A dual-parameter fiber optic sensing method for dissolved oxygen and turbidity in water bodies

Abstract

This invention provides a dual-parameter fiber optic sensing method for dissolved oxygen and turbidity in water, belonging to the field of optical testing technology. The method includes: selecting a detection point in the water body to be tested and collecting ambient light interference irradiance parameters at the detection point; calculating the ambient light interference index based on the ambient light interference irradiance parameters; collecting probe deployment depth constraint parameters and calculating the maximum and minimum deployable depths; constructing a correction function to generate an ambient light interference compensation deployment depth; comparing the ambient light interference compensation deployment depth with the maximum deployable depth, and generating a judgment decision based on the comparison result. This invention can effectively suppress the interference of external ambient light on the detection signal, ensuring the signal-to-noise ratio and reliability of dissolved oxygen and turbidity data, and avoid the influence of ambient light due to shallow probe insertion or the disturbance of bottom sediments due to excessively deep insertion. Therefore, it can obtain safe and accurate detection results under different water conditions, different lighting conditions, and different wave conditions.

Description

Technical Field

[0001] This invention relates to the field of optical testing technology, specifically to a two-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water. Background Technology

[0002] When using fiber optic sensing technology to detect dissolved oxygen and turbidity in water, ambient light can enter the photosensitive area of ​​the fiber optic probe through transmission, refraction, or diffuse reflection from the water surface. This light can then superimpose with the sensor's own signal light, causing interference. This results in a significant decrease in the signal-to-noise ratio of measurement signals such as dissolved oxygen fluorescence lifetime or turbidity scattered light intensity. Consequently, dissolved oxygen concentration readings may drift, and turbidity values ​​may rise or fluctuate abnormally. In severe cases, the sensor may even be unable to effectively distinguish between ambient light noise and the actual sensing signal, ultimately leading to reduced detection accuracy and poor repeatability. The negative impact of ambient light interference on measurement results is particularly pronounced in shallow water areas, clear water bodies, or under direct sunlight.

[0003] In the prior art, patent CN105548126A discloses a sliding in-situ measurement device and method for dissolved oxygen at the mud-water interface. This technology includes a dissolved oxygen micro-photometer main unit connected to a detection probe, which extends to measure dissolved oxygen. The device further includes a detection box that can be placed on the mud-water interface. The detection box has a vertically penetrating water passage cavity and a transversely penetrating detection cavity, which intersects with the detection cavity. The device also includes an insert with a probe groove whose contour matches the probe's contour. The probe is fixed in the probe groove. The insert can be inserted into the detection cavity and slide up and down within it. Adjusting the insertion depth of the insert adjusts the probe's horizontal position, and sliding the insert up and down adjusts the height between the probe and the mud-water interface. This solution has the advantage of enabling accurate in-situ measurement of dissolved oxygen at a specific height at the mud-water interface.

[0004] However, in the aforementioned existing technologies, the fiber optic sensing detection uses a fixed depth or determines the probe insertion depth based on experience. This approach neither quantifies the impact of external interference nor considers physical constraints such as actual water depth, effective wave height, and probe length. Therefore, in actual detection, it is often difficult to balance resistance to ambient light interference and avoid bottom disturbance. On the one hand, insufficient insertion depth can lead to direct entry of ambient light into the probe, resulting in a decrease in signal-to-noise ratio and unreliable measurement accuracy. On the other hand, excessive insertion may approach the bottom, causing sediment resuspension, which can interfere with turbidity measurement or even damage the probe. Furthermore, conventional solutions cannot dynamically adjust the depth according to waves. In areas with large waves, the probe may emerge above the water surface or accidentally touch the bottom, ultimately causing data distortion or making safe deployment impossible.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-parameter fiber optic sensing method for dissolved oxygen and turbidity in water, thereby addressing the problems mentioned in the background section. This invention effectively suppresses interference from ambient light on the detection signal, ensuring the signal-to-noise ratio and reliability of dissolved oxygen and turbidity data. It also avoids the influence of ambient light due to shallow probe insertion or disturbance of bottom sediments due to excessively deep insertion. Therefore, it can adaptively obtain safe and accurate detection results under different water conditions, lighting conditions, and wave conditions.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A two-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water includes the following steps:

[0009] S1: Select the detection point in the water area to be tested, and collect the ambient light interference irradiance parameters at the detection point. The ambient light interference irradiance parameters include: spectral irradiance on the water surface, total visible light irradiance, and narrowband ambient light irradiance.

[0010] S2: Preprocess the collected ambient light interference irradiance parameters. The preprocessing includes normalization and calculating the ambient light interference index based on the ambient light interference irradiance parameters. The ambient light interference index is used to quantify the degree of interference caused by external ambient light on the detection accuracy of dissolved oxygen and turbidity fiber optic sensors in the water under test.

[0011] S3: Collect probe deployment depth constraint parameters, which include the actual water depth at the measuring point, the effective wave height of the water surface waves, the bottom safety avoidance distance, and the vertical length of the probe; based on the probe deployment depth constraint parameters, calculate and obtain the maximum and minimum deployable depths;

[0012] S4: Construct a correction function, and couple the minimum deployable depth and the calculated ambient light interference index into the correction function to generate an ambient light interference compensation deployment depth.

[0013] S5: Compare the ambient light interference compensation deployment depth with the maximum deployable depth, and generate a judgment decision based on the comparison result. The judgment decision is used to determine whether the ambient light interference compensation deployment depth is available.

[0014] Furthermore, the ambient light interference irradiance parameter acquisition process in S1 is as follows:

[0015] The process for collecting spectral irradiance on the water surface is as follows: collect spectral irradiance on the water surface directly above the selected detection point. The collection process must cover the visible light to near-infrared bands, and record the irradiance values ​​corresponding to each wavelength.

[0016] The process for collecting total visible light illuminance is as follows: at the selected detection point, the total visible light integrated illuminance is collected facing the sky. During the collection process, the irradiance energy of the visible light band needs to be integrated in a hemispherical space to obtain the total visible light illuminance value.

[0017] The narrowband ambient light irradiance acquisition process is as follows: at the selected detection point, the narrowband irradiance is acquired using the narrowband wavelength used for dissolved oxygen and turbidity sensing in subsequent fiber optic sensing detection. During acquisition, the ambient light energy of the corresponding narrowband band is extracted by optical filtering, and the total irradiance within the narrowband is recorded as the narrowband ambient light irradiance.

[0018] Furthermore, during the process of collecting spectral irradiance on the water surface, multiple repeated samplings are performed, and outliers are removed from the irradiance sequence at each wavelength. The arithmetic mean at each wavelength is calculated to obtain the spectral irradiance on the water surface at the selected detection point.

[0019] During the total visible light illuminance acquisition process, a multiple repeated measurement strategy is adopted, with uniform intervals between each measurement. After eliminating outliers caused by instantaneous external interference, the arithmetic mean of the remaining valid sampled values ​​is taken as the total visible light illuminance of the selected detection point.

[0020] During the narrowband ambient light irradiance acquisition process, the processed narrowband ambient light irradiance value is obtained through multiple sampling, outlier removal, and mean value processing.

[0021] Furthermore, the formula used to calculate the ambient light interference index based on the ambient light interference irradiance parameter is as follows:

[0022]

[0023] in:

[0024] The ambient light interference index after preprocessing;

[0025] The spectral irradiance on the water surface after pretreatment is represented, with a value range of [0,1].

[0026] The total visible light illuminance after preprocessing, with a value range of [0,1];

[0027] The preprocessed narrowband ambient light irradiance has a value range of [0,1].

[0028] ε is a very small positive number used to avoid the denominator being zero.

[0029] Furthermore, the formula used to calculate the maximum deployable depth is as follows:

[0030]

[0031] The formula for calculating the minimum deployable depth is as follows:

[0032]

[0033] in:

[0034] D represents the actual water depth at the measuring point, indicating the distance from the still water surface to the bottom.

[0035] To ensure a safe avoidance distance at the bottom;

[0036] The vertical length of the probe;

[0037] The effective wave height of the water surface waves;

[0038] These are the minimum deployable depth and the maximum deployable depth, respectively.

[0039] Calculated and Must meet Otherwise, the selected detection points cannot be safely used to place the probes, and the points need to be reselected or wave protection measures need to be taken.

[0040] Furthermore, it also includes the bottom safety avoidance distance. Calculation process:

[0041] The disturbance threshold of bottom sediments was assessed using a transparency disc to determine the critical distance at which the probe significantly increased turbidity when approaching the bottom sediment. Under still water conditions, the probe was slowly lowered to the bottom, and the height reading on the scale was recorded. The probe was then raised to the minimum distance at which the turbidity returned to background levels; this minimum distance served as the initial avoidance distance. The minimum distance was then corrected based on the average current flow velocity: when the velocity was less than 0.1 m / s, the minimum distance was directly taken as the bottom safe avoidance distance; when the velocity was between 0.1 and 0.5 m / s, an additional 20% to 30% correction was added as the bottom safe avoidance distance; when the velocity was greater than 0.5 m / s, probe oscillation interference occurred, and the vertical length of the probe was calculated in this case. The sum of half of the value and the correction value is used as the final bottom safe avoidance distance.

[0042] Furthermore, the formula used to determine the deployment depth for generating ambient light interference compensation is as follows:

[0043]

[0044] in:

[0045] The deployment depth for compensating for ambient light interference represents the actual insertion depth of the fiber optic sensor probe from the still water surface, calculated after comprehensively considering the minimum physical depth and ambient light interference.

[0046] α is the ambient light weighting coefficient, used to adjust the sensitivity of the interference index to depth compensation.

[0047] Furthermore, it also includes the process for obtaining the ambient light weighting coefficient:

[0048] Select test points in the water area to be tested, and connect the fiber optic sensing probes respectively from: Start by increasing the depth by 0.1 to 0.2 meters each time until you reach approximately [the desired depth]. Different depths were inserted into the water body to simultaneously collect dissolved oxygen and turbidity signals, and the signal-to-noise ratio (SNR) at each depth was recorded. The depth at which the SNR first reached the preset threshold of the detection system was taken as the effective anti-interference depth under the corresponding ambient light interference index. Then, using the known test points... and Through the formula: The ambient light weight coefficient test value at this test point is obtained by reverse calculation.

[0049] Furthermore, N test points were repeatedly selected for testing under different time periods and different water turbidity conditions, with N≥5. The average value of the ambient light weighting coefficient test values ​​of all test points was taken as the default ambient light weighting coefficient for the water body under test. A conservative upward margin of 20% is set so that the final ambient light weighting coefficient is: .

[0050] Furthermore, the logic of the judgment and decision is as follows:

[0051] when When the ambient light interference compensation deployment depth is determined to be usable, it indicates that the currently calculated ambient light interference compensation deployment depth simultaneously meets the physical immersion requirements and bottom safety requirements, and has the ability to resist ambient light interference.

[0052] when When the ambient light interference compensation deployment depth is deemed unavailable, it indicates that the current ambient light interference is too strong and the required compensation depth exceeds the maximum deployment depth actually allowed in the water area. At this time, it is impossible to suppress ambient light interference by simply increasing the insertion depth.

[0053] Compared with the prior art, the beneficial effects of the present invention are:

[0054] This invention quantifies the spectral irradiance, total visible light irradiance, and narrowband ambient light irradiance on the water surface to calculate the ambient light interference index. It then determines a feasible depth range that allows for complete immersion without touching the bottom. Based on the ambient light interference index, a dedicated compensation deployment depth is dynamically adjusted. This achieves the following: it effectively suppresses the interference of external ambient light on the detection signal, ensuring the signal-to-noise ratio and reliability of dissolved oxygen and turbidity data. It also avoids the probe being affected by ambient light due to shallow insertion or disturbing bottom sediments due to deep insertion. Thus, it can adaptively obtain safe and accurate detection results under different water conditions, lighting conditions, and wave conditions. Attached Figure Description

[0055] Figure 1 This is a flowchart of the dual-parameter fiber optic sensing detection method for dissolved oxygen and turbidity in water according to the present invention. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0057] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0058] Example:

[0059] Please see Figure 1 The present invention provides the following technical solutions:

[0060] A two-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water includes the following steps:

[0061] S1: After selecting the detection point in the water area to be tested, collect all the irradiance parameters related to ambient light interference at the point. These parameters can effectively characterize the potential impact of external ambient light on the subsequent fiber optic sensing detection process, including the spectral irradiance on the water surface that can reflect the spectral distribution characteristics of water surface reflection and transmission, the total visible light irradiance used to evaluate the overall radiation intensity of the visible light band, and the narrowband ambient light irradiance specifically for the narrowband band used in fiber optic sensing.

[0062] The process for collecting ambient light interference irradiation parameters is as follows:

[0063] The process for collecting spectral irradiance on the water surface is as follows: Spectral irradiance is collected on the water surface directly above the selected detection point. The collection must cover the visible to near-infrared bands to comprehensively acquire the spectral energy distribution characteristics of water surface reflection and transmission, and the irradiance values ​​corresponding to each wavelength are recorded. To ensure the representativeness and stability of the measurement results, multiple repeated samplings are required during the spectral irradiance collection process. Each sampling should be conducted under the same environmental conditions, and outliers caused by transient disturbances or abnormal reflections are removed from the irradiance sequence at each wavelength. Then, the arithmetic mean of the remaining valid data at each wavelength is calculated, ultimately yielding a reliable spectral irradiance on the water surface at the selected detection point.

[0064] The total visible illuminance acquisition process is as follows: At the selected detection point, the total visible integrated illuminance is acquired facing the sky. During the acquisition process, the irradiance energy in the visible light band is integrated in a hemispherical space to obtain the total visible illuminance value that reflects the total visible light radiation intensity within the entire sky hemisphere. During the total visible illuminance acquisition process, a multiple-repetition measurement strategy is adopted, with uniform intervals between each measurement to avoid errors introduced by time variations. After removing outliers caused by transient external interference such as rapid cloud movement or birds flying by, the arithmetic mean of the remaining valid samples is taken as the stable and reliable total visible illuminance at the selected detection point. The acquisition process for all the above irradiance parameters must comply with optical metrology traceability requirements, and the spectroradiometer used should be calibrated regularly to ensure the accuracy and comparability of the measurement data.

[0065] The narrowband ambient light irradiance acquisition process is as follows: At selected detection points, narrowband irradiance is acquired using the narrowband wavelengths used for dissolved oxygen and turbidity sensing in subsequent fiber optic sensing. During acquisition, the ambient light energy of the corresponding narrowband band is accurately extracted using optical filtering to eliminate interference from other bands. The total irradiance within this narrowband is recorded as the narrowband ambient light irradiance. During the narrowband ambient light irradiance acquisition process, multiple samples are taken to obtain sufficient data. Then, outlier removal and averaging are performed to obtain a smoothed narrowband ambient light irradiance value, which is used to accurately characterize the interference intensity of ambient light in a specific narrowband band.

[0066] S2: The collected ambient light interference irradiance parameters are systematically preprocessed. This preprocessing includes data normalization to eliminate differences in dimensions and numerical magnitudes between different parameters, ensuring that all parameters can participate in subsequent calculations on a unified scale. Based on this, an ambient light interference index is calculated using the normalized ambient light interference irradiance parameters. This index is used to comprehensively quantify the degree of interference from external ambient light on the measurement accuracy during dissolved oxygen and turbidity fiber optic sensing.

[0067] The formula used to calculate the ambient light interference index based on the ambient light interference irradiance parameter is:

[0068]

[0069] in:

[0070] The ambient light interference index after preprocessing;

[0071] The spectral irradiance on the water surface after pretreatment is defined as [0,1]. also with There is a positive correlation: the greater the broadband irradiance on the water surface, the stronger the sunlight or sky light received by the water surface. This light will enter the probe through reflection, refraction or scattering by the water surface, increasing interference, so the index increases accordingly.

[0072] The total visible light illuminance after preprocessing, with a value range of [0,1]. When the denominator is small, its influence is relatively small, and the external multiplier plays a dominant role. Follow Increase and rise; but when Once a certain threshold is exceeded, the squared term in the denominator causes the fraction to drop sharply, and the logarithmic term tends to zero. At this point, the external multiplier still grows linearly, but the overall growth rate slows down, and may even decline. Follow The phenomenon of increasing but decreasing growth rate;

[0073] This represents the preprocessed narrowband ambient light irradiance, with values ​​ranging from [0,1]. It shows a clear positive correlation with the ambient light interference index: The larger the value, the larger the logarithmic term. It also increases accordingly, thus making the entire Increase;

[0074] ε is a very small positive number used to avoid the denominator being zero. ε itself has a very small value and does not affect the correlation trend between variables under normal circumstances; it only ensures the stability of numerical calculations.

[0075] S3: Collect probe deployment depth constraint parameters. These parameters define the depth range within which the probe can operate safely and effectively in the water body, including the actual water depth at the measurement point, the effective wave height of surface waves, the bottom safety avoidance distance, and the probe's vertical length. The actual water depth at the measurement point reflects the overall vertical distance from the water surface to the bottom at the detection point. The effective wave height of surface waves is used to assess the impact of wave-induced water level fluctuations on the probe deployment depth. The bottom safety avoidance distance is used to prevent the probe from getting too close to the bottom, causing sediment disturbance or probe damage. The probe's vertical length is the vertical dimension of the probe itself. Based on these probe deployment depth constraint parameters, the maximum and minimum permissible deployment depths of the probe in the measured water body can be calculated comprehensively.

[0076] The formula used to calculate the maximum deployable depth is:

[0077]

[0078] The formula for calculating the minimum deployable depth is as follows:

[0079]

[0080] in:

[0081] D represents the actual water depth at the measuring point, indicating the distance from the still water surface to the bottom.

[0082] To ensure a safe avoidance distance at the bottom, This indicates the minimum safe distance that must be maintained between the lower end of the probe and the bottom of the water body to avoid disturbing the bottom sediment or hitting the bottom. It has a clear negative correlation with the maximum deployable depth: the larger the bottom safety avoidance distance, the farther the probe needs to be from the bottom, and therefore the smaller the maximum usable depth from the water surface.

[0083] The vertical length of the probe is the maximum water depth required to ensure that the entire sensing end is completely submerged in the water and to prevent any part of it from being exposed above the water surface.

[0084] The significant wave height is the maximum wave height. The larger the wave, the greater the half-value of the significant wave height. The corresponding increase is due to the physical logic behind this design: the presence of waves causes the probe to oscillate up and down underwater with the wave current. To avoid the probe hitting the bottom at wave troughs, the maximum deployment depth needs to be appropriately increased (i.e., allowing the probe to be deployed deeper in still water). This ensures that the probe maintains a safe distance from the bottom even at wave peaks. Therefore, the formula for calculating the maximum deployment depth uses... The form in which it participates in the calculation;

[0085] When waves are present on the water surface, the water level at the trough will temporarily be lower than the still water level. If the probe is deployed only at the minimum depth under still water conditions, the top of the probe may protrude above the water surface at the trough, resulting in the sensing end not being fully submerged or unstable signal acquisition. Therefore, the formula for calculating the minimum deployable depth also considers… It participates in the calculation in the form of .

[0086] These are the minimum deployable depth and the maximum deployable depth, respectively.

[0087] Maximum deployment depth This is the upper limit to which the probe can be lowered in actual water bodies; exceeding this depth may result in contact with the bottom or disturbance of sediment. It comprehensively reflects three factors: water depth, bottom safety avoidance requirements, and wave undulation.

[0088] Minimum deployable depth This is the lower limit at which the probe can be lowered in actual water bodies; below this depth, safe immersion and normal detection cannot be guaranteed. It comprehensively reflects the physical requirements of the probe's dimensions as well as the dynamic impact of wave fluctuations on immersion conditions.

[0089] Calculated and Must meet Otherwise, the selected detection points cannot be safely used to place the probes, and the points need to be reselected or wave protection measures need to be taken.

[0090] Bottom safety avoidance distance Calculation process:

[0091] The disturbance threshold of bottom sediments is assessed in the field using a transparency disc. By slowly lowering the transparency disc close to the bottom, the critical distance at which the probe or transparency disc begins to agitate the bottom sediment and cause a significant increase in turbidity in the water is observed and recorded. This allows us to obtain the closest position where the probe can approach the bottom sediment without causing an abnormal increase in turbidity.

[0092] Under still water conditions, slowly lower the probe until it touches the bottom. Record the accurate reading on the height scale above the bottom. Then gradually lift the probe upwards until the turbidity data returned to the background value unaffected by bottom sediment disturbance. Record the minimum distance the probe was lifted during this process. This minimum distance is the initial avoidance distance.

[0093] To adapt to the impact of different water flow environments on the actual deployment safety, in this embodiment, the minimum distance is reasonably corrected based on the average flow velocity of the current water flow: when the flow velocity is less than 0.1 meters per second, the water flow disturbance is weak, and the minimum distance can be directly taken as the bottom safety avoidance distance; when the flow velocity is between 0.1 and 0.5 meters per second, the suspension effect of the water flow on the bottom sediment is enhanced, and an additional correction value of 20% to 30% needs to be added to the minimum distance, and the corrected distance is taken as the bottom safety avoidance distance; when the flow velocity is greater than 0.5 meters per second, the water flow will cause the probe to produce obvious swing interference. At this time, it is necessary to calculate half of the vertical length of the probe, add this half length to the correction value obtained above, and the sum of the two is taken as the final bottom safety avoidance distance. This calculation process can be carried out with reference to the relevant standardized operating procedures for water sediment disturbance testing to ensure that the avoidance distance obtained by different water areas and different operators is consistent and reproducible, so as to ensure that the probe can still safely avoid bottom sediment disturbance under strong water flow conditions.

[0094] S4: Construct a correction function. Based on the minimum deployable depth and the calculated ambient light interference index, the correction function is coupled with the minimum deployable depth. Through internal coupling operations, the minimum deployable depth receives incremental compensation based on the strength of the ambient light interference, ultimately generating a compensated deployment depth corrected for ambient light interference. This compensated deployment depth adds an extra depth margin to the physical minimum depth to resist ambient light interference, ensuring that the probe meets basic immersion requirements while also suppressing ambient light interference in the measurement signal during actual testing.

[0095] The formula used to determine the deployment depth for ambient light interference compensation is as follows:

[0096]

[0097] in:

[0098] The deployment depth for compensating for ambient light interference represents the actual insertion depth of the fiber optic sensor probe from the still water surface, calculated after comprehensively considering the minimum physical depth and ambient light interference.

[0099] When there is no ambient light interference ( )hour, This means that only the minimum physical immersion depth of the probe needs to be guaranteed; when the interference increases, the compensation depth increases proportionally based on the minimum depth, which meets the requirement that the stronger the interference, the deeper the insertion.

[0100] α is the ambient light weighting coefficient, used to adjust the sensitivity of the interference index to depth compensation.

[0101] The process of obtaining the ambient light weighting coefficient:

[0102] Select test points in the water area to be tested, and connect the fiber optic sensing probes respectively from: Start by increasing the depth by 0.1 to 0.2 meters each time until you reach approximately [the desired depth]. The sensor was inserted into the water at different depths, and remained stationary at each designated depth while simultaneously collecting dissolved oxygen and turbidity signals. The signal-to-noise ratio (SNR) at each depth was also recorded. By comparing the SNR at each depth, the depth at which the SNR first reached the preset threshold of the detection system was identified. This depth was then taken as the effective anti-interference depth under the current ambient light interference index. Then, using the known test points... and Through the formula: The ambient light weighting coefficient at that test point is then calculated by reverse calculation. This testing process can also be used to verify the detection performance of new materials such as the sensitive membrane used in fiber optic probes and to evaluate their signal response stability under real water ambient light interference.

[0103] In this embodiment, to obtain a more universally applicable ambient light weighting coefficient, five test points were repeatedly selected for testing under different time periods and different water turbidity conditions. The arithmetic mean of the ambient light weighting coefficient test values ​​obtained from all test points was taken, and this mean is the default ambient light weighting coefficient for the water body under test. A conservative upward margin of 20% is set so that the final ambient light weighting coefficient is: .

[0104] S5: Compare the calculated ambient light interference compensation deployment depth with the previously determined maximum deployment depth item by item, and generate corresponding judgment decisions based on the relationship between the two. The core function of this judgment decision is to determine whether the currently obtained ambient light interference compensation deployment depth can be reasonably and effectively put into use in actual testing.

[0105] The logic for judgment and decision-making is as follows:

[0106] when When the ambient light interference compensation deployment depth is determined to be usable, it indicates that the current calculated ambient light interference compensation deployment depth can meet both the physical immersion requirement of the probe being completely submerged in the water and the bottom safety requirement of the probe not contacting the bottom or disturbing the sediment. At the same time, this depth also has the ability to resist external ambient light interference, and reliable dissolved oxygen and turbidity fiber optic sensing detection can be carried out at this depth.

[0107] when At this point, it was determined that the ambient light interference compensation deployment depth was unavailable. This conclusion indicates that the external ambient light interference at the current detection point was too strong, to the point that the additional compensation depth required to effectively suppress the influence of ambient light exceeded the maximum deployment depth allowed by the actual conditions of the water area. In this situation, simply inserting the probe deeper cannot suppress ambient light interference; other measures or a reassessment of the detection conditions are necessary. This detection method can be validated and its capabilities assessed by a third-party certification and accreditation service organization to meet the quality requirements of rapid on-site detection technology in the environmental monitoring field.

[0108] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0109] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0110] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0111] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water, characterized in that, Includes the following steps: S1: Select the detection point in the water area to be tested, and collect the ambient light interference irradiance parameters at the detection point. The ambient light interference irradiance parameters include: spectral irradiance on the water surface, total visible light irradiance, and narrowband ambient light irradiance. S2: Preprocess the collected ambient light interference irradiance parameters. The preprocessing includes normalization and calculating the ambient light interference index based on the ambient light interference irradiance parameters. The ambient light interference index is used to quantify the degree of interference caused by external ambient light on the detection accuracy of dissolved oxygen and turbidity fiber optic sensors in the water under test. S3: Collect probe deployment depth constraint parameters, which include the actual water depth at the measuring point, the effective wave height of the water surface waves, the bottom safety avoidance distance, and the vertical length of the probe; based on the probe deployment depth constraint parameters, calculate and obtain the maximum and minimum deployable depths; S4: Construct a correction function, and couple the minimum deployable depth and the calculated ambient light interference index into the correction function to generate an ambient light interference compensation deployment depth. S5: Compare the ambient light interference compensation deployment depth with the maximum deployable depth, and generate a judgment decision based on the comparison result. The judgment decision is used to determine whether the ambient light interference compensation deployment depth is available.

2. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 1, characterized in that: The ambient light interference irradiance parameter acquisition process in S1 is as follows: The process for collecting spectral irradiance on the water surface is as follows: collect spectral irradiance on the water surface directly above the selected detection point. The collection process must cover the visible light to near-infrared bands, and record the irradiance values ​​corresponding to each wavelength. The process for collecting total visible light illuminance is as follows: at the selected detection point, the total visible light integrated illuminance is collected facing the sky. During the collection process, the irradiance energy of the visible light band needs to be integrated in a hemispherical space to obtain the total visible light illuminance value. The narrowband ambient light irradiance acquisition process is as follows: at the selected detection point, the narrowband irradiance is acquired using the narrowband wavelength used for dissolved oxygen and turbidity sensing in subsequent fiber optic sensing detection. During acquisition, the ambient light energy of the corresponding narrowband band is extracted by optical filtering, and the total irradiance within the narrowband is recorded as the narrowband ambient light irradiance.

3. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 2, characterized in that: During the process of collecting spectral irradiance on the water surface, multiple repeated samplings are performed, and outliers are removed from the irradiance sequence at each wavelength. The arithmetic mean of each wavelength is calculated to obtain the spectral irradiance on the water surface at the selected detection point. During the total visible light illuminance acquisition process, a multiple repeated measurement strategy is adopted, with uniform intervals between each measurement. After eliminating outliers caused by instantaneous external interference, the arithmetic mean of the remaining valid sampled values ​​is taken as the total visible light illuminance of the selected detection point. During the narrowband ambient light irradiance acquisition process, the processed narrowband ambient light irradiance value is obtained through multiple sampling, outlier removal, and mean value processing.

4. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 1, characterized in that: The formula used to calculate the ambient light interference index based on the ambient light interference irradiance parameter is as follows: in: The ambient light interference index after preprocessing; The spectral irradiance on the water surface after pretreatment is represented, with a value range of [0,1]. The total visible light illuminance after preprocessing, with a value range of [0,1]; The preprocessed narrowband ambient light irradiance has a value range of [0,1]. ε is a very small positive number used to avoid the denominator being zero.

5. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 1, characterized in that: The formula used to calculate the maximum deployable depth is as follows: The formula for calculating the minimum deployable depth is as follows: in: D represents the actual water depth at the measuring point, indicating the distance from the still water surface to the bottom. To ensure a safe avoidance distance at the bottom; The vertical length of the probe; The effective wave height of the water surface waves; These are the minimum deployable depth and the maximum deployable depth, respectively. Calculated and Must meet Otherwise, the selected detection points cannot be safely used to place the probes, and the points need to be reselected or wave protection measures need to be taken.

6. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 5, characterized in that: It also includes bottom safety avoidance distance Calculation process: The disturbance threshold of bottom sediments was assessed using a transparency disc to determine the critical distance at which the probe significantly increased turbidity when approaching the bottom sediment. Under still water conditions, the probe was slowly lowered to the bottom, and the height reading on the scale was recorded. The probe was then raised to the minimum distance at which the turbidity returned to background levels; this minimum distance served as the initial avoidance distance. The minimum distance was then corrected based on the average current flow velocity: when the velocity was less than 0.1 m / s, the minimum distance was directly taken as the bottom safe avoidance distance; when the velocity was between 0.1 and 0.5 m / s, an additional 20% to 30% correction was added as the bottom safe avoidance distance; when the velocity was greater than 0.5 m / s, probe oscillation interference occurred, and the vertical length of the probe was calculated in this case. The sum of half of the value and the correction value is used as the final bottom safe avoidance distance.

7. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 5, characterized in that: The formula used to determine the deployment depth for generating ambient light interference compensation is as follows: in: The deployment depth for compensating for ambient light interference represents the actual insertion depth of the fiber optic sensor probe from the still water surface, calculated after comprehensively considering the minimum physical depth and ambient light interference. α is the ambient light weighting coefficient, used to adjust the sensitivity of the interference index to depth compensation.

8. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 7, characterized in that: It also includes the process for obtaining the ambient light weight coefficient: Select test points in the water area to be tested, and connect the fiber optic sensing probes respectively from: Start by increasing the depth by 0.1 to 0.2 meters each time until you reach approximately [the desired depth]. Different depths were inserted into the water body to simultaneously collect dissolved oxygen and turbidity signals, and the signal-to-noise ratio (SNR) at each depth was recorded. The depth at which the SNR first reached the preset threshold of the detection system was taken as the effective anti-interference depth under the corresponding ambient light interference index. Then, using the known test points... and Through the formula: The ambient light weight coefficient test value at this test point is obtained by reverse calculation.

9. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water as described in claim 1, characterized in that: Tests were conducted repeatedly at N test points under different time periods and turbidity conditions in the water body, with N≥5. The average value of the ambient light weighting coefficient test values ​​from all test points was taken as the default ambient light weighting coefficient for the water body under test. A conservative upward margin of 20% is set so that the final ambient light weighting coefficient is: .

10. The dual-parameter fiber optic sensing method for detecting dissolved oxygen and turbidity in water according to claim 7, characterized in that: The logic behind the judgment and decision is as follows: when When the ambient light interference compensation deployment depth is determined to be usable, it indicates that the currently calculated ambient light interference compensation deployment depth simultaneously meets the physical immersion requirements and bottom safety requirements, and has the ability to resist ambient light interference. when When the ambient light interference compensation deployment depth is deemed unavailable, it indicates that the current ambient light interference is too strong and the required compensation depth exceeds the maximum deployment depth actually allowed in the water area. At this time, it is impossible to suppress ambient light interference by simply increasing the insertion depth.

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