A target screening method for a V-shaped electronic fence

Abstract

The application relates to a target over-screen detection method of a V-shaped electronic fence, and belongs to the technical field of space target monitoring. According to the motion law of a target, sufficient conditions of target over-screen detection are set, when a target simultaneously satisfies a longitude constraint of a vertical projection screen, a azimuth angle constraint of passing through the vertical projection screen and a maximum latitude constraint that can be reached by a target subsolar point, the target can be considered to simultaneously pass through the V-shaped fence screen. The method does not need to directly search whether the target can pass through the screen, avoids the compromise selection of operation time and orbit prediction accuracy, and effectively improves the calculation efficiency of target over-screen detection.

Description

Technical Field

[0001] This invention relates to a target crossing detection method for a V-shaped electronic fence, belonging to the field of space target monitoring technology. Background Technology

[0002] With the increasing number of space activities and the rapid growth in the number of man-made targets in space, coupled with the deteriorating near-Earth space environment, higher demands are being placed on space situational awareness capabilities. Electronic fencing, with its advantages of wide coverage, high monitoring efficiency, strong ability to detect new space targets, simultaneous detection of multiple targets, and immunity to weather conditions, has become a primary means of monitoring ground-based space targets. Currently, international electronic fencing systems are represented by the US Navy Space Surveillance System (NAFSASUR) and the French Space Surveillance Network (Grand Réseau Adaptéàla VEilleSpatiale GRAVES).

[0003] With the increasing frequency of space launches in my country, the development of high-precision real-time space target monitoring technology has become imperative. Furthermore, my country's vast territory, spanning approximately 60 degrees of longitude, provides excellent geographical support for the deployment of electronic fencing surveillance systems. The V-shaped electronic fencing system can achieve orbit determination in a single pass, improving monitoring efficiency and offering significant advantages. It also represents the direction for the improvement and upgrading of the US electronic fencing system. The structure of the V-shaped electronic fencing system is as follows: Figure 1a and Figure 1b As shown, the deployment and construction first requires solving the problems of site selection and electronic beam interception screen layout. In the optimization of site selection and electronic screen layout, a large amount of calculation is needed for different deployment sites and different electronic screen layouts to find their variation patterns. However, the current target passing-through algorithm has the following problems: 1) The calculation of searching for the target passing through the screen is very large, and calculating a large number of targets one by one is too time-consuming; 2) Judging whether the target is within the azimuth and elevation range of the electronic screen based on the target's azimuth and elevation angle cannot guarantee that the target can pass through the V-shape at the same time; 3) Using SGP and SDP models to calculate the target's state at any time is inefficient. Using the two-body model is efficient, but the accuracy is poor. Summary of the Invention

[0004] The purpose of this invention is to provide a target crossing detection method for V-shaped electronic fences, so as to solve the trade-off between computation time and trajectory prediction accuracy in the current target crossing detection process of V-shaped electronic fences.

[0005] To solve the above-mentioned technical problems, this invention provides a method for detecting targets passing through a V-shaped electronic fence. The method includes the following steps:

[0006] 1) Determine the longitude range spanned by the vertical projection area of ​​the V-shaped electronic fence screen, and determine whether the longitude of the sub-satellite point when the target passes the station is within the longitude range;

[0007] 2) If so, calculate the azimuth angle of the target when it passes through the vertical projection screen, and determine whether it is less than the maximum azimuth angle of the target passing through the vertical projection screen;

[0008] 3) If it is less than, calculate the maximum latitude of the target star's nadir point and determine whether the maximum latitude is greater than or equal to the latitude value corresponding to the north screen at that location. If so, it means that the target can pass through the V-shaped electronic fence.

[0009] This invention establishes sufficient conditions for target crossing the screen based on the target's motion characteristics. When a target simultaneously satisfies the longitude constraint of crossing the vertical projection screen, the azimuth constraint of crossing the vertical projection screen, and the maximum latitude constraint that the target's nadir point can reach, it can be considered that the target can simultaneously cross the V-shaped fence screen. This method eliminates the need for directly searching whether the target can cross the screen, avoiding trade-offs between computation time and orbit prediction accuracy, and effectively improving the computational efficiency of target crossing detection.

[0010] Furthermore, the process for determining the longitude range spanned by the vertical projection area of ​​the V-shaped electronic fence screen in step 1) is as follows:

[0011] Calculate the time and position of the target passing the station based on the station's latitude;

[0012] Determine the target's distance from the station based on the target's location, and calculate the geocentric angle corresponding to the arc length using the target's distance from the station, the Earth's radius, and the angle between the vertical projection area of ​​the screen;

[0013] The longitude angle corresponding to the target passing through the vertical projection screen is calculated using the geocentric angle. The longitude range corresponding to this angle is the longitude range spanned by the vertical projection area of ​​the V-shaped electronic fence screen.

[0014] This invention calculates the geocentric angle corresponding to the arc length based on the target's distance from the station height, the Earth's radius, and the angle between the target and the vertical projection area of ​​the screen. It then uses the geocentric angle to determine the longitude angle corresponding to the target passing through the vertical projection screen, thereby obtaining the longitude range spanned by the vertical projection area of ​​the screen. This method can simply and accurately determine the longitude range spanned by the vertical projection area of ​​the screen.

[0015] Furthermore, the formula used to calculate the longitude of the nadir point when the target passes the station is as follows:

[0016] λ=arctan(cositanu)+Ω-ω e t-S0

[0017] Where i is the orbital inclination, u is the angular distance from the ascending node, Ω is the right ascension of the ascending node, S0 is the Greenwich mean sidereal time at t=0, and ω eThis is the Earth's rotational angular velocity.

[0018] Furthermore, the formula used to calculate the azimuth angle when the target passes through the vertical projection screen in step 2) is as follows:

[0019]

[0020] Where A is the required azimuth angle when the target passes through the vertical projection screen, i is the orbital inclination angle, u is the ascending intersection angle, μ is the gravitational constant, p is the target orbital semi-circle, e is the orbital eccentricity, and f is the true anomaly angle.

[0021] Furthermore, the maximum azimuth angle A of the target across the vertical projection screen max The calculation formula used is:

[0022]

[0023]

[0024] Where Δλ is the difference between the longitude of the target when it crosses the vertical projection screen and the longitude of the left side of the longitude interval crossed by the projection screen, Δδ is the difference between the latitude of the target when it crosses the vertical projection screen and the latitude of the north screen, and ∠S is the azimuth angle of the target when it passes the edge of the north screen, which is the maximum azimuth angle A of the target when it crosses the vertical projection screen. max .

[0025] Furthermore, the maximum latitude of the target sub-satellite point is calculated using the following formula:

[0026] δ max =δ+Δδ

[0027] Where δ max δ represents the maximum latitude of the target satellite's nadir point, and δ represents the latitude of the station. Attached Figure Description

[0028] Figure 1a This is a side view of a V-shaped electronic fence structure;

[0029] Figure 1b This is a front view of the V-shaped electronic fence structure;

[0030] Figure 2 This is a flowchart of the target over-screen detection method for the V-shaped electronic fence of the present invention;

[0031] Figure 3 This is a schematic diagram illustrating the calculation of the longitude angle when the target passes the measuring station in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram illustrating the calculation of the azimuth range in an embodiment of the present invention;

[0033] Figure 5This is a schematic diagram of the calculation of Δδ in an embodiment of the present invention (a planar view cut along the meridian where the target (i.e., point S in the figure) is located, and point A is the tangent point where the target S and Beiping are tangent).

[0034] Figure 6 This is the target coverage rate of the large triangular distribution (Kashgar, Sansha, Jiamusi) during the testing of this invention;

[0035] Figure 7 This is the target coverage rate of the present invention along the longitude distribution (Jiamusi, Shanghai, Sansha) during testing;

[0036] Figure 8 This is the target coverage rate of the present invention along the latitude distribution (Kashgar, Chengdu, Shanghai) during testing. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0038] This invention addresses the problems of existing target crossing detection algorithms for V-shaped electronic fence structures. It proposes a new method for target crossing detection in V-shaped electronic fences. This method does not directly search and determine whether a target can cross the V-shaped electronic fence. Instead, it proposes sufficient conditions for a target to cross the fence based on the characteristics and rules governing target crossing. Specifically, a target is considered to be able to cross the V-shaped electronic fence if it simultaneously meets the following three conditions: a) It can cross the local vertical projection screen (the projection of the V-shaped electronic fence onto the local vertical plane); b) It satisfies the azimuth range constraint at the moment of crossing the vertical projection screen; c) The target's trajectory intersects with the north screen. Through this method, this invention can quickly and accurately achieve target crossing detection. The implementation process of this method is as follows: Figure 2 As shown below, a detailed explanation will follow.

[0039] 1. Determine whether the target can pass through the local vertical projection screen.

[0040] The vertical projection screen refers to the projection of the V-shaped electronic fence onto the local vertical plane. Assuming that the angle of the V-shaped electronic fence screen in this embodiment is α, and the included angle between the two screens is β, the fan-shaped angle of the projection of the two screens onto the local vertical screen can be obtained as follows:

[0041] α ⊥ =2{90°-tan -1 [tan(90°-α / 2)cos(β / 2)]} (1)

[0042] The equation of the target's nadir trajectory is:

[0043]

[0044] in The difference in right ascension between the nadir and the ascending node is represented by i, the orbital inclination, u, the angular distance from the ascending node, Ω, the right ascension of the ascending node, and δ, the geographic latitude.

[0045] If the Greenwich Mean Sidereal Time at t=0 is S0, then the geographic longitude of the nadir point is:

[0046] λ=α r =arctan(cositanu) + Ω - ω e t-S0 (3)

[0047] Where α r ω is the difference in right ascension between the sub-satellite point and the vernal equinox. e This is the Earth's rotational angular velocity.

[0048] The formula for calculating the sub-satellite point can be used to calculate the time when the target passes the geographical latitude of the station and the corresponding longitude.

[0049] If the longitude of the target's nadir point when passing the station's latitude falls within the longitude range spanned by the screen's vertical projection area, then the target may have passed the V-shaped electronic fence screen. The process for determining the longitude range spanned by the screen's vertical projection area is as follows:

[0050] 1) Obtain the geographic latitude of the station, calculate the time when the target passes through that latitude, and calculate the target's position at that time.

[0051] 2) Calculate the height of the target (satellite) from the station based on its position coordinates. Calculate the corresponding arc length based on the Earth's radius and the angle between the Earth's radius and the vertical projection area of ​​the screen. Then calculate the corresponding geocentric angle based on the arc length. The formula is as follows:

[0052]

[0053] Where R H R is the altitude of the target (satellite) from the station. e Let α be the radius of the Earth. ⊥ α' is the angle between the vertical projection areas of the screen and α′ is the geocentric angle corresponding to the arc length.

[0054] 3) Calculate the longitude angle corresponding to the obtained geocentric angle and the geographic latitude of the target star's nadir point, such as... Figure 3 As shown, the longitude range corresponding to this included angle is the longitude range spanned by the vertical projection area of ​​the screen to be calculated. The calculation formula used is:

[0055]

[0056] Where δ is the geographic latitude of the target star's nadir point, and ξ is the corresponding longitude angle.

[0057] Based on this formula, the longitude range that the target must cross to pass through the vertical projection screen can be calculated. The target must fall within this longitude range in order to be able to cross the north and south V-shaped electronic fence screens simultaneously.

[0058] 2. Determine whether the azimuth range constraint at the moment of penetrating the vertical projection screen is met.

[0059] Even if a target falls within the longitude range when passing through a vertical projection screen, it cannot be guaranteed that the target will pass through the screen, and an azimuth constraint judgment is required. This invention determines whether the target passes through the screen or not by calculating whether the azimuth of the target when passing through the vertical projection screen falls within the range that allows passage through the V-shaped electronic fence screen.

[0060] First, based on the geometric relationship of the azimuth angle of the trajectory of the point beneath the rotating Earth, we can obtain the formula for calculating the azimuth of the target when it passes through the vertical projection screen:

[0061]

[0062] like Figure 4 As shown, if the target is located at point S in the diagram, the distance from the target's center to the ground and the span of the vertical projection screen at this point can be calculated to obtain the result. Figure 4 The two meridians L1 and L2 are located in a spherical right triangle T. Δλ is a known quantity, and the maximum V-shaped orientation of the target can be calculated based on Δδ.

[0063] like Figure 5 This can be viewed as a planar diagram cut along the meridian containing the target (i.e., point S in the diagram), with point A being the tangent point between target S and the north screen. Assuming the geocentric distance of the target when it passes the vertical projection screen is equal to the geocentric distance when it passes the north and south screens, S is the target, O is the Earth's center, and C is the projection of S onto the Earth's surface, in planar triangle AOC, OA = R. e +R H OC = R e Given ∠ACS = β / 2 (β is the angle between the screens), ∠AOC can be calculated, and Δδ can be calculated using the following formula:

[0064]

[0065] After calculating Δδ using this formula, Figure 4 Using Nerpi's rule, the maximum azimuth angle of the target across the perpendicular projection screen can be calculated within the spherical right triangle T:

[0066]

[0067] in:

[0068]

[0069] The azimuth angle of the target when it passes through the vertical projection screen (calculated by formula (6)) is compared with the maximum azimuth angle of the target when it passes through the vertical projection screen (refer to formula (8)). It is determined whether the azimuth angle range constraint at the moment of passing through the vertical projection screen is satisfied. If the azimuth angle of the target when it passes through the vertical projection screen is not greater than the maximum azimuth angle of the target when it passes through the vertical projection screen, it means that the azimuth angle range constraint at the moment of passing through the vertical projection screen is satisfied. Otherwise, it is not satisfied, that is, the target cannot pass through the V-shaped electronic fence screen at this time.

[0070] 3. Determine whether the maximum latitude constraint of the target star's nadir point is satisfied.

[0071] When the target satisfies constraints 1 and 2, it means that the target may cross the V-shaped electronic fence screen. However, since the north screen is tilted to the north, even if the target satisfies the constraints of crossing the longitude range and azimuth angle, there is still a possibility that the target will not be able to reach the north screen and return (e.g., if the target is tangent to the vertical projection screen, the target cannot reach the north screen at all). Therefore, it is also necessary to satisfy that the maximum latitude value that the target's nadir point can reach cannot be less than the latitude value corresponding to the north screen at that location (the extreme case is that the target's orbit is tangent to the north screen).

[0072] First, the maximum latitude of the target's nadir point needs to be calculated: when the target's nadir point reaches its maximum latitude, the corresponding ascending node angular distance u = π / 2, from which the corresponding time can be calculated, and the geocentric distance of the target can be calculated. According to formula (7), Δδ can be calculated, the geographical latitude of the station is δ, and the maximum latitude of the target's nadir point is:

[0073] δ max =δ+Δδ (10)

[0074] The maximum latitude value δ of the target sub-satellite point obtained max Compare with the latitude value corresponding to the northern screen at that location, if δ max If the latitude value is not less than the latitude value corresponding to the north screen at that location, it indicates that the target can pass through the V-shaped electronic fence screen.

[0075] As shown in the above process, if a target simultaneously satisfies the longitude constraint of crossing the vertical projection screen, the azimuth constraint of passing the vertical projection screen, and the maximum latitude constraint that the target's nadir point can reach, then the target can be considered to have simultaneously traversed the V-shape. Compared with existing detection methods, this invention does not require directly searching whether the target can pass through the screen. Based on the target's motion law, it provides sufficient conditions for the target to pass through the screen, effectively improving the calculation efficiency of target passing through the screen. At the same time, it avoids the trade-off between computation time and orbit prediction accuracy; it only needs to determine the sufficient conditions for the target to pass through the screen, enabling rapid and high-precision determination of whether the target has passed through the screen. This invention can also quantitatively calculate the coverage characteristics of V-shaped electronic fences on targets with different structural parameters (the angle of the electronic fence screen, the angle between the two screens) and different deployment locations, determining the optimal electronic fence design structural parameters and deployment. This method can be implemented using analytical algorithms, effectively addressing the rapidly increasing spatial target cataloging database.

[0076] To further illustrate the effects of the present invention, the detection method of the present invention is tested and verified below. The test is implemented using the MATLAB language.

[0077] This test uses TLE data downloaded from www.Space-track.org on December 7, 2022 as the source of space target data.

[0078] Data volume: Number of targets involved in the calculation: 24361; Calculation time for each target: 3 days (that is, if a target crosses the dual screens at least once within 3 days, it is considered that the target can be detected).

[0079] Computer processor: Intel(R) Core(TM) i7-10510U CPU@1.80GHz, memory: 16G, code is written in MATLAB.

[0080] V-shaped electronic fence configuration: screen angle is 100 degrees, and the angle between screens is 20 degrees; deployment locations: Jiamusi, Shanghai, Sansha, Chengdu and Kashgar; deployment methods are: distributed along latitude (Kashgar, Chengdu, Shanghai), distributed along longitude (Jiamusi, Shanghai, Sansha), and distributed in a large triangle (Kashgar, Sansha, Jiamusi).

[0081] The existing technology uses the SGP4 model for orbit prediction at 1-second intervals. Based on the predicted target azimuth and elevation angles, it determines whether the target is within the azimuth and elevation range of the electronic screen. For a 3-day calculation period, one target requires 259,200 orbit predictions using SGP4 (existing methods can be found in the paper "Signal Processing Algorithm for Space Target Monitoring Electronic Fence System" (author: Du Chunxia)). In contrast, this invention only requires one SGP4 orbit prediction per cycle, and with a minimum orbit cycle of 90 minutes, a maximum of 48 predictions are needed. Based on these calculation conditions, completing the detection calculation for one deployment site takes 408.8 seconds, and the average time to determine if a target passes the screen is 0.0167 seconds.

[0082] The target coverage ratios for the triangular distribution (Kashgar, Sansha, Jiamusi), the longitude distribution (Jiamusi, Shanghai, Sansha), and the latitude distribution (Kashgar, Chengdu, Shanghai) are respectively as follows: Figure 6 , Figure 7 and Figure 8 As shown, combining multiple stations can significantly improve coverage. Comparing the three combinations, the combination along longitude (Jiamusi, Shanghai, Sansha) yielded the highest target coverage. This is because low-latitude stations have a higher number of transit targets but a higher percentage of missed targets; while high-latitude stations have fewer transit targets but a lower percentage of missed targets. Combining these two methods allows for complementary advantages and improves target coverage.

[0083] This method plays a role in site selection optimization and screen parameter optimization during the construction of the V electronic fence system. It can quickly and qualitatively provide the target coverage characteristics under different deployment locations, different combination methods, and different screen parameter conditions.

Claims

1. A method for detecting target crossing through a V-shaped electronic fence, characterized in that, The detection method includes the following steps: 1) Determine the longitude range spanned by the vertical projection area of ​​the V-shaped electronic fence screen, and determine whether the longitude of the sub-satellite point when the target passes the station is within the longitude range; 2) If so, calculate the azimuth angle of the target when it passes through the vertical projection screen, and determine whether it is less than the maximum azimuth angle of the target passing through the vertical projection screen; 3) If it is less than, calculate the maximum latitude of the target star's nadir point and determine whether the maximum latitude is greater than or equal to the latitude value corresponding to the north screen at that location, so as to avoid the target being unable to reach the north screen when it is tangent to the vertical projection screen. If so, it means that the target can pass through the V-shaped electronic fence.

2. The target overpass detection method for a V-shaped electronic fence according to claim 1, characterized in that, The process for determining the longitude range spanned by the vertical projection area of ​​the V-shaped electronic fence screen in step 1) is as follows: Calculate the time and position of the target passing the station based on the station's latitude; Determine the target's distance from the station based on the target's location, and calculate the geocentric angle corresponding to the arc length using the target's distance from the station, the Earth's radius, and the angle between the vertical projection area of ​​the screen; The longitude angle corresponding to the target passing through the vertical projection screen is calculated using the geocentric angle. The longitude range corresponding to this angle is the longitude range spanned by the vertical projection area of ​​the V-shaped electronic fence screen.

3. The target clearance detection method for a V-shaped electronic fence according to claim 1 or 2, characterized in that, The formula used to calculate the longitude of the nadir point when the target passes the station is: in For the track inclination angle, Angular distance of ascending node Right ascension of the ascending node, for Greenwich Mean Sidereal Time This is the Earth's rotational angular velocity.

4. The target overpass detection method for a V-shaped electronic fence according to claim 3, characterized in that, The formula used to calculate the azimuth angle when the target passes through the vertical projection screen in step 2) is as follows: Where A is the azimuth angle of the target when it passes through the vertical projection screen. For the track inclination angle, Angular distance of ascending node The gravitational constant of Earth, For the target orbital semi-drillpoint, For orbital eccentricity, It is the true near point angle.

5. The target overpass detection method for a V-shaped electronic fence according to claim 3, characterized in that, Maximum azimuth angle of the target through the vertical projection screen The calculation formula used is: ； in The difference between the longitude of the target when it crosses the vertical projection screen and the longitude to the left of the longitude interval crossed by the projection screen. The difference between the latitude of the target when it crosses the vertical projection screen and the latitude of the north screen. The azimuth angle of the target when it passes the edge of the North Screen.

6. The target overpass detection method for a V-shaped electronic fence according to claim 1, characterized in that, The maximum latitude of the target sub-satellite point is calculated using the following formula: in The maximum latitude of the target star's nadir point. The latitude of the station. The difference between the latitude of the target when it crosses the vertical projection screen and the latitude of the north screen.

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