A method and device for processing oceanographic lidar data to eliminate noise and light interference

Abstract

The present application provides a method and device for processing oceanographic laser radar data that eliminates noise light interference. The method provided in the present application: receives scattered light of a mixed light beam, divides the scattered light into mixed light and noise light, receives a mixed light signal based on a first photomultiplier tube, and receives a noise light signal based on a second photomultiplier tube; calculates the mixed light intensity value and the noise light intensity value respectively, and obtains filtered signal light according to the difference between the mixed light intensity value and the noise light intensity value; traverses each sampling point from far to near, calculates the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, and takes the sampling point with a signal-to-noise ratio of 1 as the farthest detection point; calculates the effective signal distance according to the farthest detection distance and the margin; and filters the target signal light from the filtered signal light according to the effective signal distance. The method and device for processing oceanographic laser radar data that eliminates noise light interference provided in the present application can effectively suppress sunlight noise and multiple scattered light from water bodies.

Description

Technical Field

[0001] The present application relates to the field of ocean laser radar technology, and in particular to a method and device for processing oceanographic laser radar data for eliminating noise light interference. Background Art

[0002] In the fields of marine science research, marine engineering construction, underwater target detection, etc., sea surveying lidar can quickly detect and analyze the underwater environment by emitting laser beams and receiving scattered echo signals from water bodies. It is a technical means to achieve long-distance and high-resolution underwater detection.

[0003] The weak underwater laser echo signals from oceanographic lidars are susceptible to interference from sunlight background noise and multiple scattered light from the water, causing the effective echo signal to be submerged in the background signal, significantly limiting the effective detection range and accuracy of oceanographic lidars. Existing technologies typically employ nighttime operations or narrowband filtering techniques to reduce the proportion of noise light entering the receiving system. Nighttime operations cannot achieve all-day detection of water areas. Because noise light has a wide spectral range and large intensity fluctuations, and the emitted light band highly overlaps with the ambient noise band, narrowband filtering techniques are difficult to completely block the noise light from entering the receiving system through water scattering. This results in a high proportion of noise light in the mixed echo signal, severely obscuring the weak laser scattered signal. Furthermore, traditional data processing methods often rely on fixed thresholds or simple filtering algorithms to distinguish signal light from interference light. These methods are unable to adapt to dynamic changes in noise light intensity. In strong light conditions, valid laser signals are easily misclassified as noise, while in weak light conditions, excessive noise light interference may remain. This results in poor stability and reliability of the data processing results, making it difficult to meet the high-precision detection requirements of oceanographic lidars in complex environments. Summary of the Invention

[0004] In view of this, the present application provides a method and device for processing oceanographic lidar data for eliminating noise light interference, so as to suppress the interference of sunlight background noise and multiple scattered light of water bodies on weak underwater laser echo signals.

[0005] Specifically, this application is implemented through the following technical solutions:

[0006] In a first aspect, the present application provides a method for processing oceanographic laser radar data to eliminate noise light interference, the method comprising:

[0007] Emitting circularly polarized laser light toward the water body to be measured, wherein the circularly polarized laser light is mixed with ambient light on the surface of the water body to be measured to form a mixed light beam;

[0008] receiving scattered light of the mixed light beam based on a receiving module, and dividing the scattered light into mixed light and noise light, receiving a mixed light signal based on a first photomultiplier tube, and receiving a noise light signal based on a second photomultiplier tube;

[0009] Calculating a mixed light intensity value of the mixed light signal, calculating a noise light intensity value of the noise light signal, and obtaining a filtered signal light according to a difference between the mixed light intensity value and the noise light intensity value;

[0010] Traversing each sampling point from far to near, for each sampling point, calculating the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, taking the sampling point with a signal-to-noise ratio of 1 as the farthest detection point, and determining the distance between the farthest detection point and the water surface to be measured as the farthest detection distance;

[0011] Calculating the effective signal distance according to the maximum detection distance and the margin;

[0012] Filter target signal light from the filtered signal light according to the effective signal distance.

[0013] The second aspect of the present application provides a data processing device for oceanographic laser radar that eliminates noise and light interference, the device comprising a transmitting module, a processing module, and a screening module; wherein,

[0014] The transmitting module is used to transmit circularly polarized laser light to the water body to be measured, and the circularly polarized laser light is mixed with ambient light on the surface of the water body to be measured to form a mixed light beam;

[0015] The processing module is configured to receive scattered light of the mixed light beam based on the receiving module, and separate the scattered light into mixed light and noise light, receive a mixed light signal based on the first photomultiplier tube, and receive a noise light signal based on the second photomultiplier tube;

[0016] The processing module is further configured to calculate a mixed light intensity value of the mixed light signal, calculate a noise light intensity value of the noise light signal, and obtain filtered signal light according to a difference between the mixed light intensity value and the noise light intensity value;

[0017] The processing module is further configured to traverse each sampling point from far to near, and for each sampling point, calculate the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, determine the sampling point with a signal-to-noise ratio of 1 as the farthest detection point, and determine the distance between the farthest detection point and the surface of the water body to be measured as the farthest detection distance;

[0018] The screening module is used to calculate the effective signal distance according to the farthest detection distance and the margin;

[0019] The screening module is further configured to screen target signal light from the filtered signal light according to the effective signal distance.

[0020] The present application provides a method and device for processing oceanographic lidar data to eliminate noise interference. By splitting scattered light containing noise from water, the noise signal in the mixed light is filtered based on the intensity difference between the separated mixed light and the noise light, effectively eliminating noise interference from the lidar data processing, thereby obtaining pure target signal light. First, circularly polarized laser light is emitted, and a receiving module is used to separate the mixed light and the noise light in the scattered light. The mixed light and the noise light are received by a first photomultiplier tube and a second photomultiplier tube, respectively. The noise is initially filtered out by calculating the difference between the mixed light intensity and the noise light intensity. The signal-to-noise ratio is then calculated by traversing sampling points from far to near, and the maximum detection range is determined based on the sampling point with a signal-to-noise ratio of 1. The effective signal distance is calculated based on the margin, and the target signal light is filtered. This method systematically eliminates noise interference, and the resulting target signal light eliminates the influence of sunlight background noise and multiple scattered light from water, significantly improving the signal-to-noise ratio and reliability of the signal. This provides a high-quality signal foundation for subsequent applications such as water parameter measurement and inversion, effectively enhancing the detection performance of lidar in complex water environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flowchart of Example 1 of the method for processing oceanographic lidar data to eliminate noise and light interference provided by this application;

[0022] Figure 2 This is a structural diagram of Example 1 of the oceanographic lidar data processing device for eliminating noise light interference provided in this application. DETAILED DESCRIPTION

[0023] Exemplary embodiments are described in detail herein, with examples illustrated in the accompanying drawings. When the following description refers to the drawings, identical numerals in different drawings represent identical or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with this application.

[0024] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms "a," "the," and "the" used in this application are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0025] It should be understood that although the terms first, second, third, etc. may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0026] Specific embodiments are given below to introduce the technical solutions of the present application in detail.

[0027] Figure 1 This is a flow chart of Example 1 of the method for processing oceanographic laser radar data to eliminate noise and light interference provided by this application. Figure 1 The method provided in this embodiment may include:

[0028] S101 , emitting circularly polarized laser light toward a water body to be measured, wherein the circularly polarized laser light is mixed with ambient light on the surface of the water body to be measured to form a mixed light beam.

[0029] Specifically, a hydrographic lidar emits circularly polarized laser light toward the water body. Before entering the water, the circularly polarized laser light interacts with noise light, such as sunlight, in the air, forming a mixed beam that enters the water. Both the emitted circularly polarized light and the sunlight are backscattered in the water, and their scattered signals are synchronously received by the receiving module.

[0030] S102 : Receive scattered light of the mixed light beam based on a receiving module, and separate the scattered light into mixed light and noise light, receive a mixed light signal based on a first photomultiplier tube, and receive a noise light signal based on a second photomultiplier tube.

[0031] Specifically, after the mixed light beam is incident on the water body to be tested, it will be scattered in the water body to generate scattered light. The scattered light is emitted from the water body to be tested and received by the receiving module. The emitted scattered light includes the signal light of the circularly polarized laser, ambient light, and noise light generated by the underwater scattered light. At this time, the emitted scattered light includes a stable interference base generated by the sunlight background noise and the multiple scattered light of the water body, that is, the background value. The background value (sunlight noise and multiple scattered light) mainly exists in a linearly polarized or unpolarized form; the receiving module receives the scattered light and modulates the scattered light, dividing the scattered light into two beams of light, one of which is mixed light, which includes the signal light of the circularly polarized laser and noise light, and the other is noise light. The mixed light signal corresponding to the mixed light is received based on the first photomultiplier tube, and the noise light signal corresponding to the noise light is received based on the second photomultiplier tube.

[0032] Furthermore, before the first photomultiplier tube and the second photomultiplier tube receive the scattered light, the method includes:

[0033] (1) emitting circularly polarized laser light to a first photomultiplier tube and a second photomultiplier tube, respectively, receiving a mixed light signal based on the first photomultiplier tube, receiving a noise light signal based on the second photomultiplier tube, and constructing a correction equation based on the mixed light signal and the noise light signal;

[0034] (2) Solving a correction coefficient of the first photomultiplier tube according to the correction equation, and correcting the mixed light signal received by the first photomultiplier tube based on the correction coefficient.

[0035] Specifically, due to imperfections in optical components (including low extinction ratios and parasitic polarization) and variations in the response of photomultiplier tubes (PMTs), direct data measurement cannot theoretically eliminate sunlight and multiply scattered light. Effective filtering of sunlight and multiply scattered light requires a meticulous adjustment process and meeting specific testing standards. In a darkroom environment, standard circularly polarized light is injected into the first and second PMTs, causing the first PMT to receive the mixed light signal and the second PMT to receive the noise light signal.

[0036] Furthermore, the specific implementation steps of constructing a correction equation based on the mixed optical signal and the noise optical signal include:

[0037] calculating a ratio of the mixed optical signal to the noise optical signal;

[0038] A correction equation is constructed based on the product of the coefficient and the ratio, and the coefficient corresponding to when the product is equal to 1 is determined as the correction coefficient of the first photomultiplier tube.

[0039] The correction equation can be expressed by the following formula:

[0040] ;

[0041] in, is the coefficient;

[0042] is a mixed optical signal;

[0043] is the noise optical signal;

[0044] Substituting the received mixed light signal and noise light signal into the correction equation, the correction coefficient can be solved. Based on this correction equation, the mixed light signal received by the first photomultiplier tube is corrected. This can effectively compensate for signal deviations caused by imperfect optical components (such as low extinction ratio and parasitic polarization) and differences in photomultiplier tube response, ensuring that the background signal ratios of the two channels are consistent.

[0045] Furthermore, changes in solar radiation will affect the background signals of the first and second photomultiplier tubes. Under different solar irradiances, the ratio of the distant background signals of the two photomultiplier tubes is not 1. Therefore, it is necessary to select an appropriate calibration coefficient based on the irradiance so that the ratio of the background signals of the two photomultiplier tubes is 1. The specific implementation steps include:

[0046] (1) Divide the irradiance into multiple intervals based on the irradiance changes of the measured ambient sunlight conditions;

[0047] Specifically, irradiance refers to the light radiation power received per unit area. The irradiance monitor can be used to monitor the changes in solar irradiance in the measurement environment in real time. The continuous irradiance value is divided into several discrete ranges based on the irradiance changes to match the correction requirements under different lighting conditions.

[0048] For example, in one embodiment, the solar irradiance on a certain day varies from 0 to 500 W / m², which is divided into five irradiance intervals, each of which corresponds to a sunlight condition.

[0049] (2) Traverse each irradiance interval and select the representative irradiance value of the currently calculated irradiance interval;

[0050] Specifically, for each irradiance interval, a typical value is selected as a representative irradiance value to simulate the lighting conditions in the interval and serve as a benchmark for subsequent calibration of the correction coefficient.

[0051] (3) emitting circularly polarized laser light having an irradiance representing an irradiance value to the first photomultiplier tube and the second photomultiplier tube, respectively, and constructing a correction equation including a correction coefficient based on the mixed light signal and the noise light signal received by the first photomultiplier tube and the second photomultiplier tube;

[0052] Specifically, under the representative irradiance value, the mixed light signal received by the first photomultiplier tube and the noise light signal received by the second photomultiplier tube are obtained. Combined with the above description, the background values ​​of the mixed light signal and the noise light signal are substituted into the correction equation to obtain the correction coefficient under the irradiance range.

[0053] (4) Solve the correction coefficient corresponding to the first photomultiplier tube in the currently calculated irradiance range according to the correction equation, and store each correction coefficient in correspondence with the corresponding irradiance range.

[0054] Specifically, after obtaining the correction coefficient corresponding to each irradiance interval, the irradiance interval and the correction coefficient are stored in association. During actual measurement, the irradiance interval in which the current irradiance falls is determined, the corresponding correction coefficient is searched, and the mixed light signal received by the first photomultiplier tube is corrected based on the corresponding correction coefficient. By dividing and matching the correction coefficients according to the irradiance interval, the system can dynamically adapt to ambient light interference under different sunlight conditions, effectively suppressing sunlight noise and multiple scattered light.

[0055] S103 , calculating a mixed light intensity value of the mixed light signal, calculating a noise light intensity value of the noise light signal, and obtaining filtered signal light according to a difference between the mixed light intensity value and the noise light intensity value.

[0056] Specifically, the steps of calculating the mixed light intensity value and the noise light intensity value include:

[0057] The receiving module receives the scattered light of the mixed light beam and separates the scattered light into mixed light and noise light, and the receiving module includes a quarter-wave plate and a Wollaston lens; and includes:

[0058] (1) determining a first Stokes vector according to the circularly polarized laser light, determining a second Stokes vector according to the noise light, and calculating a third Stokes vector of the scattered light based on the first Stokes vector and the second Stokes vector;

[0059] Specifically, the total light intensity of the circularly polarized laser is determined, and the total light intensity is used as the first element of the first Stokes vector to represent the total radiation intensity of the circularly polarized laser. Since the laser is circularly polarized light, it does not contain linear polarization components in a specific direction. Therefore, the second and third elements of the first Stokes vector related to linear polarization are 0 respectively. According to the polarization characteristics of the circularly polarized laser, the fourth element of the first Stokes vector reflects the intensity and direction of the circular polarization. According to the modulation parameters of the circularly polarized laser, the first Stokes vector is expressed as ; Similarly, the second Stokes vector corresponding to the noise light is expressed as , the third Stokes vector of the scattered light after scattering is ;

[0060] (2) determining a fourth Stokes vector of the scattered light after passing through the quarter-wave plate according to the product of the Mueller matrix of the quarter-wave plate and the third Stokes vector;

[0061] Specifically, according to the parameters of the quarter-wave plate, its Mueller matrix is ​​determined as:

[0062] ;

[0063] The fourth Stokes vector can be calculated by the following formula:

[0064] ;

[0065] (3) The scattered light is modulated by the Wollaston lens and is divided into the mixed light and the noise light, and the fifth Stokes vector of the mixed light and the sixth Stokes vector of the noise light are calculated according to the Mueller matrix of the Wollaston lens;

[0066] Specifically, the Wollaston lens is a polarization splitter prism that can split a beam of light into two beams of light. The Mueller matrix of the Wollaston lens is:

[0067] , ;

[0068] The scattered light is divided into mixed light and noise light after passing through the Wollaston lens. The fifth Stokes vector corresponding to the mixed light is:

[0069] ;

[0070] The sixth Stokes vector corresponding to the noise light is:

[0071] ;

[0072] (4) Calculating the mixed light intensity value received by the first photomultiplier tube according to the fifth Stokes vector, and calculating the noise light intensity value received by the second photomultiplier tube according to the sixth Stokes vector.

[0073] Specifically, the photomultiplier tube only detects the intensity of the received light, that is, the first element in the Stokes vector, so the mixed light intensity value received by the first photomultiplier tube is , the noise light intensity received by the second photomultiplier tube is .

[0074] Furthermore, after obtaining the mixed light intensity value and the noise light intensity value, the noise light intensity value is subtracted from the mixed light intensity value to eliminate the background value interference in the mixed light signal. The background value of the mixed light signal refers to the stable interference base generated by non-target sources, which may include sunlight background noise and multiple scattered light from water bodies; the circularly polarized component in the circularly polarized laser is obtained. Since the Stokes vector of ambient light does not contain a circular polarization component, the circularly polarized laser degenerates into a large amount of linear polarization components after multiple scattering underwater. Based on this, it is theoretically possible to remove the linear polarization light generated by solar background light and water multiple scattering, and obtain the circular polarization component basically coming from the laser light source, that is, the filtered signal light.

[0075] S104. Traverse each sampling point from far to near, and for each sampling point, calculate the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, and set the sampling point with a signal-to-noise ratio of 1 as the farthest detection point. The distance between the farthest detection point and the water surface to be measured is determined as the farthest detection distance.

[0076] Specifically, traversing each sampling point from far to near means starting from the position farthest from the water surface and gradually checking the sampling points of each laser echo signal in the direction of the water surface. The interval between sampling points can be determined by the sampling frequency of the lidar. Combined with the description above, for each sampling point, the mixed light intensity value and the noise light intensity value at that sampling point are calculated. The signal-to-noise ratio is calculated based on the ratio of the mixed light intensity value to the noise light intensity value. The signal-to-noise ratio reflects the relative strength of the effective signal and the noise. The larger the ratio, the higher the proportion of effective signal and the stronger the data reliability. When the signal-to-noise ratio drops to 1, it means that the mixed light intensity value is equal to the noise light intensity value. At this time, the effective signal is too weak to be distinguished from the noise. Therefore, the sampling point corresponding to the signal-to-noise ratio equal to 1 is regarded as the farthest detection point, and the distance between the farthest detection point and the water surface is measured as the farthest detection distance. The farthest detection distance is the limit of the range within which the system can effectively identify the target signal under the current environment.

[0077] S105: Calculate the effective signal distance according to the maximum detection distance and the margin.

[0078] The specific implementation steps include:

[0079] (1) Taking a position halfway between the emission point and the farthest detection point as a starting point, dividing the farthest detection distance along a first direction and a second direction using the margin as a distance interval to obtain a plurality of interval points; the first direction and the second direction are opposite;

[0080] Specifically, the position halfway between the emission point and the farthest detection point is in the middle area within the effective detection range, which can minimize the impact of boundary errors on the determination of the effective signal interval. The first direction refers to the direction from the starting point to the farthest detection point, and the second direction refers to the direction from the starting point to the emission point. Taking the position halfway as the starting point can balance the search range of the first direction and the second direction, avoid unilateral interval misjudgment due to the starting point being biased towards one end, and ensure that the effective signal distance calculated subsequently is more in line with the actual stable signal interval.

[0081] Furthermore, the margin is the minimum acquisition resolution determined according to the sampling frequency of the laser radar. The margin is used as the distance interval, and the optical path of the laser underwater is divided into multiple interval points starting from the starting point along the first direction and the second direction at the same time.

[0082] (2) respectively calculating the first slope corresponding to each interval point in the water body profile curve in the first direction, and the second slope corresponding to each interval point in the water body profile curve in the second direction;

[0083] Specifically, the water profile curve reflects the change in laser signal intensity as a function of underwater distance. It is constructed with underwater distance (vertical distance from the water surface) as the horizontal axis and circular polarization component signal intensity after eliminating ambient light interference as the vertical axis. The slope corresponding to each interval point represents the signal attenuation rate at that location. The local interval corresponding to a particular interval point is formed by selecting adjacent acquisition points before and after the interval point as the center. This local interval is calculated using the least squares method to obtain the slope corresponding to each interval point. The slope corresponding to the interval point calculated along the first direction is the first slope, and the slope corresponding to the interval point calculated along the second direction is the second slope.

[0084] (3) Determine a first curve point according to the first slope, determine a second curve point according to the second slope, and determine the distance between the first curve point and the second curve point as the effective signal distance.

[0085] Specifically, after obtaining the first slope of each interval point in the first direction and the second slope of each interval point in the second direction, taking the first direction as an example, starting from the starting point, the difference between the first slope of each interval point and the slope corresponding to the starting point is sequentially compared. The first interval point in the first direction whose difference is greater than the threshold is determined as the first curve point. Similarly, the second curve point in the second direction is determined. The first curve point is used as the lower limit of the effective signal distance, and the second curve point is used as the upper limit of the effective signal distance. In this way, the distance between the first curve point and the second curve point is used as the effective signal distance. It should be noted that the threshold for determining the curve point is set according to actual needs and is not limited in this embodiment.

[0086] By taking the position halfway between the emission point and the farthest detection point as the starting point and dividing the interval points in both directions with a margin, the near-field and far-field search ranges can be balanced, and the interference of boundary errors on the signal interval determination can be reduced; by calculating the slope of each interval point on the water profile curve, the changes in signal attenuation rates at different positions can be accurately captured; and then the first curve point corresponding to the first direction and the second curve point corresponding to the second direction are determined based on the slope difference exceeding the threshold, thereby defining the effective signal distance. This can accurately lock the interval where the signal attenuation is stable, eliminate the influence of near-field interference and far-end noise, and ensure that the water parameters (such as the attenuation coefficient) subsequently calculated based on the effective signal distance are more in line with the actual optical characteristics of the water body, significantly improving the measurement accuracy and data reliability of the oceanographic lidar in complex environments.

[0087] S106 , screening target signal light from the filtered signal light according to the effective signal distance.

[0088] Specifically, from the filtered signal light, the signal segments within the effective signal distance range are extracted, which are the target signal light. This screening ensures that the signal used to calculate parameters such as the water attenuation coefficient comes only from a stable and reliable range, avoiding measurement errors caused by invalid signals.

[0089] Furthermore, after screening out the target signal light, the method further includes:

[0090] (1) Drawing a water body profile curve based on the target signal light;

[0091] Specifically, the steps for drawing a water body profile curve include:

[0092] The initial optical signal intensity at the emission point is obtained; starting from the emission point, the optical signal intensity of multiple collection points is collected at intervals of a sampling frequency; the effective optical signal intensity corresponding to the effective signal distance is obtained; a coordinate system is constructed with the optical signal intensity as the ordinate and the underwater distance as the abscissa, and the emission point, multiple collection points, and the effective optical signal intensity corresponding to the effective signal distance are substituted into the coordinate system to obtain a water body profile curve.

[0093] Specifically, the light signal intensity corresponding to the emission point and multiple collection points can be directly measured by a photomultiplier tube. The distance between the collection point and the emission point is used as the horizontal coordinate, and the light signal intensity corresponding to the collection point is used as the vertical coordinate to obtain the coordinates of the collection point. The coordinates of each collection point are substituted into the coordinate system, and the coordinates of each interval point are connected in sequence to obtain the water body profile curve.

[0094] (2) Determine the water body attenuation coefficient based on the slope of the water body profile curve.

[0095] The specific implementation steps include:

[0096] Calculating the slope corresponding to each sampling point in the water body profile curve among the multiple sampling points;

[0097] An average is calculated based on multiple sampling points and their corresponding slopes, and the average is used as the water body attenuation coefficient.

[0098] Specifically, the slope corresponding to each sampling point in the water profile curve is calculated by the least squares method. For the multiple slopes of the water profile curve corresponding to the effective signal distance, the average is calculated according to the multiple slopes and the number of sampling points, and the average is used as the water attenuation coefficient within the effective signal distance interval.

[0099] By drawing a water profile curve based on the target signal light, the coordinates are constructed using the initial light intensity at the emission point, the multi-point light intensity collected at the sampling frequency, and the light intensity within the effective signal distance, the attenuation law of the laser signal with underwater distance is intuitively presented; then the slope of each sampling point in the effective signal interval is calculated and the average is taken to determine the water attenuation coefficient. By using the screened stable signal, the influence of near-field interference and far-end noise is eliminated, so that the water profile curve can truly reflect the optical properties of the water body, and the calculated attenuation coefficient is more accurate, which effectively improves the accuracy and reliability of the oceanographic laser radar in measuring the optical parameters of the water body, and provides accurate data support for marine environment monitoring, underwater optical property analysis, etc.

[0100] The present embodiment provides a method for processing oceanographic lidar data to eliminate noise interference. The method emits circularly polarized laser light and uses a receiving module containing a quarter-wave plate and a Wollaston lens to separate scattered light into mixed light and noise light. A first photomultiplier tube receives the mixed light, while a second photomultiplier tube receives the noise light. The Stokes vector, the wave plate, and the Mueller matrix of the lens are used to calculate the mixed light intensity and the noise light intensity. The circularly polarized component of the target light is calculated by calculating the difference between the mixed light intensity and the noise light intensity. This method directly filters out noise from the mixed light, eliminating sunlight background noise and multiple scattered light from water. The signal-to-noise ratio is then calculated by traversing sampling points from far to near. The farthest detection point is defined using a signal-to-noise ratio of 1 as the criterion, thereby determining the maximum detection range of the lidar. Furthermore, interval points are bidirectionally divided based on a position halfway between the farthest detection range. The effective signal range is determined by combining slope mutation analysis, balancing the near-field and far-field search ranges and eliminating boundary error interference. Finally, the target signal light is filtered based on the effective signal distance, ensuring that only high-quality signals with stable attenuation are retained for accurate water analysis. This method breaks through the time limitations of nighttime detection and the spectral limitations of narrow-band filtering, achieving high-precision detection throughout the day. It also significantly improves the signal-to-noise ratio and data reliability, effectively extending the detection range of the ocean-surveying lidar, and providing a pure signal basis for the inversion of water parameters (such as the attenuation coefficient), thereby enhancing the system's adaptability and detection performance in complex water environments.

[0101] Corresponding to the aforementioned embodiment of a method for processing oceanographic laser radar data for eliminating noise and light interference, the present application also provides an embodiment of a device for processing oceanographic laser radar data for eliminating noise and light interference.

[0102] Figure 2 This is a structural diagram of the first embodiment of the oceanographic laser radar data processing device for eliminating noise and light interference provided by this application. Figure 2 The device provided in this embodiment includes a transmitting module 210, a processing module 220 and a screening module 230; wherein,

[0103] The transmitting module 210 is used to transmit circularly polarized laser light to the water body to be measured, and the circularly polarized laser light is mixed with ambient light on the surface of the water body to be measured to form a mixed light beam;

[0104] The processing module 220 is configured to receive scattered light of the mixed light beam based on the receiving module, separate the scattered light into mixed light and noise light, receive a mixed light signal based on the first photomultiplier tube, and receive a noise light signal based on the second photomultiplier tube;

[0105] The processing module 220 is further configured to calculate a mixed light intensity value of the mixed light signal, calculate a noise light intensity value of the noise light signal, and obtain filtered signal light according to a difference between the mixed light intensity value and the noise light intensity value;

[0106] The processing module 220 is further configured to traverse each sampling point from far to near, and for each sampling point, calculate the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, determine the sampling point with a signal-to-noise ratio of 1 as the farthest detection point, and determine the distance between the farthest detection point and the surface of the water body to be measured as the farthest detection distance;

[0107] The screening module 230 is configured to calculate the effective signal distance based on the maximum detection distance and the margin;

[0108] The screening module 230 is further configured to screen target signal light from the filtered signal light according to the effective signal distance.

[0109] The device of this embodiment can be used to perform Figure 1 The steps, specific implementation principles and implementation processes of the method embodiment shown are similar and will not be repeated here.

[0110] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0111] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present application scheme. A person of ordinary skill in the art can understand and implement it without paying any creative work.

[0112] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for processing oceanographic lidar data to eliminate noise and light interference, characterized in that: The method comprises: emitting circularly polarized laser light toward the water body to be measured, wherein the circularly polarized laser light is mixed with ambient light on the surface of the water body to be measured to form a mixed light beam; receiving scattered light of the mixed light beam based on a receiving module, and dividing the scattered light into mixed light and noise light, receiving a mixed light signal based on a first photomultiplier tube, and receiving a noise light signal based on a second photomultiplier tube; Calculating a mixed light intensity value of the mixed light signal, calculating a noise light intensity value of the noise light signal, and obtaining a filtered signal light according to a difference between the mixed light intensity value and the noise light intensity value; Traversing each sampling point from far to near, for each sampling point, calculating the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, taking the sampling point with a signal-to-noise ratio of 1 as the farthest detection point, and determining the distance between the farthest detection point and the water surface to be measured as the farthest detection distance; Calculate the effective signal distance based on the maximum detection distance and the margin, where the margin is the minimum acquisition resolution determined by the sampling frequency of the laser radar; The step of calculating the effective signal distance according to the maximum detection distance and the margin includes: Taking a position halfway between the emission point and the farthest detection point as a starting point, dividing the farthest detection distance along a first direction and a second direction using the margin as a distance interval to obtain a plurality of interval points; the first direction and the second direction are opposite; Calculate the first slope corresponding to each interval point in the water body profile curve in the first direction, and the second slope corresponding to each interval point in the water body profile curve in the second direction; determining a first curve point according to the first slope, determining a second curve point according to the second slope, and determining the distance between the first curve point and the second curve point as the effective signal distance; Filter target signal light from the filtered signal light according to the effective signal distance.

2. The method according to claim 1, characterized in that The method further comprises: emitting circularly polarized laser light to a first photomultiplier tube and a second photomultiplier tube respectively, receiving a mixed light signal based on the first photomultiplier tube, receiving a noise light signal based on the second photomultiplier tube, and constructing a correction equation based on the mixed light signal and the noise light signal; A correction coefficient of the first photomultiplier tube is solved according to the correction equation, and the mixed light signal received by the first photomultiplier tube is corrected based on the correction coefficient.

3. The method according to claim 2, characterized in that The constructing of a correction equation based on the mixed optical signal and the noise optical signal comprises: calculating a ratio of the mixed optical signal to the noise optical signal; A correction equation is constructed based on the product of the coefficient and the ratio, and the coefficient corresponding to when the product is equal to 1 is determined as the correction coefficient of the first photomultiplier tube.

4. The method according to claim 2, characterized in that The method further comprises: Divide the irradiance into multiple intervals based on the irradiance changes of the measured ambient sunlight conditions; Traverse each irradiance interval and select the representative irradiance value of the currently calculated irradiance interval; emitting circularly polarized laser light having an irradiance representing an irradiance value to the first photomultiplier tube and the second photomultiplier tube, respectively, and constructing a correction equation including a correction coefficient based on the mixed light signal and the noise light signal received by the first photomultiplier tube and the second photomultiplier tube; The correction coefficient corresponding to the first photomultiplier tube in the currently calculated irradiance interval is solved according to the correction equation, and each correction coefficient is stored in correspondence with the corresponding irradiance interval.

5. The method according to claim 1, wherein After screening out the target signal light, the method includes: Drawing a water body profile curve based on the target signal light; The water body attenuation coefficient is determined according to the slope of the water body profile curve.

6. The method according to claim 5, characterized in that Drawing a water body profile curve based on the target signal light includes: Obtaining the initial optical signal strength of the emission point; Collecting light signal intensities at a plurality of collection points starting from the emission point at intervals of a sampling frequency; Obtain the effective optical signal strength corresponding to the effective signal distance; A coordinate system is constructed with the optical signal intensity as the ordinate and the underwater distance as the abscissa. The effective optical signal intensity corresponding to the emission point, multiple collection points and the effective signal distance is substituted into the coordinate system to obtain a water body profile curve.

7. The method according to claim 5, characterized in that The method of determining the water body attenuation coefficient according to the slope of the water body profile curve comprises: Calculating the slope corresponding to each sampling point in the water body profile curve among the multiple sampling points; An average is calculated based on multiple sampling points and their corresponding slopes, and the average is used as the water body attenuation coefficient.

8. The method according to claim 1, characterized in that The receiving module receives the scattered light of the mixed light beam and separates the scattered light into mixed light and noise light, and the receiving module includes a quarter-wave plate and a Wollaston lens; and includes: determining a first Stokes vector according to the circularly polarized laser light, determining a second Stokes vector according to the noise light, and calculating a third Stokes vector of the scattered light based on the first Stokes vector and the second Stokes vector; determining a fourth Stokes vector of the scattered light after passing through the quarter-wave plate according to a product of the Mueller matrix of the quarter-wave plate and the third Stokes vector; The scattered light is modulated by the Wollaston lens and is divided into the mixed light and the noise light, and the fifth Stokes vector of the mixed light and the sixth Stokes vector of the noise light are calculated according to the Mueller matrix of the Wollaston lens; The mixed light intensity value received by the first photomultiplier tube is calculated according to the fifth Stokes vector, and the noise light intensity value received by the second photomultiplier tube is calculated according to the sixth Stokes vector.

9. A data processing device for oceanographic laser radar that eliminates noise and light interference, characterized in that: The device includes a transmitting module, a processing module and a screening module; wherein, The transmitting module is used to transmit circularly polarized laser light to the water body to be measured, and the circularly polarized laser light is mixed with ambient light on the surface of the water body to be measured to form a mixed light beam; The processing module is configured to receive scattered light of the mixed light beam based on the receiving module, and separate the scattered light into mixed light and noise light, receive a mixed light signal based on the first photomultiplier tube, and receive a noise light signal based on the second photomultiplier tube; The processing module is further configured to calculate a mixed light intensity value of the mixed light signal, calculate a noise light intensity value of the noise light signal, and obtain filtered signal light according to a difference between the mixed light intensity value and the noise light intensity value; The processing module is further configured to traverse each sampling point from far to near, and for each sampling point, calculate the ratio of the mixed light intensity value to the noise light intensity value to obtain a signal-to-noise ratio, determine the sampling point with a signal-to-noise ratio of 1 as the farthest detection point, and determine the distance between the farthest detection point and the surface of the water body to be measured as the farthest detection distance; The screening module is used to calculate the effective signal distance according to the farthest detection distance and the margin, where the margin is the minimum acquisition resolution determined according to the sampling frequency of the laser radar; The step of calculating the effective signal distance according to the maximum detection distance and the margin includes: Taking a position halfway between the emission point and the farthest detection point as a starting point, dividing the farthest detection distance along a first direction and a second direction using the margin as a distance interval to obtain a plurality of interval points; the first direction and the second direction are opposite; Calculate the first slope corresponding to each interval point in the water body profile curve in the first direction, and the second slope corresponding to each interval point in the water body profile curve in the second direction; determining a first curve point according to the first slope, determining a second curve point according to the second slope, and determining the distance between the first curve point and the second curve point as the effective signal distance; The screening module is further configured to screen target signal light from the filtered signal light according to the effective signal distance.

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