Infrared radiation calibration precision test method based on Boltzmann constant

Abstract

The invention provides an infrared radiation calibration precision test method based on a Boltzmann constant, and the method comprises the steps: enabling a reference black body to be switched into an infrared camera light path in a satellite in-orbit calibration mode, carrying out the full-aperture calibration, and obtaining the temperature of the black body, the state of a platinum resistor, and other parameters; acquiring calibration data such as gain and bias released by a calibration responsibility unit; calculating black body radiation brightness according to the Planck radiation law; radiance is calculated according to data such as calibration parameters and pixel DN values; constructing a precision test variable S1; according to data such as blackbody temperature, wavelength and radiation brightness, calculating a Boltzmann constant value under a specific inversion condition; constructing a precision test variable S2; and data such as variance, deviation and sensitivity are further calculated on the basis of S1 and S2, and the calibration precision is finely inspected and judged.

Description

Technical Field

[0001] The invention belongs to the technical field of aerospace quantitative remote sensing and relates to an on-orbit infrared band temperature measurement calibration method. Background Art

[0002] The calibration of the payload of Earth observation satellites in orbit is generally divided into four aspects: ground-based simulated space environment calibration, space on-orbit calibration, site on-orbit calibration, and satellite cross-calibration. The first two are the key to the calibration of space remote sensors. Before the spacecraft carrying the space reference blackbody source is launched into orbit, the calibration physical model of the blackbody source has been established. After long-term on-orbit operation, the blackbody emissivity, platinum resistance temperature measurement characteristics, infrared remote sensing payload detector characteristics, etc. are all changing, which will cause deviations in remote sensing data. Therefore, the data and model parameters measured in the laboratory before the remote sensor is launched must be calibrated and calibrated on-orbit before further advanced data products can be produced. This is of great significance for improving the quantification level of space remote sensors, maintaining the long-term validity of the values, and coordinating detection and consistency processing of multi-source data.

[0003] After entering orbit, aerospace remote sensors are placed in a space environment of high vacuum, low gravity, and strong radiation. After a large number of tests and data accumulation, the industry believes that common physical and chemical constants (such as the speed of light, charge, Boltzmann constant, etc.) remain unchanged, atomic transition frequency remains unchanged, and emission spectrum remains unchanged, while other equipment-related characteristics, such as emissivity, resistance, and responsiveness, will change. For aerospace remote sensors working in the infrared band, in order to achieve on-orbit calibration, they generally carry a space reference blackbody and place a platinum resistor inside the blackbody for temperature measurement. Platinum resistance thermometers on orbit are affected by shock, vibration, and natural aging. The drift of the value will reduce the measurement accuracy of temperature and increase the uncertainty in the calibration process.

[0004] In order to ensure the effectiveness of the traceability of key values ​​during the on-orbit period, the platinum resistance thermometer needs to be regularly recalibrated. The usual practice is to install a miniature phase change fixed point device on the black body, which has a phase change material encapsulated in its shell and presents a standard temperature value at the phase change point. Since the phase change material is sealed, it is less affected by the external environment. This method has the following main disadvantages: 1) The phase change fixed point increases the complexity of the on-board black body design and maintenance, and has a certain impact on the black body radiation characteristics; 2) Multiple platinum resistance sensors need to be deployed, which increases the development cost; 3) In the actual use of space, the operation process is cumbersome, which will introduce more uncertain parameters, and multiple measurement operations are difficult. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides an infrared radiation calibration accuracy inspection method based on the Boltzmann constant. By comparing the radiation brightness and analyzing the change of the Boltzmann constant, the range of the calibration parameter change and the attenuation degree can be judged, and then whether the radiation calibration data meets the use requirements can be judged, providing a judgment basis for the accuracy of the subsequent quantitative inversion parameters.

[0006] The present application provides an infrared radiation calibration accuracy inspection method based on the Boltzmann constant, comprising:

[0007] M1: In the satellite on-orbit calibration working mode, the on-board reference black body is cut into the imaging optical path of the infrared radiation imaging system, and the on-board reference black body is heated to the set black body temperature T, and the infrared radiation emitted by the on-board reference black body is detected by the detector of the infrared radiation imaging system;

[0008] M2: According to Planck's law of blackbody radiation, the spectral radiation brightness of the blackbody is inverted based on the blackbody temperature T to obtain the blackbody spectral radiation brightness L(λ,T); the spectral radiation brightness L at the entrance pupil is obtained by the detector of the infrared radiation imaging system λ ;

[0009] M3: Construct the first precision test variable

[0010] M4: Based on the spectral radiance L at the entrance pupil λ , inversely calculate the Boltzmann value k at the blackbody temperature T T , and construct a second precision test variable S2, the second precision test variable S2 is the Boltzmann value k T The difference between the theoretical value k of the Boltzmann constant;

[0011] M5: Count the deviation, variance and relative error of the first precision test variable S1 under different blackbody temperatures T, and count the deviation, variance and relative error of the second precision test variable S2 under different blackbody temperatures T as indicators for the accuracy test of infrared radiation calibration.

[0012] In at least one embodiment, step M5 includes:

[0013] M51: If any one of the first accuracy test variables S1 under different blackbody temperatures T is greater than or equal to the first set threshold, it is determined that the infrared radiation calibration accuracy is unqualified and the test method is terminated; if the first accuracy test variables S1 under different blackbody temperatures T are all less than the first set threshold, proceed to step M52;

[0014] M52: Use the second precision test variable S2 to determine the accuracy of infrared radiation calibration, including: if any one of the deviation, variance, and relative error of the second precision test variable S2 under different blackbody temperatures T is greater than or equal to the second set threshold, the infrared radiation calibration accuracy is determined to be unqualified; if the deviation, variance, and relative error of the second precision test variable S2 under different blackbody temperatures T are all less than the second set threshold, the infrared radiation calibration accuracy is determined to be qualified.

[0015] In at least one embodiment, the first set threshold value ranges from 5% to 10%; the second set threshold value ranges from 0.1% to 1%.

[0016] In at least one embodiment, the blackbody temperature T is obtained by measuring a platinum temperature measuring resistor embedded in a reference blackbody on board a satellite.

[0017] In at least one embodiment, the infrared radiation imaging system includes a satellite-borne infrared camera, a spectral imaging system, including a lens, a detector, and an electronics system.

[0018] In at least one embodiment, in step M1, the on-board reference black body is inserted into the imaging optical path of the infrared radiation imaging system with full aperture and full field of view.

[0019] In at least one embodiment, in step M2, the detector of the infrared radiation imaging system obtains the spectral radiation brightness L at the entrance pupil. λ The steps include:

[0020] After the infrared radiation imaging system is imaged, according to the formula L λ =DN λ ·g λ +Lo λ , convert the detector pixel grayscale value of each band of the medium and long wave infrared channel into the spectral radiation brightness L at the detector entrance pupil λ , where L λ is the spectral radiance at the central wavelength λ, in W·m -2 ·sr -1 μm -1 , D.N. λ is the grayscale value of the detector pixel at wavelength λ, g λ is the gain at the center wavelength λ, Lo λ is the offset at the center wavelength λ.

[0021] In at least one embodiment, in step M4, the Boltzmann value k at the blackbody temperature T is calculated based on the following formula: T :

[0022]

[0023] Where h is Planck's constant, c is the speed of light in vacuum, and λ is the central wavelength.

[0024] In at least one embodiment, in step M5,

[0025] Pass-through Calculating the deviation of the second precision test variable S2;

[0026] Pass-through Calculate the variance of the second precision test variable S2;

[0027] Pass-through Calculate the relative error of the second accuracy test variable S2;

[0028] Among them, k Ti For multiple temperature points T i Different Boltzmann values ​​under .

[0029] The present application also provides a computer-readable storage medium having software instructions stored thereon, wherein the software instructions implement the above method when executed.

[0030] The advantages of the present invention over the prior art are that the method of the present invention does not require too many additional equipment and systems. Without increasing the complexity of common satellite systems, only a small amount of hardware (such as platinum resistance) and working modes (such as collecting calibration data for each orbit) are added. By using on-board processing or integrated space-ground processing and constructing specific parameter variables, the accuracy of the on-board calibration system parameters can be tested, and the long-term state change trend can be judged, which greatly reduces the calculation complexity and improves the efficiency of information acquisition and information processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The following will further explain the above characteristics, technical features, advantages and implementation methods of the present application in a clear and understandable manner through the description of the preferred embodiments and in combination with the accompanying drawings. The following drawings are only intended to illustrate and explain the present application, and do not limit the scope of the present application. Among them:

[0032] Figure 1 The schematic diagram of the on-board system involved in the method of the present invention;

[0033] Figure 2 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0034] In order to have a clearer understanding of the technical features, purposes and effects of the present application, the specific implementation methods of the present application are now described with reference to the accompanying drawings.

[0035] It should be noted that the definition of the accuracy of infrared radiation calibration for medium and long wave channels usually includes two aspects: one is the accuracy of the radiation calibration system, which requires the system error to be controlled within the allowable index; the other is the accuracy of the radiation calibration coefficient, which requires the correct reflection of the functional relationship between the output signal value and the input radiation, or the approximately correct reflection within a certain error range. The accuracy of the calibration system mainly comes from the influence of the uniformity, stability, temperature measurement accuracy, emissivity error, etc. of the surface source blackbody. The method of the present invention does not judge the accuracy of the radiation calibration system, but only tests the accuracy of the radiation calibration coefficient.

[0036] The system involved in the method of the present invention is as follows Figure 1 As shown, it mainly includes:

[0037] On-star reference black body (standard black body);

[0038] Platinum resistor, embedded in the on-board reference black body, used to measure the temperature of the on-board reference black body;

[0039] A / D converter;

[0040] Infrared radiation imaging system, such as a spaceborne infrared camera or spectral imaging system, including lenses, detectors and electronic systems;

[0041] The onboard computer and data transmission system are used for data collection, data processing and data transmission to the ground.

[0042] The process of the infrared radiation calibration accuracy inspection method based on the Boltzmann constant provided by the present invention is as follows: Figure 2 As shown, the specific steps include:

[0043] M1: In the satellite on-orbit calibration working mode, the on-board reference black body is cut into the imaging optical path of the infrared radiation imaging system with full aperture and full field of view, and the on-board reference black body is heated to the set temperature T. The detector of the infrared radiation imaging system senses the black body radiation brightness at the entrance pupil, which is electronically transformed into the DN value of the image (the gray value of the detector pixel, which is a digital quantity).

[0044] The platinum resistor embedded in the satellite's reference black body will change its resistance when the standard black body temperature changes. Through relevant circuits (such as preamplifier circuit, etc.) and A / D conversion, and then through curve fitting, the black body temperature T under the ITS-90 temperature scale can be obtained.

[0045] M2: According to Planck's law of blackbody radiation and the formula (as shown in the following formula (1)), calculate the blackbody spectral radiation brightness of the blackbody at temperature T:

[0046]

[0047] Where λ is the center wavelength of the channel, L(λ,T) is the spectral radiance at the center wavelength λ (in W·m -2 ·sr -1 μm -1 ), T is the black body temperature, h is Planck's constant, c is the speed of light in vacuum, and k is the Boltzmann constant.

[0048] If the radiation brightness is determined, the black body temperature T can be inverted according to formula (1):

[0049]

[0050] If T, L(λ,T) and wavelength λ can be determined, the value of the Boltzmann constant can be further inverted:

[0051]

[0052] After the infrared radiation imaging system is imaged, the DN value of each band of the long-wave infrared channel in the image is converted into the spectral radiation brightness at the entrance pupil of the detector:

[0053] L λ =DN λ ·g λ +Lo λ (4)

[0054] Among them, L λ is the spectral radiance at the central wavelength λ (in W·m -2 ·sr -1 μm -1 ), DN λ is the DN value of wavelength λ, g λ and Lo λ They are respectively the gain and bias at the central wavelength λ (usually released together with the remote sensing data, and their parameter information can be obtained through the information release channels of the calibration processing responsible unit).

[0055] From the perspective of energy conservation, the optical path from the onboard reference blackbody radiation to the detector of the infrared radiation imaging system is very short, and its energy loss can be ignored, or considered to be a very small and relatively stable invariant. Then, the sum of the radiation brightness of all pixels is comparable to the radiation brightness of the onboard reference blackbody.

[0056] M3: Construct the accuracy test variable S1 for the measured values ​​and theoretical values ​​obtained above:

[0057] The measurement errors of the measured value and the theoretical value corresponding to the central wavelength of the long-wave infrared channel of the infrared radiation imaging system are calculated respectively, and the ratio of the measurement error to the theoretical value is calculated as the accuracy test variable S1:

[0058]

[0059] Among them, L λ is the measured value calculated according to formula (4), and L(λ,T) is the theoretical value calculated according to formula (1).

[0060] M4: Based on the temperature, wavelength, and radiant brightness of the reference black body on the satellite, calculate and invert the value of the Boltzmann constant under specific conditions. For the radiant brightness obtained based on the measured value, invert and calculate the Boltzmann value k at temperature T. T :

[0061]

[0062] Among them, k T is the Boltzmann value at blackbody temperature T, L λ is the measured spectral radiance calculated according to formula (4).

[0063] Construct accuracy test variable S2;

[0064] S2=k T -k (7)

[0065] Among them, k T is the Boltzmann value at temperature T obtained based on the inversion of the measured radiance, and k is the theoretical value of the Boltzmann constant.

[0066] M5: Count the deviation, variance and relative error of the first precision test variable S1 under different blackbody temperatures T, and count the deviation, variance and relative error of the second precision test variable S2 under different blackbody temperatures T as indicators for the accuracy test of infrared radiation calibration, and test and judge the calibration accuracy.

[0067] Because the accuracy test variables S1 and S2 contain calibration parameter information, their further statistical deviation, variance, relative error, etc. can reflect the accuracy of the on-orbit calibration system and calibration parameters. For example, according to the accuracy requirements of different satellites, the threshold of the relative error of S2 can be set, such as 0.1%, 0.5%, 1%... etc., so as to conduct a comprehensive test and evaluation of the calibration accuracy.

[0068] The calculation method of S2 deviation is as follows:

[0069]

[0070] The variance of S2 is calculated as follows:

[0071]

[0072] The relative error of S2 is calculated as follows:

[0073]

[0074] In the three equations (8), (9), and (10), k Ti are different Boltzmann values ​​at multiple temperature points Ti.

[0075] In the process of checking and judging the calibration accuracy, the first accuracy test variable S1 is first used to make a preliminary judgment. If the preliminary judgment is qualified, the second accuracy test variable S2 is used to make a final judgment. The specific process includes:

[0076] M51: If any of the first accuracy test variables S1 under different blackbody temperatures T is greater than or equal to the first set threshold, it is determined that the infrared radiation calibration accuracy is unqualified and the test method is terminated; if the first accuracy test variables S1 under different blackbody temperatures T are all less than the first set threshold, then proceed to step M52

[0077] M52: Use the second precision test variable S2 to determine the accuracy of infrared radiation calibration, including: if any one of the deviation, variance, and relative error of the second precision test variable S2 under different blackbody temperatures T is greater than or equal to the second set threshold, the infrared radiation calibration accuracy is determined to be unqualified; if the deviation, variance, and relative error of the second precision test variable S2 under different blackbody temperatures T are all less than the second set threshold, the infrared radiation calibration accuracy is determined to be qualified.

[0078] The following is an example of HJ-2IRS calibration. The process is as follows:

[0079] M1: In the satellite on-orbit calibration mode, the on-board reference black body is inserted into the imaging optical path of the onboard infrared camera with full aperture and full field of view to perform full aperture calibration and obtain parameters such as the reference black body temperature. The specific steps include:

[0080] M11: The imaging / calibration optical path switching is realized through the front-end pointing mirror, and the variable temperature black body and related facilities of the on-board calibration equipment are used to realize the radiation information collection of the full-aperture and full-optical path medium and long-wave infrared channels in orbit.

[0081] M12: The satellite infrared camera calibration system can use multiple sets of black bodies for multi-temperature point calibration, or can use one set of black bodies to achieve calibration at different temperature points. Take HJ-2IRS calibration as an example (set the low temperature end T l With high temperature end T h Two temperature points), the process is: when the satellite is in the shadow area, heat the black body to T h , the swing mirror rotates to point to the black body, and the focal plane circuit of the medium and long wave channel is turned on to collect the black body radiation data; the black body heating is stopped, and the black body is cooled to T l , collect blackbody radiation data again.

[0082] M13: The blackbody temperature is measured by a high-precision temperature measuring resistor (a platinum resistance measurement circuit is used in this embodiment), and the temperature measurement accuracy meets the requirements of on-orbit application indicators. The platinum resistance measurement circuit uses multi-point layout, preamplification and 16-bit A / D conversion technology to collect data on the change in resistance value in response to temperature and calculate the blackbody temperature T.

[0083] M2: Collect calibration data such as gain and bias; invert the spectral radiance L(λ,T) of the blackbody based on the blackbody temperature T; calculate the spectral radiance L at the entrance pupil based on calibration parameters, pixel DN value and other data λ . Specifically include:

[0084] M21: The calibration data such as gain and bias used for infrared camera radiation correction are usually released with remote sensing data. Its parameter information can be obtained through the information release channels of the calibration responsible unit.

[0085] M22: According to formula (1), at the low temperature end T l With high temperature end T h Under these conditions, the blackbody spectral radiation brightness corresponding to the central wavelength of the satellite's medium and long-wave infrared channel is inverted and calculated:

[0086]

[0087] M23: According to formula (4), the DN value of each band of the long-wave infrared channel in the image is converted into the spectral radiance at the sensor entrance pupil:

[0088] L λ =DN λ ·g λ +Lo λ (4)

[0089] It should be noted that when the DN value is flat, it indicates that the uniformity of the black body is good, and the radiance value of each unit area on the black body is consistent. In particular, to ensure the accuracy of the test, the DN value of each spectral band can be obtained by taking the average of all DN values ​​of the corresponding spectral band.

[0090] M3: The measured value obtained above (i.e., the spectral radiance L at the entrance pupil) λ ) and the theoretical value (i.e., the blackbody spectral radiation brightness L(λ,T)), construct the accuracy test variable S1;

[0091] According to formula (5), the measurement errors between the measured value and the theoretical value corresponding to the central wavelength of the long-wave infrared channel of the mid-infrared camera are calculated respectively:

[0092]

[0093] M4: Based on the blackbody temperature, wavelength, radiation brightness and other data, calculate the value of the Boltzmann constant under specific inversion conditions; construct the accuracy test variable S2.

[0094] M41: For the radiance obtained based on the measured value, the Boltzmann value k at temperature T can be calculated by inversion according to formula (6): T ;

[0095]

[0096] M42: For the Boltzmann value at temperature T obtained by inversion based on the measured radiance, the error between it and the Boltzmann constant is calculated according to formula (7), and the accuracy test variable S2 is constructed:

[0097] S2=k T -k

[0098] M5: Statistically calculate the deviation, variance, and relative error of the first precision test variable S1 and the second precision test variable S2 at different blackbody temperatures T as indicators for the accuracy test of infrared radiation calibration.

[0099] The further statistical deviation, variance, sensitivity, etc. of the precision test variables S1 and S2 obtained above can reflect the accuracy of the on-orbit calibration system and calibration parameters, and can comprehensively test and evaluate the calibration accuracy. Through example calculation, the deviation of S2 is less than 1%, proving that the method is effective.

[0100] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

[0101] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0102] The above description is only an illustrative embodiment of the present application and is not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by any technician in the field without departing from the concept and principle of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for testing the accuracy of infrared radiation calibration based on the Boltzmann constant, comprising: M1: In the satellite on-orbit calibration working mode, the on-board reference black body is cut into the imaging optical path of the infrared radiation imaging system, and the on-board reference black body is heated to the set black body temperature T, and the infrared radiation emitted by the on-board reference black body is detected by the detector of the infrared radiation imaging system; M2: According to Planck's law of blackbody radiation, the spectral radiation brightness of the blackbody is inverted based on the blackbody temperature T to obtain the blackbody spectral radiation brightness L(λ,T); the spectral radiation brightness L at the entrance pupil is obtained by the detector of the infrared radiation imaging system λ ; M3: Construct the first precision test variable M4: Based on the spectral radiance L at the entrance pupil λ , inversely calculate the Boltzmann value k at the blackbody temperature T T , and construct a second precision test variable S2, the second precision test variable S2 is the Boltzmann value k T The difference between the theoretical value k of the Boltzmann constant; M5: Count the deviation, variance and relative error of the first precision test variable S1 under different blackbody temperatures T, and count the deviation, variance and relative error of the second precision test variable S2 under different blackbody temperatures T as indicators for the accuracy test of infrared radiation calibration.

2. The method according to claim 1, wherein: Step M5 includes: M51: If any one of the first accuracy test variables S1 under different blackbody temperatures T is greater than or equal to the first set threshold, it is determined that the infrared radiation calibration accuracy is unqualified and the test method is terminated; if the first accuracy test variables S1 under different blackbody temperatures T are all less than the first set threshold, proceed to step M52; M52: Use the second precision test variable S2 to determine the accuracy of infrared radiation calibration, including: if any one of the deviation, variance, and relative error of the second precision test variable S2 under different blackbody temperatures T is greater than or equal to the second set threshold, the infrared radiation calibration accuracy is determined to be unqualified; if the deviation, variance, and relative error of the second precision test variable S2 under different blackbody temperatures T are all less than the second set threshold, the infrared radiation calibration accuracy is determined to be qualified.

3. The method according to claim 2, wherein: The first set threshold value ranges from 5% to 10%; the second set threshold value ranges from 0.1% to 1%.

4. The method according to claim 1, wherein: The blackbody temperature T is measured by a platinum temperature measuring resistor embedded in a reference blackbody on board the satellite.

5. The method according to claim 1, wherein: The infrared radiation imaging system includes a satellite-borne infrared camera and a spectral imaging system, including lenses, detectors and electronics systems.

6. The method according to claim 1, wherein: In step M1, the on-board reference black body is inserted into the imaging optical path of the infrared radiation imaging system with full aperture and full field of view.

7. The method according to claim 1, wherein: In step M2, the detector of the infrared radiation imaging system obtains the spectral radiation brightness L at the entrance pupil. λ The steps include: After the infrared radiation imaging system is imaged, according to the formula L λ =DN λ ·g λ +Lo λ , convert the detector pixel grayscale value of each band of the medium and long wave infrared channel into the spectral radiation brightness L at the detector entrance pupil λ , where L λ is the spectral radiance at the central wavelength λ, in W·m -2 ·sr -1 μm -1 , D.N. λ is the grayscale value of the detector pixel at wavelength λ, g λ is the gain at the center wavelength λ, Lo λ is the offset at the center wavelength λ.

8. The method according to claim 1, wherein: In step M4, the Boltzmann value k at the blackbody temperature T is calculated based on the following formula: T : Where h is Planck's constant, c is the speed of light in vacuum, and λ is the central wavelength.

9. The method according to claim 1, wherein: In step M5, Pass-through Calculating the deviation of the second precision test variable S2; Pass-through Calculate the variance of the second precision test variable S2; Pass-through Calculate the relative error of the second accuracy test variable S2; Among them, k Ti For multiple temperature points T i Different Boltzmann values ​​under .

10. A computer-readable storage medium having stored thereon software instructions which, when executed, implement the method of any one of claims 1-9.

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