CN111912748B - Method for calculating linear depolarization ratio of carbon-containing aerosol - Google Patents
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Abstract
The invention relates to a method for calculating a linear depolarization ratio of carbon-containing aerosol, which is characterized by obtaining micro forms, chemical components and mixing modes at different aging stages according to a time-varying micro physical model of the current carbon-containing aerosol; solving a normalized Stokes scattering matrix of the carbon-containing aerosol at each target moment under each wavelength condition by adopting a superposition T matrix method, and recording elements of a 1 st row and a 1 st column of a 1 st row and elements of a 2 nd row and a 2 nd column of a 2 nd row; respectively carrying out time integral from fresh discharge at the current moment and spectral integral set by a laser radar wave band, calculating a linear depolarization ratio, and forming a linear depolarization ratio lookup table of each target moment under each wavelength condition of different aging stages; and searching a linear depolarization ratio lookup table according to the current wavelength of the laser radar and the aging period of the current carbon-containing aerosol to obtain a corresponding linear depolarization ratio. The quantitative inversion accuracy and the application level of atmospheric remote sensing are improved by improving the input lookup table simulation accuracy required by remote sensing inversion.
Description
Technical Field
The invention relates to the technical field of positioning methods, in particular to a method for calculating a linear depolarization ratio of carbon-containing aerosol.
Background
The carbonaceous aerosol is generally from artificial emissions of coal, automobile exhaust, biomass combustion and the like, and is an important factor causing heavy pollution weather such as dust haze. The carbonaceous aerosol is composed of black carbon, brown carbon, organic carbon and a mixture of the black carbon, the brown carbon and the organic carbon with other aerosols, has strong light absorption and is one of the most uncertain influencing factors in global climate change. Therefore, the monitoring of carbon-containing aerosol pollution by wide-range satellite remote sensing becomes an indispensable technical means, and the environment monitoring sites scattered on the ground are effectively supplemented.
Based on backward scattering observation of satellite, aviation and foundation, linear Depolarization Ratio (LDR) is a main parameter acquired by a laser radar and is also one of the technical means for quantitative monitoring of carbon-containing aerosol. Previous studies have shown that the linear depolarization ratio of carbonaceous aerosols is typically between 0.067 and 0.119 at 0.532 μm and between 0.009 and 0.027 at 1.064 μm. The specific definition is as follows:
wherein, F 11 And F 22 Are the (1, 1) and (2, 2) elements of the normalized Stokes scattering matrix (F) calculated for randomly oriented aerosol particles. The divergence angle is typically set to 180, while in optical calculations F is also typically set 11 Called the scattering phase function, is one of the important parameters describing the optical properties.
The linear depolarization ratio data obtained by the laser radar is used for quantitatively and remotely sensing and inverting parameters of the carbon-containing aerosol, and accurate optical characteristics of the carbon-containing aerosol are required to be used as input. The transmission process of radiation in an earth surface-atmosphere coupling medium is quantitatively described by utilizing a vector radiation transmission model, different carbon-containing aerosol optical characteristics, earth gas states and observation geometries are traversed, and a lookup table is generated for remote sensing inversion calling. In the currently common aerosol satellite remote sensing inversion model and vector radiation transmission model, the sphere which is similar to the carbon-containing aerosol and is regarded as a standard is generally used for optical simulation, and the single scattering property of the sphere is obtained by utilizing Mie scattering (Mie). However, due to the fact that the microscopic morphology and the aging process of the carbon-containing aerosol are not reasonably considered in the simulation, large errors exist in the results of physicochemical characteristics and optical characteristics obtained through real observation and Mie scattering calculation, inversion cannot be directly conducted on the carbon-containing aerosol in remote sensing or the inversion accuracy is low, and the method is also one of the main reasons for restricting the optical thickness remote sensing inversion accuracy of aerosol fine particles at present. Moreover, because the design index of the remote sensor is not considered, the generation of the lookup table at present cannot effectively serve the remote sensing application of the domestic load.
Disclosure of Invention
In order to improve the accuracy of quantitative remote sensing inversion of carbon-containing aerosol parameters, the invention provides a calculation method of a carbon-containing aerosol linear depolarization ratio, wherein a design waveband and a spectral response function of a laser radar and a mixed growth process of the carbon-containing aerosol changing along with time in a real atmospheric scene are introduced into the calculation method of the carbon-containing aerosol linear depolarization ratio.
In order to achieve the purpose, the invention provides a method for calculating the linear depolarization ratio of carbon-containing aerosol, which comprises the following steps:
(1) Respectively constructing a time-varying micro physical model of the carbon-containing aerosol according to the fresh discharge time of the current carbon-containing aerosol, and obtaining the micro morphology, the chemical components and the mixing mode of different aging stages;
(2) According to the laser radar wave band setting, according to the set interval sampling wavelength condition, taking the time-varying micro physical model at each target time as input, solving the normalized Stokes scattering matrix of the carbon-containing aerosol at each target time under each wavelength condition by adopting a superposition T matrix method, and recording the (1, 1) element of the 1 st row and the 1 st column and the (2, 2) element of the 2 nd row and the 2 nd column of each target time under each wavelength condition;
(3) Integrating the elapsed time from the fresh discharge at the current time and performing spectral integration on the (1, 1) element of the 1 st row and the 1 st column and the (2, 2) element of the 2 nd row and the 2 nd column to obtain an integrated (1, 1) element F of the 1 st row and the 1 st column 11 (180 °) and (2, 2) element F of row 2, column 2 22 (180 ℃), calculating a linear depolarization ratio, and forming a linear depolarization ratio lookup table at each target moment under each wavelength condition in different aging stages;
(4) Verifying the linear depolarization ratio lookup table according to actual observation data of the laser radar, entering the step (5) if the linear depolarization ratio lookup table meets the precision requirement, and returning to the step (1) to optimize time periods corresponding to different aging stages in the time-varying micro physical model;
(5) And searching a linear depolarization ratio lookup table according to the current wavelength of the laser radar and the aging period of the current carbon-containing aerosol to obtain a corresponding linear depolarization ratio.
Further, the time-varying physical model simulates the growth process of carbon-containing aerosol in different areas and different emission types.
Further, the time-varying micro physical model is divided into 4 aging time periods according to the aging time; the time from the current moment to the fresh discharge accounts for less than 10% of the total aging time, and a pure black carbon form is assumed; the time from the current moment to the fresh discharge accounts for 10 to 50 percent of the total aging time, and the mixture of the black carbon and other components is assumed to be in a partial package form; the time from the current time to the fresh discharge accounts for 50 to 70 percent of the total aging time, and the mixture of the black carbon and other components is assumed to be in a partially embedded form; the time elapsed from the current time of fresh discharge is more than 70% of the total aging time, assuming that the mixture of black carbon and other ingredients is in a fully encapsulated form.
Further, each of the 4 aging periods selects one time as a target time.
Further, the wavelength band of the laser radar is 520nm-550nm, and the interval is 5nm.
Further, the formula for calculating the linear depolarization ratio is as follows:
further, the method for constructing the linear depolarization ratio lookup table at each target time under each wavelength condition by using the time-varying micro-physical model of the carbon-containing aerosol to obtain the micro-morphology, the chemical composition and the mixing mode at different aging stages comprises the following steps: respectively constructing a corresponding linear depolarization ratio lookup table for each time-varying micro-physical model type; the linear depolarization ratio lookup table contains linear depolarization ratio values at different aging periods and different wavelengths.
Further, specifically, the searching and finding the linear depolarization ratio lookup table according to the current wavelength of the laser radar and the aging period of the current carbon-containing aerosol comprises:
firstly, searching a linear depolarization ratio lookup table corresponding to the type of the time-varying micro physical model according to the time from the current carbon-containing aerosol to fresh discharge; and searching a corresponding linear depolarization ratio value in a linear depolarization ratio lookup table corresponding to the type of the time-varying physical model according to the current wavelength and the aging period of the current carbon-containing aerosol, and using the linear depolarization ratio value for the laser radar inversion calculation.
Further, performing the integration of the elapsed time from the fresh emission at the current time and the spectral integration specifically is:
<δ>＝∫∫δ(t,λ)N(t)N(λ)dtdλ
wherein t is the time from the current time to the fresh discharge, λ is the current wavelength, N (t) is the number of the carbonaceous aerosol at the current time, N (λ) is the weight of the current wavelength in the spectral response function, and δ (t, λ) is the linear depolarization ratio of the carbonaceous aerosol at the current wavelength at the current time.
The technical scheme of the invention has the following beneficial technical effects:
(1) The invention provides a calculation method of a carbon-containing aerosol linear depolarization ratio, which utilizes a time-varying micro-physical model to improve the micro-physical characteristic representation of the carbon-containing aerosol, more accurately describes the mixed growth process of the carbon-containing aerosol in a real atmospheric scene along with time variation, designs a waveband and a spectral response function for a load of a satellite-borne laser radar, develops time and spectral integration of the linear depolarization ratio to obtain a more accurate load observation result, can effectively serve technical means such as backscatter observation of the laser radar and the like, and improves the simulation precision of an input lookup table necessary for remote sensing inversion, thereby improving the quantitative reflection precision and the application level of atmospheric remote sensing.
(2) The invention can optimize and adjust according to the design index, the area and the emission type of the laser radar, so that the linear depolarization ratio of the lookup table can be better applied to the inversion calculation of the laser radar, and the remote sensing application of domestic loads is effectively served.
Drawings
FIG. 1 is a schematic flow chart of the calculation of the linear depolarization ratio of the carbonaceous aerosol;
FIG. 2 is a schematic diagram of a time-varying micro-physical model for simulating a hybrid growth process;
FIG. 3 (a) is a schematic diagram showing the linear depolarization ratio of a laser radar at a wavelength of 532 nm; (b) Is a schematic diagram of the linear depolarization ratio when the laser radar has a wavelength of 1064 nm.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The currently adopted calculation method for the linear depolarization rate of the carbon-containing aerosol qualitatively assumes that different carbon-containing aerosol models exist, does not consider the influences in the aspects of time change and spectral response, cannot provide accurate input for remote sensing reflection, and restricts the quantitative application of atmospheric remote sensing. The invention provides corresponding improvement aiming at the designed wave band and the spectral response function of the laser radar and the mixed growth process of the carbonaceous aerosol in the real atmospheric scene, which changes along with time, so that the calculation of the linear depolarization rate of the carbonaceous aerosol can effectively serve the technical means of backward scattering observation and the like of the laser radar, and the simulation precision of the input lookup table required by remote sensing inversion is improved.
The calculation flow of the linear depolarization ratio of the carbon-containing aerosol in combination with the calculation flow of the carbon-containing aerosol 1 is as follows:
(1) Respectively constructing a time-varying micro physical model of the carbon-containing aerosol according to the time from the current carbon-containing aerosol to the fresh discharge to obtain the micro morphology, the chemical components and the mixing mode at different aging stages.
And simulating a mixed growth process between strong absorption aerosol such as black carbon and the like, weak absorption aerosol such as brown carbon and the like and nonabsorbable aerosol such as sulfate and the like based on the time-varying micro physical model to generate the carbon-containing aerosol micro physical model at the current moment. Typical physical and chemical preset parameters of the aerosol mainly comprise microscopic morphology, chemical composition, mixing mode and the like. In the microscopic morphology, black carbon is assumed to be in a cluster form, and the other components are assumed to be in a spherical form. The total aging time is empirically obtained as 1-5 days depending on the area and the type of emissions. The mixing mode is determined by the current time and the total aging time, namely the time between the current time and the fresh discharge accounts for 10% of the total aging time, and pure black carbon is assumed; the time from the current moment to the fresh discharge accounts for 10 to 50 percent of the total aging time, and the mixture of the black carbon and other components is assumed to be in a partial packaging form; the time from the current moment to the fresh discharge accounts for 50 to 70 percent of the total aging time, and the mixture of the black carbon and other components is assumed to be in a partially embedded form; the time elapsed from the current time of fresh discharge was more than 70% of the total aging time, assuming that the mixture of black carbon and other ingredients is in a fully encapsulated form, as shown in fig. 2. These periods may vary with region and emission type and may be optimized using actual observations from the lidar.
And verifying the time-varying micro-physical model by adopting actual observation data of the laser radar, and optimizing and adjusting the model according to different regions and emission types.
(2) Based on the design wave band of the laser radar, aiming at the carbon-containing aerosol real-variation micro-physical models at different moments, a normalized Stokes scattering matrix under each interval wavelength is obtained through calculation by utilizing a superposition T matrix method. And taking the real-variation micro physical model at a certain moment as the input of the T matrix method, so as to obtain the normalized Stokes scattering matrix under each corresponding interval wavelength. For example, using a commonly used 520-550nm wavelength band as an example, with a wavelength interval of 5nm, a normalized Stokes scattering matrix of the carbon-containing aerosol at a target time under several wavelength conditions of 520, 525, 530, 535, 540, 545 and 550nm can be obtained, the scattering angle is set to 180 °, and the (1, 1) element in the 1 st column of the 1 st row and the (2, 2) element in the 2 nd column of the 2 nd row are respectively recorded for subsequent integration.
(3) Aiming at the time and the spectral response function required by each observation of the real load, developing the time and the spectral integral which are elapsed from the fresh discharge at the current moment, and obtaining the (1, 1) element F of the 1 st row and the 1 st column of the normalized Stokes scattering matrix of the carbon-containing aerosol after the integral 11 (180 °) and (2, 2) element F of row 2, column 2 22 (180 degrees), calculating to obtain the linear depolarization ratio of the carbon-containing aerosol, and constructing a linear depolarization ratio lookup table.
The formula for calculating the integral is:
<δ>＝∫∫δ(t,λ)N(t)N(λ)dtdλ
wherein t is the time from the current time to the fresh discharge, λ is the current wavelength, N (t) is the number of the carbonaceous aerosol at the current time, N (λ) is the weight of the current wavelength in the spectral response function, and δ (t, λ) is the linear depolarization ratio of the carbonaceous aerosol at the current wavelength at the current time.
The linear depolarization ratio of the carbon-containing aerosol is obtained by calculation according to the formula:
and calculating the linear depolarization ratio of each time of the time-varying micro physical model of each emission type in each region, and constructing a depolarization ratio lookup table.
(4) And verifying the simulation result of the time-varying micro physical model by using the actual observation data of the laser radar, thereby providing accurate carbon-containing aerosol optical characteristics for remote sensing inversion. If the precision requirement is not met, returning to modify the time-varying micro physical model, if the precision requirement is met, applying the depolarization ratio lookup table to the laser radar, and entering the step (5).
(5) And selecting a corresponding depolarization ratio lookup table of the time-varying micro physical model type according to the time between the current carbon-containing aerosol and the fresh discharge, and obtaining a corresponding linear depolarization ratio according to the lookup table of the time between the current time and the fresh discharge. And when the laser radar calculates the aerosol parameters in an inversion way, the accurate linear depolarization ratio is obtained through the table look-up way, and the inversion calculation is carried out.
The method is used for designing a wave band and a spectral response function for the load of the satellite-borne laser radar, and developing time and spectral integration of linear depolarization rate to obtain a more accurate load observation result, so that the method can effectively serve technical means such as backscattering observation of the laser radar. Based on the design waveband of the laser radar, a normalized Stokes scattering matrix under each interval wavelength is calculated by using a superposition T matrix method, time and spectrum integration is carried out based on a spectrum response function, and a linear depolarization rate result of the carbon-containing aerosol is obtained, wherein as shown in figure 3, results of different aging stages have large difference, and particularly, the results can be well distinguished in a severe aging stage. And verifying the simulation result by adopting the actual observation data of the laser radar, thereby providing accurate carbon-containing aerosol optical characteristics for remote sensing inversion.
In summary, the invention provides a method for calculating the linear depolarization rate of carbon-containing aerosol, which comprises the steps of respectively constructing time-varying micro physical models of the carbon-containing aerosol according to different shapes of the current carbon-containing aerosol from the time of fresh discharge, and obtaining the micro forms, chemical components and mixing modes of different aging stages; solving a normalized Stokes scattering matrix of the carbon-containing aerosol at each target moment under each wavelength condition by adopting a superposition T matrix method, and recording elements of a 1 st row and a 1 st column of a 1 st row and elements of a 2 nd row and a 2 nd column of a 2 nd row; respectively carrying out integral and spectrum integral of time which is past from the current time to the fresh discharge, calculating a linear depolarization ratio, forming time-varying micro-physical models of the carbon-containing aerosol at different aging stages, and looking up tables of the linear depolarization ratio at each target time under each wavelength condition; and searching a linear depolarization ratio lookup table according to the current wavelength of the laser radar and the aging period of the current carbon-containing aerosol to obtain a corresponding linear depolarization ratio. The invention utilizes the time-varying micro physical model to improve the micro physical characteristic representation of the carbon-containing aerosol, more accurately describes the mixed growth process of the carbon-containing aerosol in a real atmospheric scene along with the time change, designs wave bands and spectral response functions for the load of the satellite-borne laser radar, develops the time and spectral integral of the linear depolarization rate to obtain more accurate load observation results, can effectively serve the technical means of backscattering observation of the laser radar and the like, improves the simulation precision of an input lookup table required by remote sensing inversion, and further improves the quantitative inversion precision and the application level of atmospheric remote sensing.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modifications, equivalents, improvements and the like which are made without departing from the spirit and scope of the present invention shall be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundary of the appended claims, or the equivalents of such scope and boundary.
Claims (9)
1. A method for calculating the linear depolarization ratio of carbon-containing aerosol is characterized by comprising the following steps:
(1) Respectively constructing time-varying micro physical models of the carbon-containing aerosol according to the current time from the carbon-containing aerosol to the fresh discharge to obtain the micro morphology, the chemical components and the mixing mode of different aging stages;
(2) According to the laser radar wave band setting, according to the set interval sampling wavelength condition, taking the time-varying micro physical model at each target moment as input, solving the normalized Stokes scattering matrix of the carbon-containing aerosol at each target moment under each wavelength condition by adopting a superposition T matrix method, and recording the (1, 1) element of the 1 st row and the 1 st column and the (2, 2) element of the 2 nd row and the 2 nd column of each target moment under each wavelength condition;
(3) Integrating the elapsed time from the fresh discharge at the current time and performing spectral integration on the (1, 1) element of the 1 st row and the 1 st column and the (2, 2) element of the 2 nd row and the 2 nd column to obtain an integrated (1, 1) element F of the 1 st row and the 1 st column 11 (180 °) and (2, 2) element F of row 2, column 2 22 (180 degrees), calculating a linear depolarization ratio, and forming a linear depolarization ratio lookup table at each target moment under each wavelength condition in different aging stages;
(4) Verifying the linear depolarization ratio lookup table according to actual observation data of the laser radar, entering the step (5) if the linear depolarization ratio lookup table meets the precision requirement, and returning to the step (1) to optimize time periods corresponding to different aging stages in the time-varying micro physical model;
(5) And searching a linear depolarization ratio lookup table according to the current wavelength of the laser radar and the aging period of the current carbon-containing aerosol to obtain a corresponding linear depolarization ratio.
2. The method for calculating the linear depolarization ratio of the carbonaceous aerosol according to claim 1, wherein the time-varying physical model simulates the growth process of carbonaceous aerosols with different emission types in different regions.
3. The method for calculating the linear depolarization ratio of the carbonaceous aerosol according to claim 1 or 2, wherein the time-varying physical model is divided into 4 aging periods according to an aging time; the time from the current moment to the fresh discharge accounts for less than 10% of the total aging time, and a pure black carbon form is assumed; the time from the current moment to the fresh discharge accounts for 10 to 50 percent of the total aging time, and the mixture of the black carbon and other components is assumed to be in a partial wrapping form; the time from the current moment to the fresh discharge accounts for 50 to 70 percent of the total aging time, and the mixture of the black carbon and other components is assumed to be in a partial embedding form; the time elapsed from the current time of fresh discharge is more than 70% of the total aging time, assuming that the mixture of black carbon and other ingredients is in a fully encapsulated form.
4. The method according to claim 3, wherein a time is selected as the target time for each of the 4 aging periods.
5. The method for calculating the linear depolarization ratio of the carbonaceous aerosol according to claim 1 or 2, wherein the wavelength band of the lidar is 520nm to 550nm, and the interval is 5nm.
6. The method for calculating the linear depolarization ratio of the carbonaceous aerosol according to claim 1 or 2, wherein the formula for calculating the linear depolarization ratio is as follows:
7. the method for calculating the linear depolarization ratio of the carbon-containing aerosol according to claim 1 or 2, wherein the step of obtaining the microscopic morphology, the chemical composition and the mixing mode at different aging stages by using the time-varying micro-physical model of the carbon-containing aerosol and the step of constructing the linear depolarization ratio lookup table at each target time under each wavelength condition comprise the steps of: respectively constructing a corresponding linear depolarization ratio lookup table for each time-varying micro-physical model type; the linear depolarization ratio lookup table is provided with linear depolarization ratio values in different aging periods and different wavelengths.
8. The method of claim 7, wherein the searching the lookup table for linear depolarization ratio according to the current wavelength of the lidar and the aging period of the current carbonaceous aerosol comprises:
firstly, a linear depolarization ratio lookup table corresponding to the type of the time-varying micro physical model is searched according to the distance between the current carbon-containing aerosol and the fresh discharge time; and searching a corresponding linear depolarization ratio numerical value in a linear depolarization ratio lookup table corresponding to the type of the time-varying physical model according to the current wavelength and the aging period of the current carbon-containing aerosol, and using the linear depolarization ratio numerical value for the laser radar inversion calculation.
9. The method for calculating the linear depolarization ratio of the carbonaceous aerosol according to claim 1 or 2, wherein the performing of the integration of the elapsed time from the current time to the fresh discharge and the spectral integration specifically comprises:
<δ>＝∫∫δ(t,λ)N(t)N(λ)dtdλ
wherein t is the time from the current time to the fresh discharge, λ is the current wavelength, N (t) is the number of the carbonaceous aerosol at the current time, N (λ) is the weight of the current wavelength in the spectral response function, and δ (t, λ) is the linear depolarization ratio of the carbonaceous aerosol at the current wavelength at the current time.
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