Seawater nitrate in-situ sensor, measurement data processing method thereof and calibration assembly

Abstract

The present application relates to nitrate sensor and its measurement data processing method, specifically relates to a kind of seawater nitrate in-situ sensor and its measurement data processing method, calibration assembly, to solve the long-term drift of existing technology, detection accuracy is not high and the deficiency of complex calibration process.The seawater nitrate in-situ sensor of the present application includes ultraviolet light source, beam splitter optical fiber, optical switch, connecting optical fiber and first collimating lens, beam splitter optical fiber is connected with ultraviolet light source, and forms measurement light path and reference light path;It also includes micro spectrometer and control unit, control unit is used to control the working state of optical switch, ultraviolet light source and micro spectrometer, and receives the measurement data of measurement light path and reference light path by micro spectrometer, analyzes and stores the measurement result;The present application also includes a kind of calibration assembly of seawater nitrate in-situ sensor, when calibration, can be placed in measurement light path by calibration assembly with ultrapure water, standard sample.

Description

Technical Field

[0001] This invention relates to nitrate sensors and their measurement data processing methods, specifically to an in-situ seawater nitrate sensor, its measurement data processing method, and calibration components. Background Technology

[0002] Nitrate is an essential nutrient for the reproduction and growth of marine organisms, and its content determination is one of the standard procedures for marine ecological and biogeochemical observations. In practical applications, by placing an in-situ nitrate sensor on a comprehensive oceanographic observation platform, in conjunction with other miniature, low-power physical, biological, and chemical sensors, six core variables, including nitrate, are measured to achieve marine ecological monitoring and marine biogeochemical analysis. Currently, the nitrate sensors commonly used on integrated oceanographic observation platforms rely on ultraviolet spectroscopy for in-situ monitoring of nitrates. However, their single-path structure cannot monitor changes in the ultraviolet light source and internal luminous flux, leading to severe sensor drift. Furthermore, subsequent data quality control and adjustments cannot be corrected using a single function. The sensor also employs multiple linear regression to establish a nitrate calibration model, which depends on pre-measured known component information and cannot effectively distinguish overlapping spectra. Therefore, the introduction of new components may result in poor fitting, affecting nitrate detection accuracy. The calibration process is complex, requiring the wrapping of a sealing film around the optical window, followed by a small hole in the top layer of the wrapping area to inject deionized water for updating the reference spectrum. The semi-transparent sealing film is susceptible to ambient light interference during measurement. Therefore, existing technologies suffer from long-term drift, low detection accuracy, and complex calibration procedures. Summary of the Invention

[0003] To address the shortcomings of existing technologies, such as long-term drift, low detection accuracy, and complex calibration procedures, this invention provides an in-situ seawater nitrate sensor, its measurement data processing method, and calibration components.

[0004] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0005] A seawater nitrate in-situ sensor, which is unique in that:

[0006] The system includes a first housing, a second housing, and a connector. Both the first and second housings are sealed structures and are connected by the connector. The first housing houses an ultraviolet light source, the emitting end of which is connected to the input end of a splitting fiber. The two output ends of the splitting fiber are sequentially connected to an optical switch, a connecting fiber, and a first collimating lens, forming a measurement optical path and a reference optical path. The second housing houses a miniature spectrometer and a control unit. The input end of the miniature spectrometer is connected to the output end of a combining fiber, and the two input ends of the combining fiber are each connected to a second collimating lens. The connector has a countersunk hole on its sidewall, forming an open flow cell. The open flow cell has a first through-hole and a second through-hole on its sidewall, respectively connecting the interiors of the first and second housings. The first and second through-holes are positioned opposite each other. The first and second through-holes each contain a first optical window and a second optical window. The first and second optical windows correspond to the first collimating lens and the second collimating lens of the measurement optical path, respectively. The first and second optical windows are sealed to the connector. A third through hole is provided in the connector, and the two ends of the third through hole are connected to the interior of the first housing and the interior of the second housing, respectively. A third optical window and a fourth optical window are respectively provided on the connector at both ends of the third through hole, and the third and fourth optical windows correspond to the first collimating lens and the other second collimating lens of the reference optical path, respectively. The control unit is connected to the miniature spectrometer and is connected to two optical switches and an ultraviolet light source located in the first housing through the fourth through hole provided on the connector. It is used to power the optical switches, the ultraviolet light source and the miniature spectrometer, control their working status, and receive and process the measurement data of the miniature spectrometer, and store the measurement data and processing results.

[0007] Furthermore, it also includes an antifouling component, which is a copper mesh, covering the opening of the open flow pool.

[0008] Furthermore, a first end cap and a second end cap are respectively provided at the ends of the first housing and the second housing away from the connector. A watertight connector is provided on the first end cap. The connecting wire at the inner end of the watertight connector passes through the first housing and the fourth through hole and connects to the control unit. The connecting wire at the outer end connects to the external observation platform.

[0009] Furthermore, it also includes two support components respectively disposed inside the first housing and the second housing. The ultraviolet light source, the splitting optical fiber, the two optical switches, the two connecting optical fibers, the combining optical fiber, the miniature spectrometer and the control unit are respectively fixed inside the first housing and the second housing through the support components.

[0010] Furthermore, an O-ring seal is provided at the connection between the first housing and the first end cap;

[0011] An O-ring seal is provided at the connection between the second housing and the second end cap;

[0012] O-ring seals are provided at the connection between the first housing and the connector, and at the connection between the second housing and the connector;

[0013] Both the first housing and the second housing are pressure-resistant housings;

[0014] The splitting fiber, connecting fiber, combining fiber, first collimating lens and second collimating lens are all made of quartz.

[0015] The first, second, third, and fourth optical windows are all made of quartz, fused silica, or sapphire.

[0016] Meanwhile, the present invention also provides a method for processing measurement data from an in-situ seawater nitrate sensor, which is characterized by including the following steps:

[0017] Step 1: Establish a calibration model for nitrate measurement.

[0018] 1.1 Measurement of Spectral Data of Ultrapure Water

[0019] Ultrapure water was placed in an open flow cell, and the dark spectral data I of the ultrapure water was measured using a miniature spectrometer. w_dark Reference spectral data I w_light and ultrapure water spectral data I w ;

[0020] 1.2 Spectral data of standard samples for measuring gradient concentration

[0021] Standard samples with different nitrate concentrations were set up in an open flow cell, and the dark spectral data of each standard sample were measured using a micro spectrometer. Reference spectral data and spectral data of each standard sample

[0022] 1.3 Based on ultrapure water spectral data I w Dark spectral data of ultrapure water I w_dark Reference spectral data I w_light and reference spectral data for each standard sample. Dark spectral data The calibration reference spectral data of each standard sample were calculated.

[0023] 1.4 Based on the spectral data of each standard sample Dark spectral data Calibration reference spectral data of corresponding standard samples The absorbance matrix of each standard sample was calculated.

[0024] 1.5 Utilizing the different concentrations of multiple sets of standard samples and their corresponding absorbance matrices A quantitative prediction model for seawater nitrate concentration was established based on partial least squares method:

[0025]

[0026] in, A represents the regression coefficient in the quantitative prediction model. Mes This is the absorbance matrix of the sample to be tested; The nitrate concentration of the sample to be tested is expressed in μmol / L.

[0027] Step 2: Measure the spectral data of the sample to be tested.

[0028] The sample to be tested was placed in an open flow cell, and the dark spectral data I of the sample was measured using a miniature spectrometer. Mes_dark Reference spectral data I Mes_light and the spectral data of the sample to be tested I Mes ;

[0029] Step 3: Calculate the nitrate concentration of the sample to be tested.

[0030] 3.1 Calculate calibration reference spectral data

[0031] Using the ultrapure water spectral data I from step 1 w Dark spectral data of ultrapure water I w_dark Reference spectral data Ix _light And the dark spectral data of the sample to be tested in step 2 I Mes_dark Reference spectral data I Mes_light The calibration reference spectral data I of the sample to be tested were obtained by calculation. Mes_ref ;

[0032] 3.2 Calculate the absorbance matrix of the sample to be tested.

[0033] Through the spectral data of the sample to be tested in step 2 I Mes Dark spectral data I Mes_dark And the calibration reference spectral data I from step 3.1 Mes_ref The absorbance matrix A of the sample to be tested was calculated. Mes ;

[0034] 3.3 The absorbance matrix A of the sample to be tested Mes Substituting these values ​​into the quantitative prediction model yields the nitrate concentration of the sample to be tested.

[0035] Further, in step 1.3, the calibration reference spectral data of the calibration sample The calculation formula is as follows:

[0036]

[0037] In step 1.4, the absorbance matrix of the standard sample The calculation formula is as follows:

[0038]

[0039] In step 3.1, the calibration reference spectral data I of the sample to be tested Mes_ref The calculation formula is as follows:

[0040]

[0041] In step 3.2, the absorbance matrix A of the sample to be tested Mes The calculation formula is as follows:

[0042]

[0043] In steps 1.1, 1.2, and 2, the micro spectrometer measures the data ten times and takes the average value as the final result.

[0044] Furthermore, in step 1.2, the standard samples with different nitrate concentrations are samples with concentration gradients prepared from low-nutrient seawater and superior pure nitrate standard solutions;

[0045] The nutrient-poor seawater is surface seawater with a nitrate concentration of <0.1 μmol / L, and is filtered through a 0.45 μm filter membrane.

[0046] Furthermore, the dark spectral data I of the ultrapure water in step 1.1 w_dark Dark spectral data of each standard sample in step 1.2 And the dark spectral data of the sample to be tested in step 2 I Mes_dark The measurement method is as follows:

[0047] Turn off the ultraviolet light source, turn on the optical switch of the measurement optical path, turn off the optical switch of the reference optical path, and measure the dark spectral data of ultrapure water, standard sample and test sample using a miniature spectrometer.

[0048] The reference spectral data I of ultrapure water in step 1.1 w_light Reference spectral data of each standard sample in step 1.2 Reference spectral data I of the sample to be tested in step 2 Mes_light The measurement method is as follows:

[0049] Turn on the ultraviolet light source, turn off the optical switch of the measurement optical path, turn on the optical switch of the reference optical path, and measure the reference spectral data of ultrapure water, standard sample and sample to be tested using a miniature spectrometer;

[0050] The ultrapure water spectral data I in step 1.1 w Spectral data of each standard sample in step 1.2 Step 2: Spectral data of the sample to be tested (I) Mes The measurement method is as follows:

[0051] Turn on the ultraviolet light source, turn on the optical switch of the measurement optical path, turn off the optical switch of the reference optical path, and measure the spectral data of ultrapure water, standard sample and sample to be tested using a miniature spectrometer.

[0052] Meanwhile, this invention also provides a calibration component for a seawater nitrate in-situ sensor used in the measurement data processing method of the seawater nitrate in-situ sensor, for setting ultrapure water in the open flow cell as described in step 1.1 and setting standard samples with different nitrate concentrations in the open flow cell as described in step 1.2. Its special feature is that:

[0053] The calibration component includes a housing with a fifth through hole. Both ends of the fifth through hole are provided with sealing rings. The side wall of the housing has a water inlet communicating with the fifth through hole, and a sealing plug is installed on the water inlet.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] 1. The seawater nitrate in-situ sensor of the present invention adopts a dual-optical-path transmission structure. No deionized water reference sample is placed in the reference optical path, which reduces the risk of changes in the internal light flux of the reference optical path due to deionized water pollution or deterioration.

[0056] 2. This invention proposes a nitrate measurement data processing method based on partial least squares. This method can update the background dark spectrum and calibration reference spectrum in real time when measuring the sample to be tested, and compensate for the influence caused by changes in the ultraviolet light source and the micro spectrometer. At the same time, it utilizes the characteristic of partial least squares to eliminate spectral collinearity, establishes a high-precision seawater nitrate concentration prediction model, and accurately inverts the nitrate concentration.

[0057] 3. The seawater nitrate in-situ sensor of the present invention is based on ultraviolet spectroscopy. It has a simple overall structure and is easy to deploy on a comprehensive oceanographic observation platform. When the shell pressure resistance reaches 22MPa, it can perform in-situ nitrate profile monitoring of seawater at a depth of 2000m. When the shell is made of low-pressure material and the pressure resistance reaches 1MPa, it can be used for in-situ nitrate monitoring in shallow water areas.

[0058] 4. The anti-fouling component of this invention, installed at the opening of the open flow cell of the nitrate sensor, effectively prevents biological adhesion near the optical window during long-term monitoring by releasing copper ions. At the same time, it can prevent large external particles from entering the open flow cell, damaging the optical window, and affecting the test results.

[0059] 5. The present invention uses a calibration component for a seawater nitrate sensor in calibration, which can conveniently and quickly calibrate and standardize the sensor. Attached Figure Description

[0060] Figure 1 This is a cross-sectional view of an embodiment of the seawater nitrate in-situ sensor of the present invention (the fourth through hole is not shown in the figure);

[0061] Figure 2 This is a three-dimensional structural schematic diagram of an embodiment of the seawater nitrate in-situ sensor of the present invention;

[0062] Figure 3 This is a schematic diagram of the external structure of an embodiment of the seawater nitrate in-situ sensor of the present invention;

[0063] Figure 4 This is a schematic diagram of the calibration component structure of the seawater nitrate sensor of the present invention;

[0064] Explanation of reference numerals in the attached figures:

[0065] 1-Second end cap, 2-O-ring, 3-Miniature spectrometer, 4-Support assembly, 5-Circuit control board, 6-Control unit, 7-Bundled fiber optic cable, 8-Connector, 91-First optical window, 92-Second optical window, 93-Third optical window, 94-Fourth optical window, 10-Second collimating lens, 11-Open flow cell, 12-First collimating lens, 13-Connecting fiber optic cable, 14-Optical switch, 15-Bundled fiber optic cable, 16-Ultraviolet light source, 17-First end cap, 18-Watertight connector, 19-Anti-fouling assembly, 20-First housing, 21-Second housing, 221-Outer shell, 222-Sealing plug, 223-Sealing ring. Detailed Implementation

[0066] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0067] The present invention provides an in-situ sensor for seawater nitrate, such as... Figures 1 to 2 As shown, the device includes a first housing 20, a second housing 21, and a connector 8. The first housing 20 and the second housing 21 are connected by the connector 8, and a first end cap 17 and a second end cap 1 are respectively provided at the end away from the connector 8. A watertight connector 18 is provided on the first end cap 17. An O-ring 2 is provided to seal the connection between the first housing 20 and the first end cap 17. An O-ring 2 is provided to seal the connection between the second housing 21 and the second end cap 1. An O-ring 2 is provided to seal the connection between the first housing 20 and the connector 8, and the connection between the second housing 21 and the connector 8. Both the first housing 20 and the second housing 21 are pressure-resistant housings.

[0068] The first housing 20 houses an ultraviolet light source 16, the emitting end of which is connected to the input end of a split fiber 15. The two output ends of the split fiber 15 are connected sequentially to an optical switch 14, a connecting fiber 13, and a first collimating lens 12, forming a measurement optical path and a reference optical path. The second housing 21 houses a miniature spectrometer 3 and a control unit 6. The input end of the miniature spectrometer 3 is connected to the output end of a bundled fiber 7, and the two input ends of the bundled fiber 7 are connected to a second collimating lens 10. The miniature spectrometer 3 and its circuit control board 5 are set separately, and the overall volume of the nitrate in-situ sensor is reduced through reasonable layout. The split fiber 15, the connecting fiber 13, the bundled fiber 7, the first collimating lens 12, and the second collimating lens 10 are all made of quartz.

[0069] The first housing 20 and the second housing 21 are respectively provided with support components 4. The ultraviolet light source 16, the split fiber 15, the two optical switches 14, the two connecting fibers 13, the bundled fiber 7, the miniature spectrometer 3, the circuit control board 5 and the control unit 6 are respectively fixed in the first housing 20 and the second housing 21 through the support components 4.

[0070] The sidewall of the connector 8 has a countersunk hole to form an open flow pool 11. The sidewall of the open flow pool 11 has a first through hole and a second through hole that respectively connect the interior of the first housing 20 and the interior of the second housing 21. The first through hole and the second through hole are arranged opposite to each other. The first through hole and the second through hole are respectively provided with a first optical window 91 and a second optical window 92. The first optical window 91 and the second optical window 92 correspond to the first collimating lens 12 and the second collimating lens 10 of the measurement optical path, respectively. The first optical window 91 and the second optical window 92 are respectively sealed to the connector 8. The first optical window 91, the second optical window 92, the third optical window 93 and the fourth optical window 94 are all made of quartz, fused silica or sapphire, and have high transmittance to ultraviolet light.

[0071] The connector 8 has a third through hole, and the two ends of the third through hole are respectively connected to the interior of the first housing 20 and the interior of the second housing 21. The connector 8 has a third optical window 93 and a fourth optical window 94 respectively located at the two ends of the third through hole. The third optical window 93 and the fourth optical window 94 correspond to the first collimating lens 12 and the other second collimating lens 10 of the reference optical path, respectively.

[0072] The connecting wire at the inner end of the watertight connector 18 passes through the fourth through hole provided on the first housing 20 and the connector 8 and connects to the control unit 6 for powering the control unit 6. The connecting wire at the outer end connects to the external observation platform. The control unit 6 is connected to the miniature spectrometer 3 and is connected to two optical switches 14 and an ultraviolet light source 16 located in the first housing 20 through the fourth through hole. It is used to power the optical switches 14, the ultraviolet light source 16 and the miniature spectrometer 3 and control their working status. At the same time, it receives the measurement data of the measurement optical path and the reference optical path through the miniature spectrometer 3, analyzes and stores the measurement results.

[0073] The open flow pool 11, the third through hole, and the fourth through hole are arranged to be mutually isolated; as follows: Figure 3 As shown, the opening of the open flow cell 11 is covered with a copper mesh as an antifouling component 19, which releases copper ions to effectively prevent biological adhesion near the optical window during long-term monitoring. At the same time, it can prevent large external particles from entering the open flow cell and damaging the optical window, thus affecting the test results.

[0074] The seawater nitrate in-situ sensor of this invention measures relevant spectra using a miniature spectrometer 3, and after further analysis, obtains the nitrate concentration. Before use, calibration is required to obtain a quantitative prediction model for seawater nitrate concentration. The sensor is then placed on an oceanographic observation platform and left in the deep sea for long-term in-situ nitrate monitoring. Based on the quantitative prediction model, the actual nitrate content is calculated from the measured spectral data. The specific usage method is as follows:

[0075] Step 1: Establish a calibration model for nitrate measurement.

[0076] 1.1 Measurement of Spectral Data of Ultrapure Water

[0077] Ultrapure water was placed in the open flow cell 11, and the dark spectral data I of the ultrapure water was measured by the micro spectrometer 3. w_dark Reference spectral data I w_light and ultrapure water spectral data I w ;

[0078] 1.2 Spectral data of standard samples for measuring gradient concentration

[0079] Standard samples with different nitrate concentrations were set up in the open flow cell 11, and the dark spectral data of each standard sample were measured by the micro spectrometer 3. Reference spectral data and spectral data of each standard sample

[0080] 1.3 Based on ultrapure water spectral data I w Dark spectral data of ultrapure water I w_dark Reference spectral data I w_lightand reference spectral data for each standard sample. Dark spectral data The calibration reference spectral data of each standard sample were calculated. The calculation formula is as follows:

[0081]

[0082] 1.4 Based on the spectral data of each standard sample Dark spectral data Calibration reference spectral data of corresponding standard samples The absorbance matrix of each standard sample was calculated. The calculation formula is as follows:

[0083]

[0084] 1.5 Utilizing the different concentrations of multiple sets of standard samples and their corresponding absorbance matrices A quantitative prediction model for seawater nitrate concentration was established based on partial least squares method:

[0085]

[0086] in, A represents the regression coefficient in the quantitative prediction model. Mes This is the absorbance matrix of the sample to be tested; The nitrate concentration of the sample to be tested is expressed in μmol / L.

[0087] Step 2: Measure the spectral data of the sample to be tested.

[0088] The sample to be tested is placed in the open flow cell 11, and the dark spectral data I of the sample is measured by the miniature spectrometer 3. Mes_dark Reference spectral data I Mes_lig ht and the spectral data of the sample to be tested I Mes ;

[0089] Step 3: Calculate the nitrate concentration of the sample to be tested.

[0090] 3.1 Calculate calibration reference spectral data

[0091] Using the ultrapure water spectral data I from step 1 w Dark spectral data of ultrapure water I w_dark Reference spectral data I w_light And the dark spectral data of the sample to be tested in step 2 I Mes_dark Reference spectral data I Mes_light The calibration reference spectral data I of the sample to be tested were obtained by calculation. Mes_ref The calculation formula is as follows:

[0092]

[0093] 3.2 Calculate the absorbance matrix of the sample to be tested.

[0094] Through the spectral data of the sample to be tested in step 2 I Mes Dark spectral data I Mes_dark And the calibration reference spectral data I from step 3.1 Mes_ref The absorbance matrix A of the sample to be tested was calculated. Mes The calculation formula is as follows:

[0095]

[0096] 3.3 The absorbance matrix A of the sample to be tested Mes Substituting these values ​​into the quantitative prediction model yields the nitrate concentration of the sample to be tested.

[0097] During the calibration process, a calibration assembly is used to place the ultrapure water from step 1.1 and the standard samples with different nitrate concentrations from step 1.2 into the open flow cell 11. The structure of the calibration assembly is as follows: Figure 4 As shown, the device includes a housing 221 with a fifth through hole. Sealing rings 223 are provided at both ends of the fifth through hole. A water inlet communicating with the fifth through hole is provided on the side wall of the housing 221, and a sealing plug 222 is installed on the water inlet. In use, the calibration assembly is placed in an open flow cell 11. The two ends of the fifth through hole are connected to the first optical window 91 and the second optical window 92 respectively through the sealing rings 223, forming a calibration cavity within the fifth through hole. The ultrapure water or standard sample is placed in the calibration cavity through the water inlet. In other embodiments of the invention, the seawater nitrate in-situ sensor can also be directly immersed in ultrapure water or standard samples of different nitrate concentrations, allowing the ultrapure water or standard samples of different nitrate concentrations to flow through the open flow cell 11. All other measurement steps remain the same.

[0098] The standard samples with different nitrate concentrations in step 1.2 are samples with concentration gradients prepared by mixing low-nutrient seawater with superior pure nitrate standard solution; the low-nutrient seawater is surface seawater with a nitrate concentration of <0.1μmol / L and filtered through a 0.45μm filter membrane.

[0099] The dark spectral data I of ultrapure water in step 1.1 w_dark Dark spectral data of each standard sample in step 1.2 And the dark spectral data of the sample to be tested in step 2 I Mes_dark The measurement method is as follows:

[0100] Turn off the ultraviolet light source 16, turn on the optical switch 14 of the measurement optical path, turn off the optical switch 14 of the reference optical path, and measure the dark spectral data of ultrapure water, standard sample and test sample through the miniature spectrometer 3.

[0101] The reference spectral data I of ultrapure water in step 1.1 w_light Reference spectral data of each standard sample in step 1.2 Reference spectral data I of the sample to be tested in step 2 Mes_light The measurement method is as follows:

[0102] Turn on the ultraviolet light source 16, turn off the optical switch 14 of the measurement optical path, turn on the optical switch 14 of the reference optical path, and measure the reference spectral data corresponding to ultrapure water, standard sample and sample to be tested through the miniature spectrometer 3.

[0103] The ultrapure water spectral data I in step 1.1 w Spectral data of each standard sample in step 1.2 Step 2: Spectral data of the sample to be tested (I) Mes The measurement method is as follows:

[0104] Turn on the ultraviolet light source 16, turn on the optical switch 14 of the measurement optical path and turn off the optical switch 14 of the reference optical path, and measure the spectral data of ultrapure water, standard sample and sample to be tested through the miniature spectrometer 3.

[0105] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A seawater nitrate in-situ sensor, characterized in that: The device includes a first housing (20), a second housing (21), and a connector (8). Both the first housing (20) and the second housing (21) are sealed structures. The first housing (20) and the second housing (21) are connected by the connector (8). The first end cap (17) and the second end cap (1) are respectively provided at the ends of the first housing (20) and the second housing (21) away from the connector (8). An ultraviolet light source (16) is provided inside the first housing (20). The emitting end of the ultraviolet light source (16) is connected to the input end of the split fiber (15). The two output ends of the split fiber (15) are respectively connected to the optical switch (14), the connecting fiber (13), and the first collimating lens (12) to form a measurement optical path and a reference optical path. The second housing (21) is equipped with a micro spectrometer (3) and a control unit (6). The input end of the micro spectrometer (3) is connected to the output end of the bundled fiber (7), and the two input ends of the bundled fiber (7) are respectively connected to a second collimating lens (10). The sidewall of the connector (8) is provided with a countersunk hole to form an open flow pool (11). The sidewall of the open flow pool (11) is provided with a first through hole and a second through hole that respectively connect the interior of the first housing (20) and the interior of the second housing (21). The first through hole and the second through hole are arranged opposite to each other. The first through hole and the second through hole are respectively provided with a first optical window (91) and a second optical window (92). The first optical window (91) and the second optical window (92) correspond to the first collimating lens (12) and a second collimating lens (10) of the measurement optical path, respectively. The first optical window (91) and the second optical window (92) are respectively sealed with the connector (8). The connector (8) has a third through hole, and the two ends of the third through hole are respectively connected to the interior of the first housing (20) and the interior of the second housing (21); the connector (8) has a third optical window (93) and a fourth optical window (94) respectively located at the two ends of the third through hole, and the third optical window (93) and the fourth optical window (94) correspond to the first collimating lens (12) and another second collimating lens (10) of the reference optical path respectively; The control unit (6) is connected to the micro spectrometer (3) and is connected to two optical switches (14) and an ultraviolet light source (16) located in the first housing (20) through the fourth through hole provided on the connector (8). It is used to power the optical switches (14), the ultraviolet light source (16) and the micro spectrometer (3), control their working status, and receive and process the measurement data of the micro spectrometer (3), and store the measurement data and processing results. O-rings (2) are provided for sealing at the connection between the first housing (20) and the first end cap (17), and at the connection between the second housing (21) and the second end cap (1); O-rings (2) are provided for sealing at the connection between the first housing (20) and the connector (8) and at the connection between the second housing (21) and the connector (8); Both the first housing (20) and the second housing (21) are pressure-resistant housings; The splitting fiber (15), connecting fiber (13), combining fiber (7), first collimating lens (12) and second collimating lens (10) are all made of quartz. The first optical window (91), the second optical window (92), the third optical window (93) and the fourth optical window (94) are all made of quartz, fused silica or sapphire. It also includes a contamination prevention component (19), which is a copper mesh covering the opening of the open flow pool (11).

2. The in-situ seawater nitrate sensor according to claim 1, characterized in that: A watertight connector (18) is provided on the first end cap (17). The connecting wire at the inner end of the watertight connector (18) passes through the first housing (20) and the fourth through hole to connect to the control unit (6) for powering the control unit (6). The connecting wire at the outer end is connected to the external observation platform.

3. The in-situ seawater nitrate sensor according to claim 1 or 2, characterized in that: It also includes two support components (4) respectively disposed inside the first housing (20) and the second housing (21). The ultraviolet light source (16), the split fiber (15), the two optical switches (14), the two connecting fibers (13), the bundled fiber (7), the micro spectrometer (3) and the control unit (6) are respectively fixed inside the first housing (20) and the second housing (21) by the support components (4).

4. A method for processing measurement data from a seawater nitrate in-situ sensor according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Establish a calibration model for nitrate measurement; Step 1.1: Measure the spectral data of ultrapure water; Ultrapure water was placed in an open flow cell (11), and the dark spectral data of the ultrapure water were measured by a micro spectrometer (3). Reference spectral data and ultrapure water spectral data ; Step 1.2: Measure the spectral data of standard samples with gradient concentrations; Standard samples with different nitrate concentrations were set up in an open flow cell (11), and the dark spectral data of each standard sample were measured by a micro spectrometer (3). Reference spectral data and spectral data of each standard sample. ; Step 1.3, based on the ultrapure water spectral data Dark spectral data of ultrapure water Reference spectral data and reference spectral data for each standard sample. Dark spectral data The calibration reference spectral data of each standard sample were calculated. ; Step 1.4, based on the spectral data of each standard sample Dark spectral data Calibration reference spectral data of corresponding standard samples The absorbance matrix of each standard sample was calculated. ; Step 1.5: Utilize the different concentrations of multiple sets of standard samples and their corresponding absorbance matrices. A quantitative prediction model for seawater nitrate concentration was established based on partial least squares method: ； in, These are the regression coefficients in the quantitative prediction model; This is the absorbance matrix of the sample to be tested; The nitrate concentration of the sample to be tested is expressed in μmol / L. Step 2: Measure the spectral data of the sample to be tested; The sample to be tested is placed in an open flow cell (11), and the dark spectral data of the sample to be tested is measured by a micro spectrometer (3). Reference spectral data and the spectral data of the sample to be tested. ; Step 3: Calculate the nitrate concentration of the sample to be tested; Step 3.1: Calculate the calibration reference spectral data; Using the ultrapure water spectral data from step 1 Dark spectral data of ultrapure water Reference spectral data Dark spectral data of the sample to be tested in step 2 Reference spectral data The calibration reference spectral data of the sample to be tested were calculated. ; Step 3.2: Calculate the absorbance matrix of the sample to be tested; Using the spectral data of the sample to be tested in step 2 Dark spectral data and the calibration reference spectral data from step 3.1 Calculate the absorbance matrix of the sample to be tested. ; Step 3.3: Calculate the absorbance matrix of the sample to be tested. Substituting these values ​​into the quantitative prediction model yields the nitrate concentration of the sample to be tested.

5. The data processing method for the in-situ seawater nitrate sensor according to claim 4, characterized in that: In step 1.3, the calibration reference spectral data of each standard sample The calculation formula is as follows: ； In step 1.4, the absorbance matrix of the standard sample The calculation formula is as follows: ； In step 3.1, the calibration reference spectral data of the sample to be tested... The calculation formula is as follows: ； In step 3.2, the absorbance matrix of the sample to be tested... The calculation formula is as follows: ； In steps 1.1, 1.2 and 2, the micro spectrometer (3) measures the data ten times and takes the average value as the final result.

6. The method for processing measurement data from the in-situ seawater nitrate sensor according to claim 5, characterized in that: In step 1.2, the standard samples with different nitrate concentrations are samples with concentration gradients prepared from low-nutrient seawater and superior pure nitrate standard solutions; The nutrient-poor seawater is surface seawater with a nitrate concentration of <0.1 μmol / L, and is filtered through a 0.45 μm filter membrane.

7. The method for processing measurement data from the in-situ seawater nitrate sensor according to any one of claims 4-6, characterized in that: Dark spectral data of ultrapure water in step 1.1 Dark spectral data of each standard sample in step 1.2 Dark spectral data of the sample to be tested in step 2 The measurement method is as follows: Turn off the ultraviolet light source (16), turn on the optical switch (14) of the measurement optical path, turn off the optical switch (14) of the reference optical path, and measure the dark spectral data of ultrapure water, standard sample and sample to be tested through the micro spectrometer (3); The reference spectral data of ultrapure water in step 1.1 Reference spectral data of each standard sample in step 1.2 Reference spectral data of the sample to be tested in step 2 The measurement method is as follows: Turn on the ultraviolet light source (16), turn off the light switch (14) of the measurement optical path, turn on the light switch (14) of the reference optical path, and measure the reference spectral data corresponding to ultrapure water, standard sample and sample to be tested through the micro spectrometer (3); The ultrapure water spectral data in step 1.1 Spectral data of each standard sample in step 1.2 Spectral data of the sample to be tested in step 2 The measurement method is as follows: Turn on the ultraviolet light source (16), turn on the optical switch (14) of the measurement optical path, turn off the optical switch (14) of the reference optical path, and measure the spectral data of ultrapure water, standard sample and sample to be tested through the micro spectrometer (3).

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