A camera system and method for capturing tracking modulated beacon light

Abstract

The application belongs to the technical field of space laser communication, and discloses a camera system and method for capturing and tracking modulated beacon light. The camera system uses a beam splitter to divide the modulated beacon light incident on the camera system into a first light beam and a second light beam. A pulse synchronization module generates a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the first light beam. An image sensor control module controls an image acquisition module to acquire images of the second light beam using the pulse signal, so that the image acquisition module acquires images with the optimal exposure time and the same frequency, phase and duty cycle as the modulated beacon light. An image processing module processes the acquired images, and a beacon tracking module identifies and tracks the modulated beacon light in the processed images, thereby achieving maximum power capture of the modulated beacon light. The application can significantly improve the signal-to-noise ratio of the captured modulated beacon light images while ensuring the image frame rate, and is more widely and flexibly used.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of space laser communication, and more particularly relates to a camera system and method for capturing and tracking modulated beacon light. BACKGROUND

[0002] A space laser communication system is an optical communication system taking laser light as a carrier and taking atmosphere as a transmission medium. The space laser communication has the advantages of large communication capacity, high-speed transmission and strong confidentiality. In the process of space optical communication, the communication terminal needs to accurately obtain the position information of the opposite terminal and achieve the extremely accurate mutual alignment between the two communication terminals, otherwise the communication cannot be completed. Therefore, each communication terminal needs to have complete acquisition, tracking and aiming functions. The telescope as the communication terminal acquires the beacon light signal from the communication object, and the positions of the beacon light spots on the image sensor are used for mutual positioning to achieve tracking positioning. The beacon light is affected by the attenuation and turbulence of the atmosphere during the atmospheric transmission process, resulting in very weak beacon light signal reaching the receiving end and serious light intensity fluctuation, which causes the tracking camera to fail to correctly obtain the target position information, and further causes tracking failure, affecting the communication transmission distance. Meanwhile, the frame rate of the tracking camera will greatly affect the tracking effect of the entire system. By using a modulated light source, the signal-to-noise ratio of beacon detection can be improved through the pulse light working mode. Meanwhile, in the process of beacon light acquisition and tracking, the target detection process will inevitably be affected by various background light noises. The background light noise will seriously affect the signal-to-noise ratio of the target image and is one of the main reasons for the failure of beacon light acquisition and tracking. At present, the commonly used method for removing background light noise is to use a narrow-band optical filter. Although this method can filter out most of the background light noise, most of the background light noise received by the receiving end is from sunlight, moonlight and starlight, which are all wide-spectrum light sources and have overlapping spectrum with the beacon light source. The performance of the narrow-band filter is limited.

[0003] The existing camera system usually uses a large-aperture lens and a high-sensitivity sensor to achieve high-power acquisition of weak modulated beacon light signals, resulting in high cost. In addition, the fixed frequency, phase and duty cycle information need to be agreed in advance, which makes it difficult to be flexibly applied to different scenes.

[0004] In addition, the current machine vision system uses FPGA to complete timing control and image preprocessing functions, and a large number of high-performance image processing functions are realized by additional DSP or GPU, or even some image processing is realized by a computer. However, in different environments, the image preprocessing function requirements are different, and the use of traditional development process for the re-writing and burning of preprocessing code will inevitably increase the development time and cost of the entire system. SUMMARY

[0005] The application solves the problem of low signal-to-noise ratio in capturing a beacon light in the prior art by providing a camera system and method for capturing and tracking a modulated beacon light.

[0006] The application provides a camera system for capturing and tracking a modulated beacon light, comprising a beam splitter, a pulse synchronization module, an image sensor control module, an image acquisition module, an image processing module and a beacon tracking module.

[0007] The beam splitter is used to divide the incident modulated beacon light into a first light beam and a second light beam; the first light beam is transmitted to the pulse synchronization module, and the second light beam is transmitted to the image acquisition module.

[0008] The pulse synchronization module is used to generate a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the first light beam and transmit it to the image sensor control module.

[0009] The image sensor control module is used to control the image acquisition module to acquire images of the second light beam using the pulse signal, so that the image acquisition module acquires images with optimal exposure time and settings of the same frequency, phase and duty cycle as the modulated beacon light, and obtains acquisition images.

[0010] The image processing module is used to process the acquisition images to obtain processed images.

[0011] The beacon tracking module is used to identify and track the modulated beacon light in the processed images, so as to achieve maximum power capture of the modulated beacon light.

[0012] Preferably, the pulse synchronization module comprises a photodetector module and a signal processing module; the photodetector module is used to convert the optical signal of the first light beam into an electrical signal; the signal processing module is used to shape the electrical signal, perform frequency spectrum analysis on the shaped signal through Fourier transform, obtain modulation information containing the modulation frequency, modulation phase and modulation duty cycle of the modulated beacon light, and output a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the modulation information.

[0013] Preferably, the image acquisition module comprises an image sensor; the image sensor control module uses the pulse signal to realize real-time setting of the optimal exposure time, working frequency and phase of the image sensor by using the pulse control mode of the image sensor.

[0014] Preferably, the image processing module contains multiple or all functions of image filtering, image erosion, image segmentation, image shape recognition and image binarization; the image binarization includes global binarization and local binarization.

[0015] Preferably, the camera system for capturing and tracking modulated beacon light further comprises: a master module; the master module is configured to set the number of calls and the order of calls of a plurality of functions in the image processing module, and to configure parameters of the plurality of functions in the image processing module.

[0016] Preferably, the master module is further configured to perform human-computer interaction and to perform initial configuration of each module when the camera system is initialized.

[0017] Preferably, after the beacon tracking module identifies the target modulated beacon light, the beacon tracking module calculates the barycentric coordinates of the target light spot and performs real-time tracking of the modulated beacon light based on the barycentric coordinates.

[0018] Preferably, when the maximum power of the modulated beacon light is captured, the image signal-to-noise ratio SNR2 obtained is:

[0019]

[0020] wherein n is a light splitting coefficient of the light splitting mirror, the light splitting coefficient corresponds to a power ratio of the first light beam to the total light beam entering the camera system, that is, the light splitting coefficient is a ratio of the power of the first light beam to a sum of the powers of the first light beam and the second light beam; p s is an average optical power of the modulated beacon light, d is a duty cycle of the modulated beacon light, p n is an average power of the background light noise.

[0021] In another aspect, the present application provides a method for capturing and tracking modulated beacon light, which is implemented by using the camera system for capturing and tracking modulated beacon light described above, and the method comprises the following steps:

[0022] The light splitting mirror splits the modulated beacon light incident to the camera system into a first light beam and a second light beam, the first light beam is transmitted to the pulse synchronization module, and the second light beam is transmitted to the image acquisition module;

[0023] The pulse synchronization module generates a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the first light beam, and transmits the pulse signal to the image sensor control module;

[0024] The image sensor control module controls the image acquisition module to acquire images of the second light beam by using the pulse signal, so that the image acquisition module acquires images with optimal exposure time and with the same frequency, phase and setting as the modulated beacon light, and obtains acquisition images;

[0025] The image processing module processes the acquisition images to obtain processing images;

[0026] The beacon tracking module is used for identifying and tracking the modulated beacon light, so that the maximum power of the modulated beacon light can be captured.

[0027] Preferably, the number of times and the order of calling the multiple functions in the image processing module are set by a master module in the camera system, and the multiple functions in the image processing module are configured with parameters.

[0028] The one or more technical solutions provided in the application have at least the following technical effects or advantages:

[0029] 1. The pulse synchronization module in the camera system generates a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light, and the image sensor control module in the camera system uses the pulse signal to control the image acquisition module to perform image acquisition, so that the camera image acquisition and the modulated beacon light are the same frequency and phase, and the image acquisition is performed with the optimal exposure time setting, which can significantly improve the signal-to-noise ratio of the captured modulated beacon light image while ensuring the image frame rate. The application is suitable for real-time free-space optical communication modulated beacon light signal detection, and can improve the signal-to-noise ratio of the captured image, realize real-time tracking of the modulated beacon light and maximum power capture of the weak modulated beacon light, and solve the problem of difficult high-power capture of the modulated beacon light in the field of free-space optical communication.

[0030] 2. The pulse synchronization module can autonomously obtain the frequency, phase and duty cycle information of the beacon light without needing to agree on fixed frequency, phase and duty cycle information in advance, so that the application scenarios of the application are more extensive and flexible.

[0031] 3. The photoelectric detector module in the pulse synchronization module has a very short reaction time, and when the frequency, phase or duty cycle of the modulated beacon light changes, the method and the designed system can quickly obtain the frequency, phase and duty cycle information of the modulated beacon light after the change, and re-implement the maximum power capture of the modulated beacon light in a very short time.

[0032] 4. The master module can set the number of times and the order of calling the multiple functions in the image processing module, and can configure the multiple functions in the image processing module with parameters, that is, the application can call and adjust the parameters of the pre-stored image processing algorithm of the camera system through the master module, and can improve the development flexibility of the whole system. Based on the image processing module and the master module, the pre-stored image processing algorithm can be called and adjusted based on the image information obtained in different environments, so that real-time adjustment of the image processing algorithm in different environments can be realized, and the development time and cost of the image processing function can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A schematic diagram of a camera system for capturing and tracking modulated beacon light according to an embodiment of the present application. DETAILED DESCRIPTION

[0034] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings and specific embodiments of the specification.

[0035] Embodiment 1:

[0036] Embodiment 1 provides a camera system for capturing and tracking modulated beacon light, as shown in Figure 1 , comprising a beam splitter 101, a pulse synchronization module 104, an image sensor control module 103, an image acquisition module 102, an image processing module 105 and a beacon tracking module 106.

[0037] The beam splitter 101 is used to divide the incident modulated beacon light into a first light beam (i.e. beam 1 in Figure 1 ) and a second light beam (i.e. beam 2 in Figure 1 ); the first light beam is transmitted to the pulse synchronization module 104, and the second light beam is transmitted to the image acquisition module 102.

[0038] The pulse synchronization module 104 is used to generate a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the first light beam, and transmit it to the image sensor control module 103.

[0039] The image sensor control module 103 is used to control the image acquisition module 102 to acquire images of the second light beam using the pulse signal, so that the image acquisition module 102 acquires images with optimal exposure time and settings of the same frequency, phase and duty cycle as the modulated beacon light. That is, the image sensor control module 103 uses the pulse signal generated by the pulse synchronization module 104 to set the exposure time, working frequency and phase of the image acquisition module 102 in real time.

[0040] The image processing module 105 is used to process the acquisition image to obtain a processed image.

[0041] The beacon tracking module 106 is used to identify and track the modulated beacon light in the processed image, so as to achieve maximum power capture of the modulated beacon light.

[0042] The pulse synchronization module 104 comprises a photodetector module (avalanche photodiode APD or photodiode PIN) and a signal processing module; the photodetector module is used for converting the optical signal of the first light beam into an electrical signal; the signal processing module is used for shaping the electrical signal, performing frequency spectrum analysis on the shaped signal through Fourier transform to obtain modulation information containing the modulation frequency, modulation phase and modulation duty cycle of the modulation beacon light, and outputting a pulse signal with the same frequency, phase and duty cycle as the modulation beacon light according to the modulation information.

[0043] The photodetector module has the characteristics of short response time and high upper limit frequency for the modulation beacon light, can ensure that the output waveform has no frequency distortion and has good response time, so that the modulation frequency, modulation phase and modulation duty cycle information of the modulation beacon light can be accurately obtained.

[0044] The image acquisition module 102 comprises an image sensor; the image sensor control module 103 uses the pulse signal to realize real-time setting of the optimal exposure time, working frequency and phase of the image sensor by using the pulse control mode of the image sensor.

[0045] The image processing module 105 comprises but is not limited to image filtering, image erosion, image segmentation, image shape recognition and image binarization functions; the image binarization comprises global binarization and local binarization. The image filtering is a Gaussian filtering process of the image; the image erosion function is used for filtering out the salt and pepper noise in the image background; the image segmentation function is used for region segmentation of the image to realize different image processing in different image regions; the image shape recognition function is used for shape recognition and extraction of specific shape image pixel information; and the image binarization function is used for image binarization segmentation.

[0046] The beacon tracking module 106 calculates the barycentric coordinates of the target light spot after target recognition of the modulation beacon light, and performs real-time tracking on the modulation beacon light based on the barycentric coordinates.

[0047] The theoretical analysis of the maximum power capture of the modulation beacon light is as follows:

[0048] Suppose that the average optical power of the modulation beacon light is p s , the duty cycle is d, the splitting coefficient (the splitting coefficient corresponds to the power ratio of the first light beam and the total light beam entering the camera system) of the beam splitter is n, and the average power of the background light noise is p nIf the maximum power capture method is not used, the image signal-to-noise ratio SNR1 obtained is:

[0049]

[0050] If the maximum power capture method is used, the image signal-to-noise ratio SNR2 obtained is:

[0051]

[0052] Since the receiving sensitivity of the photodetector module is high, the light splitting coefficient of the light splitter is usually small (for example, the modulated beacon light signal is split into a first light beam and a second light beam with a light power ratio of 1:99 by the light splitter), and the duty cycle of the modulated beacon light is usually small, and in actual use The value of the image signal-to-noise ratio obtained by the present application is much greater than 1. Therefore, the image signal-to-noise ratio obtained by the present application is higher than that of the original method

[0053] In addition, in order to further improve the development flexibility of the entire system and reduce the development time and cost of the image processing function, the camera system for capturing and tracking the modulated beacon light further comprises a main control module 107; the main control module 107 is used for setting the calling times and calling sequences of a plurality of functions in the image processing module 105 and performing parameter configuration on the plurality of functions in the image processing module 105.

[0054] For example, in the camera system provided by the present application, the photodetector module in the pulse synchronization module 104 and the image sensor in the image acquisition module 102 are external independent modules, and the remaining modules, including the image sensor control module 103, the signal processing module in the pulse synchronization module 104, the image processing module 105, the beacon tracking module 106, and the main control module 107, are all implemented in an FPGA (for example, ZYNQ7020).

[0055] The image sensor control module 103 configures the image sensor chip (NOIP1SN1300A-D) in the image acquisition module 102 through the SPI interface of the ZYNQ7020, so that the image sensor works stably in a set mode. The image processing module 105 processes the image data output by the image acquisition module 102 through the ZYNQ7020, and simultaneously calls and sets parameters of the image processing function pre-stored in the image processing module 105 by using the ZYNQ7020, so that the image processing effect reaches the expectation.

[0056] The following examples illustrate how the main control module 107 configures parameters and sets the number of calls and the order of calling each function in the image processing module 105 according to different external environment and background light information to meet the requirements in different environments.

[0057] When the external environment has a relatively uniform background light, the main control module 107 can set the image processing module 105 to directly call the global binarization function to pre-process the image. When the external environment has a relatively complex and non-uniform background light, the main control module 107 can set the image processing module 105 to directly call the local binarization function to pre-process the image. When the external environment has a relatively complex and non-uniform background light and there is a certain amount of noise (such as Gaussian noise), the main control module 107 can set the image processing module 105 to first call the Gaussian filter function to filter the image and then call the local binarization function to process the image.

[0058] In different external environments, the parameters under the same function will also change according to the different external environments. For example, when using the global binarization function, if the background light is strong, the threshold parameter of the global binarization function will correspondingly increase, and if the background light is weak, the threshold parameter of the global binarization function will correspondingly decrease. The main control module 107 can be used to set the relevant threshold parameters to achieve parameter adjustment and configuration.

[0059] In addition, the main control module 107 can also be used for human-computer interaction, and the main control module 107 can also perform initial configuration of each module when the camera system is initialized. For example, during system initialization and human-computer interaction, the main control module 107 controls the image sensor control module 103 to complete the setting of the exposure time, working frequency, and phase of the image sensor.

[0060] Embodiment 2

[0061] Embodiment 2 provides a method for capturing a tracking modulated beacon light, which is implemented by using the camera system for capturing a tracking modulated beacon light as described in embodiment 1, and the method comprises the following steps:

[0062] The modulated beacon light incident to the camera system is split into a first light beam and a second light beam by using a beam splitter, the first light beam is transmitted to a pulse synchronization module, and the second light beam is transmitted to an image acquisition module;

[0063] The pulse synchronization module generates a pulse signal with the same frequency, phase, and duty cycle as the modulated beacon light according to the first light beam, and transmits the pulse signal to the image sensor control module;

[0064] The image sensor control module controls the image acquisition module to acquire the second light beam by using the pulse signal, so that the image acquisition module acquires the second light beam at an optimal exposure time and with a same frequency and phase as the modulated beacon light, and acquires an acquired image;

[0065] The image processing module processes the acquired image to obtain a processed image;

[0066] The beacon tracking module identifies and tracks the modulated beacon light in the processed image, so that the maximum power of the modulated beacon light is captured.

[0067] The main control module can be used to set the number of times and the order of calling the multiple functions in the image processing module, and to configure parameters of the multiple functions in the image processing module; after the configuration is completed, the image processing module processes the acquired image.

[0068] The method for capturing and tracking the modulated beacon light provided in Embodiment 2 corresponds to the functions of the devices and modules in the camera system provided in Embodiment 1, and thus can be understood based on Embodiment 1, and will not be described herein again.

[0069] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A camera system that captures a tracking modulated beacon light, characterized by, The camera system comprises a beamsplitter, a pulse synchronization module, an image sensor control module, an image acquisition module, an image processing module and a beacon tracking module. The beamsplitter is used to divide the incident modulated beacon light into a first light beam and a second light beam; the first light beam is transmitted to the pulse synchronization module, and the second light beam is transmitted to the image acquisition module. The pulse synchronization module is used to generate a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the first light beam and transmit it to the image sensor control module. The image sensor control module is used to control the image acquisition module to acquire images of the second light beam by using the pulse signal, so that the image acquisition module acquires images with optimal exposure time and settings with the same frequency, phase and duty cycle as the modulated beacon light, and obtains acquired images. The image processing module is used to process the acquired images to obtain processed images. The beacon tracking module is used to identify and track the modulated beacon light in the processed images to achieve maximum power capture of the modulated beacon light. The pulse synchronization module comprises a photodetector module and a signal processing module; the photodetector module is used to convert the optical signal of the first light beam into an electrical signal; the signal processing module is used to shape the electrical signal, perform frequency spectrum analysis on the shaped signal by Fourier transform, obtain modulation information containing the modulation frequency, modulation phase and modulation duty cycle of the modulated beacon light, and output a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the modulation information. The image acquisition module comprises an image sensor; the image sensor control module uses the pulse signal to realize real-time setting of the optimal exposure time, working frequency and phase of the image sensor by using the pulse control mode of the image sensor. Image signal-to-noise ratio obtained when maximum power capture of modulated beacon light is achieved To: wherein n is the splitting factor of the splitting optics, which corresponds to the power ratio of the first light beam to the total light beam entering the camera system; is the average optical power of the modulated beacon light, d is the duty cycle of the modulated beacon light, is the average power of the background light noise.

2. The camera system of claim 1, wherein, The image processing module contains multiple or all functions of image filtering, image erosion, image segmentation, image shape recognition and image binarization; the image binarization includes global binarization and local binarization.

3. The camera system of claim 1, wherein, Further comprising:

4. The camera system of claim 3, wherein, a main control module; The main control module is used to set the number of calls and the calling order of multiple functions in the image processing module, and configure parameters for multiple functions in the image processing module. The main control module is also used for human-computer interaction and initial configuration of each module when the camera system is initialized.

5. The camera system of claim 4, wherein, After the beacon tracking module identifies the target of the modulated beacon light, it calculates the barycentric coordinates of the target light spot and performs real-time tracking of the modulated beacon light based on the barycentric coordinates.

6. The camera system of claim 1, wherein, The method for capturing and tracking modulated beacon light by using the camera system as claimed in any one of claims 1-6 comprises the following steps:

7. A method of capturing a tracking modulated beacon light, characterized by, The beamsplitter is used to divide the incident modulated beacon light into a first light beam and a second light beam, the first light beam is transmitted to the pulse synchronization module, and the second light beam is transmitted to the image acquisition module; The pulse synchronization module generates a pulse signal with the same frequency, phase and duty cycle as the modulated beacon light according to the first light beam and transmits it to the image sensor control module; ​ The image sensor control module controls the image acquisition module to acquire the second light beam by using the pulse signal, so that the image acquisition module acquires the second light beam at an optimal exposure time and with a same frequency and phase as the modulated beacon light, and acquires an acquired image; The image processing module processes the acquired image to obtain a processed image; The beacon tracking module identifies and tracks the modulated beacon light from the processed image, so as to achieve maximum power capture of the modulated beacon light.

8. The method of capturing tracking modulated beacon light of claim 7, wherein, The master module in the camera system sets the number of calls and the calling sequence of multiple functions in the image processing module, and configures parameters of the multiple functions in the image processing module. After the configuration is completed, the image processing module processes the acquired image.

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