Method for retrieving marine aerosol optical depth from space-borne lidar noise

Abstract

The application discloses a method for inverting marine aerosol optical depth by using spaceborne lidar noise, belongs to the technical field of laser remote sensing, and is used for quantitatively inverting aerosol optical depth. Under the premise that system hardware parameters of the spaceborne lidar and total background noise data detected by the spaceborne lidar, environmental parameters of a corresponding region and moment are given, a noise model of solar radiation items corresponding to water surface white froth diffuse reflection and water surface specular reflection, a water-leaving noise model (a noise model of solar radiation items of water body backscattering), and an atmospheric noise model (a noise model of solar radiation items of Rayleigh scattering of atmospheric molecules and Mie scattering of aerosol particles) are respectively constructed. Water surface noise, water-leaving noise and atmospheric Rayleigh scattering noise are removed from total noise rate of the atmosphere top detected by the lidar, and aerosol scattering noise results are obtained. Finally, marine aerosol optical depth of a satellite transit region and moment is quantitatively inverted by using the aerosol scattering noise results and the aerosol scattering noise model.

Description

Technical Field

[0001] This invention discloses a method for inverting the optical thickness of marine aerosols using noise from a spaceborne lidar, belonging to the field of laser remote sensing technology. Background Technology

[0002] Aerosol optical depth (AOD) is the integral result of the aerosol extinction coefficient in the vertical direction of the total atmospheric column, reflecting the aerosol concentration and the degree of turbidity and pollution in the air. While AOD can be observed through ground-based stations, these stations cannot achieve large-area coverage observations over vast ocean areas. Satellite remote sensing, with its wide coverage and high timeliness, is the most effective detection method for studying the large-scale spatiotemporal evolution of atmospheric aerosols, effectively overcoming the limitations of ground-based observations. Traditional passive optical remote sensing (such as the widely used MODIS passive optical image data, Moderate-resolution Imaging Spectroradiometer) typically retrieves AOD by building a look-up table (LUT), i.e., retrieving results based on the actual geographical area observed by the satellite, corresponding solar altitude conditions, and surface reflection conditions. However, this method requires pre-calculation, resulting in long computation times and large storage space requirements. Summary of the Invention

[0003] The purpose of this invention is to provide a method for inverting the optical thickness of marine aerosols using noise from a spaceborne lidar, in order to solve the problem that ground-based stations cannot observe marine areas under the requirements of existing technologies, and to supplement passive optical remote sensing.

[0004] Methods for retrieving the optical thickness of marine aerosols using noise inversion from spaceborne lidar include:

[0005] S1. Modeling the water surface noise term of the spaceborne lidar, calculating the proportion of white foam covering the water surface, and based on this, calculating the noise rate f of solar radiation reflected by the white foam. wc ;

[0006] S2. Modeling of water-leaving radiation noise term for spaceborne lidar;

[0007] S3. Atmospheric Rayleigh noise modeling for spaceborne lidar;

[0008] S4. Remove sea surface noise, water-away noise, and atmospheric Rayleigh noise from the total noise detected by the spaceborne lidar to obtain atmospheric aerosol noise. Using the total noise at the top of the atmosphere detected by the spaceborne lidar and the sea surface noise, water-away noise, and atmospheric Rayleigh noise calculated in S1 to S3, obtain the atmospheric aerosol noise rate f. a ;

[0009] S5. Model the solar radiation noise rate of the spaceborne lidar based on Mie scattering by aerosol particles, and perform aerosol optical thickness inversion based on this.

[0010] In S1, the water surface noise modeling includes the noise rate modeling of solar radiation reflected by water foam and the noise rate modeling of solar radiation reflected by water mirror.

[0011] Noise rate modeling for solar radiation reflected by white foam on the water surface includes:

[0012] Calculate the proportion of the sea surface covered by white foam, W: W = 2.95 × 10 -6 ·U w 3.52 (1), Among them, U w The wind speed is 10 meters above the sea surface, when the solar zenith angle is θ. s That is, the corresponding solar altitude angle is 90°-θ s At that time, the solar background noise rate f received by the spaceborne lidar from the reflection of white foam on the water surface wc for: Where F is the calibration coefficient of the lidar system, η r For the efficiency of the receiving optical system, η q Let θ be the detector quantum efficiency, Δλ be the filter bandwidth, and θ be the... r For the half field of view of the receiving aperture, A r The effective area of ​​the receiving telescope, hv is the energy of a single photon at the corresponding wavelength, and θ v Let N be the nadir angle corresponding to the optical axis of the lidar's field of view. For a given spaceborne lidar system, all of the above parameters are known values; N0 is the solar irradiance at the average Earth-Sun distance, determined by the optical power density N. λ Calculation, i.e.: N0 = N λ ×(1+0.0167×cos(2π×(Day-3) / 365)) 2 Where Day represents the accumulated days of a year, and N λ For a given wavelength that is fixed, for a wavelength of 532nm, N λ =1.832W / (m 2 ·nm); ρ1 is the reflectivity of the foam, which is a fixed value for a given wavelength. For a wavelength of 532nm, ρ1=0.2; θ s The atmospheric diffuse transmittance is related to the satellite's transit area and time. t(θ) is the atmospheric transmittance using Rayleigh scattering. R (θ) substitution, denoted as t R (θ)=exp{-τ R / [2cos(θ)]}, the Rayleigh optical thickness τ given the atmospheric pressure P at the Earth's surface or sea surface and the wavelength λ. R for: Where, τ Ro The Rayleigh optical thickness is the equivalent of one standard atmosphere P0 (1013.25 hPa), and is a fixed value. P is in hPa and λ is in mm.

[0013] Noise rate modeling for solar radiation reflected by a water surface includes:

[0014] The noise rate f of solar radiation reflected from the water surface by the spaceborne lidar g for:

[0015] Among them, s 2 The wind speed at a height of 10 meters above the water surface is the square of the average slope of the sea surface, calculated as: s 2 =0.003 + 0.00512 × U w ;ρ s The specular reflectance of the water surface is calculated using Fresnel's law. For a wavelength of 532 nm, ρ s =0.02; T is the atmospheric direct transmittance, expressed as T(θ) = exp[-τ R / cos(θ)],τ R It is given by formula (3).

[0016] S2 includes: On the ocean surface without bottom reflection, the solar radiation noise term corresponding to the water backscattering of solar radiation noise from the spaceborne lidar is the cumulative backscattering of sunlight from all depths between the bottom and the surface, expressed as:

[0017] Among them, R rs For water body remote sensing reflectance, which corresponds to the ratio of water radiance to downflow irradiance, is a known constant term on the surface of a clean ocean.

[0018] S3 includes: calculating the solar radiation noise rate f caused by Rayleigh scattering of atmospheric molecules in the atmosphere using the single scattering approximation. R , is represented as: Where, p r It is calculated from the Rayleigh scattering phase function and expressed as: p r (θ s θ v ) = P r (θ- )+[r(θ s )+r(θ v )]P r (θ + (7), P r (θ) is the Rayleigh scattering phase function, and θ is the input angle; θ ± θ in space s and θ v The acute angle between them is negative θ when the normal is on the same side. - Different sides are positive θ + , is represented as:

[0019] θ ± =arccos[±cosθ s cosθ v -sinθ s sinθ v cos(φ v -φ s )](8), φ s φ is the solar azimuth angle. v θ is the azimuth angle of the optical axis of the field of view of the spaceborne lidar, which is a known value for a given lidar; r(θ) is the Fresnel reflectivity of the interface at a given wavelength and incident angle θ, expressed as: Where θ1 is the angle of refraction, which is calculated from the angle of incidence θ, i.e.: θ1=arcsin[sin(θ) / n], and n is the refractive index. The refractive index n in water is chosen to be a constant of 1.333.

[0020] S4 includes: the total noise f detected by spaceborne lidar at the top of the atmosphere in the ocean region. t Rayleigh scattering by atmospheric molecules f R Mie scattering of aerosol particles f a Water surface mirror reflection f g White foam on the water surface reflects f wc Water backscattering f w and detector dark count noise f d Composition: Ignoring the detector dark count rate, which is much smaller than the other terms during the day, and removing the contributions of other terms from the total atmospheric top noise rate detected by the spaceborne lidar, the noise rate caused by aerosol scattering of solar radiation is obtained, expressed as: f a =f t -(f R +f g +f wc +f w ).

[0021] S5 includes: Based on the single-scattering approximation, the solar radiation noise rate caused by aerosol scattering is expressed as:

[0022] Where w a It is the aerosol single scattering ratio, expressed as:

[0023] w a =(-0.0032AM+0.972)·exp(3.06×10 -4 RH)(12), Among them, AM represents the aerosol type, ranging from 1 to 10, corresponding to typical high seas aerosols to typical continental aerosols; RIH represents atmospheric relative humidity.

[0024] In formula (11) p a Given the aerosol scattering phase function P a The result is obtained through calculation and is expressed as:

[0025] p a (θ s θ v ) = P a (θ - )+[r(θ s )+r(θ v )]P a (θ + (13), In formula (13) θ - θ + With r(θ) s ), r(θ) v The results are obtained by formulas (8) and (9) respectively;

[0026] The aerosol noise rate f of the spaceborne lidar is calculated using formulas (1) to (10). a Given the known values, the aerosol scattering solar radiation noise rate model is combined with formulas (11) to (13) and the obtained p a and w a The optical thickness τ of marine aerosols a Obtained by inversion using formula (14):

[0027] Compared with existing technologies, this invention has the following advantages: This invention can quantitatively apply the "useless" noise data of active lidar systems, and by constructing an atmospheric radiative transfer model and a spaceborne lidar data processing algorithm, it can accurately invert the optical thickness of marine aerosols in the area and time of lidar satellite transit, providing a new solution for obtaining marine aerosol optical thickness through satellite remote sensing; at the same time, it has reference value for the quality inspection of atmospheric correction of water color remote sensing (and even atmospheric correction of lidar) and atmospheric models. Attached Figure Description

[0028] Figure 1 This is a technical flowchart of the present invention;

[0029] Figure 2 It shows the total noise rate of a typical oceanic atmosphere top as detected by the single-photon lidar carried by the ICESat-2 satellite, and the calculated noise rate contribution curves.

[0030] Figure 3 This is a comparison between the marine aerosol optical thickness retrieved using the method of this invention and the total noise rate data of the atmospheric top detected by ICESat-2, and the marine aerosol optical thickness measured by the existing MODIS. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] Methods for retrieving the optical thickness of marine aerosols using noise inversion from spaceborne lidar include:

[0033] S1. Modeling the water surface noise term of the spaceborne lidar, calculating the proportion of white foam covering the water surface, and based on this, calculating the noise rate f of solar radiation reflected by the white foam. wc ;

[0034] S2. Modeling of water-leaving radiation noise term for spaceborne lidar;

[0035] S3. Atmospheric Rayleigh noise modeling for spaceborne lidar;

[0036] S4. Remove sea surface noise, water-away noise, and atmospheric Rayleigh noise from the total noise detected by the spaceborne lidar to obtain atmospheric aerosol noise. Using the total noise at the top of the atmosphere detected by the spaceborne lidar and the sea surface noise, water-away noise, and atmospheric Rayleigh noise calculated in S1 to S3, obtain the atmospheric aerosol noise rate f.a ;

[0037] S5. Model the solar radiation noise rate of the spaceborne lidar based on Mie scattering by aerosol particles, and perform aerosol optical thickness inversion based on this.

[0038] In S1, the water surface noise modeling includes the noise rate modeling of solar radiation reflected by water foam and the noise rate modeling of solar radiation reflected by water mirror.

[0039] Noise rate modeling for solar radiation reflected by white foam on the water surface includes:

[0040] Calculate the proportion of the sea surface covered by white foam, W: W = 2.95 × 10 -6 .U w 3.52 (1), Among them, U w The wind speed is 10 meters above the sea surface, when the solar zenith angle is θ. s That is, the corresponding solar altitude angle is 90°-θ s At that time, the solar background noise rate f received by the spaceborne lidar from the reflection of white foam on the water surface wc for: Where F is the calibration coefficient of the lidar system, η r For the efficiency of the receiving optical system, η q Let θ be the detector quantum efficiency, Δλ be the filter bandwidth, and θ be the... r For the half field of view of the receiving aperture, A r The effective area of ​​the receiving telescope, hv is the energy of a single photon at the corresponding wavelength, and θ v Let N be the nadir angle corresponding to the optical axis of the lidar's field of view. For a given spaceborne lidar system, all of the above parameters are known values; N0 is the solar irradiance at the average Earth-Sun distance, determined by the optical power density N. λ Calculation, i.e.: N0 = N λ ×(1+0.0167×cos(2π×(Day-3) / 365)) 2 Where Day represents the accumulated days of a year, and N λ For a given wavelength that is fixed, for a wavelength of 532nm, N λ =1.832W / (m 2 ·nm); ρ1 is the reflectivity of the foam, which is a fixed value for a given wavelength. For a wavelength of 532nm, ρ1=0.2; θ s The atmospheric diffuse transmittance is related to the satellite's transit area and time. t(θ) is the atmospheric transmittance using Rayleigh scattering. R (θ) substitution, denoted as t R(θ)=exp{-τ R / [2cos(θ)]}, the Rayleigh optical thickness τ given the atmospheric pressure P at the Earth's surface or sea surface and the wavelength λ. R for: Where, τ Ro The Rayleigh optical thickness is the equivalent of one standard atmosphere P0 (1013.25 hPa), and is a fixed value. P is in hPa and λ is in mm.

[0041] Noise rate modeling for solar radiation reflected by a water surface includes:

[0042] The noise rate f of solar radiation reflected from the water surface by the spaceborne lidar g for:

[0043] Among them, s 2 The wind speed at a height of 10 meters above the water surface is the square of the average slope of the sea surface, calculated as: s 2 =0.003 + 0.00512 × U w ;ρ s The specular reflectance of the water surface is calculated using Fresnel's law. For a wavelength of 532 nm, ρ s =0.02; T is the atmospheric direct transmittance, expressed as T(θ) = exp[-τ R / cos(θ)],τ R It is given by formula (3).

[0044] S2 includes: On the ocean surface without bottom reflection, the solar radiation noise term corresponding to the water backscattering of solar radiation noise from the spaceborne lidar is the cumulative backscattering of sunlight from all depths between the bottom and the surface, expressed as:

[0045] Among them, R rs For water body remote sensing reflectance, which corresponds to the ratio of water radiance to downflow irradiance, is a known constant term on the surface of a clean ocean.

[0046] S3 includes: calculating the solar radiation noise rate f caused by Rayleigh scattering of atmospheric molecules in the atmosphere using the single scattering approximation. R , is represented as: Where, p r It is calculated from the Rayleigh scattering phase function and expressed as: p r (θ s θ v) = P r (θ - )+[r(θ s )+r(θ v )]P r (θ + (7), P r (θ) is the Rayleigh scattering phase function, and θ is the input angle; θ ± θ in space s and θ v The acute angle between them is negative θ when the normal is on the same side. - Different sides are positive θ + , is represented as:

[0047] θ ± =arccos[±cosθ s cosθ v -sinθ s sinθ v cos(φ v -φ s )](8), φ s φ is the solar azimuth angle. v θ is the azimuth angle of the optical axis of the field of view of the spaceborne lidar, which is a known value for a given lidar; r(θ) is the Fresnel reflectivity of the interface at a given wavelength and incident angle θ, expressed as: Where θ1 is the angle of refraction, which is calculated from the angle of incidence θ, i.e.: θ1=arcsin[sin(θ) / n], and n is the refractive index. The refractive index n in water is chosen to be a constant of 1.333.

[0048] S4 includes: the total noise f detected by spaceborne lidar at the top of the atmosphere in the ocean region. t Rayleigh scattering by atmospheric molecules f R Mie scattering of aerosol particles f a Water surface mirror reflection f g White foam on the water surface reflects f wc Water backscattering f w and detector dark count noise f d Composition: Ignoring the detector dark count rate, which is much smaller than the other terms during the day, and removing the contributions of other terms from the total atmospheric top noise rate detected by the spaceborne lidar, the noise rate caused by aerosol scattering of solar radiation is obtained, expressed as: f a =f t -(f R +f g +f wc +f w ).

[0049] S5 includes: Based on the single-scattering approximation, the solar radiation noise rate caused by aerosol scattering is expressed as:

[0050] Where w a It is the aerosol single scattering ratio, expressed as:

[0051] w a =(-0.0032AM+0.972)·exp(3.06×10 -4 RH)(12), AM represents the aerosol type, ranging from 1 to 10, corresponding to typical high seas aerosols to typical continental aerosols; RH represents atmospheric relative humidity.

[0052] In formula (11) p a Given the aerosol scattering phase function P a The result is obtained through calculation and is expressed as:

[0053] p a (θ s θ v ) = P a (θ - )+[r(θ s )+r(θ v )]P a (θ + (13), In formula (13) θ - θ + With r(θ) s ), r(θ) v The results are obtained by formulas (8) and (9) respectively;

[0054] The aerosol noise rate f of the spaceborne lidar is calculated using formulas (1) to (10). a Given the known values, the aerosol scattering solar radiation noise rate model is combined with formulas (11) to (13) and the obtained p a and w a The optical thickness τ of marine aerosols a Obtained by inversion using formula (14):

[0055] This invention uses background noise data and system hardware parameters acquired by the US ICESat-2 lidar system as examples. ICESat-2 is the world's first single-photon lidar satellite, carrying an ATLAS (Advanced Topographic Laser Altimeter System) single-photon lidar that emits six 532nm wavelength green laser beams towards the Earth's surface. ICESat-2's ATL03 data product provides the specific time, latitude, longitude, and altitude information of the detected photon point cloud, and provides the total solar background noise rate f at the top of the atmosphere for the corresponding geographical location and time. t and the solar zenith angle θ s data.

[0056] The example selected in this embodiment is the total solar background noise rate f obtained by the ICESat-2 single-photon lidar during a daytime flight over the Pacific Ocean (clean ocean area) on March 22, 2020. t and the solar zenith angle θ s Data. Marine environmental data in the embodiments (including wind speed U above the sea surface) w Sea surface atmospheric pressure (P) and relative humidity (RH) were obtained from the global reanalysis dataset provided by the National Centers for Environmental Prediction (NCEP), based on the geographical location (latitude and longitude) and time (UTC, Coordinated Universal Time) of ICESat-2 transit, through spatial bilinear interpolation and temporal linear interpolation.

[0057] For the lidar mounted on ICESat-2, its system hardware parameters are known values. In this embodiment, these parameters are taken as: F = 1 / 0.5, Δλ = 0.038nm, A r =0.503m 2 λ=532nm, θ r = 87.5 / 2μrad, θ v =0.38°; Meanwhile, the ATL03 data product also directly provides parameter B, which is related to detection efficiency. ret This parameter includes the efficiency η of the receiving optical system. r Quantum efficiency of detector η q The single photon energy hv corresponding to 532nm, i.e.: B ret =η r η q / hv.

[0058] Because the nadir angle of the optical axis of the receiving field of view of the spaceborne lidar is θ v Typically less than 5°, sinθv The value is very small, for example, θ in ICESat-2. v =0.38°, therefore the two azimuth angles φ in formula (8) are... s and φ v The effect is negligible; meanwhile, due to θ v =0.38°, cosθ in all the aforementioned formulas v ≈1, sinθ v ≈0.

[0059] For the 532nm wavelength used by the lidar on ICESat-2, the following environmental parameters can all be calculated as known values: R rs The typical value for clean oceans is 0.002 sr. -1 N λ =1.832w / m 2 ·nm; ρ1=0.2; ρ s =0.02; AM is 1 in typical high seas aerosols.

[0060] In this embodiment, the Rayleigh scattering phase function P is selected. r (θ)=3 / 4(1+cos 2 θ), where θ is the input angle; the aerosol scattering phase function is expressed as the HG (Henyey-Greenstein) scattering phase function:

[0061] Where θ is the input angle; g represents the asymmetric scattering factor, g = 0 indicates isotropic scattering, when g approaches 1, forward scattering increases; when g approaches -1, backscattering is enhanced. In this embodiment, g is chosen to be 0.74.

[0062] The technical process of this invention is as follows: Figure 1 As shown in the embodiment, the contributions of various noises detected by the spaceborne lidar at the top of the atmosphere are as follows: Figure 2 As shown, in this embodiment, the system hardware parameters of the lidar carried by the ICESat-2 satellite, the acquired noise rate and solar zenith angle data, and the sea surface wind speed U provided by NCEP are used. w The sea surface atmospheric pressure (P) and relative humidity (RH) data were used to finally invert and calculate the optical thickness of marine aerosols in the Pacific Ocean. These inverted aerosol optical thicknesses were compared and verified with the aerosol optical thickness (corresponding to daily average data) provided by the existing MODIS L2 product MOD04. Figure 3As shown, the comparison along the latitudinal direction yields a root mean square error (RMSE) of 0.0289 and a mean absolute percentage error (MAPE) of 9.49%. Therefore, this invention can rapidly and accurately invert and calculate local marine aerosol optical thickness results using background noise data obtained by a spaceborne lidar flying over different sea areas. This will contribute to the quantitative study of the spatiotemporal variations of marine aerosol optical thickness and the research on marine atmospheric correction.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for retrieving the optical thickness of marine aerosols using noise inversion from a spaceborne lidar, characterized in that, include: S1. Model the water surface noise term of the spaceborne lidar, calculate the proportion of white foam covering the water surface, and based on this, calculate the noise rate f of solar radiation reflected by the white foam. wc ; S2. Modeling of water-leaving radiation noise term for spaceborne lidar; S3. Atmospheric Rayleigh noise modeling for spaceborne lidar; S4. Remove surface noise, water-leaving radiation noise, and atmospheric Rayleigh noise from the total noise detected by the spaceborne lidar to obtain atmospheric aerosol noise. Using the total noise at the top of the atmosphere detected by the spaceborne lidar and the surface noise, water-leaving radiation noise, and atmospheric Rayleigh noise calculated in S1 to S3, obtain the atmospheric aerosol noise rate f. a ; S5. Model the solar radiation noise rate of the spaceborne lidar based on Mie scattering by aerosol particles, and perform aerosol optical thickness inversion based on this.

2. The method for inverting the optical thickness of marine aerosols using noise from a spaceborne lidar according to claim 1, characterized in that, In S1, the water surface noise modeling includes the noise rate modeling of solar radiation reflected by water foam and the noise rate modeling of solar radiation reflected by water mirror.

3. The method for inverting the optical thickness of marine aerosols using noise from a spaceborne lidar according to claim 2, characterized in that, Noise rate modeling for solar radiation reflected by white foam on the water surface includes: Calculate the proportion of the sea surface covered by white foam, W: W = 2.95 × 10 -6 ·U w 3.52 (1), where U w The wind speed is 10 meters above the sea surface, when the solar zenith angle is θ. s That is, the corresponding solar altitude angle is 90°-θ s At that time, the solar background noise rate f received by the spaceborne lidar from the reflection of white foam on the water surface wc for: Where F is the calibration coefficient of the lidar system, η r For the efficiency of the receiving optical system, η q Let θ be the detector quantum efficiency, Δλ be the filter bandwidth, and θ be the... r For the half field of view of the receiving aperture, A r The effective area of ​​the receiving telescope, hv is the energy of a single photon at the corresponding wavelength, and θ v Let N be the nadir angle corresponding to the optical axis of the lidar's field of view. For a given spaceborne lidar system, all of the above parameters are known values; N0 is the solar irradiance at the average Earth-Sun distance, determined by the optical power density N. λ Calculation, i.e.: N0 = N λ ×(1+0.0167×cos(2π×(Day-3) / 365)) 2 Where Day represents the accumulated days of a year, and N λ For a given wavelength that is fixed, for a wavelength of 532nm, N λ =1.832W / (m 2 ·nm); ρ1 is the reflectivity of the foam, which is a fixed value for a given wavelength. For a wavelength of 532nm, ρ1=0.2; θ s The atmospheric diffuse transmittance is related to the satellite's transit area and time. t(θ) is the atmospheric transmittance using Rayleigh scattering. R (θ) substitution, denoted as t R (θ)=exp{-τ R / [2cos(θ)]}, the Rayleigh optical thickness τ given the atmospheric pressure P at the Earth's surface or sea surface and the wavelength λ. R for: Where, τ Ro The Rayleigh optical thickness is the equivalent of one standard atmosphere P0 (1013.25 hPa), and is a fixed value. P is in hPa and λ is in mm.

4. The method for inverting the optical thickness of marine aerosols using noise from a spaceborne lidar according to claim 3, characterized in that, Noise rate modeling for solar radiation reflected by a water surface includes: The noise rate f of solar radiation reflected from the water surface by the spaceborne lidar g for: (4)， Among them, s 2 The wind speed at a height of 10 meters above the water surface is the square of the average slope of the sea surface, calculated as: s 2 =0.003 + 0.00512 × U w ;ρ s The specular reflectance of the water surface is calculated using Fresnel's law. For a wavelength of 532 nm, ρ s =0.02; T is the atmospheric direct transmittance, expressed as T(θ) = exp[-τ R / cos(θ)],τ R It is given by formula (3).

5. The method for inverting the optical thickness of marine aerosols using spaceborne lidar noise according to claim 4, characterized in that, S2 includes: On the ocean surface without bottom reflection, the solar radiation noise term corresponding to the water backscattering of solar radiation noise from the spaceborne lidar is the cumulative backscattering of sunlight from all depths between the bottom and the surface, expressed as: Among them, R rs For water body remote sensing reflectance, which corresponds to the ratio of water radiance to downflow irradiance, is a known constant term on the surface of a clean ocean.

6. The method for inverting the optical thickness of marine aerosols using spaceborne lidar noise according to claim 5, characterized in that, S3 includes: calculating the solar radiation noise rate f caused by Rayleigh scattering of atmospheric molecules in the atmosphere using the single scattering approximation. R , is represented as: Where, p r It is calculated from the Rayleigh scattering phase function and expressed as: p r (i s ,i v )=P r (i _ )+[r(θ s )+r(θ v )]P r (i + )(7), P r (θ) is the Rayleigh scattering phase function, and θ is the input angle; θ ± θ in space s and θ v The acute angle between them is negative θ when the normal is on the same side. － Different sides are positive θ + , is represented as: i ± =arccos[±cosθ s cosθ v -sinθ s sinth v cos(φ v -f s )](8), φ s φ is the solar azimuth angle. v Let θ be the azimuth angle of the optical axis of the spaceborne lidar's field of view, which is a known value for a given lidar; r(θ) is the Fresnel reflectivity of the interface at a given wavelength and incident angle θ, expressed as: r(θ) = (r s 2 +r v 2 ) / 2; Where θ1 is the angle of refraction, which is calculated from the incident angle θ, i.e.: θ1=arcsin[sin(θ) / n], and n is the refractive index. The refractive index n in water is chosen to be a constant of 1.

333.

7. The method for inverting the optical thickness of marine aerosols using noise from a spaceborne lidar according to claim 6, characterized in that, S4 This includes: the total noise f detected by spaceborne lidar at the top of the atmosphere in the ocean region. t Rayleigh scattering by atmospheric molecules f R Mie scattering of aerosol particles f a Water surface mirror reflection f g White foam on the water surface reflects f wc Water backscattering f w and detector dark count noise f d Composition: Ignoring the detector dark count rate, which is much smaller than the other terms during the day, and removing the contributions of other terms from the total atmospheric top noise rate detected by the spaceborne lidar, the noise rate caused by aerosol scattering of solar radiation is obtained, expressed as: f a =f t -(f R +f g +f wc +f w ).

8. The method for inverting the optical thickness of marine aerosols using spaceborne lidar noise according to claim 7, characterized in that, S5 include: According to the single-scattering approximation, the solar radiation noise rate caused by aerosol scattering is expressed as: Where w a It is the aerosol single scattering ratio, expressed as: w a =(-0.0032AM+0.972)·exp(3.06×10 -4 RH)(12), AM represents the aerosol type, ranging from 1 to 10, corresponding to typical high seas aerosols to typical continental aerosols; RH represents atmospheric relative humidity. In formula (11) p a Given the aerosol scattering phase function P a The result is obtained through calculation and is expressed as: p a (i s ,i v )=P a (i _ )+[r(θ s )+r(θ v )]P a (i + )(13), In formula (13) θ － θ + With r(θ) s ), r(θ) v The results are obtained by formulas (8) and (9) respectively; The aerosol noise rate f of the spaceborne lidar is calculated using formulas (1) to (10). a Given the known values, the aerosol scattering solar radiation noise rate model is combined with formulas (11) to (13) and the obtained p a and w a The optical thickness τ of marine aerosols a Obtained by inversion using formula (14):

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