High-precision normalized radiometric calibration method for satellite-borne infrared camera

Abstract

The invention discloses a satellite-borne infrared camera high-precision normalized radiometric calibration method, which mainly comprises the following five steps of: (1) constructing a radiometric calibration model based on laboratory radiometric calibration data before emission; (2) performing high-frequency on-orbit radiation calibration on the satellite-borne infrared camera based on the high-frequency on-satellite calibration data; (3) monitoring radiation response characteristics of the satellite-borne infrared camera based on the high-frequency satellite calibration data; (4) checking the precision of the calibration coefficient regularly; and (5) correcting the on-satellite radiometric calibration model based on autonomous site calibration or cross calibration according to a calibration precision verification result or user requirements fed back in the previous step. By adopting the method, the frequency and the precision of on-orbit radiometric calibration of the satellite-borne infrared camera are improved, and a basis is provided for quantitative application of the satellite-borne infrared camera.

Description

Technical Field

[0001] The invention relates to the field of satellite-borne infrared remote sensing, and in particular to a high-precision normalized radiation calibration method for a satellite-borne infrared camera. Background Art

[0002] At present, satellite-borne infrared remote sensing technology is developing rapidly. It has become the main means of detecting land surface temperature and sea surface temperature. A large number of satellite remote sensing temperature products based on satellite remote sensing detection are also widely used. During the on-orbit operation of satellite-borne infrared cameras, due to the interference of various components aging, space environment and other factors, the performance and sensitivity of the camera will continue to decay, resulting in a certain deviation between the radiation performance of the entire remote sensing system and the laboratory calibration results before launch, thus affecting the quantitative application of infrared remote sensing. Therefore, it is necessary to perform high-precision normalized radiation calibration on satellite-borne infrared cameras, monitor the radiation performance of infrared cameras and the accuracy of on-orbit calibration, so as to ensure the calibration accuracy of satellite thermal infrared cameras, thereby ensuring the inversion accuracy of satellite remote sensing temperature products.

[0003] Some of the traditional radiation calibration methods based on autonomous calibration fields (calibration sites equipped with automated infrared radiation measurement devices are referred to as autonomous calibration fields) establish the relationship between the response value of the thermal infrared camera and the automated measurement data of the entrance pupil. They do not consider the change in the bottom level of the thermal infrared camera each time it is turned on, and do not use the on-board calibration data. Some are not systematic enough and do not consider the calibration frequency issue. Summary of the invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a high-precision normalized radiation calibration method for a satellite-borne infrared camera, which can effectively improve the on-orbit radiation quality for satellite-borne medium- and long-wave infrared cameras.

[0005] The technical solution of the present invention is: 1. A high-precision normalized radiation calibration method for a satellite-borne infrared camera, comprising:

[0006] (1) Obtain an on-orbit calibration model through laboratory calibration;

[0007] (2) Based on the on-board calibration data at different calibration times, on-orbit radiation calibration is performed, the on-board internal calibration equation is calculated, and the entrance pupil calibration equation is obtained through the on-orbit calibration model;

[0008] (3) Based on the onboard calibration data and onboard internal calibration equation at each calibration time, monitor the radiation response characteristics of the infrared camera, including monitoring the NETD, the slope and intercept of the onboard internal calibration equation;

[0009] (4) Based on monitoring results or user needs, the on-orbit calibration accuracy is verified through the pupil entrance calibration equation. The verification methods include: Method 1: Based on the observation data and measured data of the autonomous calibration field, the on-board calibration accuracy is given; Method 2: Based on the cross-reference satellite, the on-board calibration accuracy is evaluated through several cross-validation areas;

[0010] (5) Based on the calibration accuracy verification results or user requirements, the on-orbit calibration model is corrected through the entrance pupil calibration equation; the correction methods include: Method 1: Correcting the on-orbit calibration model based on the observation data and measured data of the autonomous calibration field; Method 2: Correcting the on-orbit calibration model through several cross calibration areas based on the cross reference satellite;

[0011] Whether to use method 1 or method 2 in step (3) and step (4) is determined based on the frequency with which the infrared camera can image the autonomous calibration field.

[0012] Furthermore, step (1) obtains an on-orbit calibration model through laboratory calibration, specifically in the following manner:

[0013] (1.1) Analyze the temperature changes of different parts of the infrared camera, obtain the relationship between the temperature change of each part and the change of the infrared camera response caused by the temperature change, and determine the temperature correction method of each part;

[0014] (1.2) After correcting the temperature of each part of the calibration data, analyze the linearity between the corrected data and the incident radiance;

[0015] (1.3) According to the above linearity, determine the linear or nonlinear on-board internal calibration equation and the entrance pupil calibration equation;

[0016] (1.4) The conversion relationship between the on-board internal calibration equation and the entrance pupil calibration equation is established, thus obtaining the on-orbit calibration model.

[0017] Furthermore, the parts include a camera body, a focal plane and a dewar.

[0018] Furthermore, step (2) performs on-orbit radiation calibration based on the on-board calibration data at different calibration times, calculates the on-board internal calibration equation, and obtains the entrance pupil calibration equation through the on-orbit calibration model, specifically in the following manner:

[0019] (2.1) Screen the on-board blackbody temperature and the response stability of the high-temperature and low-temperature blackbody calibration on the satellite, and select the high-temperature and low-temperature blackbody temperatures T on the satellite that can be used for subsequent calculations h 、T l And the response DN of high temperature and low temperature black body calibration on the satellite h DN l ;

[0020] (2.2) According to the temperature correction method obtained in the laboratory calibration process, the temperature correction is performed on the corresponding parts of the response of the high-temperature and low-temperature black bodies in the on-board calibration after screening, and the effective on-board calibration response DN is obtained. h ′、DN l ′;

[0021] (2.3) Calculate the high and low temperature blackbody temperatures T on the star h , T l The corresponding equivalent radiance value Le h ,Le l Based on Le h ,Le l and DN h ′、DN l ′, calculate the internal calibration equation Le = K N DN+C N , and based on the on-orbit calibration model obtained by laboratory calibration, the calibration equation at the entrance pupil Le = K W DN+C W ; Among them, K N , C N is the slope and intercept of the internal calibration equation on board, K W , C W are the slope and intercept of the calibration equation at the entrance pupil, Le represents the equivalent radiance value of the black body on the star, and DN represents the response of the calibration black body on the star.

[0022] Furthermore, in step (3), the radiation response characteristics of the infrared camera are monitored according to the on-board calibration data and the on-board internal calibration equation at each calibration time, specifically in the following manner:

[0023] (3.1) Based on the onboard calibration data, calculate the radiation sensitivity of the infrared camera at each different calibration time:

[0024]

[0025] Where NETD is the radiation sensitivity, T h , T l are the temperatures of the high-temperature and low-temperature black bodies calibrated on the satellite, DN h DN l are the responses of the high-temperature and low-temperature black bodies calibrated on the satellite, respectively. h Noi l They are the noise of high-temperature and low-temperature black bodies calibrated on the satellite respectively;

[0026] (3.2) Establish the slope and intercept of the on-board internal calibration equation under the same imaging parameters, as well as the statistical table of radiation sensitivity, and statistically analyze the changes in the slope and intercept of the on-board calibration equation and NETD each time.

[0027] Further, in step (4), method 1: providing the on-board calibration accuracy based on the observation data and measured data of the autonomous calibration field, comprises the following steps:

[0028] Based on the observation value of the autonomous calibration field observed by the infrared camera synchronously, the equivalent radiance value Le at the entrance pupil of the infrared camera is obtained by substituting it into the calibration equation at the entrance pupil. i1 , and then converted to brightness temperature T i1 , i=1,2,…,M1, M1 is the number of autonomous calibration fields;

[0029] Based on the measured values ​​of the self-calibrated field radiometer measured by the infrared camera synchronous observation, the measured equivalent radiance value is obtained by spectral matching;

[0030] Using the measured equivalent radiance value and the satellite observation geometric path, the atmospheric transmittance and atmospheric path radiation are simulated. The atmospheric transmittance and atmospheric path radiation are integrated with the response function of the satellite infrared channel to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera. i2 , and then converted to brightness temperature T i2 ;

[0031] Calculate the calibration error σ i =T i1 -T i2 , calculate the mean and variance of the M1 autonomous calibration field errors as the result of the on-board calibration accuracy.

[0032] Further, in step (5), method 1: based on the observation data and measured data of the autonomous calibration field, the on-orbit calibration model is corrected, specifically:

[0033] Based on the observation value of the autonomous calibration field observed by the infrared camera synchronously, the equivalent radiance value Le at the entrance pupil of the infrared camera is obtained by substituting it into the calibration equation at the entrance pupil. x1 , x=1,2,…,X, X is the number of autonomous calibration fields;

[0034] Based on the measured values ​​of the self-calibrated field radiometer measured by the infrared camera synchronous observation, the measured equivalent radiance value is obtained by spectral matching;

[0035] Using the measured equivalent radiance value and the satellite observation geometric path, the atmospheric transmittance and atmospheric path radiation are simulated. The atmospheric transmittance and atmospheric path radiation are integrated with the response function of the satellite infrared channel to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera. x2 ;

[0036] Based on the equivalent radiance value Le obtained multiple times over a period of time x1 and equivalent radiance value Le x2 , established Le x1 and Le x2The linear or nonlinear relationship between them is used to correct the on-orbit calibration model.

[0037] Further, in step (4), method 2: based on the cross-reference star, the on-board calibration accuracy is evaluated through a number of cross-validation areas, including the following steps:

[0038] Calculate the spectral matching factor between the satellite to be evaluated and the cross-reference satellite through the spectral response curve and the cross-validation area;

[0039] Extract the response I of the cross-validation area of ​​the satellite infrared camera to be evaluated, and convert the response value I into the equivalent radiance value Le at the entrance pupil of the satellite infrared camera to be evaluated j1 , and then converted to brightness temperature T j1 , j = 1, 2, ..., M2, M2 is the number of cross-validation regions;

[0040] Extract the response II of the cross-validation area of ​​the cross-reference star infrared camera, convert the response value II into the equivalent radiance value at the entrance pupil of the cross-reference star infrared camera, and then calculate the equivalent radiance value Le at the entrance pupil of the infrared camera of the satellite to be evaluated through the spectral matching factor. j2 , and then converted to brightness temperature T j2 ;

[0041] Calculate the calibration error σ j =T j1 -T j2 , calculate the mean and variance of the M2 cross-validation area errors as the result of the on-board calibration accuracy.

[0042] Further, in step (5), method 2: based on the cross reference satellite, the on-orbit calibration model is corrected through a number of cross calibration areas, specifically:

[0043] Calculate the spectral matching factor between the satellite to be evaluated and the cross-reference satellite through the spectral response curve and the cross-calibration area;

[0044] Extract the response I of the cross-calibration area of ​​the satellite infrared camera to be evaluated, and convert the response value I into the equivalent radiance value Le at the entrance pupil of the satellite infrared camera to be evaluated y1 , y=1,2,…,Y, Y is the number of cross calibration areas;

[0045] Extract the response II of the cross-calibration area of ​​the cross-reference star infrared camera, convert the response value II into the equivalent radiance value at the entrance pupil of the cross-reference star infrared camera, and then calculate the equivalent radiance value Le at the entrance pupil of the infrared camera of the satellite to be evaluated through the spectral matching factor. y2 ;

[0046] Based on the equivalent radiance value Le j1 and equivalent radiance value Le j2, established Le j1 and Le j2 The linear or nonlinear relationship between them is used to correct the on-orbit calibration model. The advantages of the present invention compared with the prior art are:

[0047] The present invention proposes a high-precision normalized radiation calibration method for satellite-borne infrared cameras on orbit. Normalized radiation calibration is carried out based on the on-board calibration device, the autonomous calibration field, and the cross-reference satellite. The radiation performance of the camera is monitored. After changes are detected, the camera is recalibrated based on the autonomous calibration field or the cross-reference satellite. This patent is more comprehensive and systematic than the traditional calibration method.

[0048] 1) The present invention takes into account the changes in the bottom level of the infrared spectrum, conducts normalized radiation calibration based on the on-board calibration device, establishes a calibration relationship between the radiance after on-board calibration and the field automation observation data, and monitors and corrects the on-board calibration model based on the autonomous calibration field to further improve the on-orbit calibration accuracy;

[0049] 2) The present invention proposes an analysis of the laboratory calibration model, and multiple temperature corrections and linearity analysis are more conducive to improving the accuracy of on-orbit calibration;

[0050] 3) This invention adds calibration quality assessment to the normalized calibration for the first time, proposes to monitor the radiation characteristics of the infrared payload on orbit, and plans to carry out observations based on the autonomous calibration field based on the radiation performance monitoring results;

[0051] 4) The present invention regularly evaluates the on-board calibration accuracy based on the autonomous calibration field, which can ensure the radiation calibration accuracy within the entire payload cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a process flow chart of the present invention. DETAILED DESCRIPTION

[0053] In order to better understand the technical solution of the present invention, the specific implementation mode of the present invention is described in detail below with reference to the accompanying drawings.

[0054] The satellite-borne infrared camera described in the present invention mainly refers to an earth observation infrared camera in the medium and long wave spectrum, and does not involve near-infrared and short-wave infrared cameras. Near-infrared and short-wave infrared cameras are generally calibrated using diffuse reflection plates on the satellite.

[0055] The main process of the method of the present invention can be referred to as follows Figure 1 , mainly includes the following steps:

[0056] Step 1: Obtain an on-orbit calibration model through laboratory calibration

[0057] (1.1) Analysis of the impact of temperature on calibration;

[0058] Infrared cameras are particularly sensitive to the temperature environment of imaging, and it is necessary to analyze the temperature changes of various parts, mainly including the focal plane temperature, camera body temperature and Dewar temperature.

[0059] Camera body temperature: ΔDN1=F1(ΔT1,ΔT2,…,ΔT N )

[0060] Focal surface temperature: ΔDN2 = F2 (ΔT 焦面 )

[0061] Dewar and other temperatures: ΔDN3=F3(ΔT 杜瓦 )

[0062] Among them, ΔDN is the change in the infrared camera response caused by temperature change, F1, F2, F3 are the correction functions of the camera body temperature, focal plane temperature, Dewar temperature, etc.; ΔT1, ΔT2, …, ΔT N are the changes of the actual temperature of lens 1, lens 2, ..., lens N relative to the reference temperature in the infrared camera; ΔT 焦面 is the change in actual focal surface temperature relative to its reference temperature; ΔT 杜瓦 It is the change of the actual temperature of the Dewar relative to its reference temperature.

[0063] (1.2) Linearity analysis

[0064] After the calibration data is corrected for temperature such as focal plane temperature, camera body temperature, and Dewar temperature, the linearity between the corrected data and the incident radiant brightness is analyzed. If the linearity is poor, a nonlinear calibration equation needs to be established.

[0065] (1.3) Calibration equation establishment

[0066] Based on the analysis results of the previous step, linear or nonlinear calibration equations for on-board internal calibration (i.e., half-optical path on-board calibration) and entrance pupil calibration (i.e., full optical path calibration) are obtained.

[0067] (1.4) Establish the conversion relationship between the internal calibration equation on the satellite and the calibration equation at the entrance pupil

[0068] Based on the obtained on-board internal calibration equation Le = K N DN+C N And the calibration equation at the entrance pupil Le = K W DN+C W , establish the conversion relationship K between the two w ,C w =F(K N ,C N ), that is, the on-orbit calibration model is obtained, which provides a model for the processing of calibration data on the on-orbit satellite. N , CN is the slope and intercept of the internal calibration equation on board, K W , C W is the slope and intercept of the calibration equation at the entrance pupil, C W Also characterized as the bottom level of the infrared camera.

[0069] Step 2: Conduct on-orbit high-frequency radiation calibration based on high-frequency on-board calibration data

[0070] (2.1) Screening of onboard calibration data validity

[0071] The on-board blackbody temperature and the response stability of the on-board calibration high-temperature and low-temperature blackbody are screened, and the high-temperature and low-temperature blackbody temperatures T on the on-board blackbody that can be used for subsequent calculations are screened. h , T l And the response DN of high temperature and low temperature black body calibration on the satellite h DN l .

[0072] (2.2) Ambient temperature correction

[0073] Based on the focal plane temperature, camera body temperature and Dewar temperature correction method obtained in 1.1, the responses of the high-temperature and low-temperature black bodies screened in the previous step are corrected to obtain the effective on-board calibration response DN h ′、DN l ′.

[0074] (2.3) Calibration equation calculation

[0075] First, based on formula (1) and formula (2), the equivalent radiance values ​​Le corresponding to the high and low temperature black bodies on the star are calculated: h ,Le l ; Then, based on the equivalent radiance Le of the high and low temperature black bodies on the star h ,Le l The effective response DN of high and low temperature black bodies on the satellite h ′、DN l ′, use the two-point method to calculate the internal calibration equation Le = K N DN+C N , and based on the on-orbit calibration model K obtained in 1.4 w ,C w =F(K N ,C N ) to obtain the calibration equation Le = K at the entrance pupil W DN+C W .

[0076]

[0077] Where ε is the blackbody emissivity on the star; λ1 and λ2 are the starting wavelength and cutoff wavelength (μm); R(λ) is the relative spectral response of the infrared camera; L(λ,T) is the spectral radiance at different wavelengths and temperatures calculated by Planck's formula (W / sr.m2).

[0078] Step 3: Monitor the infrared camera radiation response characteristics based on high-frequency onboard calibration data and onboard internal calibration equations

[0079] (3.1) Based on the high-frequency on-board calibration data, calculate the radiation sensitivity NETD of the infrared camera at each different calibration time

[0080]

[0081] T h 、T l are the temperatures of the high-temperature and low-temperature black bodies calibrated on the star respectively;

[0082] DN h DN l They are the responses of the high-temperature and low-temperature black bodies calibrated on the satellite respectively;

[0083] Noi h Noi l They are the noise of high-temperature and low-temperature black bodies calibrated on the satellite respectively;

[0084] (3.2) Statistical analysis of the changes in the internal calibration equation and NETD on board each time.

[0085] The on-board internal calibration equation and radiation sensitivity database under the same imaging parameters (integration time and gain) are established, as shown in the following table.

[0086] Table 1 Statistics of camera radiation response characteristics

[0087] Serial number Imaging time Slope of onboard internal calibration equation On-board internal calibration equation intercept NETD 1 2 … N

[0088] Step 4: Based on monitoring results or user needs, verify the on-orbit calibration accuracy through the pupil entrance calibration equation

[0089] (4.1) For a satellite-borne infrared camera that can frequently image the autonomous calibration field, the on-board calibration accuracy within a stage is given based on the observation data and measured data of multiple autonomous calibration fields. The specific process is as follows:

[0090] a) Substitute the observed value DN of the autonomous calibration field based on the synchronous observation of the infrared camera into the calibration equation at the entrance pupil to be evaluated to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera i1 , and then converted to brightness temperature T i1, i=1,2,…,M1, M1 is the number of autonomous calibration fields. When extracting satellite channel count values, it is necessary to ensure that the extraction area is the synchronous observation area of ​​the radiation calibration field to ensure the accuracy of spatial matching. In order to minimize the impact of image noise, try to select the average value of multiple uniform pixels for matching;

[0091] b) Based on the infrared camera synchronously observing the measured value of the autonomous calibration field radiometer, the equivalent radiance value measured in the autonomous calibration field is obtained through spectral matching;

[0092] c) Input the atmospheric and ground observation parameters (i.e., the measured equivalent radiance values) at the time of satellite transit and the satellite's observation geometric path into MODTRAN to simulate the atmospheric transmittance and atmospheric path radiation. Then, integrate them with the response function of the satellite's infrared channel to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera. i2 , and then converted to brightness temperature T i2 ;

[0093] d) Calculate the calibration error σ i =T i1 -T i2 , and finally calculate the mean and variance of the errors of M1 autonomous calibration fields,

[0094] As a result of the onboard calibration accuracy.

[0095] (4.2) For satellite-borne infrared cameras with poor maneuverability and few opportunities to image the autonomous calibration field, the accuracy of on-board calibration is evaluated based on cross-reference satellites (i.e., reference satellites with similar imaging spectrum to the infrared camera of the satellite to be evaluated and high calibration accuracy) and multiple cross-validation areas (observation data of the satellite to be evaluated and the reference satellite at approximately the same time and location). The specific process is as follows:

[0096] a) Calculate the spectral matching factor between the satellite to be evaluated and the cross-reference satellite based on the spectral response curve and the cross-validation area;

[0097] b) Extract the response DN of the cross-validation area of ​​the satellite infrared camera to be evaluated, and convert it into the equivalent radiance value Le at the satellite entrance pupil according to the on-board calibration coefficient j1 , and then converted to brightness temperature T j1 , j = 1, 2, ..., M2, M2 is the number of cross-validation regions;

[0098] c) Extract the response of the cross-validation area of ​​the cross-reference star infrared camera, convert it into the equivalent radiance value at the entrance pupil of the cross-reference star infrared camera according to the on-board calibration coefficient, and then calculate the equivalent radiance value Le at the entrance pupil of the infrared camera of the satellite to be evaluated based on the spectral matching factor j2 , and then converted to brightness temperature T j2 ;

[0099] d) Calculate the calibration error σ j =T j1 -T j2 , and finally calculate the mean and variance of the M2 cross-region errors,

[0100] As a result of the onboard calibration accuracy.

[0101] Step 5: Based on the calibration accuracy verification results or user requirements, the on-orbit calibration model is modified through the entrance pupil calibration equation.

[0102] (5.1) For a spaceborne infrared camera that can frequently image the autonomous calibration field, the on-orbit calibration model is corrected based on the observation data and measured data of multiple autonomous calibration fields. The specific steps are as follows:

[0103] a) Based on the observation value of the autonomous calibration field observed by the infrared camera synchronously, substitute it into the calibration equation at the entrance pupil to be corrected to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera x1 , x=1,2,…,X, X is the number of autonomous calibration fields;

[0104] b) Based on the infrared camera synchronously observing the measured value of the autonomous calibration field radiometer, the equivalent radiance value measured in the autonomous calibration field is obtained through spectral matching;

[0105] c) Input the atmospheric and ground observation parameters at the time of satellite transit and the satellite's observation geometric path into MODTRAN to simulate the atmospheric transmittance and atmospheric path radiation, and then integrate them with the response function of the satellite infrared channel to obtain the equivalent radiance value Le at the entrance pupil x2 ;

[0106] d) Based on multiple Le x1 and Le x2 , establish a linear or nonlinear relationship between the two x2 =F Z (Le x1 );

[0107] e) Based on the Le obtained in the previous step x2 =F Z (Le x1 ) Modify the model in Section 1.4 to K w ,C w =F′(K N ,C N ).

[0108] (5.2) For spaceborne infrared cameras with poor maneuverability and little chance of imaging the autonomous calibration field, the on-orbit calibration model is corrected based on cross-calibration with reference satellites with high calibration accuracy and similar imaging spectrum. The specific steps are as follows:

[0109] a) Calculate the spectral matching factor between the satellite to be evaluated and the reference satellite based on the spectral response curve and the cross-calibration area (the observation data of the satellite to be evaluated and the reference satellite at approximately the same time and location);

[0110] b) Extract the response of the cross-calibration area of ​​the satellite infrared camera to be evaluated, and convert it into the equivalent radiance value Le at the satellite entrance pupil according to the on-board calibration coefficient y1 , y=1,2,…,Y, Y is the number of cross calibration areas;

[0111] c) Extract the response of the cross-calibration area of ​​the cross-reference star infrared camera, convert it into the equivalent radiance value at the entrance pupil of the cross-reference star infrared camera according to the on-board calibration coefficient, and then calculate the equivalent radiance value Le at the entrance pupil of the infrared camera of the satellite to be evaluated based on the spectral matching factor y2 ;

[0112] d) Based on cross-calibration data and Le y1 and Le y2 , establish a linear or nonlinear relationship between the two

[0113] Le y2 =F J (Le y1 );

[0114] e) Based on the Le obtained in the previous step y2 =F J (Le y1 ) Modify the model K in Section 1.4 w ,C w =F″(K N ,C N )

[0115] It is to be understood that the present invention is described by way of embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and embodiments that can fall within the scope of the claims of this application all fall within the scope protected by the present invention.

[0116] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A high-precision normalized radiation calibration method for a satellite-borne infrared camera, characterized in that: include: (1) Obtain an on-orbit calibration model through laboratory calibration; (2) Based on the on-board calibration data at different calibration times, on-orbit radiation calibration is performed, the on-board internal calibration equation is calculated, and the entrance pupil calibration equation is obtained through the on-orbit calibration model; (3) Based on the onboard calibration data and onboard internal calibration equation at each calibration time, monitor the radiation response characteristics of the infrared camera, including monitoring the NETD, the slope and intercept of the onboard internal calibration equation; (4) Based on monitoring results or user needs, the on-orbit calibration accuracy is verified through the pupil entrance calibration equation. The verification methods include: Method 1: Based on the observation data and measured data of the autonomous calibration field, the on-board calibration accuracy is given; Method 2: Based on the cross-reference satellite, the on-board calibration accuracy is evaluated through several cross-validation areas; (5) Based on the calibration accuracy verification results or user requirements, the on-orbit calibration model is corrected through the entrance pupil calibration equation; the correction methods include: Method 1: Correcting the on-orbit calibration model based on the observation data and measured data of the autonomous calibration field; Method 2: Correcting the on-orbit calibration model through several cross calibration areas based on the cross reference satellite; Whether to use method 1 or method 2 in step (3) and step (4) is determined based on the frequency with which the infrared camera can image the autonomous calibration field.

2. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: Step (1) obtains the on-orbit calibration model through laboratory calibration, and the specific method is as follows: (1.1) Analyze the temperature changes of different parts of the infrared camera, obtain the relationship between the temperature change of each part and the change of the infrared camera response caused by the temperature change, and determine the temperature correction method of each part; (1.2) After correcting the temperature of each part of the calibration data, analyze the linearity between the corrected data and the incident radiance; (1.3) According to the above linearity, determine the linear or nonlinear on-board internal calibration equation and the entrance pupil calibration equation; (1.4) The conversion relationship between the on-board internal calibration equation and the entrance pupil calibration equation is established, thus obtaining the on-orbit calibration model.

3. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 2 is characterized in that: The parts include a camera body, a focal plane and a dewar.

4. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: Step (2) performs on-orbit radiation calibration based on the on-board calibration data at different calibration times, calculates the on-board internal calibration equation, and obtains the entrance pupil calibration equation through the on-orbit calibration model, specifically in the following manner: (2.1) Screen the on-board blackbody temperature and the response stability of the high-temperature and low-temperature blackbody calibration on the satellite, and select the high-temperature and low-temperature blackbody temperatures T on the satellite that can be used for subsequent calculations h , T l And the response DN of high temperature and low temperature black body calibration on the satellite h DN l ; (2.2) According to the temperature correction method obtained in the laboratory calibration process, the temperature correction is performed on the corresponding parts of the response of the high-temperature and low-temperature black bodies in the on-board calibration after screening, and the effective on-board calibration response DN is obtained. h ′、DN l ′; (2.3) Calculate the high and low temperature blackbody temperatures T on the star h , T l The corresponding equivalent radiance value Le h ,Le l Based on Le h ,Le l and DN h ′、DN l ′, calculate the internal calibration equation Le = K N DN+C N , and based on the on-orbit calibration model obtained by laboratory calibration, the calibration equation at the entrance pupil Le = K W DN+C W ; Among them, K N , C N is the slope and intercept of the internal calibration equation on board, K W , C W are the slope and intercept of the calibration equation at the entrance pupil, Le represents the equivalent radiance value of the black body on the star, and DN represents the response of the calibration black body on the star.

5. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: In step (3), the radiation response characteristics of the infrared camera are monitored according to the on-board calibration data and the on-board internal calibration equation at each calibration time. The specific method is as follows: (3.1) Based on the onboard calibration data, calculate the radiation sensitivity of the infrared camera at each different calibration time: Where NETD is the radiation sensitivity, T h , T l are the temperatures of the high-temperature and low-temperature black bodies calibrated on the satellite, DN h DN l are the responses of the high-temperature and low-temperature black bodies calibrated on the satellite, respectively. h Noi l They are the noise of high-temperature and low-temperature black bodies calibrated on the satellite respectively; (3.2) Establish the slope and intercept of the on-board internal calibration equation under the same imaging parameters, as well as the statistical table of radiation sensitivity, and statistically analyze the changes in the slope and intercept of the on-board calibration equation and NETD each time.

6. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: In step (4), method 1: based on the observation data and measured data of the autonomous calibration field, the on-board calibration accuracy is given, including the following steps: Based on the observation value of the autonomous calibration field observed by the infrared camera synchronously, the equivalent radiance value Le at the entrance pupil of the infrared camera is obtained by substituting it into the calibration equation at the entrance pupil. i1 , and then converted to brightness temperature T i1 , i=1,2,…,M1, M1 is the number of autonomous calibration fields; Based on the measured values ​​of the self-calibrated field radiometer measured by the infrared camera synchronous observation, the measured equivalent radiance value is obtained by spectral matching; Using the measured equivalent radiance value and the satellite observation geometric path, the atmospheric transmittance and atmospheric path radiation are simulated. The atmospheric transmittance and atmospheric path radiation are integrated with the response function of the satellite infrared channel to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera. i2 , and then converted to brightness temperature T i2 ; Calculate the calibration error σ i =T i1 -T i2 , calculate the mean and variance of the M1 autonomous calibration field errors as the result of the on-board calibration accuracy.

7. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: In step (5), method 1: based on the observation data and measured data of the autonomous calibration field, the on-orbit calibration model is corrected. The specific method is as follows: Based on the observation value of the autonomous calibration field observed by the infrared camera synchronously, the equivalent radiance value Le at the entrance pupil of the infrared camera is obtained by substituting it into the calibration equation at the entrance pupil. x1 , x=1,2,…,X, X is the number of autonomous calibration fields; Based on the measured values ​​of the self-calibrated field radiometer measured by the infrared camera synchronous observation, the measured equivalent radiance value is obtained by spectral matching; Using the measured equivalent radiance value and the satellite observation geometric path, the atmospheric transmittance and atmospheric path radiation are simulated. The atmospheric transmittance and atmospheric path radiation are integrated with the response function of the satellite infrared channel to obtain the equivalent radiance value Le at the entrance pupil of the infrared camera. x2 ; Based on the equivalent radiance value Le obtained multiple times over a period of time x1 and the equivalent radiance value Le x2 , established Le x1 and Le x2 The linear or nonlinear relationship between them is used to correct the on-orbit calibration model.

8. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: In step (4), method 2: based on the cross-reference star, the on-board calibration accuracy is evaluated through several cross-validation areas, including the following steps: Calculate the spectral matching factor between the satellite to be evaluated and the cross-reference satellite through the spectral response curve and the cross-validation area; Extract the response I of the cross-validation area of ​​the satellite infrared camera to be evaluated, and convert the response value I into the equivalent radiance value Le at the entrance pupil of the satellite infrared camera to be evaluated j1 , and then converted to brightness temperature T j1 , j = 1, 2, ..., M2, M2 is the number of cross-validation regions; Extract the response II of the cross-validation area of ​​the cross-reference star infrared camera, convert the response value II into the equivalent radiance value at the entrance pupil of the cross-reference star infrared camera, and then calculate the equivalent radiance value Le at the entrance pupil of the infrared camera of the satellite to be evaluated through the spectral matching factor. j2 , and then converted to brightness temperature T j2 ; Calculate the calibration error σ j =T j1 -T j2 , calculate the mean and variance of the M2 cross-validation area errors as the result of the on-board calibration accuracy.

9. The high-precision normalized radiation calibration method for a satellite-borne infrared camera according to claim 1, characterized in that: In step (5), method 2: based on the cross reference satellite, the on-orbit calibration model is corrected through a number of cross calibration areas. The specific method is: Calculate the spectral matching factor between the satellite to be evaluated and the cross-reference satellite through the spectral response curve and the cross-calibration area; Extract the response I of the cross-calibration area of ​​the satellite infrared camera to be evaluated, and convert the response value I into the equivalent radiance value Le at the entrance pupil of the satellite infrared camera to be evaluated y1 , y=1,2,…,Y, Y is the number of cross calibration areas; Extract the response II of the cross-calibration area of ​​the cross-reference star infrared camera, convert the response value II into the equivalent radiance value at the entrance pupil of the cross-reference star infrared camera, and then calculate the equivalent radiance value Le at the entrance pupil of the infrared camera of the satellite to be evaluated through the spectral matching factor. y2 ; Based on the equivalent radiance value Le j1 and the equivalent radiance value Le j2 , established Le j1 and Le j2 The linear or nonlinear relationship between them is used to correct the on-orbit calibration model.

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