Seawater quality detector based on wide-band absorption spectrum and detection method

Abstract

The invention discloses a seawater quality detector based on a wide-band absorption spectrum and a detection method, and belongs to the technical field of spectral measurement and marine environment monitoring. According to the detector, a micro spectrometer is combined with a transmission-type optical measurement unit, and an absorption spectrum of a seawater sample in a broadband range is collected and analyzed, so that rapid detection and evaluation of seawater quality parameters are realized. The micro spectrometer comprises an optical fiber coupling interface, a slit piece, a collimating mirror, a plane diffraction blazed grating, a focusing mirror and a linear array photoelectric detector. Aiming at the characteristics of high salinity, high turbidity, strong bubble and scattering background and the like of seawater, the invention provides a data processing flow of reference channel / blank calibration, scattering correction, baseline drift correction and temperature compensation, and can adapt to samples with different turbidity through a cuvette / flow cell with a replaceable optical path. The device is small in size, low in cost, good in portability and suitable for offshore field monitoring, buoy / unmanned platform integration and mariculture water quality on-line monitoring.

Description

Technical Field

[0001] This invention relates to the field of spectral measurement and marine environmental monitoring, specifically to a seawater quality analyzer and detection method based on broadband absorption spectroscopy. Background Technology

[0002] Seawater quality monitoring is of great significance for marine ecological security, red tide early warning, mariculture, and port and nearshore environmental supervision. Seawater contains high concentrations of dissolved salt ions, abundant colloids and suspended particles, and dissolved organic matter such as humic substances, resulting in strong scattering background, significant baseline drift, and prominent bubble interference in optical detection, making stable measurement under field conditions quite difficult.

[0003] Spectroscopic detection technology utilizes the differences in absorption of light of different wavelengths by dissolved substances in water to achieve water quality analysis. Among them, absorption spectroscopy has advantages such as fast analysis speed, simple operation, non-destructive nature, and wide wavelength coverage. Ultraviolet-visible absorption spectroscopy is often used to analyze inorganic ions (such as nitrates and nitrites), organic matter (such as UV absorption caused by dissolved organic matter / humus), color, and some biologically related indicators in water.

[0004] Traditional commercial spectrometers are typically large, expensive, and complex, making them unsuitable for deployment at sea or on distributed platforms. Miniature spectrometers can achieve miniaturization and cost reduction while maintaining a certain level of accuracy, but they still present the following problems when directly used in seawater scenarios: (1) Seawater turbidity and scattering cause baseline drift in the absorption spectrum and a decrease in the signal-to-noise ratio; (2) Seawater samples are prone to generating bubbles during flow measurements, causing optical path obstruction and reading jumps; (3) Temperature changes cause drift in light source intensity, detector response, and water sample absorption characteristics; (4) Seawater samples with different concentration ranges have different optical path requirements, and a fixed optical path is difficult to meet the detection needs of both high turbidity and low concentration. Therefore, a broadband absorption spectrometer for complex seawater matrices is needed, which can balance miniaturization and engineering adaptability, and provide corresponding calibration and processing methods to improve on-site reliability. Summary of the Invention

[0005] This invention addresses the problems existing in the prior art by providing a seawater quality analyzer and detection method based on broadband absorption spectroscopy, thereby solving the problems of large equipment size, poor on-site adaptability, and measurement instability caused by seawater scattering / bubbles / temperature drift in existing seawater spectral detection methods.

[0006] To solve the above technical problems, the present invention provides the following technical solution: a seawater quality analyzer based on broadband absorption spectroscopy, comprising:

[0007] The system comprises a light source for emitting a light beam covering a predetermined wide wavelength range; a sample measurement unit for containing a seawater sample and allowing the light beam to pass through; a miniature spectrometer for dispersing the transmitted light and forming an absorption spectrum; and a data processing system for acquiring the spectrum and outputting seawater quality parameters. The miniature spectrometer's internal optical path adopts a cross-type Czerny-Turner structure and includes: a housing, an optical fiber coupling interface, a slit, a collimating mirror, a plane diffraction blazed grating, a focusing mirror, and a linear array photodetector. The light source introduces the light beam into the sample measurement unit via a first optical fiber. The light emitted from the sample measurement unit enters the miniature spectrometer via a second optical fiber and the optical fiber coupling interface. The light beam sequentially passes through the slit, collimating mirror, diffraction grating, and focusing mirror to form a spectral band on the focal plane, which is then acquired by the linear array photodetector.

[0008] Furthermore, the aforementioned wideband is at least one segment of the ultraviolet-visible-near infrared spectrum, preferably covering at least a portion of the 190-900 nm band.

[0009] Furthermore, the aforementioned light source is a xenon lamp, a deuterium lamp, a halogen tungsten lamp, a broadband LED light source, or a combination thereof, preferably a xenon lamp light source.

[0010] Furthermore, the aforementioned slit is located near the fiber optic coupling interface on the housing, and the surface of the slit is treated with oxidation and blackening; the slit width is replaceable or adjustable to optimize resolution while controlling light throughput.

[0011] Furthermore, the aforementioned fiber optic coupling interface is an SMA905 interface.

[0012] Furthermore, the aforementioned linear photodetector is a linear CCD or a linear CMOS detector, preferably a linear CCD.

[0013] Furthermore, the aforementioned diffraction grating is a planar scribed blazed grating, and the diffraction efficiency in a specific band is improved by selecting gratings with different scribed densities or blazed wavelengths.

[0014] Furthermore, the aforementioned sample measurement unit is a cuvette or a flow cell, and has a replaceable optical path; the optical path is 0.5 mm to 100 mm, preferably 1 mm to 50 mm, to adapt to seawater samples with different turbidity.

[0015] Furthermore, the aforementioned sample measurement unit includes an anti-bubble structure and / or a filter structure, wherein the anti-bubble structure includes one or more of an upper exhaust chamber, a guide slope, or a bypass exhaust channel.

[0016] Furthermore, the aforementioned data processing system includes a reference spectrum calibration and scattering correction algorithm. The algorithm includes at least the step of calculating the ratio of blank spectrum I0 to sample spectrum I to obtain the absorbance spectrum A(λ) = -log10(I / I0), and performing baseline correction on the scattering background caused by turbidity.

[0017] The present invention also provides a detection method using the aforementioned seawater quality analyzer based on broadband absorption spectroscopy, comprising the following steps:

[0018] Step 1: Obtain the blank reference spectrum: Pass the light beam through the blank medium and collect the reference spectrum I0(λ);

[0019] Step 2: Obtain the sample spectrum: Pass the light beam through the seawater sample and collect the sample spectrum I(λ);

[0020] Step 3: Calculate the absorption spectrum: Obtain the absorption spectrum based on A(λ) = -log10(I(λ) / I0(λ));

[0021] Step 4: Perform scattering / baseline correction and temperature compensation on the absorption spectrum, and output at least one seawater quality parameter.

[0022] Furthermore, the aforementioned seawater quality parameters include one or more of the following: nitrate, nitrite, dissolved organic matter / humus index, color, turbidity-related index, chlorophyll or algae-related spectral characteristic parameters.

[0023] Compared with the prior art, the beneficial technical effects of the present invention using the above technical solution are as follows:

[0024] 1. Miniaturization and low cost: It adopts a fiber-coupled miniature spectrometer, which is small in size and highly integrated, making it suitable for field and platform deployment.

[0025] 2. Wideband detection: Covers at least one band of ultraviolet-visible-near infrared, and can extract a variety of water quality-related spectral features.

[0026] 3. Seawater Adaptability: Improved measurement stability for complex seawater samples through replaceable optical path length, anti-bubble structure, and scattering / baseline correction algorithm.

[0027] 4. Scalable: It can be used in application scenarios such as buoys, unmanned vessels, and aquaculture sites, making it easy to form a distributed monitoring system. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the seawater quality testing process of the present invention.

[0029] Figure 2 This is a schematic diagram of the internal structure of a miniature spectrometer.

[0030] Figure 3 This is a schematic diagram of the sample measurement unit (cuvette / flow cell) coupled with the optical fiber.

[0031] Figure 4 This is a schematic diagram of the data processing flow. Detailed Implementation

[0032] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0033] In this invention, various aspects of the invention are described with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. Embodiments of the invention are not limited to those depicted in the drawings. It should be understood that the invention is implemented through any of the various concepts and embodiments described above, as well as the concepts and embodiments described in detail below, because the concepts and embodiments disclosed herein are not limited to any particular implementation. Furthermore, some aspects of the invention disclosed may be used alone or in any suitable combination with other aspects of the invention disclosed.

[0034] Example 1: Device Structure and Optical Path

[0035] like Figure 1 As shown, the broadband light emitted by the light source is incident on the sample measurement unit (cubic cuvette or flow cell) via the first optical fiber. The transmitted light is coupled into the miniature spectrometer via the second optical fiber, collected by the linear array detector, and then sent to the host computer or embedded processing module for analysis and output. Figure 2 As shown, the miniature spectrometer internally includes an optical fiber coupling interface, a slit, a collimating mirror, a diffraction grating, a focusing mirror, and a linear array detector. After being confined by the slit, the light beam is collimated by the collimating mirror and reflected to the grating. The grating decomposes the polychromatic light into monochromatic light of different wavelengths, which are then reflected to the focusing mirror. The focusing mirror focuses the different wavelengths at fixed intervals onto the focal plane to form spectral bands. The linear array detector then collects the wavelength-intensity information corresponding to different pixels.

[0036] Example 2: Seawater Sample Measurement Unit (Replaceable Optical Path, Anti-bubble)

[0037] like Figure 3 As shown, the sample measurement unit can adopt a flow cell structure with interchangeable optical paths (preferably 1 mm to 50 mm). When the seawater turbidity is high, a short optical path (e.g., 1 to 5 mm) is selected to avoid absorption saturation and excessive scattering; when the target concentration is low or higher sensitivity is required, a long optical path (e.g., 10 to 50 mm) is selected. The flow cell can be equipped with an exhaust chamber or bypass exhaust channel to reduce the influence of bubbles, and a filter membrane can be installed at the inlet to reduce particle entry.

[0038] Example 3: Detection Method and Data Processing

[0039] like Figure 4As shown, the following steps were used to perform broadband absorption spectroscopy detection of seawater:

[0040] Step 1, Blank calibration: Use deionized water or seawater with suspended particles removed as blank medium to collect reference spectrum I0(λ);

[0041] Step 2, Sample Measurement: Inject the seawater to be tested into a cuvette / flow cell and collect the sample spectrum I(λ);

[0042] Step 3, Absorbance Calculation: Calculate the absorption spectrum using A(λ) = -log10(I(λ) / I0(λ));

[0043] Step 4 Scattering / Baseline Correction: Baseline fitting and subtraction are performed on the absorption spectrum to reduce the influence of turbidity scattering;

[0044] Step 5, Temperature Compensation: Collect temperature data and compensate for light source intensity drift and detector response drift;

[0045] Step 6, Parameter Output: Output nitrate, nitrite, dissolved organic matter index, color / turbidity related index or algae related characteristic parameters based on characteristic band absorbance, spectral characteristics or model fitting.

[0046] While the present invention has been described above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A seawater quality analyzer based on broadband absorption spectroscopy, characterized in that, include: A light source used to emit a beam of light covering a predetermined wide wavelength band; The sample measurement unit is used to contain seawater samples and allow the light beam to pass through; a miniature spectrometer is used to disperse the transmitted light and form an absorption spectrum; a data processing system is used to acquire the spectrum and output seawater quality parameters; wherein, the internal optical path of the miniature spectrometer adopts a cross-type Czerny-Turner structure and includes: a shell, an optical fiber coupling interface, a slit, a collimating mirror, a plane diffraction blazed grating, a focusing mirror, and a linear array photodetector; the light source introduces the light beam into the sample measurement unit through a first optical fiber, and the light emitted from the sample measurement unit enters the miniature spectrometer through the optical fiber coupling interface via a second optical fiber. The light beam passes sequentially through the slit, collimating mirror, diffraction grating, and focusing mirror to form a spectral band on the focal plane and is acquired by the linear array photodetector.

2. The seawater quality analyzer based on broadband absorption spectroscopy as described in claim 1, characterized in that, The broadband band is at least one segment of the ultraviolet-visible-near infrared spectrum, preferably covering at least a portion of the 190–900 nm band.

3. The seawater quality analyzer based on broadband absorption spectroscopy as described in claim 1, characterized in that, The light source is a xenon lamp, a deuterium lamp, a halogen tungsten lamp, a broadband LED light source, or a combination thereof.

4. The seawater quality analyzer based on broadband absorption spectrum as described in claim 1, characterized in that, The slit is located near the fiber optic coupling interface on the outer shell, and the surface of the slit is treated with oxidation and blackening. The slit width is replaceable or adjustable to optimize resolution while controlling light throughput.

5. The seawater quality analyzer based on broadband absorption spectroscopy as described in claim 1, characterized in that, The diffraction grating is a planar scribed blazed grating, and the diffraction efficiency in a specific band can be improved by selecting gratings with different scribed densities or blazed wavelengths.

6. The seawater quality analyzer based on broadband absorption spectroscopy as described in claim 1, characterized in that, The sample measurement unit is a cuvette or a flow cell, and has a replaceable optical path; the optical path is 0.5 mm to 100 mm.

7. The seawater quality analyzer based on broadband absorption spectroscopy as described in claim 1, characterized in that, The sample measurement unit includes an anti-bubble structure and / or a filter structure, wherein the anti-bubble structure includes one or more of an upper exhaust chamber, a guide slope, or a bypass exhaust channel.

8. The seawater quality analyzer based on broadband absorption spectroscopy as described in claim 1, characterized in that, The data processing system includes a reference spectrum calibration and scattering correction algorithm. The algorithm includes at least the step of calculating the ratio of blank spectrum I0 to sample spectrum I, and performing baseline correction on the scattering background caused by turbidity.

9. A detection method using a seawater quality analyzer based on broadband absorption spectroscopy as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Obtain the blank reference spectrum: Pass the light beam through the blank medium and collect the reference spectrum I0(λ); Step 2: Obtain the sample spectrum: Pass the light beam through the seawater sample and collect the sample spectrum I(λ); Step 3: Calculate the absorption spectrum: Obtain the absorption spectrum based on A(λ) = -log10(I(λ) / I0(λ)); Step 4: Perform scattering / baseline correction and temperature compensation on the absorption spectrum, and output at least one seawater quality parameter.

10. The detection method as described in claim 9, characterized in that, The seawater quality parameters include one or more of the following: nitrate, nitrite, dissolved organic matter / humus index, color, turbidity-related index, chlorophyll or algae-related spectral characteristic parameters.

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