A method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance

Abstract

This invention discloses a method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance. It obtains the remote sensing reflectance at any wavelength below the sea surface and the ratios related to inherent optical quantities using satellite-provided remote sensing data. For clear seawater and relatively clear coastal seawater, the QAA_v5 algorithm is used to obtain the absorption and backscattering coefficients at any wavelength; for turbid coastal seawater, the QAA-RGR algorithm is used. Different models for solving the scattering coefficients are used for different sea areas. The global ocean optical attenuation coefficient is obtained by adding the absorption and scattering coefficients. This invention divides the global ocean into regions and provides models for solving the absorption and scattering coefficients for different regions. It can directly calculate the optical attenuation characteristics of different sea areas using satellite-provided data, improving the reliability of solving the optical attenuation coefficient and enabling dynamic monitoring of the variation of the global ocean optical attenuation coefficient.

Description

Technical Field

[0001] This invention relates to the field of marine communication channel research, and to a remote sensing inversion method for optical attenuation coefficients based on water turbidity classification and global sea area partitioning, particularly a method for inverting global marine optical attenuation coefficients based on remote sensing reflectance. Background Technology

[0002] Analyzing the attenuation characteristics of seawater for specific wavelength laser signals has become a crucial aspect of underwater laser communication research. Given the vastness of the ocean, it is impossible to obtain the laser transmission characteristics of all regions through on-site measurements. Therefore, combining on-site measurement results from limited stations with satellite remote sensing data for water color remote sensing inversion is the only way to overcome these challenges.

[0003] The optical properties of seawater include apparent optical properties and intrinsic optical properties. Apparent optical properties are determined by the light field and the composition of the water and can be measured by methods such as remote sensing. Intrinsic optical properties are only related to the distribution of the components in the water and their absorption and scattering characteristics. They represent the inherent optical properties of seawater, are independent of the light field, and are the fundamental factors that determine the characteristics of laser transmission in seawater.

[0004] According to Jerlov's "Marine Optics," published in the second revised edition of "Optical Oceanography" by Elsevier in 1976, seawater can be divided into clear seawater, relatively clear coastal seawater, and turbid coastal seawater. Clear seawater refers to type I, IA, and IB seawater in open sea areas as proposed by Jerlov; relatively clear coastal seawater refers to type 1 seawater in coastal areas as proposed by Jerlov; and turbid coastal seawater refers to type 9 seawater in coastal areas as proposed by Jerlov.

[0005] Most marine optical measurement methods derive inherent optical properties from apparent optical characteristics. Traditional marine remote sensing inversion employs empirical statistical algorithms, using regression analysis to establish the relationship between seawater optical spectral properties and water component concentrations, and then estimates the attenuation and reflection characteristics of seawater. These methods have significant errors and are only applicable to deep-sea waters with clear water. Continental coastal waters are typical coastal seawater areas with complex optical properties, necessitating the development of suitable remote sensing inversion algorithms to meet the needs of underwater optical communication applications in continental coastal waters.

[0006] Currently, the most representative and widely accepted method is the semi-analytical method. It first inverts intrinsic optical quantities from apparent optical quantities obtained through remote sensing observations, and then uses the relationship between intrinsic optical quantities and water component concentrations to invert water color products. The fifth version of the QAA algorithm (Quasi-Analytical Algorithm Version 5, or QAA_v5) and the Quasi-Analytical Algorithm-RGR (QAA-RGR) algorithm, released by the International Ocean Color Remote Sensing Organization, require no prior parameters such as chlorophyll absorption spectra and are portable compared to traditional empirical algorithms. However, the QAA_v5 algorithm shows high accuracy in clear and relatively clear coastal waters, but is slightly less accurate in turbid coastal waters. In QAA_v5, remote sensing reflectance at 443nm, 490nm, 555nm, and 667nm is used to invert optical parameters. For the visible light channel, the Moderate-resolution Imaging Spectroradiometer (MODIS) only has three high spatial resolution land bands: 469 nm, 555 nm, and 645 nm. Therefore, QAA_v5 does not directly apply to all three land bands. Furthermore, since optical coefficients are highly saturated at the 667 nm band, QAA_v5 cannot be directly applied to turbid coastal seawater. The QAA-RGR algorithm can compensate for this problem. The QAA-RGR algorithm inverts optical parameters by comparing the remotely sensed reflectance between the 555 nm and 645 nm bands. This combination of blue-green band ratios not only avoids the high saturation of optical coefficients at the 670 nm band but also improves the algorithm's robustness. These two inversion algorithms can provide the absorption and backscattering coefficients of seawater in a certain area, but studying the optical transmission characteristics of the ocean also requires understanding its overall scattering characteristics. Summary of the Invention

[0007] Accurately assessing the transmission attenuation characteristics of lasers in seawater is crucial for channel research. This invention provides a method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance. This method obtains corresponding absorption and backscattering coefficients for different sea areas based on water quality conditions, making the obtained absorption and backscattering coefficients at different wavelengths more accurate. Furthermore, this method provides different models for solving the scattering coefficients for different sea areas, which improves the completeness and reliability of solving the optical attenuation coefficients.

[0008] The solution adopted by this invention to solve its technical problem is:

[0009] The QAA_v5 algorithm and the QAA-RGR algorithm are applied to different sea areas according to different seawater types, and different scattering models are used for different sea areas to establish the relationship between remote sensing reflectivity and light attenuation coefficient.

[0010] A method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance includes:

[0011] I. Based on the remote sensing reflectance provided by the satellite, obtain the remote sensing reflectance at any wavelength below the sea surface and the relationship between the remote sensing reflectance and inherent optical quantities;

[0012] 2. The QAA_v5 algorithm is used to obtain the absorption coefficient and backscattering coefficient at any wavelength for clear seawater and relatively clear coastal seawater; the QAA-RGR algorithm is used to obtain the absorption coefficient and backscattering coefficient at any wavelength for turbid coastal seawater.

[0013] III. Using different models for solving scattering coefficients for different sea areas:

[0014] The scattering coefficient of the East China Sea or Yellow Sea was calculated by analyzing the water inherent optical quantity measurement data of various sea areas by Song Qingjun in 2006 through station fixed-point measurement. The relationship between the backscattering coefficient and the scattering coefficient was obtained by fitting the National Satellite Ocean Application Service (NSOAS) model. The scattering coefficient of the seawater in the East China Sea or Yellow Sea was obtained by inverting the NSOAS model.

[0015] The scattering coefficient of the Bohai Sea was calculated by using the relationship between the backscattering coefficient and the scattering coefficient obtained by Gu Yanzhen et al. through field measurement fitting in 2007.

[0016] To calculate the scattering coefficients of other sea areas or oceans, we used 875 angular scattering coefficients obtained by Vladimir I. Haltrin et al. in 2002 through aerial surveys off the coast of New Jersey. We then derived the relationship between the backscattering coefficients and scattering coefficients of other sea areas or oceans, and obtained the scattering coefficients of other sea areas or oceans.

[0017] Fourth, the global ocean optical attenuation coefficient can be obtained by adding the absorption coefficient and the scattering coefficient.

[0018] The above method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance includes the following steps:

[0019] Step 1) Obtain the remotely sensed reflectance r below the sea surface by inverting satellite remote sensing data. rs (λ):

[0020] r rs (λ)=R rs (λ) / (0.52+1.7R rs (λ)) (1)

[0021] Among them, R rs (λ) represents the remotely sensed reflectance received by the sensor, r rs (λ) represents the remote sensing reflectance just below the sea surface, and both have a wavelength of λ; r rs The relationship between (λ) and inherent optical quantities is shown in Equation (2):

[0022]

[0023] In formula (2), u(λ) represents the ratio function of the absorption coefficient and the backscattering coefficient at wavelength λ, a(λ) represents the total absorption coefficient at wavelength λ, and b b (λ) represents the backscattering coefficient at wavelength λ;

[0024] Step 2) Different methods are used to solve for the absorption coefficient and backscattering coefficient for clear seawater, relatively clear coastal seawater, and turbid coastal seawater:

[0025] Step 2-1): Using the improved QAA_v5 algorithm for clear seawater and relatively clear coastal seawater, obtain...

[0026]

[0027] Where λ0 represents the reference wavelength, taken as 555 nm, a _1 (λ0) represents the absorption coefficient of clear seawater and relatively clear coastal seawater at the reference wavelength, a w (λ0) is the absorption coefficient of pure water at the reference wavelength, and χ represents the remote sensing reflectance r below the sea surface. rs (λ) is a ratio function for wavelengths of 443nm, 490nm, and 667nm;

[0028]

[0029] Step 2-1-1): Substitute the MODIS remote sensing data at a wavelength of 555nm into formula (1) to calculate the underwater remote sensing reflectance r at a wavelength of 555nm. rs (555), then u(555) can be obtained. Combining formulas (3)-(4), the total absorption coefficient a of clear seawater with a wavelength of 555nm and relatively clear coastal seawater can be obtained. _1 (555); Backscattering coefficient b of clear seawater and relatively clear coastal seawater b_1 (555) then by a_1 Substituting (555) into formula (2) yields the result;

[0030] Using formula (5), the backscattering coefficient b for all wavebands of clear seawater and relatively clear coastal seawater is calculated. b_1 (λ):

[0031]

[0032]

[0033] b bw (λ) represents the backscattering coefficient of pure water at wavelength λ, b bp (λ0) represents the backscattering coefficient of suspended particulate matter at the reference wavelength, and η represents the power parameter; where when a _1 (λ0), u(λ0) and b bw (λ0) is known, b bw (λ0) represents the backscattering coefficient of pure water at the reference wavelength, b bp (λ0) can be obtained through formulas (1)-(2) and (5);

[0034] Step 2-1-2), by b b_1 (λ) is applied to formula (2), and then the total absorption coefficient a of clear seawater and relatively clear coastal seawater is calculated using algebraic methods. _2 (λ):

[0035]

[0036] Step 2-2), apply the QAA-RGR algorithm to turbid coastal seawater:

[0037] As shown in step 1), the remote sensing reflectance r below the sea surface is obtained by inversion from satellite remote sensing data. rs (λ) and the ratio u(λ) of the absorption coefficient and the backscattering coefficient is obtained;

[0038] Using the dataset fitting analysis method proposed by the International Ocean-Colour Coordinating Group (IOCCG), the absorption coefficient α of turbid coastal seawater at a wavelength of 555 nm was obtained through linear fitting. _3 (555), a _3 (555) can be measured by the remote sensing reflectance (R) of the 645nm and 555nm wavelength bands. rs (645) / (R rs 555)) estimates yielded:

[0039] a_3 (λ0)=0.0596+0.52(R rs 645 / R rs 555) 1.432 -0.04782 (8)

[0040] Where λ0 is the reference wavelength, taken as 555 nm; a _3 (λ0) represents the absorption coefficient of turbid coastal seawater at the reference wavelength;

[0041] Step 2-2-1): The backscattering coefficient at 555nm wavelength can be obtained from formulas (1)-(2), and then the backscattering coefficient b of all wavelengths of turbid coastal seawater can be calculated. b_2 (λ):

[0042]

[0043] Where Y represents the backscattering coefficient of turbid coastal seawater. b_2 The spectral distribution of (λ) has the following empirical relationship with the backscattering coefficient at 555 nm wavelength in turbid coastal seawater:

[0044]

[0045] Step 2-2-2), if the remote sensing reflectance R of other bands rs (λ) is known, and the total absorption coefficient a of turbid coastal seawater can be derived from formulas (1)-(2) and (10). _4 (λ):

[0046]

[0047] Step 3) Obtain the total scattering coefficient b(λ) for different sea areas:

[0048] To obtain the scattering coefficients of the East China Sea or the Yellow Sea, we analyze the intrinsic optical quantity measurement data of the water bodies in the East China Sea and the Yellow Sea through fixed-point measurements at air stations, and fit the data to derive the backscattering coefficients b of clear seawater and relatively clear coastal seawater. b_1 (λ) and the scattering coefficient b of relatively clear coastal water _1 The relationship of (λ):

[0049]

[0050] Formula (12) is derived by fitting the scattering coefficient data of the Yellow Sea and East China Sea. It is called the National Satellite Ocean Application Service (NSOAS) model. The coefficient 0.0142 in the formula is close to the coefficient obtained by correcting the data of the HS6 instrument.

[0051] We need to obtain the scattering coefficient of the Bohai Sea area, and then obtain the backscattering coefficient b of the turbid coastal seawater through fitting. b_2 (λ) and the scattering coefficient b of turbid coastal seawater _21 (λ), b _22 The relationship of (λ):

[0052] Category 1: Relationship between backscattering coefficient and scattering coefficient at the Yellow River Estuary offshore section:

[0053]

[0054] Category 2: Relationship between backscattering coefficient and scattering coefficient in the Bohai Bay, Liaodong Bay, and Qinhuangdao sections:

[0055]

[0056] Where b w (λ) is the scattering coefficient of pure water, b bw (λ) is the backscattering coefficient of pure water, which is a constant;

[0057] To obtain the scattering coefficients from other sea areas or oceans, 875 angular scattering coefficients were obtained through aerial surveys off the coast of New Jersey. From these, the backscattering coefficients (b) of clear seawater and relatively clear coastal water were derived. b_1 (λ) and the scattering coefficient b of clear seawater _3 The relationship of (λ):

[0058]

[0059] Of which 0.0012m -1 ≤b b_1 (λ)≤0.3724m -1 ;

[0060] Step 4), the global ocean optical attenuation coefficient is obtained according to formula (16):

[0061] c(λ)=a(λ)+b(λ) (16)

[0062] Where a(λ) represents the total absorption coefficient at wavelength λ, b(λ) represents the total scattering coefficient at wavelength λ, and c(λ) represents the total attenuation coefficient at wavelength λ;

[0063] In step 2-1), the absorption coefficient α of clear seawater and relatively clear coastal seawater is obtained. _2 (λ) and the scattering coefficient b of the relatively clear coastal seawater obtained in step 3). _1 Adding (λ) together yields the attenuation coefficient c for relatively clear coastal seawater. _1 (λ);

[0064] The absorption coefficient α of clear seawater and relatively clear coastal seawater _2 (λ) and the scattering coefficient b of clear seawater obtained in step 3). _3 (λ) addition yields the attenuation coefficient c of clear seawater. _3 (λ);

[0065] In step 2-2), the absorption coefficient α of the turbid coastal seawater is obtained. _4 (λ) and the scattering coefficient b of the turbid coastal seawater obtained in step 3). _21 (λ) or b _22 (λ) addition yields the attenuation coefficient c of turbid coastal seawater. _2 (λ).

[0066] Advantages or beneficial effects of the present invention:

[0067] (1) This invention divides the global sea area and uses the QAA_v5 algorithm to obtain the corresponding absorption coefficient and backscattering coefficient for clear seawater and relatively clear coastal seawater, while using the QAA-RGR algorithm to obtain the corresponding absorption coefficient and backscattering coefficient for relatively turbid coastal seawater. This division makes the absorption coefficient and backscattering coefficient more accurate.

[0068] (2) This invention provides different models for solving the scattering coefficient for different sea areas, which improves the completeness and reliability of solving the light attenuation coefficient;

[0069] (3) The method proposed in this invention can directly calculate the transmission attenuation characteristics of lasers in various sea areas from data provided by satellites, and dynamically monitor the variation law of global ocean optical attenuation coefficient, which is of great significance for dynamic analysis and understanding of the global seawater optical characteristics in my country. Attached Figure Description

[0070] Figure 1 This is a flowchart of a method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance in an embodiment of the present invention. Detailed Implementation

[0071] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Examples of the embodiments are shown in the accompanying drawings, and the embodiments described in the drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0072] Example:

[0073] The following description, with reference to the accompanying drawings, illustrates a method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance, as proposed in an embodiment of the present invention.

[0074] Due to the large volume of global ocean remote sensing data, this embodiment uses remote sensing data from January 1, 2022, with longitude of 120.59°, latitude of 38.64° and wavelength of 488nm in the South China Sea, longitude of 130.08°, latitude of 29.763° and wavelength of 488nm in the East China Sea, and longitude of 105.14°, latitude of 7.13° and wavelength of 488nm in the Bohai Sea as examples to illustrate the implementation steps.

[0075] like Figure 1 As shown, a method for retrieving the global ocean optical attenuation coefficient based on remote sensing reflectance includes the following steps: Step (1), the remote sensing reflectance R provided by the satellite under the corresponding conditions can be obtained using the known time, latitude and longitude, and wavelength. rs (λ), the remote sensing reflectance R corresponding to a longitude of 105.14°, latitude of 7.13°, and wavelength of 488nm in the South China Sea on January 1, 2022. rs_南海 (488) is the remote sensing reflectance R corresponding to a longitude of 130.08°, latitude of 29.76°, and wavelength of 488nm in the East China Sea. rs_东海 (488) is the remote sensing reflectance R corresponding to a longitude of 120.59°, latitude of 38.64°, and wavelength of 488nm in the Bohai Sea. rs_渤海 (488) is 0.154;

[0076] Then, by substituting into formula (1), the remote sensing reflectance at a wavelength of 488 nm under the sea surface in different sea areas can be obtained. Among them, the calculated remote sensing reflectance under the sea surface in the South China Sea is r. rs_南海 (488) = 0.079, the remote sensing reflectance beneath the sea surface in the East China Sea is r rs_东海 (488) = 0.096, the remote sensing reflectance of the sea surface in the Bohai Sea is r rs_渤海 (488) = 0.196;

[0077] The formula for retrieving remotely sensed reflectance below the sea surface is as follows:

[0078] r rs(λ)=R rs (λ) / (0.52+1.7R rs (λ)) (1)

[0079] Published in the *Journal of Geophysical Research*, September 1988, Vol. 93, pp. 10909-10924, Gordon's "A semianalytic radiance model of ocean color" and in *Applied Optics*, September 1998, Vol. 37, No. 27, Lee et al.'s "Hyperspectral remote sensing for shallow waters: 2. Deriving bottom depths and water properties by optimization," respectively, both established r through algebraic calculations. rs The relationship between (λ) and inherent optical quantities is shown in Equation (2):

[0080]

[0081] The calculated r rs_南海 (488), r rs_东海 (488), r rs_渤海 (488) Substituting these values ​​into formula (2), we can obtain the ratio of the absorption coefficient to the backscattering coefficient for different sea areas at a wavelength of 488 nm. The calculated ratio of the absorption coefficient to the backscattering coefficient in the South China Sea is u. _南海 (488) = 0.008, the ratio of absorption coefficient to backscattering coefficient in the East China Sea is u. _东海 (488) = 0.0091, the ratio of absorption coefficient to backscattering coefficient in the Bohai Sea is u. _渤海 (488) = 0.014;

[0082] Step (2), according to Jerlov's "Marine Optics" published by Elsevier in 1976, the second revised edition of "Optical Oceanography", the South China Sea is classified as clear seawater, the East China Sea as relatively clear coastal seawater, and the Bohai Sea as turbid coastal seawater. Different methods are used to solve for the absorption coefficient and backscattering coefficient for different sea types:

[0083] Step (2-1) uses the QAA_v5 algorithm for clear seawater and relatively clear coastal seawater, specifically for the South China Sea and East China Sea:

[0084]

[0085] In formula (3), the reference wavelength λ0 is taken as 555 nm, a _1 (λ0) represents the absorption coefficient at the reference wavelength, a w (λ0) is the absorption coefficient of pure water at the reference wavelength. Based on the absorption coefficients of pure water at various wavelengths measured in "Absorption spectrum (380-700nm) of pure water. II. Integrating cavity measurements" published in *Applied Optics*, November 1997, Vol. 36, No. 33, by Pope and Edward et al., it can be known that a w (555) = 0.0596, where χ is the remotely sensed reflectance r below the sea surface. rs (λ) is a ratio function between wavelengths of 443 nm, 490 nm, and 667 nm. The remote sensing reflectance provided by the satellite for wavelengths of 443 nm, 490 nm, 555 nm, and 667 nm are R0, R1, R2, R3, R4, R5, R6 rs_南海 (443)=0.067、R rs_南海 (490)=0.044、 R rs_南海 (555) = 0.00848, R rs_南海 (667)=0.00146、R rs_南海 (443)=0.067、R rs_南海 (490)=0.044、 R rs_南海 (555) = 0.00848, R rs_南海 (667)=0.00146、R rs_东海 (443)=0.09、R rs_东海 (490)=0.065、 R rs_东海 (555) = 0.016, R rs_东海 (667) = 0.00194, where R rs_南海 (λ) represents the remote sensing reflectance of the sea area being the South China Sea at wavelength λ, R rs_东海 (λ) represents the remote sensing reflectance of the East China Sea when the wavelength is λ.

[0086] The remote sensing reflectance r of the sea surface at these four wavelengths can be obtained by inversion from step (1). rs_南海 (443)=0.1057、 r rs_南海 (490)=0.074、r rs_南海 (555) = 0.0158, r rs_南海 (667) = 0.0028. r rs_东海 (443)=0.134、 r rs_东海 (490) = 0.103, r rs_东海 (555) = 0.0292, r rs_东海 (667) = 0.0037;

[0087] Where r rs_南海 (λ) represents the remote sensing reflectance below the sea surface at wavelength λ in the South China Sea. rs_东海 (λ) represents the remote sensing reflectance under the sea surface when the sea area is the East China Sea and the wavelength is λ. Substituting the remote sensing reflectance under the sea surface obtained from different sea areas into formula (4) yields χ. _南海 =11.004, χ _东海 =7.94; where χ _南海 This represents the ratio of remote sensing reflectance at wavelengths of 443nm, 490nm, and 667nm for the sea area in the South China Sea, expressed as χ². _东海 This represents the ratio of remote sensing reflectance of the sea area in the East China Sea at wavelengths of 443nm, 490nm, and 667nm.

[0088]

[0089] Step (2-1-1), the obtained r rs_南海 (555), r rs_东海 (555) Substituting these values ​​into formula (2), we obtain the ratio u of the absorption coefficient to the backscattering coefficient for different sea areas at a wavelength of 555 nm. _南海 (555) = 0.0023, u _东海 (555) = 0.0038. Combining formulas (3) and (4), the absorption coefficient α at a wavelength of 555 nm for different sea areas is obtained. _南海 (555) = 0.0596, a _东海 (555) = 0.0596; Based on the backscattering coefficient of pure water at various wavelengths measured by Morel, it can be known that b bw (555) = 0.000009, so a _南海 (555), u _南海 (555), a _东海 (555), u _东海(555) Substituting into formula (2), we obtain the backscattering coefficient b for wavelengths of 555nm in different sea areas. b_南海 (555) = 0.00014, b b_东海 (555) = 0.00023, so b bw (555), b b_南海 (555), b b_东海 (555) Substituting into formula (5), we obtain the backscattering coefficient b of suspended particulate matter at a wavelength of 555 nm in different sea areas. bp_南海 (555) = 0.000131, b bp_东海 (555) = 0.000221:

[0090]

[0091]

[0092] r rs_南海 (443), r rs_南海 (555), r rs_东海 (443), r rs_东海 (555) Substituting these values ​​into formula (6) yields η _南海 =1.9942, η _东海 =1.9614;

[0093] The backscattering coefficients of pure water at various wavelengths measured by Morel can be found in "Optical properties of pure water and pure sea water" by Morel et al., published by Acad Press, 1974, pp. 1-24.

[0094] Step (2-1-2): Based on the book "Optical properties of pure water and pure sea water" by Morel et al., the backscattering coefficients of pure water at various wavelengths are measured, where b bw (488) = 0.0015, so b bw (488), b bp_南海 (555), b bp_东海 (555), η _南海 η _东海 Substituting these values ​​into formula (5), we obtain the backscattering coefficient b for different sea areas at a wavelength of 488 nm. b_南海 (488) = 0.00167, b b_东海 (488) = 0.00178;

[0095] By b b_南海 (488), u _南海 (488), b b_东海 (488), u _东海 (488) Substitute into formula (7) and then use algebraic methods to calculate the total absorption coefficient a. _南海 (488) = 0.112, a _东海 (488) = 0.1339:

[0096]

[0097] Step (2-2) uses the QAA-RGR algorithm for turbid coastal seawater, specifically for the Bohai Sea:

[0098] As shown in step 1), the remote sensing reflectance r below the sea surface is obtained by inversion from satellite remote sensing data. rs_渤海 (λ) and the ratio u of the absorption coefficient and the backscattering coefficient are obtained. _渤海 (λ);

[0099] Published in *Optics Express*, June 2015, Vol. 23, No. 11, the paper "Evaluation of a QAA-based algorithm using MODIS land bands data for retrieval of IOPs in the Eastern China Seas" by Chen Shuguo et al. uses the IOCCG dataset fitting analysis method and finds that the total absorption coefficient α _渤海 (555) can be measured by the remote sensing reflectance (R) of the 645nm and 555nm wavelength bands. rs (645) / (R rs 555)) estimates yielded:

[0100] a _3 (λ0)=0.0596+0.52(R rs 645 / R rs 555) 1.432 -0.04782 (8) where λ0 is the reference wavelength of 555nm, R rs_渤海 (555) = 0.172, R rs_渤海 (645) = 0.108, and a can be obtained from formula (8). _渤海 (555) = 0.2788;

[0101] Step (2-2-1), the backscattering coefficient b at a wavelength of 555nm can be obtained from formulas (1)-(2). b_渤海 (555) = 0.0044, from which the backscattering coefficient b of all wavebands of turbid coastal seawater can be calculated. b_2 (λ):

[0102]

[0103] Where Y represents the backscattering coefficient of turbid coastal seawater. b_2 The spectral distribution of (λ) has the following empirical relationship with the backscattering coefficient at 555 nm wavelength in turbid coastal seawater:

[0104]

[0105] Because of b b_渤海 (555)≤0.03, so Y=-2.3171. According to formula (9), b can be obtained. b_渤海 (488) = 0.0033;

[0106] Step (2-2-2), b b_渤海 (488) and the ratio u of the absorption coefficient to the backscattering coefficient in the Bohai Sea obtained from step (1). _渤海 (488) Substitute into formula (11) to derive the total absorption coefficient a _渤海 (488) = 0.2324:

[0107]

[0108] Step (3) yields the total scattering coefficient b(λ) for different sea areas:

[0109] The backscattering coefficient b of the East China Sea is obtained from step (2-1-2). b_东海 Substituting (488) into formula (12), we can obtain b. _东海 (488) = 0.211:

[0110]

[0111] Formula (12) is derived by fitting scattering coefficient data from the Yellow Sea and East China Sea, and is called the NSOAS model. Formula (12) is derived from the backscattering coefficient b obtained by fitting data from fixed-point measurements at the navigation station in the book "Study on the Scattering Characteristics of Water Bodies in the Yellow Sea and East China Sea" by Song Qingjun et al., published in the Journal of Ocean University of China, July 2006, Vol. 28, No. 4. b_1 (λ) and scattering coefficient b _1 The relationship of (λ) has a coefficient of 0.0142 that is close to the coefficient obtained by correcting the data from the HS6 instrument.

[0112] The backscattering coefficient b of the Bohai Sea area obtained from step (2-2-1) b_渤海 (488) Substitute into formula (14):

[0113] Category 1: Relationship between backscattering coefficient and scattering coefficient at the Yellow River Estuary offshore section:

[0114]

[0115] Category 2: Relationship between backscattering coefficient and scattering coefficient in the Bohai Bay, Liaodong Bay, and Qinhuangdao sections:

[0116]

[0117] Where b w (λ) is the scattering coefficient of pure water, b bw (λ) is the backscattering coefficient of pure water, which is a constant;

[0118] Formula (14) is derived from the article "Statistical Relationship between Backscattering Coefficient and Beam Scattering Coefficient of Particulate Matter in the Bohai Sea Area" by Gu Yanzhen et al., published in the December 2007 issue of the Journal of Ocean University of China, Vol. 37, Supplement II. The scattering coefficient b was obtained through fitting based on field measurements. b_2 (λ) and scattering coefficient b _21 (λ), b _22 The relational expression for (λ);

[0119] Backscattering coefficient b of pure water in the Bohai Sea bw_渤海 (488) From step (2-1-2), the scattering coefficient of pure water can be obtained from the record in "Analysis of variations in ocean color" by Morel et al., published in Limnology and Oceanography, July 1977, Vol. 22, No. 4. The scattering coefficient of pure water at various wavelengths can be measured to know b. w_渤海 (488) = 0.0024, and b can be obtained from formula (14). _渤海 (488) = 0.241;

[0120] The backscattering coefficient b of the South China Sea is obtained from step (2-1-2). b_南海 (488) Substituting the equations from aerial surveys off the New Jersey coast, we obtain the relationship between the backscattering coefficient and the scattering coefficient:

[0121]

[0122] The scattering coefficient b in the 488nm band of the South China Sea was calculated. _南海 (488) = 0.088, where 0.0012m -1 ≤b b_1 (λ)≤0.3724m -1 ;

[0123] Formula (15) is published in the Office of Nawal Research, Ocean, Atmosphare, and Space Department, USA, November 2002, page 94, in “Relationship between backscattering and beamscattering coefficients derived from new measurements of light scattering phase functions” by Vladimir I. Haltrin et al.

[0124] In step (4), step (2-1), or step (2-2), the absorption coefficient α at a wavelength of 488 nm for different sea areas is obtained. _东海 (488), a _南海 (488), a _渤海 (488), and the scattering coefficients b for different sea areas with a wavelength of 488 nm obtained in step (3). _东海 (488), b _南海 (488), b _渤海 (488) Substitute into formula (16):

[0125] c(λ)=a(λ)+b(λ) (16)

[0126] The light attenuation coefficients at a wavelength of 488nm were obtained for different sea areas: c _东海 (488)=0.3449, c _南海 (488)=0.2, c _渤海 (488) = 0.4734.

[0127] Data acquisition methods include, but are not limited to, ocean observation websites. In this embodiment, the MODIS ocean observation network is used as an example to acquire satellite remote sensing data of global sea areas in January 2022. First, the remote sensing data is substituted into step (1) to obtain the remote sensing reflectance of the sea surface under various wavelengths in different sea areas and the ratio values ​​related to the absorption coefficient and backscattering coefficient. Then, the obtained remote sensing reflectance and ratio values ​​of the sea surface are substituted into step (2-1) or step (2-2) to obtain the absorption coefficient and backscattering coefficient of each wavelength under different sea areas and different water quality conditions. The backscattering coefficient of each wavelength obtained in step (2-1) or step (2-2) is substituted into step (3) to obtain the scattering coefficient of each wavelength in different sea areas. Finally, the absorption coefficient calculated in step (2-1) or step (2-2) and the scattering coefficient obtained in step (3) are substituted into step (4) to obtain the optical attenuation coefficient of each wavelength in different sea areas.

[0128] The preferred embodiments of the present invention disclosed above are merely illustrative and do not limit the invention to the specific implementations described. Obviously, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention.

Claims

1. A method for retrieving global ocean optical attenuation coefficients based on remote sensing reflectance, characterized in that, Includes the following steps: Step 1) Obtain the remote sensing reflectance beneath the sea surface by inverting satellite remote sensing data. : (1) in, For the remotely sensed reflectance received by the sensor, The wavelengths of both are the remote sensing reflectance below the sea surface. ; The relationship between the intrinsic optical quantities and the intrinsic optical quantities is shown in equation (2): (2) In formula (2), Indicates wavelength as The ratio function of the absorption coefficient and the backscattering coefficient, Indicates wavelength as The total absorption coefficient at that time Indicates wavelength as Backscattering coefficient at time; Step 2) Different methods are used to solve for the absorption coefficient and backscattering coefficient for clear seawater, relatively clear coastal seawater, and turbid coastal seawater: Step 2-1) uses the improved QAA_v5 algorithm for clear seawater and relatively clear coastal seawater to obtain... （3） in This indicates the reference wavelength, taken as 555nm. This represents the absorption coefficient of clear seawater and relatively clear coastal seawater at a reference wavelength. The absorption coefficient of pure water at the reference wavelength, Represents the remote sensing reflectance below the sea surface A ratio function between wavelengths of 443nm, 490nm, and 667nm; （4） Step 2-1-1), substitute the MODIS remote sensing data at a wavelength of 555nm into formula (1) to calculate the underwater remote sensing reflectance at a wavelength of 555nm. Further obtained Combining formulas (3) and (4), the total absorption coefficients of clear seawater with a wavelength of 555 nm and relatively clear coastal seawater are obtained. Backscattering coefficient of clear seawater and relatively clear coastal seawater Then by Substituting into formula (2), we obtain the result; Using formula (5), the backscattering coefficients for all wavebands of clear seawater and relatively clear coastal seawater are calculated. : （5） (6) Indicates wavelength as The backscattering coefficient of pure water, This represents the backscattering coefficient of suspended particulate matter at the reference wavelength. Represents the power parameter; where when , and It is known that This represents the backscattering coefficient of pure water at the reference wavelength. It is obtained through formulas (1)-(2) and (5); Step 2-1-2), by The total absorption coefficients of clear seawater and relatively clear coastal seawater were then calculated using algebraic methods, applied to formula (2). : （7）； Step 2-2), using the QAA-RGR algorithm for turbid coastal seawater: As shown in step 1), the remote sensing reflectance beneath the sea surface is obtained by inversion from satellite remote sensing data. And the ratio of absorption coefficient to backscattering coefficient was obtained. ; Using the dataset fitting analysis method proposed by the International Ocean Color Coordination Group, the absorption coefficient of turbid coastal seawater at a wavelength of 555 nm was obtained through linear fitting. , Remote sensing reflectance in the 645nm and 555nm bands ( The estimate yielded the following: （8） in The reference wavelength is 555nm; This represents the absorption coefficient of turbid coastal seawater at a reference wavelength. Step 2-2-1): The backscattering coefficient at 555nm wavelength is obtained from formulas (1)-(2), and then the backscattering coefficients of all wavelengths of turbid coastal seawater are calculated. : （9） in Backscattering coefficient, a characterization of turbid coastal seawater The spectral distribution of [the substance] has the following empirical relationship with the backscattering coefficient at 555 nm wavelength in turbid coastal seawater: （10） Step 2-2-2), if the remote sensing reflectance of other bands It is known that the total absorption coefficient of turbid coastal seawater can be derived by formulas (1)-(2) and (10). : （11）； Step 3), obtain the total scattering coefficient for different sea areas. : To obtain the scattering coefficients of the East China Sea or the Yellow Sea, we analyze the intrinsic optical quantity measurement data of the water bodies in the East China Sea and the Yellow Sea through fixed-point measurements at air stations, and fit the data to derive the backscattering coefficients of clear seawater and relatively clear coastal seawater. Scattering coefficient compared to relatively clear coastal waters Relationship: （12）； We need to obtain the scattering coefficient of the Bohai Sea area, and then obtain the backscattering coefficient of the turbid coastal seawater through fitting. Scattering coefficient with turbid coastal waters , Relationship: Category 1: Relationship between backscattering coefficient and scattering coefficient at the Yellow River Estuary offshore section: （13） Category 2: Relationship between backscattering coefficient and scattering coefficient in the Bohai Bay, Liaodong Bay, and Qinhuangdao sections: （14） in Let be the scattering coefficient of pure water. Here are the backscattering coefficients of pure water, all of which are constants; To obtain the scattering coefficients from other sea areas or oceans, 875 angular scattering coefficients were obtained through aerial surveys along the New Jersey coast, which were then used to derive the backscattering coefficients of clear seawater and relatively clear coastal water. Scattering coefficient with clear seawater Relationship: （15） in ; Step 4), the global ocean optical attenuation coefficient is obtained according to formula (16): （16） in Indicates wavelength as The total absorption coefficient at that time Indicates wavelength as The total scattering coefficient at that time Indicates wavelength as Total attenuation coefficient at time; In step 2-1), the absorption coefficients of clear seawater and relatively clear coastal seawater were obtained. The scattering coefficient of the relatively clear coastal seawater obtained in step 3) The attenuation coefficient of relatively clear coastal seawater is obtained by summing them. ; Absorption coefficient of clear seawater and relatively clear coastal seawater The scattering coefficient of clear seawater obtained in step 3) The attenuation coefficient of clear seawater is obtained by adding them together. ; In step 2-2), the absorption coefficient of turbid coastal seawater is obtained. The scattering coefficient of the turbid coastal seawater obtained in step 3) or The attenuation coefficient of turbid coastal seawater is obtained by adding them together. .

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