Coastal low-altitude atmospheric waveguide multi-path processing method based on GNSS occultation

Abstract

The invention provides a coastal low-altitude atmospheric waveguide multi-path processing method based on GNSS occultation. The coastal low-altitude atmospheric waveguide multi-path processing method comprises the following steps: reading GNSS observation data; calculating a GNSS signal waveguide emergence angle; extracting a coastal GNSS occultation event; estimating multiple paths of each GNSS occultation event; performing multi-path modeling according to the GNSS signal waveguide emergent angle and the satellite number; and the multi-path influence of the atmospheric waveguide is eliminated. The method has the beneficial effects that a multi-path effect elimination algorithm for low-altitude atmospheric waveguide signal processing based on a GNSS occultation detection technology is optimized, the influence of the multi-path effect on signal delay calculation is reduced, the precision of low-altitude atmospheric waveguide calculation is improved, and the application effects of the method in the aspects of radar detection, communication, navigation and the like are improved.

Description

Technical Field

[0001] The invention belongs to the field of atmospheric waveguide detection, and in particular relates to a method for multi-path processing of low-altitude atmospheric waveguide near the sea based on GNSS occultation. Background Art

[0002] Monitoring low-altitude atmospheric ducts can help more accurately predict extreme weather events, help radar systems detect low-altitude targets, and guide low-altitude aircraft to avoid dangerous areas. It can also optimize electronic warfare strategies and increase the ability to obtain and interfere with meteorological elements. The refractive index of the area where low-altitude atmospheric ducts occur forms a negative gradient as the altitude changes. The coastal GNSS occultation detection technology can obtain the bottom elevation angle GNSS occultation signal in the coastal direction, extract the delay information of the GNSS signal through data processing, and process it to obtain the atmospheric refractive index parameters. The change gradient of the refractive index parameters is obtained to determine the occurrence of atmospheric ducts, which has important engineering application value for radar detection, communication and navigation.

[0003] There is a serious multipath effect in the low-altitude atmospheric waveguide obtained based on GNSS occultation detection processing. The multipath effect is a common interference problem in GNSS signal propagation. It refers to the satellite signal forming multiple propagation paths after being reflected by the ground, buildings, etc., causing the receiver to capture mixed signals (superposition of direct waves and reflected waves), causing ranging errors and phase ambiguity. It is particularly significant in scenarios such as low-altitude atmospheric detection and urban navigation, and it is very important to effectively eliminate the impact of the multipath effect. Summary of the invention

[0004] In view of this, the present invention aims to propose a multipath processing method for low-altitude atmospheric waveguide near the sea based on GNSS occultation, so as to solve the problem of multipath effect of low-altitude atmospheric waveguide detection signals based on GNSS occultation.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows: A method for processing multipath of low-altitude atmospheric waveguide near the sea based on GNSS occultation comprises the following steps: S1. Read GNSS observation data; S2, calculate the GNSS signal waveguide emission angle; S3, extracting GNSS occultation events near the sea; S4, estimate the multipath for each GNSS occultation event; S5. Perform multipath modeling based on the GNSS signal waveguide emission angle and satellite number; S6. Eliminate the multipath effects of atmospheric waveguides.

[0006] Furthermore, in step S1, reading GNSS observation data includes: S11. The GNSS signal receiving device receives the GNSS signal and generates a GNSS observation event; S12. Obtaining the time series, dual-frequency signal-to-noise ratio, dual-frequency carrier phase and dual-frequency pseudorange information of GNSS observation events.

[0007] Furthermore, in step S2, the GNSS signal waveguide emission angle is calculated, including: S21. Define the GNSS signal waveguide emission angle as θ; S22, estimating the gain size G1 using the GNSS signal strength; S23. Define the GNSS antenna gain pattern, with the horizontal axis x being the angle and the vertical axis y being the gain magnitude. Draw a straight line l with y=G1 parallel to the horizontal axis x. The straight line l intersects the GNSS antenna gain pattern at points A and B. Draw a perpendicular line to the horizontal axis x through point A and intersect the horizontal axis x at point C. Draw a perpendicular line to the horizontal axis x through point B and intersect the horizontal axis x at point D. The horizontal axis x values ​​corresponding to points C and D are two estimated values ​​of the GNSS signal waveguide emission angle θ.

[0008] Furthermore, in step S3, extracting the seaside GNSS occultation events includes: S31. Define the GNSS occultation event judgment threshold R: -2°~+2°; S32. Determine whether the GNSS observation event is a GNSS occultation event: If the GNSS signal waveguide emission angle θ of the GNSS observation event is within the occultation event judgment threshold R, it is determined to be a GNSS occultation event; otherwise, it is determined to be a non-GNSS occultation event and is not processed.

[0009] Furthermore, in step S4, the multipath of each GNSS occultation event is estimated, including: S41, calculating the multipath value M1 at the first frequency point by formula (1); S42, calculating the multipath value M2 at the second frequency point by formula (2); (1) (2) Wherein, P1 and P2 are the pseudoranges at the first frequency and the second frequency respectively, L1 and L2 are the carrier phases at the first frequency and the second frequency respectively, and γ1 and γ2 are the wavelengths corresponding to the first frequency and the second frequency respectively.

[0010] Further, in step S5, multipath modeling is performed according to the GNSS signal waveguide emission angle and the satellite number, including: S51, based on steps S2 to S5, construct a relationship between the GNSS satellite number PRN(i), the GNSS signal waveguide emission angle θ(i), and the first frequency point multipath information M1(i), where i=1,2,3,…,N, and the relationship between the three exists in the form of a multipath modeling table, and the data testing process is no less than one week; S52, based on steps S2 to S5, constructing a relationship between the GNSS satellite number PRN(i), the GNSS signal waveguide emission angle θ(i), and the second frequency point multipath information M2(i), where i=1,2,3,…,N, and the relationship between the three exists in the form of a multipath modeling table, and the data testing process is not less than one week; The format of the multipath modeling table is as follows: The row is the GNSS satellite number, and the column is the GNSS signal waveguide emission angle θ. The GNSS signal waveguide emission angle θ ranges from -2° to +2°, with one point at every 0.2° interval. The GNSS signal waveguide emission angle θ is rounded off to determine the column position.

[0011] Furthermore, in step S6, eliminating the atmospheric duct multipath influence includes: S61, calculating the satellite number and the GNSS signal waveguide emission angle θ corresponding to the GNSS occultation event; S62, obtaining multipath values ​​of the first frequency point and the second frequency point from a multipath modeling table by looking up the table; S63. In the process of calculating the atmospheric waveguide, the multipath values ​​corresponding to the first frequency point and the second frequency point are eliminated.

[0012] Furthermore, the GNSS signal receiving device includes a GNSS antenna, a GNSS low-altitude sea occultation receiver, and corresponding power supplies and cables.

[0013] Compared with the prior art, the method for processing multipath in low-altitude atmospheric waveguide near the sea based on GNSS occultation described in the present invention has the following advantages: Optimize the multipath effect elimination algorithm for low-altitude atmospheric waveguide signal processing based on GNSS occultation detection technology, reduce the impact of multipath effect on signal delay calculation, improve the accuracy of low-altitude atmospheric waveguide calculation, and enhance its application effect in radar detection, communication, and navigation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 A technical roadmap for the embodiments of the present invention; Figure 2A schematic diagram of an atmospheric waveguide for low-altitude GNSS occultation observation near the sea according to an embodiment of the present invention; Figure 3 This is the GNSS antenna gain pattern described in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0016] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0017] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0018] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0019] like Figures 1 to 3 As shown, the method for processing multipath of low-altitude atmospheric waveguide near the sea based on GNSS occultation includes the following steps: S1. Read GNSS observation data; S2, calculate the GNSS signal waveguide emission angle; S3, extracting GNSS occultation events near the sea; S4, estimate the multipath for each GNSS occultation event; S5. Perform multipath modeling based on the GNSS signal waveguide emission angle and satellite number; S6. Eliminate the multipath effects of atmospheric waveguides.

[0020] The present invention reads the observation data of coastal low-altitude GNSS (China's Beidou, the United States' GPS, Russia's GLONASS and Europe's GALILEO), splits it according to GNSS observation events, calculates the departure angle of the observed GNSS satellite in each arc segment, judges and extracts the event of coastal GNSS occultation, performs wide-lane combination of occultation observation quantities to reduce the multipath effect, calculates the multipath values ​​at two frequency points of each occultation event by using mathematical formulas, mathematically models the residual multipath according to the GNSS signal waveguide departure angle of the GNSS occultation and the satellite number, and then eliminates the multipath influence.

[0021] The specific process of the present invention is as follows: a) Read GNSS observation data Read the low-altitude GNSS observation data near the sea to obtain the time series, dual-frequency signal-to-noise ratio, dual-frequency carrier phase, and dual-frequency pseudorange information of each event.

[0022] b) Calculate the GNSS signal waveguide incidence angle Schematic diagram of atmospheric waveguide for low-altitude GNSS occultation observation over the sea Figure 2 As shown, after the GNSS navigation satellite with the satellite number PRN transmits the GNSS signal, it propagates through the ionosphere and atmosphere to the nearby sea surface and enters the waveguide layer, where a wave-like reflection propagation occurs. After multiple propagations, it is received by the GNSS receiver antenna set up in the coastal direction. The GNSS signal waveguide emission angle is θ, and the center of the earth is O. The GNSS low-altitude occultation signal receiving equipment deployed at the receiving site includes a GNSS antenna, a GNSS low-altitude occultation receiver near the sea, and the corresponding power supply and cables. The GNSS signal waveguide emission angle θ is estimated using the received GNSS signal strength and the gain pattern of the GNSS antenna. The gain pattern of the GNSS antenna is shown in Figure 3 As shown, the horizontal axis x is the angle, and the vertical axis y is the gain size. The gain size G1 is estimated using the GNSS signal strength. A straight line l with y=G1 parallel to the horizontal axis is drawn, which intersects with the GNSS antenna gain pattern at points A and B. Points A and B are used to draw perpendicular lines to the x-axis, which intersect with the x-axis at points C and D respectively. The x-axis values ​​corresponding to points C and D are two estimated values ​​of the GNSS signal waveguide emission angle θ, where Figure 2 The state at a certain moment of the occultation event, at which the GNSS signal waveguide emission angle θ is positive.

[0023] c) Extracting GNSS occultation events near the sea The GNSS observation events are judged according to the size of the GNSS signal waveguide emission angle θ. The occultation event judgment threshold R is set to -2°~+2°. Events with the GNSS signal waveguide emission angle θ within the range of R are occultation events, and events with the GNSS signal waveguide emission angle θ outside the range of R are non-occultation events. Non-occultation events are not processed. In actual use, the GNSS signal waveguide emission angle θ is judged for the two estimated values ​​based on the GNSS signal waveguide emission angle θ being within ±2° during the occultation event. The estimated value within ±2° is the GNSS signal waveguide emission angle, and the value outside ±2° is discarded.

[0024] d) Estimate the multipath for each occultation event F1 and F2 are the first and second frequencies of GNSS satellite observation data, respectively. The multipath values ​​M1 and M2 at the two frequencies F1 and F2 are calculated by combining the carrier phase and pseudorange observation information. The multipath values ​​M1 and M2 at the first and second frequencies can be calculated according to formula (1) and formula (2). In the following formula, P1 and P2 are the pseudoranges at the F1 and F2 frequencies, L1 and L2 are the carrier phases at the F1 and F2 frequencies, and γ1 and γ2 are the wavelengths corresponding to the F1 and F2 frequencies.

[0025] (1) (2) e) Multipath modeling based on GNSS signal waveguide emission angle and satellite number Test at least one week of GNSS occultation-based sea-based observation data, and calculate the GNSS satellite number PRN(i), GNSS signal waveguide emission angle θ(i), dual-frequency multipath information M1(i) and M2(i) corresponding to N GNSS occultation observation events through the above steps a) to d), where i=1,2,3,…,N. Construct the relationship between the GNSS satellite number PRN(i), the GNSS signal waveguide emission angle θ(i) and the first frequency point multipath information M1(i), and construct the relationship between the GNSS satellite number PRN(i), the GNSS signal waveguide emission angle θ(i) and the second frequency point multipath information M2(i). The specific multipath construction strategy for the first frequency point and the second frequency point is shown in Table 1. The row is the GNSS satellite number, C represents the Beidou system, the following two digits are the Beidou satellite number, G represents the GPS system, R represents the GLONASS system, and E represents the Galileo system; the column is the GNSS signal waveguide emission angle θ, the GNSS signal waveguide emission angle θ ranges from -2° to +2°, and one point is spaced 0.2° apart. The values ​​calculated for the above N GNSS occultation events are filled in the table in the form of a table. The table is filled in using the principle of rounding the GNSS signal waveguide emission angle. The multipath modeling tables for the first and second frequency points of the GNSS occultation observation data are established with reference to Table 1.

[0026] f) Eliminate multipath effects Calculate the satellite number PRN1 corresponding to the GNSS occultation event and the corresponding GNSS signal waveguide emission angle θ1, find the row corresponding to the system and satellite number of the specific PRN1 satellite from Table 1, and then find the column closest to the GNSS signal waveguide emission angle θ1 from the column to confirm the multipath value. The search method for the first frequency point and the second frequency point is similar. In the process of calculating the atmospheric waveguide based on GNSS occultation observation data, eliminate the multipath values ​​corresponding to the first frequency point and the second frequency point obtained by the lookup table, reduce the multipath effect introduced by the low-altitude observation based on the sea of ​​GNSS occultation, and improve the accuracy and effect of atmospheric waveguide processing.

[0027] Table 1 Multipath modeling table

[0028] Advantages of the present invention: Optimize the multipath effect elimination algorithm for low-altitude atmospheric waveguide signal processing based on GNSS occultation detection technology, reduce the impact of multipath effect on signal delay calculation, improve the accuracy of low-altitude atmospheric waveguide calculation, and enhance its application effect in radar detection, communication, and navigation.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for processing multipath of low-altitude atmospheric waveguide near the sea based on GNSS occultation, characterized by: The following steps are involved: S1. Read GNSS observation data; S2, calculate the GNSS signal waveguide emission angle; S3, extracting GNSS occultation events near the sea; S4, estimate the multipath for each GNSS occultation event; S5. Perform multipath modeling based on the GNSS signal waveguide emission angle and satellite number; S6. Eliminate the multipath effects of atmospheric waveguides.

2. The method for processing low-altitude atmospheric waveguide multipath near the sea based on GNSS occultation according to claim 1, characterized in that: In step S1, GNSS observation data is read, including: S11. The GNSS signal receiving device receives the GNSS signal and generates a GNSS observation event; S12. Obtaining the time series, dual-frequency signal-to-noise ratio, dual-frequency carrier phase and dual-frequency pseudorange information of GNSS observation events.

3. The method for processing low-altitude atmospheric waveguide multipath near the sea based on GNSS occultation according to claim 1, characterized in that: In step S2, the GNSS signal waveguide emission angle is calculated, including: S21. Define the GNSS signal waveguide emission angle as θ; S22, estimating the gain size G1 using the GNSS signal strength; S23. Define the GNSS antenna gain pattern, with the horizontal axis x being the angle and the vertical axis y being the gain magnitude. Draw a straight line l with y=G1 parallel to the horizontal axis x. The straight line l intersects the GNSS antenna gain pattern at points A and B. Draw a perpendicular line to the horizontal axis x through point A and intersect the horizontal axis x at point C. Draw a perpendicular line to the horizontal axis x through point B and intersect the horizontal axis x at point D. The horizontal axis x values ​​corresponding to points C and D are two estimated values ​​of the GNSS signal waveguide emission angle θ.

4. The method for processing low-altitude atmospheric waveguide multipath near the sea based on GNSS occultation according to claim 1, characterized in that: In step S3, extracting the seaside GNSS occultation events includes: S31. Define the GNSS occultation event judgment threshold R: -2°~+2°; S32. Determine whether the GNSS observation event is a GNSS occultation event: If the GNSS signal waveguide emission angle θ of the GNSS observation event is within the occultation event judgment threshold R, it is determined to be a GNSS occultation event; otherwise, it is determined to be a non-GNSS occultation event and is not processed.

5. The method for processing low-altitude atmospheric waveguide multipath near the sea based on GNSS occultation according to claim 1, characterized in that: In step S4, the multipath of each GNSS occultation event is estimated, including: S41, calculating the multipath value M1 at the first frequency point by formula (1); S42, calculating the multipath value M2 at the second frequency point by formula (2); (1) (2) Wherein, P1 and P2 are the pseudoranges at the first frequency and the second frequency respectively, L1 and L2 are the carrier phases at the first frequency and the second frequency respectively, and γ1 and γ2 are the wavelengths corresponding to the first frequency and the second frequency respectively.

6. The method for processing multipath in low-altitude atmospheric waveguide near the sea based on GNSS occultation according to claim 1, characterized in that: In step S5, multipath modeling is performed according to the GNSS signal waveguide emission angle and the satellite number, including: S51, based on steps S2 to S5, construct a relationship between the GNSS satellite number PRN(i), the GNSS signal waveguide emission angle θ(i), and the first frequency point multipath information M1(i), where i=1,2,3,…,N, and the relationship between the three exists in the form of a multipath modeling table, and the data testing process is no less than one week; S52, based on steps S2 to S5, constructing a relationship between the GNSS satellite number PRN(i), the GNSS signal waveguide emission angle θ(i), and the second frequency point multipath information M2(i), where i=1,2,3,…,N, and the relationship between the three exists in the form of a multipath modeling table, and the data testing process is not less than one week; The format of the multipath modeling table is as follows: The row is the GNSS satellite number, and the column is the GNSS signal waveguide emission angle θ. The GNSS signal waveguide emission angle θ ranges from -2° to +2°, with one point at every 0.2° interval. The GNSS signal waveguide emission angle θ is rounded off to determine the column position.

7. The method for processing multipath of low-altitude atmospheric waveguide near the sea based on GNSS occultation according to claim 1, characterized in that: In step S6, eliminating the atmospheric duct multipath effect includes: S61, calculating the satellite number and the GNSS signal waveguide emission angle θ corresponding to the GNSS occultation event; S62, obtaining multipath values ​​of the first frequency point and the second frequency point from a multipath modeling table by looking up the table; S63. In the process of calculating the atmospheric waveguide, the multipath values ​​corresponding to the first frequency point and the second frequency point are eliminated.

8. The method for processing low-altitude atmospheric waveguide multipath near the sea based on GNSS occultation according to claim 2, characterized in that: The GNSS signal receiving device comprises a GNSS antenna, a GNSS low-altitude sea occultation receiver and corresponding power supplies and cables.

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