Fast exposure adjustment system and method for space high speed camera

Abstract

The application provides a fast exposure adjustment system and method for a space high-speed camera, belongs to the field of deep space exploration, combines camera image gray scale statistics and PIN tube photometry technology, collects the advantages of two traditional exposure time adjustment methods, can meet the fast exposure time adjustment of the high-speed camera in a transient light scene, avoids overexposure of continuous images of the camera due to impact of transient high light, and can also realize fine adjustment of the exposure time in a slowly changing target scene, so as to ensure the imaging effect of a sputtering cloud of sputtering objects generated by impact. The exposure time adjustment method combining fast adjustment with slow adjustment and coarse adjustment with fine adjustment is realized, so that the imaging effect of a complex scene in the whole process of kinetic energy impact can be effectively ensured.

Description

Technical Field

[0001] This invention belongs to the field of deep space exploration, specifically relating to a rapid exposure adjustment system and method for a high-speed space camera. Background Technology

[0002] Near-Earth asteroids are those with a perihelion distance of less than 1.3 AU (astronomical units, defined as the average distance between the Earth and the Sun). Near-Earth asteroids are numerous and pose a significant threat upon impact. For near-Earth asteroid defense demonstration and verification missions that combine impact assessment and evaluation, the impactor system alters the target asteroid's orbital period around the Sun through kinetic energy impacts to initially verify the on-orbit handling capability for near-Earth asteroids. In the asteroid defense demonstration and verification mission, a high-speed space camera will be deployed to observe and acquire high-dynamic data of the entire kinetic energy impact process by approaching the target asteroid, deepening the evaluation of kinetic energy impact effects and supporting research on the mechanism of ultra-high-speed kinetic energy impacts.

[0003] In the near-Earth asteroid defense demonstration and verification mission that combines impact assessment and evaluation, firstly, the impact observation adopts close-range high-speed imaging technology for the first time, enabling high spatial and temporal resolution observation of the entire kinetic impact process; secondly, the relative velocity and impact mass of kinetic impacts vary greatly, which may lead to phase transitions in the impactor rather than just physical changes, and the changes in the brightness of the target in the impact scene may be more dramatic; finally, the characteristics of the impact target asteroid are unknown, and the information on ejecta, ejecta clouds, and the brightness of the impact point are also unknown.

[0004] Setting the exposure time for high-speed space cameras faces challenges due to the uncertainty of target brightness and the need for rapid response. The target light source in a hypersonic kinetic impact process originates from two parts: first, sunlight reflected from asteroid ejecta and ejecta clouds caused by the kinetic impact; the different characteristics of these ejecta result in significant brightness variations, and the simulation of ejecta states depends on the characteristics of the target asteroid; second, intense light radiation resulting from the phase transition of the impactor and asteroid target materials caused by the hypersonic kinetic impact. The impactor's composition is complex, potentially containing residual propellant, and the asteroid target material is unknown, limiting the confidence level of the simulated light radiation caused by hypersonic kinetic impacts. To achieve rapid exposure at high frame rates, high-speed space cameras require adjustable single-frame exposure times for the imaging array sensor. Furthermore, to ensure high dynamic range target imaging, the camera needs to complete target brightness measurement and exposure time adjustment within several frames. This places stringent requirements on the high-speed camera's operating timing design and the accuracy of exposure time adjustment.

[0005] Exposure time adjustments for conventional aerial or aerospace cameras are typically made either based on camera grayscale information or using a PIN diode metering module. Adjusting exposure time based on camera grayscale measurements offers advantages such as high spatial resolution and fine-grained exposure time adjustments, but its adjustment speed is limited. It requires adjusting exposure time based on statistical results from multiple frames of images, limiting its applicability to complex and rapidly changing scenarios such as ultra-high-speed kinetic energy impacts. The relatively delayed exposure time adjustments can lead to continuous overexposure or underexposure risks for high-speed cameras. PIN diode metering modules, on the other hand, offer advantages such as high dynamic range and high metering rate, but their single-pixel spatial resolution is limited. Their exposure time adjustment accuracy is limited when dealing with irregularly distributed sputtered objects in kinetic energy impact scenarios. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a rapid exposure adjustment system and method for high-speed space cameras. By combining camera image grayscale statistics and PIN tube metering technology, it satisfies the need for rapid exposure time adjustment of high-speed cameras in transiently bright scenes and achieves fine adjustment of exposure time in slowly changing target scenes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A fast exposure adjustment system for a high-speed space camera, comprising:

[0009] The grayscale measurement module has its input end connected to the image data bus of the high-speed space camera, and is used to receive image grayscale in real time and output overexposure ratio signal and underexposure ratio signal.

[0010] The high-speed metering module has its photosensitive surface aligned with the main optical axis of the space high-speed camera. Its output is connected in parallel with the output of the grayscale measurement module to the exposure time adjustment decision module, and outputs the target radiance change rate signal.

[0011] The exposure time adjustment decision module is connected to the exposure time register bus of the high-speed space camera. It is used to output corresponding exposure time adjustment commands in the four stages of impact initial stage, fast sputtering stage, slow sputtering stage, and sputtering completion stage, based on the overexposure ratio signal, underexposure ratio signal, and target radiance change rate signal of the high-speed metering module, so as to drive the high-speed space camera to complete the exposure time switching.

[0012] This invention also provides a method for fast exposure adjustment of a space high-speed camera using the aforementioned fast exposure adjustment system for a space high-speed camera, comprising the following steps:

[0013] Step 1: The grayscale measurement module statistically analyzes the grayscale distribution of the camera image of the high-speed spatial camera frame by frame, and outputs the overexposure ratio signal and the underexposure ratio signal.

[0014] Step 2: The high-speed photometric module acquires the target radiance at nanosecond intervals and calculates the rate of change of the target radiance, and outputs the target radiance and the rate of change of the target radiance signal;

[0015] Step 3: The exposure time adjustment decision module receives the overexposure ratio signal, underexposure ratio signal and target radiance change rate signal in parallel, and determines the current stage according to the impact stage logic to obtain the judgment result;

[0016] Step 4: Based on the judgment result, the exposure time adjustment decision module writes the corresponding exposure time value to the exposure time register of the high-speed space camera, and it takes effect in the next frame;

[0017] Step 5: Repeat steps 1-4, going through the initial impact stage, the rapid sputtering stage, the slow sputtering stage until the sputtering is completed, and the camera exposure time is locked to a preset fixed value.

[0018] Beneficial effects:

[0019] This invention combines camera image grayscale statistics and PIN tube metering technology, integrating the advantages of two traditional exposure time adjustment methods. It can meet the needs of high-speed cameras for rapid exposure time adjustment in transiently bright scenes, avoiding overexposure of consecutive images due to transient brightness caused by impact; and it can also achieve fine-tuning of exposure time in scenes with gradually changing targets, ensuring imaging quality of sputter clouds generated by impacts. This invention implements an exposure time adjustment method that combines fast and slow adjustments, as well as coarse and fine adjustments, effectively guaranteeing imaging quality in complex scenes throughout the kinetic energy impact process. This invention can also provide some reference for the design of imaging strategies for complex, rapidly changing scenes. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a rapid exposure adjustment system for a high-speed space camera according to the present invention.

[0021] Figure 2 A schematic diagram of regional metering for a high-speed camera;

[0022] Figure 3 This is a schematic diagram of the high-speed photometry module. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] like Figure 1As shown, a rapid exposure adjustment system for a high-speed space camera according to the present invention includes:

[0025] The grayscale measurement module calculates the target radiance based on the photoelectric sensor response value of the high-speed space camera itself, and statistically analyzes the overexposure and underexposure ratios within the image plane to determine whether the image is overexposed or underexposed.

[0026] The high-speed photometry module measures the target radiance based on the external photodiode and preamplifier circuit of the high-speed space camera. It works with a high-speed analog-to-digital converter to convert the target analog signal into a digital signal and obtain information such as the rate of change of the target radiance.

[0027] The exposure time adjustment decision module adopts corresponding exposure time adjustment strategies based on the measurement results of the target radiance from the grayscale measurement module and the high-speed metering module, the determination of overexposure or underexposure in imaging, and the rate of change of target radiance.

[0028] Specifically, the input of the grayscale measurement module is connected to the image data bus of the high-speed space camera, and is used to receive image grayscale in real time and output overexposure ratio signal and underexposure ratio signal.

[0029] Specifically, the photosensitive surface of the high-speed metering module is aligned with the main optical axis of the space high-speed camera, and its output is connected in parallel with the output of the grayscale measurement module to the exposure time adjustment decision module, outputting the target radiance change rate signal.

[0030] Specifically, the control terminal of the exposure time adjustment decision module is connected to the exposure time register bus of the space high-speed camera. It is used to output corresponding exposure time adjustment commands in the four stages of impact initial stage, fast sputtering, slow sputtering, and sputtering completion according to the overexposure ratio signal, underexposure ratio signal and the target radiance change rate signal of the high-speed metering module, so as to drive the space high-speed camera to complete the exposure time switching within a few frames.

[0031] Specifically, the grayscale measurement module is equipped with an FPGA histogram counter. The FPGA histogram counter reads the images of the high-speed spatial camera frame by frame through the data bus, and writes the statistically obtained overexposure ratio signal and underexposure ratio signal into the first input buffer of the exposure time adjustment decision module in real time through the parallel bus.

[0032] Specifically, the high-speed metering module is composed of a PIN diode (photodiode), a preamplifier, and a high-speed analog-to-digital converter cascaded in sequence. The anode of the PIN diode is connected to the input terminal of the preamplifier, the output terminal of the preamplifier is DC coupled to the analog input terminal of the high-speed analog-to-digital converter, and the digital output terminal of the high-speed analog-to-digital converter is connected to the second input buffer of the exposure time adjustment decision module.

[0033] Specifically, the exposure time adjustment decision module performs stage discrimination. The input of the exposure time adjustment decision module simultaneously receives the overexposure / underexposure flags obtained from the overexposure ratio signal and underexposure ratio signal of the grayscale measurement module, as well as the target radiance change rate flag of the high-speed metering module. Its output writes the minimum limit value (i.e., the minimum allowable exposure time value), the 20% step increase value, the PID closed-loop correction value, or the fixed maximum value (i.e., the maximum allowable exposure time value) corresponding to the current stage to the exposure time register of the space high-speed camera.

[0034] Specifically, the grayscale measurement module, the high-speed metering module, and the exposure time adjustment decision module share the same onboard clock source. The differential clock lines of the onboard clock source are respectively connected to the clock input terminals of the grayscale measurement module, the high-speed metering module, and the exposure time adjustment decision module to ensure that the exposure time adjustment command is strictly synchronized with the image frame timing.

[0035] Specifically, the grayscale measurement module is mainly based on the grayscale measurement values ​​of the photoelectric sensor of the high-speed space camera. It uses a regional photometric method and utilizes the embedded FPGA histogram counter to statistically analyze the grayscale distribution in different regions and calculate the grayscale mean. Using the camera radiometric calibration coefficient, the target radiance is calculated as shown in equation (1):

[0036] (1)

[0037] Where L is the target radiance, n is the total number of pixel partitions, and i is the pixel partition number. Let be the average value of the corresponding values ​​in the i-th pixel region. denoted as the radiometric response coefficient of a high-speed space camera.

[0038] The grayscale measurement module consists of the following components: Figure 2 As shown, the photoelectric sensor performs regional photometry, dividing the area into 5×5 regions (i.e., Figure 2 The 5×5 dynamic ROI division is used to perform gray-level statistics on the regional imaging results of the image through the gray-level histogram statistical unit, so as to obtain the radiance of the target scene and the overexposure or underexposure ratio in the image, and realize the determination of light intensity overexposure or underexposure. Figure 2 In this context, ROI represents the region of interest.

[0039] Furthermore, based on the characteristics of kinetic impact images, the determination of overexposure and underexposure of light intensity is as follows:

[0040] Overexposure: The percentage of pixels with the highest grayscale value is greater than 5%;

[0041] Underexposure: The percentage of pixels with the lowest grayscale value (limited to 0~100) is greater than 30%.

[0042] In other words, the logical judgment sequence during the impact phase is as follows: First, determine whether the target radiance change rate signal is greater than a preset rate threshold. If it is, proceed directly to the initial impact phase; otherwise, differentiate between the rapid sputtering phase, slow sputtering phase, or sputtering completion phase based on the overexposure ratio signal, underexposure ratio signal, and target radiance change rate signal. Specifically, an overexposure signal is generated when the saturated grayscale value ratio is greater than 20%; an underexposure signal is generated when the percentage of pixels with grayscale values ​​less than 1000 is greater than 20%.

[0043] Specifically, such as Figure 3 As shown, the high-speed photometric module utilizes the advantages of PIN tube photometric speed and large dynamic range, combined with a high-speed analog-to-digital converter, to complete the target radiance measurement within nanoseconds, and obtains the target radiance change rate (i.e., ...) through data processing. Figure 3 (Light intensity and rate of change). The high-speed metering module not only provides higher frequency target radiance information for accurate setting of exposure time, but also obtains the rate of change of target radiance by statistically calculating it, allowing for advance setting of exposure time.

[0044] The target radiance is calculated based on the photovoltage response of the PIN tube as shown in equation (2):

[0045] (2)

[0046] Where U is the output voltage of the PIN diode. This represents the radiation response coefficient of the high-speed photometry module.

[0047] Specifically, the exposure time adjustment decision module makes decisions on the exposure time adjustment strategy according to the characteristics of the kinetic energy impact scene, based on the target radiance change rate and overexposure / underexposure statistics provided by the grayscale measurement module, the target radiance and target radiance change rate provided by the high-speed metering module, and the situation in different levels.

[0048] Scenario 1, Initial Stage of Impact: The grayscale measurement module has not yet responded, and the high-speed photometric module detects light intensity exceeding the preset value and the rate of light intensity change is >10. 6 W / s. The emergency exposure time adjustment response mechanism is activated, adjusting the exposure time of the high-speed space camera to its minimum limit.

[0049] Scenario 2, Rapid Sputtering Stage: The grayscale measurement module shows underexposure, and the high-speed metering module detects that the light intensity is within the threshold of the high-speed space camera, with a light intensity change rate < 10. 3 W / s. Based on the light intensity measured by the high-speed metering module, the exposure time adjustment decision module generates the next frame's exposure time value with the current exposure time value as a reference, increasing by 20% increments. The target gray value is set at 2 / 3 of the maximum gray value of the spatial high-speed camera, and the exposure time is adjusted by maintaining the target gray value through closed-loop feedback.

[0050] Scenario 3, Slow Sputtering Stage: The grayscale measurement module shows no overexposure or underexposure indicators, the high-speed metering module detects light intensity less than the threshold of the high-speed space camera, and the light intensity change rate is <10. 3 W / s. Based on the light intensity measured by the grayscale measurement module, the exposure time of the high-speed space camera is adjusted in 5% increments. The exposure time adjustment decision module enables PID control, with the target grayscale value set as 2 / 3 of the maximum grayscale value of the high-speed space camera. The difference between the average grayscale value of the image and 2 / 3 of the maximum grayscale value (i.e., the target grayscale value) is used as the error input to correct the exposure time, and the corrected exposure time value is output frame by frame.

[0051] Scenario 4, Sputtering Completion Stage: The grayscale measurement module displays an underexposure indicator, and the high-speed metering module detects that the light intensity is close to the lower limit of 20% of the dynamic range of the space high-speed camera. The exposure time of the space high-speed camera is set to the specified value of 10μs and will not be adjusted further.

[0052] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rapid exposure adjustment system for a high-speed space camera, characterized in that, include: The grayscale measurement module has its input end connected to the image data bus of the high-speed space camera, and is used to receive image grayscale in real time and output overexposure ratio signal and underexposure ratio signal. The high-speed metering module has its photosensitive surface aligned with the main optical axis of the space high-speed camera. Its output is connected in parallel with the output of the grayscale measurement module to the exposure time adjustment decision module, and outputs the target radiance and the target radiance change rate signal. The exposure time adjustment decision module is connected to the exposure time register bus of the high-speed space camera. It is used to output corresponding exposure time adjustment commands in the four stages of impact initial, fast sputtering, slow sputtering and sputtering completion according to the overexposure ratio signal, underexposure ratio signal and the target radiance and target radiance change rate signal of the high-speed metering module, so as to drive the high-speed space camera to complete the exposure time switching. In the initial stage of the impact, the grayscale measurement module has not yet responded, while the high-speed photometry module detects that the target radiance exceeds the threshold of the high-speed space camera and the rate of change of the target radiance is greater than 10. 6 W / s; The emergency exposure time adjustment response mechanism is activated to adjust the exposure time of the high-speed space camera to the minimum limit; During the rapid sputtering stage, the grayscale measurement module indicates underexposure, while the high-speed metering module detects that the target radiance equals the threshold of the high-speed space camera, and the target radiance change rate is <10. 3 W / s; Based on the target radiance measured by the high-speed metering module, the exposure time adjustment decision module generates the next frame exposure time value with the current exposure time value as the reference, increasing by 20% increments. The target gray value is set as 2 / 3 of the maximum gray value of the spatial high-speed camera, and the target gray value is maintained through closed-loop feedback to adjust the exposure time. During the slow sputtering phase, the grayscale measurement module showed no overexposure or underexposure indicators, the high-speed metering module detected that the target radiance was less than the threshold of the high-speed space camera, and the target radiance change rate was <10. 3 W / s; Based on the target radiance measured by the high-speed metering module, the exposure time of the space high-speed camera is adjusted in 5% increments. The exposure time adjustment decision module enables PID control, and the target gray value is set as 2 / 3 of the maximum gray value of the space high-speed camera. The difference between the average gray value of the image and 2 / 3 of the maximum gray value is used as the error input to correct the exposure time, and the corrected exposure time value is output frame by frame. During the sputtering completion stage, the grayscale measurement module showed an underexposure indicator, and the high-speed metering module detected that the target radiance was close to the lower limit of 20% of the dynamic range of the space high-speed camera; the exposure time of the space high-speed camera was set to a fixed maximum value and would not be adjusted.

2. The rapid exposure adjustment system for a high-speed space camera according to claim 1, characterized in that, The grayscale measurement module is equipped with an FPGA histogram counter. The FPGA histogram counter reads the images of the high-speed spatial camera frame by frame through the data bus, and writes the statistically obtained overexposure ratio signal and underexposure ratio signal into the first input buffer of the exposure time adjustment decision module in real time through the parallel bus.

3. The rapid exposure adjustment system for a high-speed space camera according to claim 1, characterized in that, The high-speed metering module consists of a photodiode, a preamplifier, and a high-speed analog-to-digital converter cascaded in sequence. The anode of the photodiode is connected to the input terminal of the preamplifier, the output terminal of the preamplifier is DC coupled to the analog input terminal of the high-speed analog-to-digital converter, and the digital output terminal of the high-speed analog-to-digital converter is connected to the second input buffer of the exposure time adjustment decision module.

4. The rapid exposure adjustment system for a high-speed space camera according to claim 1, characterized in that, The exposure time adjustment decision module performs stage discrimination. The input of the exposure time adjustment decision module simultaneously receives the overexposure / underexposure flags obtained from the overexposure ratio signal and underexposure ratio signal of the grayscale measurement module, as well as the target radiance and target radiance change rate flags of the high-speed metering module. The output of the exposure time adjustment decision module writes the minimum limit value, 20% step increase value, PID closed-loop correction value, or fixed maximum value corresponding to the current stage to the exposure time register of the space high-speed camera.

5. A rapid exposure adjustment system for a high-speed space camera according to any one of claims 1 to 4, characterized in that, The grayscale measurement module, high-speed metering module, and exposure time adjustment decision module share the same onboard clock source. The differential clock lines of the onboard clock source are respectively connected to the clock input terminals of the grayscale measurement module, high-speed metering module, and exposure time adjustment decision module to ensure that the exposure time adjustment command is strictly synchronized with the image frame timing.

6. A method for fast exposure adjustment of a space high-speed camera implemented using the fast exposure adjustment system for a space high-speed camera according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: The grayscale measurement module statistically analyzes the grayscale distribution of the camera image of the high-speed spatial camera frame by frame, and outputs the overexposure ratio signal and the underexposure ratio signal. Step 2: The high-speed photometric module acquires the target radiance at nanosecond intervals and calculates the rate of change of the target radiance, and outputs the target radiance and the rate of change of the target radiance signal. Step 3: The exposure time adjustment decision module receives the overexposure ratio signal, underexposure ratio signal, target radiance and target radiance change rate signal in parallel, and determines the current stage according to the impact stage logic to obtain the judgment result; Step 4: Based on the judgment result, the exposure time adjustment decision module writes the corresponding exposure time value to the exposure time register of the high-speed space camera, and it takes effect in the next frame; Step 5: Repeat steps 1-4, going through the initial impact stage, the rapid sputtering stage, the slow sputtering stage until the sputtering is completed. The camera exposure time is then locked and no longer adjusted.

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