Fixed star observation and evaluation method suitable for satellite-borne laser communication system

Abstract

The invention provides a fixed star observation and evaluation method suitable for a satellite-borne laser communication system, and the method comprises the following steps: S1, substituting the magnitude and the star temperature of a target fixed star into a fixed star irradiance model, and calculating the irradiance of the target fixed star; s2, dividing a working wave band when the satellite-borne laser communication system observes the fixed star into a plurality of sub-wave bands, and calculating the number of target photoelectrons acquired by a single pixel of a detector in each sub-wave band within single-frame integral time; s3, substituting the target photoelectron number obtained by the single pixel of the detector in each sub-band in the single frame integration time into the satellite-borne laser communication system fixed star observation signal-to-noise ratio calculation model, and calculating the satellite-borne laser communication system fixed star observation signal-to-noise ratio; and S4, comparing the star observation signal-to-noise ratio of the spaceborne laser communication system with a preset threshold, if the star observation signal-to-noise ratio of the spaceborne laser communication system is greater than the preset threshold, considering that the target star can be observed by the spaceborne laser communication system, otherwise, considering that the target star cannot be observed by the spaceborne laser communication system.

Description

Technical Field

[0001] The invention provides a star observation and evaluation method suitable for a satellite-borne laser communication system, belonging to the field of laser communication. Background Art

[0002] With the development of globalization and information technology, laser communication technology, as an emerging communication technology, uses laser as a carrier for communication. Compared with traditional microwave communication, it has the advantages of large communication capacity, fast communication rate, long transmission distance and good confidentiality. It has huge development potential. Laser communication links will definitely become the development trend of inter-satellite backbone links and even satellite networking communications.

[0003] Due to the influence of ground calibration errors, vibration shocks during the launch phase, platform vibrations, temperature changes, material stress release and other factors during the on-orbit period, the actual pointing angle of the satellite-borne laser communication system will deviate greatly from the target pointing angle after entering orbit. Therefore, after the satellite-borne laser communication system enters orbit, after completing normal unlocking and health status checks, the on-orbit calibration of the optical axis must be completed before the normal on-orbit capture, tracking, and communication of the satellite-borne laser communication system can be carried out. The on-orbit calibration of the satellite-borne laser communication system can be divided into three types: satellite calibration, star calibration, and inter-satellite calibration. Among them, star calibration mainly completes the initial pointing error calibration. Whether the satellite-borne laser communication system can complete the star calibration, and which stars of which magnitude need to be selected as target stars, requires an assessment of the system's star observation capabilities in advance.

[0004] Therefore, improving the calculation model of the signal-to-noise ratio of star observation in satellite-borne laser communication systems and studying the star observation evaluation method of satellite-borne laser communication systems are of great significance for promoting the development of calibration technology of satellite-borne laser communication systems and improving system performance. Summary of the invention

[0005] The technical problem solved by the present invention is: in view of the imperfection of the existing star observation evaluation method of the satellite-borne laser communication system, a star observation evaluation method suitable for the satellite-borne laser communication system is proposed, which takes into account that the transmission efficiency of the system receiving optical path and the quantum efficiency of the detector vary with the wavelength, improves the calculation model of the signal-to-noise ratio of the star observation of the satellite-borne laser communication system, and comprehensively evaluates the star observation capability of the satellite-borne laser communication system.

[0006] The technical solution of the present invention is: a star observation and evaluation method applicable to a satellite-borne laser communication system, the method comprising the following steps:

[0007] S1. Substitute the magnitude and temperature of the target star into the stellar irradiance model to calculate the irradiance of the target star;

[0008] S2, dividing the working band of the satellite-borne laser communication system when observing stars into multiple sub-bands, and calculating the number of target photoelectrons acquired by a single pixel of the detector in each sub-band within a single frame integration time;

[0009] S3, substituting the number of target photoelectrons obtained by a single pixel of the detector in each sub-band within a single frame integration time into the calculation model of the star observation signal-to-noise ratio of the satellite-borne laser communication system to calculate the star observation signal-to-noise ratio of the satellite-borne laser communication system;

[0010] S4. Compare the star observation signal-to-noise ratio of the satellite-borne laser communication system with a preset threshold. If the star observation signal-to-noise ratio of the satellite-borne laser communication system is greater than the preset threshold, it is considered that the satellite-borne laser communication system can observe the target star. Otherwise, it is considered that the satellite-borne laser communication system cannot observe the target star.

[0011] Preferably, the stellar irradiance model is as follows:

[0012]

[0013] Among them, E is the stellar irradiance, λ is the wavelength, m is the stellar magnitude, T is the stellar color temperature, c is the speed of light, h is Planck's constant, k is the Boltzmann constant, and λ1 and λ2 are the lower and upper limits of the visible light band, respectively.

[0014] Preferably, the number of target photoelectrons s acquired by a single pixel of the detector in the i-th sub-band within a single frame integration time is i for:

[0015]

[0016] Where s is the number of target photoelectrons acquired by a single pixel of the detector within a single frame integration time, λ il is the lower limit of the ith sub-band, λ ih is the upper limit of the ith sub-band.

[0017] Preferably, the number of target photoelectrons acquired by a single pixel of the detector within a single frame integration time is:

[0018]

[0019] Among them, s is the number of target photoelectrons acquired by a single pixel of the satellite-borne laser communication system detector within a single frame integration time, A is the system entrance pupil area, K is the dispersion coefficient of the target on the pixel, t is the system detector integration time, and n is the system receiving optical path transmission efficiency.

[0020] Preferably, the calculation model of the signal-to-noise ratio of star observation in the satellite-borne laser communication system is:

[0021]

[0022] Where SNR is the signal-to-noise ratio of star observation in the satellite-borne laser communication system, n D is the number of dark current electrons per second for a single pixel in the satellite-borne laser communication system detector, n r is the mean square value of the system detector readout noise, s i is the number of target photoelectrons acquired by a single pixel of the detector within the i-th sub-band within the single-frame integration time; η i is the detector quantum efficiency within the i-th sub-band.

[0023] Preferably, the preset threshold is above 5dB.

[0024] Preferably, the wavelength span of each sub-band does not exceed 50 nm.

[0025] Compared with other existing methods, the star observation and evaluation method for a satellite-borne laser communication system provided by the present invention has the following advantages:

[0026] (1) Based on the existing methods, the present invention takes into account that the reflectivity / transmittance of each lens in the satellite-borne laser communication system is different due to processing errors, and the transmission efficiency of the receiving optical path varies with the wavelength within the system working band. This can more accurately calculate the number of target photoelectrons obtained by a single pixel of the system detector within a single frame integration time.

[0027] (2) The present invention takes into account that the quantum efficiency of the detector of the satellite-borne laser communication system when observing stars is not a constant value within the entire system operating band, and is related to the selected band range. Therefore, the system operating band is divided into segments to calculate the system star observation signal-to-noise ratio, and the calculation result is more accurate.

[0028] (3) The present invention is not restricted by the system structure of the satellite-borne laser communication system and the star observation method, and the evaluation method is more universal. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Attached Figure 1 The figure is a schematic diagram of the optical path of the star-observing branch of the satellite-borne laser communication system of the present invention.

[0030] Attached Figure 2 This is a schematic diagram of star observation of the satellite-borne laser communication system of the present invention.

[0031] The specific numbers in the figure are as follows:

[0032] 1. Window mirror 2. Reflector 3. First Coudé mirror 4. Second Coudé mirror 5. Third Coudé mirror 6. Fourth Coudé mirror 7. λ / 4 wave plate 8. Focusing mirror 9. Stargazing camera 10. Stars DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0034] like Figure 1 As shown, in a specific embodiment of the present invention, the star-gazing branch of the satellite-borne laser communication system includes a window mirror 1, a reflector 2, a first Coode mirror 3, a second Coode mirror 4, a third Coode mirror 5, a fourth Coode mirror 6, a λ / 4 wave plate 7, a focusing mirror 8, and a star-gazing camera 9.

[0035] When the satellite-borne laser communication system observes stars in orbit, the star light beam enters the optical system through the window mirror 1, is reflected by the reflector 2, the first Coode mirror 3, the second Coode mirror 4, the third Coode mirror 5, and the fourth Coode mirror 6, passes through the λ / 4 wave plate 7, and is imaged on the star-gazing camera 9 through the focusing mirror 8. In-orbit calibration is performed based on the observed stars, and then the normal operation of the satellite-borne laser communication system such as in-orbit capture, tracking, and communication is carried out.

[0036] Schematic diagram of star observation of the system Figure 2 shown.

[0037] The present invention proposes a star observation evaluation method for a satellite-borne laser communication system, which is established by considering the changes of the system receiving optical path transmission efficiency and the detector quantum efficiency with the wavelength. The method combines the star irradiance function and the system parameters of the satellite-borne laser communication system, and considers the changes of the system receiving optical path transmission efficiency and the detector quantum efficiency with the wavelength, improves the calculation model of the star observation signal-to-noise ratio of the satellite-borne laser communication system, and comprehensively evaluates the star observation capability of the satellite-borne laser communication system. Specifically, the method includes the following steps:

[0038] S1. Substitute the magnitude and temperature of the target star into the stellar irradiance model to calculate the irradiance of the target star;

[0039] For the intersatellite link of the laser communication system, except for the sun, other brighter stars can be basically equivalent to parallel incident light due to their long distance. Therefore, the magnitude and temperature of the target star can be substituted into the stellar irradiance function to establish the target star irradiance model:

[0040]

[0041] Among them, E is the stellar irradiance, λ is the wavelength, m is the stellar magnitude, T is the stellar color temperature, c is the speed of light, h is Planck's constant, and k is the Boltzmann constant; λ1 and λ2 are the lower and upper limits of the visible light band, respectively. Since the visual magnitude is defined based on the visible light range, the integration limits λ1 and λ2 are 0.38μm and 0.72μm, respectively.

[0042] S2, dividing the working band of the satellite-borne laser communication system when observing stars into multiple sub-bands, and calculating the number of target photoelectrons acquired by a single pixel of the detector in each sub-band within a single frame integration time;

[0043] According to the system parameters of the satellite-borne laser communication system, the photon flux density of the target star is calculated:

[0044]

[0045] Among them, λ a ~λ b is the working band range of the satellite-borne laser communication system when observing stars. Considering that the transmission efficiency of the receiving optical path is affected by the reflectivity / transmittance of the window mirror, Coode mirror, reflector, focusing mirror, etc. when the system observes stars, and the reflectivity / transmittance of each lens corresponding to different wavelengths is different due to processing errors, the transmission efficiency of the receiving optical path changes with the wavelength. Therefore, the target photoelectron number obtained by a single pixel of the system detector within a single frame integration time is derived:

[0046]

[0047] Among them, s is the number of target photoelectrons obtained by a single pixel of the system detector within a single frame integration time, A is the system entrance pupil area, K is the dispersion coefficient of the target on the pixel, t is the system detector integration time, n is the system receiving optical path transmission efficiency, which is the cumulative multiplication of the reflectivity / transmittance of the window mirror, Coode mirror, reflector, focusing mirror, etc. For the window mirror, Coode mirror, reflector, take the reflectivity, and for the focusing mirror, take the transmittance. S3. Substitute the number of target photoelectrons obtained by a single pixel of the detector in each sub-band within a single frame integration time into the calculation model of the star observation signal-to-noise ratio of the satellite-borne laser communication system to calculate the star observation signal-to-noise ratio of the satellite-borne laser communication system;

[0048] Considering that the transmission efficiency of the receiving optical path of the system is affected by the reflectivity / transmittance of the window mirror, Coode mirror, reflector, focusing mirror, etc., and the reflectivity / transmittance of each lens corresponding to different wavelengths is different, the target photoelectron number s obtained by a single pixel of the detector in the i-th sub-band within the single frame integration time is derived. i for:

[0049]

[0050] Where s is the number of target photoelectrons acquired by a single pixel of the detector within a single frame integration time, λ il is the lower limit of the ith sub-band, λ ih is the upper limit of the ith sub-band.

[0051] Since the quantum efficiency of the detector of the satellite-borne laser communication system is not a constant within the system working band, and is related to the selected band range, the number of dark current electrons and readout noise of the detector are considered, the system working band is segmented to calculate the system star observation signal-to-noise ratio, and the calculation model of the system star observation signal-to-noise ratio is improved:

[0052]

[0053] Among them, SNR is the system star observation signal-to-noise ratio, n D is the number of dark current electrons per second for a single pixel in the system detector, n r Read the mean square noise value for the system detector;

[0054] S4. Compare the star observation signal-to-noise ratio of the satellite-borne laser communication system with a preset threshold. If the star observation signal-to-noise ratio of the satellite-borne laser communication system is greater than the preset threshold, it is considered that the satellite-borne laser communication system can observe the target star. Otherwise, it is considered that the satellite-borne laser communication system cannot observe the target star.

[0055] In order to ensure that the image processing unit of the satellite-borne laser communication system detector can reliably and accurately extract the position of the target star, the system star observation signal-to-noise ratio SNR must be greater than or equal to 5. Therefore, according to the calculation result of SNR in step S3, the star observation capability of the satellite-borne laser communication system can be evaluated.

[0056] In summary, the present invention substitutes the magnitude and temperature of the target star into the stellar irradiance function to establish a target star irradiance model; according to the system parameters of the satellite-borne laser communication system, the photon flux density of the target star is calculated, and the number of target photoelectrons acquired by a single pixel of the system detector within a single frame integration time is derived; considering the quantum efficiency, dark current electron number, and readout noise of the system detector, the calculation model of the signal-to-noise ratio of star observation of the satellite-borne laser communication system is improved, and the star observation capability of the system is evaluated.

[0057] The method proposed in the present invention can comprehensively calculate the star observation signal-to-noise ratio of the satellite-borne laser communication system under different system parameters, providing an important basis for its application evaluation.

[0058] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A star observation and evaluation method suitable for a satellite-borne laser communication system, characterized in that Included in Follow these steps: S1. Substitute the magnitude and temperature of the target star into the stellar irradiance model to calculate the irradiance of the target star; S2, dividing the working band of the satellite-borne laser communication system when observing stars into multiple sub-bands, and calculating the number of target photoelectrons acquired by a single pixel of the detector in each sub-band within a single frame integration time; S3, substituting the number of target photoelectrons obtained by a single pixel of the detector in each sub-band within a single frame integration time into the calculation model of the star observation signal-to-noise ratio of the satellite-borne laser communication system to calculate the star observation signal-to-noise ratio of the satellite-borne laser communication system; S4. Compare the star observation signal-to-noise ratio of the satellite-borne laser communication system with a preset threshold. If the star observation signal-to-noise ratio of the satellite-borne laser communication system is greater than the preset threshold, it is considered that the satellite-borne laser communication system can observe the target star. Otherwise, it is considered that the satellite-borne laser communication system cannot observe the target star.

2. A star observation and evaluation method suitable for a satellite-borne laser communication system according to claim 1, characterized in that The stellar irradiance model is as follows: Among them, E is the stellar irradiance, λ is the wavelength, m is the stellar magnitude, T is the stellar color temperature, c is the speed of light, h is Planck's constant, k is the Boltzmann constant, and λ1 and λ2 are the lower and upper limits of the visible light band, respectively.

3. The star observation and evaluation method applicable to a satellite-borne laser communication system according to claim 1, characterized in that: The number of target photoelectrons acquired by a single pixel of the detector in the i-th sub-band within a single frame integration time s i for: Where s is the number of target photoelectrons acquired by a single pixel of the detector within a single frame integration time, λ il is the lower limit of the ith sub-band, λ ih is the upper limit of the ith sub-band.

4. The star observation and evaluation method applicable to a satellite-borne laser communication system according to claim 1, characterized in that: The number of target photoelectrons acquired by a single pixel of the detector within a single frame integration time is: Among them, s is the number of target photoelectrons acquired by a single pixel of the satellite-borne laser communication system detector within a single frame integration time, A is the system entrance pupil area, K is the dispersion coefficient of the target on the pixel, t is the system detector integration time, and n is the system receiving optical path transmission efficiency.

5. The star observation and evaluation method applicable to a satellite-borne laser communication system according to claim 1, characterized in that: The calculation model of the signal-to-noise ratio of star observation in the satellite-borne laser communication system is: Where SNR is the signal-to-noise ratio of star observation in the satellite-borne laser communication system, n D is the number of dark current electrons per second for a single pixel in the satellite-borne laser communication system detector, n r is the mean square value of the system detector readout noise, s i is the number of target photoelectrons acquired by a single pixel of the detector within the i-th sub-band within the single-frame integration time; η i is the detector quantum efficiency within the i-th sub-band.

6. The star observation and evaluation method applicable to a satellite-borne laser communication system according to claim 1, characterized in that: The preset threshold is above 5dB.

7. The star observation and evaluation method applicable to a satellite-borne laser communication system according to claim 1, characterized in that: The wavelength span of each sub-band does not exceed 50nm.

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