Remote sensing reflectivity data acquisition method based on anisotropic correction

Abstract

The invention discloses a remote sensing reflectivity data acquisition method based on anisotropic correction. The method comprises the following steps: acquiring remote sensing reflectivity of a water body and a corresponding relative azimuth angle, an observation angle and a solar zenith angle; judging the type of the water body according to the remote sensing reflectivity of the water body; according to the method, water body classification is considered, and a correction coefficient lookup table is established for spectral characteristics and optical characteristics of different water bodies; matching a correction coefficient at the current angle from a corresponding self-established lookup table according to the relative azimuth angle, the observation angle, the solar zenith angle and the water body type; the remote sensing reflectivity at the target angle is calculated according to the correction coefficient at the target angle in the lookup table and inherent optical characteristic parameters based on the QAA algorithm, the method has good applicability in various water bodies, and the limitation of a common fixed observation angle when the remote sensing reflectivity is obtained can be broken through through angle-adjustable water surface optical floating equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing reflectivity acquisition, and in particular to a remote sensing reflectivity data acquisition method based on anisotropy correction. Background Art

[0002] Remote sensing reflectivity ( , ) is usually defined as the water-leaving radiance ( ) and the downward irradiance from the water surface ( ), defined as just above the sea surface, is an apparent optical parameter commonly used in ocean color remote sensing. It is expressed as follows: ;

[0003] in, It means just on the water surface; represents the solar zenith angle; represents the instrument observation angle; represents the relative azimuth of the sensor relative to the plane of the sun, Represents wavelength.

[0004] The ideal solar observation geometry, that is, the solar zenith angle of 0° and the angle of nadir observation, cannot be effectively measured in reality. This is determined by physical limitations, 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, the data obtained by field measurements or satellite remote sensing observations are The data usually changes with the changes in the solar observation geometry and the composition and bio-optical properties of the water body. Therefore, before inverting the water color remote sensing data products, it is necessary to The pre-processing step of anisotropy correction is to convert the water body remote sensing reflectance data obtained from observations at various angles into the water body reflectance data under specific observation conditions through correction methods. , such as the solar zenith angle of 0° and nadir observation conditions. At present, there are more studies on open oceans and waters dominated by chlorophyll concentrations CHL, while there are fewer studies on the anisotropy of coastal waters with higher concentrations of mineral particles MIN. The Lee2011 method is currently in commercial use and has advantages in performance 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-wave bands and waters dominated by mineral particles MIN needs to be improved. Therefore, establishing an anisotropy correction scheme applicable to all types of water bodies not only helps to provide standardized remote sensing reflectance data products, but also serves as the basis for the inversion of water quality parameters.

[0005] In addition, the common field measurement methods for obtaining remote sensing reflectance data can be roughly divided into three categories: surface measurement method, underwater measurement method and near-surface method. Among them, the surface measurement method needs to avoid solar flares and perform radiation correction, which is easily affected by the measurement error of sky light radiance. The underwater measurement method measures the radiance and irradiance data at different depths and extrapolates them to the water-air interface. , attenuation correction, interface refraction correction, etc. are required. The surface observation method is to directly measure the upward radiance under the water surface. , combined with the underwater irradiance Among them, the optical floating system OFS proposed by Talone et al. can obtain the most common It consists of three parts: an irradiance sensor fixed on the ship's pole, and two radiance sensors deployed at a depth of about 2 cm on a towed T-shaped floating frame to measure the nadir ( ) and the non-nadir observation angle ( )of , with a tilt sensor and compass, the frame tilt angle and orientation are recorded, and the relative azimuth is calculated based on the solar azimuth. However, the existing optical floating system cannot obtain data with autonomously adjustable angles, which limits the standardized correction of data products and requires improvement. Summary of the Invention

[0006] The purpose of the present invention is to provide a remote sensing reflectance data acquisition method based on anisotropy correction in response to the shortcomings of the existing technology.

[0007] To achieve the above object, the present invention provides a method for acquiring remote sensing reflectance data based on anisotropy correction, comprising: Obtain remote sensing reflectivity of water bodies and their corresponding relative azimuth, observation angle and solar zenith angle; Distinguishing water body types based on spectral characteristics of remote sensing reflectance of the water body; According to the remote sensing reflectance mean value, spectral variability parameter threshold and inherent optical characteristic parameter law of each type of water body, a correction coefficient lookup table suitable for each type of water body is established; Matching a correction coefficient at a current angle from a corresponding self-established lookup table according to the relative azimuth, observation angle, solar zenith angle, and water body type; The remote sensing reflectivity 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 to obtain a standardized remote sensing reflectivity data product.

[0008] Furthermore, the types of water bodies include several types of water bodies in nature, ranging from clear to turbid, and are divided into clear water bodies and optically complex water bodies according to the spectral characteristics of remote sensing reflectance. The optically complex water bodies include eutrophic water bodies mainly characterized by chlorophyll concentration CHL and turbid water bodies mainly characterized by mineral particles MIN. The correction coefficients corresponding to the clear water body and the eutrophic water body with chlorophyll concentration CHL as the main Including the correction factor for the first water molecule , the correction factor for the second water molecule , the correction factor for the first particulate matter and the second correction factor for particulate matter , the correction coefficient corresponding to the turbid water body mainly composed of mineral particles MIN Including the correction factor for the first particulate matter and the second correction factor for particulate matter .

[0009] Furthermore, the remote sensing reflectivity at the target angle is calculated as follows: ; in, is the calculated remote sensing reflectivity at the target angle, is the first water molecule correction coefficient for the target angle, is the first water molecule correction coefficient for the target angle, is the first particle correction factor of the target angle, is the second particle correction factor for the target angle, 、 、 、 The wavelengths of water reflection are The total absorption coefficient, backscattering coefficient, water molecule backscattering coefficient and particle backscattering coefficient are calculated based on the remote sensing reflectivity of the water body. and the correction coefficient at the current angle , and calculated according to the QAA algorithm.

[0010] Furthermore, when establishing the clear water lookup table, remote sensing reflectivity is introduced The mean and spectral variability parameters of all clear water data were selected, and the two groups of data with the largest and smallest spectral variability parameters, as well as the two groups of data with the largest and smallest mean values, were selected as the data sets used for correction coefficient fitting; When establishing a lookup table for eutrophic water bodies with a predominantly chlorophyll concentration of CHL, the portion of the eutrophic water body data with a mean less than the median is screened out, and the two sets of data with the maximum and minimum spectral variability parameters in this portion are calculated as the data sets used for correction coefficient fitting; When establishing a lookup table for turbid water bodies mainly composed of mineral particles MIN, water bodies with turbidity higher than the set threshold are selected. The spectral features are used as correction coefficients to fit the data set.

[0011] Furthermore, the remote sensing reflectivity of the water body The way to obtain is as follows: Voyage measured data records the current relative azimuth , observation angle and the solar zenith angle , collecting the upward radiance below the water surface or water-leaving radiance on the water surface , and the irradiance below the water surface or irradiance on the water surface , calculate the remote sensing reflectivity of the water body ; Furthermore, the remote sensing reflectivity of the water body The way to obtain is as follows: Based on the radiation transfer model and measured data, a water bio-optical model combination is built, and the water concentration and water environment are input. The water concentration and water environment are based on the measured data, and numerical simulation is performed to obtain a specific relative azimuth. , observation angle and the solar zenith angle The corresponding water-leaving radiance and irradiance , and then calculate the remote sensing reflectivity of the water body .

[0012] Furthermore, the upward radiance under the water surface The data is collected by a radiance radiometer installed on an optical floating device on the water surface; The surface optical floating device includes a floating frame and a first clamping assembly arranged on the floating frame and located on the water surface, the first clamping assembly includes a support for being fixedly connected to the floating frame, a first mounting plate is installed on the outer side of the support, the first mounting plate is fixedly connected to one end of a connecting rod, the other end of the connecting rod is fixedly connected to a second mounting plate, a clamp is installed on the second mounting plate, the clamp is used to fix the radiance radiometer, a first angle measuring component and a second angle measuring component are fixed on the first mounting plate and the second mounting plate respectively, the first angle measuring component is used to collect relative azimuth The second angle measuring component is used to collect the observation angle .

[0013] Furthermore, the floating frame is provided with a second clamping assembly located under the water surface, and the irradiance under the water surface is The data is collected by the irradiance radiometer fixed on the second clamping component.

[0014] Furthermore, the floating frame includes a T-shaped frame and a plurality of floats fixed on the frame.

[0015] Furthermore, the first angle measuring component and the second angle measuring component are both angle disks, and a bubble level is fixed on the connecting rod.

[0016] Beneficial effects: The present invention takes into account water body classification and establishes a correction coefficient lookup table for the spectral characteristics and optical properties of different water bodies, which greatly reduces the relative differences in the remote sensing reflectance data of the first-level water color remote sensing product due to anisotropy, and meets the standardization requirements of water color products in natural water environments; when determining the correction scheme, the present invention obtains each correction coefficient lookup table based on a small number of typical samples that fully consider the spectral differences of various types of water bodies. It has excellent performance and removes the applicability restrictions of various water body types; the surface optical floating device provided by the present invention can quickly determine the relative azimuth during observation, and the angle can be adjusted in real time according to needs. In addition to the commonly used observation angle of 40° and the nadir observation angle, it also includes a relative azimuth with a measurement range of 0° to 180°, and the measurement range of the observation angle is 0° to 90°. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flowchart of a method for acquiring remote sensing reflectance data based on anisotropy correction; Figure 2 This is the number of data samples and spectrum diagram involving clean water before improvement; Figure 3 1 is a schematic diagram of the number of data samples and spectra related to clean water after improvement in an embodiment of the present invention; Figure 4 This is a performance comparison diagram of the clean water voyage data corrected by the Lee 2011 method and the present application; Figure 5 This is a schematic diagram comparing the performance of eutrophic water body voyage data corrected by the Lee 2011 method and the present application; Figure 6 This is a schematic diagram of the performance of Lee2011's method under different conditions for turbid water numerical simulation data; Figure 7 It is a schematic diagram of the performance of this application under different conditions of turbid water numerical simulation data.

[0018] Figure 8 This is a schematic structural diagram of a water surface optical floating device according to an embodiment of the present invention; Figure 9 yes Figure 8 Schematic diagram of the local enlarged structure of area A in the middle; DETAILED DESCRIPTION

[0019] 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. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0020] like Figure 1 As shown, an embodiment of the present invention provides a method for acquiring remote sensing reflectance data based on anisotropy correction, comprising: Obtaining remote sensing reflectance of water bodies and its corresponding relative azimuth , observation angle and the solar zenith angle . Among them, the relative azimuth That is, the azimuth of the sensor (radiance radiometer) relative to the plane where the sun is located, the relative azimuth The value range is: 0° to 360° (or -180° to 180°), usually the absolute value is taken and defined within the range of 0° to 180°. =0°: The sun is in the same plane as the sensor, i.e. the sun is directly in front of the observer. =180°: The sun is in the opposite direction to the sensor. The change is determined by the date, time and geographical location. The solar zenith angle can be determined based on the specific collection date, time and geographical location. Observation angle It is the angle between the sensor's line of sight and the zenith direction of the ground observation point, also known as the sensor zenith angle. The value range of is: 0° (sensor is located at the zenith) to 90° (sensor is located at the horizon), which affects the radiation brightness received by the sensor. In the present invention, according to the on-site observation habits and the coordinate habits of the numerical simulation software, when expressing on-site observations, =0° means the observation is in the forward direction (facing the sun). =180° represents the backward observation angle (facing away from the sun), and when expressing the coordinates of numerical simulation software, =180° means the observation is in the forward direction (facing the sun). =0° represents the backward observation angle (facing away from the sun).

[0021] It should be noted that the remote sensing reflectivity of the above water bodies and its corresponding relative azimuth , observation angle and the solar zenith angle It can be obtained based on numerical simulation data, data observed by other people published on the website, or other classic synthetic data sets. Taking numerical simulation data as an example: based on the radiation transfer model and measured data, a water body bio-optical model combination is built, and the water body concentration and water body environment are input. The various inherent optical parameter models are existing technologies and need to be combined and verified according to specific water body types. The water body concentration and water body environment are based on the measured data to perform numerical simulations to obtain specific relative azimuths. , observation angle and the solar zenith angle The corresponding water-leaving radiance and irradiance , calculate the remote sensing reflectivity of the water body When the existing data sources are limited, the surface optical floating system provided by the present invention or other existing equipment can be used to survey the corresponding data and calculate the remote sensing reflectivity of the water body. , specifically as follows: Voyage measured data records the current relative azimuth , observation angle and the solar zenith angle , collecting the upward radiance below the water surface or water-leaving radiance on the water surface , and the irradiance below the water surface or irradiance on the water surface , calculate the remote sensing reflectivity of the water body .

[0022] According to the remote sensing reflectivity of water Determine the type of water body. Water body types are divided into clear water body and optically complex water body. Optically complex water body includes nutrient water body with chlorophyll concentration CHL as the main component and turbid water body with mineral particles MIN as the main component. Specifically, first calculate the remote sensing reflectance of the water body according to the preliminary calculation. generate spectral data, Spectral data is a set The curve graph drawn from the data of different wavelengths is equivalent to , read through programming software Spectral data can be used to obtain the water type number. According to the spectral characteristics, the optical water type is divided into 23 types from clear to turbid, and the corresponding water type numbers are ID1 to ID23. Obtaining the type number of water bodies is a prior art and will not be described in detail here. This application classifies water bodies with water type numbers ID1 to ID12 as clear water bodies, and water body types with ID13 to ID23 as optically complex water bodies. In addition, ID10 to ID13 can also be considered as transitional water bodies, and the anisotropy of the schemes classified as clear water bodies or optically complex water bodies can be improved to a certain extent, especially for water bodies whose water type numbers are identified as optically complex water bodies but whose remote sensing reflectance spectral values ​​are generally low, such as remote sensing reflectance. , a clear water correction scheme can still be used. The primary basis for distinguishing eutrophic water (defined as chlorophyll concentration, CHL) from turbid water (defined as mineral particles, MIN) lies in fundamental differences in their optical properties and component concentrations. Based on absorption and scattering characteristics, eutrophic water (defined as chlorophyll concentration, CHL) exhibits strong absorption valleys in the blue (~440nm) and red (~675nm) bands. Absorption is weaker in the green (~550-570nm) band, resulting in relatively high reflectivity (forming a reflectance peak). A characteristic fluorescence emission peak occurs in the near-red (~680-690nm) band (when excited by blue or red light). Consequently, the reflectance spectrum curve and trend exhibit distinct absorption valleys near 440nm and 675nm, a reflectance peak near 550-580nm, and a pronounced "peak" in the green band. Turbid water, primarily composed of mineral particles (MIN), exhibits strong light scattering (dominated by Mie scattering) throughout the visible and near-infrared bands (especially at short wavelengths), resulting in generally high reflectivity. Reflectivity typically decreases monotonically with increasing wavelength (especially in the near-infrared band), lacking the characteristic absorption dips and fluorescence peaks of chlorophyll. The absorption coefficient is relatively low and varies relatively gently across the visible light band, typically lacking sharp absorption peaks.

[0023] According to the relative azimuth , observation angle , solar zenith angle The correction coefficient at the current angle is matched from the corresponding self-established lookup table according to the type of water body. , where the correction coefficients for clear water and eutrophic water with chlorophyll concentration CHL as the main factor are Including the correction factor for the first water molecule , the correction factor for the second water molecule , the correction factor for the first particulate matter and the second correction factor for particulate matter , the correction coefficient corresponding to the turbid water body mainly composed of mineral particles MIN Including the correction factor for the first particulate matter and the second correction factor for particulate matter For details, please refer to Tables 1 to 3, where Table 1 shows the correction coefficients of clear water at certain angles. Lookup table, Table 2 shows the correction coefficients of eutrophic water bodies based on chlorophyll concentration CHL at some angles Lookup table, Table 3 shows the correction coefficients of turbid water bodies mainly composed of mineral particles MIN at some angles Lookup table, relative azimuth in Table 1, Table 2, Table 3 , observation angle , solar zenith angle The units are all degrees, as follows: Table 1 shows the correction factors for clean water Partial example of a lookup table: ; Table 2 shows the correction coefficients for eutrophic water bodies with chlorophyll concentration CHL as the main factor. Example of a lookup table section: ; Table 3 shows the correction coefficients for turbid water bodies mainly composed of mineral particles MIN Example of a lookup table section:

[0024] According to the preliminary calculation of the remote sensing reflectivity of the water body and the correction coefficient at the current angle , and the wavelength of water reflection is calculated based on the QAA algorithm. The total absorption coefficient , backscatter coefficient , water molecule backscattering coefficient and particle backscattering coefficient The QAA algorithm is an existing technology and will not be described in detail here.

[0025] Correction coefficient at target angle according to the lookup table , total absorption coefficient , backscatter coefficient , water molecule backscattering coefficient and particle backscattering coefficient Calculate remote sensing reflectivity at target angle for: ; in, is the first water molecule correction coefficient for the target angle, is the first water molecule correction coefficient for the target angle, is the first particle correction factor of the target angle, is the second particle correction factor for the target angle.

[0026] Correction coefficients in the lookup table The data set required for fitting is not limited to the measurement data collected by surface optical floating equipment, but 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. The relative ratio data before and after data correction are used as the object, and the relative ratio of the radiance data of the corresponding voyage is used as the reference standard to verify the anisotropy correction scheme applicable to various water bodies. The specific implementation is as follows: Taking the clear waters near the Mediterranean and the eutrophic waters dominated by CHL near Monterey Bay as examples, the measured Through the interface factor conversion relationship mentioned by Gordon Transformed into water .based on The absorption and scattering coefficients of each water component are obtained by combining the IOPs parameter model into the method of the present invention to improve the correction coefficient lookup table for the water body. The traditional method is to fit the correction data based on a large number of data samples when establishing the lookup table. However, considering the specific ID data subset, The spectral morphology is similar, but the numerical value and spectral variability are different. The mean M and the spectral variability parameter ,Right now Taking the clear water bodies near the Mediterranean Sea as an example, we screen out The two largest and smallest data sets (four sets in total), as well as the two largest and smallest data sets of M in all clear water data, are used as the data sets for calibration coefficient fitting. Figure 2 and Figure 3 , Figure 2 This is the number of data samples and spectrum diagram involving clean water before improvement. Figure 3 The number of data samples and spectrum diagram of the improved clean water in this application are shown in Figure 2. The data were corrected using the Lee 2011 method and the improved scheme respectively. Combining the correction coefficient lookup table of each scheme, we get . After correction, we can get and a specific observation angle of According to the formula, / and Equivalent. See Figure 4 and Figure 5,Comparison and verification show that the performance of Lee2011 method and the improved method of this application are basically the same.

[0027] By using Hydrolight 5.0 software to perform numerical simulation, the numerical simulation remote sensing reflectance data of water bodies with different turbidity levels mainly composed of mineral particles MIN at different solar observation geometric angles were used as the research object. The remote sensing reflectance data obtained under 0° and nadir observation conditions are used as the standard to compare and obtain the relative difference before and after correction. , relative azimuth , solar zenith angle The performance of the Lee2011 method and the present application is compared under various conditions such as water type and wavelength. Figure 6 and Figure 7 As shown, Figure 6 and Figure 7 The dot on the left represents the solar zenith angle. It is 45°, and the polar axis direction represents the observation angle (0°-87.5°), the direction of the specified angle rotation represents the relative azimuth , =180°: The sun and the sensor are in the same plane, i.e. 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 the common observation angle For reference. The white contour lines represent , that is, remote sensing reflectivity The actual accuracy requirement for the observed data is a relative difference of 5%. Darker areas outside the contour lines represent values ​​exceeding 5%. This application significantly outperforms the Lee 2011 method.

[0028] Based on the above embodiments, those skilled in the art can easily understand that the present invention also provides a method for observing remote sensing reflectivity. Surface optical floating device for data, uplink radiance under the water surface The data is collected by a radiance radiometer installed on an optical floating device on the water surface. Figure 8 and Figure 9The surface optical floating device includes a floating frame 1 and a first clamping assembly 2 mounted on the floating frame 1. When in use, the first clamping assembly 2 is positioned above the water surface, thereby positioning the radiance radiometer above the water surface. The floating frame 1 includes a T-shaped frame 11 and a plurality of floats 12 secured to the frame 11. The floats 12 can be secured to the frame 11 by sleeves and lashings. The frame 11 can be made of a stainless steel cylindrical tube. The ends of the frame 11 can be welded and sealed with stainless steel discs. The floats 12 can be foam floats. The first clamping assembly 2 in this embodiment of the present invention includes a support 21, which can be secured to the frame 11 via a plurality of bolts. A first mounting plate 22 is mounted on the outside of the support 21 and bolted to the support 21. Loosening the bolts allows the first mounting plate 22 to be rotated to adjust its angle. Once the angle is adjusted, tightening the bolts secures 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 installed on the second mounting plate 24. The clamp 25 can also be installed on the second mounting plate 24 by bolts. After loosening the bolts, the angle of the clamp 25 can be adjusted. After adjustment, tighten the bolts to fix the clamp 25 to the second mounting plate 24. The clamp 25 is used to fix the radiance radiometer. The first angle measurement component 26 and the second angle measurement component 27 are fixed to the first mounting plate 22 and the second mounting plate 24 respectively. The first angle measurement component 26 is used to collect the relative azimuth angle. The second angle measuring component 27 is used to collect the observation angle In order to facilitate observation and record the relative azimuth , a first arrow 28 can be set in the middle of the support 21, when the middle axis of the connecting rod 23 is perpendicular to the vertical rod of the frame 11, the relative azimuth angle When the angle of the first mounting plate 22 is adjusted, the first angle measuring component 26 will rotate along with the first mounting plate 22, and the angle pointed by the first arrow 28 is the current relative azimuth angle. In order to facilitate observation and recording of the observation angle A second arrow 29 may also be provided on the fixture 25 to indicate the current observation angle. The first angle measuring component 26 and the second angle measuring component 27 are both preferably angle rulers. The first angle measuring component 26 is preferably a flat, annular angle ruler, conveniently positioned outside the first mounting plate 22. The second angle measuring component 27 is preferably a thin-walled angle ruler, conveniently positioned on the periphery of the second mounting plate 24. A bubble level 210 is also fixed to the end of the connecting rod 23 connected to the first mounting plate 22. During data collection, the bubble level 210 facilitates confirmation that the end of the connecting rod 23 connected to the first mounting plate 22 is vertical.

[0029] If the irradiance data used is the irradiance under the water surface It is also preferred to set a second clamping assembly 3 on the floating frame 1, and the irradiance under the water surface The data is collected by the irradiance radiometer fixed on the second clamping assembly 3. Compared with the first clamping assembly 2, the second clamping assembly 3 only lacks the first angle measurement component 26 and the second angle measurement component 27, and the rest of the components are the same. If the irradiance data used is the irradiance on the water surface , the irradiance radiometer can be fixed on the ship deck or on the water surface.

[0030] Collecting upwelling radiance beneath the water surface , underwater irradiance and determine the relative azimuth and observation angle The specific process is as follows: Step 1. Preparation. Determine the measurement area covering the required water body and ensure that it meets the observation requirements. For example, maintain observation conditions such as clear weather and wind speeds <5m / s. Calibrate and check the radiance radiometer and irradiance radiometer. Secure the first clamping assembly 2 to the frame 11, then secure an appropriate number of floats 12. Secure the radiance radiometer to the fixture 25. Use a tow rope to lower the optical floating device to the water surface to confirm and record the waterline. Adjust the number of floats 12 as needed to ensure that the radiance radiometer's optical lens is positioned just below the water surface (approximately 2cm underwater) at the waterline to collect the upwelling radiance radiation.

[0031] Step 2: Determine the relative bearing Adjust the first mounting plate 22 to the desired horizontal angle and lock it, then the relative azimuth can be determined based on the first angle measuring component 26. , ranging from 0° to 180°.

[0032] Step 3: Determine the observation angle According to the bubble level 210 on the connecting rod 23, complete the vertical detection, and then adjust the angle of the clamp 25 according to the second angle measuring component 27 and lock it to determine the observation angle. .

[0033] Step 4: Conduct on-site measurement. Use the towing rope to drag the optical floating device on the water surface until it is completely facing away from the sun (the shadow appears directly in front). After the optical floating system is stable in the water, the surveyor fixes the irradiance radiometer in the vertical direction of the second clamping component 3 near the measurement point on the ship. The operator uses the equipped display and interactive unit to synchronously observe and record the upward radiance under the water surface. and underwater irradiance The data collection time can be from 8 am to 4 pm, preferably from 10 am to 2 pm, and the collection period is usually half an hour. It is usually used to study the anisotropy of remote sensing reflectance data. 0° to 180° in 15° intervals, and The angle can be adjusted in 10-degree increments from 0° to 90° for on-site measurements. It can also be used in conjunction with other water quality parameter instrumentation, such as chlorophyll concentration (CHL) and turbidity.

[0034] Step 5: Data screening and preprocessing. Disassemble and restore the equipment. Export the data and exclude the data from observation times such as those with strong sea waves (wind speed > 5m / s) and cloudy weather. , irradiance on the water surface or underwater irradiance To calculate the remote sensing reflectance of water bodies. and irradiance on the water surface To calculate the remote sensing reflectance of water bodies, it is necessary to use the method mentioned by Bertrand Lubac and Hubert Loisel (2007) to convert the upward radiance under the water surface into Converted into water-leaving radiance , and then calculate the water-leaving radiance Irradiance on the water surface The ratio of the water surface reflectance can be calculated to get the preliminary remote sensing reflectance of the water body. and underwater irradiance To calculate the remote sensing reflectivity of water bodies, first calculate the upward radiance under the water surface and underwater irradiance The ratio of the water surface remote sensing reflectivity is obtained , and then through the interface factor conversion relationship mentioned by Gordon Multiplying them together, we can calculate the remote sensing reflectivity of the water body .

[0035] The above description is merely a preferred embodiment of the present invention. It should be noted that any other aspects not specifically described are considered prior art or common knowledge to those skilled in the art. Improvements and modifications may be made without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention.

Claims

1. A method for acquiring remote sensing reflectance data based on anisotropy correction, characterized in that: include: Obtain remote sensing reflectivity of water bodies and their corresponding relative azimuth, observation angle and solar zenith angle; Distinguishing water body types based on spectral characteristics of remote sensing reflectance of the water body; According to the remote sensing reflectance mean value, spectral variability parameter threshold and inherent optical characteristic parameter law of each type of water body, a correction coefficient lookup table suitable for each type of water body is established; Matching a correction coefficient at a current angle from a corresponding self-established lookup table according to the relative azimuth, observation angle, solar zenith angle, and water body type; The remote sensing reflectivity 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 to obtain a standardized remote sensing reflectivity data product.

2. The method for acquiring remote sensing reflectance data based on anisotropy 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, and are divided into clear water bodies and optically complex water bodies according to the remote sensing reflectance spectral characteristics. The optically complex water bodies include eutrophic water bodies mainly characterized by chlorophyll concentration CHL and turbid water bodies mainly characterized by mineral particles MIN; The correction coefficients corresponding to the clear water body and the eutrophic water body with chlorophyll concentration CHL as the main Including the correction factor for the first water molecule , the correction factor for the second water molecule , the correction factor for the first particulate matter and the second correction factor for particulate matter , the correction coefficient corresponding to the turbid water body mainly composed of mineral particles MIN Including the correction factor for the first particulate matter and the second correction factor for particulate matter .

3. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 2, characterized in that: The calculation method of the remote sensing reflectivity at the target angle is as follows: ； in, is the calculated remote sensing reflectivity at the target angle, is the first water molecule correction coefficient for the target angle, is the first water molecule correction coefficient for the target angle, is the first particle correction factor of the target angle, is the second particle correction factor for the target angle, 、 、 、 The wavelengths of water reflection are The total absorption coefficient, backscattering coefficient, water molecule backscattering coefficient and particle backscattering coefficient are calculated based on the remote sensing reflectivity of the water body. and the correction factor at the current angle , and calculated according to the QAA algorithm.

4. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 2, wherein: When establishing the clear water lookup table, remote sensing reflectivity is introduced The mean and spectral variability parameters of all clear water data were selected, and the two groups of data with the largest and smallest spectral variability parameters, as well as the two groups of data with the largest and smallest mean values, were selected as the data sets used for correction coefficient fitting; When establishing a lookup table for eutrophic water bodies with a predominantly chlorophyll concentration of CHL, the portion of the eutrophic water body data with a mean less than the median is screened out, and the two sets of data with the maximum and minimum spectral variability parameters in this portion are calculated as the data sets used for correction coefficient fitting; When establishing a lookup table for turbid water bodies mainly composed of mineral particles MIN, water bodies with turbidity higher than the set threshold are selected. The spectral features are used as correction coefficients to fit the data set.

5. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 1, characterized in that: The remote sensing reflectivity of the water body The way to obtain is as follows: Record the current relative azimuth , observation angle and the solar zenith angle , collecting the upward radiance below the water surface or water-leaving radiance on the water surface , and the irradiance below the water surface or irradiance on the water surface , calculate the remote sensing reflectivity of the water body .

6. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 1, characterized in that: The remote sensing reflectivity of the water body The way to obtain is as follows: Based on the radiation transfer model and measured data, a water bio-optical model combination is built, and the water concentration and water environment are input. The water concentration and water environment are based on the measured data, and numerical simulation is performed to obtain a specific relative azimuth. , observation angle and the solar zenith angle The corresponding water-leaving radiance and irradiance , and then calculate the remote sensing reflectivity of the water body .

7. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 5, characterized in that: The subsurface upward radiance The data is collected by a radiance radiometer installed on an optical floating device on the water surface; The surface optical floating device includes a floating frame and a first clamping assembly arranged on the floating frame and located on the water surface, the first clamping assembly includes a support for being fixedly connected to the floating frame, a first mounting plate is installed on the outer side of the support, the first mounting plate is fixedly connected to one end of a connecting rod, the other end of the connecting rod is fixedly connected to a second mounting plate, a clamp is installed on the second mounting plate, the clamp is used to fix the radiance radiometer, a first angle measuring component and a second angle measuring component are fixed on the first mounting plate and the second mounting plate respectively, the first angle measuring component is used to collect relative azimuth The second angle measuring component is used to collect the observation angle .

8. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 7, characterized in that: The floating frame is also provided with a second clamping assembly located under the water surface. The data is collected by the irradiance radiometer fixed on the second clamping component.

9. The method for acquiring remote sensing reflectance data based on anisotropy correction according to claim 7, characterized in that: The floating frame includes a T-shaped frame and a plurality of floats fixed on the frame.

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

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