A compact multi-spectral photoelectric sand measuring instrument sharing a probe and a measuring method

Abstract

The application discloses a compact multi-spectral photoelectric sand measuring instrument sharing a detector and a measuring method. The sand measuring instrument comprises two symmetrical light source channels, a shared optical modulation module, a photoelectric detection module and a data processing module. The two light sources are symmetrically arranged on the two sides of the horizontal vertical plane of the protection glass, and the detector is arranged on the vertical plane to detect 90-degree and 135-degree scattered light. The application introduces an air gap, so that the collimated light successively passes through a light guide prism, the air gap and the protection glass to produce a significant horizontal displacement, enters the water body at an angle of 45 degrees, reduces the diameter of the instrument at a very small vertical thickness, and realizes miniaturization design. Through the sharing of the detector, multi-spectral data weighted fusion, first derivative monotonicity interval judgment and improved particle swarm algorithm segmentation fitting, the interference of particle size and color is effectively eliminated, and the measurement concentration range is widened. The application has the advantages of compact structure, high integration, high test precision and good engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of suspended sediment particle concentration detection technology, and in particular, a compact multispectral photoelectric sand measuring instrument and measurement method with a shared detector. Background Technology

[0002] Optical scattering is a widely used method in the field of suspended sediment concentration measurement. Its basic principle is as follows: a collimated infrared beam is incident on the water body through a protective glass, and the suspended particles in the water body will scatter the incident light; the detector receives the scattered light signal at a specific angle and processes it to estimate the concentration of suspended particles.

[0003] In traditional designs, two typical backscattering angles are usually used for signal reception: 90° and 135° angles relative to the incident light. This combination of angles can balance measurement accuracy under different concentration conditions. Although the two angle detection methods can reflect the concentration changes of suspended particles in the water to some extent, the measurement results are easily affected by the non-uniformity of particle distribution and density because the scattering points are not completely consistent. More importantly, such optical path arrangements require a large amount of space.

[0004] To ensure effective detection of scattered light, traditional optical path designs typically require thicker protective glass or increased detector spacing. This layout directly increases the overall diameter of the instrument, making it unsuitable for applications with stringent size and installation requirements. Therefore, existing suspended sediment concentration measuring instruments based on optical scattering methods suffer from significant limitations in terms of structural compactness and miniaturization, becoming a key obstacle to their widespread application. Achieving optical path optimization and instrument miniaturization within limited space would not only improve the device's adaptability to complex aquatic environments but also expand its application scope in hydrological monitoring, water conservancy project management, and other fields. This would provide a more accurate, reliable, and efficient means of measuring sediment concentration for related scientific research and engineering practices, possessing significant engineering importance and practical application value. Summary of the Invention

[0005] The purpose of this invention is to overcome the limitations of existing suspended sediment concentration measuring instruments in terms of structural compactness and miniaturization, and to provide a compact dual-spectrum photoelectric sand measuring instrument with a shared detector. By introducing an air gap in the incident light path and utilizing the design of the prism, air gap, and protective glass, a large horizontal displacement of the light path is achieved under limited vertical thickness conditions, thereby reducing the diameter of the instrument while meeting the performance requirements.

[0006] The technical solution for achieving the objective of this invention is as follows: On one hand, a compact multispectral photoelectric sand measuring instrument with a shared detector is provided, comprising:

[0007] The light source module is used to emit at least two collimated light signals with different spectra;

[0008] An optical modulation module is disposed on the propagation path of the collimated light signal to change the propagation path of the light, so that each collimated light signal enters the water body to be measured at a preset incident angle.

[0009] The photoelectric detection module includes multiple shared photoelectric detectors, which are used to collect scattered light signals with different scattering angles generated after each collimated light signal enters the water body being measured.

[0010] The data processing module, electrically connected to the photoelectric detection module, is used to perform weighted fusion processing on the collected multi-path scattered light signals to obtain the measurement results of suspended particle concentration in the water body being measured.

[0011] Furthermore, the light source module includes two symmetrically configured light source channels; in addition to the light source module, the optical modulation module, the photoelectric detection module, and the data processing module are all shared by the two light source channels.

[0012] Furthermore, the optical modulation module includes a light guide prism, an air gap, and a protective glass arranged sequentially from top to bottom; the collimated light signal is horizontally displaced by passing through the light guide prism and the air gap in sequence, and then transmitted into the water through the protective glass.

[0013] Furthermore, the light guide prism is a cylindrical light wedge structure made of K9 optical glass, with a flat bottom surface and an upper side surface at a 51° angle to the bottom surface; the collimated light signal emitted by the light source module is incident on the light guide prism at a 39° angle to the vertical direction.

[0014] Furthermore, the air gap is disposed between the protective shell of the sand measuring instrument and the protective glass, and its thickness is 1mm. The collimated light signal is refracted from the light guide prism and enters the air gap at an exit angle of 70° to 72°, and the horizontal displacement generated in the air gap is 2.7mm to 3.1mm.

[0015] Furthermore, the protective glass is a circular glass sheet made of K9 optical glass; the protective glass has a thickness of 2mm to 3mm; the refraction angle of the collimated light signal in the protective glass is 39°, and the horizontal displacement generated within the protective glass is 1.6mm to 2.4mm; the preset incident angle of the collimated light signal entering the water body is 45°.

[0016] Furthermore, the photoelectric detection module includes a first detector and a second detector; with the vertical plane of the protective glass in the horizontal direction as a reference plane, the two light sources in the light source module are symmetrically placed on both sides of the reference plane, and the first detector and the second detector are both placed on the reference plane for detecting 135° backscattered light and 90° scattered light, respectively.

[0017] On the other hand, a measurement method based on the sand measuring instrument is provided, the method comprising the following steps:

[0018] Step 1, Optical signal modulation and incidence: At least two collimated optical signals are emitted through the light source module and sequentially pass through the light guide prism, air gap and protective glass of the optical modulation module to enter the water body to be measured at a preset incident angle;

[0019] Step 2, Scattered signal acquisition: Using a shared detector set at different locations in the photoelectric detection module, the scattered light signals with different scattering angles generated after each light signal enters the water body are acquired.

[0020] Step 3, Multispectral Data Fusion: The data processing module performs weighted fusion calculations on the received multi-path scattered light signals to eliminate particle size and color interference and construct a fusion curve sequence;

[0021] Step 4, Concentration Result Output: Based on the piecewise fitting relationship model established by the particle swarm optimization algorithm, the suspended particle concentration result of the tested water body is calculated and output according to the fusion curve sequence.

[0022] Furthermore, the calculation process for multispectral data fusion in step 3 includes:

[0023] Step 31, Data preprocessing: The collected scattered light signal is subjected to abnormal signal removal and interpolation correction, zero-point correction based on pure water, frequency domain filtering and noise reduction based on wavelet transform, and inter-band normalization processing.

[0024] Step 32, Monotonicity Interval Determination: Use the first derivative sign to determine the monotonicity of each photoelectric signal curve;

[0025] Step 33, Average Gradient and Weight Calculation: The central difference method is used to calculate the gradient estimate of each photoelectric signal curve at each data point. Combined with the absolute value of the average gradient before and after the peak, the weight of each photoelectric signal curve is calculated using the following weight allocation function. :

[0026]

[0027] In the formula, Let be the mean of the gradient before the peak of the k-th photoelectric signal curve. Let be the mean of the gradients after the peak value of the k-th photoelectric signal curve; Let be the mean of the gradient before the peak of the j-th photoelectric signal curve. Let be the mean of the gradient after the peak of the j-th photoelectric signal curve, and α and β be hyperparameters that control the gradient sensitivity. α is used to enhance the rising segment, and β is used to suppress the falling segment.

[0028] Step 34, Construction of the fused curve sequence: Detect the peak point y_max of each photoelectric signal curve, accumulate the absolute value of the decrease in the peak value of each point starting from y_max to construct an increasing sequence, and combine each signal sequence according to the aforementioned weights. The superposition of these curves creates a sequence of fusion curves.

[0029] Furthermore, the calculation process for the concentration result output in step 4 includes:

[0030] Initialize the particle swarm, where each particle represents a combination of a breakpoint and a polynomial order;

[0031] Particle fitness is evaluated using the Bayesian Information Criterion (BIC).

[0032] By iteratively updating the position and velocity of particles, and performing Cauchy mutation on the globally optimal particle when there is no significant improvement in the global optimal solution for several consecutive iterations, the optimal piecewise multiple function relationship between the fused curve signal value and the sand content is converged. Here, no significant improvement indicates that the difference between the globally optimal solutions obtained from adjacent iterations is less than a preset threshold, and the piecewise multiple function relationship satisfies:

[0033] When x ≤ 0.1, the polynomial expression is:

[0034]

[0035] When 0.1 < x ≤ 10, the polynomial expression is:

[0036]

[0037] When x > 10, the polynomial expression is:

[0038] .

[0039] Compared with the prior art, the significant advantages of this invention are:

[0040] (1) By introducing an air gap in the incident light path and utilizing a combination design of a light guide prism, air gap, and protective glass, a large horizontal displacement of the light path was achieved under limited vertical thickness conditions. This effectively reduced the overall diameter of the instrument, making the structure highly integrated and compact, and very suitable for use in complex aquatic environments with strict requirements for volume and installation dimensions.

[0041] (2) The sand measuring instrument cleverly realizes the sharing of multiple detectors. The intersection of the optical paths of the two light sources and the backscattering detector is set at the light outlet of the protective glass, and the two light sources are symmetrically distributed on both sides of the optical path of the receiver. This symmetrical optical path design of "dual light source channel and shared detector" not only saves a lot of internal installation space, but also reduces the redundancy of system hardware.

[0042] (3) By collecting test data from at least two different spectra and performing weighted fusion processing, the system can effectively reduce and eliminate the interference of the particle size and color of the suspended particles being tested on the measurement results, and significantly improve the accuracy of the test and the reliability of the data.

[0043] (4) The optical modulation module enables light to enter the water body at a reasonable geometric angle (45° incident angle). Combined with a shared photodetector set at different distances (two photodetectors at certain distances near and outside the protective glass), it can simultaneously collect backscattered light signals from different positions such as 90° and 135°. This takes into account the measurement needs of both low and high concentrations of suspended sediment, greatly expanding the instrument's sediment content measurement range.

[0044] (5) The data processing module incorporates abnormal signal processing, wavelet transform filtering for noise reduction, zero-point correction, and piecewise function fitting based on an improved particle swarm optimization algorithm. This complete approach enables the instrument to operate stably in harsh conditions such as complex aquatic environments and limited space, and has strong engineering application value.

[0045] (6) The present invention has a compact structure and the measurement modules work together. It can operate stably under conditions such as limited installation space and complex water environment, and has strong engineering adaptability.

[0046] (7) The present invention has a compact overall design, high integration, and is easy to operate. Its measurement accuracy and data reliability are superior to those of traditional optical scattering sand measuring instruments, and it has good engineering application value and industrialization prospects.

[0047] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0048] Figure 1 This is a top-view schematic diagram of a compact multispectral photoelectric sand measuring instrument with a shared detector in one embodiment.

[0049] Figure 2 This is a side view schematic diagram of a compact multispectral photoelectric sand measuring instrument with a shared detector in one embodiment. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0051] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0052] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0053] Traditional suspended sediment concentration measuring instruments based on optical scattering methods typically employ two backscattering angles, 90° and 135°, to receive signals and accommodate measurement needs under varying concentration conditions. However, due to the non-uniformity of scattering point locations, measurement results are easily affected by uneven particle distribution. Furthermore, the optical path design requires significant installation space, often relying on thick protective glass or wide detector spacing. This results in an increased overall instrument size, making it difficult to meet miniaturization and compact design requirements, thus limiting its application in complex aquatic environments with limited space or stringent installation conditions. Overcoming these optical path layout limitations and achieving a compact design would not only improve the equipment's adaptability but also expand its application value in hydrological monitoring and water conservancy projects.

[0054] In one embodiment, combined Figure 1 and Figure 2 A compact multispectral photoelectric sand measuring instrument with a shared detector is proposed, comprising:

[0055] The light source module is used to emit at least two collimated light signals with different spectra;

[0056] An optical modulation module is disposed on the propagation path of the collimated light signal to change the propagation path of the light, so that each collimated light signal enters the water body to be measured at a preset incident angle.

[0057] The photoelectric detection module includes multiple shared photoelectric detectors, which are used to collect scattered light signals with different scattering angles generated after each collimated light signal enters the water body being measured.

[0058] The data processing module, electrically connected to the photoelectric detection module, is used to perform weighted fusion processing on the collected multi-path scattered light signals to obtain the measurement results of suspended particle concentration in the water body being measured.

[0059] Furthermore, in one embodiment, the light source module includes two symmetrically arranged light source channels; in addition to the light source module, the optical modulation module, the photoelectric detection module, and the data processing module are all shared by the two light source channels.

[0060] Furthermore, in one embodiment, the optical modulation module includes a light guide prism, an air gap, and a protective glass arranged sequentially from top to bottom; the collimated light signal is horizontally displaced by passing through the light guide prism and the air gap in sequence, and then transmitted into the water through the protective glass.

[0061] Furthermore, in one embodiment, the light guide prism is a cylindrical light wedge structure made of K9 optical glass, with a flat bottom surface and an upper side surface at a 51° angle to the bottom surface; the collimated light signal emitted by the light source module is incident on the light guide prism at a 39° angle to the vertical direction.

[0062] Here, the 51° wedge angle ensures that collimated light rays incident at 39° are precisely refracted and projected onto the interface at the bottom of the prism after entering the prism, preparing the angle for the next abrupt refraction. K9 glass offers excellent transmittance in the infrared band and is cost-effective.

[0063] It should be noted that material K9 can be replaced with fused silica or high-refractive-index flint glass (such as ZF2). If high-refractive-index glass is used, the angle of the upper side of the optical wedge can be further widened to 40°–45° due to the increased refractive index of the medium. This allows for a flatter prism assembly, further reducing the instrument's height.

[0064] Furthermore, in one embodiment, the air gap is disposed between the protective shell of the sand measuring instrument and the protective glass, and its thickness is 1 mm. The collimated light signal is refracted from the light guide prism and enters the air gap at an exit angle of 70° to 72°, and the horizontal displacement generated in the air gap is 2.7 mm to 3.1 mm.

[0065] Furthermore, in one embodiment, the protective glass, used to isolate the external environment and ensure optical path stability, is a circular glass sheet made of K9 optical glass; the protective glass has a thickness of 2mm to 3mm.

[0066] Furthermore, in one embodiment, the collimated light signal is refracted at an angle of 39° in the protective glass, and the horizontal displacement generated within the protective glass is 1.6 mm to 2.4 mm; the preset incident angle of the collimated light signal entering the water body is 45°.

[0067] In traditional designs, if light is directly incident from air into the protective glass, the angle of refraction within the glass is only 24.6°. To achieve a 4.6mm horizontal offset, the protective glass must be an astonishing 9.6mm thick, directly resulting in a bulky instrument. This invention uses a light wedge to guide the light, causing it to abruptly refract from the high-refractive-index K9 glass (approximately 1.51) into an air gap with a refractive index of approximately 1.0. According to Snell's law, the exit angle is dramatically amplified to 70°–72°. At this point, within a mere 1mm vertical thickness, the light directly achieves a horizontal displacement (d1) of 2.7mm–3.1mm using the geometric amplification effect of tan(70°–72°).

[0068] Here, the light is refracted again through the air gap into the protective glass, with the refraction angle returning to 39°. Within a 3mm thickness, this produces a horizontal displacement of approximately 2.4mm (d2) (compared to 1.6mm if the thickness were 2mm). Finally, the light penetrates the water sample at a perfect 45° angle of incidence. The total horizontal displacement (d1+d2) reaches approximately 5.1mm, achieving the same horizontal displacement effect as traditional designs requiring 9.6mm of thickness with only about 4mm of total vertical thickness, significantly reducing the instrument's diameter.

[0069] This embodiment achieves sufficient horizontal displacement while maintaining a compact structure, significantly improving the instrument's miniaturization performance and installation adaptability.

[0070] Furthermore, in one embodiment, the photoelectric detection module includes a first detector and a second detector; with the vertical plane of the protective glass in the horizontal direction as a reference plane, two light sources in the light source module are symmetrically placed on both sides of the reference plane, and the first detector and the second detector are both placed on the reference plane for detecting 135° backscattered light and 90° scattered light, respectively.

[0071] Here, the axes of the two light sources are symmetrically distributed on both sides of the receiver's optical path axis. Their axes lie within a common conical surface inside the protective glass, and their intersection points perfectly converge at the light-emitting point of the protective glass. This overlapping axis design of "dual light source channels, shared detector" allows the first and second detectors to receive scattered signals from two different light source channels in a time-sharing manner. This not only reduces the number of detectors by half in terms of hardware but also ensures that the multispectral measurements are of "the same group of sediment particles in the same water body," fundamentally eliminating systematic errors caused by uneven spatial distribution of sediment.

[0072] In one embodiment, a measurement method based on the sand analyzer is provided, the method comprising the following steps:

[0073] Step 1, Optical signal modulation and incidence: At least two collimated optical signals are emitted through the light source module and sequentially pass through the light guide prism, air gap and protective glass of the optical modulation module to enter the water body to be measured at a preset incident angle;

[0074] Step 2, Scattered signal acquisition: Using a shared detector set at different locations in the photoelectric detection module, the scattered light signals with different scattering angles generated after each light signal enters the water body are acquired.

[0075] Step 3, Multispectral Data Fusion: The data processing module performs weighted fusion calculations on the received multi-path scattered light signals to eliminate particle size and color interference and construct a fusion curve sequence;

[0076] Step 4, Concentration Result Output: Based on the piecewise fitting relationship model established by the particle swarm optimization algorithm, the suspended particle concentration result of the tested water body is calculated and output according to the fusion curve sequence.

[0077] Furthermore, in one embodiment, the calculation process for multispectral data fusion in step 3 includes:

[0078] Step 31, Data preprocessing: The collected scattered light signal is subjected to abnormal signal removal and interpolation correction, zero-point correction based on pure water, frequency domain filtering and noise reduction based on wavelet transform, and inter-band normalization processing.

[0079] Step 32, Monotonicity Interval Determination: Use the first derivative sign to determine the monotonicity of each photoelectric signal curve;

[0080] Step 33, Average Gradient and Weight Calculation: The central difference method is used to calculate the gradient estimate of each photoelectric signal curve at each data point. Combined with the absolute value of the average gradient before and after the peak, the weight of each photoelectric signal curve is calculated using the following weight allocation function. :

[0081]

[0082] In the formula, Let be the mean of the gradient before the peak of the k-th photoelectric signal curve. Let be the mean of the gradients after the peak value of the k-th photoelectric signal curve; Let be the mean of the gradient before the peak of the j-th photoelectric signal curve. Let be the mean of the gradient after the peak of the j-th photoelectric signal curve, and α and β be hyperparameters that control the gradient sensitivity. α is used to enhance the rising segment, and β is used to suppress the falling segment.

[0083] Step 34, Construction of the fused curve sequence: Detect the peak point y_max of each photoelectric signal curve, accumulate the absolute value of the decrease in the peak value of each point starting from y_max to construct an increasing sequence, and combine each signal sequence according to the aforementioned weights. The superposition of these curves creates a sequence of fusion curves.

[0084] Furthermore, in one embodiment, the calculation process for the concentration result output in step 4 includes:

[0085] Initialize the particle swarm, where each particle represents a combination of a breakpoint and a polynomial order;

[0086] Particle fitness is evaluated using the Bayesian Information Criterion (BIC).

[0087] By iteratively updating the position and velocity of particles, and performing Cauchy mutation on the globally optimal particle when there is no significant improvement in the global optimal solution for several consecutive iterations, the optimal piecewise multiple function relationship between the fused curve signal value and the sand content is converged. Here, no significant improvement indicates that the difference between the globally optimal solutions obtained from adjacent iterations is less than a preset threshold, and the piecewise multiple function relationship satisfies:

[0088] When x ≤ 0.1, the polynomial expression is:

[0089]

[0090] When 0.1 < x ≤ 10, the polynomial expression is:

[0091]

[0092] When x > 10, the polynomial expression is:

[0093] .

[0094] Here, by converting the post-peak attenuation amount into an absolute value accumulation sequence, the bottleneck of traditional optical sand measuring instruments being unable to measure high-concentration water bodies due to "multi-value ambiguity" is completely overcome. Combined with a piecewise logarithmic multiple polynomial model optimized by Cauchy variation, the fitting correlation coefficient R of this invention is achieved across the entire measurement range. 2 All values ​​reached above 0.999, achieving extremely high full-range inversion accuracy.

[0095] In one embodiment, a sand-measuring system with a shared detector is provided, the system comprising:

[0096] The first module is used to realize optical signal modulation and incident: it emits at least two collimated optical signals and makes them pass through the light guide prism, air gap and protective glass in sequence, and enter the water body to be measured at a preset incident angle;

[0097] The second module is used to collect scattered light signals: by setting up a common detector at different locations, it collects multiple scattered light signals with different scattering angles generated after each light signal enters the water body.

[0098] The third module is used to realize multispectral data fusion: weighted fusion calculation is performed on the received multi-path scattered light signals to eliminate particle size and color interference and construct a fusion curve sequence.

[0099] The fourth module is used to output concentration results: based on the piecewise fitting relationship model established by the particle swarm optimization algorithm, the suspended particle concentration results of the tested water body are calculated and output according to the fusion curve sequence.

[0100] Specific limitations regarding the sand measurement system using shared detectors can be found in the above description of the compact multispectral photoelectric sand measuring instrument and method using shared detectors, and will not be repeated here. Each module in the aforementioned sand measurement system using shared detectors can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the corresponding operations of each module.

[0101] This invention achieves photoelectric sand measurement with two light source channels while sharing two photodetectors, enabling at least two spectra. Data fusion between the spectra improves testing accuracy. It achieves significant optical path misalignment within a limited thickness, resulting in a compact structure and small size, making it suitable for applications with strict size requirements and demonstrating promising application prospects.

[0102] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention without departing from its spirit and scope should be included within the protection scope of the present invention.

Claims

1. A compact multispectral photoelectric sand measuring instrument with a shared detector, characterized in that, include: The light source module is used to emit at least two collimated light signals with different spectra; An optical modulation module is disposed on the propagation path of the collimated light signal to change the propagation path of the light, so that each collimated light signal enters the water body to be measured at a preset incident angle. The photoelectric detection module includes multiple sets of shared photoelectric detectors, which are used to collect scattered light signals with different scattering angles generated after each collimated light signal enters the water body being measured. The data processing module, electrically connected to the photoelectric detection module, is used to perform weighted fusion processing on the collected multi-path scattered light signals to obtain the measurement results of suspended particle concentration in the water body being measured.

2. The compact multispectral photoelectric sand measuring instrument with shared detector according to claim 1, characterized in that, The light source module includes two symmetrically arranged light source channels; in addition to the light source module, the optical modulation module, the photoelectric detection module, and the data processing module are all shared by the two light source channels.

3. The compact multispectral photoelectric sand measuring instrument with shared detector according to claim 1, characterized in that, The optical modulation module includes a light guide prism, an air gap, and a protective glass arranged sequentially from top to bottom; the collimated light signal is horizontally displaced by passing through the light guide prism and the air gap in sequence, and then transmitted into the water after passing through the protective glass.

4. The compact multispectral photoelectric sand measuring instrument with shared detector according to claim 3, characterized in that, The light guide prism is a cylindrical wedge structure made of K9 optical glass, with a flat bottom surface and an upper side surface at a 51° angle to the bottom surface; the collimated light signal emitted by the light source module is incident on the light guide prism at a 39° angle to the vertical direction.

5. The compact multispectral photoelectric sand measuring instrument with shared detector according to claim 3, characterized in that, The air gap is located between the protective shell of the sand measuring instrument and the protective glass, and its thickness is 1mm. The collimated light signal is refracted from the light guide prism and enters the air gap at an exit angle of 70° to 72°, and the horizontal displacement generated in the air gap is 2.7mm to 3.1mm.

6. The compact multispectral photoelectric sand measuring instrument with shared detector according to claim 3, characterized in that, The protective glass is a circular glass sheet made of K9 optical glass; the protective glass has a thickness of 2mm to 3mm; the refraction angle of the collimated light signal in the protective glass is 39°, and the horizontal displacement generated in the protective glass is 1.6mm to 2.4mm; the preset incident angle of the collimated light signal entering the water body is 45°.

7. The compact multispectral photoelectric sand measuring instrument with shared detector according to claim 1, characterized in that, The photoelectric detection module includes a first detector and a second detector; with the vertical plane of the protective glass in the horizontal direction as the reference plane, the two light sources in the light source module are symmetrically placed on both sides of the reference plane, and the first detector and the second detector are both placed on the reference plane for 135° backscattered light detection and 90° scattered light detection, respectively.

8. A measurement method based on the sand measuring instrument according to any one of claims 1 to 7, characterized in that, The method includes the following steps: Step 1, Optical signal modulation and incidence: At least two collimated optical signals are emitted through the light source module and sequentially pass through the light guide prism, air gap and protective glass of the optical modulation module to enter the water body to be measured at a preset incident angle; Step 2, Scattered signal acquisition: Using a shared detector set at different locations in the photoelectric detection module, the scattered light signals with different scattering angles generated after each light signal enters the water body are acquired. Step 3, Multispectral Data Fusion: The data processing module performs weighted fusion calculations on the received multi-path scattered light signals to eliminate particle size and color interference and construct a fusion curve sequence; Step 4, Concentration Result Output: Based on the piecewise fitting relationship model established by the particle swarm optimization algorithm, the suspended particle concentration result of the tested water body is calculated and output according to the fusion curve sequence.

9. The measurement method according to claim 8, characterized in that, The calculation process for multispectral data fusion in step 3 includes: Step 31, Data preprocessing: The collected scattered light signal is subjected to abnormal signal removal and interpolation correction, zero-point correction based on pure water, frequency domain filtering and noise reduction based on wavelet transform, and inter-band normalization processing. Step 32, Monotonicity Interval Determination: Use the first derivative sign to determine the monotonicity of each photoelectric signal curve; Step 33, Average Gradient and Weight Calculation: The central difference method is used to calculate the gradient estimate of each photoelectric signal curve at each data point. Combined with the absolute value of the average gradient before and after the peak, the weight of each photoelectric signal curve is calculated using the following weight allocation function. : In the formula, Let be the mean of the gradient before the peak of the k-th photoelectric signal curve. Let be the mean of the gradients after the peak value of the k-th photoelectric signal curve; Let be the mean of the gradient before the peak of the j-th photoelectric signal curve. Let be the mean of the gradient after the peak of the j-th photoelectric signal curve, and α and β be hyperparameters that control the gradient sensitivity. α is used to enhance the rising segment, and β is used to suppress the falling segment. Step 34, Construction of the fused curve sequence: Detect the peak point y_max of each photoelectric signal curve, accumulate the absolute value of the decrease in the peak value of each point starting from y_max to construct an increasing sequence, and combine each signal sequence according to the aforementioned weights. The superposition of these curves creates a sequence of fusion curves.

10. The measurement method according to claim 9, characterized in that, The calculation process for the concentration result output in step 4 includes: Initialize the particle swarm, where each particle represents a combination of a breakpoint and a polynomial order; Particle fitness is evaluated using the Bayesian Information Criterion (BIC). By iteratively updating the position and velocity of particles, and performing Cauchy mutation on the globally optimal particle when there is no significant improvement in the global optimal solution for several consecutive iterations, the optimal piecewise multiple function relationship between the fused curve signal value and the sand content is converged. Here, no significant improvement indicates that the difference between the globally optimal solutions obtained from adjacent iterations is less than a preset threshold, and the piecewise multiple function relationship satisfies: When x ≤ 0.1, the polynomial expression is: When 0.1 < x ≤ 10, the polynomial expression is: When x > 10, the polynomial expression is: 。

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