Linked calibration measurement method for water turbidity and chlorophyll a concentration based on spectral technology

Abstract

The invention discloses a method for calibrating and measuring the turbidity of a water body and the concentration of chlorophyll a based on spectral technology. The method comprises the following steps: a spectral probe and a light emitted by a light source are at 90 degrees, the light source emits and irradiates the water body, and the turbidity of the water body is measured based on the intensity of scattered light: the spectral probe collects the scattered light, and the proportional relationship between the intensity of scattered light and the turbidity is used to calculate the corresponding turbidity of the water body by measuring the intensity of scattered light; the chlorophyll a concentration is measured based on the intensity of fluorescent light: the spectral probe collects the intensity of fluorescent light, and the proportional relationship between the intensity of fluorescent light and the concentration of chlorophyll a is used to calculate the corresponding concentration of chlorophyll a by measuring the intensity of fluorescence; the chlorophyll a concentration value is calibrated by the turbidity value: the turbidity value is calibrated by the chlorophyll a concentration value: the invention realizes the function of dual measurement of one probe, and improves the measurement accuracy and efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of spectral information processing calibration, and in particular to a spectral technology-based linkage calibration measurement method for water turbidity and chlorophyll a concentration. Background Art

[0002] Spectral detection has the advantages of being fast, accurate, and non-destructive. In addition, due to its compact structure and low power consumption, it is very suitable for unattended real-time monitoring applications. At present, there are many detection devices based on spectral technology that have been applied to the real-time monitoring of various indicators of water bodies, such as water turbidity monitoring based on scattered light intensity and water chlorophyll a concentration monitoring based on fluorescence intensity. However, the products on the market often use a single wavelength light source combined with a single-point single-wavelength light probe to measure a certain parameter index. At present, there are no products that can measure multiple indicators with one probe. Therefore, in multi-indicator measurement projects, a large number of probes are often matched. More importantly, the current spectral-based water quality detection technology and products on the market lack relevant methods to resist environmental interference, and spectral detection is very susceptible to the influence of the external environment. For example, the turbidity of the water body, the incident angle and intensity of sunlight, etc., have a serious impact on the spectral measurement results, resulting in abnormal detection results. Summary of the invention

[0003] In order to overcome the defects and shortcomings of the prior art, the present invention provides a water turbidity and chlorophyll a concentration linkage calibration measurement method based on spectral technology. According to the technical characteristics of measuring water turbidity and chlorophyll a concentration based on spectral intensity, two semiconductor lasers with different wavelengths are used as light sources, and a wide-band spectral probe is used. Through mutual calibration and linkage measurement of parameters, the integrated measurement of turbidity and chlorophyll a concentration is realized, which overcomes the disadvantage that spectral detection is easily affected by the external environment, so that the spectral-based water turbidity and chlorophyll a concentration measurement can be effectively applied to outdoor water bodies, realizing unattended real-time monitoring.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for measuring the linkage calibration of water turbidity and chlorophyll a concentration based on spectral technology, comprising the following steps:

[0006] Set the spectrum probe at 90 degrees to the light emitted by the light source, and the light source shines on the water body;

[0007] Water turbidity measurement based on scattered light intensity: The spectral probe collects scattered light, and uses the proportional relationship between scattered light intensity and turbidity to calculate the corresponding water turbidity by measuring the intensity of scattered light;

[0008] Chlorophyll a concentration measurement based on fluorescence intensity: The spectral probe collects fluorescence intensity, and uses the proportional relationship between fluorescence intensity and chlorophyll a concentration to calculate the corresponding chlorophyll a concentration by measuring the intensity of fluorescence;

[0009] Calibrate the chlorophyll a concentration value by turbidity value: set the attenuation coefficient of fluorescence corresponding to turbidity, preset the chlorophyll a concentration, adjust the turbidity, obtain the corresponding chlorophyll a concentration calculation value based on fluorescence intensity measurement, find the corresponding attenuation coefficient by turbidity, and obtain the calibrated chlorophyll a concentration by the chlorophyll a concentration calculation value;

[0010] Calibrate the turbidity value by the chlorophyll a concentration value: determine whether the real-time measured turbidity value increases. When the real-time measured turbidity value increases, determine whether the chlorophyll a concentration value decreases. If it decreases, no calibration correction is performed. If it does not decrease, the turbidity value at the previous moment is used as the output value.

[0011] As a preferred technical solution, the intensity of the scattered light is measured to calculate the corresponding water turbidity. The specific calculation formula is expressed as:

[0012] T=A*I scatter

[0013] Among them, T represents the turbidity of water, A is the coefficient, I scatter Represents the scattered light intensity. The scattered light intensity I is obtained by calculating the integral area of ​​the selected characteristic peak. scatter .

[0014] As a preferred technical solution, the integrated area of ​​the selected characteristic peak is calculated to obtain the scattered light intensity I scatter , the specific steps include:

[0015] Convert selected feature peaks to Gaussian form:

[0016]

[0017] Among them, b s is the peak position, a s and c s is the undetermined parameter, and a is constantly changing s and c s The value of , so that it finally satisfies:

[0018]

[0019] Solve for parameter a s , b s and c s The value of the characteristic peak is obtained by obtaining the Gaussian function f s (x), for the Gaussian function f s (x) Integrate to obtain the scattered light intensity Iscatter .

[0020] As a preferred technical solution, the corresponding chlorophyll a concentration is calculated by measuring the intensity of fluorescence, and the specific formula is expressed as:

[0021] Con=B*I fluorescence

[0022] Where Con is the chlorophyll a concentration, B is the coefficient, I fluorescence is the fluorescence intensity, and the integrated area of ​​the selected characteristic peak is calculated to obtain the fluorescence intensity I fluorescence .

[0023] As a preferred technical solution, the integrated area of ​​the selected characteristic peak is calculated to obtain the fluorescence intensity I fluorescence , the specific steps include:

[0024] Convert selected feature peaks to Gaussian form:

[0025]

[0026] Among them, b e is the peak position, a e and c e is the undetermined parameter, and a is constantly changing e and c e The value of , so that it finally satisfies:

[0027]

[0028] Solve for a e 、b e 、c e Three parameters to obtain the Gaussian function f corresponding to the characteristic peak e (x), for the Gaussian function f e (x) Integral to obtain the fluorescence intensity I fluorescence .

[0029] As a preferred technical solution, the chlorophyll a concentration value is calibrated by the turbidity value, and after the attenuation coefficient is set, the calculation formula is adjusted to:

[0030]

[0031] Among them, Con is the chlorophyll a concentration, B is the coefficient, I fluorescence is the fluorescence intensity, and the integrated area of ​​the selected characteristic peak is calculated to obtain the fluorescence intensity I fluorescence .

[0032] As a preferred technical solution, the attenuation coefficient of fluorescence corresponding to turbidity is specifically calculated as follows:

[0033]

[0034] Among them, δ k Con represents the attenuation coefficient of fluorescence corresponding to turbidity. o Indicates the chlorophyll a concentration, Con k Indicates the calculated value of chlorophyll a concentration corresponding to turbidity.

[0035] As a preferred technical solution, the light source consists of two narrow-band semiconductor laser sources of 852nm and 405nm, wherein the 852nm semiconductor laser is used as the light source for turbidity scattering measurement, and the 405nm is used as the excitation light source for chlorophyll a fluorescence measurement.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] (1) The present invention takes into account the turbidity monitoring based on scattered light intensity and the chlorophyll a concentration monitoring based on fluorescence intensity, and their optical path designs are highly consistent. By integrating the light source and replacing the broadband spectrum probe, the function of dual measurement with one probe is realized. Compared with the current single-probe single-index measurement method and equipment, it has a more compact structure and improves the measurement accuracy and efficiency.

[0038] (2) The present invention can calibrate the chlorophyll a concentration value by the turbidity value, or calibrate the turbidity value by the chlorophyll a concentration value, and has higher anti-interference ability and self-adaptation ability than the current detection method and detection equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic flow chart of the method for linking calibration and measuring water turbidity and chlorophyll a concentration based on spectral technology of the present invention;

[0040] Figure 2 It is a schematic diagram of the optical path equipment in the water turbidity and chlorophyll a concentration linkage calibration measurement method based on spectral technology of the present invention;

[0041] Figure 3 A schematic diagram of a spectrum drawn for the spectrum data of the present invention;

[0042] Figure 4 The figure is a schematic diagram of the process of calibrating the turbidity value by the chlorophyll a concentration value of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] like Figure 1As shown, this embodiment provides a method for calibrating and measuring the turbidity and chlorophyll a concentration of water based on spectral technology, and the specific steps include:

[0045] Water turbidity measurement based on scattered light intensity: Figure 2 As shown, the spectrum probe is at 90 degrees to the light emitted by the light source. When the light emitted by the light source encounters particles suspended in the water, it will be scattered. The more particles there are (that is, the higher the turbidity), the stronger the scattered light that can be detected by the spectrum probe. Conversely, the fewer particles there are (that is, the lower the turbidity), the light at 90 degrees to the spectrum probe will not enter the probe, and the scattered light will be weaker.

[0046] In this embodiment, the water turbidity measurement based on the scattered light intensity is carried out by using the proportional relationship between the scattered light intensity and the turbidity. By measuring the intensity of the scattered light, the corresponding water turbidity is calculated. The specific formula is:

[0047] T=A*I scatter (1)

[0048] Where T is turbidity, I scatter is the scattered light intensity, I scatter It is obtained by calculating the integrated area of ​​the selected characteristic peak (central wavelength 852nm), A is the coefficient, and A is obtained by measuring series I scatter The relationship with T shows that for a fixed device, the value of A is fixed;

[0049] In this embodiment, the characteristic peak integral area of ​​turbidity scattered light is solved: after the spectrum probe measures and obtains data, a set of x i and i The data composed of x i refers to the value of the i-th wavelength, y i means x i The corresponding light intensity is given by x i and i The shape of the entire characteristic peak can be depicted, such as Figure 3 As shown. Set the characteristic peak to the Gaussian form of the following formula (2):

[0050]

[0051] Among them, b s is the peak position, i.e. b s =852, and a s and c s are unknown parameters, which are related to the amplitude and width of the Gaussian function. i and i The data composed of a, combined with formula (2), continuously changes a s and c s The value of , so that it finally satisfies:

[0052]

[0053] Then we can find all a s 、b s 、c s Three parameters, and then obtain the Gaussian function f corresponding to the characteristic peak s (x);

[0054] Then for f s (x) Integrate to get I scatter ;

[0055] In addition, for the measurement of chlorophyll a concentration based on fluorescence, the spectrum probe is at 90 degrees to the light emitted by the light source. When the short-wavelength light emitted by the light source shines on substances or microorganisms containing chlorophyll a, chlorophyll a will produce fluorescence. The higher the chlorophyll a concentration, the stronger the fluorescence intensity detected by the spectrum probe. Conversely, the lower the chlorophyll a concentration, the weaker the fluorescence intensity detected by the spectrum probe.

[0056] In this embodiment, the fluorescence-based chlorophyll a concentration measurement uses the proportional relationship between the chlorophyll a fluorescence intensity and the chlorophyll a concentration to calculate the corresponding chlorophyll a concentration by measuring the intensity of the fluorescence. The specific formula is:

[0057] Con=B*I fluorescence (4)

[0058] Where Con is the chlorophyll a concentration, I fluorescence is the fluorescence intensity, I fluorescence is obtained by calculating the integrated area of ​​the selected characteristic peak (central wavelength ~ 670nm), B is the coefficient, and B is obtained by measuring series I fluorescence The relationship with Con shows that for a fixed device, the value of B is fixed;

[0059] In this embodiment, the characteristic peak integral area of ​​chlorophyll a fluorescence is solved: after the spectrum probe measures and obtains data, a set of x i and i The data composed of x i refers to the value of the i-th wavelength, y i means x i The corresponding light intensity is given by x i and i The shape of the entire characteristic peak can be depicted, such as Figure 3 As shown. Set the characteristic peak to the Gaussian form shown in formula (5):

[0060]

[0061] Among them, be is the peak position, i.e. b e ≈670, and a e and c e are unknown parameters, which are related to the amplitude and width of the Gaussian function respectively.

[0062] According to x i and i The data composed of a, combined with formula (5), continuously transforms a e and c e The value of , so that it finally satisfies:

[0063]

[0064] Then we can find all a e , b e 、c e Three parameters, and then obtain the Gaussian function f corresponding to the characteristic peak e (x), and then f e (x) Integrate to get I fluorescence ;

[0065] In this embodiment, the chlorophyll a concentration value is calibrated by the turbidity value: when the chlorophyll a concentration remains unchanged, the turbidity increases, and the fluorescence signal detected by the spectral probe will decrease. According to formula (4), the chlorophyll a concentration calculated by light intensity will also decrease, which is inconsistent with the actual situation. In order to overcome the influence of turbidity changes on chlorophyll a concentration measurement, formula (4) is optimized as follows:

[0066]

[0067] where δ k For a certain turbidity T k The corresponding fluorescence attenuation coefficient. Considering the relationship between chlorophyll a concentration and δ k It does not matter. You can set a fixed known chlorophyll a concentration Con o , and constantly changing the turbidity T k , the corresponding chlorophyll a concentration calculated value Con is obtained based on the fluorescence intensity measurement k , according to formula (4) and formula (7), we can get:

[0068]

[0069] Therefore, the turbidity T is obtained k and the corresponding chlorophyll a concentration calculated value Con k After that, the turbidity T k Find the corresponding δ k , then through Con k Obtain the calibrated chlorophyll a concentration;

[0070] In this embodiment, the turbidity value is calibrated by the chlorophyll a concentration value: the turbidity measurement based on spectral intensity is easily affected by sunlight. When the sunlight is strong, the calculated turbidity value will be larger than the actual value. However, the chlorophyll a concentration measurement relies on the fluorescence intensity, which is little affected by sunlight. If the actual turbidity value increases, it will inevitably lead to the calculated chlorophyll a concentration value Con k If the turbidity value increases due to sunlight, it will not cause the calculated chlorophyll a concentration Con k Using this feature, such as Figure 4 As shown, the steps to set up a turbidity calibration are:

[0071] Determine whether the real-time measured turbidity value increases. When the real-time measured turbidity value increases, determine whether the chlorophyll a concentration value decreases. If it decreases, no correction is required. If it does not decrease, the turbidity value at the previous moment (before the increase) is used as the output value instead.

[0072] This embodiment uses full-band spectral analysis instead of single-wavelength or multi-wavelength spectral analysis to make the test more accurate, significantly enhance the anti-interference ability of the water chlorophyll a concentration test, and measure turbidity and chlorophyll a with a single probe, which is more power-saving and has a more compact system structure;

[0073] In this embodiment, the spectrum probe adopts a micro-spectrometer with a wavelength measurement range of 340nm-1100nm and a spectral resolution of 10nm. The light source consists of two narrow-band semiconductor laser sources of 852nm and 405nm, of which the 852nm semiconductor laser is used as the turbidity scattering measurement light source and the 405nm is used as the excitation light source for chlorophyll a fluorescence measurement; the parameters are 405nm, 150mW, G Pin Code,Laser Diode and 852nm,300mW, H Pin Code,Laser Diode.

[0074] By measuring known turbidity samples and standard samples with different chlorophyll a concentrations, the system calculates A=0.015 (corresponding to turbidity unit NTU) and B=0.02 (corresponding to chlorophyll a concentration unit μg / L) according to formula (1) and formula (4).

[0075] according to Figure 3 The measured data, as well as formula (2) and formula (3), can be used to calculate that the integral of the 670nm fluorescence peak is 1647, and the integral of the 852nm scattering peak is 3141. Therefore, the corresponding water chlorophyll a concentration is 32.94μg / L, and the water turbidity is 47.12NTU.

[0076] At the same time, according to the measurement results of the standard material, δ 47 (That is, the turbidity is 47 NTU, so the corresponding loss coefficient is 0.73, so the actual chlorophyll a concentration should be 32.94 μg / L ÷ 0.73 = 45.12 μg / L.

[0077] In addition, the system monitored that the turbidity increased rapidly from 29NTU to 46NTU at a specific moment, and during this process, the test value corresponding to the chlorophyll a concentration remained unchanged. Therefore, it can be determined that this is a change caused by sunlight. Therefore, according to the operation of the present invention, 46NTU is corrected to 29NTU.

[0078] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for measuring the linkage calibration of water turbidity and chlorophyll a concentration based on spectral technology, characterized in that: The steps include: Set the spectrum probe at 90 degrees to the light emitted by the light source, and the light source shines on the water body; Water turbidity measurement based on scattered light intensity: The spectral probe collects scattered light, and uses the proportional relationship between scattered light intensity and turbidity to calculate the corresponding water turbidity by measuring the intensity of scattered light; The intensity of the scattered light is measured to calculate the corresponding water turbidity. The specific calculation formula is expressed as: T=A*I scatter Among them, T represents the turbidity of water, A is the coefficient, I scatter Represents the scattered light intensity. The scattered light intensity I is obtained by calculating the integral area of ​​the selected characteristic peak. scatter ; The integrated area of ​​the selected characteristic peak is calculated to obtain the scattered light intensity I scatter , the specific steps include: Convert selected feature peaks to Gaussian form: Among them, b s is the peak position, a s and c s is the undetermined parameter, and a is constantly changing s and c s The value of , so that it finally satisfies: Solve for parameter a s、 b s and c s The value of the characteristic peak is obtained by obtaining the Gaussian function f s (x), for the Gaussian function f s (x) Integrate to obtain the scattered light intensity I scatter ; Chlorophyll a concentration measurement based on fluorescence intensity: The spectral probe collects fluorescence intensity, and uses the proportional relationship between fluorescence intensity and chlorophyll a concentration to calculate the corresponding chlorophyll a concentration by measuring the intensity of fluorescence; The corresponding chlorophyll a concentration is calculated by measuring the intensity of fluorescence, and the specific formula is expressed as: Con=B*I fluorescence Among them, Con is the chlorophyll a concentration, B is the coefficient, I fluorescence is the fluorescence intensity, and the integrated area of ​​the selected characteristic peak is calculated to obtain the fluorescence intensity I fluorescence ; The integrated area of ​​the selected characteristic peak is calculated to obtain the fluorescence intensity I fluorescence , the specific steps include: Convert selected feature peaks to Gaussian form: Among them, b e is the peak position, a e and c e is the undetermined parameter, and a is constantly changing e and c e The value of , so that it finally satisfies: Solve for a e 、b e 、c e Three parameters to obtain the Gaussian function f corresponding to the characteristic peak e (x), for the Gaussian function f e (x) Integral to obtain the fluorescence intensity I fluorescence ; Calibrate the chlorophyll a concentration value by turbidity value: set the attenuation coefficient of fluorescence corresponding to turbidity, preset the chlorophyll a concentration, adjust the turbidity, obtain the corresponding chlorophyll a concentration calculation value based on fluorescence intensity measurement, find the corresponding attenuation coefficient by turbidity, and obtain the calibrated chlorophyll a concentration by the chlorophyll a concentration calculation value; Calibrate the turbidity value by the chlorophyll a concentration value: determine whether the real-time measured turbidity value increases. When the real-time measured turbidity value increases, determine whether the chlorophyll a concentration value decreases. If it decreases, no calibration correction is performed. If it does not decrease, the turbidity value at the previous moment is used as the output value.

2. The method for calibrating and measuring water turbidity and chlorophyll a concentration based on spectral technology according to claim 1, characterized in that: The chlorophyll a concentration value is calibrated by the turbidity value. After setting the attenuation coefficient, the calculation formula is adjusted to: Among them, Con is the chlorophyll a concentration, B is the coefficient, I fluorescence is the fluorescence intensity, and the integrated area of ​​the selected characteristic peak is calculated to obtain the fluorescence intensity I fluorescence .

3. The method for calibrating and measuring the turbidity and chlorophyll a concentration of water bodies based on spectral technology according to claim 1, characterized in that: The specific calculation formula of the fluorescence attenuation coefficient corresponding to turbidity is: Among them, δ k Con represents the attenuation coefficient of fluorescence corresponding to turbidity. o Indicates the chlorophyll a concentration, Con k Indicates the calculated value of chlorophyll a concentration corresponding to turbidity.

4. The method for calibrating and measuring water turbidity and chlorophyll a concentration based on spectral technology according to claim 1, characterized in that: The light source consists of two narrow-band semiconductor laser sources, 852nm and 405nm. The 852nm semiconductor laser is used as the light source for turbidity scattering measurement, and the 405nm is used as the excitation light source for chlorophyll a fluorescence measurement.

Images