An efficient calibration method for wide dynamic range infrared radiation measurement system

Abstract

The present invention discloses an efficient calibration method for a wide dynamic range infrared radiation measurement system, which belongs to the field of infrared radiation measurement. The method comprises: step one, according to the energy transfer process of the infrared radiation measurement system with variable attenuation plate and integration time, establishing an infrared radiation measurement system response model that considers the influence of attenuation plate and integration time; step two, executing the acquisition strategy of black body image; step three, according to the infrared radiation measurement system response model that considers the influence of attenuation plate and integration time in step one, using weighted least square method to establish the objective function, and using optimization algorithm to minimize the objective function, so as to solve the calibration coefficient in the infrared radiation measurement system response model. According to the technical solution of the present invention, the infrared radiation measurement system with a wide dynamic range can save time and efficiently complete the radiation calibration task, and compared with the conventional calibration method, the calibration speed can be increased several times without reducing the calibration accuracy.

Description

Technical Field

[0001] The invention belongs to the field of infrared radiation measurement, and in particular relates to an efficient calibration method for a wide dynamic range infrared radiation measurement system. Background Art

[0002] Infrared radiation measurement is a technology that obtains the amount of infrared radiation emitted / reflected by the target itself without contact. It plays an important role in target detection and perception, infrared stealth performance evaluation, non-contact temperature measurement, quantitative remote sensing and other fields. In view of the importance of infrared radiation measurement technology, various countries have developed space-based, air-based and ground-based multi-platform systems; in order to measure multiple types of targets, infrared radiation measurement systems often achieve the purpose of wide dynamic range measurement by adding attenuation plates and integration time. The traditional infrared radiation calibration method uses a linear model to calibrate each integration time and attenuation plate position in turn, which requires a large number of calibration temperature points, resulting in a long calibration time (for wide dynamic range infrared radiation measurement systems, it often takes more than 10 hours of calibration time); this not only makes the radiation measurement task time-consuming and labor-intensive, but also the change in ambient temperature during the calibration process causes inaccurate calibration coefficients and reduces the accuracy of radiation measurement. Summary of the invention

[0003] The object of the present invention is to provide an efficient calibration method for a wide dynamic range infrared radiation measurement system, in an effort to solve or at least alleviate the above-mentioned problems.

[0004] The technical solution adopted by the present invention is an efficient calibration method for a wide dynamic range infrared radiation measurement system, the method comprising:

[0005] Step 1: According to the energy transfer process of the infrared radiation measurement system with variable attenuation sheet and integration time, a response model of the infrared radiation measurement system considering the influence of attenuation sheet and integration time is established;

[0006] Step 2, executing the acquisition strategy of black body image;

[0007] Step three, based on the infrared radiation measurement system response model considering the influence of attenuation plate and integration time in step one, the objective function is established using weighted least squares method, and the objective function is minimized using optimization algorithm to solve the calibration coefficient in the infrared radiation measurement system response model.

[0008] The beneficial effects of the present invention are:

[0009] (1) Considering a complete radiation calibration model: The influence of the attenuation plate and the integration time is taken into account in the infrared radiation calibration model. The advantage of this model is that efficient infrared radiation calibration can be achieved using only a few blackbody temperature calibration points;

[0010] (2) Time-saving and efficient: The wide dynamic range infrared radiation measurement system can save time and efficiently complete the radiation calibration task. Compared with the conventional calibration method, it can increase the calibration speed several times without reducing the calibration accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A flow chart showing an efficient calibration method for a wide dynamic range infrared radiation measurement system according to an embodiment of the present invention is shown.

[0012] Figure 2 The relative error comparison between the calibration method of the present invention and the conventional method is shown.

[0013] Figure 3 The relative error deviation between the calibration method of the present invention and the conventional method is shown. DETAILED DESCRIPTION

[0014] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms, and the present disclosure should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0015] The technical solution of the present invention first involves establishing an infrared radiation measurement system response model that takes into account the influence of attenuation plates and integration time according to the energy transfer process of the infrared radiation measurement system with variable attenuation plates and integration time, and then designing a specific and efficient calibration method based on the model, including a blackbody image acquisition strategy, objective function establishment and minimizing the objective function to obtain the model calibration coefficient.

[0016] Figure 1 A flow chart of an efficient calibration method for a wide dynamic range infrared radiation measurement system according to an embodiment of the present invention is shown. Figure 1 As shown, the specific steps of this method are as follows:

[0017] Step 1: According to the energy transfer process of the infrared radiation measurement system with variable attenuation plate and integration time, a response model of the infrared radiation measurement system considering the influence of attenuation plate and integration time is established.

[0018] The purpose of radiation calibration is to establish a quantitative relationship between the target incident radiation and the output value of the infrared radiation measurement system. Traditional infrared radiation calibration model:

[0019] (1)

[0020] In the formula, is the image gray value, To calibrate the radiation of a black body, is the response gain of the system, Is the system response bias. If the influence of integration time is considered, the response gain of the infrared detector is in direct proportion to the integration time, and the response bias of the infrared radiation measurement system is mainly composed of the infrared detector's own bias and the infrared radiation measurement system's thermal stray radiation. The infrared detector's own bias has nothing to do with the integration time, and the bias caused by the infrared radiation measurement system's thermal stray radiation is also in direct proportion to the integration time. Therefore, the infrared radiation calibration model considering the integration time is:

[0021] (2)

[0022] In the formula, is the integration time, is the system response gain per unit time, is the bias caused by stray radiation of the infrared radiation measurement system, is the bias caused by the detector dark current.

[0023] If the influence of the attenuation sheet is considered, the infrared radiation before the attenuation sheet will be attenuated by the attenuation sheet, and the attenuation sheet itself will also generate infrared radiation. Considering the integration time and the infrared radiation calibration model of the attenuation sheet:

[0024] (3)

[0025] In the formula, is the transmittance of the attenuator, is the bias caused by stray radiation of the infrared radiation measurement system in front of the attenuator, is the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the emissivity of the attenuator, This is the bias caused by the attenuator’s own radiation.

[0026] However, there is a certain deviation between the actual transmittance of the attenuation film and the design value, and the transmittance of the attenuation film may also change over time; therefore, directly bringing the design value into the calibration model will cause a large error and is not convenient for long-term use of the model; ideally, the actual transmittance of the attenuation film is equal to the design value, but in practice they are mainly linearly related, and a quadratic relationship is needed to correct the deviation between the ideal and actual conditions. Furthermore, the emissivity ε of the attenuation film is also unknown, which can be expressed by an empirical formula as , so the infrared radiation calibration model considering the integration time and attenuation sheet is finally:

[0027] (4)

[0028] In the formula, is the functional relationship between the actual transmittance of the attenuator and the design value, , , It is the quadratic term coefficient, linear term coefficient and constant term coefficient of the functional relationship between the actual transmittance of the attenuator and the design value. is the emissivity of the attenuator, is the correction factor related to the emissivity of the attenuation film. Sometimes, the integration time and the response are not in strict proportional relationship. The integration time is brought into the quadratic and cubic correction coefficients, and the final integration time and the radiation calibration mathematical model of the attenuation film are:

[0029] (5)

[0030] is a first-order correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the secondary correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, It is the third correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator.

[0031] Step 2: Execute the acquisition strategy of the blackbody image. The acquisition strategy of the blackbody image may include: selecting a temperature point under each attenuation film gear to make the included integration time gear the largest, and then selecting 1 or 2 temperature points to supplement the attenuation film gear with a larger calibration temperature span, and making the selected temperature cover the low temperature segment, and the collected blackbody images are not less than 11. The larger calibration temperature span means that the span range reaches 70% of the calibration blackbody temperature range, and the low temperature segment means that it is lower than 15% of the highest temperature of the calibration blackbody. The infrared imaging aperture used in the example is 600mm, the medium wave band is 3.7~4.8μm, it is a mercury cadmium telluride detector, the number of pixels is 640×512, the pixel size is 15μm, and Stirling cooling is used. The integration time gears are 0.02ms, 0.1ms, 0.5ms and 2.5ms, and the transmittance of the neutral attenuation film used in the three gears is 100%, 10%, and 1%. The calibration is carried out using a normal temperature surface blackbody, a high temperature cavity blackbody and a collimator, and the calibrable temperature range is 25 to 1200 degrees. The linear temperature range of each integration time position and attenuation plate position of the infrared imaging system is shown in Table 1.

[0032] Table 1

[0033]

[0034] Now select a temperature point under each attenuation gear to make the most integral time gears included. It can be seen that the 100% attenuation gear can be selected at 50℃, the 10% attenuation gear can be selected at 150℃, and the 1% attenuation gear can be selected at 850℃. In order to make the calibration have better accuracy in the low radiation range and the high radiation range, two temperature points of 100℃ and 550℃ are added. Therefore, only 5 blackbody temperature points are required to complete the high-efficiency radiation calibration of the infrared radiation measurement system in all gears.

[0035] Step 3: Based on the infrared radiation measurement system response model considering the influence of the attenuation plate and the integration time in step 1, the objective function is established by using the weighted least square method, and the objective function is minimized by using the optimization algorithm to solve the calibration coefficient in the infrared radiation measurement system response model;

[0036] The objective function for solving the calibration coefficients using the weighted least squares method is:

[0037] (6)

[0038] The same symbols as in formula (5) have the same physical meanings. For the A black body image, Indicates shared A black body image, is the gray value of the i-th image, is the radiation amount of the calibrated black body when collecting the i-th image, is the integration time of the i-th image, is the transmittance of the attenuation sheet for the i-th image, is the functional relationship between the actual transmittance of the attenuation sheet for the i-th image and the designed value, is the emissivity of the attenuation sheet for the i-th image, is the objective function; the objective function is minimized using the fastest gradient method, quasi-Newton method, and conjugate gradient method. , find the calibration coefficient , , , , , , , , , , .

[0039] In one example, the calibration temperature points are 50 to 1200 degrees with intervals of 50 degrees. When the black body reaches the temperature, the black body image under each attenuation plate gear and integration time gear is collected, and the 24 black body calibration temperature points are used for conventional calibration. The radiation brightness is inverted by the calibration method of the present invention, and its relative error is calculated and compared with the relative error of the conventional calibration method, such as Figure 2 and Figure 3 shown. Figure 2 The relative error comparison between the calibration method of the present invention and the conventional method is shown; Figure 3 The relative error deviation of the calibration method of the present invention and the conventional method is shown. It can be seen that the relative error of the calibration method of the present invention is relatively close to the relative error of the conventional calibration method. The relative error mean of the conventional calibration method is 1.04%, and the relative error mean of the method of this invention is 1.84%. The average deviation of the relative error is 0.8%, and only the deviation of individual points is relatively large. Therefore, the calibration method considering the integration time and the attenuation sheet gear at 5 temperature points is close to the performance of the conventional calibration method at 24 temperature points, meeting the actual use requirements.

[0040] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be put into practice without these specific details. In some instances, known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description. Although the present invention has been described according to a limited number of embodiments, it is understood by those skilled in the art, with the benefit of the above description, that other embodiments can be envisioned within the scope of the present invention thus described. In addition, it should be noted that the language used in this description is mainly selected for the purpose of readability and teaching, rather than for explaining or limiting the subject matter of the present invention.

Claims

1. An efficient calibration method for a wide dynamic range infrared radiation measurement system, characterized in that: The following steps are involved: Step 1: According to the energy transfer process of the infrared radiation measurement system with variable attenuation plate and integration time, a response model of the infrared radiation measurement system considering the influence of attenuation plate and integration time is established; Step 2, executing the acquisition strategy of black body image; Step 3: Based on the infrared radiation measurement system response model considering the influence of the attenuation plate and the integration time in step 1, the objective function is established using the weighted least squares method, and the objective function is minimized using the optimization algorithm to solve the calibration coefficient in the infrared radiation measurement system response model. The step one comprises: The response model of the infrared radiation measurement system considering the influence of the attenuation sheet and integration time is: ， is the image gray value, To calibrate the radiation of a black body, is the integration time, is the system response gain per unit time, is the transmittance of the attenuator, is the bias caused by the stray radiation of the infrared system in front of the attenuator, is a first-order correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the secondary correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the third-order correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the bias caused by the attenuator’s own radiation, is the functional relationship between the actual transmittance of the attenuator and the design value, is the emissivity of the attenuator, is the correction factor for the emissivity of the attenuator, , , It is the quadratic term coefficient, linear term coefficient and constant term coefficient of the functional relationship between the actual transmittance of the attenuator and the design value. is the bias caused by the detector dark current; The step three comprises: The weighted least squares method is used to establish the objective function for solving the calibration coefficient: ， in, Indicates A black body image, Indicates shared A black body image, is the objective function, is the gray value of the i-th image, is the radiation amount of the calibrated black body when collecting the i-th image, is the integration time of the i-th image, is the system response gain per unit time, is the transmittance of the attenuation sheet for the i-th image, is the bias caused by the stray radiation of the infrared system in front of the attenuator, is a first-order correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the secondary correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the third-order correction term for the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator, is the bias caused by the attenuator’s own radiation, is the functional relationship between the actual transmittance of the attenuation sheet for the i-th image and the design value, is the emissivity of the attenuation sheet for the i-th image, is the correction factor for the emissivity of the attenuator, , , It is the quadratic term coefficient, linear term coefficient and constant term coefficient of the functional relationship between the actual transmittance of the attenuator and the design value. is the bias caused by the detector dark current; Optimization algorithms include the steepest gradient method, quasi-Newton method, and conjugate gradient method; The calibration coefficients include: the quadratic coefficient, linear coefficient and constant coefficient of the functional relationship between the actual transmittance of the attenuator and the design value , , , the system response gain per unit time , the bias caused by the stray radiation of the infrared system in front of the attenuator , the first correction term of the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator , the secondary correction term of the bias caused by stray radiation of the infrared radiation measurement system after the attenuation plate , the third correction term of the bias caused by stray radiation of the infrared radiation measurement system behind the attenuator , correction factor for the emissivity of the attenuator , the bias caused by the attenuator's own radiation , the detector dark current bias .

2. The high-efficiency calibration method for a wide dynamic range infrared radiation measurement system according to claim 1, characterized in that: The second step comprises: The blackbody image acquisition strategy includes: selecting a temperature point under each attenuation sheet gear to maximize the number of integral time gears included, and then selecting 1 or 2 temperature points to supplement the attenuation sheet gear with a larger calibration temperature span, and making the selected temperature cover the low temperature segment. The number of collected blackbody images is not less than 11. The larger calibration temperature span refers to a span range that reaches 70% of the calibration blackbody temperature range, and the low temperature segment refers to a temperature that is 15% lower than the highest temperature of the calibration blackbody.

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