A method for radiant calibration with wide band and large dynamic range under variable color temperature integrating sphere light source

Abstract

The invention discloses a wide-band and large-dynamic-range radiation calibration method under a variable color temperature integrating sphere light source. The method comprises the following steps: 1) confirming a calibration test environment, completing equipment layout and parameter debugging; 2) measuring the spectral radiance of the light source at different levels by using a standard radiometer according to the dynamic range of the integrating sphere light source, and completing the integrating sphere radiation calibration; 3) establishing a conversion relationship between the color temperature spectrum at different calibration energy levels and the color temperature spectrum when the integrating sphere is fully opened based on the spectral response function of the optical remote sensor; 4) setting the integrating sphere calibration energy level according to the dynamic range of the optical remote sensor, and recording the output value of the standard detector and the output count value of the optical remote sensor at different energy levels; 5) calculating the equivalent spectral radiance corresponding to the output value of the standard detector by using an interpolation method according to the relationship between the equivalent spectral radiance of different energy levels and the output value of the standard detector, obtaining the calibration coefficient and performance parameters of the optical remote sensor, and completing the radiation calibration of the optical remote sensor.

Description

Technical Field

[0001] The invention relates to the technical field of optical instrument radiation calibration, and in particular to a wide-band and large-dynamic-range radiation calibration method under a variable-color-temperature integrating sphere light source. Background Art

[0002] With the increasing requirements for the quantitative application of space remote sensing products, the high-precision calibration of space remote sensors is becoming increasingly important and necessary. The calibration accuracy of satellite data directly affects the accuracy of inversion parameters and the reliability of other related research, restricting the depth and breadth of the global quantitative application of satellite data. At present, the radiation calibration stage is divided into three categories: pre-launch calibration, on-orbit replacement calibration, and on-orbit calibration. Laboratory calibration is the easiest and most accurate calibration method for remote sensor calibration. It is an important task before the launch of space remote sensors. It provides an initial reference for the on-orbit calibration of remote sensors. It uses laboratory conditions to simulate the on-orbit working environment of the instrument. It has a strict quality system to ensure the control of the calibration process and make it traceable to the international unit standard value.

[0003] At present, the radiance calibration methods of instruments mainly include the integrating sphere method and the standard lamp-diffuse reflector method. Due to the calibration requirements of the aperture, field of view and energy level of space remote sensors, laboratories usually use an integrating sphere light source system with excellent stability, surface uniformity and angle uniformity to conduct radiation calibration tests for space remote sensors. In order to achieve radiance calibration of instruments with a large dynamic range or low illumination, the calibration light source generally uses a cascade integrating sphere light source with equal color temperature changes, for example, a low-light camera radiation calibration method (patent CN106840198A). For other types of integrating sphere light sources, the number of light sources and the variable aperture adjustment can also obtain continuous radiance output under a large dynamic range or low illumination, but due to factors such as the differences in light sources and the limitations of the variable aperture, this adjustment method cannot guarantee the stable color temperature spectrum output of the integrating sphere at any energy level. Due to the dynamic differences in radiation of various optical instruments, the inconsistency of their light source color temperature makes it difficult to meet the needs of multi-energy level calibration in laboratory radiation calibration, which limits the laboratory calibration accuracy of optical remote sensing instruments at low irradiance levels and large dynamic radiation ranges. The inconsistency of their light source color temperature has a particularly significant impact on the calibration accuracy of wide-band channels. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a high-precision calibration method for a wide-band optical remote sensor laboratory with large radiation dynamic range consistency under a variable color temperature integrating sphere light source.

[0005] The technical solution adopted by the present invention to solve the technical problem is as follows: a wide-band and large-dynamic-range radiation calibration method under a variable-color temperature integrating sphere light source, wherein the adopted radiation calibration device comprises an integrating sphere 1 and a corresponding computer control system 2, wherein the integrating sphere 1 is composed of a standard detector 3 cooled by TEC, a halogen light source 4 and a variable aperture 5, and the optical instrument comprises a standard radiometer 6 and an optical remote sensor 7, wherein the standard radiometer 6 is used to establish a radiance standard of the integrating sphere 1, and the optical remote sensor 7 uses the integrating sphere 1 for radiation calibration, and is characterized in that the method comprises the following steps:

[0006] Step 1: Confirm that the test environment meets the calibration technical requirements, including darkroom construction, temperature and humidity, anti-static and grounding measures, open the calibration integrating sphere 1 control software and optical instrument data acquisition software, align the optical instrument light inlet with the center of the luminous surface of the integrating sphere 1, and the distance is greater than 0.5m, turn on the standard detector 3 inside the integrating sphere 1, turn off the laboratory lighting, measure the dark level of the standard detector 3, then power on the optical instrument and integrating sphere 1, turn on all the halogen lamp light sources 4 in the integrating sphere 1, and wait for the optical instrument and the integrating sphere 1 light source to work stably;

[0007] Step 2: Based on step 1, complete the layout of calibration equipment and instrument parameter debugging, use the standard radiometer 6 to perform multi-energy level calibration on the radiance within a large dynamic range of the integrating sphere 1, gradually reduce the number of halogen lamp light sources 4 and the size of the variable iris 5 starting from the maximum incident radiation, design N calibration energy levels according to the differences in light sources and radiation levels, adjust the size of the variable iris 5 to obtain the low-end radiance energy level, use the standard radiometer 6 to measure the spectral radiance corresponding to different energy levels of the integrating sphere 1, and record the output value of the standard detector 3 of the integrating sphere 1 to complete the radiation calibration of the integrating sphere 1 light source;

[0008] Step 3: According to the output value and spectral radiance of the standard detector 3 corresponding to the calibrated energy level of integrating sphere 1 in step 2, convert the color temperature spectrum of integrating sphere 1 at different energy levels to the color temperature spectrum when the light source of integrating sphere 1 is fully turned on, and calculate the equivalent spectral radiance at the nth energy level:

[0009]

[0010] Wherein, λ is the wavelength position, R(λ) is the spectral response function of the optical remote sensor 7, λ1 and λ2 are the starting wavelength and the ending wavelength of the spectral response function of the optical remote sensor 7, respectively, and L 全开 (λ) is the spectral radiance at wavelength λ at the entrance pupil of the optical remote sensor 7 when the integrating sphere 1 is fully open, L n (λ) is the spectral radiance measured at the nth energy level of the integrating sphere 1, is the spectral radiance of the equivalent fully open spectrum shape at the nth energy level, at which the output value of the standard detector 3 is A n , establish A nand The functional relationship between them is:

[0011] Standard detector

[0012] Step 4: Based on step 1, complete the layout and parameter debugging of the optical remote sensor 7, set M integrating spheres 1 calibration energy levels within the dynamic range of the optical remote sensor 7, obtain the output data of each channel under the radiance condition of the full-scale signal of the optical remote sensor 7, control the size of the variable aperture 5 of the integrating sphere 1 and the number of halogen lamp light sources 4, gradually reduce the incident radiation, collect the count values ​​input by each channel of the optical remote sensor 7 under different radiation amounts, and record the output value A of the standard detector 3 at each calibration energy level. m , until all are closed, cover the light entrance of the optical remote sensor 7 with a black cover, and collect the count value and noise value of the optical remote sensor 7 under the condition of complete darkness;

[0013] Step 5: Based on the calibration data obtained in step 4, the relationship between the spectral radiance output by the integrating sphere 1 and the output value of the standard detector 3 is established by using formulas (1) and (2) in step 3, and the output value A of the standard detector 3 is calculated by linear interpolation. m The corresponding equivalent spectral radiance Radiance output from integrating sphere 1 at the instrument entrance pupil

[0014]

[0015] Where: is the equivalent spectral radiance outputted by the mth energy level of the integrating sphere 1, [λ3, λ4] is the nominal spectral response range of the optical remote sensor 7, and the linear calibration formula is used to fit the input and output data of each channel to calculate the calibration coefficient of each channel:

[0016]

[0017] Where: DN m is the output code value of the m-level optical remote sensor 7, a0 and a1 are the calibration coefficients under linear response. When performing calibration, when the remote sensing application requires spectral radiance as the main factor, the spectral radiance output by the integrating sphere 1 at the entrance pupil of the instrument

[0018]

[0019] According to formula (4) and formula (5), the quantitative relationship between the output value of the optical remote sensor 7 and the incident equivalent radiance is established. The signal-to-noise ratio is calculated through the output signal, noise and dark background of the channel under typical radiance conditions. The dynamic range of the channel is obtained by the maximum output value of the channel and the calibration coefficient, and the radiation calibration of the optical remote sensor 7 is completed.

[0020] Furthermore, the calibration test is carried out in a dimly lit darkroom of the laboratory, the walls, ceiling, windows and doors of the laboratory are covered with black materials, the main environmental conditions are temperature 20±5°C, humidity 45%±5%, and cleanliness level 100,000.

[0021] Furthermore, the spectral range of the integrating sphere 1 covers the operating band of the optical remote sensor 7, the output radiant brightness adjustment range covers the response dynamic range of the optical remote sensor 7, the radiant brightness stability of the integrating sphere 1 should generally be better than 99%, the radiant brightness surface uniformity and angular uniformity should generally be better than 98%, and the luminous surface of the integrating sphere 1 covers the full aperture and full field of view of the entrance pupil of the optical remote sensor 7.

[0022] Furthermore, the standard detector 3 is used to monitor and calculate the radiance output by the integrating sphere 1, and the radiance coverage range is from 1×10 -6 To 150W / (m 2 ·sr).

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention is a method for calibrating radiation with a wide band and a large dynamic range under a variable color temperature integrating sphere light source. Aiming at the color temperature slowly changing characteristics of the integrating sphere light source, the system spectral response function of the optical remote sensor is utilized. By establishing the spectral radiation relationship between the standard radiometer under multiple radiation energy levels and the integrating sphere standard detector with a variable color temperature, the radiation calibration problem of the wide band channel of the optical remote sensor under the variable color temperature integrating sphere light source with eight orders of magnitude dynamic range is solved, and the accuracy of the radiation consistency calibration under the large dynamic range of the laboratory integrating sphere light source is achieved. For various types of optical equipment, the use conditions of this method are relatively simple, and the accurate conversion of color temperature under any brightness within the large radiation dynamic range of the integrating sphere is achieved, which effectively improves the radiation calibration accuracy and applicability of the integrating sphere under the condition of variable color temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 This is the layout diagram of the radiation calibration of the laboratory integrating sphere light source in the present invention.

[0026] Figure 2 This is a flow chart of the radiation calibration of the color temperature-variable integrating sphere light source in the present invention. DETAILED DESCRIPTION

[0027] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to the accompanying drawings and in combination with embodiments.

[0028] The present invention provides a method for calibrating radiation with a wide band and large dynamic range under a variable color temperature integrating sphere light source. In the method of the present invention, Figure 1As shown, the radiation calibration device used includes an integrating sphere 1 and a corresponding computer control system 2. The integrating sphere 1 is composed of a TEC-cooled standard detector 3, a halogen lamp light source 4 and a variable aperture 5. The optical instrument includes a standard radiometer 6 and an optical remote sensor 7. The standard radiometer 6 is used to establish the radiance standard of the integrating sphere 1. The optical remote sensor 7 uses the integrating sphere 1 for radiation calibration. Figure 2 As shown, the specific implementation requires the following five steps:

[0029] Step 1: Confirm that the test environment meets the calibration technical requirements, including darkroom construction, temperature and humidity, anti-static and grounding measures, open the calibration integrating sphere 1 control software and optical instrument data acquisition software, align the optical instrument light inlet with the center of the luminous surface of the integrating sphere 1, and the distance is greater than 0.5m, turn on the standard detector 3 inside the integrating sphere 1, stabilize for 15 minutes, turn off the laboratory lighting, measure the dark level of the standard detector 3, then power on the optical instrument and integrating sphere 1, turn on all halogen light sources 4 in the integrating sphere 1, stabilize for 15 minutes, and wait for the optical instrument and integrating sphere 1 light source to work stably;

[0030] Step 2: Based on step 1, complete the layout of calibration equipment and instrument parameter debugging, use the standard radiometer 6 to perform multi-energy level calibration on the radiance within a large dynamic range of the integrating sphere 1, gradually reduce the number of halogen lamp light sources 4 and the size of the variable iris 5 starting from the maximum incident radiation, design N calibration energy levels according to the differences in light sources and radiation levels, adjust the size of the variable iris 5 to obtain the low-end radiance energy level, use the standard radiometer 6 to measure the spectral radiance corresponding to different energy levels of the integrating sphere 1, and record the output value of the standard detector 3 of the integrating sphere 1 to complete the radiation calibration of the integrating sphere 1;

[0031] Step 3: According to the output value and spectral radiance of the standard detector 3 corresponding to the calibrated energy level of integrating sphere 1 in step 2, convert the color temperature spectrum of integrating sphere 1 at different energy levels to the color temperature spectrum when the light source of integrating sphere 1 is fully turned on, and calculate the equivalent spectral radiance at each energy level:

[0032]

[0033] Wherein, λ is the wavelength position, R(λ) is the spectral response function of the optical remote sensor 7, λ1 and λ2 are the starting wavelength and the ending wavelength of the spectral response function of the optical remote sensor 7, respectively, and L 全开 (λ) is the spectral radiance at wavelength λ at the entrance pupil of the optical remote sensor 7 when the integrating sphere 1 is fully open, L n (λ) is the spectral radiance measured at the nth energy level of the integrating sphere 1, is the spectral radiance of the equivalent fully open spectrum shape at the nth energy level, at which the output value of the standard detector 3 is A n , establish A n and The functional relationship between them is:

[0034] Standard detector

[0035] Step 4: Based on step 1, complete the layout and parameter debugging of the optical remote sensor 7, set M integrating spheres 1 calibration energy levels within the dynamic range of the optical remote sensor 7, obtain the output data of the channel under the radiance condition of the full-scale signal of the optical remote sensor 7, control the size of the variable aperture 5 of the integrating sphere 1 and the number of halogen lamp light sources 4, gradually reduce the incident radiation, collect the channel count values ​​input by the optical remote sensor 7 under different radiation amounts, and record the output value A of the standard detector 3 at each calibration energy level. m , until all are closed, cover the light entrance of the optical remote sensor 7 with a black cover, and collect the count value and noise value of the optical remote sensor 7 under the condition of complete darkness;

[0036] Step 5: Based on the calibration data obtained in step 4, the relationship between the spectral radiance output by the integrating sphere 1 and the output value of the standard detector 3 is established by using formulas (1) and (2) in step 3, and the output value A of the standard detector 3 is calculated by linear interpolation. m The equivalent spectral radiance under Radiance output from integrating sphere 1 at the instrument entrance pupil

[0037]

[0038] Where: is the equivalent spectral radiance outputted by the mth energy level of the integrating sphere 1, [λ3, λ4] is the nominal spectral response range of the optical remote sensor 7, and the linear calibration formula is used to fit the input and output data of each channel to calculate the calibration coefficient of each channel:

[0039]

[0040] Where: DN m is the output code value of the m-level optical remote sensor 7, a0 and a1 are the calibration coefficients under linear response. When performing calibration, when the remote sensing application requires spectral radiance as the main factor, the spectral radiance output by the integrating sphere 1 at the entrance pupil of the instrument

[0041]

[0042] According to formula (4) and formula (5), the quantitative relationship between the output value of the optical remote sensor 7 and the incident equivalent radiance is established. The signal-to-noise ratio is calculated by the channel output signal, noise and dark background under typical radiance. The dynamic range of the channel is obtained by using the maximum output value of the channel and the calibration coefficient, and the radiation calibration of the optical remote sensor 7 is completed.

[0043] The calibration test is carried out in a dimly lit darkroom in the laboratory. The walls, ceiling, windows and doors of the laboratory are covered with black materials. The main environmental conditions are temperature 20±5℃, humidity 45%±5%, and cleanliness level 100,000. The spectral range of integrating sphere 1 covers the working band of optical remote sensor 7, and the output radiance adjustment range covers the response dynamic range of optical remote sensor 7. The radiance stability of integrating sphere 1 should generally be better than 99%, and the radiance surface uniformity and angular uniformity should generally be better than 98%. The luminous surface of integrating sphere 1 covers the full aperture and full field of view of the entrance pupil of optical remote sensor 7. Standard detector 3 is used to monitor and calculate the spectral radiance output by integrating sphere 1. The radiance coverage range is from 1×10 -6 To 150W / (m 2 ·sr).

[0044] Obviously, the above embodiments are only examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims

1. A method for calibrating radiation with a wide band and a large dynamic range under a variable color temperature integrating sphere light source, wherein the calibration method is based on a radiation calibration device comprising an integrating sphere (1) and a corresponding computer control system (2), wherein the integrating sphere (1) is composed of a standard detector (3) cooled by TEC, a halogen light source (4) and a variable aperture (5), wherein the optical instrument used in the calibration method comprises a standard radiometer (6) and an optical remote sensor (7), wherein the standard radiometer (6) is used to establish a radiance standard of the integrating sphere (1), and the optical remote sensor (7) uses the integrating sphere (1) for radiation calibration, and wherein the calibration method comprises: The calibration method comprises the following steps: Step 1: Confirm that the test environment meets the calibration technical requirements, including darkroom construction, temperature and humidity, anti-static and grounding measures, open the calibration integrating sphere (1) control software and optical instrument data acquisition software, align the optical instrument light inlet with the center of the luminous surface of the integrating sphere (1), with a distance greater than 0.5m, turn on the standard detector (3) inside the integrating sphere (1), turn off the laboratory lighting, measure the dark level of the standard detector (3), then power on the optical instrument and integrating sphere (1), turn on all halogen lamp light sources (4) in the integrating sphere (1), and wait for the optical instrument and integrating sphere (1) light sources to work stably; Step 2: Based on step 1, complete the layout of the calibration equipment and the debugging of the instrument parameters, use the standard radiometer (6) to perform multi-energy level calibration on the radiance within a large dynamic range of the integrating sphere (1), gradually reduce the number of halogen lamp light sources (4) and the size of the variable diaphragm (5) starting from the maximum incident radiation, design N calibration energy levels according to the differences in light sources and the radiation level, adjust the size of the variable diaphragm (5) to obtain the low-end radiance energy level, use the standard radiometer (6) to measure the spectral radiance corresponding to different energy levels of the integrating sphere (1), and record the output value of the standard detector (3) of the integrating sphere (1), so as to complete the radiation calibration of the integrating sphere (1); Step 3: According to the output value and spectral radiance of the standard detector (3) corresponding to the calibrated energy level of the integrating sphere (1) in step 2, the color temperature spectrum of the integrating sphere (1) at different energy levels is converted to the color temperature spectrum when the light source of the integrating sphere (1) is fully turned on, and the equivalent spectral radiance at the nth energy level is calculated: Wherein, λ is the wavelength position, R(λ) is the spectral response function of the optical remote sensor (7), λ1 and λ2 are the starting wavelength and the ending wavelength of the spectral response function of the optical remote sensor (7), respectively, and L 全开 (λ) is the spectral radiance at wavelength λ at the entrance pupil of the optical remote sensor (7) when the integrating sphere (1) is fully open, L n (λ) is the spectral radiance measured at the nth energy level of the integrating sphere (1), is the spectral radiance of the equivalent fully open spectrum shape at the nth energy level, at which the output value of the standard detector (3) is A n , establish A n and The functional relationship between them is: Step 4: Based on step 1, complete the layout and parameter debugging of the optical remote sensor (7), set the calibration energy levels of M integrating spheres (1) within the dynamic range of the optical remote sensor (7), obtain the output data of the channel under the condition of the full-scale radiance of the optical remote sensor (7), control the size of the variable aperture (5) of the integrating sphere (1) and the number of halogen lamp light sources (4), gradually reduce the incident radiation, collect the count values ​​input by each channel of the optical remote sensor (7) under different radiation amounts, and record the output value A of the standard detector (3) at each calibration energy level m , until all are closed, the light inlet of the optical remote sensor (7) is covered with a black cover, and the count value and noise value of the optical remote sensor (7) under completely dark conditions are collected; Step 5: Based on the calibration data obtained in step 4, the relationship between the spectral radiance output by the integrating sphere (1) and the output value of the standard detector (3) is established by using formula (1) and formula (2) in step 3, and the output value A of the standard detector (3) is calculated by linear interpolation method. m The equivalent spectral radiance under The radiance output by the integrating sphere (1) at the instrument entrance pupil Where: is the equivalent spectral radiance of the mth energy level output of the integrating sphere (1), [λ3, λ4] is the nominal spectral response range of the optical remote sensor (7), and the linear calibration formula is used to fit the input and output data of each channel to calculate the calibration coefficient of each channel: Where: DN m is the output code value of the m-level optical remote sensor (7), a0 and a1 are the calibration coefficients under linear response. When performing calibration, if the remote sensing application requires spectral radiance as the main factor, the spectral radiance output by the integrating sphere (1) at the entrance pupil of the instrument is According to equations (4) and (5), a quantitative relationship between the output value of the optical remote sensor (7) and the incident equivalent radiance is established. The signal-to-noise ratio is calculated by the output signal, noise and dark background of the channel under typical radiance conditions. The dynamic range of the channel is obtained using the maximum output code value of the channel and the calibration coefficient, and the radiation calibration of the optical remote sensor (7) is completed.

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