Method and device for calibrating absolute radiation of satellite-borne visible light camera to moon

Abstract

The invention discloses a lunar absolute radiation calibration method and calibration device for a satellite-borne visible light camera, and the method comprises the steps: building a transfer link model from the sun to the moon and then to a to-be-calibrated satellite-borne visible light camera, i.e., unifying the space coordinates of the sun, the moon and the to-be-calibrated satellite-borne visible light camera into a geocentric coordinate system; through orbit planning, the moon is perpendicular to the visual axis direction of the high-orbit area-array camera, the distance between the sun and the moon and the distance between the moon and the to-be-calibrated camera and the incident angle of sunlight are obtained, and then the sun radiance received by the remote sensor is obtained, so that the atmosphere transmission path is eliminated, the accurate entrance pupil radiance can be obtained, and the accuracy of calibration is improved. And further, an accurate absolute calibration coefficient is obtained. According to the invention, the in-orbit radiation calibration precision and frequency can be improved.

Description

Technical Field

[0001] The invention belongs to the field of on-orbit absolute radiation calibration of satellite-borne imaging payloads, and in particular relates to a method and a device for calibrating absolute radiation of a satellite-borne visible light camera for the moon. Background Art

[0002] As the application requirements of remote sensing data continue to increase, the demand for further improving the accuracy of quantitative application of remote sensing data has been widely recognized. The importance of remote sensor radiation calibration has gradually gained widespread consensus, and the requirements for radiation calibration accuracy have also become apparent.

[0003] The limitations of traditional field calibration methods are as follows: 1) The number of calibration sites is insufficient and unevenly distributed, making it difficult to adapt to the diversity of payloads; 2) The radiation and spectral characteristics of existing sites are single, making it difficult to take into account the requirements of on-orbit calibration of multiple parameters; 3) The areas of calibration sites are different, making it difficult to meet the relative calibration requirements of payloads with different field of view scales; 4) Due to the influence of factors such as the atmosphere and ground scenery characteristics, the accuracy of field calibration is difficult to meet the needs of quantitative application of remote sensing data. The calibration accuracy is difficult to improve. In order to avoid the influence of the surface and atmosphere on the accuracy of radiation calibration, the early satellite calibration used a built-in lamp method. This method uses artificial light sources, but has the disadvantages of non-full optical path and large differences in spectral distribution with the sun, which affects the calibration accuracy. Later satellite calibration returned to the sun itself. On-orbit diffuse reflector calibration is to carry a diffuse reflector on the satellite and place it at the front end of the remote sensor. However, in this calibration method, the diffuse reflector can only be used by one remote sensor, which limits the calibration accuracy to a certain extent, and also cannot realize data exchange between remote sensors. Summary of the invention

[0004] The present invention uses the moon to carry out on-orbit absolute calibration of satellite-borne visible light cameras. The moon is the largest and brightest light source that we can observe except the sun, and is also the extraterrestrial target with the largest viewing angle except the sun. Reflecting sunlight can be used as a secondary light source. Using the moon to calibrate satellites has many advantages that other calibration sources cannot match:

[0005] (1) The spectral characteristics of the moon are very stable, and the rate of change of its surface reflectivity is about 10 -8 / year, the moon spectrum has the advantage of covering the entire visible and near-infrared spectrum, making the moon very suitable as a reference radiation benchmark source for the satellite solar reflection channel;

[0006] (2) The lunar calibration is not affected by the atmosphere, the background is deep space, the influence of stray light from other sources can be minimized, and it has a suitable dynamic range;

[0007] (3) The traditional field synchronous test calibration method is limited by the observation time and number, and the calibration frequency is generally only once a year. The lunar calibration method can significantly increase the calibration frequency on the basis of improving the calibration accuracy as long as the lunar phase angle during observation is within a certain range and the solar radiation brightness reflected by the moon is within the dynamic range of the current earth imaging parameters. It can also realize the full life dynamic monitoring of the radiation calibration response of the remote sensing instrument.

[0008] Therefore, in view of the current situation that the accuracy of existing on-orbit absolute calibration is not high, the present invention provides a method for absolute radiation calibration of a satellite-borne visible light camera for the moon, establishes a transmission link model from the sun to the moon and then to the camera to be calibrated, gets rid of the atmospheric transmission path, and can obtain accurate entrance pupil radiance, and then obtain accurate absolute calibration coefficients.

[0009] The idea of ​​the present invention is to unify the spatial coordinates of the sun, the moon and the camera to be calibrated into the geocentric coordinate system, and realize the moon perpendicular to the visual axis direction of the high-orbit array camera through orbit planning. The distances between the sun and the moon, the moon and the camera to be calibrated, and the incident angle of sunlight can be obtained, and then the solar radiance received by the remote sensor can be obtained.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for calibrating the absolute radiometric quality of a satellite-borne visible light camera for the moon, the method comprising the following steps:

[0012] S1: Based on the ephemeris, the spatial position motion equations of the sun and the moon in the geocentric coordinate system are established to obtain the sun's position vector R sun , velocity vector V sun , and the moon's position vector R Lunar and velocity vector V Lunar ;

[0013] The position vector R of the onboard visible light camera to be calibrated in the geocentric coordinate system is calculated based on the ephemeris, orbital parameters and the Earth orbit dynamics model. RS and velocity vector V RS ;

[0014] S2: Based on the calculation results of S1, calculate the distance between the moon and the satellite-borne visible light camera respectively , the distance between the sun and the moon , and the angles between the sun, moon and the principal optical axis of the onboard visible light camera ;

[0015] S3: The distance between the sun and the moon calculated from S2 , calculate the solar spectral irradiance incident on the lunar surface ;

[0016] S4: Solar spectral irradiance obtained from S3 According to Lambert's cosine law and the lunar reflection model, the radiance L of the lunar reflection corresponding to the spectral band i of the spaceborne visible light camera to be calibrated is calculated. REF,i ;

[0017] S5: Calculate the observed moon phase angle ;

[0018] S6: Determine the orbit that meets the following three conditions as the lunar calibration arc segment, and execute S7; otherwise, return to S2;

[0019] (1) The lunar phase angle during imaging is consistent with the phase angle of the reference lunar radiation model;

[0020] (2) The radiance L of the moon reflected by the visible light camera to be calibrated REF,i It is within the response dynamic range of the onboard visible light camera to be calibrated;

[0021] (3) The lunar calibration area is within the field of view of the visible light camera on board the satellite to be calibrated;

[0022] S7: Establish the output DN of the onboard visible light camera to be calibrated at the calibration time i The value is related to the radiance L reflected by the moon REF,i The linear relationship between them is used to calculate the absolute calibration coefficient k corresponding to the i-th spectral segment of the onboard visible light camera to be calibrated. i and b i , the calibration is completed.

[0023] Furthermore, in S1, the sun's position vector R is calculated. sun and velocity vector V sun The specific steps include the following:

[0024] (1) First convert the given date into the Julian century:

[0025] ;

[0026] ;

[0027] In the formula, T represents the Julian century, JD represents the Julian day, y represents the year, m represents the month, and d represents the day number;

[0028] (2) Based on the Julian century number obtained in step (1), calculate the orbital parameters of the approximate elliptical orbit of the sun's relative motion with respect to the center of the earth, including the eccentricity e, mean anomaly M, solar geometric mean ecliptic longitude Lo, solar center difference C, and true anomaly V:

[0029] ;

[0030] ;

[0031] ;

[0032] ;

[0033] ;

[0034] (3) Based on the orbital elements obtained in step (2), the spatial position motion equation of the sun in its perifocal coordinate system is established, with the sun's state vector (R S ,V S )express:

[0035] ;

[0036] ;

[0037] Among them, R S 、V S are the position vector and velocity vector of the sun in the perifocal coordinate system, a is the semi-major axis of the orbit, is the Earth-Sun gravitational parameter, represents angular momentum;

[0038] (4) Calculate the transformation matrix Conv from the solar perifocal coordinate system to the Earth's geocentric coordinate system SUN :

[0039] ;

[0040] Where γ is the solar orbit inclination, is the right ascension of the ascending node of the solar orbit, is the argument of perigee of the solar orbit, and are two orbit corrections;

[0041] (5) Based on the state vector of the sun in its perifocal coordinate system obtained in step (3) and the transformation matrix obtained in step (4), the spatial position motion equation of the sun in the earth's geocentric coordinate system is established to obtain the sun's position vector R sun and the velocity vector V sun , with the sun's state vector (R sun ,V sun )express:

[0042] ;

[0043] .

[0044] Further, calculate the position vector R of the moonLunar and velocity vector V Lunar and calculate the sun's position vector R sun and velocity vector V sun The method is the same as that of , that is, the motion state vector (R) of the moon in the perifocal coordinate system is calculated in turn according to the lunar ephemeris and orbital parameters. Lunar_0 , V Lunar_0 ), the transformation matrix Conv from the near-focus coordinate system to the geocentric coordinate system Lunar and the state vector of the moon in the geocentric coordinate system (R Lunar , V Lunar ).

[0045] Furthermore, the position vector R of the satellite-borne visible light camera to be calibrated in the geocentric coordinate system is calculated RS and velocity vector V RS , specifically including the following sub-steps:

[0046] (1) Based on the orbit determination of the global navigation satellite system, the six orbital elements of the onboard visible light camera are calculated to calculate the initial state vector (R RS_0 , V RS_0 );

[0047] (2) Calculate the satellite's motion state vector after Δt time according to the following formula:

[0048] ;

[0049] ;

[0050] In the formula, R RS 、V RS They represent the motion state vector after Δt time, f, g, , are the Lagrange coefficient and its first-order derivative, respectively, and the expressions are as follows:

[0051] ;

[0052] ;

[0053] ;

[0054] ;

[0055] In the formula, R RS_0 represents the modulus of the initial state vector; R RS represents the modulus of the motion state vector after Δt time, is the global anomaly of the orbit, which is solved iteratively by the following global Kepler equation, and the expression is as follows:

[0056] ;

[0057] In the formula, is the Earth's gravitational constant, is the inverse of the semi-major axis of the orbit, S(z) and C(z) are Stumpf functions, expressed as follows:

[0058] ;

[0059] ;

[0060] (3) Establish an iterative solution model for the satellite motion state, and solve the final motion state vector (R RS , V RS ).

[0061] Furthermore, the distance between the moon and the onboard visible light camera is calculated. , the distance between the sun and the moon The calculation formula is as follows:

[0062]

[0063] ;

[0064] Among them, (x Lunar ,y Lunar , z Lunar )、(x RS ,y RS , z RS )、(x sun ,y sun , z sun ) are the coordinates of the moon, the spaceborne visible light camera to be calibrated, and the sun in the geocentric coordinate system.

[0065] Furthermore, L REF,i The calculation formula is as follows:

[0066] ;

[0067] ;

[0068] ;

[0069] ;

[0070] in, is the spectral response function of the i-th spectral band of the spaceborne visible light camera; is the lunar spectral reflectance provided by the lunar radiation model; λ is the wavelength of the sun incident on the moon, λ1 and λ2 are the lower and upper limits of the spectrum of the i-th spectral band of the onboard visible light camera to be calibrated; is the solar spectral irradiance incident on the moon; is the process quantity; ρ i is the equivalent lunar reflectivity of the i-th spectral band of the onboard visible light camera; E i is the equivalent solar spectral irradiance of the i-th spectrum incident on the lunar surface; d is the sun-moon distance factor, which is the ratio of the real-time sun-moon distance to the standard sun-moon distance; θ is the angle between the incident solar ray and the normal of the lunar surface.

[0071] Furthermore, the moon phase angle is observed in S5 The calculation formula is as follows:

[0072] ;

[0073] Among them, in, em and They are respectively the incident zenith angle of the sun on the moon at a certain moment in the calibration arc, the observation zenith angle of the visible light camera on the satellite to be calibrated, and the relative azimuth angle between the two.

[0074] Furthermore, in S7, the absolute calibration coefficient k i and b i The calculation formula is as follows:

[0075] ;

[0076] ;

[0077] Among them, k i is the calibration slope of the i-th spectrum segment, in units of DN i is the observation value of the i-band of the onboard visible light camera; b i is the calibration intercept of the i-th spectral segment, in units of ; , are the two lunar reflected radiances in the i-th spectral band, , These are the numerical quantified values ​​corresponding to the two lunar reflection radiances.

[0078] A device for calibrating the absolute radiometry of a satellite-borne visible light camera to the moon comprises one or more processors for implementing a method for calibrating the absolute radiometry of a satellite-borne visible light camera to the moon.

[0079] An electronic device, comprising:

[0080] one or more processors;

[0081] The storage device is used to store one or more programs. When the one or more programs are executed by the electronic device, the electronic device implements a method for calibrating the absolute radiation of the moon for a space-borne visible light camera.

[0082] The beneficial effects of the present invention are as follows:

[0083] (1) The radiance received by the optical camera in the present invention can be traced back to the solar irradiance.

[0084] (2) The calibration method of the present invention can get rid of the influence of imaging target characteristics or atmospheric conditions and improve the accuracy of on-orbit radiation calibration.

[0085] (3) The moon in the present invention can be used as a standard source for on-orbit calibration of remote sensing satellites. As long as the optical satellite arc meets the requirements, on-orbit calibration can be performed, thereby increasing the frequency of on-orbit radiation calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0087] Figure 1 The present invention is a flowchart of a method for calibrating the absolute radiometric quality of a satellite-borne visible light camera for the moon according to an embodiment of the present invention.

[0088] Figure 2 Schematic diagram of the lunar calibration of the space-borne visible light camera.

[0089] Figure 3 Schematic diagram of observed phase angle.

[0090] Figure 4 Schematic diagram of the spectral response curve of the space-borne visible light camera.

[0091] Figure 5 Schematic diagram of the spectral irradiance curve of the sun incident on the lunar surface. DETAILED DESCRIPTION

[0092] The present invention will be described in detail below based on the accompanying drawings and preferred embodiments, and the purpose and effects of the present invention will become more clear. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0093] like Figure 1 As shown, the method for calibrating the moon's absolute radiation of a spaceborne visible light camera in this embodiment includes the following steps:

[0094] Step 1: Based on the ephemeris, establish the spatial position motion equations of the sun and the moon in the geocentric coordinate system, and obtain the sun's position vector R sun , velocity vector V sun , and the moon's position vector R Lunar and the velocity vector V Lunar ;

[0095] The position vector R of the onboard visible light camera to be calibrated in the geocentric coordinate system is calculated based on the ephemeris, orbital parameters and the Earth orbit dynamics model. RS and the velocity vector V RS .

[0096] Among them, calculate the sun's position vector R sun and the velocity vector V sun The specific steps include the following:

[0097] (1.1) For the position of the Sun in the geocentric coordinate system, first convert the given date into the Julian century:

[0098] ;

[0099]

[0100] Where T is the Julian century, JD is the Julian day, y is the year, m is the month, and d is the day.

[0101] (1.2) Based on the Julian century number obtained in step (1.1), calculate the orbital parameters of the approximate elliptical orbit of the sun's relative motion to the center of the earth, including the eccentricity e, mean anomaly M, solar geometric mean ecliptic longitude Lo, solar center difference C, and true anomaly V:

[0102] ;

[0103] ;

[0104] ;

[0105] ;

[0106] ;

[0107] (1.3) According to the orbital elements obtained in step (1.2), the spatial position motion equation of the sun in its perifocal coordinate system is established, with the state vector (R S ,V S )express:

[0108] ;

[0109] ;

[0110] Among them, R S 、V S are the position vector and velocity vector of the sun in the perifocal coordinate system, a is the semi-major axis of the orbit, is the Earth-Sun gravitational parameter, represents angular momentum;

[0111] (1.4) Calculate the transformation matrix from the solar perifocal coordinate system to the Earth's geocentric coordinate system :

[0112] ;

[0113] Where γ is the solar orbit inclination, is the right ascension of the ascending node of the solar orbit, is the argument of perigee of the solar orbit, and are the two orbit corrections.

[0114] (1.5) Based on the state vector of the sun in its perifocal coordinate system obtained in step (1.3) and the coordinate system transformation matrix obtained in step (1.4), the spatial position motion equation of the sun in the earth's geocentric coordinate system is established to obtain the sun's position vector R sun and the velocity vector V sun , with the sun's state vector (R sun ,V sun )express:

[0115] ;

[0116] .

[0117] Calculate the moon's position vector R Lunar and the velocity vector V Lunar and calculate the sun's position vector R sun and the velocity vector V sun The method is the same as that of , that is, the motion state vector (R) of the moon in the perifocal coordinate system is calculated in turn according to the lunar ephemeris and orbital parameters. Lunar_0 , V Lunar_0 ), the transformation matrix Conv from the near-focus coordinate system to the geocentric coordinate system Lunar and the state vector of the moon in the geocentric coordinate system (R Lunar , V Lunar ), which will not be described in detail here.

[0118] Calculate the position vector R of the onboard visible light camera in the geocentric coordinate system RS and the velocity vector V RSThe specific steps include the following:

[0119] For a spaceborne visible light camera, when the Global Navigation Satellite System (GNSS) determines the orbit and gives the six orbital elements, its initial state vector (R) in the geocentric coordinate system can be calculated. RS_0 , V RS_0 ).

[0120] After Δt time, the satellite's motion state vector can be calculated as follows:

[0121] ;

[0122] ;

[0123] In the formula, R RS 、V RS They represent the motion state vector after Δt time, f, g, , are the Lagrange coefficient and its first-order derivative, respectively, and the expressions are as follows:

[0124] ;

[0125] ;

[0126] ;

[0127] ;

[0128] In the formula, R RS_0 represents the modulus of the initial state vector; R RS represents the modulus of the motion state vector after Δt time, is the global anomaly of the orbit, which is solved iteratively by the following global Kepler equation, and the expression is as follows:

[0129] ;

[0130] Where μ is the Earth's gravitational constant, is the inverse of the semi-major axis of the orbit, S(z) and C(z) are Stumpf functions, expressed as follows:

[0131] ;

[0132] ;

[0133] Therefore, by establishing an iterative solution model for the satellite motion state, the final motion state vector (R RS , V RS ).

[0134] Step 2: Based on the calculation results of step 1, calculate the distance between the moon and the satellite-borne visible light camera respectively , the distance between the sun and the moon .

[0135] The calculation formula is as follows:

[0136] ;

[0137] ;

[0138] Among them, (x Lunar ,y Lunar , z Lunar )、(x RS ,y RS , z RS )、(x sun ,y sun , z sun ) are the coordinates of the moon, the spaceborne visible light camera to be calibrated, and the sun in the geocentric coordinate system.

[0139] Step 3: The distance between the sun and the moon calculated in step 2 , calculate the solar irradiance incident on the lunar surface .

[0140] The solar radiation incident on the moon is calculated using the recognized solar radiation calculation method. By analyzing the positional relationship between the sun and the moon in the geocentric ecliptic coordinate system, the relationship between the distance between the sun and the moon and the change of the solar radiation incident angle over time, the longitude and latitude of the sun's direct rays, etc. is determined, and the solar spectral irradiance incident on the lunar surface is calculated. .

[0141] Step 4: Solar spectral irradiance obtained according to step 3 According to Lambert's cosine law and the lunar reflection model, the radiance L of the lunar reflection corresponding to the spectral band i of the calibrated satellite-borne visible light camera is calculated. REF,i .

[0142] In the process of lunar calibration, there is no gas absorption or scattering in the solar reflection spectrum, and the angle between the incident solar light and the normal of the lunar surface is θ. The classical solar radiation reflection model is used to obtain the radiance L of the lunar reflection corresponding to the i-spectrum of the spaceborne visible light camera to be calibrated. REF,i :

[0143] ;

[0144] ;

[0145] in, is the process quantity; ρ i is the equivalent lunar reflectivity of the i-th spectral band of the onboard visible light camera to be calibrated; E i is the equivalent solar spectral irradiance of the i-th spectrum incident on the lunar surface; d is the sun-moon distance factor, which is the ratio of the real-time sun-moon distance to the standard sun-moon distance; θ is the angle between the incident solar ray and the normal of the lunar surface.

[0146] The solar spectrum irradiance, lunar model reflectivity and camera spectral response function corresponding to different spectral bands of the spaceborne visible light camera are different. The equivalent value is calculated by the following formula;

[0147] ;

[0148] ;

[0149] in, is the spectral response function of the i-th spectral band of the satellite-borne visible light camera, such as Figure 4 As shown; The lunar spectral reflectance provided by the lunar radiation model. Common lunar radiation models include Apollo-16, Selene, MS-3, CE-3 and other internationally recognized models; λ is the wavelength of the sun incident on the moon, λ1 and λ2 are the lower and upper limits of the spectrum of the i-th spectral band of the onboard visible light camera to be calibrated; is the solar spectral irradiance incident on the moon, such as Figure 5 As shown;

[0150] Step 5: Calculate the observed moon phase angle :

[0151] ;

[0152] Among them, in, em and They are respectively the incident zenith angle of the sun on the moon at a certain moment in the calibration arc, the observation zenith angle of the visible light camera on the satellite to be calibrated, and the relative azimuth angle between the two.

[0153] Step 6: Determine the orbit that meets the following three conditions as the lunar calibration arc segment and execute step 7; otherwise, return to step 2;

[0154] (1) The lunar phase angle during imaging is consistent with the phase angle of the reference lunar radiation model;

[0155] (2) The radiance L of the moon reflected by the visible light camera to be calibrated REF,iIt is within the response dynamic range of the onboard visible light camera to be calibrated;

[0156] (3) The lunar calibration area is within the field of view of the visible light camera on board the satellite to be calibrated.

[0157] Step 7: Establish the calibration time and output DN of the visible light camera on board to be calibrated i The value is related to the radiance L reflected by the moon REF,i The linear relationship between them is used to calculate the absolute calibration coefficient k corresponding to the i-th spectral segment of the onboard visible light camera to be calibrated. i and b i , complete the calibration:

[0158] ;

[0159] ;

[0160] ;

[0161] Among them, k i is the calibration slope of the i-th spectrum segment, in units of DN i is the observation value of the i-band of the onboard visible light camera; b i is the calibration intercept of the i-th spectral segment, in units of ; , are the two lunar reflected radiances in the i-th spectral band, , These are the numerical quantified values ​​corresponding to the two lunar reflection radiances.

[0162] After the calibration is completed, the various error sources generated during the lunar on-orbit radiation calibration process are analyzed and the total uncertainty δ of the radiation calibration is calculated:

[0163] ;

[0164] Among them, δ1 is the measurement uncertainty of the distance from the moon to the sun, δ2 is the measurement uncertainty of the distance from the moon to the entrance pupil of the visible light camera on the satellite to be calibrated; δ3 and δ4 are the uncertainty of solar irradiance and angle measurement of sunlight incident on the lunar surface, respectively; δ5 is the attitude pointing uncertainty; δ6 is the uncertainty of the lunar reflection model.

[0165] Corresponding to the above-mentioned embodiment of the method for calibrating the absolute radiation of the moon for a space-borne visible light camera, the present invention also provides an embodiment of an apparatus for calibrating the absolute radiation of the moon for a space-borne visible light camera.

[0166] The device for calibrating the absolute radiometry of the moon for a spaceborne visible light camera provided in an embodiment of the present invention includes one or more processors for implementing the method for calibrating the absolute radiometry of the moon for a spaceborne visible light camera in the above embodiment.

[0167] The embodiments of the device for calibrating the absolute radiation of the moon for a satellite-borne visible light camera of the present invention can be applied to any device with data processing capabilities, and the device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented by software, or by hardware or a combination of software and hardware. Taking software implementation as an example, as a device in a logical sense, it is formed by the processor of any device with data processing capabilities in which it is located reading the corresponding computer program instructions in the non-volatile memory into the memory for execution. From the hardware level, in addition to the processor, memory, network interface, and non-volatile memory, the device with data processing capabilities in which the device in the embodiment is located can also include other hardware according to the actual functions of the device with data processing capabilities, which will not be described in detail.

[0168] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0169] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The device embodiment described above is only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of the present invention. Ordinary technicians in this field can understand and implement it without paying creative work.

[0170] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, the method for calibrating the absolute radiation of the moon for a spaceborne visible light camera in the above embodiment is implemented.

[0171] The computer-readable storage medium may be an internal storage unit of any device with data processing capability described in any of the aforementioned embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device, such as a plug-in hard disk, a smart memory card (SmartMedia card, SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capability and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capability, and may also be used to temporarily store data that has been output or is to be output.

[0172] Those skilled in the art will readily appreciate other embodiments of the present application after considering the description and practicing the contents disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The description and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the claims.

[0173] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for calibrating the absolute radiometric quality of a satellite-borne visible light camera on the moon, characterized in that: The method comprises the following steps: S1: Based on the ephemeris, the spatial position motion equations of the sun and the moon in the geocentric coordinate system are established to obtain the sun's position vector R sun , velocity vector V sun , and the moon's position vector R Lunar and velocity vector V Lunar ; The position vector R of the onboard visible light camera to be calibrated in the geocentric coordinate system is calculated based on the ephemeris, orbital parameters and the Earth orbit dynamics model. RS and velocity vector V RS ; S2: Based on the calculation results of S1, calculate the distance between the moon and the satellite-borne visible light camera respectively , the distance between the sun and the moon , and the angles between the sun, moon and the principal optical axis of the onboard visible light camera ; S3: The distance between the sun and the moon calculated from S2 , calculate the solar spectral irradiance incident on the lunar surface ; S4: Solar spectral irradiance obtained from S3 According to Lambert's cosine law and the lunar reflection model, the radiance L of the lunar reflection corresponding to the spectral band i of the spaceborne visible light camera to be calibrated is calculated. REF,i ; S5: Calculate the observed moon phase angle ; S6: Determine the orbit that meets the following three conditions as the lunar calibration arc segment, and execute S7; Otherwise, return to S2; (1) The lunar phase angle during imaging is consistent with the phase angle of the reference lunar radiation model; (2) The radiance L of the moon reflected by the visible light camera to be calibrated REF,i It is within the response dynamic range of the onboard visible light camera to be calibrated; (3) The lunar calibration area is within the field of view of the visible light camera on board the satellite to be calibrated; S7: Establish the output DN of the onboard visible light camera to be calibrated at the calibration time i The value is related to the radiance L reflected by the moon REF,i The linear relationship between them is used to calculate the absolute calibration coefficient k corresponding to the i-th spectral segment of the onboard visible light camera to be calibrated. i and b i , the calibration is completed.

2. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 1, characterized in that: In S1, the sun's position vector R is calculated. sun and velocity vector V sun The specific steps include the following: (1) First convert the given date into the Julian century: ； ； In the formula, T represents the Julian century, JD represents the Julian day, y represents the year, m represents the month, and d represents the day number; (2) Based on the Julian century number obtained in step (1), calculate the orbital parameters of the approximate elliptical orbit of the sun's relative motion with respect to the center of the earth, including the eccentricity e, mean anomaly M, solar geometric mean ecliptic longitude Lo, solar center difference C, and true anomaly V: ； ； ； ； ； (3) Based on the orbital elements obtained in step (2), the spatial position motion equation of the sun in its perifocal coordinate system is established, with the sun's state vector (R S ,V S )express: ； ； Among them, R S 、V S are the position vector and velocity vector of the sun in the perifocal coordinate system, a is the semi-major axis of the orbit, is the Earth-Sun gravitational parameter, represents angular momentum; (4) Calculate the transformation matrix Conv from the solar perifocal coordinate system to the Earth's geocentric coordinate system SUN : ； Where γ is the solar orbit inclination, is the right ascension of the ascending node of the solar orbit, is the argument of perigee of the solar orbit, and are two orbit corrections; (5) Based on the state vector of the sun in its perifocal coordinate system obtained in step (3) and the transformation matrix obtained in step (4), the spatial position motion equation of the sun in the earth's geocentric coordinate system is established to obtain the sun's position vector R sun and velocity vector V sun , with the sun's state vector (R sun ,V sun )express: ； 。 3. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 2, characterized in that: Calculate the moon's position vector R Lunar and velocity vector V Lunar and calculate the sun's position vector R sun and velocity vector V sun The method is the same as that of , that is, the motion state vector (R) of the moon in the perifocal coordinate system is calculated in turn according to the lunar ephemeris and orbital parameters. Lunar_0 , V Lunar_0 ), the transformation matrix Conv from the near-focus coordinate system to the geocentric coordinate system Lunar and the state vector of the moon in the geocentric coordinate system (R Lunar , V Lunar ).

4. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 1, characterized in that: Calculate the position vector R of the satellite-borne visible light camera to be calibrated in the geocentric coordinate system RS and velocity vector V RS , specifically including the following sub-steps: (1) Based on the orbit determination of the global navigation satellite system, the six orbital elements of the onboard visible light camera are calculated to calculate the initial state vector (R RS_0 , V RS_0 ); (2) Calculate the satellite's motion state vector after Δt time according to the following formula: ； ； In the formula, R RS 、V RS They represent the motion state vector after Δt time, f, g, , are the Lagrange coefficient and its first-order derivative, respectively, and the expressions are as follows: ； ； ； ； In the formula, R RS_0 represents the modulus of the initial state vector; R RS represents the modulus of the motion state vector after Δt time, is the global anomaly of the orbit, which is solved iteratively by the following global Kepler equation, and the expression is as follows: ； In the formula, is the Earth's gravitational constant, is the inverse of the semi-major axis of the orbit, S(z) and C(z) are Stumpf functions, expressed as follows: ； ； (3) Establish an iterative solution model for the satellite motion state, and solve the final motion state vector (R RS , V RS ).

5. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 1, characterized in that: Calculating the distance between the moon and a visible light camera on board , the distance between the sun and the moon The calculation formula is as follows: ； ； Among them, (x Lunar ,y Lunar , z Lunar )、(x RS ,y RS , z RS )、(x sun ,y sun , z sun ) are the coordinates of the Moon, the spaceborne visible light camera to be calibrated, and the Sun in the geocentric coordinate system.

6. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 1, characterized in that: L REF,i The calculation formula is as follows: ； ； ； ； in, is the spectral response function of the i-th spectral band of the spaceborne visible light camera; is the lunar spectral reflectance provided by the lunar radiation model; λ is the wavelength of the sun incident on the moon, λ1 and λ2 are the lower and upper limits of the spectrum of the i-th spectral band of the onboard visible light camera to be calibrated; is the solar spectral irradiance incident on the moon; is the process quantity; ρ i is the equivalent lunar reflectivity of the i-th spectral band of the onboard visible light camera; E i is the equivalent solar spectral irradiance of the i-th spectrum incident on the lunar surface; d is the sun-moon distance factor, which is the ratio of the real-time sun-moon distance to the standard sun-moon distance; θ is the angle between the incident solar ray and the normal of the lunar surface.

7. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 1, characterized in that: The moon phase angle is observed in S5 The calculation formula is as follows: ； Among them, in, em and They are respectively the incident zenith angle of the sun on the moon at a certain moment in the calibration arc, the observation zenith angle of the visible light camera on the satellite to be calibrated, and the relative azimuth angle between the two.

8. The method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to claim 1, characterized in that: In S7, the absolute calibration coefficient k i and b i The calculation formula is as follows: ； ； Among them, k i is the calibration slope of the i-th spectrum segment, in units of DN i is the observation value of the i-band of the onboard visible light camera; b i is the calibration intercept of the i-th spectral segment, in units of ; , are the two lunar reflected radiances in the i-th spectral band, , These are the numerical quantified values ​​corresponding to the two lunar reflection radiances.

9. A device for calibrating the absolute radiometric quality of a satellite-borne visible light camera for the moon, characterized in that: The method comprises one or more processors for implementing the method for calibrating the lunar absolute radiation of a spaceborne visible light camera according to any one of claims 1 to 8.

10. An electronic device, characterized in that: include: one or more processors; A storage device for storing one or more programs. When the one or more programs are executed by the electronic device, the electronic device implements the method for calibrating the lunar absolute radiation of a space-borne visible light camera as described in any one of claims 1 to 8.

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