noise spectrum is calculated, and is recorded as A pn (T), and the integral range is the single sideband frequency scanning range of the phase frequency characteristic with the optical carrier radio frequency signal frequency as the starting frequency.

[0027] Further, a seawater turbidity calculation model is constructed, and the seawater turbidity T is calculated based on the integral area value A pn (T) of the phase noise spectrum:

[0028] A pn (T)=∝0+∝1T+∝2T 2 +···+∝ n T n ;

[0029] Among them, ∝0, ∝1, ··· ∝ n are fitting coefficients under Taylor polynomial expansion, which are equivalent to the calibration parameters of the measurement system in a specific environment;

[0030] According to a single frequency modulation, the phase measurement step is less than π, and the relationship between the phase measurement step and the background group delay is obtained as:

[0031]

[0032] Among them, indicates the phase measurement step, f steprepresents the single frequency modulation step, τ0 represents the group delay of the optical carrier radio frequency signal through the vacuum sensing chamber, which is equivalent to the background group delay.

[0033] Further, according to the relationship between the phase measurement step of single frequency modulation and the background group delay, the single frequency modulation step f step of the system is determined.

[0034]

[0035] Based on the single frequency modulation step f step , the sweep frequency f scan of the seawater salinity and turbidity measurement system is determined. According to the relationship between the system group delay and the measurement phase difference, the system group delay is calculated:

[0036]

[0037] Wherein, τ g is the system group delay, which is equivalent to the total group delay of the seawater to be measured after the optical carrier transmission, is the measurement phase difference.

[0038] Further, the system group delay is fully differentiated to calculate the system group delay measurement accuracy error Δτ:

[0039]

[0040] Wherein, represents the measurement phase difference change accuracy, df scan represents the system sweep frequency change accuracy, and Δθ represents the initial and final phase difference.

[0041] Further, according to the system group delay measurement accuracy error Δτ and the measurement phase difference change accuracy , the sweep frequency of the system is calculated to determine the sampling point number n of the sweep frequency interval of the seawater salinity and turbidity measurement system in the measurement of the system group delay τ g .

[0042]

[0043]

[0044] The group delay measurement accuracy is improved by the traversal loop scanning and the difference method between frequency points to carry out the measurement of the system group delay of the seawater to be measured.

[0045] Further, the system salinity and turbidity decoupling model is constructed, the integral area value of the phase noise spectrum and the group delay data are combined, the influence of turbidity on the system group delay is excluded by the decoupling algorithm, the component of the system group delay caused by the change of salinity is reserved, and the salinity of the seawater is calculated based on the system group delay caused by the change of salinity.

[0046] y s = a * tau g + b * A pn + c

[0047] Wherein, y s is the seawater salinity to be measured, a is the calibration coefficient of the system about group delay in the calibration environment, b is the calibration coefficient of the system phase noise mathematical model in the calibration environment, and c is the compensation coefficient of the whole system.

[0048] Compared with the prior art, the present application has the following beneficial effects:

[0049] The present application focuses on exploring the influence mechanism of suspended particles in seawater on salinity sensing, constructs a seawater salt and turbidity measurement system, obtains seawater measurement signals based on a double-mixing measurement scheme, and saves the salt and turbidity information of seawater in the radio frequency characteristics of the seawater measurement signals. By extracting group delay data and phase noise data caused only by the difference in salt and turbidity of seawater in the seawater measurement signals, a seawater turbidity calculation model is established using the phase noise data to calculate the seawater turbidity.

[0050] The present application constructs a system salt and turbidity decoupling model, measures the seawater salinity using group delay data and phase noise data, and at the same time ensures the accuracy and stability of the salinity measurement results, eliminates the turbidity component in the system group delay, eliminates the influence of seawater turbidity on seawater salinity measurement, and significantly improves the environmental adaptability of the system and the measurement accuracy of seawater salinity. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The overall schematic diagram of the seawater salt and turbidity measurement system provided by the embodiment of the present application.

[0052] Figure 2 The overall flowchart of the seawater salt and turbidity measurement method provided by the embodiment of the present application.

[0053] Figure 3 The flowchart of the system salt and turbidity decoupling model provided by the embodiment of the present application.

[0054] Figure 4 The phase noise characteristic spectrum corresponding to the 0 scattering turbidity provided by the embodiment of the present application.

[0055] Figure 5 The phase noise characteristic spectrum corresponding to the 2.0016 scattering turbidity provided by the embodiment of the present application.

[0056] Figure 6 The phase noise characteristic spectrum corresponding to the 3.3355 scattering turbidity provided by the embodiment of the present application. DETAILED DESCRIPTION

[0057] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0058] As shown in Figure 1 A seawater salt turbidity measurement system based on optical carrier radio frequency, comprising: a tunable signal source, an electro-optic modulator, a laser, a collimating emission light path, a seawater sensing chamber, a coupling receiving light path, a photoelectric detector and a radio frequency receiving module, the tunable signal source, the electro-optic modulator, the collimating emission light path, the seawater sensing chamber and the photoelectric detector are connected in sequence to form a detection link; the seawater measurement radio frequency signal is obtained through the detection link.

[0059] The tunable signal source emits double channels, and the frequencies of the first radio frequency signal and the second radio frequency signal are f1 and f2 respectively. The frequency difference between the first radio frequency signal and the second radio frequency signal is fixed, and the fixed frequency difference is Δf = |f1-f2|. The phase difference value of the first radio frequency signal and the second radio frequency signal is which is equivalent to the initial phase difference of the first radio frequency signal and the second radio frequency signal. The initial phase of the tunable signal source when configuring the output signal is artificially controllable, so which is an artificially controllable factor. Since the frequency difference between the first radio frequency signal and the second radio frequency signal is fixed, the initial phase difference of the first radio frequency signal and the second radio frequency signal is also fixed.

[0060] The phase time delay difference value of the first radio frequency signal and the second radio frequency signal is τ, which is a to-be-measured value. According to the relationship between the phase time delay difference value, the phase difference value and the frequency difference the phase time delay difference value τ is calculated.

[0061] The electro-optic modulator is connected with the laser. Under the action of an external electric field, the refractive index of the material is changed, so as to modulate the amplitude, phase and polarization state of the light wave. The radio frequency signal emitted by the tunable signal source is loaded onto the light wave emitted by the laser through the electro-optic effect to generate an optical carrier radio frequency signal, and then the signal is transmitted through an optical fiber.

[0062] The collimating emission light path is connected with the electro-optic modulator and the seawater sensing chamber, and is used for irradiating the optical carrier radio frequency signal to the seawater sensing chamber. The collimating emission light path focuses, adjusts and aligns the optical carrier radio frequency signal emitted by the electro-optic modulator through a collimator, gathers the scattered light beam into parallel light rays by changing the shape and size of the light beam, ensures the alignment of the light paths between various components of the optical system, and meets the specific experimental or application requirements.

[0063] The seawater sensing chamber is used for optical measurement of seawater, which can adjust certain specific measurement information of the seawater to be measured, such as salinity, turbidity and temperature according to the needs of experiments or applications, and complete the optical measurement of specific parameters of seawater. After the optical carrier radio frequency signal enters the seawater sensing chamber, the propagation of the signal is affected by seawater with different salinity and turbidity, resulting in changes in the group delay data and phase noise data of the signal due to the influence of different salinity and turbidity.

[0064] The salinity change of seawater salinity has a linear relationship with the change of optical refractive index. The refractive index changes 2x10 -4 The change of optical refractive index directly affects the transmission speed of optical carrier radio frequency signal in seawater, thereby changing the group delay. At the same time, the increase of suspended particles in seawater increases the light scattering and absorption, introduces phase noise, and the increase of seawater turbidity leads to the attenuation of transmitted light energy and the reduction of signal-to-noise ratio.

[0065] The coupling receiving light path connects the seawater sensing chamber and the photoelectric detector, and is used for combining the optical power of the same wavelength;

[0066] The photoelectric detector is used for converting the optical carrier radio frequency signal into a radio frequency signal; the photoelectric detector converts the optical signal into an electrical signal by causing the conductivity of the irradiated material to change through radiation.

[0067] The radio frequency receiving module is used for mixing frequency measurement of the radio frequency signals emitted by the tunable signal source and the photoelectric detector.

[0068] The tunable signal source is provided with a 50:50 power divider, which divides the first radio frequency signal into a first radio frequency first path signal and a first radio frequency second path signal, and divides the second radio frequency signal into a second radio frequency first path signal and a second radio frequency second path signal. The first radio frequency second path signal is used for optical measurement of seawater in the seawater sensing chamber to obtain seawater measurement radio frequency signal. The first radio frequency second path signal is converted into an optical carrier radio frequency signal by an electro-optical modulator, and enters the seawater sensing chamber through the collimating emission light path. In the seawater sensing chamber, the propagation of the optical carrier radio frequency signal is affected by seawater with different salinity and turbidity, and the phase noise data and group delay data of the signal also change due to the influence of seawater salinity and turbidity. The signal passes through the seawater sensing chamber to obtain an optical carrier transmission signal, the optical carrier transmission signal enters the photoelectric detector through the coupling receiving light path, the optical carrier transmission signal is converted from the optical carrier radio frequency signal to the radio frequency signal by the photoelectric detector, and the salinity and turbidity information of the seawater is reflected on the radio frequency characteristics of the radio frequency signal to obtain the seawater measurement radio frequency signal.

[0069] Assuming that the input signal of the seawater salinity and turbidity measurement system is: the first radio frequency signal and the second radio frequency signal wherein A and B are the initial amplitudes of the first radio frequency signal and the second radio frequency signal, and initial phase, t represents time, the first radio frequency signal and the second radio frequency signal are initially out of phase by

[0070] The first radio frequency signal is evenly divided by a 50:50 power divider into a first radio frequency first path signal and a first radio frequency second path signal, wherein the first radio frequency second path signal enters the detection link as an input signal to perform optical measurement on seawater, and a seawater measurement radio frequency signal is obtained, denoted as

[0071] A mixing measurement module is integrated in the radio frequency receiving module, and a left-side mixer and a right-side mixer are arranged in the mixing measurement module. The mixing measurement module performs mixing measurement on the radio frequency signals emitted by the tunable signal source and the photoelectric detector based on a double mixing measurement method, and obtains a seawater measurement signal, including:

[0072] First mixing:

[0073] The left-side mixer of the mixing measurement module obtains a background mixing signal S IF11 :

[0074]

[0075] The mixer outputs the sum frequency and difference frequency of the input signals:

[0076]

[0077] After filtering, the mixer filters out high-frequency components and only retains low-frequency terms, so the background mixing signal S IF11 is:

[0078]

[0079] Wherein, Δf1 is the frequency of the background mixing signal, Δf1 = |f1-f2|.

[0080] The right-side mixer of the mixing measurement module obtains a measurement mixing signal S IF12 :

[0081] Right-side mixer (S1` and S2)

[0082]

[0083] After filtering, only low-frequency terms are retained, so the measurement mixing signal S IF12 is:

[0084]

[0085] The first mixing is mixing the first radio frequency first signal and the second radio frequency first signal through the left mixer of the mixing measurement module to obtain the background mixing signal, which is equivalent to the reference mixing signal; the frequency of the background mixing signal is Δf1=Δf=f1-f2; the sea water measurement radio frequency signal and the second radio frequency second signal are mixed through the right mixer of the mixing measurement module to obtain the measurement mixing signal, and the frequency of the measurement mixing signal is Δf2=Δf=f1-f2, and the measurement mixing signal carries the depth information of the group delay and the phase noise caused by different salt turbidity.

[0086] The second mixing is:

[0087] The background mixing signal S IF11 and the measurement mixing signal S IF12 are mixed again to obtain the sea water measurement signal S IF2 ,

[0088] S IF2 =S IF11 ·S IF12 ;

[0089]

[0090] The trigonometric identity is expanded:

[0091]

[0092] After filtering, only the low-frequency term is reserved:

[0093]

[0094] Therefore, the phase of the final signal is cos(2πf1τ g ), and the group delay of the measurement link is measured according to the phase of the final signal, which is equivalent to the system group delay τ g :

[0095]

[0096] Where θ is the measured final output phase, that is, the phase shift.

[0097] The second mixing is mixing the background mixing signal with a frequency of Δf1 and the measurement mixing signal with a frequency of Δf2 through the mixing measurement module to obtain the sea water measurement signal, and the sea water measurement signal carries the depth information of the group delay and the phase noise caused by only the difference in salt turbidity of the sea water. Based on the double mixing method, the influence of background noise on the signal is excluded, and the group delay data and the phase noise data caused by only the difference in salt turbidity of the sea water are extracted.

[0098] According to actual conditions, different deblurring schemes are used to obtain the real solution of the group delay of the measurement link, and the application scope, advantages and disadvantages of different deblurring schemes are shown in Table 1:

[0099] Table 1 Application scope and advantages and disadvantages of different deblurring schemes

[0100] method Scope of application advantage shortcoming multi-frequency method Suitable for large group delay Suitable for broadband systems Multiple measurements are required Coherence scanning method Suitable for continuous measurement Suitable for high-precision systems High frequency resolution is required Reference path differential Suitable for long distance measurement Avoid large-scale blur Requires additional reference path Higher-order harmonic method Suitable for low bandwidth systems Simple calculation Harmonic processing is required High time resolution sampling Suitable for short delay measurements Increase resolution High-speed sampler required

[0101] As Figure 2 shown in a seawater salt turbidity measurement method based on optical carrier radio frequency, comprising:

[0102] S1. Obtain the seawater measurement signal based on the seawater salt turbidity measurement system, and extract the group delay data and phase noise data caused only by the difference in seawater salt turbidity in the seawater measurement signal; the phase noise data includes phase noise spectrum data under different turbidity.

[0103] S2. Data preprocessing is performed on the group delay data and the phase noise data, and the integral area value of the phase noise spectrum is calculated; the data preprocessing includes noise reduction and smoothing processing and integration processing.

[0104] S3. Construct a seawater turbidity calculation mathematical model, calculate the seawater turbidity based on the integral area value of the phase noise spectrum according to the mathematical relationship between the phase noise integral area and the seawater turbidity.

[0105] S4. Construct a system salt turbidity decoupling model, and calculate the seawater salinity based on the integral area value of the phase noise spectrum and the group delay data.

[0106] Based on the double-mixing method, the phase frequency characteristic signal to be demodulated is extracted, and the phase noise data is extracted according to the phase frequency characteristic signal to be demodulated The extraction formula of the phase noise is:

[0107]

[0108] Among them, is the phase noise data at frequency offset f, P phase (f) is the phase noise data at frequency offset f, P carrier is the carrier power;

[0109] Under the condition of the optical carrier radio frequency signal in the same bandwidth, the phase noise spectrum corresponding to different turbidity is extracted, the phase noise spectrum is subjected to smoothing and noise reduction processing and integration processing, the integral area value of the phase noise spectrum is calculated, and is recorded as A pn (T), and the integral range is the single sideband frequency scanning range of the phase frequency characteristic with the optical carrier radio frequency signal frequency as the starting frequency.

[0110] A seawater turbidity calculation model is constructed, and the integral area value A of the phase noise spectrum is taken as the basis pn (T) Reverse calculation of seawater turbidity T:

[0111] A pn (T) = a0 + a1T + a2T 2 + ··· + a n T n ;

[0112] Wherein, a0, a1, ··· a n are fitting coefficients under Taylor polynomial expansion, which are equivalent to the calibration parameters of the measurement system in a specific environment.

[0113] As Figure 3 shown in the extraction process of system group delay, first, the system is subjected to vacuum sensing condition calculation determination to obtain the background group delay τ0, that is, the group delay amount of the optical carrier radio frequency signal passing through the vacuum sensing chamber, as the reference quantity of system normalization, then pure water with zero salinity is added to the seawater sensing chamber, and the light color transmission measurement of zero salinity seawater is carried out based on the seawater salinity measurement system, the group delay of zero salinity seawater is extracted, and the system is normalized and calibrated based on the background group delay and the group delay of zero salinity seawater, and the calibrated seawater salinity measurement system is used, the to-be-demodulated phase frequency characteristic signal is extracted based on the double mixing method, and the to-be-measured phase According to single frequency modulation, the phase measurement step is less than n, and the relationship between the phase measurement step and the background group delay is:

[0114]

[0115] Wherein, represents the phase measurement step, f step represents the single frequency modulation step, and τ0 represents the group delay amount of the optical carrier radio frequency signal passing through the vacuum sensing chamber, which is equivalent to the background group delay.

[0116] According to the relationship between the phase measurement step and the background group delay during single frequency modulation, the constraint condition of the single frequency modulation step f step set by the system is determined as:

[0117]

[0118] Based on the single frequency modulation step f step , the sweep frequency f scan of the seawater salinity measurement system is determined, and the system group delay is calculated according to the relationship between the to-be-measured group delay amount and the measurement phase difference:

[0119]

[0120] Wherein, τ is the system group delay, To measure the phase difference, f scan is the sweep frequency of the system.

[0121] The system group delay τ g is measured, and the measurement accuracy error Δτ of the system group delay is calculated by full differentiation:

[0122]

[0123] wherein, represents the measurement phase difference change accuracy, and Δθ represents the initial and final phase difference.

[0124] According to the measurement accuracy error Δτ of the system group delay and the measurement phase difference change accuracy , the sweep frequency f of the system is calculated: scan , and the number of sampling points n of the sweep interval in the measurement of the seawater salinity and turbidity measurement system in the system group delay τ g is determined:

[0125]

[0126]

[0127] The measurement accuracy of the group delay is improved by the loop scanning and the difference method between frequency points, and the measurement of the system group delay of the seawater to be measured is carried out.

[0128] A system salinity and turbidity decoupling model is constructed, the integral area value of the phase noise spectrum and the group delay data are combined, the influence of turbidity on the system group delay is excluded by the decoupling algorithm, the component of the system group delay caused by the change of salinity is reserved, and the salinity of seawater is calculated:

[0129] y s =a·τ g +b·A pn (T)+c;

[0130] wherein, y s is the salinity of the seawater to be measured, a is the calibration coefficient of the system about the group delay in the calibration environment, b is the calibration coefficient of the phase noise mathematical model of the system in the calibration environment, and c is the compensation coefficient of the entire system.

[0131] Figures 4 to 6 is the phase frequency characteristic curve diagram extracted by the photoelectric detector under the same optical carrier radio frequency signal with a frequency of 120MHz and with the scattering turbidity as a single variable after the measurement link of the optical carrier radio frequency signal, Figure 4 is the phase noise characteristic spectrum diagram corresponding to 0 scattering turbidity (NTU), i.e. the phase noise characteristic spectrum diagram corresponding to the clear seawater, Figure 5 is the phase noise characteristic spectrum diagram corresponding to 2.0016 scattering turbidity, Figure 6The phase noise characteristic spectrum diagram corresponding to the 3.3355 scattering turbidity provided by the embodiment of the present application is obtained by comparing and analyzing Figure 4 , Figure 5 and Figure 6 According to the single sideband phase noise spectrum extracted from the phase frequency characteristic curve, it can be concluded that the integral area in the phase noise characteristic spectrum is positively correlated with the actual turbidity, and the phase noise under the same bandwidth frequency increases with the turbidity of seawater, so the higher the turbidity of seawater, the greater the influence on the measurement of seawater salinity.

[0132] The above is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A seawater turbidity measurement system based on light-carrying radio frequency, characterized in that: include: A tunable signal source, an electro-optical modulator, a laser, a collimated emission optical path, a seawater sensing chamber, a coupled receiving optical path, a photodetector, and a radio frequency receiving module are connected in sequence to form a detection link; The tunable signal source is used to transmit dual-channel radio frequency signals with a fixed frequency difference; The electro-optic modulator is connected to the laser and is used to modulate the radio frequency signal onto the optical signal emitted by the laser through the electro-optic effect to generate an optically carried radio frequency signal; The collimated emission optical path is connected to the electro-optical modulator and the seawater sensing chamber, and is used to irradiate the light-carrying radio frequency signal into the seawater sensing chamber; The seawater sensing chamber is used for optical measurement of seawater; The coupled receiving optical path connects the seawater sensing chamber and the photodetector, and is used to combine optical powers of the same wavelength; The photodetector is used to convert the light-carrying radio frequency signal into a radio frequency signal; The radio frequency receiving module is used to perform frequency mixing measurement on radio frequency signals transmitted by the tunable signal source and the photoelectric detector.

2. The seawater salinity turbidity measurement system based on light-carrying radio frequency according to claim 1 is characterized in that: The tunable signal source transmits a dual-channel first radio frequency signal and a second radio frequency signal with frequencies f1 and f2 respectively. The frequency difference between the first radio frequency signal and the second radio frequency signal is fixed, and the fixed frequency difference is Δf=|f1-f2|. The phase difference between the first radio frequency signal and the second radio frequency signal is The tunable signal source is provided with a 50:50 power splitter, which divides the first radio frequency signal into a first radio frequency first-path signal and a first radio frequency second-path signal, and divides the second radio frequency signal into a second radio frequency first-path signal and a second radio frequency second-path signal. The first radio frequency second-path signal enters the detection link to perform optical measurement of the seawater in the seawater sensing chamber to obtain a seawater measurement radio frequency signal.

3. The seawater salinity turbidity measurement system based on light-carrying radio frequency according to claim 2, characterized in that: The RF receiving module is integrated with a frequency mixing measurement module, which performs frequency mixing measurement on the RF signals emitted by the tunable signal source and the photodetector based on a dual frequency mixing measurement method to obtain a seawater measurement signal, including: The first mixing is performed by mixing the first RF signal and the second RF signal through the left mixer of the mixing measurement module to obtain a background mixing signal, which is equivalent to the reference mixing signal. The seawater measurement RF signal and the second RF signal are mixed through the right mixer of the mixing measurement module to obtain a measurement mixing signal. The measurement mixing signal carries depth information of group delay and phase noise caused by different salinity turbidity of seawater. The second mixing is to mix the background mixing signal and the measurement mixing signal through the mixing measurement module to obtain the seawater measurement signal. The seawater measurement signal carries the depth information of the group delay and phase noise caused only by the different seawater salinity turbidity.

4. A method for measuring seawater turbidity based on light-carrying radio frequency, using a seawater turbidity measurement system based on light-carrying radio frequency according to any one of claims 1 to 3 to perform optical measurement of seawater turbidity, characterized in that: include: S1. Obtain a seawater measurement signal based on a seawater salinity turbidity measurement system and extract group delay data and phase noise data from the seawater measurement signal caused only by differences in seawater salinity turbidity. S2. Process the group delay data and phase noise data to calculate the integrated area value of the phase noise spectrum; S3. Construct a mathematical model for calculating seawater turbidity, and calculate the seawater turbidity based on the integrated area value of the phase noise spectrum; S4. Construct a system salt-turbidity decoupling model and calculate seawater salinity based on the integrated area value of the phase noise spectrum and group delay data.

5. The method for measuring seawater turbidity based on light-carrying radio frequency according to claim 4, characterized in that: Extract the phase-frequency characteristic signal to be demodulated based on the double-mixing method, and extract the phase noise data based on the phase-frequency characteristic signal to be demodulated. The phase noise extraction formula is: in, Phase noise data The value at frequency offset f, P phase (f) is the phase noise data The phase noise power spectral density at the frequency offset f, P carrier is the carrier power; Under the condition of the same bandwidth of optical radio frequency signal, the phase noise spectrum corresponding to different turbidity is extracted, the phase noise spectrum is smoothed and denoised and integrated, and the integral area value of the phase noise spectrum is calculated, which is recorded as A. pn (T), the integration range is the single sideband frequency sweep range of the phase-frequency characteristic with the frequency of the optically carried RF signal as the starting frequency.

6. The method for measuring seawater turbidity based on light-carrying radio frequency according to claim 5, characterized in that: Construct a seawater turbidity calculation model based on the integral area value A of the phase noise spectrum pn (T), reverse calculation of seawater turbidity T: A pn (T)=∝0+∝1T+∝2T 2 +···+∝ n T n ; Among them, ∝0,∝1,···,∝ n is the fitting coefficient under the Taylor polynomial expansion, which is equivalent to the calibration parameter of the measurement system under specific conditions; According to the fact that the phase measurement step is less than π in single frequency modulation, the relationship between the phase measurement step and the background group delay is: in, Indicates the phase measurement step, f step represents the single frequency modulation step length, and τ0 represents the group delay of the optical RF signal passing through the vacuum sensing chamber, which is equivalent to the background group delay.

7. The method for measuring seawater turbidity based on light-carrying radio frequency according to claim 6, characterized in that: According to the relationship between the phase measurement step size and the background group delay during single FM, the single FM step size f set by the system is determined. step The constraints are: Based on a single frequency modulation step f step , determine the sweep frequency f of the seawater turbidity measurement system scan , according to the relationship between the system group delay and the measured phase difference, the system group delay is calculated: Among them, τ g is the system group delay, which is equivalent to the total group delay variable of the seawater to be measured after the light carrier is transmitted. To measure the phase difference.

8. The method for measuring seawater turbidity based on light-carrying radio frequency according to claim 7, characterized in that: Perform full differentiation on the system group delay and calculate the system group delay measurement accuracy error Δτ: in, Represents the measurement accuracy of phase difference change, df scan represents the frequency variation accuracy of the system sweep frequency, and Δθ represents the initial and ending phase difference.

9. The method for measuring seawater salinity based on light-carrying radio frequency according to claim 8, characterized in that: According to the system group delay measurement accuracy error Δτ and the measurement phase difference change accuracy Calculate the system's sweep frequency and determine the number of sampling points n in the sweep interval of the seawater salinity turbidity measurement system during the system group delay measurement: The accuracy of group delay measurement is improved by traversal cyclic scanning and frequency difference method, and the system group delay of the measured salinity and turbidity seawater is measured.

10. The method for measuring seawater turbidity based on light-carrying radio frequency according to claim 9, characterized in that: A system salt-turbidity decoupling model is constructed. Based on the integrated area value of the phase noise spectrum and the group delay data, a decoupling algorithm is used to eliminate the influence of turbidity on the system group delay. The component of the system group delay caused only by salinity changes is retained. The salinity of seawater is calculated based on the system group delay caused only by salinity changes: y s =a·τ g +b·A pn (T)+c; Among them, y s is the salinity of the seawater to be measured, a is the calibration coefficient of the system regarding group delay under the calibration environment, b is the calibration coefficient of the mathematical model of the system phase noise under the calibration environment, and c is the compensation coefficient of the entire system.

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