Method for constructing multi-dimensional on-orbit imaging mode of space optical infrared camera

Abstract

The invention relates to a method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera, and belongs to the technical field of on-orbit application of space optical infrared cameras. The construction method comprises the following steps: firstly, obtaining the calibration absolute responsivity and the optimal response linear interval of the space optical infrared camera; acquiring a global surface temperature database, a global surface feature emissivity database and a global atmosphere profile database, and performing simulation calculation on entrance pupil equivalent spectral radiance of the space optical infrared camera from multiple dimensions; constructing a multi-dimensional on-orbit imaging mode of the space optical infrared camera according to the entrance pupil equivalent spectral radiance database and the calibration absolute responsivity, enabling the space optical infrared camera to work in an optimal response linear interval, and obtaining an initial value of the on-orbit imaging mode; and finally, after the space optical infrared camera enters the orbit, optimizing the multi-dimensional on-orbit imaging mode of the space optical infrared camera according to the response characteristics of the space optical infrared camera at the initial on-orbit stage. According to the construction method, the imaging capability of the space optical camera is exerted through a proper imaging mode, and the detection capability of the space optical camera is exerted to the greatest extent.

Description

Technical Field

[0001] The present invention relates to a method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera, and in particular to a method for constructing a four-dimensional on-orbit imaging mode of a space optical infrared camera by using an absolute response function of the space optical infrared camera and a global surface temperature library, and belongs to the technical field of on-orbit application of space optical infrared cameras. Background Art

[0002] Space optical infrared cameras can realize ground and air imaging, and are widely used in marine / land / air military target reconnaissance, land survey, agricultural quantitative remote sensing and other fields. Large-aperture long-focus optical-mechanical systems, high-performance (quantum efficiency, D*) infrared focal planes, and high-precision assembly and integration technology can ensure that space infrared optical cameras have high-performance imaging capabilities, and appropriate imaging mode settings are the key to bringing out the imaging capabilities of space optical cameras. In order to maximize the detection capabilities of space optical cameras, it is necessary to plan and design the on-orbit imaging mode table of space optical infrared cameras.

[0003] The links of the imaging link of space optical infrared camera are: ground object spectral radiation, atmospheric transmission, optical system, detector and electronic system, data compression and storage, data transmission, data reception and processing, etc. Ground objects are scenes on the surface of the earth. Ground objects emit infrared radiation energy upward through their own radiation, which reaches the satellite through atmospheric radiation transmission and is imaged by space optical infrared camera to obtain the image corresponding to the ground object. When atmospheric absorption and scattering are ignored and only the infrared radiation of the target ground object itself is discussed, the image grayscale output by the infrared camera is the product of the transmittance of the optical system and filter and the response of the infrared focal plane detector and the infrared radiation energy of the ground object, that is, the radiation response equation of the space optical infrared camera is shown in (Equation 1).

[0004]

[0005] Where: DN is the digital output value of the image; L(T,σ) is the infrared radiation brightness of the object at temperature T and emissivity σ; τ atm is the atmospheric transmittance; D is the camera aperture; f is the camera focal length; τ opt is the transmittance of the optical system; τ fil is the filter transmittance; R det is the absolute responsivity of the infrared focal plane; β e is the gain of the electronics system; t int is the integration time, DN dark is the background radiation response of the space optical infrared camera.

[0006] From (Equation 1), we can see that the radiation response of a space optical infrared camera mainly depends on factors such as the radiation characteristics of the ground object (the infrared radiation brightness of the ground object), the atmospheric transmission characteristics (atmospheric transmittance), and the transmission characteristics of the space optical infrared camera (absolute responsivity). In 2015, the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences proposed a method for establishing the on-orbit imaging mode of a space optical visible camera. First, the atmospheric radiation simulation software was used to calculate the radiation brightness before the camera entered the pupil. Secondly, the camera's radiation calibration data was analyzed, including the responsivity, radiation brightness range, and integration time relationship of each mode. Then, the integration time relationship between the camera's pendulum imaging and level flight imaging was analyzed to obtain the radiation brightness range of each imaging mode at each side swing angle of the camera. Finally, based on the radiation brightness range of the imaging mode and the radiation brightness range of the scene at each sun high angle, a two-dimensional imaging mode table under the combination of sun high angle and camera side swing angle was established (Optical Precision Engineering, 2015, (07): 1852-1858). However, this method is not suitable for space optical infrared cameras. Summary of the invention

[0007] In view of this, in order to ensure that the space optical infrared camera adopts the most suitable imaging mode during on-orbit imaging to achieve the best performance of the space optical infrared camera, the present invention proposes a method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera.

[0008] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows.

[0009] The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera of the present invention comprises the following steps:

[0010] The first step is to obtain the calibration absolute responsivity and the best response linear interval of the space optical infrared camera;

[0011] The second step is to obtain the global surface temperature, global ground object emissivity and global atmospheric profile database, simulate and calculate the entrance pupil equivalent spectral radiance of the space optical infrared camera from multiple dimensions, and establish the entrance pupil equivalent spectral radiance database of the space optical infrared camera;

[0012] The third step is to construct a multi-dimensional on-orbit imaging mode of the space optical infrared camera based on the entrance pupil equivalent spectral radiance database and the calibrated absolute responsivity of the space optical infrared camera, so that the space optical infrared camera works in the optimal response linear interval and obtains the initial value of the multi-dimensional on-orbit imaging mode of the space optical infrared camera;

[0013] The fourth step is to optimize the multi-dimensional on-orbit imaging mode of the space optical infrared camera based on its initial response characteristics after it enters orbit.

[0014] Preferably, in the first step, a space optical infrared camera radiation calibration system is used to obtain a calibration absolute responsivity and an optimal response linear interval of the space optical infrared camera through an infrared radiation calibration test;

[0015] The space optical infrared camera radiation calibration system consists of a vacuum low-temperature environment simulation device, an infrared black body, a low-temperature baffle, a satellite integrated simulator and an image data acquisition system. The vacuum low-temperature environment simulation device provides a vacuum low-temperature environment for the space optical infrared camera. The space optical infrared camera, the infrared black body and the low-temperature baffle are placed in the vacuum low-temperature environment simulation device. The infrared black body provides the space optical infrared camera with simulated on-orbit ground object radiation, and the low-temperature baffle provides the space optical infrared camera with background radiation. The satellite integrated simulator and the image data acquisition system are both connected to the space optical infrared camera. The satellite integrated simulator injects suitable imaging parameters into the space optical infrared camera, and the image data acquisition system acquires and stores image data of the space optical infrared camera.

[0016] More preferably, the method of the infrared radiation calibration test is:

[0017] The infrared black body is set to the lowest temperature T1 of the dynamic range of the space optical infrared camera. After the infrared black body is stable, the low temperature baffle is cut out, and the space optical infrared camera saves the image of the infrared black body and the image of the low temperature baffle. Then the low temperature baffle is cut in, and the space optical infrared camera saves the image of the infrared black body and the image of the low temperature baffle.

[0018] The temperature of the infrared black body is set at a 5K heating interval until the highest temperature T2 in the dynamic range is reached. After the temperature stabilizes, the image of the infrared black body and the image of the low-temperature baffle saved by the space optical infrared camera are collected respectively;

[0019] The response DN values ​​of the infrared black body and the cryogenic baffle at different temperatures are counted, and the radiation brightness of the infrared black body and the cryogenic baffle is calculated as L by Planck's formula. The radiation calibration coefficients k and b are obtained by fitting using the least squares method.

[0020]

[0021] DN = k*L + b (Formula 3)

[0022] In equations 2 and 3, T is the temperature of the infrared black body; ε is the emissivity of the infrared black body; λ1 and λ2 are the starting wavelength and ending wavelength of the space optical infrared camera, respectively; λ is the wavelength of the space optical infrared camera; c1 is the first radiation constant, c1 = 3.7148e16 (W·m 2); c2 is the second radiation constant, c2 = 1.4388e-2 (m·K); R(λ) is the spectral response curve of the space optical infrared camera; L(T,ε) is the integrated radiation brightness of the infrared black body with temperature T and emissivity ε in the response spectrum of the space optical infrared camera; DN is the response value of the space optical infrared camera, k is the absolute response slope of the space optical infrared camera; b is the absolute response slope of the space optical infrared camera.

[0023] Preferably, in the second step, the dimensions are four: longitude dimension, latitude dimension, month dimension and day and night dimension.

[0024] More preferably, in the second step, the granularity of the longitude dimension is 5 degrees, with a total of 72 intervals; the granularity of the latitude dimension is 5 degrees, with a total of 36 intervals; the granularity of the month dimension is 1 month, with a total of 12 intervals; the day and night dimension is divided into two intervals based on the positive and negative solar altitude angle.

[0025] Preferably, in the second step, the global surface temperature, global object emissivity and global atmospheric profile database are substituted into the atmospheric radiation transmission software to calculate the entrance pupil equivalent spectral radiance of the space optical infrared camera.

[0026] Preferably, in the second step, the databases are all mean databases.

[0027] Preferably, in the fourth step, the initial period is within one week of entering orbit.

[0028] Preferably, in the fourth step, after the space optical infrared camera enters orbit, the response DN values ​​and corresponding multi-dimensional information of typical objects of the space optical infrared camera at the initial stage of orbit are counted;

[0029] The entrance pupil equivalent spectral radiance of the space optical infrared camera is calculated based on multiple dimensional information, and the response DN value of typical objects is calculated as the theoretical expected value based on the calibrated absolute responsivity.

[0030] The deviation between the statistical value and the theoretical expected value is compared. If the deviation is within a reasonable range, there is no need to adjust the imaging mode. Otherwise, the imaging mode is updated based on the deviation and the calibration absolute responsivity calculation.

[0031] More preferably, the reasonable range is within 20%.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The method for constructing a multi-dimensional imaging mode of a space optical infrared camera of the present invention brings out the imaging capability of the space optical infrared camera through a suitable imaging mode, thereby maximizing the detection capability of the space optical infrared camera. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A flowchart of a method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera of the present invention;

[0036] Figure 2 It is a structural schematic diagram of the radiation calibration system of the space optical infrared camera of the present invention;

[0037] In the figure: 1. Vacuum low-temperature environment simulation device, 2. Space optical infrared camera, 3. Infrared black body, 4. Low-temperature baffle, 5. Satellite integrated simulator, 6. Image data acquisition system. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to the accompanying drawings.

[0039] like Figure 1 As shown in the figure, the method for constructing the multi-dimensional on-orbit imaging mode of a space optical infrared camera is as follows:

[0040] In the first step, the space optical infrared camera radiation calibration system is used to obtain the calibration absolute responsivity and the best response linear range of the space optical infrared camera 2 through infrared radiation calibration test. Figure 2 As shown, the space optical infrared camera radiation calibration system consists of a vacuum low temperature environment simulation device 1, an infrared black body 3, a cryogenic baffle 4, a satellite integrated simulator 5 and an image data acquisition system 6. The vacuum low temperature environment simulation device 1 provides a vacuum low temperature environment (preferably 1E-3Pa, 100K) for the space optical infrared camera 2, the space optical infrared camera 2, the infrared black body 3, and the cryogenic baffle 4 are placed in the vacuum low temperature environment simulation device 1, the infrared black body 3 provides the space optical infrared camera 2 with infrared black body radiation of any temperature within the dynamic range to simulate the radiation of the on-orbit ground objects, the cryogenic baffle 4 provides the space optical infrared camera 2 with background radiation (preferably 100K), the satellite integrated simulator 5 is connected to the space optical infrared camera 2, the image data acquisition system 6 is connected to the space optical infrared camera 2, the satellite integrated simulator 5 injects suitable imaging parameters into the space optical infrared camera 4, and the image data acquisition system 6 collects and stores image data of the space optical infrared camera 4.

[0041] The method of the infrared radiation calibration test is as follows: the infrared black body 3 is set to the lowest temperature T1 of the dynamic range of the space optical infrared camera 2, after the infrared black body 3 is stable, the low temperature baffle 4 is cut out, and the space optical infrared camera 2 saves the image of the infrared black body 3 and the image of the low temperature baffle 4, and then the low temperature baffle 4 is cut in, and the space optical infrared camera 2 saves the image of the infrared black body 3 and the image of the low temperature baffle 4; the temperature of the infrared black body 3 is set in 5K heating intervals in sequence until the highest temperature T2 of the dynamic range is reached, and after the temperature is stable, the image of the infrared black body 3 and the image of the low temperature baffle 4 saved by the space optical infrared camera 2 are respectively collected;

[0042] The response DN values ​​of the images of the infrared black body 3 and the cryogenic baffle 4 at different temperatures are counted, and the radiation brightness of the infrared black body 3 and the cryogenic baffle 4 is calculated as L by Planck's formula. The radiation calibration coefficients k and b are obtained by fitting using the least squares method.

[0043]

[0044] DN = k*L + b (Formula 3)

[0045] In equations 2 and 3, T is the temperature of the infrared black body 3; ε is the emissivity of the infrared black body 3; λ1 and λ2 are the starting wavelength and the ending wavelength of the space optical infrared camera 2, respectively; λ is the wavelength of the space optical infrared camera 2; c1 is the first radiation constant, c1=3.7148e16(W·m 2 ); c2 is the second radiation constant, c2 = 1.4388e-2 (m·K); R(λ) is the spectral response curve of the space optical infrared camera 2; L(T,ε) is the integrated radiation brightness of the infrared black body 3 with a temperature of T and an emissivity of ε in the response spectrum of the space optical infrared camera 2; DN is the response value of the space optical infrared camera 2, k is the absolute response slope of the space optical infrared camera 2; b is the absolute response slope of the space optical infrared camera 2.

[0046] The second step is to obtain the global surface temperature, global object emissivity and global atmospheric profile database, simulate and calculate the entrance pupil equivalent spectral radiance of the space optical infrared camera 2 from multiple dimensions, and establish the entrance pupil equivalent spectral radiance database of the space optical infrared camera 2; the preferred dimensions are longitude dimension, latitude dimension, month dimension and day and night dimension. Define the granularity of the four dimensions according to the needs, such as the granularity of the longitude dimension is 5 degrees, with a total of 72 intervals; the granularity of the latitude dimension is 5 degrees, with a total of 36 intervals; the granularity of the month dimension is 1 month, with a total of 12 intervals; the day and night dimension is divided into two intervals based on the positive and negative solar altitude angle as the criterion. Substitute the global surface temperature, global object emissivity and global atmospheric profile database into the atmospheric radiation transmission software to calculate the entrance pupil equivalent spectral radiance of the space optical infrared camera 2, and establish the entrance pupil equivalent spectral radiance database of the space optical infrared camera 2. The first-level lookup table of the entrance pupil equivalent spectral radiance database and the second-level lookup table 1 of the entrance pupil equivalent spectral radiance are shown in Table 1 and Table 2 respectively.

[0047] Table 1. Primary lookup table of entrance pupil equivalent spectral radiance database

[0048]

[0049]

[0050] Table 2 Secondary lookup table 1 of entrance pupil equivalent spectral radiance (month: mon = 1, solar altitude angle: sl ≤ 0°)

[0051]

[0052] The third step is to construct the multi-dimensional on-orbit imaging mode of the space optical infrared camera 2 according to the entrance pupil equivalent spectral radiance database of the space optical infrared camera 2 and the calibrated absolute responsivity of the space optical infrared camera 2, so that the space optical infrared camera 2 works in the optimal response linear interval, and obtain the initial value of the multi-dimensional on-orbit imaging mode of the space optical infrared camera 2; for example, taking four dimensions (longitude dimension, latitude dimension, month dimension and day and night dimension) as an example, the imaging parameter lookup table is divided into two levels of lookup tables, and the imaging parameter first level lookup table and the imaging parameter second level lookup table 1 are shown in Table 3 and Table 4 respectively. The granularity of the four dimensions is as follows: the granularity of the longitude dimension is 5 degrees, with a total of 72 intervals; the granularity of the latitude dimension is 5 degrees, with a total of 36 intervals; the granularity of the month dimension is 1 month, with a total of 12 intervals; the day and night dimension is divided into two intervals based on the positive and negative solar altitude angle as the criterion.

[0053] Table 3 Imaging parameter first level lookup table

[0054]

[0055] Table 4 Imaging parameter secondary lookup table 1 (month: mon = 1, solar altitude angle: sl ≤ 0°)

[0056]

[0057] Step 4: After the space optical infrared camera 2 is put into orbit, the response DN values ​​of typical objects and the corresponding longitude dimension, latitude dimension, month dimension and day and night dimension of the space optical infrared camera 2 in the early stage of orbit (preliminarily within one week) are counted;

[0058] The entrance pupil equivalent spectral radiance of the space optical infrared camera 2 is calculated according to the information of the longitude dimension, latitude dimension, month dimension and day and night dimension, and the response DN value of the typical ground object is calculated as the theoretical expected value according to the calibrated absolute responsivity;

[0059] The deviation between the statistical value and the theoretical expected value is compared. If the deviation is within 20%, there is no need to adjust the imaging mode. Otherwise, the imaging mode is updated according to the deviation and the calibration absolute response calculation.

Claims

1. A method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera, characterized in that: The following steps are involved: The first step is to obtain the calibration absolute responsivity and the best response linear interval of the space optical infrared camera (2); The second step is to obtain a database of global surface temperature, global ground object emissivity and global atmospheric profile, simulate and calculate the entrance pupil equivalent spectral radiance of the space optical infrared camera (2) from multiple dimensions, and establish an entrance pupil equivalent spectral radiance database of the space optical infrared camera (2); The third step is to construct a multi-dimensional on-orbit imaging mode of the space optical infrared camera (2) according to the entrance pupil equivalent spectral radiance database of the space optical infrared camera (2) and the calibrated absolute responsivity of the space optical infrared camera (2), so that the space optical infrared camera (2) works in the optimal response linear interval, and obtain the initial value of the multi-dimensional on-orbit imaging mode of the space optical infrared camera (2); The fourth step is to optimize the multi-dimensional on-orbit imaging mode of the space optical infrared camera (2) according to the response characteristics of the space optical infrared camera (2) in the early stage of on-orbit after the space optical infrared camera (2) enters orbit.

2. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 1, characterized in that: In the first step, a space optical infrared camera radiation calibration system is used to obtain the calibration absolute response and the best response linear range of the space optical infrared camera (2) through an infrared radiation calibration test; The space optical infrared camera radiation calibration system is composed of a vacuum low temperature environment simulation device (1), an infrared black body (3), a low temperature baffle (4), a satellite integrated simulator (5) and an image data acquisition system (6). The vacuum low temperature environment simulation device (1) provides a vacuum low temperature environment for the space optical infrared camera (2). The space optical infrared camera (2), the infrared black body (3) and the low temperature baffle (4) are placed in the vacuum low temperature environment simulation device (1). The infrared black body (3) provides the space optical infrared camera (2) with simulated on-orbit ground object radiation. The low temperature baffle (4) provides the space optical infrared camera (2) with background radiation. The satellite integrated simulator (5) and the image data acquisition system (6) are both connected to the space optical infrared camera (2). The satellite integrated simulator (5) injects suitable imaging parameters into the space optical infrared camera (4). The image data acquisition system (6) acquires and stores image data of the space optical infrared camera (4).

3. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 2, characterized in that: The method of the infrared radiation calibration test is: The infrared black body (3) is set to the lowest temperature T1 of the dynamic range of the space optical infrared camera (2); after the infrared black body (3) is stabilized, the low temperature baffle (4) is cut out, and the space optical infrared camera (2) saves the image of the infrared black body (3) and the image of the low temperature baffle (4); and then the low temperature baffle (4) is cut in, and the space optical infrared camera (2) saves the image of the infrared black body (3) and the image of the low temperature baffle (4); The temperature of the infrared black body (3) is set in 5K increments until the highest temperature T2 in the dynamic range is reached, and after the temperature is stabilized, an image of the infrared black body (3) and an image of the low temperature baffle (4) stored by the space optical infrared camera (2) are respectively collected; The response DN values ​​of the images of the infrared black body (3) and the cryogenic shield (4) at different temperatures are counted, and the radiation brightness of the infrared black body (3) and the cryogenic shield (4) is calculated as L by Planck's formula, and the radiation calibration coefficients k and b are obtained by fitting using the least square method; DN=k*L+b (Formula 3) In equations 2 and 3, T is the temperature of the infrared black body (3); ε is the emissivity of the infrared black body (3); λ1 and λ2 are the starting wavelength and the ending wavelength of the space optical infrared camera (2), respectively; λ is the wavelength of the space optical infrared camera (2); c1 is the first radiation constant, c1 = 3.7148e16 (W·m 2 ); c2 is the second radiation constant, c2=1.4388e-2(m·K); R(λ) is the spectral response curve of the space optical infrared camera (2); L(T,ε) is the integrated radiation brightness of the infrared black body (3) with a temperature of T and an emissivity of ε in the response spectrum of the space optical infrared camera (2); DN is the response value of the space optical infrared camera (2), k is the absolute response slope of the space optical infrared camera (2); and b is the absolute response slope of the space optical infrared camera (2).

4. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 1, characterized in that: In the second step, the dimensions are four: longitude dimension, latitude dimension, month dimension and day and night dimension.

5. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 4, characterized in that: In the second step, the granularity of the longitude dimension is 5 degrees, with a total of 72 intervals; the granularity of the latitude dimension is 5 degrees, with a total of 36 intervals; the granularity of the month dimension is 1 month, with a total of 12 intervals; the day and night dimension is divided into two intervals based on the positive and negative solar altitude angle.

6. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 1, characterized in that: In the second step, the global surface temperature, global ground object emissivity and global atmospheric profile database are substituted into the atmospheric radiation transfer software to calculate the entrance pupil equivalent spectral radiance of the space optical infrared camera (2).

7. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 1, characterized in that: In the second step, the databases are all mean databases.

8. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 1, characterized in that: In the fourth step, the initial period is within one week of entering orbit.

9. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 1, characterized in that: In the fourth step, after the space optical infrared camera (2) enters orbit, the response DN values ​​and corresponding multi-dimensional information of typical objects of the space optical infrared camera (2) at the initial stage of orbit are counted; The entrance pupil equivalent spectral radiance of the space optical infrared camera (2) is calculated according to the multi-dimensional information, and the response DN value of the typical ground object is calculated according to the calibrated absolute responsivity as a theoretical expected value; The deviation between the statistical value and the theoretical expected value is compared. If the deviation is within a reasonable range, there is no need to adjust the imaging mode. Otherwise, the imaging mode is updated based on the deviation and the calibration absolute responsivity calculation.

10. The method for constructing a multi-dimensional on-orbit imaging mode of a space optical infrared camera according to claim 9, characterized in that: The reasonable range of the deviation is within 20%.

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