In-orbit accurate calibration method for response characteristic of image sensor

Abstract

The present application relates to a kind of image sensor response characteristics on-orbit accurate calibration method, comprising the following steps: establishing on-orbit precision temperature drift correction model;Select on-orbit calibration site, on-orbit calibration task planning is carried out;Radiometric calibration temperature drift characteristic test procedure is formulated on-orbit;Precise temperature drift model parameter determination is carried out;On-orbit precision temperature drift correction is carried out by substituting precise temperature drift model parameter.The present application is suitable for long-term work on-orbit CMOS image sensor radiometric correction.The method is based on the calibration of sensor characteristics in laboratory, and the response characteristics of sensor are precisely calibrated by high-frequency on-orbit calibration mode, so that the image sensor is precisely corrected with high precision, high reliability and high timeliness, and high-quality imaging of camera on-orbit is realized.

Description

Technical Field

[0001] This invention relates to the field of high-precision on-orbit radiometric correction technology for space camera sensors, and particularly to an on-orbit precise calibration method for the response characteristics of an image sensor. Background Technology

[0002] High-precision on-orbit radiometric correction technology for space camera sensors is a key link in ensuring the quantitative application of remote sensing data. Its core lies in eliminating radiometric deviations caused by factors such as sensor response attenuation and environmental changes, thereby ensuring long-term data consistency and accuracy.

[0003] Chinese patent document "An On-Orbit Field Calibration Method for a High-Orbit Large-Area Optical Remote Sensor" (Publication No. CN116026360A) discloses a method that includes: utilizing a uniform ground-based radiometric calibration field to calculate relative radiometric calibration coefficients from stitched images using the flat-field method; selecting a suitable usable range as the calibration field based on the resolution of the payload to be calibrated; estimating the traversal time required based on the usable range, the swath width of the payload to be calibrated, and the satellite's maneuverability; adjusting the satellite's attitude control parameters according to the satellite camera's optical axis pointing and image plane detector distribution characteristics to obtain a set of related images where the calibration field region is distributed in different regions of the camera image; performing geometric correction on the obtained set of related images; extracting the ground calibration field region image from each image and stitching them together according to their corresponding positions on the image plane to form a complete calibration image; and obtaining the relative radiometric calibration coefficients using the flat-field method through calculations within sub-regions, calculations between sub-regions, and multiplication of sub-regions and sub-regions. This method, based on on-orbit calibration field calibration to correct the relative radiometrics of camera images, is significantly affected by the stability of sensor characteristics.

[0004] Chinese patent document "An Image Sensor Array and Its Temperature Drift Compensation Method" (publication number CN110519537A) discloses a method that specifically includes: performing temperature drift compensation on an uncooled infrared focal plane array; obtaining the output temperature drift of the blind pixel array in the image sensor array; obtaining the output temperature drift of the photosensitive pixels based on the output temperature drift of the blind pixel array; and removing the output temperature drift of the photosensitive pixels from the pre-acquired original output change of the image sensor array to obtain the corrected output change. This method achieves temperature drift correction in dark fields through blind pixel reading and subtraction, but fails to solve the problem of temperature drift correction in bright fields.

[0005] Chinese patent document "A Precise Correction Method for Radiation Response Characteristics of a CMOS Image Sensor" (Publication No. CN117714905A) discloses a method that specifically includes: S1, proposing a precise on-orbit temperature drift correction model for the radiation response of a CMOS image sensor, and establishing a multivariate nonlinear function relationship between the theoretical response value, actual response value, and temperature of the image sensor; S2, formulating a radiation calibration temperature drift test procedure to achieve multi-condition traversal of temperature and illumination intensity; S3, using the procedure described in step S2 to collect radiation calibration data and determine the temperature drift model parameters; S4, substituting the temperature drift model parameters and the actual response value of the image sensor into the precise on-orbit temperature drift correction model to calculate the theoretical radiation response value of the image sensor, thereby achieving precise correction of the radiation response characteristics of the image sensor. This method uses a more precise correction model to perform radiation correction on the sensor based on changes in the temperature drift characteristics of the sensor calibrated in the laboratory. While this correction method is accurate, it is only suitable for the initial stage of the sensor's on-orbit operation. As the sensor's on-orbit time accumulates, the sensor characteristics will degrade, causing a mismatch between the laboratory calibration coefficients and the sensor's on-orbit operation, thus failing to achieve high-precision imaging. Summary of the Invention

[0006] The present invention aims to solve the technical problems in the prior art by providing an on-orbit accurate calibration method for the response characteristics of an image sensor.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] An on-orbit precise calibration method for the response characteristics of an image sensor includes the following steps:

[0009] Step 1: Establish an on-orbit precision temperature drift correction model;

[0010] Step 2: Select an on-orbit calibration site and plan the on-orbit calibration task;

[0011] Step 3: Based on the on-orbit calibration mission planning in Step 2, formulate the on-orbit radiation calibration temperature drift characteristic test procedure;

[0012] Step 4: Determine the parameters of the on-orbit precision temperature drift correction model using the on-orbit radiation calibration temperature drift characteristic test procedure established in Step 3.

[0013] Step 5: Using the on-orbit precision temperature drift correction model established in Step 1, substitute the on-orbit precision temperature drift correction model parameters measured in Step 4 to perform on-orbit precision temperature drift correction.

[0014] In the above technical solution, step 1 specifically involves: the on-orbit precision temperature drift correction model is shown in formula (1):

[0015] μ y =(a*μy,real (sinθ / sinθ0)+b)*T+μ y,real (sinθ / sinθ0)+c formula (1)

[0016] Where, μ y The actual grayscale value of the sensor, μ y,real (sinθ / sinθ0) is the theoretical gray value of the sensor, T is the sensor temperature, a is the bright field temperature drift gain constant, b is the dark field temperature drift gain constant, c is the dark field temperature drift bias constant, θ is the real-time solar altitude angle, and θ0 is the initial solar altitude angle, which characterizes the change in solar irradiance during imaging.

[0017] In the above technical solution, in step 1:

[0018] Under constant illumination intensity, the on-orbit precision temperature drift correction model is expressed as the following formula (2):

[0019] μ y =(a*μ y,real +b)*T+μ y,real +c Formula (2)

[0020] In the absence of light source, i.e., in the dark, the on-orbit precision temperature drift correction model is expressed as the following formula (3):

[0021] μ y =b*T+c Formula (3)

[0022] Where, μ y The actual grayscale value of the sensor, μ y,real denoted as the initial theoretical grayscale value of the sensor, T as the sensor temperature, a as the bright field temperature drift gain constant, b as the dark field temperature drift gain constant, and c as the dark field temperature drift bias constant.

[0023] In the above technical solution, in step 1:

[0024] In-orbit dark field calibration is performed using imaging under moonless conditions at night on the sea surface. The dark field temperature drift gain constant b and dark field temperature drift bias constant c are calculated using formula (3).

[0025] During the on-orbit brightness field calibration process, the initial theoretical gray value μ of the sensor in formula (2) is... y,real The sensor response change caused by the change in solar altitude angle is corrected according to the following formula (4):

[0026] μ y,real →μ y,real (sinθ / sinθ0) Formula (4)

[0027] Where θ is the real-time solar altitude angle, and θ0 is the initial solar altitude angle;

[0028] Based on formulas (2) and (4), the on-orbit precision temperature drift correction model formula (1) is established.

[0029] The on-orbit bright field calibration adopts the imaging of the desert during the day without clouds. The dark field temperature drift gain constant b and dark field temperature drift bias constant c, the initial solar altitude angle θ0, and the independent variables real-time solar altitude angle θ and sensor temperature T are substituted into formula (1) to fit and calculate the bright field temperature drift gain constant a.

[0030] In the above technical solution, step 2 specifically involves: selecting different on-orbit calibration sites, obtaining dark field and bright field calibration data corresponding to on-orbit temperature drift calibration, limiting the specific calibration sites and imaging conditions, and realizing on-orbit calibration task planning.

[0031] In the above technical solution, step 2 also includes: performing uniformity screening on the images obtained by on-orbit calibration, and removing images with obvious non-uniform land cover types. Specifically, this involves calculating and evaluating the uniformity between columns and setting a critical threshold.

[0032] In the above technical solution, the on-orbit radiation calibration temperature drift characteristic test procedure formulated in step 3 is as follows:

[0033] (1) Before the on-orbit calibration begins, select the type of calibration site;

[0034] (2) Setting requirements for on-orbit calibration and shooting;

[0035] (3) Plan shooting tasks based on shooting requirements and satellite transit conditions;

[0036] (4) Before the shooting task begins, set the imaging parameters and power on the camera;

[0037] (5) During the shooting process, the sensor temperature is read and imaging begins. The image grayscale value and sensor temperature are saved in real time for two minutes.

[0038] (6) Power off the camera to end the shooting mission.

[0039] In the above technical solution, step (2) specifically means: when the on-orbit calibration begins, submit the shooting requirements, including: selection of satellites to be calibrated, selection of imaging area, setting of imaging parameters, cloud cover, side sway angle requirements, setting of imaging duration, setting of shooting ground features and time requirements.

[0040] In the above technical solution, step (3) specifically involves selecting a moonless, clear, and cloudless night for shooting dark scenes, and selecting a clear, cloudless daytime for shooting bright scenes.

[0041] In the above technical solution, step 5 specifically includes:

[0042] During dark-field calibration, the sensor's initial theoretical grayscale value μ y,real The value is 0, and the formula for calculating the dark field temperature drift coefficient is μ. y =b*T+c; By recording the average grayscale value μ of each column under different sensor temperatures T in different scenes. y The parameters b and c corresponding to each pixel are calculated using the least squares method.

[0043] During brightness field calibration, the actual grayscale values ​​μ of each column of the brightness field are obtained using the calculated parameter values ​​of b and c at different scene sensor temperatures T. y And the real-time solar altitude angle θ, the a parameter value corresponding to each pixel is calculated by nonlinear fitting;

[0044] The measured values ​​of a, b, and c are used as parameters for the on-orbit precision temperature drift correction model, and the actual grayscale value μ of the sensor is used. y Using the sensor temperature T, solar altitude angle θ, and θ0 at the imaging time as inputs, the initial theoretical gray value μ of the sensor after correction is calculated. y,real This invention enables precise correction of pixel response inconsistencies, fixed image noise, and temperature drift characteristics in image sensors. The invention offers the following advantages:

[0045] The present invention provides an in-orbit precise calibration method for image sensor response characteristics, applicable to radiometric correction of CMOS image sensors operating in orbit for extended periods. Based on laboratory calibration of sensor characteristics, this method employs a high-frequency in-orbit calibration process to precisely calibrate the sensor's response characteristics, thereby achieving high-precision, high-reliability, and high-timeliness calibration of the image sensor and enabling high-quality in-orbit imaging. Attached Figure Description

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0047] Figure 1 This is a flowchart of the on-orbit precise calibration method for the image sensor response characteristics according to the present invention.

[0048] Figure 2 This is a schematic diagram of the calibration field image in the on-orbit precise calibration method for the image sensor response characteristics of the present invention; wherein, (a) is a deep-sea calibration field image (the left image is multispectral and the right image is panchromatic);

[0049] (b) Image of the desert calibration site (left image is multispectral, right image is panchromatic).

[0050] Figure 3 This is a schematic diagram of the on-orbit radiometric calibration temperature drift characteristic test process for the on-orbit accurate calibration method for image sensor response characteristics of the present invention.

[0051] Figure 4This is a schematic diagram comparing the original multispectral image with the image before and after relative temperature drift correction in a specific embodiment of the present invention.

[0052] Figure 5 This is a schematic diagram comparing the original image of the B2 band with the images before and after relative temperature drift correction using 1500 lines of curves in a specific embodiment of the present invention. Detailed Implementation

[0053] The inventive concept of this invention is as follows:

[0054] The present invention provides an on-orbit precise calibration method for the response characteristics of an image sensor. By performing on-orbit temperature drift calibration on a CMOS image sensor, the precise correction of the sensor's response characteristics is achieved. By performing field calibration on uniform scenes such as deep sea and desert, the temperature drift coefficients of dark and bright fields are obtained, enabling regular maintenance and updating of the on-orbit temperature drift coefficients.

[0055] In a specific embodiment of the present invention, dark field refers to imaging a uniform deep-sea scene without illumination, and the dark field temperature drift parameter is a parameter that is independent of light intensity; bright field refers to imaging a uniform desert or deep-sea scene with illumination, and the bright field temperature drift parameter is a temperature drift parameter that is related to light intensity.

[0056] The present invention will now be described in detail with reference to the accompanying drawings.

[0057] The method for on-orbit precise calibration of image sensor response characteristics according to the present invention is as follows: Figure 1 As shown, it includes the following steps:

[0058] Step 1: Establish an on-orbit precision temperature drift correction model;

[0059] Step 2: Select an on-orbit calibration site and plan the on-orbit calibration task;

[0060] Step 3: Based on the on-orbit calibration mission planning in Step 2, formulate the on-orbit radiation calibration temperature drift characteristic test procedure;

[0061] Step 4: Determine the parameters of the on-orbit precision temperature drift correction model using the on-orbit radiation calibration temperature drift characteristic test procedure established in Step 3.

[0062] Step 5: Using the on-orbit precision temperature drift correction model established in Step 1, substitute the on-orbit precision temperature drift correction model parameters measured in Step 4 to perform on-orbit precision temperature drift correction.

[0063] The various steps of the present invention will now be described in more detail.

[0064] Step 1 is as follows:

[0065] The on-orbit precise calibration method for the image sensor response characteristics of this invention is an on-orbit precise temperature drift correction model for the radiation response characteristics of CMOS image sensors, establishing a multivariate nonlinear functional relationship between the theoretical response value and the actual response value of the image sensor, temperature, and solar altitude angle. The specific on-orbit precise temperature drift correction model is shown in formula (1):

[0066] μ y =(a*μ y,real (sinθ / sinθ0)+b)*T+μ y,real (sinθ / sinθ0)+c formula (1)

[0067] Where, μ y The actual grayscale value of the sensor, μ y,real (sinθ / sinθ0) is the theoretical gray value of the sensor, T is the sensor temperature, a is the bright field temperature drift gain constant, b is the dark field temperature drift gain constant, c is the dark field temperature drift bias constant, θ0 is the initial solar altitude angle, and θ is the real-time solar altitude angle, which characterizes the change in solar irradiance during imaging.

[0068] The on-orbit precision temperature drift correction model is actually decomposed as follows: the actual output DN value μ of the CMOS image sensor. y Due to the influence of temperature, under constant light intensity, it can be expressed as the following formula (2):

[0069] μ y =(a*μ y,real +b)*T+μ y,real +c Formula (2)

[0070] In the absence of a light source, i.e., in a dark field, i.e., μ y,real =0 can be expressed as the following formula (3):

[0071] μ y =b*T+c Formula (3)

[0072] Where, μ y The actual grayscale value of the sensor, μ y,real denoted as the initial theoretical grayscale value of the sensor, T as the sensor temperature, a as the bright field temperature drift gain constant, b as the dark field temperature drift gain constant, and c as the dark field temperature drift bias constant.

[0073] In-orbit dark field calibration uses imaging under moonless conditions at night on the sea surface. The dark field temperature drift gain constant b and dark field temperature drift bias constant c are calculated using formula (3). Here, the dark field temperature drift parameter is a parameter that is independent of the light intensity.

[0074] During the on-orbit brightness field calibration process, since a stable light source cannot be obtained in orbit, the sun is selected as the uniform light source. However, the solar elevation angle changes with the imaging time during the imaging process, causing the radiance of pseudo-uniform fields such as deserts to change constantly during the imaging process. In order to remove the influence of radiance on the calculation of the correction coefficient, the initial theoretical gray value μ of the sensor needs to be adjusted in formula (2). y,real Correction is performed according to the following formula (4).

[0075] μ y,real →μ y,real (sinθ / sinθ0) Formula (4)

[0076] Where θ is the real-time solar altitude angle, and θ0 is the initial solar altitude angle;

[0077] It can be obtained in real time from auxiliary data. Based on formulas (2) and (4), the on-orbit precision temperature drift correction model formula (1) can be established:

[0078] μ y =(a*μ y,real (sinθ / sinθ0)+b)*T+μ y,real (sinθ / sinθ0)+c formula (1)

[0079] The on-orbit bright field calibration adopts the imaging of the desert during the day without clouds. The dark field temperature drift gain constant b and dark field temperature drift bias constant c, the initial solar altitude angle θ0, and the independent variables real-time solar altitude angle θ and sensor temperature T are substituted into the formula (1) to fit and calculate the bright field temperature drift gain constant a. Here, the bright field temperature drift parameter is the temperature drift parameter related to the light intensity.

[0080] In this specific embodiment, the parameter determination process of the on-orbit precision temperature drift correction model is as follows: For on-orbit dark field calibration, the purpose is to calculate the dark field temperature drift coefficient, i.e., the dark field temperature drift gain constant b and the dark field temperature drift bias constant c, using the fitting calculation formula μ. y =b*T+c, obtained by recording μ at two or more different sensor temperatures T. y The parameter values ​​of b and c for each pixel can then be calculated using the least squares method. For imaging data of a cloudless, clear daytime desert, this on-orbit temperature drift calibration is used to calculate the brightness field temperature drift gain constant a, employing the fitting calculation formula (1). During daytime calibration of the brightness field, the calculated parameter values ​​of b and c are used to obtain μ values ​​at three or more different sensor temperatures T. y The parameter value of 'a' for each pixel can then be calculated using the nonlinear approximation fitting method.

[0081] Step 2 is as follows:

[0082] The present invention provides a precise on-orbit calibration method for image sensor response characteristics. This method selects different on-orbit calibration sites to acquire dark-field and bright-field calibration data corresponding to on-orbit temperature drift calibration. Dark-field calibration utilizes imaging data captured on a clear, moonless, cloudless night in the deep sea; bright-field calibration utilizes imaging data captured on a clear, cloudless day in the desert. Both on-orbit temperature drift calibration experiments must ensure that the imaging parameters are consistent with the conventional on-orbit imaging mode. The calibration methods during on-orbit calibration are as follows:

[0083] a. Obtain pseudo-uniform dark field data in the deep sea by satellite orbit reduction and push-broom method;

[0084] b. Obtain pseudo-uniform brightness field data in the desert by satellite orbit reduction and push-broom scanning;

[0085] Regarding the selection of calibration sites for calibration method A, deep-sea calibration sites include... Figure 2 As shown in (a), the satellite is calibrated in orbit using the normal pushbroom imaging mode, so no preprocessing is required for the calibration data. The calibration coefficients b and c are calculated by least squares fitting according to the formula (3) of the in-orbit precision temperature drift correction model.

[0086] Regarding the selection of calibration sites for calibration method b, desert calibration sites are as follows: Figure 2 As shown in (b), the satellite is calibrated in orbit using the normal pushbroom imaging mode, so no preprocessing is required for the calibration data. The coefficients a are calculated by nonlinear fitting according to the formula (1) of the in-orbit precision temperature drift correction model.

[0087] After selecting the type of terrain features at the calibration site, specific limitations need to be imposed on the calibration site and imaging conditions. To ensure the uniformity, stability, and accuracy of the on-orbit calibration data, whether it is nighttime dark-field imaging or daytime bright-field imaging, cloud cover must be limited to within 10%, lateral tilt to within 15%, imaging duration to 120 seconds, and imaging parameters must be consistent with the on-orbit usage parameters. The on-orbit calibration imaging mission is planned based on the satellite's transit time over a specific calibration area.

[0088] In addition, this step also includes a process for screening the uniformity of images acquired through on-orbit calibration, which removes images with obviously non-uniform land cover types. Specifically, the uniformity between columns is calculated and evaluated, and a critical threshold is set.

[0089] Step 3 specifically involves:

[0090] The present invention provides an on-orbit precise calibration method for the response characteristics of an image sensor. This method involves on-orbit temperature drift calibration of a CMOS image sensor, selecting a calibration site on-orbit, and performing on-orbit calibration according to a procedure to periodically calculate and update the on-orbit temperature drift coefficient of the image sensor.

[0091] The on-orbit radiometric calibration temperature drift characteristic test procedure of the on-orbit precise calibration method for image sensor response characteristics applied in this invention is as follows: Figure 3 As shown, specifically:

[0092] (1) Before the on-orbit calibration begins, the type of calibration site is selected; in this invention, the Sahara Desert is used as the shooting site for bright field calibration, and the deep sea at night is used as the shooting site for dark field calibration.

[0093] (2) Setting requirements for on-orbit calibration and shooting;

[0094] At the start of on-orbit calibration, submit the shooting requirements, including: selection of satellites to be calibrated, selection of imaging area (latitude and longitude), imaging parameter settings, cloud cover, side sway angle requirements, imaging duration settings, and shooting ground features and time requirements settings.

[0095] (3) Plan shooting tasks according to shooting needs and satellite overpass conditions. For dark scene shooting, choose a moonless, clear and cloudless night for shooting. For bright scene shooting, choose a clear and cloudless daytime for shooting.

[0096] (4) Before the shooting task begins, set the imaging parameters and power on the camera;

[0097] (5) During the shooting process, the sensor temperature is read and imaging begins. The image grayscale value and sensor temperature are saved in real time for two minutes.

[0098] (6) Power off the camera to end the shooting mission.

[0099] Step 5 specifically involves:

[0100] In the on-orbit precise calibration method for the image sensor response characteristics of the present invention, the on-orbit temperature drift coefficient is calculated as follows:

[0101] During dark field calibration, i.e., the initial theoretical gray value μ of the sensor y,real The value is 0, meaning the dark field temperature drift coefficient is calculated using the formula μ. y =b*T+c; By recording the average grayscale value μ of each column under different sensor temperatures T in different scenes. y Then, the parameters b and c corresponding to each pixel can be calculated using the least squares method;

[0102] During brightness field calibration, the actual grayscale values ​​μ of each column of the brightness field are obtained using the calculated parameter values ​​of b and c at different scene sensor temperatures T. y With the real-time solar altitude angle θ, the a-parameter value corresponding to each pixel can be calculated using nonlinear fitting.

[0103] The measured values ​​of a, b, and c are used as the on-orbit precision temperature drift correction model, and the actual gray value μ of the sensor is... yUsing the sensor temperature T at the time of imaging, the real-time solar altitude angle θ, and θ0 as inputs, the initial theoretical gray value μ of the sensor after correction can be calculated. y,real This enables precise correction of pixel response inconsistencies, fixed image noise, and temperature drift characteristics in image sensors.

[0104] In a specific embodiment of the present invention, on-orbit dark field temperature drift and bright field temperature drift images are acquired respectively, which are used to calculate the parameters of the on-orbit precision temperature drift correction model. Figure 4 The image shown is a comparison of the original multispectral image and the image before and after relative temperature drift correction. From the image visualization effect evaluation, the precision temperature drift correction effect is good, the image color difference elimination effect is significant, and the image quality has been greatly improved. Figure 5 The image shown is a comparison of 1500 lines of curves between the original image of the B2 band and the images before and after relative temperature drift correction. As can be seen from the curves in the figure, the difference in response between the columns of the curves after temperature drift correction is smaller and tends to be smoother. Compared with the curves before correction, the upward trend on the right side is significantly eliminated.

[0105] The present invention provides an in-orbit precise calibration method for image sensor response characteristics, applicable to radiometric correction of CMOS image sensors operating in orbit for extended periods. Based on laboratory calibration of sensor characteristics, this method employs a high-frequency in-orbit calibration process to precisely calibrate the sensor's response characteristics, thereby achieving high-precision, high-reliability, and high-timeliness calibration of the image sensor and enabling high-quality in-orbit imaging.

[0106] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for precise on-orbit calibration of the response characteristics of an image sensor, characterized in that, Includes the following steps: Step 1: Establish an on-orbit precision temperature drift correction model; Step 2: Select an on-orbit calibration site and plan the on-orbit calibration task; Step 3: Based on the on-orbit calibration mission planning in Step 2, formulate the on-orbit radiation calibration temperature drift characteristic test procedure; Step 4: Determine the parameters of the on-orbit precision temperature drift correction model using the on-orbit radiation calibration temperature drift characteristic test procedure established in Step 3. Step 5: Using the on-orbit precision temperature drift correction model established in Step 1, substitute the on-orbit precision temperature drift correction model parameters measured in Step 4 to perform on-orbit precision temperature drift correction. Step 1 specifically involves: The on-orbit precision temperature drift correction model is shown in formula (1): Official (1) in, This represents the actual grayscale value of the sensor. This represents the theoretical grayscale value of the sensor. For sensor temperature, The gain constant for bright field temperature drift is... The gain constant for dark field temperature drift is... This is the bias constant for dark field temperature drift. This is the real-time solar altitude angle. The initial solar elevation angle characterizes the change in solar irradiance during imaging.

2. The on-orbit precise calibration method for the response characteristics of an image sensor according to claim 1, characterized in that, In step 1: Under constant illumination intensity, the on-orbit precision temperature drift correction model is expressed as the following formula (2): Official (2) In the absence of light source, i.e., in the dark, the on-orbit precision temperature drift correction model is expressed as the following formula (3): Official (3) in, This represents the actual grayscale value of the sensor. This is the initial theoretical grayscale value of the sensor. For sensor temperature, The gain constant for bright field temperature drift is... The gain constant for dark field temperature drift is... is the dark field temperature drift bias constant.

3. The on-orbit precise calibration method for the response characteristics of an image sensor according to claim 2, characterized in that, In step 1: In-orbit dark-field calibration was performed using imaging under moonless conditions at night over the sea surface. The dark-field temperature drift gain constant was calculated using formula (3). and dark field temperature drift bias constant ; During the on-orbit brightness field calibration process, the initial theoretical grayscale value of the sensor in formula (2) is used. The sensor response change caused by the change in solar altitude angle is corrected according to the following formula (4): Official (4) in, This is the real-time solar altitude angle. This is the initial solar altitude angle; Based on formulas (2) and (4), establish formula (1) for the on-orbit precision temperature drift correction model. In-orbit bright-field calibration employs daytime cloudless desert imaging conditions, and measures the gain constant for dark-field temperature drift. and dark field temperature drift bias constant Initial solar altitude angle and the independent variable, real-time solar altitude angle Sensor temperature Substitute into formula (1) to fit and calculate the gain constant of the bright field temperature drift. .

4. The method for precise on-orbit calibration of image sensor response characteristics according to claim 1, characterized in that, Step 2 specifically involves: selecting different on-orbit calibration sites to obtain dark field and bright field calibration data corresponding to on-orbit temperature drift calibration, limiting the specific calibration sites and imaging conditions, and realizing on-orbit calibration task planning.

5. The on-orbit precise calibration method for the response characteristics of an image sensor according to claim 4, characterized in that, Step 2 also includes: performing uniformity screening on the images obtained by on-orbit calibration, and removing images with obvious non-uniform land cover types. Specifically, this involves calculating and evaluating the uniformity between columns and setting a critical threshold.

6. The on-orbit precise calibration method for the response characteristics of an image sensor according to claim 1, characterized in that, The on-orbit radiation calibration temperature drift characteristic test procedure defined in step 3 is as follows: (1) Before the on-orbit calibration begins, select the type of calibration site; (2) Setting requirements for on-orbit calibration and shooting; (3) Plan shooting tasks based on shooting requirements and satellite transit conditions; (4) Before the shooting task begins, set the imaging parameters and power on the camera; (5) During the shooting process, the sensor temperature is read and imaging begins. The image grayscale value and sensor temperature are saved in real time for two minutes. (6) Power off the camera to end the shooting mission.

7. The on-orbit precise calibration method for the response characteristics of an image sensor according to claim 6, characterized in that, Step (2) specifically involves submitting the shooting requirements at the start of on-orbit calibration, including: selection of satellites to be calibrated, selection of imaging areas, setting of imaging parameters, cloud cover and side sway angle requirements, setting of imaging duration, and setting of shooting ground features and time requirements.

8. The method for precise on-orbit calibration of image sensor response characteristics according to claim 6, characterized in that, Step (3) specifically involves choosing a moonless, clear, and cloudless night for dark scenes and a clear, cloudless daytime for bright scenes.

9. The method for on-orbit precise calibration of image sensor response characteristics according to any one of claims 1-3, characterized in that, Step 5 specifically involves: During dark-field calibration, the sensor's initial theoretical grayscale value The value is 0, and the formula for calculating the dark field temperature drift coefficient is: By recording the temperature of sensors in different scenes The average grayscale values ​​in each column below The parameters corresponding to each pixel are calculated using the least squares method. and ; During bright field calibration, the previously calculated values ​​are used. and The parameter values ​​were obtained to acquire the sensor temperature in different scenes. Actual grayscale values ​​of sensors in each column of the bright field below and real-time solar altitude angle The corresponding value for each pixel is calculated using nonlinear fitting. Parameter values; The measured The value is used as a parameter of the on-orbit precision temperature drift correction model, and the actual gray value of the sensor. and sensor temperature at the time of imaging Solar altitude angle and As input, the initial theoretical grayscale value of the sensor after correction is calculated. This enables precise correction of pixel response inconsistencies, fixed image noise, and temperature drift characteristics in image sensors.

Images