An infrared radiation calibration precision verification method based on Boltzmann constant

Abstract

The application provides an infrared radiation calibration precision verification method based on Boltzmann constant, comprising the following steps: in the satellite on-orbit calibration mode, cutting a reference black body into the infrared camera light path, performing full-aperture calibration, and acquiring black body temperature, platinum resistance state and other parameters; collecting gain, bias and other calibration data released by the calibration responsibility unit; calculating the black body radiation brightness according to the Planck radiation law; calculating the radiation brightness according to the calibration parameters, pixel DN value and other data; constructing precision verification variable S1; calculating the inversion value of the Boltzmann constant under specific conditions according to the black body temperature, wavelength, radiation brightness and other data; constructing precision verification variable S2; and further calculating the variance, deviation, sensitivity and other data on the basis of S1 and S2 to finely verify and judge the calibration precision.

Description

Technical Field

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

[0002] The calibration of payloads for Earth observation satellites in orbit generally involves four aspects: ground-based simulated space environment calibration, space-based on-orbit calibration, site-based on-orbit calibration, and satellite cross-calibration. The first two are crucial for the calibration of spaceborne remote sensors. Before launch into orbit, the calibration physical model of a spaceborne blackbody source is established. However, after long-term on-orbit operation, changes occur in the blackbody emissivity, platinum resistance thermometry characteristics, and infrared remote sensing payload detector characteristics, leading to deviations in remote sensing data. Therefore, data and model parameters measured in the laboratory before launch must undergo on-orbit calibration and verification before advanced data products can be produced. This is of great significance for improving the quantitative level of spaceborne remote sensors, maintaining the long-term validity of measurements, and coordinating and processing multi-source data.

[0003] After entering orbit, spaceborne remote sensors operate in a high-vacuum, low-gravity, and high-radiation space environment. Through extensive testing and data accumulation, the industry believes that commonly used physicochemical constants (such as the speed of light, electric charge, and Boltzmann constant) remain unchanged, atomic transition frequencies remain unchanged, and emission spectra remain unchanged. However, other equipment-related characteristics, such as emissivity, resistivity, and responsivity, will change. For spaceborne remote sensors operating in the infrared band, on-orbit calibration typically involves carrying a space reference blackbody and arranging platinum resistance thermometers within it for temperature measurement. On-orbit platinum resistance thermometers are susceptible to shock, vibration, and natural aging; the drift in their values ​​reduces the accuracy of temperature measurements and increases the uncertainty in the calibration process.

[0004] To ensure the effectiveness of traceability of critical measurements during on-orbit operation, platinum resistance thermometers need to be periodically recalibrated. A common practice is to install a miniature phase transition fixed-point device on the blackbody, with a phase transition material encapsulated within its shell, presenting a standard temperature value at the phase transition point. Because the phase transition material is sealed, it is less affected by the external environment. However, this method has the following main drawbacks: 1) The phase transition fixed point increases the complexity of the design and maintenance of the on-board blackbody and has a certain impact on the blackbody's radiation characteristics; 2) It requires the deployment of multiple platinum resistance sensors, increasing development costs; 3) In actual space use, the operation process is cumbersome, introducing more uncertain parameters, and multiple measurement operations are challenging. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for verifying the accuracy of infrared radiometric calibration based on the Boltzmann constant. By comparing radiance and analyzing changes in the Boltzmann constant, the range of changes in calibration parameters and attenuation can be determined, thereby determining whether the radiometric calibration data meets the usage requirements and providing a basis for judging the accuracy of subsequent quantitative inversion parameters.

[0006] This application provides a method for verifying the accuracy of infrared radiometric calibration based on the Boltzmann constant, including:

[0007] M1: In the satellite's on-orbit calibration mode, the on-board reference blackbody is inserted into the imaging optical path of the infrared radiation imaging system, and the on-board reference blackbody is heated to the set blackbody temperature T. The infrared radiation emitted by the on-board reference blackbody is then detected by the detector of the infrared radiation imaging system.

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

[0009] M3: Constructing the first precision test variable

[0010] M4: Based on the spectral radiance L at the entrance pupil λ The Boltzmann value k at the blackbody temperature T was calculated by inversion. T And construct a second precision test variable S2, which is the Boltzmann value k. T The difference between the theoretical value of Boltzmann's constant k and the actual value k.

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

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

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

[0014] M52: The infrared radiation calibration accuracy is determined using the second precision test variable S2, including: if any one of the deviation, variance, or relative error of the second precision test variable S2 at 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 at 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 ranges from 5% to 10%, and the second set threshold ranges from 0.1% to 1%.

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

[0017] In at least one embodiment, the infrared radiation imaging system includes a spaceborne infrared camera and 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 blackbody 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 spectral radiance L at the entrance pupil is obtained by the detector of the infrared radiation imaging system. λ The steps include:

[0020] After the infrared radiation imaging system captures an image, according to formula L λ =DN λ ·g λ +Lo λ The gray values ​​of detector pixels in each band of the mid- and long-wave infrared channel are converted into spectral radiance L at the detector entrance pupil. λ , where L λ The spectral radiance at the center wavelength λ is expressed in W·m. -2 ·sr -1 ·μm -1 DN λ Let g be the gray value of the detector pixel at wavelength λ. λ Lo is the gain at the center wavelength λ. λ This is the bias 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 center wavelength.

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

[0025] Through Calculate the deviation of the second-precision test variable S2;

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

[0027] Through Calculate the relative error of the second precision test variable S2;

[0028] Where, k Ti For multiple temperature points T i Different Boltzmann values ​​are given.

[0029] This application also provides a computer-readable storage medium having software instructions stored thereon, which, when executed, perform the above-described method.

[0030] The advantages of this invention compared to existing technologies are as follows: the method of this invention does not require many additional devices and systems. Without increasing the complexity of common satellite systems, it only adds a small amount of hardware (such as platinum resistance thermometers) and working modes (such as collecting calibration data per orbit). By using on-board processing or integrated space-ground processing to construct specific parameter variables, the accuracy of on-board calibration system parameters can be verified, and the long-term state change trend can be judged. This greatly reduces computational complexity and improves the efficiency of information acquisition and processing. Attached Figure Description

[0031] The following description, in conjunction with the accompanying drawings, will further illustrate the above-mentioned features, technical characteristics, advantages, and implementation methods of this application in a clear and understandable manner. The accompanying drawings are for illustrative and explanatory purposes only and do not limit the scope of this application. Wherein:

[0032] Figure 1 This is a schematic diagram of the on-board system composition involved in the method of the present invention;

[0033] Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0034] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments of this application will now be described with reference to the accompanying drawings.

[0035] It should be noted that the definition of accuracy for mid- and long-wavelength infrared radiometric calibration typically includes two aspects: first, the accuracy of the radiometric calibration system, requiring system errors to be controlled within allowable limits; and second, the accuracy of the radiometric calibration coefficients, requiring them to accurately reflect the functional relationship between the output signal value and the input radiation, or to approximately accurately reflect it within a certain error range. The accuracy of the calibration system mainly stems from the influence of factors such as the uniformity, stability, temperature measurement accuracy, and emissivity error of the surface source blackbody. The method of this invention does not evaluate the accuracy of the radiometric calibration system, but only verifies the accuracy of the radiometric calibration coefficients.

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

[0037] Onboard reference blackbody (standard blackbody);

[0038] Platinum resistance thermometer, embedded in an on-board reference blackbody, is used to measure the temperature of the on-board reference blackbody;

[0039] A / D converter;

[0040] Infrared radiation imaging systems, such as spaceborne infrared cameras or spectral imaging systems, include components such as lenses, detectors, and electronic systems;

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

[0042] The flowchart of the infrared radiometric calibration accuracy verification method based on the Boltzmann constant provided by this invention is as follows: Figure 2 As shown, the specific steps include:

[0043] M1: In the satellite's on-orbit calibration mode, the on-board reference blackbody is inserted into the imaging optical path of the infrared radiation imaging system with full aperture and full field of view. The on-board reference blackbody is heated to a set temperature T, and the blackbody radiation brightness at the entrance pupil is sensed by the detector of the infrared radiation imaging system. After electronic transformation, it becomes the DN value of the image (the gray value of the detector pixel, which is a digital quantity).

[0044] The platinum resistance thermometer embedded in the on-board reference blackbody changes its resistance value as the standard blackbody temperature changes. After processing with relevant circuits (such as preamplifier circuits) and A / D conversion, and then curve fitting, the blackbody temperature T under the ITS-90 temperature scale can be obtained.

[0045] M2: Calculate the blackbody spectral radiance at temperature T based on Planck's law and formula for blackbody radiation (as shown in equation (1) below):

[0046]

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

[0048] If the radiance is determined, the blackbody temperature T can be deduced from equation (1):

[0049]

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

[0051]

[0052] After imaging, the DN values ​​of each band of the long-wave infrared channel in the image are converted into spectral radiance at the entrance pupil of the detector:

[0053] L λ =DN λ ·g λ +Lo λ (4)

[0054] Among them, L λ The spectral radiance at the center wavelength λ (in W·m) -2 ·sr -1 ·μm -1 ), DN λ For the DN value of wavelength λ, g λ And Lo λ These are the gain and bias at the center wavelength λ, respectively (these parameters are usually released along with the remote sensing data, and their 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 on-board reference blackbody to the detector of the infrared radiation imaging system is very short, and its energy loss can be ignored, or considered as a very small and relatively stable invariant. Therefore, the sum of the radiance of all pixels is comparable to the radiance of the on-board reference blackbody.

[0056] M3: Construct an accuracy verification variable S1 based on the measured and theoretical values ​​obtained above.

[0057] Calculate the measurement error between the measured and theoretical values ​​corresponding to the center wavelength of the long-wave infrared channel of the infrared radiation imaging system, and calculate the ratio of the measurement error to the theoretical value as the accuracy verification variable S1:

[0058]

[0059] Among them, L λ L(λ,T) 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 data such as the on-board reference blackbody temperature, wavelength, and radiance, the Boltzmann constant value under specific conditions is calculated and retrieved. For the radiance obtained based on the measured values, the Boltzmann value k at temperature T is calculated and retrieved. T :

[0061]

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

[0063] Construct the accuracy test variable S2;

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

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

[0066] M5: Statistically calculate the first precision test variable S1 at different blackbody temperatures T, and the deviation, variance, and relative error of the second precision test variable S2 at different blackbody temperatures T. These are used as indicators to test the accuracy of infrared radiation calibration, and to verify and judge the calibration accuracy.

[0067] Because the accuracy verification variables S1 and S2 contain calibration parameter information, their further statistical bias, 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., which can comprehensively verify and evaluate the calibration accuracy.

[0068] The deviation of S2 is calculated using the following formula:

[0069]

[0070] The variance of S2 is calculated using the following formula:

[0071]

[0072] The relative error of S2 is calculated using the following formula:

[0073]

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

[0075] In the process of verifying and judging the calibration accuracy, a preliminary judgment is first made using the first accuracy verification variable S1. If the preliminary judgment is qualified, a final judgment is then made using the second accuracy verification variable S2. The specific process includes...

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

[0077] M52: The infrared radiation calibration accuracy is determined using the second precision test variable S2, including: if any one of the deviation, variance, or relative error of the second precision test variable S2 at 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 at 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 explanation uses an HJ-2IRS calibration example; the process is as follows:

[0079] M1: In the satellite's on-orbit calibration mode, the onboard reference blackbody is inserted into the imaging optical path of the onboard infrared camera with full aperture and full field of view for full aperture calibration, obtaining parameters such as the reference blackbody temperature. Specifically, this includes the following steps:

[0080] M11: The imaging / calibration optical path switching is achieved through the front-end pointing mirror. In conjunction with the on-board calibration equipment, the variable-temperature blackbody, and related facilities, it can realize the acquisition of mid- and long-wave infrared channel radiation information in orbit with full aperture and full optical path.

[0081] M12: The spaceborne infrared camera calibration system can use multiple blackbody sets for multi-temperature point calibration, or it can use a single blackbody set for calibration at different temperature points. Taking the HJ-2IRS calibration as an example (setting the low-temperature end T...),... l With high temperature end T h (Two temperature points), the procedure is as follows: when the satellite is in the shadow area, the blackbody is heated to T. h The mirror is rotated to point at the blackbody, and the focal plane circuit of the medium- and long-wave channel is activated to acquire blackbody radiation data; the blackbody heating is stopped, and the blackbody is allowed to cool down to T. l Then, blackbody radiation data were collected again.

[0082] M13: The blackbody temperature is measured using a high-precision resistance thermometer (a platinum resistance thermometer circuit is used in this embodiment), and the measurement accuracy meets the requirements for on-orbit application. The platinum resistance thermometer circuit uses multi-point deployment, pre-amplification, and 16-bit A / D conversion technology to collect data on the resistance value in response to temperature changes and calculate the blackbody temperature T.

[0083] M2: Acquire 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 values, and other data. λ Specifically, this includes:

[0084] M21: Calibration data such as gain and bias used for radiometric correction of infrared cameras. It is usually released along with remote sensing data, and its parameter information can be obtained through the information release channels of the calibration responsible unit.

[0085] M22: According to formula (1), respectively at the low temperature end T l With high temperature end T h Under the given conditions, the blackbody spectral radiance corresponding to the center wavelength of the long-wave infrared channel in the satellite is calculated through inversion:

[0086]

[0087] M23: Convert the DN values ​​of each band of the long-wave infrared channel in the image into the spectral radiance at the sensor entrance pupil according to formula (4):

[0088] L λ =DN λ ·g λ +Lo λ (4)

[0089] It should be noted that a flat DN value indicates good uniformity of the blackbody, meaning that the radiance value per unit area on the blackbody is consistent. Specifically, to ensure testing accuracy, the DN value for each spectral band can be obtained by averaging the DN values ​​of all values ​​in its 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 radiance L(λ,T)), construct the accuracy test variable S1;

[0091] According to formula (5), calculate the measurement error between the measured value and the theoretical value corresponding to the center wavelength of the long-wave infrared channel of the mid-infrared camera:

[0092]

[0093] M4: Calculate the Boltzmann constant value under specific conditions based on data such as blackbody temperature, wavelength, and radiance; construct the accuracy verification variable S2.

[0094] M41: The Boltzmann value k at temperature T can be calculated by inverting the above radiance obtained based on the measured values ​​according to formula (6). T ;

[0095]

[0096] M42: For the Boltzmann values ​​at temperature T obtained from the above-mentioned inversion based on measured radiance, calculate the error between the values ​​and the Boltzmann constant according to formula (7), and construct the accuracy verification variable S2:

[0097] S2=k T -k

[0098] M5: Statistically measure 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 verifying the accuracy of infrared radiation calibration.

[0099] The statistical bias, variance, and sensitivity of the accuracy test variables S1 and S2 obtained above can reflect the accuracy of the on-orbit calibration system and calibration parameters, enabling a comprehensive test and evaluation of the calibration accuracy. Through example calculations, the S2 bias is less than 1%, proving the method's effectiveness.

[0100] The contents not described in detail in this specification are common knowledge to 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 way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0102] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A method for verifying the accuracy of infrared radiometric calibration based on the Boltzmann constant, comprising: M1: In the satellite's on-orbit calibration mode, the on-board reference blackbody is inserted into the imaging optical path of the infrared radiation imaging system, and the on-board reference blackbody is heated to the set blackbody temperature T. The infrared radiation emitted by the on-board reference blackbody is then detected by the detector of the infrared radiation imaging system. M2: Based on Planck's law of blackbody radiation, the spectral radiance of the blackbody is inverted from the blackbody temperature T to obtain the blackbody spectral radiance L(λ,T); the spectral radiance L at the entrance pupil is obtained from the detector of the infrared radiation imaging system. λ ; M3: Constructing the first precision test variable ； M4: Based on the spectral radiance L at the entrance pupil λ The Boltzmann value k at the blackbody temperature T was calculated by inversion. T And construct a second precision test variable S2, which is the Boltzmann value k. T The difference between the theoretical value of Boltzmann's constant k and the actual value k. 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 verifying the accuracy of infrared radiation calibration. Step M5 includes: M51: If any of the first precision test variables S1 at different blackbody temperatures T is greater than or equal to the first set threshold, the infrared radiation calibration accuracy is determined to be unqualified, and the test method is terminated; if the first precision test variables S1 at different blackbody temperatures T are all less than the first set threshold, then proceed to step M52. M52: The infrared radiation calibration accuracy is determined using the second precision test variable S2, including: if any one of the deviation, variance, or relative error of the second precision test variable S2 at 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 at different blackbody temperatures T are all less than the second set threshold, the infrared radiation calibration accuracy is determined to be qualified.

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

3. The method according to claim 1, wherein, The blackbody temperature T is obtained by measuring a platinum thermocouple embedded in an on-board reference blackbody.

4. The method according to claim 1, wherein, Infrared radiation imaging systems include spaceborne infrared cameras and spectral imaging systems, including lenses, detectors, and electronic systems.

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

6. The method according to claim 1, wherein, In step M2, the spectral radiance L at the entrance pupil is obtained by the detector of the infrared radiation imaging system. λ The steps include: After the infrared radiation imaging system captures an image, according to formula L λ =DN λ ·g λ +Lo λ The gray values ​​of detector pixels in each band of the mid- and long-wave infrared channel are converted into spectral radiance L at the detector entrance pupil. λ , where L λ The spectral radiance at the center wavelength λ is expressed in W·m. -2 ·sr -1 ·μm -1 DN λ Let g be the gray value of the detector pixel at wavelength λ. λ Lo is the gain at the center wavelength λ. λ This is the bias at the center wavelength λ.

7. 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 inversion formula. T : ， Where h is Planck's constant, c is the speed of light in vacuum, and λ is the center wavelength.

8. The method according to claim 1, wherein, In step M5, Through Calculate the deviation of the second-precision test variable S2; Through Calculate the variance of the second-precision test variable S2; Through Calculate the relative error of the second precision test variable S2; Where, k Ti These represent different Boltzmann values ​​at multiple temperature points Ti.

9. A computer-readable storage medium having software instructions stored thereon, which, when executed, perform the method according to any one of claims 1-8.

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