On-orbit radiometric calibration method of optical satellite camera based on multi-linear ground features

Abstract

The invention discloses an in-orbit radiometric calibration method of an optical satellite camera based on multi-linear ground features, and belongs to the technical field of optical remote sensing. According to the method, multi-linear ground objects such as multiple gray scale targets with different reflectivity or multiple reflection point sources with different brightness levels are used as detection references, and the reflectivity of the ground objects, the atmospheric optical thickness and the diffuse radiation / total radiation ratio are measured on site. And separating the linear ground object reflection radiation response from the atmospheric path radiation and earth-gas coupling radiation response by utilizing linear regression calculation, thereby realizing the on-orbit radiation calibration of the optical satellite camera. According to the in-orbit radiometric calibration method, ground actual measurement data is used as a main part, aerosol scattering hypothesis in radiation transmission calculation is replaced, the influence of factors such as an aerosol model and an atmospheric mode on in-orbit calibration is reduced, the calibration process is simplified, the in-orbit radiometric calibration precision is improved, optical satellite camera response linear and dynamic range detection is achieved, and the in-orbit radiometric calibration accuracy is improved. And high-precision, high-frequency and full-dynamic-range business mobile calibration can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical remote sensing, and mainly to an on-orbit radiation calibration method for an optical satellite camera based on multi-linear objects. Background Art

[0002] Remote sensing images obtained by optical satellite remote sensing can clearly express the spatial structure and surface texture characteristics of objects, provide conditions and basis for effective interpretation and analysis, and have very broad application prospects in many fields of national economy such as natural resource survey, ecological environment monitoring, urban planning and construction. However, the biophysical parameters and environmental system evolution of objects observed by satellite remote sensing are directly related to the radiation response of remote sensors. Therefore, the radiation calibration accuracy of optical satellite sensors during on-orbit operation directly affects the quantitative application of satellite remote sensing information.

[0003] The reflectivity-based method and irradiance-based method of on-orbit radiation calibration are both single-point (radiance) calibration methods, and both require a large-area radiation correction field and sensor dark current measurement (or cold air measurement). The only difference is that the irradiance-based method adds the measurement of the ratio of diffuse radiation to total radiation, thereby reducing the uncertainty caused by the assumption of aerosol scattering characteristics in the reflectivity-based method. The alternative calibration method based on a large-area uniform field has high requirements for site reflectivity. When the reflectivity is low, it is necessary to extrapolate to obtain a radiance higher than the uniform field reflectivity. When the reflectivity is high, it is necessary to interpolate to obtain the unknown radiation. Therefore, the radiation calibration based on a large-area uniform field has a great impact on its accuracy. At present, the on-orbit calibration accuracy is about 5-8%, and it is difficult to achieve high-precision calibration within the full dynamic range of optical satellite cameras.

[0004] With the increasing spatial resolution of optical satellite cameras, the spatial uniformity and Lambertian properties of large-area radiation correction fields cannot meet the application requirements of high-precision calibration. The increase in optical remote sensing satellite constellations has improved the temporal resolution, but the radiation correction sites are few and single, the calibration cycle is long and easily affected by weather conditions, which makes the calibration efficiency based on large-area radiation correction fields low. It is required that the detection reference objects for optical satellite camera radiation calibration have higher optical stability, mobility and spatiotemporal adaptability. The existing on-orbit radiation calibration technology is difficult to meet the high-precision commercial calibration needs within the full dynamic range of my country's optical satellite cameras.

[0005] The improvement of spatial resolution of optical satellite cameras allows linear objects with good spectral flatness, spatial uniformity and approximate Lambertian properties to be used as detection references for on-orbit radiometric calibration of the full dynamic range of optical satellite cameras. NASA has achieved radiometric calibration of the full dynamic range of satellite-borne optical cameras using artificial targets with excellent optical properties. However, the traditional calibration method based on radiation transfer calculation requires assumptions about the aerosol scattering characteristics of the field and the reflectivity of the surrounding background environment, which is difficult to match the actual situation, especially under complex background conditions. Summary of the invention

[0006] (I) Purpose of the invention

[0007] The purpose of the present invention is to make up for the defects of the existing technology and provide an on-orbit radiation calibration method for optical satellite cameras based on multi-linear objects. The on-orbit radiation calibration method of the present invention is based on ground measured data, replacing the aerosol scattering assumption in the radiation transmission calculation, reducing the influence of factors such as aerosol models and atmospheric patterns on on-orbit calibration, simplifying the calibration process and improving the accuracy of on-orbit radiation calibration. This calibration method can not only realize the response linearity and dynamic range detection of optical satellite cameras, but also realize its high-precision, high-frequency, fully dynamic and operational mobile calibration.

[0008] (II) Technical solution

[0009] The present invention is implemented by the following technical solution: an on-orbit radiometric calibration method for an optical satellite camera based on multilinear objects, comprising the following steps:

[0010] Step 1: According to the altitude, temperature, humidity, pressure and wind meteorological parameters and background environmental parameter information of the radiation calibration site, the atmospheric transmittance calculated by the radiation transmission code MODTRAN or 6S is successively approximated to the channel atmospheric transmittance of the sun-multilinear feature path measured by the sun photometer, and then the hyperspectral atmospheric transmittance of the solar illumination path is obtained. Based on this, the geometric relationship between solar illumination and satellite observation is used to change the geometric factor in the radiation transmission code, and the hyperspectral atmospheric transmittance of the satellite camera observation path is calculated;

[0011] Step 2: Multiply the extra-atmospheric solar constant with the calculated atmospheric transmittance of the solar path and the diffuse / total radiation ratio to obtain the total radiance of the sun irradiating the ground. Then, combine the spectral response function of the satellite camera, the multilinear object reflectivity, the calculated atmospheric transmittance of the satellite camera observation path and the total ground radiance to obtain the entrance pupil radiance reflected by the multilinear object to the optical satellite camera.

[0012] Step 3: By setting multilinear objects with different reflectivity and counting the remote sensing image values ​​of multilinear objects, the influence of atmospheric radiation and ground-atmosphere coupled radiation is deducted through linear regression calculation to obtain the radiation response value of the multilinear object. Then, the entrance pupil radiance reflected by the multilinear object to the optical satellite camera and the radiation response value of the multilinear object are calculated according to the calibration equation of the optical satellite camera to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear object. At this point, the full dynamic range radiation calibration of the optical satellite camera in the working state is realized.

[0013] Furthermore, according to the radiation transfer theory, under plane-parallel atmospheric conditions, for the ground reference of multi-linear objects, the entrance pupil radiance of the optical satellite camera is expressed as:

[0014]

[0015] Where L is the entrance pupil radiance of the satellite camera, L a is the atmospheric radiation, E s is the solar constant, μ s is the solar zenith angle θ s The cosine factor, T gas is the atmospheric absorption transmittance, τ is the atmospheric optical thickness, t d (θ s ) is the downward atmospheric scattering transmittance, S is the albedo of the large balloon surface, ρ e is the background reflectivity, ρ t is the reflectivity of the multilinear feature, μ v is the cosine factor of the satellite observation zenith angle, θ v is the satellite observation zenith angle, t' d (θ v ) is the upward atmospheric scattering transmittance, α(θ s ) is the ratio of sky diffuse radiation to global radiation in the direction of solar incidence;

[0016] If the background reflectivity within the multi-linear object layout area is constant, the total ground illumination in the calibration area remains unchanged, the atmospheric radiation above the multi-linear object is the same as the ground-air coupling radiation, and the entrance pupil radiance of the optical satellite camera is rewritten as:

[0017] L=Aρ t +B=L t +B (2)

[0018] Where A is the entrance pupil radiance reflected by the ideal linear object to the optical satellite camera, that is:

[0019]

[0020] B is the sum of the atmospheric radiation and the ground-air coupled radiation, that is:

[0021]

[0022] The optical satellite camera observes and images the multi-linear objects on the ground within a certain area. At this time, the atmospheric path radiation, optical thickness, transmittance and spherical albedo, diffuse / total radiation ratio, and solar constant parameters are all fixed values. Therefore, A and B expressed by formula (3) and formula (4) are also fixed values. According to formula (2), the optical satellite camera entrance pupil radiance L and the reflectivity ρ of the multi-linear objects are obtained. t It is a univariate linear relationship. Therefore, by setting multilinear objects with different reflectivities or different energy levels within the dynamic range of the remote sensor, different multilinear object response values ​​can be obtained in the optical satellite image. Linear regression is performed on the multilinear objects with different reflectivities and their remote sensing image response values ​​to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects. Specifically, according to the optical satellite camera calibration equation (5), combined with the remote sensing image count values ​​of the multilinear objects and different reflectivities, the multilinear objects with different reflectivities and the count values ​​of the remote sensing images of the multilinear objects with different reflectivities are linearly regressed to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects:

[0023]

[0024] Among them, L epu,i is the entrance pupil equivalent radiance of the i-th channel of the satellite remote sensor, R i (λ) is the spectral response function of the i-th channel of the satellite remote sensor, A gain,i is the responsivity calibration coefficient of the i-th channel of the satellite remote sensor, DN i is the response value of the remote sensor channel i to multilinear objects, DN 0,i is the dark current response value of the i-th channel of the satellite remote sensor.

[0025] Further, the following steps are included:

[0026] (I) When the multilinear reflectivity ρ in the i-th channel of the optical satellite camera t = 0, which is equivalent to the optical satellite camera not setting up multi-linear objects in the ground observation area, that is, the optical satellite camera observes the background of the field area and images it. According to formula (2), the entrance pupil radiance of the satellite remote sensor L = B. At this time, the image count value is the intercept of the linear regression of the calibration equation.

[0027]

[0028] (II) When the multilinear ground reflectivity ρ in the i-th channel of the optical satellite camera tWhen ≠0, it is equivalent to the optical satellite camera setting up multiple linear objects with different reflectivity or different energy levels in the ground observation area, that is, the optical satellite camera observes and images the multiple linear objects in the field area. According to formula (2), the entrance pupil radiance of the satellite remote sensor is L = L t +B, then according to formula (5):

[0029]

[0030] According to formulas (6) and (7), linear regression is performed on the response values ​​of multilinear objects with different reflectivity or different energy levels and remote sensing images of multilinear objects with different reflectivity to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects:

[0031]

[0032] Furthermore, the multilinear feature reflectivity ρ t The atmospheric optical thickness τ is measured by the sun photometer, and the sky diffuse radiation / total radiation ratio α (θ s ) is measured by a spectroradiometer.

[0033] Furthermore, the It is obtained by performing linear regression calculation on multilinear object settings with different reflectivity and remote sensing image response values ​​of multilinear objects with different reflectivity, or by multiple remote sensing imaging count values.

[0034] Furthermore, the multilinear feature is a large-area diffuse source with a spatial scale not less than 10 times the ground pixel resolution of a satellite camera, or a small-size reflective source with a spatial scale not more than 10% of the ground pixel resolution of a satellite camera;

[0035] When the multi-linear feature is a diffuse source, its size should be larger than 10×10 times the ground sampling interval of the optical satellite camera;

[0036] When the multi-linear feature is a diffuse source, it has a uniformity better than 2%, and the reflectivity has good spectral flatness and Lambertian properties in the optical satellite camera channel and the difference is less than 1%.

[0037] Furthermore, when the multilinear feature is a diffuse source, the reflectivity of the feature is within the dynamic range of the optical satellite camera and has no less than 4 reflectivities.

[0038] Furthermore, when the multi-linear feature is a reflection source, it should have a uniformity better than 2%, and the reflectivity has good spectral flatness and a difference of less than 2% within the optical satellite camera channel.

[0039] Furthermore, when the multilinear feature is a reflection source, the energy level of the feature should be within more than 80% of the dynamic range of the optical satellite camera, and there should be no less than 4 energy levels, and the distance between each energy level should be no less than 10 pixels.

[0040] Furthermore, when the multi-linear object is a reflection source, it is necessary to deploy an array of at least 4×4, with a spacing of more than 5.25 pixels between objects, detect the modulation transfer function of the camera imaging system, and correct the radiation response effect of the remote sensor on the multi-linear object reflection source.

[0041] (III) Effective income

[0042] (1) The on-orbit radiation calibration method of the optical satellite camera of the present invention mainly uses ground measured data to replace the aerosol scattering assumption in the radiation transmission calculation, and deducts the influence of process radiation and ground-atmosphere coupled radiation through linear regression of multiple reflectivity linear objects and remote sensor response values, thereby reducing the influence of factors such as aerosols and atmospheric patterns on on-orbit calibration, thereby improving the accuracy of radiation calibration;

[0043] (2) The on-orbit radiation calibration method of the optical satellite camera of the present invention can realize the detection of the response linearity and dynamic range of the optical satellite camera and the high-precision operational radiation calibration of the full dynamic range under the same atmospheric environment conditions;

[0044] (3) The on-orbit radiation calibration method of an optical satellite camera of the present invention can not only break through the limitations of time, space and weather conditions on large-area radiation correction fields and reduce the requirements for the background environment of the calibration area, but also realize high-frequency mobile calibration of optical satellite cameras under complex environmental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of radiation transmission between the sun, multi-linear objects and optical satellite cameras;

[0046] Figure 2 It is the on-orbit radiometric calibration technology process of optical satellite cameras based on multi-linear objects;

[0047] Figure 3 It is a schematic diagram of the layout of multi-linear objects (large-area diffuse sources);

[0048] Figure 4 It is a schematic diagram of the layout of multi-linear features (small-sized reflection sources);

[0049] Figure 5 This is a schematic diagram of the array layout of ground objects (small-sized reflection sources). DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0051] like Figure 1 The figure shows a schematic diagram of radiation transmission between the sun, multilinear objects and optical satellite cameras.

[0052] According to one embodiment of the present invention, a method for calculating on-orbit radiation calibration of an optical satellite camera based on multi-linear objects is as follows: Figure 2 As shown in Figure 1, according to the altitude of the radiation calibration site, the temperature, humidity, pressure and wind meteorological parameters and the background environmental parameters, the atmospheric transmittance is calculated by the radiation transmission code MODTRAN / 6S, and the channel atmospheric transmittance of the sun-ground path measured by the sun photometer is gradually approached, and then the hyperspectral atmospheric transmittance of the solar illumination path can be obtained, that is, the atmospheric transmittance in formula (3) Based on this, the geometric relationship between the multi-linear objects on the ground illuminated by the sun and the multi-linear objects on the ground observed by the satellite is used to change the geometric factor in the radiation transmission code, and the hyperspectral atmospheric transmittance of the satellite camera observation path is calculated, that is,

[0053] The total radiance of the sun shining on the ground is obtained by multiplying the extra-atmospheric solar constant with the calculated atmospheric transmittance of the sun path and the diffuse / total radiation ratio (diffuse source). Then, the atmospheric transmittance of the satellite observation path, the spectral response function of the satellite camera, and the multilinear ground reflectivity are multiplied with the total ground radiance to calculate the entrance pupil radiance Aρ reflected by the multilinear ground object to the satellite camera. t .

[0054] Through the multi-linear object settings with different reflectivity and the linear object remote sensing image count values, according to the optical satellite camera calibration equation, the on-orbit radiation calibration coefficient of the optical satellite camera based on the multi-linear object can be obtained through linear regression calculation, thus realizing the full dynamic calibration of the optical satellite camera in the working state.

[0055] According to the radiation transfer theory, under plane-parallel atmospheric conditions, for ground reference of multi-linear objects, the entrance pupil radiance of the optical satellite camera can be expressed as:

[0056]

[0057] Where L is the entrance pupil radiance of the satellite camera, L a is the atmospheric radiation, E s is the solar constant, μ s is the solar zenith angle θs The cosine factor, T gas is the atmospheric absorption transmittance, τ is the atmospheric optical thickness, t d (θ s ) is the downward atmospheric scattering transmittance, S is the albedo of the large balloon surface, ρ e is the background reflectivity, ρ t is the reflectivity of the multilinear feature, μ v is the cosine factor of the satellite observation zenith angle, θ v is the satellite observation zenith angle, t' d (θ v ) is the upward atmospheric scattering transmittance, α(θ s ) is the ratio of sky diffuse radiation to global radiation in the direction of solar incidence.

[0058] If the background reflectivity within the multi-linear object layout area is constant, the total ground illumination in the calibration area remains unchanged, the atmospheric radiation above the multi-linear object is the same as the ground-air coupling radiation, and the entrance pupil radiance of the optical satellite camera can be rewritten as:

[0059] L=Aρ t +B=L t +B (2)

[0060] Where A is the entrance pupil radiance reflected by the ideal linear object to the optical satellite camera, that is:

[0061]

[0062] B is the sum of the atmospheric radiation and the ground-air coupled radiation, that is,

[0063]

[0064] The optical satellite camera observes and images the multi-linear objects on the ground within a certain area. At this time, the parameters such as atmospheric radiation, optical thickness, transmittance and spherical albedo are all fixed values. Therefore, A and B expressed by formula (3) and formula (4) are also fixed values. According to formula (2), the optical satellite camera entrance pupil radiance L and the reflectivity ρ of the multi-linear objects are obtained. t It presents a univariate linear relationship. Therefore, multilinear objects with different reflectivities or different energy levels can be set within the dynamic range of the remote sensor to obtain different multilinear object response values ​​in the optical satellite image. Linear regression is performed on the multilinear objects with different reflectivities and their remote sensing image response values ​​to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects.

[0065] According to the optical satellite camera calibration equation (5), the count values ​​of remote sensing images of multilinear objects are combined with different reflectivities. The multilinear objects with different reflectivities and the count values ​​of remote sensing images of multilinear objects with different reflectivities are linearly regressed to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on multilinear objects.

[0066]

[0067] Among them, L epu,i is the entrance pupil equivalent radiance of the i-th channel of the satellite remote sensor, R i (λ) is the spectral response function of the i-th channel of the satellite remote sensor, A gain,i is the responsivity calibration coefficient of the i-th channel of the satellite remote sensor, DN i is the response value of the remote sensor channel i to multilinear objects, DN 0,i is the dark current response value of the i-th channel of the satellite remote sensor.

[0068] (I) When the multilinear reflectivity ρ in the i-th channel of the optical satellite camera t = 0, which is equivalent to the optical satellite camera not setting up multi-linear objects in the ground observation area, that is, the optical satellite camera observes the background of the field area and images it. According to formula (2), the entrance pupil radiance of the satellite remote sensor L = B. At this time, the image count value is the intercept of the linear regression of the calibration equation.

[0069]

[0070] (II) When the multilinear ground reflectivity ρ in the i-th channel of the optical satellite camera t When ≠0, it is equivalent to the optical satellite camera setting up multiple linear objects with different reflectivity or different energy levels in the ground observation area, that is, the optical satellite camera observes and images the multiple linear objects in the field area. According to formula (2), the entrance pupil radiance of the satellite remote sensor is L = L t +B, then according to formula (5):

[0071]

[0072] According to formulas (6) and (7), linear regression is performed on the response values ​​of multilinear objects with different reflectivity or different energy levels and remote sensing images of multilinear objects with different reflectivity to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects:

[0073]

[0074] The radiation calibration coefficient will be applied to the subsequent earth observation and data quantification of optical satellite cameras. Combined with the response values ​​of satellite observations of ground objects (natural resources, atmosphere, ecological environment, etc.), the basic physical quantities (such as reflectivity / radiance, temperature / profile, etc.) that characterize the characteristics of ground objects and atmosphere are inverted, and mineral resources and atmospheric environment are analyzed. It plays a very important role in resource investigation, environmental protection, urban planning, national defense security and other aspects of national economic construction, and has broad application prospects.

[0075] The multilinear feature reflectivity ρ t , atmospheric optical thickness τ and the ratio of sky diffuse radiation to total radiation in the direction of solar incidence α(θ s ) can be obtained by simultaneous measurement of ground object spectrometer, sun photometer and spectroradiometer.

[0076] The It can be obtained by performing linear regression calculation on multi-linear objects with different reflectivity and remote sensing image response values ​​of multi-linear objects with different reflectivity, or it can be obtained through multiple remote sensing imaging count values.

[0077] Furthermore, the multilinear feature is a large-area diffuse source with a spatial scale not less than 10 times the ground pixel resolution of a satellite camera, or a small-size reflective source with a spatial scale not more than 10% of the ground pixel resolution of a satellite camera;

[0078] When the multi-linear feature is a diffuse source, its size should be larger than 10×10 times the ground sampling interval of the optical satellite camera;

[0079] When the multi-linear feature is a diffuse source, it has a uniformity better than 2%, and the reflectivity has good spectral flatness and Lambertian properties in the optical satellite camera channel and the difference is less than 1%.

[0080] Furthermore, when the multilinear feature is a diffuse source, the reflectivity of the feature is within the dynamic range of the optical satellite camera and has no less than 4 reflectivities.

[0081] Furthermore, when the multi-linear feature is a reflection source, it should have a uniformity better than 2%, and the reflectivity has good spectral flatness and a difference of less than 2% within the optical satellite camera channel.

[0082] When the multi-linear ground object is a reflection source, the ground object energy level should be within more than 80% of the dynamic range of the optical satellite camera, and there should be no less than 4 energy levels, and the distance between each energy level should be no less than 10 pixels;

[0083] When the multi-linear object is a reflection source, it is necessary to deploy an array of at least 4×4, with a spacing of more than 5.25 pixels between objects, detect the modulation transfer function of the camera imaging system, and correct the radiation response effect of the remote sensor on the multi-linear object reflection source.

[0084] The present invention does not require assumptions and calculations of parameters such as atmospheric model, aerosol model, atmospheric path radiation, spherical albedo, etc., and only requires radiation transmission to calculate the absorbing gas transmittance. The multilinear objects in the ground field are gray-scale targets with good spectral flatness, Lambertianity, uniformity and consistency in the optical satellite camera channel, reflecting point sources and similar natural objects.

[0085] 1) Linear feature layout

[0086] The linear features are laid out in a site with open areas and flat terrain. A large area of ​​black lining net can be laid out according to the site conditions to isolate the surface from the linear features and protect the linear features. The linear features are laid out in the direction of flight of the optical satellite camera, and there are no less than 4 types of linear features. The schematic diagram is as follows: Figure 3 shown.

[0087] 2) On-site synchronous measurement

[0088] The optical satellite camera passes over the linear terrain layout area half an hour before and after, measuring the optical thickness of the atmosphere, the ratio of sky diffuse radiation to total radiation (diffuse source), the reflectivity of the terrain, and the temperature, humidity, pressure, wind force and speed and other meteorological information of the test area.

[0089] 3) Experimental data processing

[0090] According to the optical remote sensor calibration equation

[0091]

[0092] Combining the multi-linear object setting with the optical satellite camera's count value of multi-linear object remote sensing image to perform linear regression, we can get:

[0093] (I) When the linear surface reflectivity ρ in the i-th channel of the optical satellite sensor t = 0, that is, the field background is observed and imaged, and the sensor entrance pupil radiance L = B. At this time, the image count value is the intercept of the linear regression of the calibration equation.

[0094]

[0095] (II) When the linear surface reflectivity ρ in the i-th channel of the optical satellite sensor t ≠0, that is, for multi-linear ground observation imaging, the remote sensor entrance pupil radiance L = L t +B, now:

[0096]

[0097] According to equations (6) and (7), the calibration coefficients of the optical satellite camera are obtained:

[0098]

[0099] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, and it should be clear that the present invention is not limited to the scope of the specific embodiments, for those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

[0100] The above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. An on-orbit radiometric calibration method for an optical satellite camera based on multilinear features, characterized in that: The steps include: Step 1: According to the altitude, temperature, humidity, pressure and wind meteorological parameters and background environmental parameter information of the radiation calibration site, the atmospheric transmittance calculated by the radiation transmission code MODTRAN or 6S is successively approximated to the channel atmospheric transmittance of the sun-multilinear feature path measured by the sun photometer, and then the hyperspectral atmospheric transmittance of the solar illumination path is obtained. Based on this, the geometric relationship between solar illumination and satellite observation is used to change the geometric factor in the radiation transmission code, and the hyperspectral atmospheric transmittance of the satellite camera observation path is calculated; Step 2: Multiply the extra-atmospheric solar constant with the calculated hyperspectral atmospheric transmittance of the solar path and the diffuse / total radiation ratio to obtain the total radiance of the sun irradiating the ground, and then combine the spectral response function of the satellite camera, the multilinear object reflectivity, the calculated atmospheric transmittance of the satellite camera observation path and the ground total radiance to obtain the entrance pupil radiance reflected by the multilinear object to the optical satellite camera; Step 3: By setting multilinear objects with different reflectivity and counting the remote sensing image values ​​of multilinear objects, the influence of atmospheric radiation and ground-atmosphere coupled radiation is deducted through linear regression calculation to obtain the radiation response value of the multilinear object. Then, the entrance pupil radiance reflected by the multilinear object to the optical satellite camera and the radiation response value of the multilinear object are calculated according to the calibration equation of the optical satellite camera to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear object. At this point, the full dynamic range radiation calibration of the optical satellite camera in the working state is realized.

2. According to claim 1, an on-orbit radiometric calibration method for an optical satellite camera based on multilinear features is characterized in that: The specific acquisition steps of step 2 are as follows: Under plane-parallel atmospheric conditions, for ground reference of multi-linear objects, the entrance pupil radiance of the optical satellite camera is expressed as: Where L is the entrance pupil radiance of the satellite camera, L a is the atmospheric radiation, E s is the solar constant, μ s is the solar zenith angle θ s The cosine factor, T gas is the atmospheric absorption transmittance, τ is the atmospheric optical thickness, t d (θ s ) is the downward atmospheric scattering transmittance, S is the albedo of the large balloon surface, ρ e is the background reflectivity, ρ t is the reflectivity of the multilinear feature, μ v is the cosine factor of the satellite observation zenith angle, θ v is the satellite observation zenith angle, t' d (θ v ) is the upward atmospheric scattering transmittance, α(θ s ) is the ratio of sky diffuse radiation to global radiation in the direction of solar incidence; If the background reflectivity within the multi-linear object layout area is constant, the total ground illumination in the calibration area remains unchanged, the atmospheric radiation above the multi-linear object is the same as the ground-air coupling radiation, and the entrance pupil radiance of the optical satellite camera is rewritten as: L=Aρ t +B=L t +B(2) Where A is the entrance pupil radiance reflected by the ideal linear object to the optical satellite camera, that is: B is the sum of the atmospheric radiation and the ground-air coupled radiation, that is:

3. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear features according to claim 2, characterized in that: The acquisition of the on-orbit absolute radiation calibration coefficient in step 3 is specifically as follows: The optical satellite camera observes and images the multi-linear objects on the ground within a certain area. At this time, the atmospheric path radiation, optical thickness, transmittance and spherical albedo, diffuse / total radiation ratio, and solar constant parameters are all fixed values. Therefore, A and B expressed by formula (3) and formula (4) are also fixed values. According to formula (2), the optical satellite camera entrance pupil radiance L and the reflectivity ρ of the multi-linear objects are obtained. t It is a univariate linear relationship. Therefore, by setting multilinear objects with different reflectivities or different energy levels within the dynamic range of the remote sensor, different multilinear object response values ​​can be obtained in the optical satellite image. Linear regression is performed on the multilinear objects with different reflectivities and their remote sensing image response values ​​to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects. Specifically, according to the optical satellite camera calibration equation (5), combined with the remote sensing image count values ​​of the multilinear objects and different reflectivities, the multilinear objects with different reflectivities and the count values ​​of the remote sensing images of the multilinear objects with different reflectivities are linearly regressed to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects: Among them, L epu,i is the entrance pupil equivalent radiance of the i-th channel of the satellite remote sensor, R i (λ) is the spectral response function of the i-th channel of the satellite remote sensor, A gain,i is the responsivity calibration coefficient of the i-th channel of the satellite remote sensor, DN i is the response value of the remote sensor channel i to multilinear objects, DN 0,i is the dark current response value of the i-th channel of the satellite remote sensor. (I) When the multilinear reflectivity ρ in the i-th channel of the optical satellite camera t = 0, which is equivalent to the optical satellite camera not setting up multi-linear objects in the ground observation area, that is, the optical satellite camera observes the background of the field area and images it. According to formula (2), the entrance pupil radiance of the satellite remote sensor L = B. At this time, the image count value is the intercept of the linear regression of the calibration equation. (II) When the multilinear ground reflectivity ρ in the i-th channel of the optical satellite camera t When ≠0, it is equivalent to the optical satellite camera setting up multiple linear objects with different reflectivity or different energy levels in the ground observation area, that is, the optical satellite camera observes and images the multiple linear objects in the field area. According to formula (2), the entrance pupil radiance of the satellite remote sensor is L = L t +B, then according to formula (5): According to formulas (6) and (7), linear regression is performed on the response values ​​of multilinear objects with different reflectivity or different energy levels and remote sensing images of multilinear objects with different reflectivity to obtain the on-orbit absolute radiation calibration coefficient of the optical satellite camera based on the multilinear objects:

4. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear features according to claim 2, characterized in that: The multilinear feature reflectivity ρ t The atmospheric optical thickness τ is measured by the sun photometer, and the sky diffuse radiation / total radiation ratio α (θ s ) is measured by a spectroradiometer.

5. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear features according to claim 3, characterized in that: The It is obtained by performing linear regression calculation on multilinear object settings with different reflectivity and remote sensing image response values ​​of multilinear objects with different reflectivity, or by multiple remote sensing imaging count values.

6. The on-orbit radiometric calibration method for an optical satellite camera based on multilinear features according to claim 1, characterized in that: The multilinear ground feature is a large-area diffuse source with a spatial scale not less than 10 times the ground pixel resolution of a satellite camera, or a small-size reflective source with a spatial scale not more than 10% of the ground pixel resolution of a satellite camera; When the multi-linear feature is a diffuse source, its size should be larger than 10×10 times the ground sampling interval of the optical satellite camera; When the multi-linear feature is a diffuse source, it has a uniformity better than 2%, and the reflectivity has good spectral flatness and Lambertian properties in the optical satellite camera channel and the difference is less than 1%.

7. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear features according to claim 1, characterized in that: When the multi-linear ground object is a diffuse source, the ground object reflectivity is within the dynamic range of the optical satellite camera and has no less than 4 reflectivities.

8. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear features according to claim 1, characterized in that: When the multi-linear feature is a reflection source, it should have a uniformity better than 2%, and the reflectivity has good spectral flatness and a difference of less than 2% within the optical satellite camera channel.

9. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear features according to claim 1, characterized in that: When the multi-linear feature is a reflection source, the energy level of the feature should be within more than 80% of the dynamic range of the optical satellite camera, and there should be no less than 4 energy levels, and the distance between each energy level should be no less than 10 pixels.

10. The on-orbit radiometric calibration method for an optical satellite camera based on multi-linear objects according to claim 1, characterized in that: When the multi-linear object is a reflection source, it is necessary to deploy an array of at least 4×4, with a spacing of more than 5.25 pixels between objects, detect the modulation transfer function of the camera imaging system, and correct the radiation response effect of the remote sensor on the multi-linear object reflection source.

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