A multi-parameter synchronous detection method based on open optical and optical path compensation

Abstract

This invention belongs to the field of water quality optical detection technology and discloses a multi-parameter synchronous detection method based on open optics and optical path compensation. The invention constructs an open optical detection device, sets a minimum test cycle of 1 second, and completes signal acquisition in stages. The core utilizes a four-stage optical path compensation algorithm—source correction, turbidity separation, path attenuation compensation, and temperature correction—to sequentially complete source attenuation correction, turbidity scattering signal separation, transmittance calculation and temperature correction, and target signal attenuation compensation. Finally, it synchronously outputs parameters such as algae species and concentration, fluorescent dissolved organic matter, turbidity, transmittance, water temperature, and water pressure in the water body. This invention achieves in-situ real-time detection of multiple parameters in the same water body, with high detection accuracy, strong long-term stability, and good real-time performance, making it suitable for various water environment monitoring scenarios such as rivers, lakes, and oceans.

Description

Technical Field

[0001] This invention belongs to the field of water quality optical detection technology, specifically relating to a multi-parameter synchronous detection method based on open optics and optical path compensation. Background Technology

[0002] In the field of water environment monitoring, parameters such as algal species and concentration, fluorescent dissolved organic matter (FDOM) content, turbidity, and transmittance are core indicators reflecting the eutrophication level and ecological health status of water bodies, and are of great significance for water environment quality assessment and early warning of water ecological disasters. Existing bio-optical detection technologies have many shortcomings in practical applications, making it difficult to meet the requirements for high-precision, in-situ, and real-time multi-parameter synchronous detection. Specific problems include: 1) Structural enclosure issues: Most detection equipment uses a closed detection chamber, requiring water samples to be extracted during detection. This not only disrupts the natural flow state of the water body, but also makes it difficult to ensure that the detection objects for different parameters are the same water body, resulting in poor correlation and insufficient accuracy of the detection data, making it difficult to reflect the in-situ characteristics of the water body. 2) Complex and difficult-to-separate optical path interference: The photoelectric signals collected during the detection process contain multiple components such as algal fluorescence, FDOM fluorescence, turbidity scattered light, ambient light, and circuit noise. Existing technologies lack effective signal separation methods, making it impossible to accurately distinguish between target signals and interference signals, leading to significant detection errors in complex water environments. 3) Signal attenuation is not quantitatively compensated: When excitation light and fluorescence propagate in water, signal attenuation occurs due to absorption and scattering by the water. Existing methods do not quantitatively compensate for this attenuation based on water transmittance, leading to a sharp drop in detection accuracy in high-turbidity or high-chromatic water. 4) The impact of light source stability is ignored: LED light sources age over time, and current fluctuations during operation also cause changes in luminous intensity. Existing technologies lack a real-time correction mechanism for light source attenuation, resulting in poor long-term detection stability. 5) The interference of temperature on transmittance is not quantified: Temperature changes alter the physical properties of water, such as molecular motion rate and dissolved gas content, thus affecting transmittance measurement results. Existing methods do not establish a quantitative relationship between temperature and transmittance, and transmittance measurement errors further interfere with the accuracy of signal attenuation compensation.

[0003] Therefore, there is an urgent need to develop a bio-optical detection method that adopts an open structure, enables simultaneous detection of multiple parameters in the same water body, and has high-precision optical path attenuation compensation capability, in order to overcome the above-mentioned defects of existing technologies and improve the accuracy, real-time performance, and stability of multi-parameter detection in the water environment. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a multi-parameter synchronous detection method based on open optics and optical path compensation. This method enables synchronous detection of multiple parameters in the same water body, minimizes interference, provides end-to-end optical path compensation, and achieves high-precision signal extraction, thus meeting the requirements for in-situ real-time monitoring of the water environment.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A multi-parameter synchronous detection method based on open optics and optical path compensation includes the following steps: S1. Construct an open optical inspection device, which includes a ring-shaped LED excitation light source array, a light source attenuation correction unit, an optical window, a transmittance detection light source, a photomultiplier tube, a signal processing module, and an environmental parameter sensor. S2. Perform preliminary calibration on the open optical inspection equipment, complete the light source reference calibration, absolute transmittance reference calibration, temperature conversion coefficient and wavelength correction coefficient calibration, turbidity correction coefficient calibration, FDOM weighting factor calibration, and store all calibration parameters to the MCU. S3. Set 1 second as the minimum test cycle and perform signal and environmental parameter acquisition in stages; S4. The MCU executes a four-stage optical path compensation algorithm: light source correction, turbidity separation, path attenuation compensation, and temperature correction. This algorithm sequentially completes light source attenuation correction, turbidity scattering signal separation, transmittance calculation and temperature correction, and target signal attenuation compensation. The target signal includes FDOM fluorescence signal and algal fluorescence signal. S5. The data processed by the optical path compensation algorithm is used to simultaneously calculate and output parameters such as algae species and concentration, FDOM content, turbidity, light transmittance, water temperature, and water pressure in the water body, and store all parameters to a 32G SD card.

[0006] Preferably, in step S1, the annular LED excitation light source array consists of 15 LEDs with different center wavelengths, namely 350nm, 380nm, 400nm, 425nm, 435nm, 445nm, 455nm, 470nm, 505nm, 525nm, 550nm, 560nm, 590nm, 610nm, and 680nm; the light source attenuation correction unit consists of 15 photodiodes corresponding one-to-one with the LEDs, used to collect the back-side luminous intensity of the corresponding LEDs; the optical window is 2mm thick sapphire glass, coated with a hydrophobic and oleophobic coating on the outside and equipped with a silicone self-cleaning brush; the transmittance detection light source is the 16th LED with a wavelength of 680nm. The LED emits 1kHz modulated light and is fixed 220mm outside the optical window by a stainless steel bracket, with the center beam not directly aligned with the optical window axis. The photomultiplier tube is coaxially arranged with the ring LED excitation light source array and the optical window, and an OD6-level 680nm filter is installed at the front end. The signal processing module includes a 24-bit ADS1256 chip, an STM32F407 MCU, and a 32G SD card. The environmental parameter sensors include a water temperature sensor and a water pressure sensor.

[0007] Preferably, the preliminary calibration in step S2 specifically includes: S21. Light Source Reference Calibration: Before algae measurement, in a laboratory ultrapure water environment, the photodiode signals of 15 LEDs in brand-new condition are collected as the light source reference value. storage; S22. Absolute transmittance benchmark calibration: In air at 25°C, the transmittance signal of the 16th LED is collected and stored as the absolute transmittance benchmark value. S23. Calibration of Temperature Conversion Factor and Wavelength Correction Factor: Within the temperature range of 0–45℃, the relative transmittance of ultrapure water and different seawater samples was collected under varying temperatures. The conversion factor for the 680nm wavelength band at temperature t compared to 25℃ was calculated using a bivariate polynomial fitting method. and the corresponding temperature t The ratio of transmittance at wavelength to relative transmittance at 680nm ; S24. Turbidity Correction Coefficient Calibration: Prepare standard turbidity water bodies of 0~1000 NTU using ultrapure water, collect the ratio of the scattered signal at each wavelength to the scattered signal at 680 nm, and take the average value to obtain the turbidity correction coefficient. ; S25. FDOM Weighting Factor Calibration: In standard water bodies with known FDOM concentrations, calibration signals at wavelengths of 350nm, 400nm, and 425nm were collected respectively. The FDOM weighting factor was determined through multiple linear regression. And satisfy .

[0008] Preferably, in step S3, each test cycle is divided into four stages: Phase 1, lasting 50ms: Turn off all 16 LEDs, collect background signal D through photomultiplier tube, the background signal D is the superposition signal of ambient light and circuit noise, and at the same time, the second channel of ADS1256 chip collects the dark current of photodiode and simplifies it to 0; Phase 2, 750ms: Control 15 ring LEDs to emit light sequentially in ascending order of wavelength, each LED emitting light for 50ms and emitting 1kHz modulated light. Simultaneously, the raw signal output from the photomultiplier tube is acquired through channel 1 of the ADS1256 chip. The photodiode signal of the corresponding LED is acquired through the second channel. ; Phase 3, 50ms: The 16th LED is turned on, and the raw 680nm absolute transmittance signal T, with ultrapure water as a reference, is acquired through the first channel of the ADS1256 chip. abs,signa ; Phase 4, taking 150ms: Water temperature t and water pressure parameters are collected by water temperature sensor and water pressure sensor, and the MCU calls the previous calibration parameters and executes the optical path compensation algorithm.

[0009] Preferably, the specific process of step S4 is as follows: S41, Light source attenuation correction is achieved through real-time light source signal. relative to light source reference value The ratio of the light source attenuation coefficient is used to calculate the light source attenuation coefficient. The calculation formula is: , in, The light source attenuation coefficient; A coefficient between 0 and 1, used to compensate for light source attenuation caused by LED aging or current fluctuations; ∈350,380,400,425,435,445,455,470,505,525,550,560,590,610,680; S42. Turbidity Scattering Signal Separation: First, calculate the scattering signal using 680nm as the standard wavelength, then based on the turbidity correction coefficient... The formula for extrapolating scattered signals at other wavelengths is as follows: , , in, The scattered signal has a wavelength of 680nm; S 680 is the signal value obtained by the photomultiplier tube after the 680nm LED is excited; D is the background signal. The light source attenuation coefficient is for a wavelength of 680nm; for Scattered signal of wavelength; S43. Transmittance Calculation and Temperature Correction: First, calculate the absolute transmittance at 680nm at 25℃, then convert it to the corresponding transmittance at temperature t. The relative transmittance of a wavelength is calculated using the following formula: , , in, The absolute transmittance at 680 nm in ultrapure water at 25°C during transmittance algorithm correction; The light signal collected by the 16th LED in ultrapure water at 25°C during transmittance algorithm correction; The light signal collected by the 16th LED in air at 25°C during transmittance algorithm correction; This is the distance from the 16th LED to the center of the optical window; When measuring algae, the corresponding temperature t is... Transmittance at a given wavelength; S44. Target signal attenuation compensation is performed by distinguishing between FDOM fluorescence signal and algal fluorescence signal and correcting them separately. After deducting dark signal and turbidity scattering signal and correcting the light source, attenuation compensation is performed according to the different propagation paths of excitation light and fluorescence. FDOM fluorescence signal correction is performed for wavelengths of 350nm, 400nm, and 425nm. The correction steps are as follows: S441. Extract the raw FDOM signal: , in, for The original FDOM signal at the specified wavelength; S442. Perform attenuation compensation along the path. The excitation light path is 15mm, and the fluorescence path is 10mm. The FDOM correction signal is obtained as follows: , in, for The FDOM correction signal for the wavelength; The transmittance at a wavelength of 680 nm at temperature t is used to measure algae. S443, Based on FDOM weighting factor Weighted summation yields the total FDOM correction signal: , in, This is the total correction signal for the FDOM; Algal fluorescence signal correction targets 14 wavelengths: 350nm, 380nm, 400nm, 425nm, 435nm, 445nm, 455nm, 470nm, 505nm, 525nm, 550nm, 560nm, 590nm, and 610nm. The correction steps are as follows: S444. Extracting raw fluorescence signals from algae: , in, for The original fluorescence signal of algae at a specific wavelength; S445. Attenuation compensation is performed according to the path. The excitation light path is 15mm and the fluorescence path is 10mm, resulting in the algal corrected fluorescence signal: , in, for Algal-corrected fluorescence signals at specific wavelengths.

[0010] Preferably, the turbidity parameter in step S5 is determined by a 680nm scattering signal. The algae species and concentration were obtained by fitting a calibration curve of turbidity gradient from 0 to 1000 NTU and converting the result using an algae-corrected fluorescence signal. The FDOM content was obtained by combining the algae calibration curve fitting function; the FDOM content was derived from the total FDOM correction signal. It is obtained by combining the FDOM calibration curve fitting function.

[0011] Preferably, in step S1, the inner diameter of the annular LED excitation light source array is 30mm, the outer diameter is 50mm, the LED spacing is uniform at 24°, and each LED is at a 45° angle to the coaxial line; the diameter of the optical window is 60mm, and the transmittance of the sapphire glass in the 300~700nm wavelength band is ≥95%; the photomultiplier tube is model H10722, the cathode photosensitiveness is 205μA / lm, and the operating voltage is ±5V; the transmittance of the 680nm filter is 90%, the half bandwidth is 10nm, and the wavelength band is 675~685nm.

[0012] Preferably, during the signal acquisition process in step S3, the median algorithm is used to extract the raw data acquired by the ADS1256 chip to reduce signal interference.

[0013] Preferably, the parameters output in step S5 can be uploaded via RS485 or serial-to-USB to achieve remote data transmission.

[0014] By adopting the above technical solution, the present invention has the following beneficial effects: 1. This invention adopts an open structure without a closed detection chamber. It directly contacts the water body during detection without interfering with the natural state of water flow. Moreover, all parameters are detected based on the same water body, resulting in high correlation and authenticity of the data. It can accurately reflect the in-situ characteristics of the water body and realize synchronous detection of multiple parameters in the same water body.

[0015] 2. Under the premise of avoiding overexposure, this invention effectively separates algal fluorescence, FDOM fluorescence from ambient light, circuit noise, turbidity scattered light and other interference signals by wavelength-sequential excitation, background signal subtraction and precise separation of turbidity scattered light, which greatly improves the signal-to-noise ratio of the detection signal. At the same time, based on the Lambert-Beer law, it realizes the path difference attenuation quantization compensation of excitation light and fluorescence, which reduces the detection error in high turbidity and high color water, improves the detection accuracy and effectively separates various interferences.

[0016] 3. This invention establishes a quantitative relationship between temperature and transmittance, through... and Temperature correction for transmittance effectively reduces the interference of temperature changes on transmittance measurement and signal attenuation compensation, further improving detection accuracy. LED excitation light with different characteristic wavelengths is adapted to the fluorescence characteristics of different algae, providing high-quality original fluorescence signals for distinguishing algae species and concentrations, enabling accurate detection of various algae. In addition, the minimum test cycle is only 1 second, enabling in-situ real-time detection and output of multiple parameters, accurately capturing parameter changes in dynamic water environments, and meeting the monitoring needs of dynamic water environments such as rivers, lakes, and oceans. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] like Figure 1 As shown, a multi-parameter synchronous detection method based on open optics and optical path compensation includes the following steps: S1. Construct an open optical inspection device, which includes a ring-shaped LED excitation light source array, a light source attenuation correction unit, an optical window, a transmittance detection light source, a photomultiplier tube, a signal processing module, and an environmental parameter sensor. In step S1, the ring-shaped LED excitation light source array consists of 15 LEDs with different center wavelengths: 350nm, 380nm, 400nm, 425nm, 435nm, 445nm, 455nm, 470nm, 505nm, 525nm, 550nm, 560nm, 590nm, 610nm, and 680nm. The light source attenuation correction unit consists of 15 photodiodes corresponding to each LED, used to collect the back-side luminous intensity of the corresponding LED. The optical window is made of 2mm thick sapphire glass, coated with a hydrophobic and oleophobic coating on the outside, and equipped with a silicone self-cleaning brush. The transmittance detection light source is the 16th LED with a wavelength of 680nm. An LED emits 1kHz modulated light and is fixed 220mm outside the optical window by a stainless steel bracket, with the center beam not directly aligned with the optical window's axis. A photomultiplier tube is coaxially arranged with the ring-shaped LED excitation light source array and the optical window, and an OD6-grade 680nm filter is mounted at its front end. The signal processing module includes a 24-bit ADS1256 chip, an STM32F407 MCU, and a 32GB SD card. The environmental parameter sensors include a water temperature sensor and a water pressure sensor. In step S1, the inner diameter of the ring-shaped LED excitation light source array is 30mm, the outer diameter is 50mm, the LED spacing is uniform at 24°, and each LED is at a 45° angle to the coaxial line; the diameter of the optical window is 60mm, and the transmittance of the sapphire glass in the 300~700nm wavelength band is ≥95%; the photomultiplier tube is model H10722, the cathode photosensitiveness is 205μA / lm, and the operating voltage is ±5V; the transmittance of the 680nm filter is 90%, the half bandwidth is 10nm, and the wavelength band is 675~685nm; S2. Perform preliminary calibration on the open optical inspection equipment, complete the light source reference calibration, absolute transmittance reference calibration, temperature conversion coefficient and wavelength correction coefficient calibration, turbidity correction coefficient calibration, FDOM weighting factor calibration, and store all calibration parameters to the MCU. The preliminary calibration in step S2 specifically includes: S21. Light Source Reference Calibration: Before algae measurement, in a laboratory ultrapure water environment, the photodiode signals of 15 LEDs in brand-new condition are collected as the light source reference value. storage; S22. Absolute transmittance benchmark calibration: In air at 25°C, the transmittance signal of the 16th LED is collected and stored as the absolute transmittance benchmark value. S23. Calibration of Temperature Conversion Factor and Wavelength Correction Factor: Within the temperature range of 0–45℃, the relative transmittance of ultrapure water and different seawater samples was collected under varying temperatures. The conversion factor for the 680nm wavelength band at temperature t compared to 25℃ was calculated using a bivariate polynomial fitting method. and the corresponding temperature t The ratio of transmittance at wavelength to relative transmittance at 680nm ; S24. Turbidity Correction Coefficient Calibration: Prepare standard turbidity water bodies of 0~1000 NTU using ultrapure water, collect the ratio of the scattered signal at each wavelength to the scattered signal at 680 nm, and take the average value to obtain the turbidity correction coefficient. ; S25. FDOM Weighting Factor Calibration: In standard water bodies with known FDOM concentrations, calibration signals at wavelengths of 350nm, 400nm, and 425nm were collected respectively. The FDOM weighting factor was determined through multiple linear regression. And satisfy ; S3. Set 1 second as the minimum test cycle and perform signal and environmental parameter acquisition in stages; In step S3, each test cycle is divided into four phases: Phase 1, lasting 50ms: Turn off all 16 LEDs, collect background signal D through photomultiplier tube, the background signal D is the superposition signal of ambient light and circuit noise, and at the same time, the second channel of ADS1256 chip collects the dark current of photodiode and simplifies it to 0; Phase 2, 750ms: Control 15 ring LEDs to emit light sequentially in ascending order of wavelength, each LED emitting light for 50ms and emitting 1kHz modulated light. Simultaneously, the raw signal output from the photomultiplier tube is acquired through channel 1 of the ADS1256 chip. The photodiode signal of the corresponding LED is acquired through the second channel. ; Phase 3, 50ms: The 16th LED is turned on, and the raw 680nm absolute transmittance signal T, with ultrapure water as a reference, is acquired through the first channel of the ADS1256 chip. abs,signa ; Phase 4, lasting 150ms: Water temperature t and water pressure parameters are collected by water temperature sensor and water pressure sensor, and the MCU calls the previous calibration parameters and executes the optical path compensation algorithm; During the signal acquisition process in step S3, the median algorithm is used to extract the raw data acquired by the ADS1256 chip in order to reduce signal interference. S4. The MCU executes a four-stage optical path compensation algorithm: light source correction, turbidity separation, path attenuation compensation, and temperature correction. This algorithm sequentially completes light source attenuation correction, turbidity scattering signal separation, transmittance calculation and temperature correction, and target signal attenuation compensation. The target signal includes FDOM fluorescence signal and algal fluorescence signal. The specific process of step S4 is as follows: S41, Light source attenuation correction is achieved through real-time light source signal. relative to light source reference value The ratio of the light source attenuation coefficient is used to calculate the light source attenuation coefficient. The calculation formula is: , in, The light source attenuation coefficient; A coefficient between 0 and 1, used to compensate for light source attenuation caused by LED aging or current fluctuations; ∈350,380,400,425,435,445,455,470,505,525,550,560,590,610,680; S42. Turbidity Scattering Signal Separation: First, calculate the scattering signal using 680nm as the standard wavelength, then based on the turbidity correction coefficient... The formula for extrapolating scattered signals at other wavelengths is as follows: , , in, The scattered signal has a wavelength of 680nm; S 680 is the signal value obtained by the photomultiplier tube after the 680nm LED is excited; D is the background signal. The light source attenuation coefficient is for a wavelength of 680nm; for Scattered signal of wavelength; S43. Transmittance Calculation and Temperature Correction: First, calculate the absolute transmittance at 680nm at 25℃, then convert it to the corresponding transmittance at temperature t. The relative transmittance of a wavelength is calculated using the following formula: , , in, The absolute transmittance at 680 nm in ultrapure water at 25°C during transmittance algorithm correction; The light signal collected by the 16th LED in ultrapure water at 25°C during transmittance algorithm correction; The light signal collected by the 16th LED in air at 25°C during transmittance algorithm correction; This is the distance from the 16th LED to the center of the optical window; When measuring algae, the corresponding temperature t is... Transmittance at a given wavelength; S44. Target signal attenuation compensation is performed by distinguishing between FDOM fluorescence signal and algal fluorescence signal and correcting them separately. After deducting dark signal and turbidity scattering signal and correcting the light source, attenuation compensation is performed according to the different propagation paths of excitation light and fluorescence. FDOM fluorescence signal correction is performed for wavelengths of 350nm, 400nm, and 425nm. The correction steps are as follows: S441. Extract the raw FDOM signal: , in, for The original FDOM signal at the specified wavelength; S442. Perform attenuation compensation along the path. The excitation light path is 15mm, and the fluorescence path is 10mm. The FDOM correction signal is obtained as follows: , in, for The FDOM correction signal for the wavelength; The transmittance at a wavelength of 680 nm at temperature t is used to measure algae. S443, Based on FDOM weighting factor Weighted summation yields the total FDOM correction signal: , in, This is the total correction signal for the FDOM; Algal fluorescence signal correction targets 14 wavelengths: 350nm, 380nm, 400nm, 425nm, 435nm, 445nm, 455nm, 470nm, 505nm, 525nm, 550nm, 560nm, 590nm, and 610nm. The correction steps are as follows: S444. Extracting raw fluorescence signals from algae: , in, for The original fluorescence signal of algae at a specific wavelength; S445. Attenuation compensation is performed according to the path. The excitation light path is 15mm and the fluorescence path is 10mm, resulting in the algal corrected fluorescence signal: , in, for Algal-corrected fluorescence signals at specific wavelengths; S5. The data processed by the optical path compensation algorithm is used to simultaneously calculate and output parameters such as algae species and concentration, FDOM content, turbidity, light transmittance, water temperature, and water pressure in the water body, and store all parameters to a 32G SD card. The turbidity parameter in step S5 is determined by the 680nm scattering signal. The algae species and concentration were obtained by fitting a calibration curve of turbidity gradient from 0 to 1000 NTU and converting the result using an algae-corrected fluorescence signal. The FDOM content was obtained by combining the algae calibration curve fitting function; the FDOM content was derived from the total FDOM correction signal. It was obtained by combining the FDOM calibration curve fitting function; The parameters output in step S5 can be uploaded via RS485 or serial-to-USB to achieve remote data transmission.

[0020] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-parameter synchronous detection method based on open optics and optical path compensation, characterized in that, Includes the following steps: S1. Construct an open optical inspection device, which includes a ring-shaped LED excitation light source array, a light source attenuation correction unit, an optical window, a transmittance detection light source, a photomultiplier tube, a signal processing module, and an environmental parameter sensor. S2. Perform preliminary calibration on the open optical inspection equipment, complete the light source reference calibration, absolute transmittance reference calibration, temperature conversion coefficient and wavelength correction coefficient calibration, turbidity correction coefficient calibration, FDOM weighting factor calibration, and store all calibration parameters to the MCU. S3. Set 1 second as the minimum test cycle and perform signal and environmental parameter acquisition in stages; S4. The MCU executes a four-stage optical path compensation algorithm: light source correction, turbidity separation, path attenuation compensation, and temperature correction. This algorithm sequentially completes light source attenuation correction, turbidity scattering signal separation, transmittance calculation and temperature correction, and target signal attenuation compensation. The target signal includes FDOM fluorescence signal and algal fluorescence signal. S5. The data processed by the optical path compensation algorithm is used to simultaneously calculate and output parameters such as algae species and concentration, FDOM content, turbidity, light transmittance, water temperature, and water pressure in the water body, and store all parameters to a 32G SD card.

2. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 1, characterized in that: In step S1, the ring-shaped LED excitation light source array consists of 15 LEDs with different center wavelengths, namely 350nm, 380nm, 400nm, 425nm, 435nm, 445nm, 455nm, 470nm, 505nm, 525nm, 550nm, 560nm, 590nm, 610nm, and 680nm; the light source attenuation correction unit consists of 15 photodiodes corresponding one-to-one with the LEDs, used to collect the back-side luminous intensity of the corresponding LEDs; The optical window is made of 2mm thick sapphire glass, coated with a hydrophobic and oleophobic layer on the outside, and equipped with a silicone self-cleaning brush. The transmittance detection light source is the 16th 680nm LED, emitting 1kHz modulated light, which is fixed 220mm outside the optical window by a stainless steel bracket, with the central beam not directly aligned with the optical window axis. The photomultiplier tube is coaxially arranged with the ring LED excitation light source array and the optical window, and an OD6-level 680nm filter is installed at the front end. The signal processing module includes a 24-bit ADS1256 chip, an STM32F407 MCU, and a 32G SD card. The environmental parameter sensors include a water temperature sensor and a water pressure sensor.

3. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 2, characterized in that, The preliminary calibration in step S2 specifically includes: S21. Light Source Reference Calibration: Before algae measurement, in a laboratory ultrapure water environment, the photodiode signals of 15 LEDs in brand-new condition are collected as the light source reference value. storage; S22. Absolute transmittance benchmark calibration: In air at 25°C, the transmittance signal of the 16th LED is collected and stored as the absolute transmittance benchmark value. S23. Calibration of Temperature Conversion Factor and Wavelength Correction Factor: Within the temperature range of 0–45℃, the relative transmittance of ultrapure water and different seawater samples was collected under varying temperatures. The conversion factor for the 680nm wavelength band at temperature t compared to 25℃ was calculated using a bivariate polynomial fitting method. and the corresponding temperature t The ratio of transmittance at wavelength to relative transmittance at 680nm ; S24. Turbidity Correction Coefficient Calibration: Prepare standard turbidity water bodies of 0~1000 NTU using ultrapure water, collect the ratio of the scattered signal at each wavelength to the scattered signal at 680 nm, and take the average value to obtain the turbidity correction coefficient. ; S25. FDOM Weighting Factor Calibration: In standard water bodies with known FDOM concentrations, calibration signals at wavelengths of 350nm, 400nm, and 425nm were collected respectively. The FDOM weighting factor was determined through multiple linear regression. And satisfy .

4. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 3, characterized in that, In step S3, each test cycle is divided into four phases: Phase 1, lasting 50ms: Turn off all 16 LEDs, collect background signal D through photomultiplier tube, the background signal D is the superposition signal of ambient light and circuit noise, and at the same time, the second channel of ADS1256 chip collects the dark current of photodiode and simplifies it to 0; Phase 2, 750ms: Control 15 ring LEDs to emit light sequentially in ascending order of wavelength, each LED emitting light for 50ms and emitting 1kHz modulated light. Simultaneously, the raw signal output from the photomultiplier tube is acquired through channel 1 of the ADS1256 chip. The photodiode signal of the corresponding LED is acquired through the second channel. ; Phase 3, 50ms: The 16th LED is turned on, and the raw 680nm absolute transmittance signal T, with ultrapure water as a reference, is acquired through the first channel of the ADS1256 chip. abs,signa ; Phase 4, taking 150ms: Water temperature t and water pressure parameters are collected by water temperature sensor and water pressure sensor, and the MCU calls the previous calibration parameters and executes the optical path compensation algorithm.

5. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 4, characterized in that, The specific process of step S4 is as follows: S41, Light source attenuation correction is achieved through real-time light source signal. relative to light source reference value The ratio of the light source attenuation coefficient is used to calculate the light source attenuation coefficient. The calculation formula is: ， in, The light source attenuation coefficient; A coefficient between 0 and 1, used to compensate for light source attenuation caused by LED aging or current fluctuations; ∈350,380,400,425,435,445,455,470,505,525,550,560,590,610,680； S42. Turbidity Scattering Signal Separation: First, calculate the scattering signal using 680nm as the standard wavelength, then based on the turbidity correction coefficient... The formula for extrapolating scattered signals at other wavelengths is as follows: ， ， in, The scattered signal has a wavelength of 680nm; S 680 is the signal value obtained by the photomultiplier tube after the 680nm LED is excited; D is the background signal. The light source attenuation coefficient is for a wavelength of 680nm; for Scattered signal of wavelength; S43. Transmittance Calculation and Temperature Correction: First, calculate the absolute transmittance at 680nm at 25℃, then convert it to the corresponding transmittance at temperature t. The relative transmittance of a wavelength is calculated using the following formula: ， ， in, The absolute transmittance at 680 nm in ultrapure water at 25°C during transmittance algorithm correction; The light signal collected by the 16th LED in ultrapure water at 25°C during transmittance algorithm correction; The light signal collected by the 16th LED in air at 25°C during transmittance algorithm correction; This is the distance from the 16th LED to the center of the optical window; When measuring algae, the corresponding temperature t is... transmittance at a given wavelength; S44. Target signal attenuation compensation is performed by distinguishing between FDOM fluorescence signal and algal fluorescence signal and correcting them separately. After deducting dark signal and turbidity scattering signal and correcting the light source, attenuation compensation is performed according to the different propagation paths of excitation light and fluorescence. FDOM fluorescence signal correction is performed for wavelengths of 350nm, 400nm, and 425nm. The correction steps are as follows: S441. Extract the raw FDOM signal: ， in, for The original FDOM signal at the specified wavelength; S442. Perform attenuation compensation along the path. The excitation light path is 15mm, and the fluorescence path is 10mm, resulting in the FDOM correction signal: ， in, for The FDOM correction signal for the wavelength; The transmittance at a wavelength of 680 nm at temperature t is used to measure algae. S443, Based on FDOM weighting factor Weighted summation yields the total FDOM correction signal: ， in, This is the total correction signal for the FDOM; Algal fluorescence signal correction targets 14 wavelengths: 350nm, 380nm, 400nm, 425nm, 435nm, 445nm, 455nm, 470nm, 505nm, 525nm, 550nm, 560nm, 590nm, and 610nm. The correction steps are as follows: S444. Extracting raw fluorescence signals from algae: ， in, for The original fluorescence signal of algae at a specific wavelength; S445. Attenuation compensation is performed according to the path. The excitation light path is 15mm and the fluorescence path is 10mm, resulting in the algal corrected fluorescence signal: ， in, for Algal-corrected fluorescence signals at specific wavelengths.

6. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 5, characterized in that: The turbidity parameter in step S5 is determined by the 680nm scattering signal. The algae species and concentration were obtained by fitting a calibration curve of turbidity gradient from 0 to 1000 NTU and converting the result using an algae-corrected fluorescence signal. It was obtained by combining the fitting function of the algae calibration curve; FDOM content is determined by the total FDOM correction signal. It is obtained by combining the FDOM calibration curve fitting function.

7. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 2, characterized in that: In step S1, the inner diameter of the ring-shaped LED excitation light source array is 30mm, the outer diameter is 50mm, the LED spacing is uniform at 24°, and each LED is at a 45° angle to the coaxial line; the diameter of the optical window is 60mm, and the transmittance of the sapphire glass in the 300~700nm wavelength band is ≥95%; the photomultiplier tube is model H10722, the cathode photosensitiveness is 205μA / lm, and the operating voltage is ±5V; the transmittance of the 680nm filter is 90%, the half bandwidth is 10nm, and the wavelength band is 675~685nm.

8. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 1, characterized in that: In the signal acquisition process of step S3, the median algorithm is used to extract the raw data acquired by the ADS1256 chip to reduce signal interference.

9. The multi-parameter synchronous detection method based on open optics and optical path compensation as described in claim 1, characterized in that: The parameters output in step S5 can be uploaded via RS485 or serial-to-USB to achieve remote data transmission.

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