An anisotropic correction-based remote sensing reflectance data acquisition method

Abstract

This invention discloses a method for acquiring remote sensing reflectance data based on anisotropic correction. The method includes acquiring the remote sensing reflectance of a water body and its corresponding relative azimuth, observation angle, and solar zenith angle; determining the type of water body based on its remote sensing reflectance; considering water body classification and establishing correction coefficient lookup tables for the spectral characteristics and optical properties of different water bodies; matching the correction coefficient at the current angle from the corresponding self-established lookup table based on the relative azimuth, observation angle, solar zenith angle, and water body type; calculating the remote sensing reflectance at the target angle based on the correction coefficient at the target angle in the lookup table and the inherent optical characteristic parameters based on the QAA algorithm. This method has good applicability to various types of water bodies and can overcome the limitation of commonly used fixed observation angles when acquiring remote sensing reflectance using an angle-adjustable floating optical device.

Description

Technical Field

[0001] This invention relates to the field of remote sensing reflectance acquisition technology, and more specifically to a method for acquiring remote sensing reflectance data based on anisotropic correction. Background Technology

[0002] Remote sensing reflectance ( , ) is usually defined as the radiance of water ( ) and downstream irradiance ( The ratio of ( ) to ( ), defined as exactly above the sea surface, is a commonly used apparent optical parameter in ocean color remote sensing. Its representation is as follows:

[0003] ;

[0004] in, It refers to being exactly on the surface of the water; Represents the zenith angle of the sun; Represents the instrument's observation angle; This represents the relative azimuth angle of the sensor with respect to the plane of the sun. Represents wavelength.

[0005] Ideal solar observation geometry, i.e., a solar zenith angle of 0° and an nadir angle, cannot be effectively measured in reality. This is determined by physical limits, operational safety, and signal validity. Therefore, the core value of remote sensing reflectance products lies in the comparability after angle normalization, rather than the idealization of absolute geometric conditions. However, data obtained from on-site measurements or satellite remote sensing observations... Data typically varies with changes in solar observation geometry, water composition, and biological optical properties, and differs across different types of water bodies. It is significantly affected by anisotropy. Therefore, before performing inversion to obtain water color remote sensing data products, it is necessary to... The preprocessing step of anisotropic correction involves converting the water remote sensing reflectance data obtained from observations at various angles into data under specific observation conditions using correction methods. For example, the solar zenith angle is 0° and the nadir observation conditions. Currently, there are many studies on open sea areas and waters dominated by chlorophyll concentration (CHL), but fewer studies on the anisotropy of coastal waters with high mineral particle (MIN) concentration. The Lee2011 method is currently in operational use and has performance advantages in typical coastal waters. However, this method is mainly applicable to common coastal clear waters and eutrophic waters, and its performance in clear water long-wavelengths and waters dominated by mineral particles (MIN) needs improvement. Therefore, establishing an anisotropy correction scheme applicable to various types of water bodies is not only helpful in providing standardized remote sensing reflectance data products, but also the foundation for water quality parameter inversion.

[0006] Furthermore, common field measurement methods for obtaining remote sensing reflectance data can be broadly categorized into three types: surface measurement, underwater measurement, and near-surface measurement. Surface measurement requires avoiding solar flares and performing radiation correction, and is easily affected by measurement errors in sky radiance. Underwater measurement measures radiance and irradiance data at different depths and extrapolates them to the water-air interface. This requires attenuation correction and interface refraction correction. The surface observation method, however, directly measures the upward radiance below the water surface. Combined with underwater irradiance Calculations. Among them, the optical levitation system (OFS) proposed by Talone et al. can obtain the most common... Data was collected under conditions of on-site observation angles and partial relative azimuth angles. It consists of three parts: one irradiance sensor fixed to the mast, and two other irradiance sensors deployed at a depth of approximately 2 cm on a towed T-shaped floating frame to measure the nadir (…). ) and non-nadir observation angle ( )of The system uses tilt sensors and a compass to record the frame's tilt angle and orientation, then calculates the relative azimuth angle based on the solar azimuth angle. However, existing optical levitation systems cannot acquire data with autonomously adjustable angles, limiting the standardization and correction of data products, necessitating improvements. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for acquiring remote sensing reflectance data based on anisotropic correction.

[0008] To achieve the above objectives, the present invention provides a method for acquiring remote sensing reflectance data based on anisotropic correction, comprising:

[0009] Obtain the remote sensing reflectance of the water body and its corresponding relative azimuth, observation angle, and solar zenith angle;

[0010] Water body types can be distinguished based on the spectral characteristics of the remote sensing reflectance of the water body;

[0011] Based on the mean remote sensing reflectance, spectral variability parameter threshold, and inherent optical characteristic parameter laws of various types of water bodies, a correction coefficient lookup table suitable for various types of water bodies is automatically established.

[0012] The correction coefficient for the current angle is matched from the corresponding self-built lookup table based on the relative azimuth, observation angle, solar zenith angle, and water type.

[0013] The remote sensing reflectance at the target angle is calculated based on the correction coefficient and inherent optical characteristic parameters at the target angle in the self-built lookup table, resulting in a standardized remote sensing reflectance data product.

[0014] Furthermore, the types of water bodies include several types of water bodies in nature, ranging from clear to turbid. According to the spectral characteristics of remote sensing reflectance, they are divided into clear water bodies and optically complex water bodies. The optically complex water bodies include eutrophic water bodies dominated by chlorophyll concentration (CHL) and turbid water bodies dominated by mineral particles (MIN).

[0015] The correction coefficients for the clear water body and the eutrophic water body dominated by chlorophyll concentration (CHL) Including the correction factor for the first water molecule. The correction factor for the second item, water molecules. The first item is the correction factor for particulate matter. The correction factor for the second particulate matter The correction coefficient corresponding to the turbid water body mainly composed of MIN mineral particles. Including the correction factor for the first particulate matter. The correction factor for the second particulate matter .

[0016] Furthermore, the remote sensing reflectance at the target angle is calculated as follows:

[0017] ;

[0018] in, To calculate the remote sensing reflectance at the target angle, The correction factor for the first water molecule at the target angle. The correction factor for the first water molecule at the target angle. The first particulate matter correction factor at the target angle. The second term, the correction factor for particulate matter, is the target angle. , , , The wavelengths reflected by the water body are respectively The total absorption coefficient, backscattering coefficient, water molecule backscattering coefficient, and particle backscattering coefficient at that time are calculated based on the remote sensing reflectance of the water body. Correction coefficient at the current angle And it is obtained by calculation according to the QAA algorithm.

[0019] Furthermore, remote sensing reflectance was introduced when creating the clear water lookup table. The mean and spectral variability parameter were used to select the two sets of data with the largest and smallest spectral variability parameter and the two sets of data with the largest and smallest mean in all the clean water data, which were then used as the datasets for fitting the correction coefficients.

[0020] When establishing a lookup table applicable to eutrophic water bodies with CHL as the main chlorophyll concentration, the portion of the eutrophic water body data with a mean less than the median is selected, and the two sets of data with the largest and smallest spectral variability parameters in this portion are calculated as the dataset used for fitting the correction coefficient.

[0021] When creating a lookup table for turbid water bodies primarily composed of MIN mineral particles, water bodies with turbidity exceeding a set threshold are included. The spectral features are used as the dataset for fitting the correction coefficients.

[0022] Furthermore, the remote sensing reflectance of the water body The methods for obtaining it are as follows:

[0023] The current relative azimuth angle is recorded in the actual data of the voyage. Observation angle and the zenith angle of the sun Collect the upward radiance below the water surface Or the radiance of water surface and underwater irradiance or irradiance on the water surface The remote sensing reflectance of the water body was calculated. ;

[0024] Furthermore, the remote sensing reflectance of the water body The methods for obtaining it are as follows:

[0025] Based on radiative transfer models and measured data, a combination of aquatic bio-optical models is constructed. Water concentration and aquatic environment are input, and numerical simulations are performed using measured data to obtain specific relative azimuth angles. Observation angle and the zenith angle of the sun Corresponding water radiance and irradiance Then, the remote sensing reflectance of the water body is calculated. .

[0026] Furthermore, the upward radiance below the water surface Data were collected using a radiance radiometer mounted on a floating optical device on the water surface.

[0027] The water surface optical floating device includes a floating frame and a first clamping assembly mounted on the floating frame and located on the water surface. The first clamping assembly includes a support for fixed connection with the floating frame. A first mounting plate is mounted on the outer side of the support. The first mounting plate is fixedly connected to one end of a connecting rod, and the other end of the connecting rod is fixedly connected to a second mounting plate. A clamp is mounted on the second mounting plate for fixing a radiometer. A first angle measuring component and a second angle measuring component are respectively fixed on the first and second mounting plates. The first angle measuring component is used to collect relative azimuth angles. The second angle measuring component is used to acquire the observed angle. .

[0028] Furthermore, the floating frame is also equipped with a second clamping assembly located underwater, wherein the irradiance underwater... Data were collected by a radiometer fixed to the second clamping assembly.

[0029] Furthermore, the floating frame includes a T-shaped frame and multiple floats fixed to the frame.

[0030] Furthermore, both the first and second angle measuring components are angle discs, and a bubble level is also fixed on the connecting rod.

[0031] Beneficial effects: This invention considers water body classification and establishes correction coefficient lookup tables for the spectral characteristics and optical properties of different water bodies, greatly reducing the relative differences in remote sensing reflectance data of primary water color remote sensing products caused by anisotropy, and meeting the standardization requirements of water color products in natural water environments; when determining the correction scheme, this invention is based on a small number of typical samples that fully consider the spectral differences of various water bodies, and obtains various correction coefficient lookup tables, which have excellent performance and remove the applicability limitations of various water body types; the water surface optical floating device provided by this invention can quickly determine the relative azimuth angle during observation, and the angle can be adjusted in real time according to the needs. In addition to the commonly used observation angle of 40° and the nadir observation angle, it also includes relative azimuth angles with a measurement range of 0° to 180°, and observation angles with a measurement range of 0° to 90°. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating a remote sensing reflectance data acquisition method based on anisotropic correction.

[0033] Figure 2 This is a schematic diagram showing the number of data samples and the spectrum of the water sample before the improvement.

[0034] Figure 3 This is a schematic diagram showing the number of data samples and the spectrum of water involved in the improved embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram comparing the performance of the data from the Qingshui cruise using Lee2011's method with that of this application;

[0036] Figure 5 This is a schematic diagram comparing the performance of eutrophic water body cruise data corrected using the Lee2011 method with that of this application.

[0037] Figure 6 This is a schematic diagram illustrating the performance of the Lee2011 method under different conditions in numerical simulation data of turbid water.

[0038] Figure 7 This is a schematic diagram illustrating the performance of this application under different conditions using numerical simulation data of turbid water.

[0039] Figure 8 This is a schematic diagram of the structure of the water surface optical flotation device according to an embodiment of the present invention;

[0040] Figure 9 yes Figure 8 A magnified schematic diagram of a portion of region A in the middle; Detailed Implementation

[0041] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] like Figure 1 As shown, this embodiment of the invention provides a method for acquiring remote sensing reflectance data based on anisotropic correction, including:

[0043] Obtaining the remote sensing reflectance of water bodies and their corresponding relative azimuth angles Observation angle and the zenith angle of the sun Among them, relative azimuth angle This refers to the azimuth angle of the sensor (radiometer) relative to the plane of the sun; relative azimuth angle. The value range is 0° to 360° (or -180° to 180°), and it is usually defined as 0° to 180° after taking the absolute value. =0°: The sun and the sensor are on the same plane, for example, the sun is directly in front of the observer. =180°: The sun is facing away from the sensor. Solar zenith angle. The variation is determined by the date, time, and geographical location. The solar zenith angle can be determined based on the specific date, time, and geographical location of the data collection. Observation angle It is the angle between the sensor's line of sight and the zenith direction at the observation point on the ground, also known as the sensor's zenith angle. Observation angle The value range is 0° (sensor at the zenith) to 90° (sensor at the horizon), affecting the radiance received by the sensor. In this invention, based on field observation habits and the coordinate conventions of numerical simulation software, when describing field observations, =0° means that the observation angle is forward (facing the sun). =180° represents the backward observation angle (facing away from the sun), while when expressing coordinates in numerical simulation software, =180° represents the observation angle when facing forward (facing the sun). =0° represents the backward observation angle (facing away from the sun).

[0044] It should be noted that the remote sensing reflectance of the aforementioned water bodies and their corresponding relative azimuth angles Observation angle and the zenith angle of the sun This data can be obtained based on numerical simulation data, publicly available data from other researchers' observations, or other classic synthetic datasets. Taking numerical simulation data as an example: using radiative transfer models and measured data as standards, a combination of aquatic biooptical models is constructed. Water concentration and aquatic environment are input, where each inherent optical parameter model is an existing technology and needs to be combined and validated according to the specific water type. Water concentration and aquatic environment are based on measured data for numerical simulation to obtain specific relative azimuth angles. Observation angle and the zenith angle of the sun Corresponding water radiance and irradiance The remote sensing reflectance of the water body was calculated. When existing data sources are limited, the water surface optical floating system provided by this invention or other existing equipment can be used to conduct aerial surveys of the relevant data and calculate the remote sensing reflectance of the water body. Specifically, the current relative azimuth angle is recorded in the actual data of the voyage. Observation angle and the zenith angle of the sun Collect the upward radiance below the water surface Or the radiance of water surface and underwater irradiance or irradiance on the water surface The remote sensing reflectance of the water body was calculated. .

[0045] Based on the remote sensing reflectance of water bodies To determine the type of water body, it is necessary to categorize water bodies into clear water bodies and optically complex water bodies. Optically complex water bodies include eutrophic water bodies dominated by chlorophyll concentration (CHL) and turbid water bodies dominated by mineral particles (MIN). Specifically, this is done by first calculating the remote sensing reflectance of the water body. generate Spectral data, Spectral data is a set A curve plotted from data of different wavelengths is equivalent to Read by programming software Spectral data can be used to obtain water body type numbers. Based on spectral characteristics, optical water body types are divided into 23 categories from clear to turbid, corresponding to water body type numbers ID1 to ID23. This is based on the remote sensing reflectance of the water body. Obtaining water body type designations is prior art and will not be elaborated upon here. This application classifies water bodies with type designations ID1 to ID12 as clear water bodies and water bodies with type designations ID13 to ID23 as optically complex water bodies. Alternatively, ID10 to ID13 can also be considered transitional water bodies. Classifying them as either clear or optically complex water bodies can improve anisotropy to some extent, especially for water bodies whose type designation is identified as optically complex but whose remote sensing reflectance spectral values ​​are generally low, such as those with low remote sensing reflectance. The water correction scheme can still be used. The main basis for distinguishing between eutrophic water bodies dominated by chlorophyll concentration (CHL) and turbid water bodies dominated by mineral particles (MIN) is the fundamental difference in their optical properties and water component concentrations. According to absorption and scattering characteristics, eutrophic water bodies dominated by chlorophyll concentration (CHL) have strong absorption valleys in the blue light band (~440nm) and red light band (~675nm). Absorption is weaker in the green light band (~550-570nm), resulting in relatively high reflectivity (forming a reflection peak). There is a characteristic fluorescence emission peak in the near-red light band (~680-690nm) (when excited by blue or red light). Therefore, the reflectance spectrum curve and trend have obvious absorption valleys near 440nm and 675nm; a reflection peak near 550-580nm; and an overall curve with a more obvious "peak" in the green light band. Turbid water bodies, primarily composed of mineral particles (MIN), exhibit strong light scattering (mainly Mie scattering) across the entire visible and near-infrared spectrum (especially at shorter wavelengths), resulting in generally high reflectivity. Reflectivity typically decreases monotonically with increasing wavelength (especially in the near-infrared band), lacking the characteristic absorption valleys and fluorescence peaks of chlorophyll. The absorption coefficient is relatively low and changes relatively smoothly in the visible light spectrum, usually without sharp absorption peaks.

[0046] According to relative azimuth Observation angle Solar zenith angle The correction factor for the current angle is obtained by matching the water body type with the corresponding self-built lookup table. Among them, the correction coefficients for clear water bodies and eutrophic water bodies dominated by chlorophyll concentration (CHL) are... Including the correction factor for the first water molecule. The correction factor for the second item, water molecules. The first item is the correction factor for particulate matter. The correction factor for the second particulate matter The correction coefficient corresponding to the turbid water body mainly composed of MIN mineral particles. Including the correction factor for the first particulate matter. The correction factor for the second particulate matter Please refer to Tables 1 to 3 for details. Table 1 shows the correction coefficients for clear water at certain angles. The lookup table, Table 2, shows the correction coefficients for eutrophic water bodies with chlorophyll concentration (CHL) as the main nutrient at certain angles. The lookup table, Table 3, shows the correction coefficients for turbid water bodies mainly composed of MIN mineral particles at certain angles. Look up the relative azimuth angles in Tables 1, 2, and 3. Observation angle Solar zenith angle All units are degrees, as detailed below:

[0047] Table 1 shows the correction factors applicable to clean water. Some examples of lookup tables:

[0048] ;

[0049] Table 2 shows the correction factors applicable to eutrophic water bodies where chlorophyll concentration (CHL) is the primary nutrient. Example of a lookup table:

[0050] ;

[0051] Table 3 shows the correction factors applicable to turbid water bodies mainly composed of mineral particles (MIN). Example of a lookup table:

[0052]

[0053] Based on preliminary calculations of the remote sensing reflectance of the water body Correction coefficient at the current angle And based on the QAA algorithm, the wavelength of water reflection was calculated to be... Total absorption coefficient at time Backscattering coefficient Water molecule backscattering coefficient and particle backscattering coefficient The QAA algorithm is existing technology and will not be elaborated upon here.

[0054] Based on the correction coefficient at the target angle in the lookup table Total absorption coefficient Backscattering coefficient Water molecule backscattering coefficient and particle backscattering coefficient Calculate remote sensing reflectance at the target angle for:

[0055] ;

[0056] in, The correction factor for the first water molecule at the target angle. The correction factor for the first water molecule at the target angle. The first particulate matter correction factor at the target angle. The second term is the correction coefficient for particulate matter at the target angle.

[0057] Correction coefficients in the lookup table The dataset required for fitting is not limited to measurement data collected by surface optical floating devices; it can also be applied to various types of remote sensing reflectance data, such as numerical simulation data, field measurement data, and satellite remote sensing observation data. For example, the remote sensing reflectance data from the SeaBASS website can be used as a reference. The relative ratios before and after data correction are used as the object, and the relative ratios of the radiance data from the corresponding cruise are used as the reference standard to verify the anisotropy correction scheme applicable to various types of water bodies. The specific implementation is as follows:

[0058] Taking the clear waters near the Mediterranean Sea and the eutrophic waters near Monterey Bay, dominated by CHL, as examples, the actual measurements taken during the cruise will be used to illustrate the results. Through the interface factor transformation relationship mentioned by Gordon Transformed onto the water surface .based on The absorption and scattering coefficients of each water body component are obtained from the data. This IOPs parameter model is then incorporated into the method of this invention to improve the determination of the applicable correction coefficient lookup table for water bodies. Traditional methods establish lookup tables by fitting correction data to a large dataset; however, considering specific ID data subsets… While their spectral morphologies are similar, their numerical values ​​and spectral variability vary. This invention introduces remote sensing reflectance. The mean M, and the spectral variability parameter ,Right now Taking clear waters suitable for the Mediterranean Sea as an example, we screened out... The two sets of data with the largest and smallest values ​​(four sets in total), as well as the two sets of data with the largest and smallest values ​​of M among all the clean water data, are used as the dataset for fitting the correction coefficients. See details in [link to documentation]. Figure 2 and Figure 3 , Figure 2 This is a diagram showing the number of data samples and the spectrum of the water sample before the improvement. Figure 3 This diagram illustrates the sample size and spectral characteristics of the improved data involving clean water presented in this application. The data were corrected using both the Lee 2011 method and the improved scheme. A lookup table of correction coefficients for each scheme was then used to obtain... After correction, the following results were obtained: and specific observation angle of Based on the formula, / and Equivalent. See also Figure 4 and Figure 5 The performance of the Lee2011 method and the improved method of this application are basically consistent.

[0059] Numerical simulations were performed using Hydrolight 5.0 software. The study focused on remote sensing reflectance data of water bodies with varying turbidity (primarily composed of MIN mineral particles) at different solar observation geometric angles. The simulations were conducted at solar zenith angles. Using remotely sensed reflectance data obtained under 0° and nadir observation conditions as a standard, a ratio was calculated to obtain the relative difference before and after correction. This difference was then applied at the observation angle. Relative azimuth Solar zenith angle The performance of the Lee2011 method and this application were compared under various conditions, including changes in water type and wavelength. Specifically, the results are as follows: Figure 6 and Figure 7 As shown, Figure 6 and Figure 7 In the center, the dot on the left represents the solar zenith angle. It is 45°, and the polar axis direction indicates the observation angle. (0°-87.5°), the direction of rotation of the specified angle indicates the relative azimuth angle. , =180°: The sun and the sensor are on the same plane, for example, the sun is directly in front of the observer. =0°: The sun is in the opposite direction to the sensor. The pole represents the nadir observation angle, i.e. Equal to 0°. The black arc represents a common observation angle. For reference. White contour lines represent... That is, remote sensing reflectance The actual accuracy requirement for the observation data is a relative difference of 5%, with darker areas outside the contour lines representing deviations exceeding 5%. This application is significantly superior to the Lee2011 method.

[0060] Based on the above embodiments, those skilled in the art will readily understand that the present invention also provides a method for observing remote sensing reflectance. Data from a floating optical instrument on the water surface, showing the upward radiance of the submerged area. Data were collected using a radiance radiometer mounted on a floating optical device on the water's surface. For details, see [link to details]. Figure 8 and Figure 9 The floating optical device includes a floating frame 1 and a first clamping assembly 2 mounted on the floating frame 1. The first clamping assembly 2 is positioned above the water surface during use, thus allowing the radiance meter to be positioned above the water. The floating frame 1 includes a T-shaped frame 11 and multiple floats 12 fixed to the frame 11. The floats 12 can be fixed to the frame 11 by sleeve and binding. The frame 11 can be made of stainless steel cylindrical tubing, and the ends of the frame 11 can be sealed with stainless steel discs. The floats 12 can be foam buoys. In this embodiment, the first clamping assembly 2 includes a support 21, which is fixed to the frame 11 by multiple bolts. A first mounting plate 22 is mounted on the outside of the support 21 by bolts. The first mounting plate 22 is mounted on the support 21 by bolts. Loosening the bolts allows the first mounting plate 22 to be rotated to adjust the angle. After the angle is adjusted, tightening the bolts fixes the first mounting plate 22 to the support 21. The first mounting plate 22 is fixedly connected to one end of the connecting rod 23, and the other end of the connecting rod 23 is fixedly connected to the second mounting plate 24. A clamp 25 is mounted on the second mounting plate 24. The clamp 25 can also be mounted on the second mounting plate 24 by bolts. Loosening the bolts allows adjustment of the angle of the clamp 25. After adjustment, tightening the bolts fixes the clamp 25 to the second mounting plate 24. The clamp 25 is used to fix the radiometer. A first angle measuring component 26 and a second angle measuring component 27 are fixed on the first mounting plate 22 and the second mounting plate 24, respectively. The first angle measuring component 26 is used to collect the relative azimuth angle. The second angle measuring component 27 is used to collect the observed angle. To facilitate observation and recording of relative azimuth angles A first arrow 28 can be set in the middle of the support 21. When the central axis of the connecting rod 23 is perpendicular to the vertical rod of the frame 11, the relative azimuth angle is... When the angle is 0°, the first arrow 28 points to the 0° position. After adjusting the angle of the first mounting plate 22, the first angle measuring component 26 will rotate with the first mounting plate 22, and the angle pointed to by the first arrow 28 is the current relative azimuth angle. To facilitate observation and recording of the observation angle A second arrow 29 can also be set on the clamp 25 to indicate the current observation angle. The first angle measuring component 26 and the second angle measuring component 27 mentioned above are both preferably angle rulers. The first angle measuring component 26 is preferably a flat, annular angle ruler, which is convenient for placement on the outer side of the first mounting plate 22. The second angle measuring component 27 is preferably a thin-walled angle ruler, which is convenient for installation on the outer periphery of the second mounting plate 24. A bubble level 210 is also fixed at the end of the connecting rod 23 connected to the first mounting plate 22. During data acquisition, the bubble level 210 facilitates confirmation that the end of the connecting rod 23 connected to the first mounting plate 22 is vertically positioned.

[0061] If the irradiance data used is the irradiance below the water surface Preferably, a second clamping component 3 is also provided on the floating frame 1 to increase the irradiance below the water surface. The irradiance data is collected by a radiometer fixed to the second clamping assembly 3. The second clamping assembly 3 is identical to the first clamping assembly 2 except that it lacks the first angle measuring component 26 and the second angle measuring component 27. If the irradiance data used is the irradiance at the water surface... The irradiance meter can be fixed on the ship's deck or on the water surface.

[0062] Collect the upward radiance below the water surface Irradiance below the water surface And determine the relative azimuth angle and observation angle The specific process is as follows:

[0063] Step 1: Preparation. Determine the measurement area covering the required water body, ensuring it meets the observation requirements. For example, maintain clear weather conditions and wind speed <5m / s. Calibrate and check the radiance and irradiance radiometers to ensure they are functioning correctly. Fix the first clamping assembly 2 to the frame 11, then fix an appropriate number of floats 12, and then fix the radiance radiometer to the clamp 25. Use a tow rope to lower the optical floating device to the water surface to confirm the waterline. Adjust the number of floats 12 as needed to ensure that the waterline of the radiance radiometer's optical lens is exactly below the water surface (approximately 2cm underwater) to collect upward radiance radiation.

[0064] Step 2: Determine the relative azimuth. After adjusting the first mounting plate 22 to the desired horizontal angle and locking it, the relative azimuth angle can be determined based on the first angle measuring component 26. The range is from 0° to 180°.

[0065] Step 3: Determine the observation angle Verticality is checked using the bubble level 210 on the connecting rod 23. Then, the angle of the clamp 25 is adjusted and locked using the second angle measuring component 27 to determine the observation angle. .

[0066] Step 4: Conduct on-site measurements. The optical floating device is towed with a tow rope until it is completely facing away from the sun (from when the shadow appears directly in front). Once the optical floating system is stable in the water, the surveyor, on the vessel, fixes the radiometer in the vertical direction of the second clamping assembly 3 near the measurement point. The operator simultaneously observes and records the upward radiance below the water surface using the provided display and interaction unit. and underwater irradiance The data collection time can be from 8:00 AM to 4:00 PM, preferably from 10:00 AM to 2:00 PM, with a typical collection cycle of half an hour. When used to study the anisotropy of remote sensing reflectance data, data can be collected separately at... The intervals are 15° from 0° to 180°, and The angle was adjusted sequentially from 0° to 90° in 10° increments for on-site measurements. In addition, it can be used in conjunction with other water quality parameter instruments to observe data, such as chlorophyll concentration (CHL) and turbidity.

[0067] Step 5: Data Filtering and Preprocessing. Disassemble and reposition the equipment. Export the data, removing data from observation times with high sea surface waves (wind speed > 5 m / s) or cloudy conditions. Analyze the upward radiance below the water surface. Irradiance on the water surface or irradiance below the water surface To calculate the remote sensing reflectance of water bodies. When using the upward radiance below the water surface... and irradiance on the water surface When calculating the remote sensing reflectance of water bodies, it is necessary to use the method mentioned by Bertrand Lubac and Hubert Loisel (2007) to calculate the upward radiance below the water surface. Converted into water radiance Then calculate the water radiance. Irradiance on the water surface The ratio can be used to obtain the preliminary calculated remote sensing reflectance of the water body. When using the upward radiance below the water surface... and underwater irradiance When calculating the remote sensing reflectance of a water body, first calculate the upward radiance below the water surface. Irradiance below the water surface The ratio is used to obtain the underwater remote sensing reflectance. Then, through the interface factor transformation relationship mentioned by Gordon... Multiplying them together allows you to calculate the remote sensing reflectance of the water body. .

[0068] The above description is merely a preferred embodiment of the present invention. It should be noted that for those skilled in the art, other parts not specifically described are existing technology or common knowledge. Several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for acquiring remote sensing reflectance data based on anisotropic correction, characterized in that, include: Obtain the remote sensing reflectance of the water body and its corresponding relative azimuth, observation angle, and solar zenith angle; Water body types can be distinguished based on the spectral characteristics of the remote sensing reflectance of the water body; Based on the mean remote sensing reflectance, spectral variability parameter threshold, and inherent optical characteristic parameter laws of various types of water bodies, a correction coefficient lookup table suitable for various types of water bodies is automatically established. The correction coefficient for the current angle is matched from the corresponding self-built lookup table based on the relative azimuth, observation angle, solar zenith angle, and water type. The remote sensing reflectance at the target angle is calculated based on the correction coefficient and inherent optical characteristic parameters at the target angle in the self-established lookup table, resulting in a standardized remote sensing reflectance data product. When creating the clean water lookup table, remote sensing reflectance was introduced. The mean and spectral variability parameter were used to select the two sets of data with the largest and smallest spectral variability parameter and the two sets of data with the largest and smallest mean in all the clean water data, which were then used as the datasets for fitting the correction coefficients. When establishing a lookup table applicable to eutrophic water bodies with CHL as the main chlorophyll concentration, the portion of the eutrophic water body data with a mean less than the median is selected, and the two sets of data with the largest and smallest spectral variability parameters in this portion are calculated as the dataset used for fitting the correction coefficient. When creating a lookup table for turbid water bodies primarily composed of MIN mineral particles, water bodies with turbidity exceeding a set threshold are included. The spectral features are used as the dataset for fitting the correction coefficients; The remote sensing reflectance of the water body The methods for obtaining it are as follows: Record the current relative azimuth angle Observation angle and the zenith angle of the sun Collect the upward radiance below the water surface Or the radiance of water surface and underwater irradiance or irradiance on the water surface The remote sensing reflectance of the water body was calculated. ; The upward radiance below the water surface Data were collected using a radiance radiometer mounted on a floating optical device on the water surface. The water surface optical floating device includes a floating frame and a first clamping assembly mounted on the floating frame and located on the water surface. The first clamping assembly includes a support for fixed connection with the floating frame. A first mounting plate is mounted on the outer side of the support. The first mounting plate is fixedly connected to one end of a connecting rod, and the other end of the connecting rod is fixedly connected to a second mounting plate. A clamp is mounted on the second mounting plate for fixing a radiometer. A first angle measuring component and a second angle measuring component are respectively fixed on the first and second mounting plates. The first angle measuring component is used to collect relative azimuth angles. The second angle measuring component is used to acquire the observed angle. .

2. The method for acquiring remote sensing reflectance data based on anisotropic correction according to claim 1, characterized in that, The types of water bodies include several types of water bodies in nature, ranging from clear to turbid. According to the spectral characteristics of remote sensing reflectance, they are divided into clear water bodies and optically complex water bodies. The optically complex water bodies include eutrophic water bodies dominated by chlorophyll concentration (CHL) and turbid water bodies dominated by mineral particles (MIN). The correction coefficients for the clear water body and the eutrophic water body dominated by chlorophyll concentration (CHL) Including the correction factor for the first water molecule. The correction factor for the second item, water molecules. The first item is the correction factor for particulate matter. The correction factor for the second particulate matter The correction coefficient corresponding to the turbid water body mainly composed of MIN mineral particles. Including the correction factor for the first particulate matter. The correction factor for the second particulate matter .

3. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 2, characterized in that, The remote sensing reflectance at the target angle is calculated as follows: ； in, To calculate the remote sensing reflectance at the target angle, The correction factor for the first water molecule at the target angle. The correction factor for the first water molecule at the target angle. The first particulate matter correction factor at the target angle. The second term, the correction factor for particulate matter, is the target angle. , , , The wavelengths reflected by the water body are respectively The total absorption coefficient, backscattering coefficient, water molecule backscattering coefficient, and particle backscattering coefficient at that time are calculated based on the remote sensing reflectance of the water body. Correction coefficient at the current angle And it is obtained by calculation according to the QAA algorithm.

4. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 1, characterized in that, The remote sensing reflectance of the water body The methods for obtaining it are as follows: Based on radiative transfer models and measured data, a combination of aquatic bio-optical models is constructed. Water concentration and aquatic environment are input, and numerical simulations are performed using measured data to obtain specific relative azimuth angles. Observation angle and the zenith angle of the sun Corresponding water radiance and irradiance Then, the remote sensing reflectance of the water body is calculated. .

5. The method for acquiring remote sensing reflectance data based on anisotropic correction according to claim 1, characterized in that, The floating frame is also equipped with a second clamping assembly located underwater, the underwater irradiance... Data were collected by a radiometer fixed to the second clamping assembly.

6. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 1, characterized in that, The floating frame includes a T-shaped frame and multiple floats fixed to the frame.

7. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 1, characterized in that, Both the first and second angle measuring components are angle discs, and a bubble level is also fixed on the connecting rod.

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