A method for constructing a simulation calculation model for space-based space target observation effectiveness considering image signal-to-noise ratio

Abstract

The present invention discloses a method for constructing a space-based space target observation efficiency simulation calculation model considering the image signal-to-noise ratio. The target brightness characteristics are calculated by space target size, observation distance and observation phase angle, and the target detection image signal-to-noise ratio is calculated in combination with the target relative motion characteristics and camera performance parameters. The system observation efficiency is simulated and calculated considering the target image signal-to-noise ratio. Compared with the traditional simulation calculation model, this model removes the targets whose signal-to-noise ratio is insufficient for image processing detection due to relative motion, effectively removes the invalid observation data of the system, and improves the calculation accuracy of the simulation model.

Description

Technical Field

[0001] The present invention belongs to the field of satellite monitoring of space targets, and in particular relates to a method for constructing a space-based space target observation efficiency simulation calculation model taking into account image signal-to-noise ratio. Background Art

[0002] In many fields such as scientific research and military, space-based observation satellite systems are equipped with visible light payloads to obtain image information of space targets, and image processing and detection are used to obtain astronomical positioning and orbit determination information of space targets. Compared with ground-based observation systems, space-based observation systems overcome the shortcomings of being limited by space (only covering the sky area above the observation equipment), time (generally requiring nighttime) and environment (rainy days are not conducive to observation), and can obtain space target observation data continuously, frequently and for a long time.

[0003] The principle of the space-based observation system is: a number of satellites form a monitoring platform constellation, and each monitoring platform collects target energy and obtains target image information during the exposure time by carrying a visible light payload with a large field of view and high detection capability. The space-based space target observation system generally adopts a natural intersection mode, that is, the monitoring platform is fixed, and the target image data is obtained by the space target passing through the field of view of the monitoring platform payload camera when it moves relative to the monitoring platform.

[0004] When designing a space-based observation system, it is necessary to analyze its observation efficiency through a simulation calculation model. However, the traditional observation efficiency calculation model only considers the observation configuration of the monitoring platform and the space target, and believes that effective observation data can be obtained when the space target passes through the visible light payload field of view. However, due to the relative motion of the space target during the exposure time, the target spot appears in the image as a "pull line", and the energy is distributed in a dozen to dozens of pixels, which will cause the target signal-to-noise ratio to decrease. The current image processing algorithm has too low a detection rate for target images with a signal-to-noise ratio lower than 2, and cannot support subsequent astronomical positioning and orbit determination. Therefore, images with too low a signal-to-noise ratio are invalid observation data. Summary of the invention

[0005] The problem solved by the present invention is: in view of the problem that the traditional simulation calculation model does not take into account the relative motion of the target, resulting in a decrease in simulation accuracy, a method for constructing a space-based space target observation efficiency simulation calculation model taking into account the image signal-to-noise ratio is provided to improve the accuracy of the observation efficiency simulation calculation.

[0006] In order to solve the above technical problems, the present invention discloses a method for constructing a space-based space target observation efficiency simulation calculation model considering the image signal-to-noise ratio. The space-based space target observation efficiency simulation calculation model is constructed by combining a traditional simulation calculation model and a target image signal-to-noise ratio calculation algorithm. The specific steps are as follows:

[0007] (1) The traditional simulation calculation model is used to calculate the time period when the space target enters the field of view: the satellite orbit and the target orbit are processed as input, the equivalent detection distance of the camera's maximum detection capability is used as the payload parameter to calculate the payload field of view coverage, and the time period when the space target enters the field of view is calculated and counted as the input for calculating the target image signal-to-noise ratio;

[0008] (2) The target image signal-to-noise ratio calculation algorithm is used to calculate the signal-to-noise ratio of the camera observation image during the time period when the space target enters the field of view: the time period when the space target enters the field of view obtained in step (1) is used as input, the space target signal rate is calculated based on the brightness of the space target during the time period when the space target enters the field of view, and the target image signal-to-noise ratio of the space-based space target observation system is obtained in combination with the detector system noise calculation, which is used as input for judging whether the target is observable;

[0009] (3) After obtaining the target image signal-to-noise ratio calculation result of the space-based space target observation system described in step (2), determine whether the image signal-to-noise ratio meets the minimum threshold of the effective image; if so, the time period when the space target enters the field of view is included in the effective observation time period, and the observation efficiency of the space-based space target observation system for the coverage rate, frequency, and arc length distribution of the space target is statistically obtained taking into account the camera detection capability.

[0010] Furthermore, the calculation steps of the traditional simulation calculation model are:

[0011] Step 1: Set the task scenario and performance simulation period;

[0012] Step 2: Establish a space-based space target observation system model;

[0013] Step 3: Establish the orbit model of space targets;

[0014] Step 4: Set visible light load parameters;

[0015] Step 5: Calculate the payload field of view coverage;

[0016] Step 6: Calculate the time period when the space target enters the field of view.

[0017] Furthermore, the space target image signal-to-noise ratio is obtained by comprehensively calculating the space target signal rate and the detector system noise, where:

[0018] The calculation formula of the signal-to-noise ratio of space target detection image is:

[0019]

[0020] In the above formula, S * is the space target signal rate, t is the exposure time, N system is the detector system noise.

[0021] Furthermore, the space target signal rate S is obtained by comprehensively calculating the effective aperture of the camera, the transmittance of the optical system, the target brightness, and the quantum efficiency of the detector. * :

[0022]

[0023] In the above formula, D is the effective aperture of the telescope (cm), τ is the transmittance of the optical system, Mv is the target brightness, and Q E is the detector quantum efficiency.

[0024] Furthermore, according to theoretical calculations and engineering experience, the estimation formula for the space target brightness Mv is:

[0025]

[0026] In the above formula, d represents the target size, in cm; ρ is the reflectivity or scattering rate of the target; l is the relative observation distance between the observer and the target, and Φ is the observation phase angle, which is defined as the angle between the observer, the observed target, and the sun.

[0027] Furthermore, the detector system noise N system The influencing factors include detector background noise, quantization noise, electronic readout noise, etc. The calculation formula is as follows:

[0028]

[0029] In the above formula, n b is the background noise, n p is the quantization noise, n read is the electronic read noise; where:

[0030] (1) The background noise n b The main sources are skylight signals and detector dark current. N b is the total number of noise electrons, calculated as follows:

[0031] N b =n pixel ·(S sky +S dark )·t

[0032] In the above formula, n pixel is the number of wire drawing pixels, t is the exposure time, S sky is the skylight signal rate, S dark is the detector dark signal rate;

[0033] (2) The quantization noise n p Related to the detector quantum efficiency, N pThe number of photoelectrons generated for the target radiation;

[0034] (3) The electronic read noise n read It is transient noise. N read The number of photoelectrons equivalent to the detector readout noise.

[0035] Furthermore, the number of wire pixels n pixel It is related to the target's relative motion speed of the visible light camera on the monitoring platform, the exposure time, and the camera's pixel angular resolution. Assuming that the target's relative motion speed on the monitoring platform is v Tar , resulting in n pixel Pull a line of dozens to dozens of pixels; consider the target relative to the image plane moving speed v when the exposure time remains unchanged Tar The number of pixels n occupied by the target diffuse spot pixel Directly proportional.

[0036] The beneficial effects of the present invention are: providing a method for constructing a space-based space target observation efficiency simulation calculation model that takes into account the image signal-to-noise ratio, calculating the target brightness characteristics through the space target size, observation distance and observation phase angle, and calculating the target detection image signal-to-noise ratio in combination with the target relative motion characteristics and camera performance parameters, and taking into account the target image signal-to-noise ratio to simulate and calculate the system observation efficiency. Compared with the traditional simulation calculation model, this model removes the targets whose signal-to-noise ratio is insufficient for image processing detection due to relative motion, effectively removes the invalid observation data of the system, and improves the calculation accuracy of the simulation model. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A flow chart of the method for constructing a simulation calculation model for space-based space target observation effectiveness considering the image signal-to-noise ratio;

[0038] Figure 2 This is a diagram of the space-based space target observation system;

[0039] Figure 3 Schematic diagram of three visible light camera payloads carried by each surveillance satellite. DETAILED DESCRIPTION

[0040] Hereinafter, the spirit and essence of the present invention will be further described in conjunction with the accompanying drawings and embodiments.

[0041] like Figure 1 As shown, a method for constructing a space-based space target observation effectiveness simulation calculation model considering the image signal-to-noise ratio is provided. The space-based space target observation effectiveness simulation calculation model is constructed by combining a traditional simulation calculation model and a target image signal-to-noise ratio calculation algorithm. The specific steps are as follows:

[0042] (1) The traditional simulation calculation model is used to calculate the time period when the space target enters the field of view: the satellite orbit and the target orbit are processed as input, the equivalent detection distance of the camera's maximum detection capability is used as the payload parameter to calculate the payload field of view coverage, and the time period when the space target enters the field of view is calculated and counted as the input for calculating the target image signal-to-noise ratio;

[0043] (2) The target image signal-to-noise ratio calculation algorithm is used to calculate the signal-to-noise ratio of the camera observation image during the time period when the space target enters the field of view: the time period when the space target enters the field of view obtained in step (1) is used as input, the space target signal rate is calculated based on the brightness of the space target during the time period when the space target enters the field of view, and the target image signal-to-noise ratio of the space-based space target observation system is obtained in combination with the detector system noise calculation, which is used as input for judging whether the target is observable;

[0044] (3) After obtaining the target image signal-to-noise ratio calculation result of the space-based space target observation system described in step (2), determine whether the image signal-to-noise ratio meets the minimum threshold of the effective image; if so, the time period when the space target enters the field of view is included in the effective observation time period, and the observation efficiency of the space-based space target observation system for the coverage rate, frequency, and arc length distribution of the space target is statistically obtained taking into account the camera detection capability.

[0045] The calculation steps of the traditional simulation calculation model are:

[0046] Step 1: Set the task scenario and performance simulation period;

[0047] Step 2: Establish a space-based space target observation system model;

[0048] Step 3: Establish the orbit model of space targets;

[0049] Step 4: Set visible light load parameters;

[0050] Step 5: Calculate the payload field of view coverage;

[0051] Step 6: Calculate the time period when the space target enters the field of view.

[0052] The signal-to-noise ratio of the space target image is obtained by comprehensively calculating the space target signal rate and the detector system noise, where:

[0053] The calculation formula of the signal-to-noise ratio of space target detection image is:

[0054]

[0055] In the above formula, S * is the space target signal rate, t is the exposure time, N system is the detector system noise.

[0056] Considering the camera effective aperture, optical system transmittance, target brightness, and detector quantum efficiency, the space target signal rate S is calculated comprehensively. * :

[0057]

[0058] In the above formula, D is the effective aperture of the telescope (cm), τ is the transmittance of the optical system, Mv is the target brightness, and Q E is the detector quantum efficiency.

[0059] According to theoretical calculations and engineering experience, the estimation formula for the brightness of space targets Mv is:

[0060]

[0061] In the above formula, d represents the target size, in cm; ρ is the reflectivity or scattering rate of the target; l is the relative observation distance between the observer and the target, and Φ is the observation phase angle, which is defined as the angle between the observer, the observed target, and the sun.

[0062] The detector system noise N system The influencing factors include detector background noise, quantization noise, electronic readout noise, etc. The calculation formula is as follows:

[0063]

[0064] In the above formula, n b is the background noise, n p is the quantization noise, n read is the electronic read noise; where:

[0065] (1) The background noise n b The main sources are skylight signals and detector dark current. N b is the total number of noise electrons, calculated as follows:

[0066] N b =n pixel ·(S sky +S dark )·t.

[0067] In the above formula, n pixel is the number of wire drawing pixels, t is the exposure time, S sky is the skylight signal rate, S dark is the detector dark signal rate;

[0068] (2) The quantization noise n p Related to the detector quantum efficiency, N p The number of photoelectrons generated for the target radiation;

[0069] (3) The electronic read noise n read It is transient noise. N read The number of photoelectrons equivalent to the detector readout noise.

[0070] The number of wire drawing pixels n pixel It is related to the target's relative motion speed of the visible light camera on the monitoring platform, the exposure time, and the camera's pixel angular resolution. Assuming that the target's relative motion speed on the monitoring platform is v Tar , resulting in n pixel Pull a line of dozens to dozens of pixels; consider the target relative to the image plane moving speed v when the exposure time remains unchanged Tar The number of pixels n occupied by the target diffuse spot pixel Directly proportional.

[0071] Reference Figure 2 The space-based space target observation system consists of 6 monitoring satellites, using the same dawn-dusk sun-synchronous orbit, with an orbital altitude of 1,000 kilometers and a descending node local time of 06:00. The 6 monitoring satellites have a phase distribution with a phase difference of 60°. The satellite attitude adopts earth orientation to ensure the camera pointing.

[0072] Reference Figure 3 Each surveillance satellite carries three visible light camera payloads, and the cameras point along the front, rear and along-light directions of the orbit, and cut down to the edge of the earth. The lower boundary observation range of the camera's field of view must be higher than the earth's limb atmosphere to avoid the influence of the earth. The height is generally 100 kilometers. The camera has an equivalent detection capability of 15.2 magnitude (@300ms, SNR=3), a pixel angular resolution of 15″, and a field of view of 20°×20°. The azimuth and elevation pointing directions of the three cameras are [0, 18.5°], [180°, 18.5°], and [90°, 18.5°], respectively.

[0073] The space target library selects the STARLINK low-orbit space target library, with a total of 1,374 satellites, updated on April 21, 2021.

[0074] The coverage rate of the space-based space target observation system is investigated with a mission time of 1 hour. The payload field of view coverage range and the time period when the space target enters the field of view are calculated in turn to obtain the observation efficiency of the space-based space target observation system for the space target coverage rate, frequency, arc length distribution, etc. The calculation results of the conventional model and the space target observation efficiency simulation calculation model considering the camera detection capability are compared, as shown in Table 1.

[0075] Table 1 Comparison of simulation results

[0076]

[0077] Taking into account the camera detection capability, the average calculated coverage of the space-based space target observation system dropped from 92.98% to 91.98%, eliminating about 1% of invalid observation data; the average observation time dropped from 9.01 minutes to 8.26 minutes, eliminating about 9.08% of invalid observation data.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for constructing a space-based space target observation efficiency simulation calculation model considering image signal-to-noise ratio, characterized by: The space-based space target observation efficiency simulation calculation model is constructed by combining the traditional simulation calculation model and the target image signal-to-noise ratio calculation algorithm. The specific steps are as follows: (1) The traditional simulation calculation model is used to calculate the time period when the space target enters the field of view: the satellite orbit and the target orbit are processed as input, the equivalent detection distance of the camera's maximum detection capability is used as the payload parameter to calculate the payload field of view coverage, and the time period when the space target enters the field of view is calculated as the input for calculating the target image signal-to-noise ratio; The signal-to-noise ratio of the space target image is obtained by comprehensively calculating the space target signal rate and the detector system noise, where: The calculation formula of the signal-to-noise ratio of space target detection image is: In the above formula, S * is the space target signal rate, t is the exposure time, N system is the detector system noise; Considering the camera effective aperture, optical system transmittance, target brightness, and detector quantum efficiency, the space target signal rate S is calculated comprehensively. * : In the above formula, D is the effective aperture of the telescope in cm, τ is the transmittance of the optical system, Mv is the target brightness, Q E is the detector quantum efficiency; (2) The target image signal-to-noise ratio calculation algorithm is used to calculate the signal-to-noise ratio of the camera observation image during the time period when the space target enters the field of view: the time period when the space target enters the field of view obtained in step (1) is used as input, the space target signal rate is calculated based on the brightness of the space target during the time period when the space target enters the field of view, and the target image signal-to-noise ratio of the space-based space target observation system is obtained in combination with the detector system noise calculation, which is used as input for judging whether the target is observable; (3) After obtaining the target image signal-to-noise ratio calculation result of the space-based space target observation system described in step (2), determine whether the image signal-to-noise ratio meets the minimum threshold of the effective image; if so, the time period when the space target enters the field of view is included in the effective observation time period, and the observation efficiency of the space-based space target observation system for the coverage rate, frequency, and arc length distribution of the space target is statistically obtained taking into account the camera detection capability.

2. The method for constructing a space-based space target observation efficiency simulation calculation model considering image signal-to-noise ratio according to claim 1, characterized in that: The calculation steps of the traditional simulation calculation model are: Step 1: Set the task scenario and performance simulation period; Step 2: Establish a space-based space target observation system model; Step 3: Establish the orbit model of space targets; Step 4: Set visible light load parameters; Step 5: Calculate the payload field of view coverage; Step 6: Calculate the time period when the space target enters the field of view.

3. The method for constructing a space-based space target observation efficiency simulation calculation model considering image signal-to-noise ratio according to claim 1, characterized in that: The estimation formula of space target brightness Mv is: Mv=-24.63-5logd-2.5logρ+5logl-2.5log((π-Φ)cosΦ+sinΦ) In the above formula, d represents the target size, in cm; ρ is the reflectivity or scattering rate of the target; l is the relative observation distance between the observer and the target, and Φ is the observation phase angle, which is defined as the angle between the observer, the observed target, and the sun.

4. The method for constructing a space-based space target observation efficiency simulation calculation model considering image signal-to-noise ratio according to claim 1, characterized in that: The detector system noise N system The calculation formula is as follows: In the above formula, n b is the background noise, n p is the quantization noise, n read is the electronic read noise; where: (1) Background noise N b is the total number of noise electrons, calculated as follows: N b =n pixel ·(S sky +S dark )·t In the above formula, n pixel is the number of wire drawing pixels, t is the exposure time, S sky is the skylight signal rate, S dark is the detector dark signal rate; (2) The quantization noise N p The number of photoelectrons generated for the target radiation; (3) The electronic read noise N read The number of photoelectrons equivalent to the detector readout noise.

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