CN100362318C - Atmosphere correction method of airosol optical thickness of aeronautical high-spectrum remote-sensing inversion boundary layer - Google Patents
Atmosphere correction method of airosol optical thickness of aeronautical high-spectrum remote-sensing inversion boundary layer Download PDFInfo
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Abstract
The present invention relates to an atmosphere correction method of the aerosol optical thickness of an aeronautical high-spectrum remote-sensing inversion boundary layer, particularly to a high-spectrum image obtained aiming at a home-made aeronautical high-spectrum remote sensor, which can realize the inversion of the aerosol optical thickness of an urban atmospheric boundary layer and belongs to the field of atmospheric environment remote sensing application. The method mainly solves the technical problems of how to extract the information of the aerosol optical thickness from an atmospheric transmission spectrum, how to carry out atmospheric correction, etc. The method extracts the information of the aerosol optical thickness of the boundary layer from the atmospheric transmission spectrum via an atmospheric radiation transmission principle, and the reinterpolation of an atmospheric mode and an aerosol mode in the boundary layer is used again for obtaining an expression reflectivity in order to calculate the aerosol optical thickness of the inversion boundary layer. The present invention has the advantages that aiming at an OMIS imaging spectrometer, the present invention combines the atmospheric radiation transmission principle of the boundary layer to extract the information of the aerosol optical thickness from the atmospheric transmission optical spectrum and carry out atmospheric correction.
Description
Technical Field
The invention relates to an atmospheric correction method for inverting boundary layer aerosol optical thickness by aviation hyperspectral remote sensing, which is applied to hyperspectral images obtained by aviation hyperspectral remote sensors developed by an aviation remote sensing research laboratory of Shanghai technical and physical research institute of Chinese academy of sciences, realizes inversion of the optical thickness of the aerosol of an urban atmospheric boundary layer by an atmospheric correction method based on a radiation transmission mechanism, and belongs to the field of atmospheric environment remote sensing application.
Background
The atmospheric aerosol refers to solid or liquid particles with the radius less than tens of microns suspended in the atmosphere, plays an important role in the balance of radiation balance of the earth atmosphere and the global climate, and is an important research object in atmospheric physics. On the one hand, aerosols directly influence the radiation absorption balance of the ground-gas system by scattering and absorbing solar radiation as well as ground radiation; on the other hand, the aerosol also participates in a plurality of physical processes of the atmosphere, such as a micro-physical mechanism formed by cloud and ozone balance; interfering in an absorptive and scattering manner with the signals received by the remote sensing sensor. Therefore, the aerosol is accurately measured and analyzed, and the method has important significance for knowing the climate change, removing the atmospheric influence in remote sensing data and improving the remote sensing quantitative application level.
The optical thickness of the aerosol is one of the most important parameters of the aerosol, is an important physical quantity for representing the turbidity of the atmosphere, and is also an important factor for determining the climate effect of the aerosol and an important parameter of an atmosphere model. The optical thickness of the aerosol can be detected by ground-based detection methods, such as solar radiometers, particle counters, radiation gauges, and the like. The ground-based detection method can accurately provide local aerosol information, but cannot obtain aerosol space-time distribution in a large range. The remote sensing inversion of the optical thickness of the aerosol can overcome the inherent deficiency of the foundation detection method, and provides possibility for people to know the aerosol change in a large range in all weather and in real time.
In recent years, remote sensing inversion of aerosol optical thickness has become a means for rapidly and effectively obtaining atmospheric aerosol information, particularly good research results have been obtained in satellite remote sensing, and a mature inversion algorithm has been provided [5-15] However, the inversion of the aerosol is mainly realized by establishing a lookup table through 6S by adopting a dark pixel method (or a dark target method), and most of the algorithms are based on satellite data. The dark pixel method utilizes the characteristic that most of land surfaces have low reflectivity in red (0.6 to 0.68 mu m) and blue (0.40 to 0.48 mu m) wave bands, judges a forest as a dark pixel according to the vegetation index (NDVI) or the reflectivity of a near infrared channel (2.1 mu m), and is used for inverting the optical thickness of the aerosol [6] . Maojietai (a Chinese character) [13] When the dark pixel method is used for inverting the optical thickness of the polluted aerosol in Beijing and hong Kong cities in a test, the method for determining the earth surface reflectivity of the vegetation dark pixels through the near infrared channel apparent reflectivity in the Beijing area in a fixed proportion coefficient relation has a large error. This shows that there is a certain difficulty in inverting the optical thickness of the aerosol in Beijing area by using the dark pixel method. The comparison method is a satellite remote sensing method for early research of land pollution aerosol [16] 。
In principle NASA in the united states can already give the optical thickness of aerosol in most regions of the world with MODIS images, but its spatial resolution is only 10km and the satellite height is more than 700 km, resulting in the optical thickness of aerosol in the whole convective layer, while aerosol is mainly concentrated in such a vertical range from the ground to the urban boundary layer, so that inverting the optical thickness of aerosol in the urban boundary layer from airborne hyperspectral image becomes a concern.
The practical modular imaging spectrometer (OMIS-I) is developed by an aviation remote sensing research laboratory of Shanghai technical and physical research institute of Chinese academy of sciences, 128 continuous spectral channels are totally formed from visible light, near infrared to thermal infrared (the wavelength range is 0.46-12.5 mu m), the spectral resolution reaches the level of 10nm, and detailed technical indexes are shown in a table-1. The average flight height of the OMIS is 2km, the ground instantaneous field of view is 3mrad, the total field of view is larger than 70 degrees, the ground resolution of the central pixel is about 6m × 6m, and the spatial resolution of the image edge points is low.
Disclosure of Invention
In order to overcome the defects, the invention mainly aims to provide a practical modular imaging spectrometer (OMIS-I) which is developed aiming at an aviation remote sensing research room of Shanghai technical and physical research institute of Chinese academy of sciences, and an atmospheric correction method for inverting the optical thickness of the aerosol at the boundary layer by aviation hyperspectral remote sensing by combining the atmospheric radiation transmission principle and extracting the optical thickness information of the aerosol at the boundary layer from the atmospheric transmission spectrum.
The technical problem to be solved by the invention is as follows: the problem of radiometric calibration of a hyperspectral remote sensing image is solved; the method aims to solve the problems that how to select a dark target on an OMIS image of a practical modular imaging spectrometer of an aviation high-spectrum remote sensor, how to obtain the apparent reflectivity, inversion of the calculation of the optical thickness of the aerosol of a boundary layer and the like; the method aims to solve the relevant technical problems of how to extract boundary layer aerosol optical thickness information from the atmospheric transmission spectrum and carry out atmospheric correction and the like.
The technical scheme adopted by the invention for solving the technical problems is as follows: the atmospheric correction method for inverting the optical thickness of the aerosol at the boundary layer by aviation hyperspectral remote sensing extracts the optical thickness information of the aerosol at the boundary layer from the atmospheric transmission spectrum through the atmospheric radiation transmission principle, and the calculation of inverting the optical thickness of the aerosol at the boundary layer is realized by carrying out interpolation again on the atmospheric mode and the aerosol mode in the boundary layer to obtain the apparent reflectivity, wherein the specific calculation steps are as follows:
step 1: radiometric calibration of hyperspectral remote sensing images
a) Reading hyperspectral remote sensing images
Reading an airborne aviation hyperspectral remote sensing image in a standard format;
b) Converted into radiation values
The output signal of the hyperspectral remote sensing image module is transmitted to the input end of a radiation value module, and according to two coefficients of a slope and an intercept corresponding to each wave band in a radiometric calibration file, the numerical serial number DN value of the hyperspectral remote sensing image is converted into a radiation value according to the formula radiation value = DN value x slope + intercept;
step 2, calculating the apparent reflectivity and selecting a dark target
a) And calculating
Calculating the radiation value output in the step 1 as the apparent reflectivity obtained on the sensor according to the following formula:
R＝π*L/(μ*f)
in the formula: r is the apparent reflectance;
l is the radiation value;
mu is the cosine of the zenith angle of the sun;
f is the solar radiation flux density of the upper atmosphere;
b) Selecting dark targets
The output signal of the radiation value module is transmitted to a dark target apparent reflectivity module, the apparent reflectivity on a near infrared 2.1um channel is selected, and the image element in the range of 0.036-0.044 is taken as a dark target;
step 3, atmospheric correction
Transmitting the output signal of the dark target apparent reflectivity module to an atmospheric correction module, and performing atmospheric correction according to the dark target apparent reflectivity obtained in the step (2); the specific working steps are as follows:
a) Defining geometrical parameters
The altitude angle, the zenith angle, the solar altitude angle, the zenith angle and the observation date of the airplane relative to the pixel are input into the geometric parameter module, and the output signal of the geometric parameter module is transmitted to the atmosphere correction module;
b) Define atmospheric mode
Defining an atmospheric mode adopted by the mode in an atmospheric mode module, and transmitting an output signal of the atmospheric mode module to an atmospheric correction module;
c) Defining an aerosol type mode
Defining extinction and meteorological sight distance types in boundary layer aerosol modes used by the modes in the aerosol types, and if visibility is defined at the same time, replacing the meteorological sight distance defined by default values in the aerosol types, and transmitting output signals of the aerosol type modules to an atmosphere correction module;
d) Defining an aerosol concentration profile
Defining an aerosol concentration mode used by the mode in the aerosol concentration, inputting 550nm aerosol optical thickness or horizontal visibility, and transmitting an output signal of the aerosol concentration module to an atmospheric correction module;
e) Inputting the elevation of the ground object
Transmitting the output signal of the input ground feature elevation module to an atmosphere correction module;
f) Inputting the flying height of the airplane
Transmitting an output signal input into the aircraft flight altitude module to an atmosphere correction module;
step 4, extracting atmospheric correction parameters
a) Signal transmission
Output signals of the atmospheric correction module are respectively transmitted to the aerosol scattering phase function module and the aerosol single scattering reflectivity module;
b) Performing atmospheric correction
According to the input parameters in the step 3, atmospheric correction is carried out on the dark target on the selected aerial hyperspectral remote sensing image;
c) Correction parameter
Extracting correction parameters of an aerosol scattering phase function and an aerosol single scattering reflectivity from the output result;
step 5, calculating the optical thickness of the aerosol of the boundary layer
a) Signal transmission
Output signals of the aerosol scattering phase function module and the aerosol single scattering reflectivity module are transmitted to the aerosol optical thickness module;
b) And calculating
Calculating the apparent reflectivity of the boundary layer atmosphere according to the following formula:
c) Calculating the optical thickness of the boundary layer aerosol
Calculating the optical thickness of the aerosol at the boundary layer according to the aerosol scattering phase function and the aerosol single scattering reflectivity obtained in the step 4;
step 6, judgment
a) Signal transmission
The output signal of the aerosol optical thickness module is transmitted to the comparison module;
b) Calculating the ground distance
Synchronous ground visibility range data according to formula
V＝3.91·H·1/τ
In the formula: v is the ground visibility range;
h is aerosol elevation in different seasons;
τ is the aerosol optical thickness;
c) And compared with each other
Comparing the calculated aerosol optical thickness value with the aerosol optical thickness value obtained in the step 5;
when the difference value of the two is less than 0.1, the output signal of the comparison module is transmitted to an output module, and the output is the optical thickness of the aerosol;
otherwise, feeding back to the atmosphere correction module, returning to the step 3 to perform atmosphere correction again, inputting various parameters required by the atmosphere correction again, and repeating the cycle.
The atmospheric mode of the atmospheric correction method for inverting the optical thickness of the aerosol at the boundary layer by aviation hyperspectral remote sensing comprises the following steps: tropical atmosphere, middle latitude summer, middle latitude winter, subpolar zone summer, subpolar zone winter, and 1976 U.S. standard atmosphere.
The aerosol type of the atmospheric correction method for inverting the optical thickness of the aerosol at the boundary layer by aviation hyperspectral remote sensing comprises the following steps: or is aerosol-free; or the country extinction coefficient, and the default meteorological sight distance =23km; or city extinction coefficient, default meteorological stadia =5km; or as convection layer extinction coefficient, default meteorological stadium =50km.
The invention has the beneficial effects that: the invention provides a detailed and complete method for inverting the optical thickness of aerosol aiming at airborne hyperspectral imaging data, particularly an OMIS imaging spectrometer, and the invention has the detailed and complete method for inverting the optical thickness of aerosol; and aiming at the OMIS imaging spectrometer, the optical thickness information of the aerosol is extracted from the atmospheric transmission spectrum and atmospheric correction is carried out by combining the atmospheric radiation transmission principle of the boundary layer.
Drawings
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is a schematic diagram of a process for calculating the optical thickness of an aerosol in an inversion boundary layer according to the present invention;
FIG. 2 is a schematic illustration of the position of a dark surface in an embodiment of the present invention;
FIG. 3 is a schematic representation of the apparent refractive index profile of a dark surface at points 13 and 14, respectively, in an example of the invention;
FIG. 4 is a graph showing calculated atmospheric transmittance as a function of wavelength for an embodiment of the present invention;
FIG. 5 is a schematic diagram of an aerosol optical thickness inverted from an airborne OMIS hyperspectral remote sensing image according to an atmospheric correction method of the embodiment of the invention;
FIG. 6 is a schematic diagram of the comparison of the calculated atmospheric transmittance based on LOWTRAN and the calculated atmospheric transmittance based on OMIS in accordance with an embodiment of the present invention;
the reference numbers in the figures indicate:
10-hyperspectral remote sensing image;
20-radiation value;
30-dark target apparent reflectance;
40-atmospheric correction;
41-geometric parameters;
42-atmospheric mode;
43-aerosol type;
44-aerosol concentration;
45-ground object elevation;
46-aircraft flying height;
51-aerosol scattering phase function;
52-aerosol single scattering reflectance;
60-aerosol optical thickness;
70-comparison;
80-output;
Detailed Description
Referring to the attached drawing 1, the invention relates to an atmospheric correction method for inverting boundary layer aerosol optical thickness by aviation hyperspectral remote sensing, which extracts boundary layer aerosol optical thickness information from atmospheric transmission spectrum by the atmospheric radiation transmission principle, and performs interpolation again on an atmospheric mode and an aerosol mode in a boundary layer to obtain apparent reflectivity so as to realize calculation of the inverse boundary layer aerosol optical thickness, wherein the specific calculation steps are as follows:
step 1: radiometric calibration of hyperspectral remote sensing images
a) Reading hyperspectral remote sensing image (10)
Reading an airborne aviation hyperspectral remote sensing image (10) in a standard format;
b) Converted to radiation value (20)
The output signal of the hyperspectral remote sensing image (10) module is transmitted to the input end of a radiation value (20) module, and the numerical serial number DN value of the hyperspectral remote sensing image (10) is converted into a radiation value (20) according to two coefficients of slope and intercept corresponding to each wave band in a radiometric calibration file and a formula radiation value = DN value x slope + intercept;
step 2, calculating the apparent reflectivity and selecting the dark target
a) And calculating
Calculating the radiation value (20) output in the step 1 as the apparent reflectivity obtained on the sensor according to the following formula:
R＝π*L/(μ*f)
in the formula: r is the apparent reflectance;
l is the radiation value;
mu is the cosine of the zenith angle of the sun;
f is the solar radiation flux density of the upper air boundary;
b) Selecting dark target
The output signal of the radiation value (20) module is transmitted to a dark target apparent reflectivity (30) module, the apparent reflectivity on a near infrared 2.1um channel is selected, and the pixel in the range of 0.036-0.044 is taken as a dark target;
step 3, atmospheric correction (40)
The output signal of the dark target apparent reflectivity (30) module is transmitted to an atmospheric correction (40) module, and the atmospheric correction (40) is carried out according to the dark target apparent reflectivity (30) obtained in the step 2; the method comprises the following specific working steps:
a) Defining geometric parameters (41)
The altitude angle, the zenith angle, the solar altitude angle, the zenith angle and the observation date of the airplane relative to the pixel are input into the geometric parameter (41) module, and an output signal of the geometric parameter (41) module is transmitted to the atmosphere correction (40) module;
b) Defining an atmospheric mode (42)
Defining an atmospheric mode adopted by the mode in an atmospheric mode (42) module, wherein an output signal of the atmospheric mode (42) module is transmitted to an atmospheric correction (40) module;
c) Defining an aerosol type (43) mode
Defining extinction and meteorological stadia types in boundary layer aerosol modes for the modes in the aerosol type (43), if visibility is defined at the same time, replacing the meteorological stadia defined by default values in the aerosol type, the output signals of the aerosol type (43) module being transmitted to an atmospheric correction (40) module;
d) Defining an aerosol concentration (44) pattern
Defining an aerosol concentration mode for a mode in the aerosol concentration (44), inputting an optical aerosol thickness or horizontal visibility of 550nm, and transmitting an output signal of the aerosol concentration (44) module to an atmosphere correction (40) module;
e) Inputting height of ground feature (45)
Transmitting an output signal input to the terrain elevation (45) module to an atmospheric correction (40) module;
f) Inputting aircraft flight altitude (46)
Transmitting an output signal input to the aircraft flight altitude (46) module to an atmospheric correction (40) module;
step 4, extracting atmospheric correction parameters
a) Signal transmission
The output signals of the atmosphere correction (40) module are respectively transmitted to an aerosol scattering phase function (51) module and an aerosol single scattering reflectivity (52) module;
b) Performing atmospheric correction
According to the input parameters in the step 3, atmospheric correction is carried out on the dark target on the selected aerial hyperspectral remote sensing image;
c) Correction parameter
Extracting correction parameters aerosol scattering phase function (51) and aerosol single scattering reflectivity (52) from the output result;
step 5, calculating the optical thickness of the boundary layer aerosol (60)
a) Signal transmission
The output signals of the aerosol scattering phase function (51) module and the aerosol single scattering reflectivity (52) module are transmitted to the aerosol optical thickness (60) module;
b) And calculating
Calculating the apparent reflectivity of the boundary layer atmosphere according to the following formula:
c) Calculating boundary layer aerosol optical thickness (60)
Calculating the boundary layer aerosol optical thickness (60) according to the aerosol scattering phase function (51) and the aerosol single scattering reflectivity (52) obtained in the step (4);
step 6, judgment
a) Signal transmission
The output signal of the aerosol optical thickness (60) module is transmitted to a comparison (70) module;
b) Calculating the ground distance
Synchronous ground visibility range data according to formula
V＝3.91·H·1/τ
In the formula: v is the ground visibility range;
h is aerosol elevation in different seasons;
τ is the aerosol optical thickness;
c) And compared with each other
Comparing (70) the calculated aerosol optical thickness value with the aerosol optical thickness (60) obtained in step 5;
when the difference value of the two is less than 0.1, the output signal of the comparison module (70) is transmitted to an output module (80), and the output is the optical thickness (60) of the aerosol;
otherwise, feeding back to the atmospheric correction (40) module, returning to the step 3 to carry out atmospheric correction again, re-inputting various parameters required by the atmospheric correction, and repeating the cycle.
The atmospheric mode (42) of the atmospheric correction method for inverting the optical thickness of the aerosol at the boundary layer by the aviation hyperspectral remote sensing comprises the following steps: tropical atmosphere, middle latitude summer, middle latitude winter, subpolar zone summer, subpolar zone winter, and 1976 U.S. standard atmosphere, etc.
The aerosol type (43) of the atmospheric correction method for inverting the optical thickness of the boundary layer aerosol by aviation hyperspectral remote sensing comprises the following steps: or is aerosol-free; or the extinction coefficient of the country, and the default meteorological stadia =23km; or city extinction coefficient, default meteorological stadia =5km; or tropospheric extinction coefficient, default meteorological stadia =50km.
The working principle of the invention is as follows: the practical modularized imaging spectrometer OMIS airborne high-spectrum remote sensing platform is an airplane, the flying height of the platform is approximately 2km in height, and the platform basically belongs to the boundary layer range, so that the boundary layer aerosol optical thickness can be inverted according to airborne high-spectrum remote sensing data and an atmospheric radiation transmission mechanism.
Apparent reflectivity for the boundary layer atmosphere can be written as
Since the aircraft is in the boundary layer, the path of the ground object reflected radiation to the sensor through the atmosphere is shortened, so the ascending radiation path needs to be modified to remove the atmospheric effect factor above the aircraft height in the ascending radiation process, which can be obtained by carrying out interpolation again on the atmospheric mode and the aerosol mode in the boundary layer.
The content in the boundary layer is very little, so that the boundary layer can be disregarded; however, the water vapor content in the boundary layer is obviously changed, and if the observation channel is sensitive to the water vapor change, the influence of the real-time water vapor change on the apparent reflectivity must be considered, and at the moment, the synchronous observation of the water vapor content of the boundary layer needs to be carried out on the airplane.
The specific working steps of the embodiment of the invention are as follows:
the method is applied to select a dark target from an OMIS image of an aviation hyperspectral remote sensor developed by an aviation remote sensing research laboratory of Shanghai technical and physical institute of Chinese academy, and the flow of inverting the optical thickness calculation of the aerosol of the boundary layer is shown in figure 1:
step 1: radiometric calibration of hyperspectral remote sensing images
Reading an airborne aerial high-spectrum remote sensing image (10) in a standard format provided by Shanghai technical and physical research institute of Chinese academy of sciences, and converting a numerical serial number DN value into a radiation value (20) according to a formula radiation value = DN value slope + intercept and two coefficients corresponding to each wave band in a radiation calibration file;
step 2, calculating the apparent reflectivity and selecting the dark target
The radiation value (20) output by the step 1 is calculated according to the formula
R＝π*L/(μ*f)
Wherein R is the apparent reflectance; l is the radiation value; mu is the excess chord of the zenith angle of the sun; f is the solar radiation flux density of the upper air boundary; and calculating to obtain the apparent reflectivity on the sensor, and selecting the pixel with the apparent reflectivity of 0.036-0.044 on the near-infrared 2.1um channel as the dark target.
Step 3, atmospheric correction
And (3) performing atmospheric correction according to the apparent reflectivity of the dark target obtained in the step (2). The method comprises the following steps:
step 3-1, defining geometric parameters
Inputting the altitude angle, the zenith angle, the solar altitude angle, the zenith angle and the observation date (MMDD) of the airplane relative to the pixel in a geometric parameter (41) module;
step 3-2, defining an atmospheric mode
Defining the atmospheric modes adopted by the modes in an atmospheric mode (42) module, wherein the atmospheric modes comprise 6 atmospheric modes such as tropical atmosphere, middle latitude summer, middle latitude winter, subpolar summer, subpolar winter, 1976 American standard atmosphere and the like;
step 3-3, defining aerosol type mode
The extinction and meteorological stadia types in the boundary layer aerosol (0-2 km height interval) mode used by the mode are defined in the aerosol type mode (43) module, and if the visibility is defined at the same time, the meteorological stadia defined by default values in the aerosol type is replaced. The aerosol types mainly include the following options: (1) no aerosol; (2) rural extinction coefficient, default meteorological stadia =23km; (3) city extinction coefficient, default meteorological stadia =5km; (4) tropospheric extinction coefficient, default meteorological stadia =50km.
Step 3-4, defining aerosol concentration mode
Defining an aerosol concentration pattern for a pattern in an aerosol concentration (44), inputting an aerosol optical thickness or horizontal visibility (km) of 550 nm;
step 3-5, inputting the height (km) of the ground feature
Step 3-6, inputting the flight altitude (km) of the airplane
Step 4, extracting atmospheric correction parameters
According to the input parameters in the step 3, atmospheric correction is carried out on the selected dark target on the aerial hyperspectral remote sensing image, and correction parameters of an aerosol scattering phase function (51) and an aerosol single scattering reflectivity (52) are extracted from an output result;
step 5, calculating the optical thickness of the aerosol of the boundary layer
Calculating the optical thickness (60) of the aerosol at the boundary layer according to the formula (1) and the aerosol scattering phase function (51) and the aerosol single scattering reflectivity (052) obtained in the step (4);
step 6,
The synchronous ground visibility range data is calculated according to the formula
V＝3.91·H·1/τ
Note that: v is the ground visibility range (m); h is aerosol elevation in different seasons (776.4 m in Shanghai in winter); τ is the aerosol optical thickness.
Comparing (07) the calculated aerosol optical thickness value with the aerosol optical thickness (06) obtained in the step (5), and when the difference value of the calculated aerosol optical thickness value and the aerosol optical thickness (06) is less than 0.1, executing (7) and outputting (06) the aerosol optical thickness; otherwise, executing 8, returning to the step 3 to carry out the atmospheric correction again, and inputting the parameters required by the atmospheric correction again.
The specific embodiment of the atmospheric correction of the invention is as follows:
referring to fig. 2, 3, 4, 5 and 6, selecting a dark target from the OMIS hyperspectral image of the practical modular imaging spectrometer in 2002, 10.7.2002 in Shanghai, inverting the optical thickness of the aerosol according to the technical flow chart of the invention, firstly converting the DN value of the OMIS hyperspectral image of the practical modular imaging spectrometer into a radiation value through step 1, and selecting a dark surface (corresponding to the polluted water body on the Huangpu river) from the radiation value, wherein fig. 2 is a position sketch map shown by the dark surface in the embodiment; FIG. 3 is a plot of apparent reflectance at 13 and 14 points, respectively, for a dark surface, with wavelength (nm) on the x-axis and apparent reflectance on the y-axis; then, selecting corresponding spectral reflectivity of the ground objects from a spectral database of the ground objects, and gradually inputting parameters (3-1: 41.8-44.8 degrees of the zenith angle of the sun, 212-219.6 degrees of the azimuth angle, 3-2: a winter atmosphere mode at a middle latitude, 3-3: an urban aerosol mode, 3-4: 8km of visibility, 3-5: 0.004km of the height of the ground objects, 3-6: 2km of the flying height of an airplane) according to the step 3 to calculate the atmospheric transmittance, wherein a graph 4 is a change curve of the calculated atmospheric transmittance along with the wavelength, a dotted line is an atmospheric transmittance curve at 13 points, an x axis is a wavelength (nanometer), and a y axis is the atmospheric transmittance; then, the optical thickness of the aerosol is calculated according to the formula 3 in the step 6, and fig. 5 shows the optical thickness of the aerosol obtained by inverting the OMIS hyperspectral remote sensing image of the airborne practical modular imaging spectrometer according to the atmospheric correction method of the invention, wherein the black line represents the optical thickness value of the aerosol at 13 points, the red line represents the optical thickness of the aerosol at 14 points, the x axis is the wavelength (nanometer), and the y axis is the optical thickness value of the aerosol.
TABLE-1: practical modular imaging spectrometer OMIS spectrometer main technical parameters
Table-1 Main parameters of the OMIS instrument
| Type (B) | Spectral range Enclose (mum) | Sampling room Partition/channel Number of | Wave band Number of | General vision Field(s) | Instantaneous moment of action Visual field | Line image Number of elements | Scanning speed Rate (line +) Second) | Number of According to Weaving machine Code |
| OMIS-I | 0.46~1. 1 1.06~1. 7 2.0~2.5 3~5 8~12.5 | 10nm/64 40nm/16 15nm/32 250nm/8 500nm/8 | 64 16 32 8 8 | ＞70° | 3mrad | 512 | 5 10 15 20 | 12b it |
| GPS (Global positioning System) device Bit precision Gyrostabile Fixed platform Velocity to height ratio System information Noise ratio | 20 m Stable precision is better than +/-4' Less than or equal to 0.216 radian/second (speed unit: kilometer/hour, height unit: meter) ≤300 | |||||||
(following page)
According to data retrieval, a detailed and complete method for inverting the optical thickness of the aerosol aiming at airborne hyperspectral imaging data (especially an OMIS imaging spectrometer) is not available so far. Therefore, the optical thickness information of the aerosol is extracted from the atmospheric transmission spectrum by combining a practical modular imaging spectrometer OMIS imaging spectrometer with a boundary layer atmospheric radiation transmission principle.
TABLE-2: utility model modularization imaging spectrometer OMIS inversion aerosol optical thickness:
inquiring and displaying according to historical air quality data of an environmental monitoring center in Shanghai city: the air quality condition of Shanghai city at about 2002-10-713 o is generally better, and sulfur dioxide (SO) 2 ) The concentration is 0.051mg/m 3 Nitrogen dioxide (NO) 2 ) The concentration is 0.044mg/m 3 Nitrogen oxide (NOx) concentration of 0.051mg/m 3 Inhalable Particles (PM) 10 ) The concentration is 0.124mg/m 3 The Air Pollution Index (API) is in a good grade, the air quality is equivalent to the level II of the environmental air quality Standard (GB 3095-1996), and the main pollutants are inhalable particles PM 10 And the pollution is weak. The optical thickness of the aerosol obtained by inversion is acceptable in value.
Aiming at the OMIS high-spectrum image data of a practical modular imaging spectrometer in 2002, 10, 7 days, combining an atmospheric radiation transmission equation, calculating the atmospheric transmittance of a boundary layer, and calculating the optical thickness of the aerosol from an atmospheric transmission characteristic spectrum, a preliminary reverse result is given, and the optical thickness value of the aerosol at a wave band of 502nm-590nm is between 0.175 and 0.314. The inversion results are compared with the aerosol optical thickness results (table-3) calculated according to the meteorological visibility and the atmospheric transmittance under the rural aerosol mode (23 km), urban aerosol (5 km) and urban aerosol (8 km) calculated by LOWTRAN radiation transmission in the graph 6, and have better consistency.
TABLE 3 Aerosol optical thickness calculated from visibility data
Table 3 Calculated AOD from visibility
| Time-piece Carving tool | (Pudong) Station Instantaneous moment Can see Distance between (m) | Pudong station Ten minutes Ping All can see distance (m) | XU HUI Station Instantaneous moment of action Can see Distance between (m) | Xuhui station Ten minutes Mean energy Distance (m) | Huangpu Park Instant standing Time energy Distance between two adjacent plates (m) | Cambodia park Standing ten minutes clock Mean energy is shown in Distance (m) | Fuel rail Instant driver station Can see when Distance (m) | Fuel rail Driver station ten Medicine for treating chronic hepatitis B All can see Distance (m) | Aod Flat plate Are all made of Value of (550 nm) |
| 13: 00 13: 10 13: 20 13: 30 13: 40 13: 50 14: 00 | 1105 0 9648 9253 1232 0 9735 8556 8693 | 9897 9397 9678 9585 9442 9775 8684 | 8536 1028 3 8217 9610 8313 8663 7390 | 9573 9273 8865 8751 8376 8485 7752 | 14917 12899 14058 14471 13846 11368 11925 | 15242 15504 16321 13295 15522 13140 12961 | 10809 12267 7145 10306 9743 9096 9931 | 10368 11102 10122 9892 9909 10231 9850 | 0.27 9 0.27 8 0.31 0 0.28 3 0.29 9 0.31 3 0.32 5 |
| 0.29 8 |
Claims (3)
1. An atmospheric correction method for inverting optical thickness of boundary layer aerosol by aviation hyperspectral remote sensing is characterized by comprising the following steps of: the method extracts boundary layer aerosol optical thickness information from an atmospheric transmission spectrum by an atmospheric radiation transmission principle, and performs interpolation again on an atmospheric mode and an aerosol mode in a boundary layer to obtain apparent reflectivity so as to realize the calculation of inverting the boundary layer aerosol optical thickness, wherein the specific calculation steps are as follows:
step 1: radiometric calibration of hyperspectral remote sensing images
a) Reading hyperspectral remote sensing image (10)
Reading an airborne aviation hyperspectral remote sensing image (10) in a standard format;
b) Converted to radiation value (20)
The output signal of the hyperspectral remote sensing image (10) module is transmitted to the input end of a radiation value (20) module, and the numerical serial number DN value of the hyperspectral remote sensing image (10) is converted into a radiation value (20) according to two coefficients of slope and intercept corresponding to each wave band in a radiometric calibration file and a formula radiation value = DN value x slope + intercept;
step 2, calculating the apparent reflectivity and selecting a dark target
a) And calculating
Calculating the radiation value (20) output in the step 1 as the apparent reflectivity obtained on the sensor according to the following formula:
R＝π*L/(μ*f)
in the formula: r is the apparent reflectance;
l is the radiation value;
mu is the cosine of the zenith angle of the sun;
f is the solar radiation flux density of the upper atmosphere;
b) Selecting dark target
The output signal of the radiation value (20) module is transmitted to a dark target apparent reflectivity (30) module, the apparent reflectivity on a near infrared 2.1um channel is selected, and the pixel in the range of 0.036-0.044 is taken as a dark target;
step 3, atmospheric correction (40)
The output signal of the dark target apparent reflectivity (30) module is transmitted to an atmospheric correction (40) module, and the atmospheric correction (40) is carried out according to the dark target apparent reflectivity (30) obtained in the step 2; the method comprises the following specific working steps:
a) Defining geometric parameters (41)
The altitude angle, the zenith angle, the solar altitude angle, the zenith angle and the observation date of the airplane relative to the pixel are input into the geometric parameter (41) module, and an output signal of the geometric parameter (41) module is transmitted to the atmosphere correction (40) module;
b) Defining an atmospheric mode (42)
Defining an atmospheric mode adopted by the mode in an atmospheric mode (42) module, wherein an output signal of the atmospheric mode (42) module is transmitted to an atmospheric correction (40) module;
c) Defining an aerosol type (43) mode
Defining extinction and meteorological stadia types in boundary layer aerosol modes for the modes in the aerosol type (43), if visibility is simultaneously defined, the output signal of the aerosol type (43) module being transmitted to the atmospheric correction (40) module in place of the meteorological stadia defined by default values in the aerosol type;
d) Defining an aerosol concentration (44) pattern
Defining an aerosol concentration mode for a mode in the aerosol concentration (44), inputting an optical aerosol thickness or horizontal visibility of 550nm, and transmitting an output signal of the aerosol concentration (44) module to an atmosphere correction (40) module;
e) Inputting height of ground feature (45)
Transmitting an output signal input to the terrain elevation (45) module to an atmospheric correction (40) module;
f) Inputting aircraft flight altitude (46)
Transmitting an output signal input to the aircraft flight altitude (46) module to an atmospheric correction (40) module;
step 4, extracting atmospheric correction parameters
a) Signal transmission
The output signals of the atmosphere correction (40) module are respectively transmitted to an aerosol scattering phase function (51) module and an aerosol single scattering reflectivity (52) module;
b) Performing atmospheric correction
According to the input parameters in the step 3, atmospheric correction is carried out on the dark target on the selected aerial hyperspectral remote sensing image;
c) Correction parameters
Extracting correction parameters aerosol scattering phase function (51) and aerosol single scattering reflectivity (52) from the output result;
step 5, calculating the optical thickness of the boundary layer aerosol (60)
a) Signal transmission
The output signals of the aerosol scattering phase function (51) module and the aerosol single scattering reflectivity (52) module are transmitted to the aerosol optical thickness (60) module;
b) And calculating
Calculating the apparent reflectivity of the boundary layer atmosphere according to the following formula:
c) Calculating boundary layer aerosol optical thickness (60)
Calculating the boundary layer aerosol optical thickness (60) according to the aerosol scattering phase function (51) and the aerosol single scattering reflectivity (52) obtained in the step (4);
step 6, judgment
a) Signal transmission
The output signal of the aerosol optical thickness (60) module is transmitted to a comparison (70) module;
b) Calculating the ground distance
Synchronous ground visibility range data according to formula
V＝3.91·H·1/τ
In the formula: v is the ground visibility range;
h is aerosol elevation in different seasons;
τ is the aerosol optical thickness;
c) And compared with each other
Comparing (70) the calculated aerosol optical thickness value with the aerosol optical thickness (60) obtained in step 5;
when the difference value of the two is less than 0.1, the output signal of the comparison module (70) is transmitted to an output module (80), and the output is the optical thickness (60) of the aerosol;
otherwise, feeding back to the atmospheric correction (40) module, returning to the step 3 to carry out atmospheric correction again, re-inputting various parameters required by the atmospheric correction, and repeating the cycle.
2. The atmospheric correction method for inverting optical thickness of aerosol at a boundary layer by aviation hyperspectral remote sensing according to claim 1, characterized in that: the atmospheric mode (42) includes: tropical atmosphere, mid-latitude summer, mid-latitude winter, subpolar summer, subpolar winter, and 1976 us standard atmosphere.
3. The atmospheric correction method for inverting optical thickness of boundary layer aerosol through aviation hyperspectral remote sensing according to claim 1 is characterized in that: said aerosol types (43) comprising: or is aerosol-free; or the country extinction coefficient, and the default meteorological sight distance =23km; or city extinction coefficient, default meteorological stadia =5km; or tropospheric extinction coefficient, default meteorological stadia =50km.
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