Method and Model for Analyzing Urban Thermal Radiation Based on Sky View Factor

Abstract

The present disclosure provides a method for analyzing urban thermal radiation based on sky view factor, including: operation S10, calculating the urban surface emissivity based on different building components; operation S20, performing atmospheric correction on the in-pupil radiance and obtaining the atmospheric effect parameters; operation S30, obtaining the sky view factor of the urban area of different building components based on the solved DSM data; operation S40, pre-constructing an urban thermal radiation analysis model based on the sky view factor, taking the urban surface temperature, urban surface emissivity, urban sky view factor, and atmospheric effect parameters as input parameters, and calculating the satellite in-pupil urban radiance. It also provides an urban thermal radiation analysis model for executing the above urban thermal radiation analysis method, which is applicable to the analysis and correction of urban area thermal radiation of satellite or airborne remote sensing data.

Description

Technical Field

[0001] The present disclosure relates to the field of thermal infrared remote sensing technology, and in particular, to a method and model for analyzing urban thermal radiation based on sky view factor. Background Art

[0002] Urban surface temperature plays a crucial role in observing and understanding the energy exchange in the urban environment. Thermal infrared remote sensing is one of the most effective methods for obtaining surface temperature and surface emissivity at the regional or global scale. The radiance received by satellite thermal infrared sensors is an important physical quantity for retrieving surface temperature.

[0003] The urban underlying surface has a complex three-dimensional structure and radiation transfer process. For a flat surface, the radiance can be calculated from the material emissivity and surface temperature through the Planck function. However, due to the complex urban geometry and material composition, radiation transfer undergoes multiple scattering within the urban canopy with a three-dimensional structure, causing the urban component surfaces to absorb more energy than a two-dimensional plane, ultimately leading to an increase in the urban surface temperature. The thermal radiation of natural and urban surfaces has strong directional characteristics, usually expressed as a function of direction. The thermal anisotropy of the city is related to the complex urban surface geometry and the heterogeneity of material emissivity. The study of directional thermal radiation can be used to correct the angular effect of remote sensing urban surface temperature observations. A correct understanding of urban thermal radiation is beneficial to improving the accuracy of retrieving urban surface temperature and emissivity.

[0004] However, existing analytical models of urban thermal radiation still have technical problems such as the neglect of atmospheric effects in estimating urban radiance, the complexity of describing the thermal radiation transfer process within the urban canopy by urban three-dimensional structure parameters, and the unclear description of the surrounding environmental radiation. Summary of the Invention

[0005] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present disclosure provides a method and model for analyzing urban thermal radiation based on sky view factor.

[0006] To achieve the above object, the technical solution of the present disclosure is as follows:

[0007] According to an embodiment of one aspect of the present disclosure, a method for analyzing urban thermal radiation based on the sky view factor is provided, including: Operation S10: calculating the urban surface emissivity based on different building components; Operation S20: performing atmospheric correction on the in-pupil radiance and obtaining the atmospheric effect parameters; Operation S30: obtaining the sky view factor of the urban area of different building components based on the solved DSM data; Operation S40: pre-constructing an urban thermal radiation analysis model based on the sky view factor, using the urban surface temperature, urban surface emissivity, urban sky view factor, and atmospheric effect parameters as input parameters, and calculating the satellite in-pupil urban radiance.

[0008] According to an embodiment of the present disclosure, Operation S10 includes: obtaining satellite data of surface temperature, using the emissivity spectrum of urban building component materials, combining with the channel response function of the thermal infrared band of the satellite sensor, and performing convolution operation to obtain the surface emissivity of different building components in the city.

[0009] According to an embodiment of the present disclosure, Operation S10 further includes: assigning the average value of the channel equivalent emissivity of common building materials to the surface of different building components; different building components include roofs, walls, and ground.

[0010] According to an embodiment of the present disclosure, in Operation S20, according to the atmospheric profile data of the urban area and the channel response function of the thermal infrared band of the satellite sensor, perform atmospheric correction on the in-pupil radiance to obtain the atmospheric effect parameters.

[0011] According to an embodiment of the present disclosure, the atmospheric effect parameters include atmospheric transmittance, atmospheric upward radiance, and atmospheric downward radiance.

[0012] According to an embodiment of the present disclosure, Operation S30 includes: according to the DSM data solved from the satellite stereo image pair; using the sky view factor automatic calculation and processing software to process the input DSM data to obtain the sky view factor image.

[0013] According to an embodiment of the present disclosure, for high-spatial-resolution satellite thermal infrared remote sensing images, when the search radius is 10 pixels and the search direction is 32 azimuth angles, high-precision sky view factors can be obtained.

[0014] According to an embodiment of the present disclosure, the in-pupil urban radiance L i The calculation formula is expressed as: ;

[0015] where τ is the atmospheric transmittance; ε i is the emissivity of pixel i in the remote sensing image, ε w is the emissivity of the wall, B(T i ) is the blackbody radiance of pixel i; B(Twi ) is the blackbody radiation luminance of the wall adjacent to pixel i; SVF i is the sky view factor of pixel i; is the downward atmospheric radiation luminance, is the upward atmospheric radiation luminance.

[0016] According to the embodiments of the present disclosure, the sky view factors of urban areas with different building components describe the radiation component composition of each component receiving radiation from the surrounding environment, including multiple scattering between walls and the ground, between walls and walls, and between roofs and walls, which are respectively expressed as:

[0017] ;

[0018] ;

[0019] ;

[0020] ;

[0021] Among them, represents the radiation luminance emitted from the wall and finally received by the sensor after being reflected by the ground, represents the radiation luminance emitted from the ground and received by the sensor after being reflected by the wall, represents the radiation luminance emitted from the surrounding walls and received by the sensor after being reflected by the wall, represents the radiation transfer between the wall and the roof, B(T g ), B(T w ) and B(T r ) respectively represent the blackbody radiation luminance of the ground, wall and roof, ε g , ε w and ε r are the emissivities of the ground, wall and roof respectively, τ represents the atmospheric transmittance, m represents the total number of multiple scatterings, i represents the i-th scattering, SVF g represents the sky view factor of the ground, SVF w represents the sky view factor of the vertical wall, SVF r represents the sky view factor of the roof.

[0022] On the other hand, the present disclosure provides an urban thermal radiation analysis model for performing the urban thermal radiation analysis method described in any one of the above, which is applicable to the analysis and correction of urban area thermal radiation of satellite or airborne remote sensing data. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, the above and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0024] Figure 1 A flowchart of a method for analyzing urban thermal radiation based on the sky view factor is shown;

[0025] Figure 2 A flowchart of the method for operation S10 is shown. Detailed implementation manners

[0026] The present disclosure provides a method and model for analyzing urban thermal radiation based on the sky view factor. In the formula for calculating the urban radiance observed by a satellite, the atmospheric transmittance, the upward atmospheric radiation, and the downward atmospheric radiation are introduced, and based on the expression of the multiple scattering effect of the thermal radiation between components, a sky view factor is adopted, which simplifies the two sky view factors used in other existing studies.

[0027] The urban thermal radiation model is based on the radiation transfer theory. Based on factors such as the urban surface temperature, the surface emissivity, and the three-dimensional structure parameters, a formula for calculating the urban radiance applicable to satellite or airborne thermal infrared sensors is constructed. Yang Jinxin et al. proposed a urban emissivity model based on the sky view factor (UEM-SVF). The UEM-SVF model aims to improve the estimation accuracy of the emissivity in urban areas, especially in areas with complex geometric structures such as the urban canopy. This model is based on the sky view factor, which is a parameter describing the openness of a specific area and is closely related to the geometric characteristics of the urban structure. Different from traditional simplified models, the UEM-SVF model takes into account the multiple scattering and reflection in urban areas due to the complexity of the building structure, and these factors will affect the actual radiance of pixels.

[0028] The UEM-SVF model calculates the total radiance of a pixel through the following equation:

[0029] ;

[0030] where ε(i) is the surface material emissivity of pixel i, V(i,sky) is the sky view factor of pixel i, B(T s (i)) is the blackbody radiance of pixel i, M is the number of surrounding pixels, and V(i,p) and V(p,sky) are the view factors from pixel i to pixel p and from pixel p to the sky, respectively.

[0031] The UEM-SVF model uses the spectral emissivity data of impervious urban materials in the spectral library and the material spectral emissivity data in ASTER spectral library 2.0 to estimate the emissivity of materials in urban areas, which is one of the input parameters of the model. This model requires the use of airborne lidar data with high spatial resolution to calculate the ground-sky view factor in urban areas, and the view factor between the central pixel and adjacent pixels is calculated with the assistance of the geographic information data of urban buildings. For the sake of simplification, the UEM-SVF model only considers the interaction between the central pixel and the four adjacent pixels around it, and the single reflection between adjacent pixels. The following equations are used in the model to calculate the view factor between the central pixel and adjacent pixels:

[0032] ;

[0033] And the view factor blocked by pixel i itself:

[0034] .

[0035] The radiance estimation in the UEM-SVF model does not consider the atmospheric effects in actual measurements, namely atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation. This will undoubtedly cause a large deviation in the actual application of the model. (Reference: Jinxin Yang, Man Sing Wong, Massimo Menenti, Janet Nichol, Modeling the effective emissivity of the urban canopy using sky view factor, ISPRS Journal of Photogrammetry and Remote Sensing, Volume 105, 2015, Pages 211-219).

[0036] In this disclosure, an analytical method and model for urban thermal radiation based on the sky view factor (UTRAM-SVF) are proposed. The calculation formula of the satellite pupil radiance in the UTRAM-SVF model is as follows:

[0037] ;

[0038] In the formula, τ is the atmospheric transmittance, and are the downward atmospheric radiation and upward atmospheric radiation respectively. Among them, represents the radiation amount received and reflected by the surfaces of different urban building components from the downward atmospheric radiation. According to Kirchhoff's law, the emissivity is equal to the absorptivity, and for almost opaque building materials, the sum of the absorptivity and reflectivity is 1. Therefore, (1 - ε i) represents the reflectance of pixel i. Additionally, due to the influence of the three-dimensional structure within the urban canopy, the portion of the energy reflected from the surfaces of different components that is ultimately received by the sensor is limited by the view factor. Therefore, the radiation reflected from each component surface multiplied by the sky view factor of each component is the reflected downward longwave radiation.

[0039] In addition, Chen Shanshan et al. proposed a physical model (UCM-RT) for describing the thermal infrared radiation transfer process over urban surfaces. This model takes into account the multiple scattering effects within the urban building canopy and also considers the thermal radiation contributions from neighboring pixels and the atmosphere. The following is the construction process of the UCM-RT model:

[0040] The UCM-RT model is based on the assumption that the urban surface has a three-dimensional structure, different from the conventional thermal radiation transfer models that only consider planar natural surfaces. The model incorporates the multiple scattering effects within the urban building canopy. In urban areas, due to the dense arrangement of buildings, thermal radiation is reflected and scattered multiple times between building surfaces, which affects the ultimately observed thermal radiation intensity. The UCM-RT model considers the influence of the thermal radiation from neighboring pixels on the central pixel. This influence is quantified by the sky view factor (SVF), which describes the amount of radiation received by a pixel from the sky. In addition, UCM-RT takes into account the influence of the atmosphere on thermal radiation, including the downward and upward longwave radiation of the atmosphere. These atmospheric effects will change the observed thermal radiation intensity. The model is based on thermal infrared data and relates the observed radiance to factors such as urban surface temperature, material emissivity, sky view factor, and atmospheric transmission. Based on the above considerations, it can be expressed as:

[0041] ;

[0042] where L toa is the observed thermal infrared radiance, is the equivalent emissivity of the urban canopy, B(T s ) is the Planck blackbody radiation function, R adj is the radiation scattered by neighboring pixels, SVF adj is the sky view factor of neighboring pixels, and are the downward and upward longwave radiation of the atmosphere respectively, and τ is the total transmittance of the atmosphere. The UCM-RT model assumes that urban pixels are homogeneous and that reflection and scattering occur within a single pixel. The channel equivalent emissivity of urban pixel i can be defined as:

[0043] ;

[0044] where SVF in is the sky view factor within the pixel, ε i(i) is the material emissivity of urban pixel i in channel i.

[0045] In the UCM-RT model, data from four thermal infrared channels of the visible and infrared multispectral sensor carried by the GF-5 satellite are used, with a spatial resolution of 40 meters. High-resolution GF-2 satellite visible light data with a spatial resolution of 1 meter is used for land use and land cover classification. The Chinese Resources Satellite-3 mapping satellite provides stereo image pairs for generating the digital surface model (DSM), and these data are used to calculate the sky view factor (SVF). The Global Forecast System NCEP is used to obtain urban atmospheric profile data, and an atmospheric radiation transfer model is used to simulate the atmospheric transmission of the GF-5 thermal infrared channels to obtain atmospheric parameters (such as atmospheric transmittance, etc.). The ASTER spectral library is used in the UCM-RT model to determine the spectral emissivity of different urban surface materials.

[0046] Although the above UCM-RT model has a relatively accurate theoretical description in the use of thermal infrared data with a 30-meter spatial resolution, its computational complexity is relatively large, especially the need to calculate two sky view factors, namely SVF in and SVF adj . And, the R adj representing the surrounding environmental radiation is replaced by the average radiation brightness of adjacent areas. This assumption will undoubtedly also bring certain errors for considering the urban heat radiation transfer process with higher spatial resolution.

[0047] Due to the technical problems existing in the above prior art, the present disclosure provides a method and model for analyzing urban heat radiation based on the sky view factor.

[0048] To make the purpose, technical solution and advantages of the present disclosure clearer and more understandable, the following further details the present disclosure in combination with specific embodiments and with reference to the accompanying drawings.

[0049] In the embodiments of the present disclosure, as Figure 1 and Figure 2 shown, a method for analyzing urban heat radiation based on the sky view factor is provided, including:

[0050] Operation S10, calculating the urban surface emissivity based on different building components;

[0051] Operation S20, performing atmospheric correction on the pupil radiance and obtaining atmospheric effect parameters;

[0052] Operation S30, obtaining the urban area sky view factor of different building components based on the solved DSM data;

[0053] Operation S40: Based on the sky view factor, pre-construct an analytical model for urban thermal radiation. Using the urban surface temperature, urban surface emissivity, urban sky view factor, and atmospheric effect parameters as input parameters, calculate the satellite in-pupil urban radiance.

[0054] In operation S10, obtain satellite surface temperature data. Using the emissivity spectra of materials in the ASTER spectral library and combining with the sensor channel response function, calculate the urban surface emissivity.

[0055] In operation S20, use the atmospheric radiative transfer model to perform atmospheric correction on the in-pupil radiance to obtain the atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation radiance.

[0056] In operation S30, according to the DSM data solved by the satellite, use the sky view factor automatic calculation software to process and obtain the urban area sky view factor.

[0057] In operation S40, according to the pre-constructed analytical model for urban thermal radiation based on the sky view factor, use the above data as input parameters to calculate the urban in-pupil radiance.

[0058] Through the embodiments of the present invention, according to the emissivity of different urban building components, urban surface temperature, sky view factors of each urban area, and atmospheric parameters solved by the atmospheric radiative transfer model, the estimation of urban in-pupil radiance can be realized.

[0059] In this embodiment, a satellite surface temperature product with high spatial resolution is used as the data source of urban surface temperature, such as the Landsat 8 satellite surface temperature product with a spatial resolution of 30 meters. Specifically, select the surface temperature product without cloud cover to prevent the lack of surface temperature data in some urban areas caused by cloud cover.

[0060] The present invention introduces the atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation into the formula for calculating the urban radiance observed by the satellite, and based on the expression of the multiple scattering effect of thermal radiation between components, adopts a sky view factor, simplifying the two sky view factors used in existing other studies.

[0061] According to Planck's blackbody radiation law, the radiance of a blackbody can be expressed as:

[0062] ;

[0063] In the formula, C 1 and C 2 are Planck constants, C 1 = 1.191×108 W / (m 2 ∙sr∙μm -4 ), C 2= 1.439×104 μm∙K, where T is the temperature in Kelvin (K) and λ is the wavelength in micrometers (μm). The emissivity of an object is defined as the ratio of its radiance to that of a blackbody at the same temperature and can be expressed as:

[0064] ;

[0065] where R(λ, T) is the radiance of the material surface, B(λ, T) is the blackbody radiance of the material surface, and ε λ is the emissivity of the material surface at wavelength λ. The construction process of the urban thermal radiation analysis model based on the sky view factor is as follows:

[0066] First, the surface thermal radiation is divided into two parts: direct emitted radiation and reflected emitted radiation from other surfaces (i.e., multiple scattering). Therefore, the total surface radiance can be expressed as:

[0067] ;

[0068] where f i (θ) is the proportion of target i in the field of view when the observation zenith angle is θ, L dir and L multi are the direct emitted radiance and reflected radiance of the surface respectively, and n represents the total number of component surfaces within the pixel. Therefore, the total radiance of each component surface in the city can be expressed as:

[0069] ;

[0070] represents the radiation emitted from the wall, which is reflected by the ground and finally received by the sensor, resulting in an increase in the radiance of the ground. Similarly, and represent the radiation emitted from the ground and surrounding walls respectively, which is reflected by the wall and then received by the sensor. Finally, represents the radiation transfer between the wall and the roof. The direct radiance of each component surface in the city can be expressed as:

[0071] ;

[0072] where ε g , ε w and ε r are the emissivities of the ground, wall, and roof respectively. τ is the atmospheric transmittance. B(T g ), B(T w ) and B(T r ) represent the blackbody radiances of the ground, wall, and roof respectively. First, for the ground radiance component, the radiation emitted from the wall and first reflected by the ground can be expressed as:

[0073] ;

[0074] In the formula, SVF g represents the sky view factor of the ground. According to Kirchhoff's law, (1 - ε w ) and (1 - ε g ) represent the reflectivities of the wall and the ground respectively. After m reflections between the ground and the wall, the radiance can be expressed as:

[0075] ;

[0076] Then the total reflected radiance can be expressed as follows:

[0077] ;

[0078] Furthermore, the radiation component of the wall can be divided into two parts. One part is the radiance reflected by the wall after the ground emits radiation. The radiance of the first reflection can be expressed as:

[0079] ;

[0080] Similarly, the radiance after m reflections can be expressed as:

[0081] ;

[0082] The other part is the radiance reflected by the wall after the rest of the walls emit radiation. The radiance of the first reflection can be expressed as:

[0083] ;

[0084] In the formula, SVF w represents the sky view factor of the vertical wall, and its calculation formula is as follows:

[0085] ;

[0086] In the formula, λ p is the plane area index, and λ f is the wall area index. The multiple scattering between the walls can finally be expressed as:

[0087] ;

[0088] In addition, the first scattering process between the roof and the wall can be expressed as:

[0089] ;

[0090] In the formula, SVF rRepresents the sky view factor of the roof. The sum of the radiation reflected by the roof from the wall emission can be expressed as:

[0091] ;

[0092] Among them, the downward atmospheric radiation also belongs to a part of the environmental radiation and affects the radiation brightness received by the sensor. The expression for the reflection of the downward atmospheric radiation by the surfaces of each component in the city is:

[0093] ;

[0094] In the formula, i represents the surface components of the city (including the roof, wall, and ground). In addition, the upward atmospheric radiation is directly received by the sensor. Therefore, the radiance at the entrance pupil can be expressed as:

[0095] ;

[0096] For satellite or airborne thermal infrared remote sensing in the nadir observation mode, this model can be adjusted and expressed as:

[0097] ;

[0098] In the formula, τ is the atmospheric transmittance, ε i represents the emissivity of pixel i, ε w is the emissivity of the wall, T i and T wi represent the surface temperatures of pixel i and the wall of the adjacent pixel respectively, T wi can be approximately replaced by the average temperature of the roof and ground adjacent to pixel i, SVF i represents the sky view factor of pixel i, B(T i ) is the blackbody radiance of pixel i; B(T wi ) is the blackbody radiance of the wall adjacent to pixel i; is the downward atmospheric radiance, is the upward atmospheric radiance.

[0099] As Figure 2 shown, in this embodiment, the calculation of the surface emissivity of the city in the above operation S10 may include operations S11 to S12.

[0100] Operation S11: Select the thermal infrared band emissivity of common building materials in the ASTER 2.0 emissivity spectral library of ground objects, select the spectral emissivity of common building materials in the range of 8 - 14 μm, such as asphalt, ceramics, cement, concrete, red bricks, and glass, etc., and then combine with the channel response function of the thermal infrared band of the satellite sensor, and adopt convolution operation to obtain the channel equivalent emissivity of the ground object.

[0101] In this embodiment, the channel equivalent emissivity ε i has the following convolution operation formula:

[0102] ;

[0103] where λ 1 and λ 2 are respectively the starting and ending wavelengths of the band, f(λ) represents the channel response function of the thermal infrared band of the sensor, and ε(λ) represents the spectral emissivity of the ground object.

[0104] In operation S12, according to the urban building surface classification data, the average value of the channel equivalent emissivity of common building materials is respectively assigned to each component surface, including the roof, wall, and ground.

[0105] In the above operation S20, using the atmospheric radiative transfer model, based on the atmospheric profile data of the urban area and the channel response function of the thermal infrared band of the satellite sensor, the atmospheric correction of the in-pupil radiance is performed to obtain the atmospheric transmittance, the upward atmospheric radiation, and the downward atmospheric radiance. In addition, if there is no timely atmospheric profile data, the user can use the reanalysis atmospheric profile data, such as the data of the National Centers for Environmental Prediction (NCEP) of the United States and the data of the European Center for Medium-Range Weather Forecasts (ECMWF).

[0106] In operation S30, according to the digital surface model (DSM) data obtained by resolving the satellite stereo image pair, using the sky view factor automatic calculation and processing software, the input DSM image is processed to obtain the sky view factor (SVF) image. The sky view factor automatic calculation and processing software needs to select the vertical scaling factor, the search radius, the total number of search directions, etc. Among them, for high-spatial-resolution thermal infrared remote sensing images, when the search radius is 10 pixels and the search direction is 32 azimuth angles, a relatively high-precision sky view factor can be obtained. In addition, the scaling factor can be default selected as 1.

[0107] In operation S40, according to the established urban thermal radiation analysis model based on the sky view factor, using the urban surface temperature, the urban component surface emissivity, the urban sky view factor, and the atmospheric parameters (atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation) as input parameters, the in-pupil urban radiance of the satellite is calculated. Specifically, the formula for calculating the urban radiance in the above operation is expressed as:

[0108] ;

[0109] wherein, L i is the radiance of the incoming pupil urban radiation; τ is the atmospheric transmittance in the thermal infrared band calculated by the atmospheric radiative transfer model; ε i is the emissivity of pixel i in the remote sensing image, which is obtained by convolving the thermal infrared emissivity spectrum in the ASTER 2.0 land cover emissivity spectral library and the sensor channel response function; B(T i ) is the blackbody radiance of pixel i, that is, the radiance of the blackbody under the same temperature condition as pixel i, which is calculated by Planck's blackbody radiation law; B(T wi ) is the blackbody radiance of the wall adjacent to pixel i, and the surface temperature of the wall can be replaced by the average value of the temperatures of the pixels adjacent to pixel i; SVF i is the sky view factor of pixel i; and are the downward atmospheric radiation and the upward atmospheric radiance respectively, which are also calculated by the atmospheric radiative transfer model.

[0110] In the present invention, the UTRAM-SVF model starts from the thermal radiation transfer on the surface of urban components, and based on the sky view factors of different components, describes the composition of the radiation components received by each component from the surrounding environment radiation, including multiple scattering between the wall and the ground, between the wall and the wall, and between the roof and the wall, and is expressed as:

[0111] ;

[0112] ;

[0113] ;

[0114] ;

[0115] wherein, represents the radiance of the radiation emitted from the wall, reflected by the ground and finally received by the sensor, represents the radiance of the radiation emitted from the ground, reflected by the wall and then received by the sensor, represents the radiance of the radiation emitted from the surrounding walls, reflected by the wall and then received by the sensor, represents the radiation transfer between the wall and the roof, B(T g ), B(T w ) and B(T r ) represent the blackbody radiances of the ground, the wall and the roof respectively, ε g , ε w and ε rThey are the emissivities of the ground, wall, and roof respectively. τ represents the atmospheric transmittance, m represents the total number of multiple scatterings, i represents the i-th scattering, and SVF g represents the sky view factor of the ground, SVF w represents the sky view factor of the vertical wall, SVF r represents the sky view factor of the roof. Physically, it is clearer than the UCM-RT model. In addition, when this invention is applied in the mode of satellite nadir observation, only the sky view factor SVF of the pixel is used i , which simplifies the calculation of the two sky view factors required in the UCM-RT model. This makes the model more convenient to apply. As can be seen from the above, the key point of this disclosure is to construct the calculation expressions for the multiple scattering and reflection of thermal radiation between the surfaces of various components inside the urban canopy. The analysis of the radiance components on the surfaces of various components can help to more accurately retrieve the three-dimensional surface temperature of the city subsequently.

[0116] This invention is applicable to the thermal radiation correction of urban areas in satellite or airborne remote sensing data. Taking the application of the satellite remote sensing platform as an example:

[0117] (1) First, obtain the atmospheric profile information in the region using a radiosonde balloon or from the ERA5 atmospheric profile reanalysis data, and then perform atmospheric correction using an atmospheric radiative transfer model to calculate the atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation.

[0118] (2) Then, calculate the sky view factor SVF of the urban area based on the ground digital surface model DSM data solved from the satellite stereo image.

[0119] (3) Secondly, obtain the spectral emissivities of common building materials from the NASA ASTER spectral library, and perform convolution operation with the spectral response function of the thermal infrared channel of the sensor on the satellite to obtain the equivalent emissivity of the ground object.

[0120] (4) Then download the high-spatial-resolution remote sensing land surface temperature product of the study area, with a spatial resolution of at least 30 meters, to ensure that the land surface temperature is close to the surface temperature of urban building components.

[0121] (5) Input the target parameters obtained in the above steps into the UTRAM-SVF model of this invention, and then the on-orbit radiance of the urban area can be recalculated to complete the radiation correction of the geometric effect of the urban area, providing a better solution for the remote sensing inversion of the land surface temperature of the urban area.

[0122] This disclosure also provides an urban thermal radiation analysis model for performing any one of the above urban thermal radiation analysis methods, which is applicable to the analysis and correction of urban area thermal radiation in satellite or airborne remote sensing data.

[0123] So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that, in the accompanying drawings or the main text of the specification, the implementation manners that are not depicted or described are all forms known to those of ordinary skill in the art, and no detailed description is provided. In addition, the definitions of the above-mentioned various elements and methods are not limited to the specific structures, shapes, or manners mentioned in the embodiments, and those of ordinary skill in the art can make simple changes or substitutions thereto.

[0124] Based on the above description, those skilled in the art should have a clear understanding of the urban thermal radiation analysis method and model of the present disclosure based on the sky view factor.

[0125] In summary, the present disclosure provides an urban thermal radiation analysis method and model based on the sky view factor. The present invention makes up for the deficiencies in the previous urban thermal radiation models, including considering the reflection of the atmospheric effect on the urban underlying surface, and constructing an expression for the multiple reflection and scattering process of the thermal radiation between the surfaces of the components inside the urban canopy based on the radiation transfer theory. In the observation of satellite thermal infrared sensors, the atmospheric effect includes atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation, and these atmospheric effects will change the observed thermal radiation intensity. Ignoring the atmospheric effect may cause a large error in the model when evaluating urban thermal radiation, thereby affecting the actual application effect of the model. The present invention focuses on considering the downward atmospheric radiation reflected by the surfaces of each component in the city, and introduces the sky view factor of the component in this process. In the present invention, an atmospheric radiation transfer model is adopted to perform atmospheric correction on the in-pupil radiance according to the atmospheric profile data of the urban area and the channel response function of the thermal infrared band of the satellite sensor, so as to obtain the atmospheric transmittance, upward atmospheric radiation, and downward atmospheric radiation brightness.

[0126] In addition, the present invention constructs an expression for the multiple reflection process of the thermal radiation between the surfaces of urban components, so that on the basis of high-spatial-resolution (meter-level) thermal infrared data, the influence of the surrounding environmental radiation on the target pixel can be more accurately reflected, thereby improving the estimation accuracy of urban thermal radiation at high spatial resolution.

[0127] It should be noted that, in this article, unless otherwise specified, an element with "one" does not mean that there is only one such element, but may have one or more such elements.

[0128] In addition, in this article, unless otherwise specified, ordinal numbers such as "first" and "second" are only used to distinguish multiple elements with the same name, and do not indicate that there is a rank, level, execution order, or process order between them. A "first" element and a "second" element may appear in the same component together, or appear in different components respectively. The existence of an element with a larger ordinal number does not necessarily mean the existence of another element with a smaller ordinal number.

[0129] In this text, unless otherwise specified, the so-called feature A “or” (or) or “and / or” (and / or) feature B means that A exists alone, B exists alone, or A and B exist simultaneously; the so-called feature A “and” (and) or “and” (and) or “and” (and) feature B means that A and B exist simultaneously; the so-called “comprising”, “including”, “having”, “containing” mean including but not limited to this.

[0130] In addition, in this text, terms such as “upper”, “lower”, “left”, “right”, “front”, “rear”, or “between” are only used to describe the relative positions between multiple components, and in the interpretation can be extended to include cases of translation, rotation, or mirror image. In addition, in this text, unless otherwise specified, the statement “a component is on another component” or a similar statement does not necessarily mean that the component contacts the other component.

[0131] In addition, unless the steps are specifically described or must occur in sequence, the order of the above steps is not limited to those listed above, and can be changed or rearranged according to the required design. And the above embodiments can be used in combination with each other or in combination with other embodiments based on considerations of design and reliability, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0132] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not used to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A method for analyzing urban thermal radiation based on sky visibility factors, comprising: Operation S10, calculating urban surface emissivity based on different building components; Operation S20, performing atmospheric correction on the entrance pupil radiance and obtaining atmospheric effect parameters; Operation S30, obtaining sky visibility factors of urban areas of different building components based on the solved DSM data; Operation S40, pre-constructing an urban thermal radiation analytical model based on a sky visibility factor, taking urban surface temperature, urban surface emissivity, urban sky visibility factor, and atmospheric effect parameters as input parameters, and calculating the satellite entrance pupil urban radiation brightness; Entrance pupil urban radiance L i The calculation formula is expressed as: ； Where τ is the atmospheric transmittance; ε i is the emissivity of pixel i in the remote sensing image, ε w is the emissivity of the wall, B(T i ) is the blackbody radiation brightness of pixel i; B(T wi ) is the blackbody radiation brightness of the wall adjacent to pixel i; SVF i is the sky visibility factor of pixel i; is the atmospheric downwelling radiance, is the atmospheric upward radiance.

2. According to the urban thermal radiation analysis method of claim 1, operation S10 comprises: The surface temperature satellite data is obtained, the emissivity spectrum of urban building component materials is used, combined with the channel response function of the thermal infrared band of the satellite sensor, and the convolution operation is used to obtain the surface emissivity of different building components in the city.

3. The urban thermal radiation analysis method according to claim 2, wherein operation S10 further comprises: Take the average value of the channel equivalent emissivity of common building materials and assign it to the surfaces of different building components; The different building components include roofs, walls and floors.

4. According to the urban thermal radiation analysis method of claim 1, in operation S20, atmospheric correction is performed on the entrance pupil radiation brightness according to the atmospheric profile data of the urban area and the channel response function of the thermal infrared band of the satellite sensor to obtain the atmospheric effect parameters. 5 . The urban thermal radiation analysis method according to claim 4 , wherein the atmospheric effect parameters include atmospheric transmittance, atmospheric upward radiation brightness, and atmospheric downward radiation brightness.

6. The urban thermal radiation analysis method according to claim 1, wherein operation S30 comprises: DSM data obtained by solving satellite stereo image pairs; The sky visible factor automatic calculation and processing software is used to process the input DSM data to obtain the sky visible factor image.

7. According to the urban thermal radiation analysis method described in claim 6, for high spatial resolution satellite thermal infrared remote sensing images, when the search radius is 10 pixels and the search direction is 32 azimuth angles, a high-precision sky visibility factor can be obtained.

8. According to the urban thermal radiation analysis method of claim 3, the urban area sky visibility factors of different building components describe the radiation component composition of each component from the surrounding environment, including multiple scattering between the wall and the ground, between the wall and the wall, and between the roof and the wall, respectively expressed as: ； ； ； ； in, It represents the radiation emitted from the wall, which is reflected by the ground and finally received by the sensor. It represents the radiation emitted from the ground, reflected by the wall and then received by the sensor. It represents the radiation emitted by the surrounding walls, which is reflected by the walls and then received by the sensor. represents the radiation transfer between the wall and the roof, B(T g ), B(T w ) and B(T r ) represent the blackbody radiation brightness of the ground, wall and roof, ε g , ε w and ε r are the emissivity of the ground, wall and roof respectively, τ represents the atmospheric transmittance, m represents the total number of multiple scatterings, i represents the i-th scattering, and SVF g Represents the sky visibility factor at the ground, SVF w Represents the sky visibility factor of the vertical wall, SVF r Represents the sky visibility factor of the roof.

9. An urban thermal radiation analysis model for executing the urban thermal radiation analysis method according to any one of claims 1 to 8, suitable for analyzing and correcting urban area thermal radiation from satellite or airborne remote sensing data.

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