Method and system for in-situ online monitoring of dissolved carbon dioxide in water bodies over a wide range of concentrations

Abstract

The application discloses a water body dissolved carbon dioxide wide-range in-situ online monitoring method and system, and relates to the technical field of water environment monitoring. The method comprises the following steps: transferring the water body dissolved carbon dioxide to a gas phase channel through a membrane degassing unit; making the gas enter a ring-down cavity and performing cavity pressure closed-loop stable control; providing a first laser and a second laser corresponding to different absorption spectral lines of carbon dioxide, which are coupled into the ring-down cavity through a polarization division multiplexer; separating the output light signal into first and second wavelength channels after wavelength division demultiplexing and independently detecting, and inversely obtaining first and second concentration results; determining the range according to the first concentration result, and selecting the optimal result output or performing weighted fusion output from the first and second concentration results according to the channel quality parameters in the overlapping range. The application aims to solve the problem that low concentration and high resolution and high concentration and wide range are difficult to be considered at the same time, and improves the measurement response speed and stability under dynamic working conditions.

Description

Technical Field

[0001] This invention relates to the fields of water environment monitoring, marine observation, gas-liquid separation and laser spectroscopy detection technology, and in particular to a wide-range in-situ online monitoring method and system for dissolved carbon dioxide in water. Background Technology

[0002] Dissolved carbon dioxide (CO2) in water is a crucial parameter for studying the carbon cycle in water bodies, air-sea exchange, carbon transport in the river-ocean transition zone, and groundwater geochemical processes. The concentration of dissolved CO2 varies significantly among different types of water bodies, especially in the source-to-sink process from river to estuary and then to the ocean, where concentrations can span one to three orders of magnitude and undergo continuous and rapid changes along the way. Existing online monitoring technologies for dissolved CO2 in water typically employ gas-liquid balancers, membrane degassing devices, or gas-liquid separation membranes to transfer dissolved gases from the water to the gas phase, followed by detection using infrared absorption, laser absorption, or cavity ring-down spectroscopy. Cavity ring-down spectroscopy, with its high sensitivity, high selectivity, and high stability, shows promising application prospects in trace gas detection and dissolved gas measurement.

[0003] However, existing technologies still generally suffer from the following problems. First, single-spectral-line or single-range detection modes cannot simultaneously achieve high resolution in low-concentration regions and anti-saturation capability in high-concentration regions. Second, traditional multi-spectral-line switching methods typically employ a serial mode of prediction, switching, and measurement. In high-concentration regions, if a low-range strong absorption spectrum is used first, the waiting time can easily be fully utilized due to the weakening of the effective decay signal, leading to a prolonged overall measurement cycle. Third, in highly dynamic environments such as shipboard navigation and river-sea transition zones, fluctuations in sample flow rate, pressure, membrane mass transfer states, and platform vibrations can easily cause measurement instability.

[0004] Therefore, how to achieve an online monitoring scheme for dissolved carbon dioxide in water that can balance high resolution and wide measurement range with high dynamic adaptability has become an urgent technical challenge. Summary of the Invention

[0005] The main objective of this invention is to provide a method and system for in-situ online monitoring of dissolved carbon dioxide in water with a wide range, aiming to achieve an online monitoring scheme for dissolved carbon dioxide in water that can balance high resolution and wide range while possessing high dynamic adaptability.

[0006] To achieve the above objectives, this invention proposes a wide-range in-situ online monitoring method for dissolved carbon dioxide in water, comprising the following steps: S1. Obtain the water body to be tested, and pass the water body to be tested through the membrane degassing unit to transfer the dissolved carbon dioxide in the water body to the gas phase channel; S2. The gas extracted from the membrane degassing unit is introduced into the decay chamber, and the gas pressure in the decay chamber is controlled in a closed loop by the chamber pressure control module. S3. Provide a first laser and a second laser, wherein the first laser and the second laser respectively correspond to different absorption intensity spectral lines of carbon dioxide, so as to correspond to different carbon dioxide measurement concentration ranges respectively; S4. The first laser and the second laser are coupled together into the ring-down cavity via a polarization-maintaining wavelength division multiplexer; S5. The optical signal output from the decaying cavity is separated into a first wavelength channel and a second wavelength channel after wave decomposition and multiplexing, and then independently detected and inverted to obtain the first concentration result and the second concentration result. S6. Determine the measurement range based on the first concentration result: When the first concentration result is within the preset first concentration range, the first concentration result is output; When the first concentration result is within the preset second concentration range, the second concentration result is output; When the first concentration result is within the preset overlap range, the result with better channel quality parameters is selected from the first concentration result and the second concentration result for output based on the channel quality parameters of the first wavelength channel and the second wavelength channel, or the first concentration result and the second concentration result are weighted and fused for output.

[0007] Preferably, the center wavelength of the first laser is The center wavelength of the second laser is .

[0008] Preferably, the measurement range corresponding to the first concentration range is: The measurement range corresponding to the second concentration range is .

[0009] Preferably, the channel quality parameters include at least one of the following: signal-to-noise ratio, fitting residual, ring-down time stability, detector output light intensity, and integration time required to achieve the target accuracy.

[0010] Preferably, the overlapping range region is Within the overlapping range, the method further includes: performing a consistency check on the first concentration result and the second concentration result.

[0011] Preferably, when the deviation between the first concentration result and the second concentration result exceeds a preset deviation threshold, an anomaly handling strategy is executed. The anomaly handling strategy includes refitting, extending the integration time, repeating the measurement, reducing the weight of the abnormal channel, disabling the abnormal channel, or outputting a quality alarm.

[0012] Preferably, the range determination adopts a hysteresis mechanism, which includes setting different upper and lower switching thresholds to ensure that the range switching maintains stable output within the range formed by the upper and lower switching thresholds.

[0013] Preferably, it further includes: a reference ring-down time measured at a preset reference position using the second wavelength channel. The mirror loss of the ring-down cavity is evaluated online; wherein the reference position includes the non-absorption baseline position of the weak spectral line, the low absorption position, the fixed reference scan position, or the bottom position of the weak spectral line after concentration compensation.

[0014] Preferably, when the reference ringback time When the change relative to the preset reference value exceeds the preset alarm threshold, an early warning is output for the maintenance, cleaning, replacement, or repair of the high-reflectivity mirror in the decay cavity.

[0015] Preferably, after step S1, the method further includes: online correction of the degassing efficiency of the membrane degassing unit based on the flow rate, pressure, temperature, salinity of the water body to be tested and the inlet and outlet pressure difference of the membrane degassing unit.

[0016] Preferably, the method is deployed on a shipborne mobile platform; the method further includes: acquiring positioning information output by the positioning module, synchronously associating the timestamp, latitude and longitude and speed information with the measurement results of dissolved carbon dioxide, and generating a spatial distribution trajectory map of dissolved carbon dioxide in the water body.

[0017] This application also discloses a wide-range in-situ online monitoring system for dissolved carbon dioxide in water, comprising: A water pump is used to extract the water body to be tested. A membrane degassing unit, connected to the water pump, is used to transfer dissolved carbon dioxide in the water to be tested to the gas phase channel; The damping chamber has its air inlet connected to the membrane degassing unit. A cavity pressure control module, connected to the decay cavity, is used for closed-loop stable control of the air pressure in the decay cavity; The first laser source and the second laser source are used to provide laser signals of different measurement wavelengths, respectively; A polarization-maintaining wavelength division multiplexer is connected to the first laser source and the second laser source respectively, and is used to couple the two laser signals into the ring-down cavity. A wavelength demultiplexer, connected to the output end of the decaying cavity, is used to separate the output optical signal into a first wavelength channel and a second wavelength channel. The first detector and the second detector are respectively connected to the first wavelength channel and the second wavelength channel; and The data processing unit is configured to perform the method described in any of the preceding methods.

[0018] Preferably, the data processing unit includes a concentration inversion module, a range determination module, a channel quality assessment module, a consistency verification module, a mirror state assessment module, and a degassing efficiency correction module.

[0019] Preferably, the first wavelength channel and the second wavelength channel share the decay cavity, the gas phase channel and the cavity pressure control module, and perform drift compensation on the inverted concentration result based on the collected common-mode interference parameters. The common-mode interference parameters include at least one of cavity pressure fluctuation residual and temperature drift parameters.

[0020] The above technical solution has the following advantages: This invention achieves parallel and independent detection of high and low concentration ranges by providing a first and second laser corresponding to different absorption intensity spectral lines of carbon dioxide and using a polarization-maintaining wavelength division multiplexer to couple the two signals into the same ring-down cavity. This design overcomes the contradiction between resolution and range in traditional single-spectral-line measurements, unifying high-resolution measurement at low concentrations with anti-saturation measurement at high concentrations within the same equipment. By introducing channel quality parameter evaluation, optimal output, and weighted fusion mechanisms in the overlapping range region, the result abrupt at the range switching point is effectively avoided, ensuring the continuity of monitoring data. Simultaneously, the combination of the cavity pressure closed-loop stabilization control module and the dual-channel shared gas path physical structure significantly improves the system's anti-interference capability and long-term operational stability in complex dynamic environments such as shipboard navigation. Attached Figure Description

[0021] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a schematic diagram of the structure of a wide-range in-situ online monitoring system for dissolved carbon dioxide in water provided in an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram illustrating the principle of wave division multiplexing optical cavity ring-down spectrum provided in an embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram illustrating the continuous change in dissolved carbon dioxide concentration in water under shipborne monitoring, as provided in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Example 1 like Figures 1 to 3 As shown, this embodiment provides a wide-range in-situ online monitoring method and system for dissolved carbon dioxide in water, mainly used to solve the problem of large range, rapid changes, and complex environmental conditions in the continuous monitoring of dissolved carbon dioxide concentration from river to ocean source. Traditional techniques usually use a single spectral line for measurement, which often faces insufficient resolution in the low concentration range, while signal saturation is prone to occur in the high concentration range. In addition, the traditional serial multi-spectral line switching logic has a significant response delay when the concentration fluctuates rapidly.

[0026] The system structure of this embodiment is as follows: Figure 1 As shown, the system includes a water pump 1 for extracting water samples from the water body to be tested. The extracted water sample first flows through a pre-filter 2, which has a pore size of 50 μm to filter out large particles such as silt and biological debris. The filtered water then enters a membrane degassing unit, the core of which is a hydrophobic and breathable membrane 3, mechanically supported by a membrane support 4 to withstand water pressure. The water body to be tested flows continuously outside the hydrophobic and breathable membrane 3, utilizing the partial pressure difference of carbon dioxide between the gas and liquid phases to allow dissolved carbon dioxide molecules to pass through the membrane pores and enter the gas phase analysis channel. The residual water after degassing is discharged from the waterproof housing after passing through a post-filter 5. To adapt to harsh outdoor or underwater environments, the above-mentioned water sampling and degassing components are all encapsulated within a waterproof housing 6.

[0027] The degassed sample gas enters the integrated ring-down cavity 12 via an optical fiber. Cavity ring-down spectroscopy requires extremely high stability of the cavity pressure, as even minute pressure fluctuations directly alter the absorption line shape and ring-down time. Therefore, this embodiment employs a high-precision cavity pressure control module. This module includes a current stabilization module 7, specifically a capillary quartz tube, as well as an air pump 8, a proportional valve 9, a pressure gauge 11, and a pressure control circuit 10. The pressure gauge 11 monitors the absolute pressure within the ring-down cavity 12 in real time, and the pressure control circuit 10 receives the pressure feedback signal and drives the proportional valve 9 and air pump 8 for closed-loop regulation. In this embodiment, the cavity working pressure is set to an absolute pressure of 25 kPa, with a pressure control accuracy better than ±0.002 kPa.

[0028] The optical measurement system adopts a dual-channel parallel architecture. The center wavelength of the first laser source 13 is... The laser signal corresponds to the absorption spectral lines of carbon dioxide in the high-concentration region, and its range covers... to The second polarization-maintaining laser 15 emits at a center wavelength of... The laser signal corresponds to the strong absorption spectral lines of carbon dioxide in the low concentration region, and its range covers... to The two laser signals are modulated and rapidly turned off by the first polarization-maintaining switch 14 and the second polarization-maintaining switch 16, respectively, and then coupled into the same ring-down cavity 12 via the polarization-maintaining wavelength division multiplexer 17.

[0029] The optical signal output from the ring-down cavity 12 is demultiplexed by the wave demultiplexer 18, separating it into a first wavelength channel and a second wavelength channel. The first detector 19 and the second detector 20 independently detect the ring-down intensity of the two channels, respectively. The data processing unit 21 acquires the detector output signals and, by performing exponential fitting on the ring-down curves, obtains the first concentration result. Second concentration results Since the two channels share the same decay chamber 12, the same gas path, and the same pressure control environment, the data processing unit 21 can perform real-time drift compensation on the concentration results based on the collected common-mode interference parameters, such as chamber pressure fluctuation residuals or temperature drift.

[0030] The range determination logic executed by the data processing unit 21 is crucial for achieving stable output across a wide range. First, the system uses the first concentration result... This serves as the primary benchmark for range determination. When the first concentration result falls within a preset first concentration range, for example, above... When the system considers the current operating condition to be high concentration, it directly outputs the first concentration result. When the first concentration result is within the preset second concentration range, for example, below... When the system assumes that it is currently in a low-concentration operating condition, it outputs a second concentration result with higher sensitivity.

[0031] To avoid step or frequent jumps in measured values ​​near range switching points, this embodiment sets an overlapping range region, specifically the range of which is... to Within the overlapping range region, the data processing unit 21 simultaneously calculates and evaluates the channel quality parameters of the first and second wavelength channels. These channel quality parameters specifically include the signal-to-noise ratio, fitting residual, ring-down time stability, detector output light intensity, and the integration time required to achieve the target accuracy.

[0032] In one preferred approach, the system selects the result with the better channel quality parameters for output. In another preferred approach, the system assigns weights to the two results based on their quality parameters. and According to the formula Weighted fusion is performed for output. Simultaneously, within the overlapping range, the system performs consistency checks on the concentration results of the two channels. If the deviation between the first and second concentration results exceeds a preset deviation threshold, for example, exceeding... If the abnormality is not detected, an anomaly handling strategy will be implemented, including re-fitting the spectrum, extending the integration time to reduce noise, repeating the measurement, or outputting a quality alarm and temporarily downweighting the abnormal channel.

[0033] Furthermore, since the method in this embodiment is deployed on a shipborne mobile platform, the system also integrates a positioning module. The data processing unit 21 acquires the positioning information output by the positioning module and synchronously correlates the precise timestamp, latitude and longitude, and speed information with the measurement results of dissolved carbon dioxide to generate a spatial distribution trajectory map of dissolved carbon dioxide in the water. During the monitoring process, the system also performs online correction of the membrane mass transfer efficiency based on the flow rate, pressure, temperature, salinity of the water body under test, and the inlet and outlet pressure difference of the membrane degassing unit to ensure the accuracy of converting the gas phase concentration back to the dissolved carbon dioxide concentration in the water. Finally, the system converts the processed gas phase carbon dioxide concentration into the dissolved carbon dioxide concentration or equivalent partial pressure in the water according to the gas-liquid equilibrium relationship, realizing continuous monitoring of the entire path from river to ocean.

[0034] Example 2 Building upon Example 1, this example details the hysteresis mechanism for range determination to further improve system stability during range switching. In actual water monitoring, if the carbon dioxide concentration fluctuates slightly around the range switching threshold, simple single-threshold logic can cause the system to frequently jump between the two channels, generating discontinuous measurement noise. Therefore, this example sets non-overlapping upper and lower switching thresholds.

[0035] Specifically, as the concentration increases from low to high, the system maintains the output of the second wavelength channel until the first concentration result is obtained. Reaching the upper switching threshold, for example Only then does it switch to the first wavelength channel or enter the fusion mode in the overlapping range region; as the concentration decreases from high to low, the system maintains the output of the first wavelength channel until the first concentration result is obtained. Lower to the next switching threshold, for example Only then does it switch back to the second wavelength channel. This hysteresis mechanism effectively avoids frequent switching near the threshold, ensuring the smoothness and logical stability of the monitoring data.

[0036] Example 3 This embodiment provides an online assessment and maintenance early warning scheme for the state of a ring-down cavity mirror. Due to the complex water monitoring environment, even minor leaks or gaseous path contamination in the membrane degassing unit can damage the high-reflectivity mirror of the ring-down cavity. This embodiment utilizes the reference ring-down time measured at a preset reference position using a second wavelength channel. The mirror loss of the decaying cavity is evaluated online.

[0037] The reference position specifically includes the non-absorption baseline position of the weak spectral line, the low absorption position, the fixed reference scan position, or the bottom position of the weak spectral line after concentration compensation. The system records a reference ring-down time baseline value in the initial calibration or clean state. During operation, the data processing unit 21 periodically acquires the current reference ring-down time. When referencing the decay time The change relative to the preset baseline value exceeds the preset alarm threshold, for example, the change exceeds... At that time, the data processing unit 21 will automatically output warnings for mirror maintenance, cleaning, replacement, or repair of the high-reflectivity mirror in the decaying cavity. In addition, the system will also combine parameters such as fitting residuals, signal-to-noise ratio, and detector output light intensity to judge the quality of the current spectral data. If the data does not meet the quality requirements, the results of the corresponding channel will be marked, downweighted, or discarded.

[0038] Example 4 This embodiment focuses on the online correction of membrane degassing efficiency. The process of dissolved carbon dioxide transferring from the aqueous phase to the gas phase is significantly affected by water flow rate, pressure, temperature, and salinity. To obtain an accurate concentration of dissolved carbon dioxide in the water, this embodiment introduces an online correction step after step S1.

[0039] The data processing unit 21 acquires the flow rate of the water pump 1, the real-time pressure, temperature, and salinity sensor data of the water body under test, and calculates the degassing efficiency correction coefficient by combining the pressure difference between the inlet and outlet of the membrane degassing unit. When environmental parameters change drastically, causing the membrane degassing efficiency to deviate from the preset range, the system will automatically compensate the output results. If the degassing efficiency is too low to guarantee accuracy through compensation, the system will issue a maintenance prompt to the user or downgrade the current data. Through this dynamic correction mechanism, this system can adapt to the monitoring needs of various complex water bodies, from inland rivers and estuarine mixing zones to high-salinity oceans.

[0040] Example 5 This embodiment further illustrates the application of the system on a shipborne underway platform and the linkage function of the positioning module. The system is installed on the shipborne automatic monitoring station, and the water inlet pipe is connected to the water intake at the bottom of the ship. In order to cope with the platform vibration during navigation, the damping cavity 12 adopts an integrated fiber optic input and output structure, and works with the cavity pressure control module for high-precision voltage stabilization.

[0041] The system is equipped with a positioning module that outputs latitude, longitude, speed, and standard timestamp information in real time. The data processing unit 21 synchronously correlates the dissolved carbon dioxide measurement results with the aforementioned positioning information. By performing spatial interpolation processing on the data obtained during continuous navigation, the system can generate a real-time spatial distribution trajectory map of carbon dioxide in the water. This method can intuitively display the changes in carbon dioxide concentration gradients in areas such as river estuaries, providing high spatial resolution data support for carbon cycle research.

[0042] Example 6 This embodiment clearly defines the modular data processing architecture and common-mode interference compensation mechanism of the system. The data processing unit 21 integrates a concentration inversion module, a range determination module, a channel quality assessment module, a consistency verification module, a mirror state assessment module, a degassing efficiency correction module, and a dissolved carbon dioxide conversion module. These modules work collaboratively to ensure fully automated processing from the raw optical signal to the final dissolved carbon dioxide concentration output.

[0043] Because the first and second wavelength channels of this system share the same ring-down cavity 12, gas phase analysis channel, and cavity pressure control module, the environmental disturbances experienced by the two channels exhibit high common-mode characteristics. When inverting concentration, the data processing unit 21 extracts common-mode interference parameters by monitoring the ring-down time drift of the non-absorption baseline, and compensates for the drift in the first and second concentration results accordingly. This shared-cavity dual-wavelength design not only reduces system size and power consumption but also enhances anti-interference capabilities at the algorithmic level by utilizing the symmetry of the physical structure.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A wide-range in-situ online monitoring method for dissolved carbon dioxide in water, characterized in that, Includes the following steps: S1. Obtain the water body to be tested, and pass the water body to be tested through the membrane degassing unit to transfer the dissolved carbon dioxide in the water body to the gas phase channel; S2. The gas extracted from the membrane degassing unit is introduced into the decay chamber, and the gas pressure in the decay chamber is controlled in a closed loop by the chamber pressure control module. S3. Provide a first laser and a second laser, wherein the first laser and the second laser respectively correspond to different absorption intensity spectral lines of carbon dioxide, so as to correspond to different carbon dioxide measurement concentration ranges respectively; S4. The first laser and the second laser are coupled together into the ring-down cavity via a polarization-maintaining wavelength division multiplexer; S5. The optical signal output from the decaying cavity is separated into a first wavelength channel and a second wavelength channel after wave decomposition and multiplexing, and then independently detected and inverted to obtain the first concentration result and the second concentration result. S6. Determine the measurement range based on the first concentration result: When the first concentration result is within the preset first concentration range, the first concentration result is output; When the first concentration result is within the preset second concentration range, the second concentration result is output; When the first concentration result is within the preset overlap range, the result with better channel quality parameters is selected from the first concentration result and the second concentration result for output based on the channel quality parameters of the first wavelength channel and the second wavelength channel, or the first concentration result and the second concentration result are weighted and fused for output.

2. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, The center wavelength of the first laser is The center wavelength of the second laser is .

3. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, The measurement range corresponding to the first concentration range is The measurement range corresponding to the second concentration range is .

4. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, The channel quality parameters include at least one of the following: signal-to-noise ratio, fitting residual, fading time stability, detector output light intensity, and integration time required to achieve the target accuracy.

5. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, The overlapping range region is ; Within the overlapping range, the method further includes: performing a consistency check on the first concentration result and the second concentration result.

6. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 5, characterized in that, When the deviation between the first concentration result and the second concentration result exceeds a preset deviation threshold, an anomaly handling strategy is executed. The anomaly handling strategy includes refitting, extending the integration time, repeating the measurement, reducing the weight of the abnormal channel, disabling the abnormal channel, or outputting a quality alarm.

7. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, The range determination adopts a hysteresis mechanism, which includes setting different upper and lower switching thresholds to ensure that the range switching maintains a stable output within the range formed by the upper and lower switching thresholds.

8. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, It also includes: the reference waning time measured at a preset reference position using the second wavelength channel. The mirror loss of the ring-down cavity is evaluated online; wherein the reference position includes the non-absorption baseline position of the weak spectral line, the low absorption position, the fixed reference scan position, or the bottom position of the weak spectral line after concentration compensation.

9. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 8, characterized in that, When the reference decay time When the change relative to the preset reference value exceeds the preset alarm threshold, an early warning is output for the maintenance, cleaning, replacement, or repair of the high-reflectivity mirror in the decay cavity.

10. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, After step S1, the method further includes: online correction of the degassing efficiency of the membrane degassing unit based on the flow rate, pressure, temperature, salinity of the water body to be tested and the inlet and outlet pressure difference of the membrane degassing unit.

11. The wide-range in-situ online monitoring method for dissolved carbon dioxide in water according to claim 1, characterized in that, The method is deployed on a shipborne mobile platform; the method further includes: acquiring the positioning information output by the positioning module, synchronously associating the timestamp, latitude and longitude and speed information with the measurement results of dissolved carbon dioxide, and generating a spatial distribution trajectory map of dissolved carbon dioxide in the water body.

12. A wide-range in-situ online monitoring system for dissolved carbon dioxide in water, characterized in that, include: A water pump is used to extract the water body to be tested. A membrane degassing unit, connected to the water pump, is used to transfer dissolved carbon dioxide in the water to be tested to the gas phase channel; The damping chamber has its air inlet connected to the membrane degassing unit. A cavity pressure control module, connected to the decay cavity, is used for closed-loop stable control of the air pressure in the decay cavity; The first laser source and the second laser source are used to provide laser signals of different measurement wavelengths, respectively; A polarization-maintaining wavelength division multiplexer is connected to the first laser source and the second laser source respectively, and is used to couple the two laser signals into the ring-down cavity. A wavelength demultiplexer, connected to the output end of the decaying cavity, is used to separate the output optical signal into a first wavelength channel and a second wavelength channel. The first detector and the second detector are respectively connected to the first wavelength channel and the second wavelength channel; and The data processing unit is configured to perform the method according to any one of claims 1 to 11.

13. The wide-range in-situ online monitoring system for dissolved carbon dioxide in water according to claim 12, characterized in that, The data processing unit includes a concentration inversion module, a range determination module, a channel quality assessment module, a consistency verification module, a mirror state assessment module, and a degassing efficiency correction module.

14. The wide-range in-situ online monitoring system for dissolved carbon dioxide in water according to claim 12, characterized in that, The first wavelength channel and the second wavelength channel share the decay cavity, the gas phase channel and the cavity pressure control module, and perform drift compensation on the inverted concentration result based on the collected common-mode interference parameters. The common-mode interference parameters include at least one of cavity pressure fluctuation residual and temperature drift parameters.

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