A driving timing control method of a spaceborne infrared spectrometer detector

Abstract

This invention specifically relates to a driving timing control method for a spaceborne infrared spectrometer detector, solving the problem that the overlapping time of pixel row transfer time and signal exposure time cannot be guaranteed to be completely consistent, resulting in inaccurate spectral bands and ultimately wasted resources. This invention includes the following steps: Step (1), determining the dead time difference b; Step (2), measuring the current frame period D; Step (3), dynamically adjusting the dead time difference a; based on the frame period D, exposure time E, and pixel row transfer time T... line The time difference b of the dead zone obtained in step (2) is used to dynamically adjust the time difference a of the dead zone; in step (4), during the satellite's operation in orbit, the frame period D and exposure time E are adjusted in real time according to the ground features and orbital altitude. Steps (2) and (3) are repeated to dynamically adjust the time difference a of the dead zone until the satellite completes a complete imaging of one orbit during its operation in orbit, thereby obtaining the target spectrum.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for improving spectral recovery accuracy, in particular to a driving timing control method of a satellite-borne infrared spectrometer detector. BACKGROUND

[0002] With the development of space remote sensing technology in China, satellite remote sensing is increasingly showing a trend of high temporal resolution, high spatial resolution and high spectral resolution, which puts higher requirements on spectral calibration and correction, and makes the requirement for target spectral recovery accuracy higher and higher.

[0003] An infrared imaging system is a system that can detect the infrared radiation of a target, and converts the infrared radiation of the target object into an image through photoelectric conversion and signal processing. The infrared detector is the core of the imaging system, and fundamentally determines the development level of the infrared system. The driving timing required for its work needs to be generated and processed by a signal processing circuit.

[0004] When the infrared imaging system is applied to satellite payloads, because the distance between the satellite and the earth is not consistent in a revisit period (non-sun synchronous orbit), the orbit of the satellite is often elliptical. Therefore, if the payload needs to be turned on during a period, the speed-height ratio needs to be calculated in real time according to the distance between the satellite and the ground. The payload control system will adjust the working frame frequency of the infrared imaging system in real time according to the speed-height ratio. At the same time, in order to adapt to the shooting of different scenes, the exposure time needs to be adjusted.

[0005] During the change of frame frequency or exposure time, the performance indicators of the spectrometer will be lost, resulting in poor spectral accuracy. The reason is that the number of rows with low output signal level is constantly changing, and there is no effective means to remove its influence, which further leads to inaccurate spectral bands falling within the influence range. As shown in Figure 1 、 Figure 2 and Figure 3 , the time of pixel row transfer before adjustment overlaps with the length of the detector integration INT signal exposure time, which is Y, representing that m rows are overlapped. But the time of pixel row transfer after adjustment overlaps with the length of the detector integration INT signal exposure time, which is Z, representing that n rows are overlapped. The overlap of the time of pixel row transfer before and after adjustment with the detector integration INT signal exposure time is not equal, resulting in inaccurate spectral band acquisition and resource waste. SUMMARY

[0006] The present application provides a driving timing control method of a satellite-borne infrared spectrometer detector, which is used to solve the problem that the obtained spectral band is not accurate due to the fact that the overlap time of pixel row transfer time and signal exposure time cannot be guaranteed to be completely consistent, and ultimately causes resource waste.

[0007] This invention provides a driving timing control method for a spaceborne infrared spectrometer detector, offering a technical approach and method for obtaining higher target spectral accuracy in spaceborne hyperspectral imaging. This method can also be applied to almost all short-wave infrared, mid-wave infrared, and long-wave infrared spectral imaging systems, increasing resource utilization.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for driving timing control of a spaceborne infrared spectrometer detector, characterized by the following steps:

[0010] Step 1, based on the shortest frame period D of the infrared detector in the infrared spectrometer min Minimum before dead time difference a min Maximum exposure time E max and pixel row transfer time T line The time difference b after the dead zone is calculated;

[0011] Step 2: The detection timing generated by the infrared spectrometer drives the infrared detector to work, and the frame period D of the detection timing is measured.

[0012] Step 3: Dynamically adjust the front dead zone time difference a by changing the frame period D and exposure time E to ensure that the rear dead zone time difference b remains unchanged.

[0013] Step 4: During the satellite's on-orbit operation, the frame period D and exposure time E are adjusted in real time based on ground features and orbital altitude. Steps 2 and 3 are repeated, and the time difference before dead zone a is dynamically adjusted until the satellite completes a complete imaging of one orbit during its on-orbit operation, thereby obtaining the target spectrum.

[0014] Furthermore, in step 2, the infrared spectrometer generates the detection timing sequence via FPGA;

[0015] The frame period D is obtained by measuring the time length of two consecutive frame frequency signals in the detection timing sequence, or by converting the frame frequency to obtain the corresponding frame period D.

[0016] Furthermore, in step 1, the formula for calculating the after-dead time difference b is as follows:

[0017] b = T line +a min -(D min -E max )

[0018] D min This is the shortest frame period of the infrared detector;

[0019] T line For pixel row transfer time;

[0020] a min is the minimum front dead time difference;

[0021] E max is the maximum exposure time.

[0022] Further, in step 3, the calculation formula of the front dead time difference a is as follows:

[0023] a=D-E-(T line -b)

[0024] Wherein, D is the frame period, E is the exposure time, b is the rear dead time difference, T line is the pixel row transfer time.

[0025] Further, in step 3, after ensuring that the rear dead time difference b remains unchanged, the infrared detector increases the gray value of the affected pixel row according to a fixed proportion, so that the gray value of the affected area is consistent with that of the unaffected area, so that the final obtained image is consistent in brightness.

[0026] Compared with the prior art, the beneficial effects of the present application are as follows:

[0027] The present application calculates the exposure time, the pixel row transfer time, the frame period, the minimum allowable length of the front dead time difference, etc., obtains the dynamic balance front dead time difference, makes the overlap time of the pixel row transfer time and the signal exposure time completely consistent, effectively improves the performance of the load system, and improves the accuracy of the collected spectral detection, so that the spectral detection accuracy is improved by about 0.5%. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the front overlap row of the infrared detector exposure time adjustment;

[0029] Figure 2 is a schematic diagram of the rear overlap row of the infrared detector exposure time adjustment;

[0030] Figure 3 is a comparison diagram of the number of affected pixel rows before and after the infrared detector exposure time adjustment, wherein figure (a) is a schematic diagram of the number of affected pixel rows before the exposure time adjustment, and figure (b) is a schematic diagram of the number of affected pixel rows after the exposure time adjustment;

[0031] Figure 4 is a traditional timing relationship diagram of the infrared detector. DETAILED DESCRIPTION

[0032] The present application will be further described below in combination with the drawings and specific embodiments.

[0033] This invention addresses infrared spectrometers with variable frame rates and exposure times by designing a driving timing control method for the detector of a spaceborne infrared spectrometer. This method ensures that the infrared camera maintains a constant relationship between the output pixel row transfer time and the exposure time. This constant relationship can reduce the acquired spectral errors, improve the accuracy of the acquired spectra, and enhance the infrared spectrometer's ability to identify and interpret targets.

[0034] According to Figure 4 The diagram shown illustrates the traditional timing relationship of the infrared detector, along with a detailed explanation of the method and steps.

[0035] In this invention, the FPGA provides timing for the infrared detector and controls the infrared detector. The FPGA and the infrared detector together form an infrared camera. The infrared camera and the infrared lens together form an infrared spectrometer, which is installed on a satellite.

[0036] Dead time difference b after step (1)

[0037] The front dead zone refers to the time difference between the end of the current exposure time and the start of the current pixel row transition.

[0038] The dead zone refers to the time difference between the end of the current pixel row transition and the start of the next frame's exposure time.

[0039] The exposure time E is less than or equal to the reciprocal of the frame rate and greater than or equal to the shortest exposure time set in the instrument.

[0040] In this embodiment, timing is generated by an FPGA to drive the short-wave infrared mercury cadmium telluride detector.

[0041] According to the maximum allowable frame rate (corresponding to the shortest frame period D) of the infrared spectrometer system design. min Minimum before dead time difference a min Maximum exposure time E max Calculate the dead time difference b;

[0042] b = T line +a min -(D min -E max )

[0043] Among them, T line This is the pixel row transfer time. Once the infrared detector is determined, this parameter is fixed. Similarly, a... min and E max This parameter is fixed once the infrared detector is determined, a min When the infrared spectrometer or camera system is determined, this parameter is fixed. When the detector is determined, the range of the frame period D is also determined accordingly, and the shortest frame period D can be obtained directly. min .

[0044] Therefore, the time difference b after the dead zone is a fixed value.

[0045] For the selected short-wave infrared mercury cadmium telluride detector, the minimum pre-dead time difference 'a' is 200 μs. Pixel row transfer time T line = Transition time per row × number of rows transferred. In this embodiment, the calculated pixel row transition time is 2300µs. Therefore, the calculated dead zone time difference is 1920µs.

[0046] Step (2) Measure the current frame period

[0047] For the internal logic gates of an FPGA device with adjustable frame rate, the frame period D is measured, which is the time length between two consecutive valid frame rate signals, and is denoted as D.

[0048] The selected short-wave infrared mercury cadmium telluride detector corresponds to a frame rate range of 250–400 fps, and therefore the corresponding frame period D value is 4 ms–2.5 ms, with a maximum frame period of 4 ms and a minimum frame period of 2.5 ms.

[0049] The exposure time is determined comprehensively based on factors such as the payload orbital height, target light intensity, and beam splitting system. For example, strong light results in a shorter exposure time, while weak light results in a longer exposure time. The longest exposure time is the reciprocal of the frame rate, and the shortest is the minimum value set by the manufacturer during production. In this embodiment, the minimum exposure time is 0.5ms, and the maximum is 1.92ms.

[0050] Step (3) Dynamic adjustment of the pre-dead time difference a

[0051] Having determined the value of the back dead zone time difference b in step (2), the front dead zone time difference a is dynamically adjusted by changing the exposure time or frame rate. The value of a is calculated as follows:

[0052] a=DE-(T line -b)

[0053] Where D is the frame period and E is the exposure time. As the frame period and exposure time change, the front dead zone time difference 'a' is continuously calculated and dynamically adjusted to ensure the rear dead zone time difference 'b' remains constant. This ensures that the image area resulting from the overlap of the pixel row transfer time and exposure time at the infrared spectrometer output remains fixed. Based on... Figure 3 As shown, Figure 3 (a) Compared to the overlapping area of ​​pixel row transfer time and exposure time Figure 3(b) from the image will be dark, the dark image in the fixed, due to each change inconsistent, resulting in processing; when the dark image in fixed can be processed, after processing can get accurate corresponding information. Therefore, in order to obtain high accuracy spectral information, according to the fixed proportion of the affected line to increase the gray value, the affected area gray and not affect the area consistent, so that the final picture is consistent with the light and dark.

[0054] FPGA through the known frame period, exposure time and the difference b, and the difference between the front dead time calculation formula, calculation of the value of the difference between the front dead time a, and the value is converted into a specific value under the internal working clock. As in step 1920us, according to the working clock 10MHz calculation, then the corresponding count value is 19200.

[0055] Step (4) repeat step (2) and step (3) complete the dynamic adjustment of the difference between the front dead time a, so that the satellite in orbit operation process of the satellite on the infrared camera to obtain a track complete imaging, through complete imaging to obtain the target spectrum, and according to the real-time adjustment of frame period and exposure time of the ground object and the height of the orbit, so that the target spectrum accuracy is higher.

[0056] Step (1) in the difference between the back dead time b in the system index fixed, only need to calculate once manually, as a constant, no longer repeated calculation in the process.

Claims

1. A method for driving timing control of a spaceborne infrared spectrometer detector, characterized in that, Includes the following steps: Step 1, calculating the shortest frame period D of the infrared detector in the infrared spectrometer min , the minimum pre dead time difference a min , the maximum exposure time E max , and the pixel row transfer time T line , the post dead time difference b is calculated Wherein: the front dead zone time difference refers to the time difference between the end of the current exposure time and the start of the current pixel row transfer; The time difference after dead zone refers to the time difference between the end of the current pixel row transition and the start of the exposure time of the next frame; The formula for calculating the after-dead time difference b is as follows: b = T line + a min - (D min - E max ) D min is the shortest frame period for the infrared detector; T line is the pixel row transfer time; a min is the minimum pre-dead time difference; E max Maximum exposure time; Step 2: The detection timing generated by the infrared spectrometer drives the infrared detector to work, and the frame period D of the detection timing is measured. Step 3: Dynamically adjust the front dead zone time difference a by changing the frame period D and exposure time E to ensure that the rear dead zone time difference b remains unchanged. The formula for calculating the pre-dead time difference 'a' is as follows: a=D-E-(T line -b) Where D is the frame period, E is the exposure time, b is the after-dead time difference, and T is the frame period. line For pixel row transfer time; Step 4: During the satellite's on-orbit operation, the frame period D and exposure time E are adjusted in real time based on ground features and orbital altitude. Steps 2 and 3 are repeated, and the time difference before dead zone a is dynamically adjusted until the satellite completes a complete imaging of one orbit during its on-orbit operation, thereby obtaining the target spectrum.

2. The driving timing control method for a spaceborne infrared spectrometer detector according to claim 1, characterized in that: In step 2, the infrared spectrometer generates the detection timing sequence via FPGA; The frame period D is obtained by measuring the time length of two consecutive frame frequency signals in the detection timing sequence, or by converting the frame frequency to obtain the corresponding frame period D.

3. The driving timing control method for a spaceborne infrared spectrometer detector according to claim 2, characterized in that: In step 3, after ensuring that the time difference b after the dead zone remains unchanged, the infrared detector increases the gray value of the affected pixel row by a fixed ratio, so that the gray value of the affected area is consistent with that of the unaffected area, and the final image is consistent in brightness.

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