CN114646616B - Atmospheric correction method for class II water body - Google Patents
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Abstract
The invention provides an atmospheric correction method for a second-class water body, belongs to the technical field of ocean water color remote sensing atmospheric correction, and solves the problem that the existing correction method is large in correction error. The method comprises the steps of collecting L1B-level spectral data in ultraviolet and short wave infrared bands and geometrical observation condition data in real time; rayleigh scattering analysis is carried out according to the geometric observation condition data to obtain a Rayleigh scattering radiance theoretical value corresponding to an ultraviolet waveband characteristic frequency and two short wave infrared waveband characteristic frequencies; correcting the Rayleigh scattering radiance theoretical value corresponding to the characteristic frequency through the acquired L1B-level spectral data, and further obtaining the aerosol reflectivity corresponding to each characteristic frequency; and judging the type of the aerosol in the atmosphere at the current moment according to the aerosol reflectivity, and fitting the aerosol reflectivity of other wave bands by selecting a strong absorption model or a weak absorption model matched with the type to obtain the aerosol reflectivity of the full wave band for atmosphere correction.
Description
Technical Field
The invention relates to the technical field of ocean water color remote sensing atmospheric correction, in particular to an atmospheric correction method for a second-class water body.
Background
The ocean water color remote sensing firstly needs atmospheric correction on atmospheric vertex radiance (TOA) observed by a satellite, atmospheric molecules and aerosol scattered radiation are removed, water leaving radiance is obtained, and then water color element information is extracted by utilizing an established water color factor inversion algorithm model.
According to the optical classification standard of water bodies, natural water systems can be divided into a first class water body and a second class water body. Among them, the optical characteristics of a class of water bodies represented by the open ocean are mainly influenced by the chlorophyll concentration of phytoplankton, the atmospheric correction algorithm for the class of water bodies is more perfect, and the water bodies are applied to a series of water color remote sensors (Gordon and Wang 1994 b). The method is characterized in that a near-shore water body with high water color component content such as suspended Sediment (SPM), chlorophyll (Chl) and yellow matter (CDOM) is generally adopted by a SWIR algorithm (Wang 2005, wang 2007) or a UV algorithm (He et al 2012), the principle is that on the premise that the water-leaving radiation of a short wave infrared band and an ultraviolet band is low and is assumed to be 0, the aerosol scattering contribution of a reference band is obtained, an aerosol reflectivity ratio parameter is defined, and the atmospheric correction is realized by extrapolating to a visible light range.
However, the SWIR algorithm and the UV algorithm gradually enlarge the extrapolation error as the spectral distance of the calculated band from the reference band increases during the extrapolation (Oo et al. 2008). In addition, due to the influence of the land-source substances, the aerosol in the near-shore water area generally has strong absorptivity, so that the reflectivity of the aerosol in the short blue band tends to be reduced, and the correction error is increased.
Disclosure of Invention
In view of the foregoing analysis, the embodiments of the present invention are directed to providing an atmospheric calibration method for a class ii water body, so as to solve the problem of large calibration error of the existing calibration method.
In one aspect, an embodiment of the present invention provides an atmospheric correction method for a class ii water body, including the following steps:
collecting L1B-level spectral data in ultraviolet, short-wave and infrared bands and geometric observation condition data in real time;
rayleigh scattering analysis is carried out according to the geometric observation condition data to obtain a Rayleigh scattering radiance theoretical value corresponding to an ultraviolet waveband characteristic frequency and two short wave infrared waveband characteristic frequencies;
respectively correcting the Rayleigh scattering radiance theoretical values corresponding to the characteristic frequencies through the collected L1B-level spectral data, and further obtaining aerosol reflectivity corresponding to each characteristic frequency;
judging the type of the aerosol in the atmosphere at the current moment according to the aerosol reflectivity corresponding to each characteristic frequency, and fitting the aerosol reflectivity of other wave bands except the two wave bands by selecting a strong absorption model or a weak absorption model matched with the type to obtain the aerosol reflectivity of the full wave band;
and performing atmospheric correction according to the aerosol reflectivity of the full wave band.
The beneficial effects of the above technical scheme are as follows: aiming at the second class of water bodies, a novel method for carrying out matching interpolation through ultraviolet and short wave infrared bands is provided. The problem that the extrapolation error of the turbid water body increases along with the increase of the spectral distance between the calculation waveband and the reference waveband in the conventional two-class water body atmosphere correction method is solved, and the influence of absorptive aerosol widely existing in the offshore sea area on the correction result is reduced, so that the atmosphere correction precision is improved, and accurate help can be provided for the inversion of other subsequent remote sensing parameters.
Based on the further improvement of the method, the step of collecting the L1B-level spectral data in the ultraviolet band, the short wave band and the infrared band and the geometric observation condition data in real time further comprises the following steps:
establishing a marine data acquisition site capable of acquiring water color remote sensing data of a second-class water body, laying an SGLI sensor, selecting a clear sky or a time period with sufficient illumination, and acquiring high-frequency continuous water body actual measurement spectrum data in each wave band through the SGLI sensor;
screening out high-frequency continuous water body actual measurement spectrum data in ultraviolet, short wave and infrared bands from the data according to the longitude and latitude of the marine data acquisition station;
and carrying out data analysis on the screened actually measured spectrum data of the high-frequency continuous water body to obtain L1B-level spectrum data in ultraviolet and short-wave infrared bands and geometric observation condition data.
Further, the L1B-level spectral data comprises the atmospheric cap apparent radiance in ultraviolet, short wave and infrared bandsL TOA （λ) (ii) a And the number of the first and second electrodes,
the geometric observation condition data comprises solar zenith anglesθ s Observing zenith angleθ v Relative azimuth angle and atmospheric top solar irradiance of each wave bandF 0 （λ) And equivalent Rayleigh optical thicknessτ r 。
Further, the step of performing rayleigh scattering analysis according to the geometric observation condition data to obtain a rayleigh scattering radiance theoretical value corresponding to an ultraviolet band characteristic frequency and two short wave infrared band characteristic frequencies further includes:
randomly selecting one characteristic frequency in an ultraviolet band and randomly selecting two characteristic frequencies in a short wave infrared band;
according to the zenith angle of the sunθ s And observing zenith angleθ v Atmospheric top solar irradiance at different wave bands, relative azimuth anglesF 0 （λ) And equivalent Rayleigh optical thicknessτ r Determining the Rayleigh scattering radiance theoretical value corresponding to each characteristic frequency by combining a Rayleigh scattering lookup tableL r （λ）。
Further, the wavelength corresponding to the ultraviolet band characteristic frequency is 380 nm, and the wavelength corresponding to the short-wave infrared band characteristic frequency is 1630 nm and 2210 nm respectively.
Further, the step of respectively correcting the rayleigh scattering radiance theoretical value corresponding to the characteristic frequency through the acquired L1B-level spectral data to further obtain the aerosol reflectivity corresponding to each characteristic frequency further includes:
respectively correcting the Rayleigh scattering radiance theoretical value corresponding to each characteristic frequency through the following formula to obtain the Rayleigh scattering radiance corrected value corresponding to each characteristic frequencyL rc （λ）
L rc （λ）=L TOA （λ）-L r （λ）
In the formula (I), the compound is shown in the specification,L TOA （λ) The atmospheric top surface radiance corresponding to the characteristic frequency,λfor the wavelength corresponding to the characteristic frequency,L r （λ) The Rayleigh scattering radiance theoretical value corresponding to the characteristic frequency;
according to the Rayleigh scattering radiance corrected value corresponding to each characteristic frequencyL rc （λ) The aerosol reflectivity corresponding to each characteristic frequency is obtained by the following formulaρ a （λ）
ρ a （λ）=πL rc （λ）/[F 0 （λ）×cosθs]
Wherein, pi is the circumference ratio,F 0 （λ) Is a wavelengthλThe characteristic frequency of (a) is corresponding to the atmospheric top solar irradiance,θand s is the zenith angle of the sun.
Further, the step of determining the aerosol type of the atmosphere at the current moment according to the aerosol reflectivity corresponding to each characteristic frequency further includes:
judging whether the aerosol reflectivity corresponding to each characteristic frequency meets the mixed pixel interference judgment condition in the following formula; if so, performing a masking process orρ a (UV) as reflectance of full band aerosolρ a （λ) Otherwise, directly executing the next step
ρ a （UV）＜ρ a （SWIR 1 ) Orρ a （UV）＜ρ a （SWIR 2 ）；
Judging whether the aerosol reflectivity corresponding to each characteristic frequency meets the screening standard in the following formula
ρ a （UV）＞ρ a （SWIR 2 ）+[ρ a （SWIR 1 ）-ρ a （SWIR 2 ）]×
（SWIR 2 -UV）/（SWIR 2 -SWIR 1 ）
Wherein UV is the wavelength corresponding to the characteristic frequency of the ultraviolet band, SWIR 1 For short-wave infrared band characteristic frequency-corresponding wavelength, SWIR 2 The wavelength is corresponding to the characteristic frequency II of the short wave infrared band; SWIR 1 ＜SWIR 2 ；
If so, judging that the type of the aerosol in the atmosphere at the current moment is a weak absorption type, otherwise, judging that the type of the aerosol in the atmosphere at the current moment is a strong absorption type.
Further, the step of selecting a strong absorption model or a weak absorption model matched with the type to fit the aerosol reflectivity of other wave bands except the two wave bands to further obtain the aerosol reflectivity of the full wave band further comprises the following steps:
for the weak absorption type aerosol, fitting the aerosol reflectivity of other wave bands except for ultraviolet, short-wave and infrared wave bands through a weak absorption model to obtain the aerosol reflectivity of other wave bands;
for the strong absorption type aerosol, fitting the aerosol reflectivity of other wave bands except for ultraviolet, short wave and infrared wave bands through a strong absorption model to obtain the aerosol reflectivity of other wave bands;
rayleigh scattering analysis is carried out according to the data of the geometric observation condition to obtain Rayleigh scattering radiance theoretical values in ultraviolet wave bands, short wave bands and infrared wave bands;
and respectively correcting Rayleigh scattering radiance theoretical values in the wave bands through the collected L1B-level spectral data, further obtaining aerosol reflectivity in ultraviolet, short-wave and infrared wave bands, and obtaining the aerosol reflectivity of all the wave bands through superposition.
Further, the weak absorption model is
ρ a （λ）=[a 1 ×λ b1 +c 1 ]×ρ a （SWIR 2 ）
In the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλThe reflectivity of the aerosol of (a) is,ρ a （SWIR 2 ) At a wavelength of SWIR 2 The reflectivity of the aerosol of (a) is,a 1 、b 1 、c 1 taking the aerosol reflectivity corresponding to each characteristic frequency as output and introducing the output into a coefficient determined by a weak absorption model; and also,
the strong absorption model is as follows:
ρ a （λ）=[a 2 ×λ 2 +b 2 ×λ+c 2 ]×ρ a （SWIR 2 ）
in the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλThe reflectivity of the aerosol of (a) is,a 2 、b 2 、c 2 and taking the aerosol reflectivity corresponding to each characteristic frequency as an output to be introduced into a coefficient determined by a strong absorption model.
Further, the step of performing atmospheric correction according to the aerosol reflectance of the full band further includes:
the aerosol reflectivity of each wave band is calculated by the following formulaρ a （λ) Conversion into radiance dataL a （λ）
L a （λ）=ρ a （λ）×[F 0 （λ）×cosθ s ]/π
The atmospheric diffuse transmittance is obtained by the following formula assuming that the contribution of the aerosol in the atmospheric transmittance is neglectedt s 、t v
t s =exp（-（300×K oz +0.5×τ r ）/cosθ s ）
t v =exp（-（300×K oz +0.5×τ r ）/cosθ v ）
In the formula (I), the compound is shown in the specification,t s is the diffuse transmittance of the atmosphere from the sun to the sea surface,t v is the diffuse transmittance of the atmosphere from the sea surface to the satellite sensors,θ s is the zenith angle of the sun,θ v is to observe the zenith angle of the earth,τ r is the equivalent rayleigh optical thickness,K oz is the ozone attenuation coefficient;
apparent radiance from atmospheric domeL TOA （λ) Radiance dataL a （λ) Rayleigh scattering radiance theoryLr（λ) In combination with the above diffuse transmittance of atmospheric airt v The water leaving radiance carrying seawater information is obtained by the following formulaL w （λ）
L w （λ）=（L TOA （λ）- L r （λ）- L a （λ））/ t v
According to the above-mentioned water leaving radiance carrying seawater informationL w （λ) Combined with atmospheric diffuse transmittancet s The final remote sensing reflectivity is obtained by the following formulaR rs （λ）
R rs （λ）=L w （λ）/[F 0 （λ）×t s ×cosθs]
Based on the remote sensing reflectivityR rs （λ) Atmospheric correction is performed.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
1. the inversion error of aerosol scattering is reduced by using ultraviolet and short wave infrared wave bands of the satellite sensor, and finally, the atmospheric correction precision is improved.
2. The performance of the method in each waveband is superior to that of the traditional SWIR algorithm and UV algorithm, the method has good applicability in two types of extremely turbid water bodies, and a new development idea is provided for an atmosphere correction algorithm.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the disclosure, nor is it intended to be used to limit the scope of the disclosure.
Drawings
The foregoing and other objects, features and advantages of the disclosure will be apparent from the following more particular descriptions of exemplary embodiments of the disclosure as illustrated in the accompanying drawings wherein like reference numbers generally represent like parts throughout the exemplary embodiments of the disclosure.
FIG. 1 is a schematic diagram showing the composition of the atmospheric correction method for the second type of water body in example 1;
FIG. 2 shows a flow diagram of a class II water atmosphere correction algorithm based on SGLI sensor data according to example 2;
FIG. 3 shows the discrimination of the presence or absence of an absorptive aerosol in example 2 using the ultraviolet and short wave infrared bands;
FIG. 4 is a comparison of the measured data of the method of example 2 with the SWIR algorithm and the UV algorithm on the platform "Haitian continent".
Reference numerals:
ρ a -aerosol reflectance;
Rrs（λ) -wavelengthλCorresponding remote sensing reflectivityR rs （λ）。
Detailed Description
Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
The term "including" and variations thereof as used herein is intended to be open-ended, i.e., "including but not limited to". Unless specifically stated otherwise, the term "or" means "and/or". The term "based on" means "based at least in part on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first," "second," and the like may refer to different or the same object. Other explicit and implicit definitions are also possible below.
Example 1
One embodiment of the invention discloses an atmospheric correction method for a class II water body, which comprises the following steps as shown in figure 1:
s1, collecting L1B-level spectral data in ultraviolet and short-wave infrared bands and geometric observation condition data in real time;
s2, performing Rayleigh scattering analysis according to the geometric observation condition data to obtain a Rayleigh scattering radiance theoretical value corresponding to an ultraviolet band characteristic frequency and two short wave infrared band characteristic frequencies;
s3, respectively correcting the Rayleigh scattering radiance theoretical values corresponding to the characteristic frequencies through the collected L1B-level spectral data, and further obtaining aerosol reflectivity corresponding to each characteristic frequency;
s4, judging the type of the aerosol in the atmosphere at the current moment according to the aerosol reflectivity corresponding to each characteristic frequency, and fitting the aerosol reflectivity of other wave bands except the two wave bands by using a strong absorption model or a weak absorption model matched with the type to obtain the aerosol reflectivity of the full wave band;
it is worth to explain that, the aerosol reflectivity in the two wave bands can be directly obtained through the Rayleigh scattering analysis method in the steps S2-S3, or obtained through the prior art, and then the aerosol reflectivity in the whole wave band can be obtained after the aerosol reflectivity is superposed with the aerosol reflectivity in other wave bands;
and S5, performing atmospheric correction according to the aerosol reflectivity of the full wave band.
There are many methods for atmospheric correction by aerosol reflectance, and in addition to the method described in example 2, see patents CN201310314382.0, cn202111670094. X.
The atmospheric correction process of ocean water color remote sensing is actually a process of converting signals received by a satellite into water surface water-leaving reflectivity signals carrying seawater information.
The complete atmospheric correction process includes the following:
1. and the atmospheric molecular Rayleigh scattering calculation part can be obtained by combining a general Rayleigh scattering lookup table with information such as a solar zenith angle, an observed zenith angle, a relative azimuth angle, rayleigh optical thicknesses of different wave bands and the like. The above information can be obtained by means of the disclosed model and satellite sensor parameters, and therefore the calculation result of the part is relatively accurate.
2. The aerosol scattering calculation part, which is the part having the greatest influence on the atmospheric correction result, is also the main innovation point of the method. And (3) assuming that the water-leaving radiation of ultraviolet and short-wave infrared bands is 0, so that the aerosol reflectivity data at two ends are approximately calculated, and then the aerosol scattering contribution of the full band is obtained by establishing an interpolation fitting function according to different aerosol types.
3. The white cap reflection calculation part is mainly calculated by wind speed data 10m above the sea surface, and can be ignored when the wind speed data or business batch processing data is lacked because the white cap contribution is small in the whole atmospheric radiation transmission process.
4. And an atmospheric diffuse transmittance calculating part, wherein the atmospheric diffuse transmittance can be divided into atmospheric diffuse transmittance from the sun to the sea surface and atmospheric diffuse transmittance from the sea surface to the satellite sensor, and the two groups of transmittances are respectively composed of atmospheric molecular Rayleigh scattering, aerosol molecular scattering, ozone molecular scattering and the like.
The method of the embodiment mainly aims at the two types of water bodies with extreme turbidity and the two types of water bodies affected by the strongly-absorptive aerosol, and improves the calculation accuracy of the aerosol scattering under the conditions.
Compared with the prior art, the method provided by the embodiment solves the problem that the extrapolation error of the turbid water body in the existing metaatmospheric correction algorithm is increased along with the increase of the spectral distance between the calculation waveband and the reference waveband, and reduces the influence of absorptive aerosol widely existing in the offshore area on the correction result, so that the atmospheric correction precision is improved, and accurate help can be provided for the inversion of other subsequent remote sensing parameters.
Example 2
The improvement is carried out on the basis of the method described in the embodiment 1, and the step S1 further comprises the following steps:
s11, establishing a marine data acquisition site capable of acquiring water color remote sensing data of the second-class water body, laying an SGLI sensor, selecting a clear air or a time period with sufficient illumination, and acquiring high-frequency continuous water body actual measurement spectrum data in each wave band through the SGLI sensor.
The processing of the L1B data of the SGLI sensor needs to read coefficients such as slope and intercept, and the atmospheric top apparent radiance of each waveband is calculatedL TOA （λ) See data, detailed description below. It is noted that since the spatial resolution of 2210 nm band is 1000 m, unlike the visible range, it is necessary to resample the data of this band.
And S12, screening high-frequency continuous water body actual measurement spectrum data in ultraviolet, short-wave and infrared bands from the data according to the longitude and latitude of the marine data acquisition station.
And S13, carrying out data analysis on the screened actually measured spectrum data of the high-frequency continuous water body to obtain L1B-level spectrum data in ultraviolet and short-wave infrared bands and geometric observation condition data.
Specifically, for a near-shore turbid two-class water body area, downloading L1B-level satellite product data of each wave band in an area corresponding to the SGLI sensor, and selecting a clear sky or a time period with sufficient illumination as far as possible.
Preferably, the L1B-level spectral data comprises atmospheric dome apparent radiance in ultraviolet, short wave and infrared bandsL TOA （λ). And, the geometric observation condition data includes a solar zenith angleθ s Observing zenith angleθ v Relative azimuth (absolute value of difference between solar azimuth and satellite azimuth) and atmospheric top solar irradiance of each bandF 0 （λ) And equivalent Rayleigh optical thicknessτ r 。
The geometric observation condition data can be directly obtained from the specification of the L1B-grade satellite product or obtained according to the specification method.
Preferably, the first and second electrodes are formed of a metal,L TOA （λ) The method needs to obtain the solar zenith angle of each pixel by means of a universal atmospheric Rayleigh scattering lookup tableθ s Observing zenith angleθ v The opposite sideAzimuth and atmospheric top solar irradiance of each wave bandF 0 （λ) And equivalent Rayleigh optical thicknessτ r Etc., the rayleigh scattering look-up table is a prior art that can be downloaded and used by those skilled in the art.
A general rayleigh scatter look-up table is presented here for reference by the skilled person: xianjiang He, yan Bai, qiankun Zhu, fan Gong, A vector radial Transfer model of matched acoustic-atmospheric system using matrix-operator method for rough sea-surface, journal of Quantitative spectral and radial Transfer, 2010, 111 (10): 1426 to 1448.
Preferably, step S2 further comprises:
s21, randomly selecting one characteristic frequency in an ultraviolet band, and randomly selecting two characteristic frequencies in a short wave infrared band;
s22, according to the zenith angle of the sunθ s Observing zenith angleθ v Relative azimuth angle and atmospheric top solar irradiance of each wave bandF 0 （λ) And equivalent Rayleigh optical thicknessτ r And determining the Rayleigh scattering radiance theoretical value corresponding to each characteristic frequency by combining a Rayleigh scattering lookup table.
The rayleigh optical thickness parameters of the SGLI sensor in each band are shown in table 1.
TABLE 1 SGLI Sensors for each bandF 0 （λ）、τ r And spatial resolution value
| Wavelength (a)λ）/nm | F 0 （λ） | τ r | Spatial resolution/m |
| 380 | 109.532673 | 0.447201 | 250 |
| 412 | 170.921545 | 0.31858 | 250 |
| 443 | 189.602499 | 0.235905 | 250 |
| 490 | 193.927723 | 0.155961 | 250 |
| 530 | 185.010559 | 0.113251 | 250 |
| 565 | 179.911442 | 0.087306 | 250 |
| 673.5 | 149.854246 | 0.042776 | 250 |
| 763 | 124.576201 | 0.025797 | 250 |
| 868.5 | 95.624436 | 0.015301 | 250 |
| 1050 | 65.346366 | 0.007128 | 1000 |
| 1380 | 36.376378 | 0.002378 | 1000 |
| 1630 | 23.954936 | 0.001253 | 250 |
| 2210 | 8.402895 | 0.000361 | 1000 |
Preferably, in step S21, the wavelength corresponding to the characteristic frequency of the ultraviolet band is 380 nm, and the wavelengths corresponding to the characteristic frequency of the short-wave infrared band are 1630 nm and 2210 nm, respectively. A large number of experiments prove that the atmospheric correction precision can be effectively improved by the optimal conditions.
Preferably, step S3 further comprises:
s31, respectively correcting the Rayleigh scattering radiance theoretical value corresponding to each characteristic frequency through the following formula to obtain a Rayleigh scattering radiance correction value corresponding to each characteristic frequencyL rc （λ）
L rc （λ）=L TOA （λ）-L r （λ）
In the formula (I), the compound is shown in the specification,L TOA （λ) For the atmospheric top surface radiance corresponding to the characteristic frequency,λfor the wavelength corresponding to the characteristic frequency,L r （λ) The Rayleigh scattering radiance theoretical value corresponding to the characteristic frequency;
s32, according to the Rayleigh scattering radiance correction value corresponding to each characteristic frequencyL rc （λ) Assuming that the water-leaving radiation values of ultraviolet, short wave and infrared bands are 0, the aerosol reflectivity corresponding to each characteristic frequency is obtained by the following formulaρ a （λ）
ρ a （λ）=πL rc （λ）/[F 0 （λ）×cosθs]
Wherein, pi is the circumference ratio,F 0 （λ) Is a wavelengthλThe characteristic frequency of (a) corresponds to the atmospheric top solar irradiance,θand s is the zenith angle of the sun.
Preferably, step S4 further comprises:
s41, judging whether the aerosol reflectivity corresponding to each characteristic frequency meets the mixed pixel interference judgment condition in the following formula; if so, performing a masking process orρ a (UV) as reflectance of full band aerosolρ a （λ) Otherwise, directly executing the next step
ρ a （UV）＜ρ a （SWIR 1 ) Orρ a （UV）＜ρ a （SWIR 2 ）；
Preferably, the first and second electrodes are formed of a metal,ρ a （380）＜ρ a (1630) Orρ a （380）＜ρ a （2210）；
S42, judging whether the aerosol reflectivity corresponding to each characteristic frequency meets the screening standard in the following formula
ρ a （UV）＞ρ a （SWIR 2 ）+[ρ a （SWIR 1 ）-ρ a （SWIR 2 ）]×
（SWIR 2 -UV）/（SWIR 2 -SWIR 1 ）
Wherein UV is the wavelength corresponding to the characteristic frequency of the ultraviolet band, SWIR 1 For short-wave infrared band characteristic frequency-corresponding wavelength, SWIR 2 The wavelength is corresponding to the characteristic frequency II of the short wave infrared band; SWIR 1 ＜SWIR 2 。
S43, if yes, judging the aerosol type of the atmosphere at the current moment to be a weak absorption type, and executing a step S44, otherwise, judging the aerosol type of the atmosphere at the current moment to be a strong absorption type, and executing a step S45.
S44, for the weak absorption type aerosol, fitting the aerosol reflectivity of other wave bands except the ultraviolet wave band, the short wave band and the infrared wave band through a weak absorption model to obtain the aerosol reflectivity of other wave bands;
preferably, the weak absorption model is
ρ a （λ）=[a 1 ×λ b1 +c 1 ]×ρ a （SWIR 2 ）
In the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλThe reflectivity of the aerosol of (a) is,ρ a （SWIR 2 ) At a wavelength of SWIR 2 The reflectivity of the aerosol of (a) is,a 1 、b 1 、c 1 for gas dissolving according to each characteristic frequencyThe glue reflectance is taken as an output into the coefficients determined by the weak absorption model.
S45, for the strong absorption type aerosol, fitting the aerosol reflectivity of other wave bands except for the ultraviolet wave band, the short wave band and the infrared wave band through a strong absorption model to obtain the aerosol reflectivity of other wave bands;
preferably, the strong absorption model is:
ρ a （λ）=[a 2 ×λ 2 +b 2 ×λ+c 2 ]×ρ a （SWIR 2 ）
in the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλThe reflectivity of the aerosol of (a) is,a 2 、b 2 、c 2 and taking the aerosol reflectivity corresponding to each characteristic frequency as an output to be introduced into a coefficient determined by a strong absorption model.
S46, rayleigh scattering analysis is carried out according to the data of the geometric observation condition to obtain Rayleigh scattering radiance theoretical values in ultraviolet wave bands, short wave bands and infrared wave bands;
and S47, respectively correcting the Rayleigh scattering radiance theoretical values in the wave bands through the collected L1B-level spectral data, and further obtaining aerosol reflectivity in ultraviolet, short wave and infrared wave bands.
S48, overlapping aerosol reflectivity machines in the ultraviolet band, the short wave infrared band and other bands to obtain aerosol reflectivity of all bandsρ a （λ）。
Preferably, step S5 further comprises:
s51, calculating the aerosol reflectivity of each wave band by the following formulaρ a （λ) Conversion into radiance dataL a （λ）
L a （λ）=ρ a （λ）×[F 0 （λ）×cosθ s ]/π
S52, assuming that the contribution of the aerosol in the atmospheric transmittance is neglected, the method is disclosed by the followingObtaining atmospheric diffuse transmittancet s 、t v
t s =exp（-（300×K oz +0.5×τ r ）/cosθ s ）
t v =exp（-（300×K oz +0.5×τ r ）/cosθ v ）
In the formula (I), the compound is shown in the specification,t s is the diffuse transmittance of the atmosphere from the sun to the sea surface,t v is the diffuse transmittance of the atmosphere from the sea surface to the satellite sensors,θ s is the zenith angle of the sun,θ v is to observe the zenith angle of the earth,τ r in order to have an equivalent rayleigh optical thickness,K oz the ozone attenuation coefficient is shown in table 2;
s53, according to the apparent radiance of the atmosphere domeL TOA （λ) Radiance dataL a （λ) Rayleigh scattering radiance theoryLr（λ) In combination with the above atmospheric diffuse transmittancet v The water leaving radiance carrying seawater information is obtained by the following formulaL w （λ）
L w （λ）=（L TOA （λ）- L r （λ）- L a （λ））/ t v
S54, according to the above-mentioned water leaving radiance carrying seawater informationL w （λ) Combined with atmospheric diffuse transmittancet s The final remote sensing reflectivity is obtained by the following formulaR rs （λ）
R rs （λ）=L w （λ）/[F 0 （λ）×t s ×cosθs]
S55, according to the remote sensing reflectivityR rs （λ) Atmospheric correction is performed. Illustratively, by cloud reflectivity, radiation characteristics and atmospheric radiationAnd (4) calculating the reflectivity of each pixel on the image by deducing the relation between the contribution and the remote sensing reflectivity to finish the atmospheric correction of the water body, see patent No. CN202110631212.X.
TABLE 2 SGLI Sensors for each bandK oz Value of coefficient
| Wavelength/nm | K oz |
| 380 | 7.97E-08 |
| 412 | 4.33E-07 |
| 443 | 3.74E-06 |
| 490 | 2.25E-05 |
| 530 | 6.79E-05 |
| 565 | 1.17E-04 |
| 673.5 | 4.42E-05 |
| 763 | 7.59E-06 |
| 868.5 | 2.10E-08 |
| 1050 | 0 |
| 1380 | 0 |
| 1630 | 0 |
| 2210 | 0 |
The principle of the whole method can be seen in fig. 2, but is not limited to fig. 2.
In turbid water, the lower water radiation signals in ultraviolet and short-wave infrared bands can be approximately regarded as 0, so that the aerosol reflectivity of the bands can be obtained by subtracting Rayleigh scattering contribution from the atmospheric top received signal. In addition, the absorptive aerosol widely existing in offshore atmosphere in China has strong absorptivity in the short-wave range of visible light, so that the reflectivity of the aerosol in the range is reduced. Based on the above, a screening criterion was developed, and the effect is shown in fig. 3.
Hangzhou bay is located between Hangzhou, shanghai and Ningbo, the northwest of the world is connected with Qiantangjiang, the Bay mouth of the east of the world is communicated with the east of the sea, and the Nanguy mouth of the Bay mouth is scattered on Zhoushan islands. Because the plane of the mouth of the Qiantangjiang river is strongly contracted, the bottom of the bay is rapidly lifted, the tidal range is rapidly increased, under the combined influence of the Qiantangjiang river runoff, the water flow of the Yangtze river mouth and the east sea tidal wave, the water in the bay has the characteristics of high dynamic, super-strong torrent, high sand content and the like, and the average concentration of suspended matters in the water is between 705 mg/L and 1950 mg/L (Wangchong and the like, 2008), so the Hangzhou bay area belongs to a typical second type of water with high sand content.
A sea-sky-continent offshore platform is built in the middle of a Hangzhou bay bridge, the platform is connected with a main line of the bridge through a ramp bridge, the platform is located inside the Hangzhou bay, the platform is a built platform for researching an ideal spectrum system for two types of high-turbidity and high-dynamic water bodies, and an offshore actual measurement data acquisition station is built on the platform and used for acquiring high-frequency continuous water body actual measurement spectrum data (Dai et al, 2012).
"Haitian continent" site coordinates of 30.46278N, 121.12528E, spectral sampling interval of 15min, sampling time range from local morning time 7 to local afternoon time 5:00, in the data acquisition system, the sensors include 2 irradiance sensors and 1 irradiance sensor. The spectral coverage is 320-950 nm. The correction effect of the method is verified by utilizing measured data of a 'Haitianyhou' station and combining L1B-level data of an SGLI sensor carried by a GCOM-C satellite, as shown in figure 4, the Root Mean Square Error (RMSE) of each waveband is calculated by comparing the correction results of a UV algorithm and a SWIR algorithm, and the RMSE is shown in a table 3.
Table 3 remote sensing reflectivity by three algorithmsR rs （λ) Root mean square error comparison
| Wavelength/nm | UV-SWIR algorithm | UV | SWIR algorithm | |
| 412 | 6.747E-04 | 7.872E-03 | 6.867E-03 | |
| 443 | 7.746E-04 | 7.040E-03 | 5.996E-03 | |
| 490 | 9.239E-04 | 6.311E-03 | 5.172E-03 | |
| 530 | 1.508E-03 | 5.594E-03 | 4.337E-03 | |
| 565 | 8.079E-04 | 6.313E-03 | 4.932E-03 | |
| 673 | 1.860E-03 | 4.589E-03 | 3.017E-03 | |
| 763 | 9.710E-04 | 7.139E-03 | 5.394E-03 | |
| 868 | 1.577E-03 | 4.482E-03 | 2.506E-03 |
It can be seen that the performance of the method of the present embodiment in each band is better than that of the two conventional algorithms.
Compared with embodiment 1, the method provided by the embodiment has the following beneficial effects:
1. the inversion error of aerosol scattering is reduced by using the ultraviolet and short wave infrared wave bands of the satellite sensor, and finally, the atmospheric correction precision is improved.
2. The performance of the method in each waveband is superior to that of the traditional SWIR algorithm and UV algorithm, the method has good applicability in two types of extremely turbid water bodies, and a new development idea is provided for an atmosphere correction algorithm.
Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles of the embodiments, the practical application, or improvements made to the prior art, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Claims (8)
1. An atmospheric correction method for a class II water body, characterized by comprising the following steps:
collecting L1B-level spectral data in ultraviolet, short-wave and infrared bands and geometric observation condition data in real time;
rayleigh scattering analysis is carried out according to the geometric observation condition data to obtain a Rayleigh scattering radiance theoretical value corresponding to an ultraviolet waveband characteristic frequency and two short wave infrared waveband characteristic frequencies;
respectively correcting the Rayleigh scattering radiance theoretical values corresponding to the characteristic frequencies through the collected L1B-level spectral data, and further obtaining aerosol reflectivity corresponding to each characteristic frequency;
judging the aerosol type of the atmosphere at the current moment according to the aerosol reflectivity corresponding to each characteristic frequency, and fitting the aerosol reflectivity of other wave bands except the two wave bands by selecting a strong absorption model or a weak absorption model matched with the type to further obtain the aerosol reflectivity of the full wave band;
carrying out atmospheric correction according to the aerosol reflectivity of the full wave band; and the number of the first and second electrodes,
the step of determining the type of the aerosol in the atmosphere at the current moment according to the aerosol reflectivity corresponding to each characteristic frequency further includes:
judging whether the aerosol reflectivity corresponding to each characteristic frequency meets the mixed pixel interference judgment condition in the following formula,
ρ a （UV）＜ρ a （SWIR 1 ) Orρ a （UV）＜ρ a （SWIR 2 ），
If so, willρ a (UV) Aerosol reflectance as full bandρ a （λ) Otherwise, directly executing the next step;
judging whether the aerosol reflectivity corresponding to each characteristic frequency meets the screening standard in the following formula,
ρ a （UV）＞ρ a （SWIR 2 ）+[ρ a （SWIR 1 ）-ρ a （SWIR 2 ）]×（SWIR 2 -UV）/（SWIR 2 -SWIR 1 ），
in the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλUV is the wavelength corresponding to the characteristic frequency of the ultraviolet band, SWIR 1 For short-wave infrared band characteristic frequency-corresponding wavelength, SWIR 2 The wavelength is corresponding to the second characteristic frequency of the short wave infrared band; SWIR 1 ＜SWIR 2 ；
If so, judging the aerosol type of the atmosphere at the current moment to be a weak absorption type, otherwise, judging the aerosol type of the atmosphere at the current moment to be a strong absorption type;
the weak absorption model is as follows:
ρ a （λ）=[a 1 ×λ b1 +c 1 ]×ρ a （SWIR 2 ），
in the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλThe reflectivity of the aerosol of (a) is,ρ a （SWIR 2 ) At a wavelength of SWIR 2 The reflectivity of the aerosol of (a) is,a 1 、b 1 、c 1 taking the aerosol reflectivity corresponding to each characteristic frequency as output to bring into a coefficient determined by a weak absorption model; and the number of the first and second electrodes,
the strong absorption model is as follows:
ρ a （λ）=[a 2 ×λ 2 +b 2 ×λ+c 2 ]×ρ a （SWIR 2 ），
in the formula (I), the compound is shown in the specification,ρ a （λ) Is a wavelengthλThe reflectivity of the aerosol of (a) is,a 2 、b 2 、c 2 and taking the aerosol reflectivity corresponding to each characteristic frequency as an output to be introduced into a coefficient determined by a strong absorption model.
2. The atmospheric correction method for class II bodies of water of claim 1, wherein the step of collecting in real time L1B-level spectral data in both ultraviolet, short wave infrared and geometrical observation condition data further comprises:
establishing a marine data acquisition site capable of acquiring water color remote sensing data of a second-class water body, laying an SGLI sensor, selecting a clear sky or a time period with sufficient illumination, and acquiring high-frequency continuous water body actual measurement spectrum data in each wave band through the SGLI sensor;
screening out high-frequency continuous water body actual measurement spectrum data in ultraviolet, short-wave and infrared bands from the data according to the longitude and latitude of the marine data acquisition station;
and carrying out data analysis on the screened actually measured spectrum data of the high-frequency continuous water body to obtain L1B-level spectrum data in ultraviolet and short-wave infrared bands and geometric observation condition data.
3. The atmospheric correction method for bodies of water of claim 2, wherein the L1B-level spectral data comprises atmospheric cap apparent radiance in the ultraviolet, short wave infrared bandsL TOA （λ) (ii) a And also,
the geometric observation condition data comprises solar zenith anglesθ s And observing zenith angleθ v Relative azimuth angle, and atmospheric top solar irradiance of each wavebandF 0 （λ) And equivalent Rayleigh optical thicknessτ r 。
4. The atmospheric correction method for class II bodies of water according to any one of claims 1 to 3, wherein the step of performing Rayleigh scattering analysis based on the geometric observation condition data to obtain a Rayleigh scattering radiance theoretical value corresponding to an ultraviolet band characteristic frequency and two short-wave infrared band characteristic frequencies further comprises:
randomly selecting one characteristic frequency in an ultraviolet band and randomly selecting two characteristic frequencies in a short-wave infrared band;
according to the zenith angle of the sunθ s And observing zenith angleθ v Relative azimuth angle and atmospheric top solar irradiance of each wave bandF 0 （λ) And equivalent Rayleigh optical thicknessτ r Determining the Rayleigh scattering radiance theoretical value corresponding to each characteristic frequency by combining a Rayleigh scattering lookup tableL r （λ）。
5. The atmospheric correction method for class II water bodies of claim 4, characterized in that the wavelength corresponding to the characteristic frequency of the ultraviolet band is 380 nm, and the wavelength corresponding to the characteristic frequency of the short wave infrared band is 1630 nm and 2210 nm respectively.
6. The atmospheric correction method for water bodies of claim 5, wherein the step of obtaining the aerosol reflectivity corresponding to each characteristic frequency by respectively correcting the theoretical rayleigh scattering radiance values corresponding to the characteristic frequencies through the acquired L1B-level spectral data further comprises:
respectively correcting the Rayleigh scattering radiance theoretical value corresponding to each characteristic frequency through the following formula to obtain the Rayleigh scattering radiance corrected value corresponding to each characteristic frequencyL rc （λ），
L rc （λ）=L TOA （λ）-L r （λ），
In the formula (I), the compound is shown in the specification,L TOA （λ) The atmospheric top surface radiance corresponding to the characteristic frequency,λfor the wavelength corresponding to the characteristic frequency,L r （λ) The Rayleigh scattering radiance theoretical value corresponding to the characteristic frequency;
according to the Rayleigh scattering radiance corrected value corresponding to each characteristic frequencyL rc （λ) The aerosol reflectivity corresponding to each characteristic frequency is obtained by the following formulaρ a （λ），
ρ a （λ）=πL rc （λ）/[F 0 （λ）×cosθs]，
Wherein, pi is the circumference ratio,F 0 （λ) Is a wavelengthλThe characteristic frequency of (a) corresponds to the atmospheric top solar irradiance,θand s is the zenith angle of the sun.
7. The atmospheric correction method for class II water bodies according to claim 6, wherein the step of fitting the aerosol reflectivities of other wave bands except the two wave bands by selecting a strong absorption model or a weak absorption model matched with the types to obtain the aerosol reflectivity of the full wave band further comprises:
for the weak absorption type aerosol, fitting the aerosol reflectivity of other wave bands except the ultraviolet band and the short wave infrared band through a weak absorption model to obtain the aerosol reflectivity of other wave bands;
for the strong absorption type aerosol, fitting the aerosol reflectivity of other wave bands except the ultraviolet band and the short wave infrared band through a strong absorption model to obtain the aerosol reflectivity of other wave bands;
rayleigh scattering analysis is carried out according to the data of the geometric observation condition to obtain Rayleigh scattering radiance theoretical values in ultraviolet, short wave and infrared bands;
and respectively correcting Rayleigh scattering radiance theoretical values in the wave bands through the collected L1B-level spectral data, further obtaining aerosol reflectivity in ultraviolet, short-wave and infrared wave bands, and obtaining the aerosol reflectivity of all the wave bands through superposition.
8. The atmospheric correction method for water bodies of class II according to claim 7, wherein the step of atmospheric correction according to the full-band aerosol reflectance further comprises:
the aerosol reflectivity of each wave band is calculated by the following formulaρ a （λ) Conversion into radiance dataL a （λ），
L a （λ）=ρ a （λ）×[F 0 （λ）×cosθ s ]/π，
The atmospheric diffuse transmittance is obtained by the following formula assuming that the contribution of the aerosol in the atmospheric transmittance is neglectedt s 、t v ，
t s =exp（-（300×K oz +0.5×τ r ）/cosθ s ），
t v =exp（-（300×K oz +0.5×τ r ）/cosθ v ），
In the formula (I), the compound is shown in the specification,t s is the diffuse transmittance of the atmosphere from the sun to the sea surface,t v is the atmosphere from the sea surface to the satellite sensorThe light-diffusing transmittance of the light-emitting element,θ s is the zenith angle of the sun,θ v is to observe the zenith angle of the earth,τ r in order to have an equivalent rayleigh optical thickness,K oz the ozone attenuation coefficient;
apparent radiance according to atmosphere domeL TOA （λ) Radiance dataL a （λ) Rayleigh scattering radiance theoretical valueLr（λ) In combination with the above atmospheric diffuse transmittancet v The off-water radiance carrying seawater information is obtained by the following formulaL w （λ），
L w （λ）=（L TOA （λ）- L r （λ）- L a （λ））/ t v ，
According to the above-mentioned water leaving radiance carrying seawater informationL w （λ) Combined with atmospheric diffuse transmittancet s The final remote sensing reflectivity is obtained by the following formulaR rs （λ），
R rs （λ）=L w （λ）/[F 0 （λ）×t s ×cosθ s ]，
According to the remote sensing reflectivityR rs （λ) Atmospheric correction is performed.
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