CN114547896B - Total reflection spectrum radiation transmission modeling method for wetland aquatic vegetation canopy - Google Patents
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Abstract
The invention relates to a method for modeling total reflection spectrum radiation transmission of a wetland aquatic vegetation canopy, which comprises the following steps: calculating to obtain blade reflection and transmission spectra based on a PROSPECT-PRO model; inputting canopy structure parameters, observation geometry and blade anti-transmissivity into a SAILH model, and calculating by combining the proportion of direct sky light and scattered light along with the change of the wave band to obtain coefficients of absorption, extinction, attenuation, scattering and the like of a vegetation main body canopy, so as to obtain 4 reflection factors of the vegetation canopy; calculating the contribution of wave water surface reflection components to scene reflection according to the simplified Cox-Munk model; the underwater vegetation is regarded as a component part of a water body, absorption and scattering coefficients of the water body and the underwater vegetation are calculated according to a Lee shallow water model and a SAILH model respectively, and the reflection distribution of an underwater medium is obtained by combining a soil layer under water; finally, the scene bi-reflectivity of the whole aquatic vegetation system is obtained through coupling. The invention has the advantages of wide spectrum range, high simulation precision, rich applicable scene and the like, and has the prospect of business popularization.
Description
One of the technical fields
The invention relates to a method for modeling total reflection spectrum radiation transmission of a wetland aquatic vegetation canopy, belongs to the field of wetland ecological remote sensing, and has important significance in the aspects of wetland remote sensing technology research and wetland ecosystem carbon circulation research.
(II) background art
Climate warming due to greenhouse gas emissions is likely to have serious consequences such as glacier regression, sea level elevation, desertification, ecosystem function changes, etc. Therefore, the government of each country gives high importance to the carbon 'source'/'sink' feature and carbon balance estimation and CO2/CH4 emission reduction and sink increase research on the national scale, and the signing and effectiveness of the 'Kyoto protocol' clearly further promotes the hot tide of carbon cycle research.
Wetland is one of the hot spots for carbon recycling research due to its huge carbon reservoir storage capacity. In general, wetlands are important carbon sinks due to lower organic matter decomposition rates and higher productivity. However, there is a great uncertainty in performing the large scale evaluation. Currently, in the context of climate change, what is the effect that elevated air temperature or altered hydrologic conditions have on the wetland carbon circulation process? What is the feedback that the large amount of organic carbon stored in the wetland will give on climate change, whether to continue to play the role of carbon "sink" or to convert to carbon "source"? Is the carbon "sink" size changed? To answer the above-mentioned problems, it is critical to comprehensively ascertain the carbon emission space-time patterns, carbon process control factors, and to evaluate the carbon balance of different wetland types.
The wetland plants can fix CO2 in the atmosphere through photosynthesis, have strong carbon storage and carbon fixation capacities, and play an important role in global carbon circulation. Therefore, in order to master the spatial distribution situation of the carbon reserves of the large-scale wetland aquatic vegetation, the space distribution, biomass, carbon reserves and other aspects of the wetland aquatic vegetation are estimated by an aviation or aerospace remote sensing technology, but the research foundation of the current aquatic vegetation remote sensing aspect is weak, and the technical reserve is lacking. Therefore, the development of the aquatic vegetation remote sensing physical model method is particularly necessary and urgent.
According to the invention, a full-band wetland aquatic vegetation canopy radiation transmission model is constructed by coupling a typical land vegetation canopy model PROSAIL model, a simplified Cox-Munk wave water surface model, a sky light irradiance model and a shallow water biological optical model, so that the high-precision simulation of the aquatic vegetation spectrum with the wavelength of 400-2500nm can be realized, and the method has important theoretical significance and application value in the aspects of accurately calculating the reflection spectrum and the direction reflection characteristic of the aquatic vegetation in shallow water remote sensing, realizing the remote sensing monitoring, parameter inversion, carbon estimation and the like of the aquatic vegetation.
(III) summary of the invention
The invention relates to a method for modeling total reflection spectrum radiation transmission of a wetland aquatic vegetation canopy, which solves the problems of insufficient consideration of a traditional model to a water body background in an aquatic vegetation scene, low simulation precision and narrow spectrum band, and adopts the technical proposal that: inputting biochemical parameters of the blade into a PROSPECT-PRO model to calculate to obtain reflectivity and transmissivity spectrum data of a single blade; inputting vegetation canopy parameters, observation geometric parameters and blade anti-transmissivity into a SAILH model, and obtaining 4 reflection factors of vegetation canopy comprising a sun-to-observation direction, a sun-to-diffusion direction, a diffusion-to-diffusion direction and a diffusion-to-observation direction by combining the proportion of direct sky light and scattered light along with the change of a wave band; calculating the contribution of the specular reflection component of the water surface to the scene reflectivity according to the simplified Cox-Munk model and the Fresnel reflectivity; the underwater vegetation is regarded as a component part of a water body, the absorption and scattering coefficients of the water body and the underwater vegetation are calculated according to a Lee shallow water model and a SAILH model respectively, and the remote sensing reflectivity of an underwater medium is obtained by combining a soil layer under water; and integrating the contribution of the components to obtain the scene dichroism of the whole aquatic vegetation system. The method comprises the following specific steps:
step one: inputting biochemical parameters of aquatic vegetation leaves including chlorophyll, anthocyanin, carotenoid, brown pigment, leaf protein and other carbon-based component contents into a PROSPECT-PRO leaf radiation transmission model to calculate and obtain reflectance and transmittance spectrum data of 400-2500nm full wave bands of single leaves; the specific calculation process is as follows:
assuming that the blade is composed of N layers of the same class, the layers are divided by N-1 layers of air; the first layer receives incident light at an angle of incidence α, assuming the light wave is isotropic, using ρ α Representing the reflectivity τ α Indicating transmittance; inside the blade, use ρ 90 And τ 90 Respectively representing the reflectivity and the transmissivity of each layer element in the blade; then the total reflectivity R of the N layers N,α And transmittance T N,α The method comprises the following steps:
step two: inputting structural parameters, incident illumination geometry, observation geometry parameters, a blade reflectivity spectrum and a transmittance spectrum of the aquatic vegetation canopy into a SAILH model, and calculating the ratio of direct sky light to scattered light along with the change of a wave band to obtain coefficients of absorption, extinction, attenuation, scattering and the like of the aquatic vegetation main canopy, so as to obtain 4 reflection factors of the vegetation canopy, wherein the 4 reflection factors comprise a solar-to-observation direction, a solar-to-diffuse reflection direction, a diffuse incidence-to-diffuse reflection direction and a diffuse incidence-to-observation direction of 400-2500nm full wave band; the calculation process of the proportion of the direct sky light and the scattered light along with the change of the wave band comprises the following steps:
first, a normalized diffuse direct spectrum in the 400-2500nm band is obtained, normalized direct and diffuse radiation P dir And P dif The following equation is satisfied:
wherein delta is i Representing the width of the spectral window; p (P) dir And P dif Two parameters can be calculated from the spectral albedo, which are related by:
wherein a is albedo, R sd And R is dd E represents hemispherical reflectivity directly into the diffuse direction and diffuse into the diffuse direction, respectively s And e d Can be obtained by experimental measurement; after calculation of the normalized spectrum of diffuse and direct radiation, the diffusion ratio E dif And direct proportion E dir The method can be obtained by the following formula:
E dir ＝(1-c)P dir (6)
E dif ＝cP dif (7)
wherein c is a solar zenith angle theta s Related correction parameters:
c＝0.847-1.61sin(90-θ s )+1.04sin 2 (90-θ s ) (8)
the specific calculation process of the vegetation canopy correlation coefficient is as follows: the absorption, extinction, attenuation and scattering coefficients are subdivided into 10 parts according to the differences of the incident direction and the observation direction and the radiation type, and the parts are respectively: extinction coefficient k of solar incidence direction s Extinction coefficient k in observation direction o Diffuse radiation attenuation coefficient k d Scattering coefficient s of incident direction of sun so Scattering coefficient s of solar incident on upstream diffusion direction su Scattering coefficient s of the incident solar light on the downstream diffusion direction sd Scattering coefficient s of up-diffusion to observation direction uo Scattering coefficient s of down diffusion to observation direction do Scattering coefficient s of diffuse upward radiation to diffuse downward radiation ud Scattered coefficient s of diffuse radiation from downlink to uplink du The expression for the ten parameters is:
wherein L' represents the relative leaf area index, ρ, τ represents the leaf reflectivity and transmittance, θ, respectively o ,θ s ,θ l Represents the observed zenith angle, solar zenith angle and leaf inclination angle, ψ is the relative azimuth angle, β 1 ,β 2 ,β 3 Is three azimuth parameters phi that can be obtained from a look-up table s ,φ o Is the critical angle for the case of incident angle and blade parallelism, expressed as:
the canopy scale parameters of the aquatic vegetation are combined to obtain 4 reflection factors of the sun to the observation direction, the sun to the diffuse reflection direction, the diffuse incidence to the diffuse reflection direction and the diffuse incidence to the observation direction, and the proportion spectrum of the direct sky light and the scattered light along with the change of the wave band is combined to obtain the bi-directional reflectivity of the aquatic vegetation canopy in the whole wave band of 400-2500 nm;
step three: calculating the contribution of the specular reflection component of the water surface to the scene reflectivity according to the simplified Cox-Munk model and the Fresnel reflectivity; the specific calculation process is as follows:
the fluctuation degree of the water surface in the aquatic vegetation scene is small, and the Cox-Munk wave reflection model is simplified, so that the model is suitable for describing the reflectivity of the fluctuation water surface of the non-open water area in the aquatic vegetation scene, and the probability distribution function of the gradient is simplified into:
wherein Z is x And Z y For the gradient value, sigma is defined as a water surface roughness factor, and is used for describing the fluctuation degree of the water surface, and the relation between the fluctuation degree and the wind speed W is as follows:
the BRDF of the wave surface at the full wave band of 400-2500nm becomes:
where r (ω) is the Fresnel reflectivity at an angle of incidence ω, p is the slope probability distribution function, θ i 、θ r And theta n Zenith angles in normal directions of incident light rays, inclined surface elements and reflecting surface elements respectively;
step four: the underwater vegetation is regarded as a component part of a water body, the absorption and scattering coefficients of the water body and the underwater vegetation are calculated according to the Lee shallow water biological optical model and the SAILH model respectively, and the remote sensing reflectivity of an underwater medium is obtained by combining a soil layer under water; the specific calculation process is as follows:
the first step: the absorption and back scattering coefficients of the water body in the whole wave band of 400-2500nm are calculated, and the specific process is as follows:
wherein a is water Represents the absorption coefficient of water molecules, a NAP ,a ph ,a CDOM Respectively represent phytoplanktonAbsorption coefficients of (Phytoplankton), non-algae particles (Non-algae particulate matter, NAP) and soluble organics (Chromophoric Dissolved Organic Matter, CDOM), SPM represents the concentration of suspended matter in water, λ represents the wavelength, b water The scattering coefficient of water molecules is represented, T is a parameter representing the turbidity of the water body, C a Represents chlorophyll concentration;
and a second step of: calculating the absorption coefficient, the extinction coefficient, the attenuation coefficient and the scattering coefficient of the underwater vegetation in the whole wave band of 400-2500nm by referring to the second step;
and a third step of: calculating the absorption coefficient and the scattering coefficient of the underwater vegetation and water mixed medium:
X＝X c +F w X w (16)
wherein X represents a mixed medium, X c Corresponding to vegetation-only medium, X w Corresponding to the medium only containing water, F w The water body accounts for the volume proportion of the mixed medium; after the correlation coefficient of the underwater vegetation and the water body mixed medium is calculated, the remote sensing reflectivity at the water-gas interface under the optical shallow water condition can be expressed as:
wherein H is w Representing the depth of water, ρ b Representing the reflectivity of the underwater medium, and the analytic expressions of the other parameters are as follows
The irradiance reflectivity at the water-air interface can be obtained from the remote sensing reflectivity at the water-air interface under the optical shallow water condition:
r d ＝Q·r rs (19)
the empirical value of Q is pi; the BRDF for a water component can be expressed as:
wherein t represents the water surface transmissivity calculated by the Fresnel equation, and theta i ,θ r Representing the angle of incidence and angle of reflection, respectively, n w Representing the refractive index, γ is an empirical factor, typically 0.48;
step five: the components are coupled to contribute to obtain the scene two-direction reflectivity and the reflection spectrum of a single observation direction of the whole aquatic vegetation system.
Compared with the prior art, the invention has the advantages that:
(1) At present, most vegetation remote sensing reflection models are aimed at land vegetation scenes, the models of the aquatic vegetation reflection spectrum characteristics and the two-way reflection characteristics are fewer, and the spectrum simulation range which can be realized by the existing aquatic vegetation spectrum models is usually not more than 1000 nm.
(2) The sky incident radiation is divided into direct light and scattered light, the proportion of the sky direct light and the scattered light is regarded as parameters which dynamically change along with the wavelength by the model, and compared with the assumption that the traditional vegetation model is usually set to be a fixed value, the sky incident radiation is more in line with the real radiation transmission process, and the simulation precision of the model is greatly improved.
(3) The coupling model integrates a plurality of component modules, is careful and comprehensive in consideration of various parameters in the aquatic vegetation scene, can analyze the action mechanism of various input parameters in the scene radiation transmission process more fully compared with other models, and has important significance and action for fully understanding the interaction influence relationship among the aquatic vegetation, the water body components, the underwater medium, the vegetation canopy and the canopy components.
(4) The invention takes a land vegetation canopy radiation transmission model PROSAIL as a technical frame, carries out tight coupling integrated modeling on a water surface reflection and transmission process, an absorption and scattering process in a vegetation canopy, an absorption and scattering process of a water body component and a water bottom reflection process, and adopts a loose coupling parameter transmission modeling mode among different modules in the prior art.
(IV) description of the drawings
FIG. 1 is a flow chart of the present invention.
(fifth) detailed description of the invention
In order to better illustrate the modeling method for total reflection spectrum radiation transmission of the wetland aquatic vegetation canopy, the model is utilized to test and verify, and good effects are obtained, and the specific implementation method is as follows:
(1) Inputting biochemical parameters of the blade into a PROSPECT-PRO model to calculate to obtain reflectivity and transmissivity spectrum data of a single blade;
(2) Inputting vegetation canopy parameters, observation geometric parameters and blade anti-transmissivity into a SAILH model, and calculating by combining the proportion of direct sky light and scattered light along with the change of a wave band to obtain coefficients such as absorption, extinction, attenuation and scattering of a vegetation main body canopy, so as to obtain 4 reflection factors of the vegetation canopy, wherein the 4 reflection factors comprise a sun-to-observation direction, a sun-to-diffusion direction, a diffusion-to-diffusion direction and a diffusion-to-observation direction;
(3) Calculating the contribution of the specular reflection component of the water surface to the scene reflectivity according to the simplified Cox-Munk model and the Fresnel reflectivity;
(4) The underwater vegetation is regarded as a component part of a water body, the absorption and scattering coefficients of the water body and the underwater vegetation are calculated according to a Lee shallow water model and a SAILH model respectively, and the remote sensing reflectivity of an underwater medium is obtained by combining a soil layer under water;
(5) And integrating the contribution of the components to obtain the scene dichroism of the whole aquatic vegetation system.
Claims (1)
1. The modeling method for total reflection spectrum radiation transmission of the wetland aquatic vegetation canopy is characterized by comprising the following steps of:
step one: inputting biochemical parameters of aquatic vegetation leaves including chlorophyll, anthocyanin, carotenoid, brown pigment, leaf protein and other carbon-based component contents into a PROSPECT-PRO leaf radiation transmission model to calculate and obtain reflectance and transmittance spectrum data of 400-2500nm full wave bands of single leaves; the specific calculation process is as follows:
the blade is composed of N layers of the same type, and the layers are divided by N-1 layers of air; the first layer receives incident light at an angle of incidence alpha, the light wave being isotropic with ρ α Representing the reflectivity τ α Indicating transmittance; inside the blade, use ρ 90 And τ 90 Respectively representing the reflectivity and the transmissivity of each layer element in the blade; then the total reflectivity R of the N layers N,α And transmittance T N,α The method comprises the following steps:
step two: inputting structural parameters, incident illumination geometry, observation geometry parameters, a blade reflectivity spectrum and a transmittance spectrum of the aquatic vegetation canopy into a SAILH model, and calculating the ratio of direct sky light to scattered light along with the change of a wave band to obtain coefficients of absorption, extinction, attenuation, scattering and the like of the aquatic vegetation main canopy, so as to obtain 4 reflection factors of the vegetation canopy, wherein the 4 reflection factors comprise a solar-to-observation direction, a solar-to-diffuse reflection direction, a diffuse incidence-to-diffuse reflection direction and a diffuse incidence-to-observation direction of 400-2500nm full wave band; the calculation process of the proportion of the direct sky light and the scattered light along with the change of the wave band comprises the following steps:
first, a normalized diffuse direct spectrum in the 400-2500nm band is obtained, normalized direct and diffuse radiation P dir And P dif The following equation is satisfied:
wherein delta is i Representing the width of the spectral window; p (P) dir And P dif Two parameters, calculated from spectral albedo, are related as:
wherein omega i R is the albedo sd And R is dd E represents hemispherical reflectivity directly into the diffuse direction and diffuse into the diffuse direction, respectively s And e d Can be obtained by experimental measurement; after calculation of the normalized spectrum of diffuse and direct radiation, the diffusion ratio E dif And direct proportion E dir The method can be obtained by the following formula:
E dir ＝(1-c)P dir (6)
E dif ＝cP dif (7)
wherein c is a solar zenith angle theta s Related correction parameters:
c＝0.847-1.61sin(90-θ s )+1.04sin 2 (90-θ s ) (8)
the specific calculation process of the vegetation canopy correlation coefficient is as follows: the absorption, extinction, attenuation and scattering coefficients are subdivided into 10 parts according to the differences of the incident direction and the observation direction and the radiation type, and the parts are respectively: extinction coefficient k of solar incidence direction s Extinction coefficient k in observation direction o Diffuse radiation attenuation coefficient k d Scattering coefficient s of incident direction of sun so Scattering coefficient s of solar incident on upstream diffusion direction su Scattering coefficient s of the incident solar light on the downstream diffusion direction sd Scattering coefficient s of up-diffusion to observation direction uo Scattering coefficient s of down diffusion to observation direction do Scattering coefficient s of diffuse upward radiation to diffuse downward radiation ud Down diffuse radiation to the upper partScattering coefficient s of diffuse radiation du The expression for the ten parameters is:
wherein L' represents the relative leaf area index, ρ, τ represents the leaf reflectivity and transmittance, θ, respectively o ,θ s ,θ l Represents the observed zenith angle, solar zenith angle and leaf inclination angle, ψ is the relative azimuth angle, β 1 ,β 2 ,β 3 Is three azimuth parameters phi that can be obtained from a look-up table s ,φ o Is the critical angle for the case of incident angle and blade parallelism, expressed as:
the canopy scale parameters of the aquatic vegetation are combined to obtain 4 reflection factors of the sun to the observation direction, the sun to the diffuse reflection direction, the diffuse incidence to the diffuse reflection direction and the diffuse incidence to the observation direction, and the proportion spectrum of the direct sky light and the scattered light along with the change of the wave band is combined to obtain the bi-directional reflectivity of the aquatic vegetation canopy in the whole wave band of 400-2500 nm;
step three: calculating the contribution of the specular reflection component of the water surface to the scene reflectivity according to the simplified Cox-Munk model and the Fresnel reflectivity; the specific calculation process is as follows:
the fluctuation degree of the water surface in the aquatic vegetation scene is small, and the Cox-Munk wave reflection model is simplified, so that the model is suitable for describing the reflectivity of the fluctuation water surface of the non-open water area in the aquatic vegetation scene, and the probability distribution function of the gradient is simplified into:
wherein Z is x And Z y For the gradient value, sigma is defined as the water surface roughness factor and is used for describing the degree of fluctuation of the water surface and the relation with the wind speed WThe method comprises the following steps:
the BRDF of the wave surface at the full wave band of 400-2500nm becomes:
wherein r (Ω) is the fresnel reflectivity at an angle of incidence Ω, p is the gradient probability distribution function, θ i 、θ r And theta n The incident zenith angle, the reflecting zenith angle and the zenith angle in the normal direction of the inclined surface element are respectively;
step four: the underwater vegetation is regarded as a component part of a water body, the absorption and scattering coefficients of the water body and the underwater vegetation are calculated according to the Lee shallow water biological optical model and the SAILH model respectively, and the remote sensing reflectivity of an underwater medium is obtained by combining a soil layer under water; the specific calculation process is as follows:
the first step: the absorption and back scattering coefficients of the water body in the whole wave band of 400-2500nm are calculated, and the specific process is as follows:
wherein a is water Represents the absorption coefficient of water molecules, a NAP ,a ph ,a CDOM Representing the absorption coefficients of phytoplankton, non-algae particles and soluble organic matter, SPM representing the concentration of suspended matter in water, lambda representing the wavelength, b water Representing the scattering coefficient of water molecules, T represents the parameter of the turbidity of the water body, C a Represents chlorophyll concentration;
and a second step of: calculating the absorption coefficient, the extinction coefficient, the attenuation coefficient and the scattering coefficient of the underwater vegetation in the whole wave band of 400-2500nm by referring to the second step;
and a third step of: calculating the absorption coefficient and the scattering coefficient of the underwater vegetation and water mixed medium:
X＝X c +F w X w (16)
wherein X represents a mixed medium, X c Corresponding to vegetation-only medium, X w Corresponding to the medium only containing water, F w The water body accounts for the volume proportion of the mixed medium; after the correlation coefficient of the underwater vegetation and the water body mixed medium is calculated, the remote sensing reflectivity-under the water-gas interface under the optical shallow water condition is expressed as:
wherein H is w Representing the depth of water, ρ b Representing the reflectivity of the underwater medium, and the analytic expressions of the other parameters are as follows
The irradiance reflectivity at the water-air interface is obtained by the remote sensing reflectivity at the water-air interface under the optical shallow water condition:
r d ＝Q·r rs (19)
the empirical value of Q is pi; BRDF-for the water composition is therefore expressed as:
wherein t represents the water surface transmissivity calculated by the Fresnel equation, and n w Representing the refractive index of the water body, wherein gamma is an empirical coefficient, and is usually 0.48;
step five: and calculating to obtain the scene two-way reflectivity and the reflection spectrum of the single observation direction of the whole aquatic vegetation system.
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| CN103632040A (en) * | 2013-11-14 | 2014-03-12 | 北京航空航天大学 | Universal aquatic vegetation radiation transmission model |
| CN103630495A (en) * | 2013-11-13 | 2014-03-12 | 北京航空航天大学 | Aquatic vegetation-atmosphere coupling radiation transfer model |
| CN104699952A (en) * | 2015-01-29 | 2015-06-10 | 北京航空航天大学 | BRDF Monte Carlo model of wetland aquatic vegetation canopies |
| CN104699953A (en) * | 2015-01-29 | 2015-06-10 | 北京航空航天大学 | Geometrical optics model of wetland aquatic vegetations |
| CN112784416A (en) * | 2021-01-25 | 2021-05-11 | 北京航空航天大学 | Geometric optics-radiation transmission hybrid modeling method for row-seeding aquatic vegetation canopy reflection |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103630495A (en) * | 2013-11-13 | 2014-03-12 | 北京航空航天大学 | Aquatic vegetation-atmosphere coupling radiation transfer model |
| CN103632040A (en) * | 2013-11-14 | 2014-03-12 | 北京航空航天大学 | Universal aquatic vegetation radiation transmission model |
| CN104699952A (en) * | 2015-01-29 | 2015-06-10 | 北京航空航天大学 | BRDF Monte Carlo model of wetland aquatic vegetation canopies |
| CN104699953A (en) * | 2015-01-29 | 2015-06-10 | 北京航空航天大学 | Geometrical optics model of wetland aquatic vegetations |
| CN112784416A (en) * | 2021-01-25 | 2021-05-11 | 北京航空航天大学 | Geometric optics-radiation transmission hybrid modeling method for row-seeding aquatic vegetation canopy reflection |
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