GNSS occultation-based low-altitude atmospheric duct multipath processing method

Abstract

The application provides a GNSS occultation-based low-altitude atmospheric duct multipath processing method, comprising the following steps: reading GNSS observation data; calculating a GNSS signal waveguide exit angle; extracting a GNSS occultation event near the sea; estimating the multipath of each GNSS occultation event; modeling the multipath according to the GNSS signal waveguide exit angle and the satellite number; and eliminating the influence of atmospheric duct multipath. The application has the beneficial effects of optimizing the multipath effect elimination algorithm of the low-altitude atmospheric duct signal processing based on the GNSS occultation detection technology, reducing the influence of the multipath effect on the signal delay calculation, improving the accuracy of the low-altitude atmospheric duct calculation, and improving the application effect in radar detection, communication and navigation and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of atmospheric waveguide detection, and particularly relates to a GNSS occultation-based coastal low-altitude atmospheric waveguide multipath processing method. BACKGROUND

[0002] Monitoring low-altitude atmospheric waveguide helps more accurately predict extreme weather events, helps radar systems detect low-altitude targets, guides low-altitude aircraft to avoid dangerous areas, and also optimizes electronic warfare strategies, increases weather element acquisition capabilities and interference capabilities. The refractive index of the area where the low-altitude atmospheric waveguide occurs changes with height, forming a negative gradient. The 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, process the atmospheric refractive index parameters, and calculate the change gradient of the refractive index parameters to determine the occurrence of atmospheric waveguide. It has important engineering application value for radar detection, communication and navigation.

[0003] The GNSS occultation-based low-altitude atmospheric waveguide detection processing exists a relatively serious multipath effect. The multipath effect is a common interference problem in GNSS signal propagation, which refers to the formation of multiple propagation paths of satellite signals reflected by the ground, buildings, etc., resulting in the receiver capturing mixed signals (direct wave and reflected wave superposition), causing ranging error and phase ambiguity. It is particularly significant in low-altitude atmospheric detection, urban navigation and other scenarios, and it is crucial to effectively eliminate the influence of multipath effect. SUMMARY

[0004] Therefore, the application aims to provide a GNSS occultation-based coastal low-altitude atmospheric waveguide multipath processing method to solve the problem of multipath effect in GNSS occultation-based low-altitude atmospheric waveguide detection signals.

[0005] To achieve the above-mentioned purposes, the technical scheme of the application is as follows:

[0006] A GNSS occultation-based coastal low-altitude atmospheric waveguide multipath processing method, comprising the following steps:

[0007] S1, reading GNSS observation data;

[0008] S2, calculating the waveguide exit angle of the GNSS signal;

[0009] S3, extracting a coastal GNSS occultation event;

[0010] S4, estimating the multipath of each GNSS occultation event;

[0011] S5, modeling the multipath according to the waveguide exit angle of the GNSS signal and the satellite number;

[0012] S6, eliminate the atmospheric waveguide multipath effect.

[0013] Further, in step S1, read GNSS observation data, including:

[0014] S11, GNSS signal receiving device receives GNSS signal and produces GNSS observation event;

[0015] S12, obtain the time series of GNSS observation event, dual frequency signal to noise ratio, dual frequency carrier phase and dual frequency pseudorange information.

[0016] Further, in step S2, calculate the waveguide exit angle of GNSS signal, including:

[0017] S21, define the waveguide exit angle of GNSS signal as θ;

[0018] S22, estimate the gain size G1 by using GNSS signal strength;

[0019] S23, define the GNSS antenna gain pattern, the horizontal axis x is the angle, the vertical axis y is the gain size, draw a straight line l parallel to the horizontal axis x with y=G1, the straight line l intersects with the GNSS antenna gain pattern at points A and B, draw a vertical line through point A intersecting with the horizontal axis x at point C, and draw a vertical line through point B intersecting with the horizontal axis x at point D, the horizontal axis x values corresponding to points C and D are the two estimated values of the waveguide exit angle θ of GNSS signal.

[0020] Further, in step S3, extract the GNSS occultation event near the sea, including:

[0021] S31, define the GNSS occultation event judgment threshold R: -2°~+2°;

[0022] S32, judge whether the GNSS observation event is a GNSS occultation event: if the waveguide exit angle θ of GNSS signal of the GNSS observation event is within the range of the occultation event judgment threshold R, it is determined as a GNSS occultation event, otherwise, it is determined as a non-GNSS occultation event and is not processed.

[0023] Further, in step S4, estimate the multipath of each GNSS occultation event, including:

[0024] S41, calculate the multipath value M1 on the first frequency point by formula (1);

[0025] S42, calculate the multipath value M2 on the second frequency point by formula (2);

[0026] (1)

[0027] (2)

[0028] In the formula, P1 and P2 are pseudo ranges at the first frequency point and the second frequency point respectively, L1 and L2 are carrier phases at the first frequency point and the second frequency point respectively, and γ1 and γ2 are wavelengths corresponding to the first frequency point and the second frequency point respectively.

[0029] Further, in step S5, the path loss is calculated according to the GNSS signal waveguide emission angle and the satellite number, including:

[0030] S51, based on steps S2 to S5, the relationship between the GNSS satellite number PRN(i) and the GNSS signal waveguide emission angle θ(i) and the first frequency point multipath information M1(i) is constructed, wherein i=1, 2, 3, …, N, the relationship between the three is in the form of a multipath modeling table, and the data test process is not less than one week;

[0031] S52, based on steps S2 to S5, the relationship between the GNSS satellite number PRN(i) and the GNSS signal waveguide emission angle θ(i) and the second frequency point multipath information M2(i) is constructed, wherein i=1, 2, 3, …, N, the relationship between the three is in the form of a multipath modeling table, and the data test process is not less than one week;

[0032] The format of the multipath modeling table is as follows:

[0033] The behavior GNSS satellite number is listed as the GNSS signal waveguide emission angle θ, and the GNSS signal waveguide emission angle θ ranges from -2° to +2°, with a point every 0.2°;

[0034] The GNSS signal waveguide emission angle θ is rounded to determine the column position.

[0035] Further, in step S6, the atmospheric waveguide multipath effect is eliminated, including:

[0036] S61, the satellite number and the GNSS signal waveguide emission angle θ corresponding to the GNSS occultation event are calculated;

[0037] S62, the first frequency point and the second frequency point multipath values are obtained from the multipath modeling table by table lookup;

[0038] S63, the first frequency point and the second frequency point corresponding multipath values are eliminated in the atmospheric waveguide process.

[0039] Further, the GNSS signal receiving device includes a GNSS antenna, a GNSS coastal low-altitude occultation receiver, and corresponding power supply and cables.

[0040] Compared with the prior art, the GNSS occultation-based coastal low-altitude atmospheric waveguide multipath processing method has the following advantages:

[0041] The application optimizes the multipath effect elimination algorithm of low-altitude atmospheric duct signal processing based on GNSS occultation detection technology, reduces the influence of multipath effect on signal delay calculation, improves the accuracy of low-altitude atmospheric duct calculation, and improves the application effect in radar detection, communication and navigation and the like. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and are used to interpret the illustrative embodiments of the present application and their descriptions, and do not constitute improper limitations to the present application. In the drawings:

[0043] Fig. 1 The technical roadmap described in the embodiments of the present application;

[0044] Fig. 2 The low-altitude GNSS occultation observation atmospheric duct schematic diagram described in the embodiments of the present application;

[0045] Fig. 3 The GNSS antenna gain direction diagram described in the embodiments of the present application. DETAILED DESCRIPTION

[0046] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0047] In the description of the present application, it should be understood that the terms “center”, “longitudinal”, “transverse”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation to the present application. In addition, the terms “first”, “second” and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by “first”, “second” and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of “a plurality of” is two or more.

[0048] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0050] like Figs. 1 to 3 As shown, the multipath processing method for low-altitude atmospheric waveguides near the sea based on GNSS occultation includes the following steps:

[0051] S1. Read GNSS observation data;

[0052] S2. Calculate the GNSS signal waveguide emission angle;

[0053] S3. Extract GNSS occultation events near the coast;

[0054] S4. Estimate the multipath for each GNSS occultation event;

[0055] S5. Perform multipath modeling based on the GNSS signal waveguide emission angle and satellite number;

[0056] S6. Eliminate the multipath effects of atmospheric waveguides.

[0057] This invention reads low-altitude GNSS (BeiDou, GPS, GLONASS, and GALILEO) observation data from coastal areas, breaks down GNSS observation events, calculates the emission angle of observed GNSS satellites within each arc segment, identifies and extracts GNSS occultation events occurring in coastal areas, performs wide-lane combination of occultation observations to reduce multipath effects, uses mathematical formulas to calculate multipath values ​​at two frequency points for each occultation event, and mathematically models the residual multipath based on the GNSS signal waveguide emission angle and satellite number of the GNSS occultation, thereby eliminating the multipath influence.

[0058] The specific process of this invention is as follows:

[0059] a) Reading GNSS observation data

[0060] Read low-altitude GNSS observation data from the coastal area and obtain the time series, dual-frequency signal-to-noise ratio, dual-frequency carrier phase, and dual-frequency pseudorange information for each event.

[0061] b) Calculate the GNSS signal waveguide emission angle

[0062] The schematic diagram of GNSS occultation observation atmospheric duct is shown in Fig. 2 The GNSS navigation satellite numbered PRN emits GNSS signal, which propagates through ionosphere and atmosphere to the sea surface, enters the duct layer, and is reflected in a wave-like manner. After multiple transmissions, the GNSS signal is received by the GNSS receiver antenna erected in the coastal direction, and the GNSS signal duct exit angle is θ, and the earth center is O. The GNSS coastal low-altitude occultation signal receiving equipment deployed at the receiving station includes a GNSS antenna, a GNSS coastal low-altitude occultation receiver, and corresponding power supply and cables. The GNSS signal duct exit angle θ is estimated by using the received GNSS signal strength and the gain pattern of the GNSS antenna. Fig. 3 The gain pattern of the GNSS antenna is shown in Fig. 3 , where the horizontal axis x is the angle, and the vertical axis y is the gain size. The gain size G1 is estimated by using the GNSS signal strength, a straight line l parallel to the horizontal axis is drawn at y=G1, and the line intersects the GNSS antenna gain pattern at points A and B. The vertical lines of points A and B intersect the x-axis at points C and D, respectively. The x-axis values of points C and D are the two estimated values of the GNSS signal duct exit angle θ, wherein Fig. 2 The state at a certain moment of the occultation event, at this moment, the GNSS signal duct exit angle θ is positive.

[0063] c) Extracting coastal GNSS occultation events

[0064] According to the size of the GNSS signal duct exit angle θ, the GNSS observation event is judged. The occultation event judgment threshold R is set to -2°~+2°. The event within the R range of the GNSS signal duct exit angle θ is an occultation event, and the event outside the R range of the GNSS signal duct exit angle θ is a non-occultation event. The non-occultation event is not processed. In actual use, the two estimated values of the GNSS signal duct exit angle θ are judged according to the GNSS signal duct exit angle θ during the occultation event, which is within ±2°. The estimated value within ±2° is the GNSS signal duct exit angle, and the estimated value outside ±2° is discarded.

[0065] d) Estimating the multipath of each occultation event

[0066] F1 and F2 are the first frequency and the second frequency of the 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. According to formulas (1) and (2), the multipath values M1 and M2 at the first frequency and the second frequency can be calculated, respectively. In the following formula, P1 and P2 are the pseudoranges at F1 and F2 frequencies, respectively, L1 and L2 are the carrier phases at F1 and F2 frequencies, respectively, and γ1 and γ2 are the wavelengths corresponding to F1 and F2 frequencies, respectively.

[0067] (1)

[0068] (2)

[0069] e) According to the GNSS signal waveguide emission angle and satellite number, the multipath modeling is carried out

[0070] Test GNSS-based occultation observation data for not less than one week, 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)~d), wherein i=1, 2, 3, …, N. The relationship between GNSS satellite number PRN(i) and GNSS signal waveguide emission angle θ(i) and first frequency point multipath information M1(i) is constructed, and the relationship between GNSS satellite number PRN(i) and GNSS signal waveguide emission angle θ(i) and second frequency point multipath information M2(i) is constructed. The specific construction strategy of the first frequency point and the second frequency point multipath is shown in Table 1, and the behavior is GNSS satellite number, C represents Beidou system, the last two digits are Beidou satellite number, G represents GPS system, R represents GLONASS system, and E represents Galileo system; the column is GNSS signal waveguide emission angle θ, the GNSS signal waveguide emission angle θ ranges from-2° to +2°, and each interval is 0.2°. The values calculated by the above N GNSS occultation events are filled in the form of filling the table, and the GNSS signal waveguide emission angle rounding principle is used to fill the table. The first frequency point and the second frequency point multipath modeling table of GNSS occultation observation data is executed with reference to Table 1.

[0071] f) Eliminate the influence of multipath

[0072] Calculate the satellite number PRN1 corresponding to the GNSS occultation event and the corresponding GNSS signal waveguide emission angle θ1, find out the corresponding row of the specific PRN1 satellite system and satellite number from Table 1, and then find out the column closest to the GNSS signal waveguide emission angle θ1 from the column to confirm the multipath value. The first frequency point and the second frequency point are similar. In the process of calculating the atmospheric waveguide of GNSS occultation observation data, the first frequency point and the second frequency point corresponding to the multipath value obtained by searching the table are eliminated, the multipath effect introduced by GNSS occultation observation at sea is reduced, and the atmospheric waveguide processing precision and effect are improved.

[0073] Table 1 Multipath modeling table

[0074]

[0075] Advantages of the present application:

[0076] Optimize the multipath effect elimination algorithm of low altitude atmospheric duct signal processing based on GNSS occultation detection technology, reduce the influence of multipath effect on signal delay calculation, improve the accuracy of low altitude atmospheric duct calculation, and improve the application effect in radar detection, communication and navigation and the like.

[0077] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement and the like within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A GNSS occultation-based method for processing low-altitude atmospheric duct multipath, the method comprising: The method comprises the following steps: ​ S1, reading GNSS observation data; S2, calculating the GNSS signal waveguide exit angle; S3, extracting a GNSS occultation event near the sea; S4, estimating the multipath of each GNSS occultation event; S5, modeling the multipath according to the GNSS signal waveguide exit angle and the satellite number; S6, eliminating the influence of atmospheric waveguide multipath; In step S4, the multipath of each GNSS occultation event is estimated, comprising: 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) In the formula, P1 and P2 are the pseudoranges at the first frequency point and the second frequency point respectively, L1 and L2 are the carrier phases at the first frequency point and the second frequency point respectively, and γ1 and γ2 are the wavelengths corresponding to the first frequency point and the second frequency point respectively; In step S5, the multipath is modeled according to the GNSS signal waveguide exit angle and the satellite number, comprising: S51, based on steps S2 to S4, the relationship between the GNSS satellite number PRN(i) and the GNSS signal waveguide exit angle θ(i) and the first frequency point multipath value M1(i) is constructed, wherein i=1, 2, 3, …, N, the relationship among the three exists in the form of a multipath modeling table, and the data test process is not less than one week; S52, based on steps S2 to S4, the relationship between the GNSS satellite number PRN(i) and the GNSS signal waveguide exit angle θ(i) and the second frequency point multipath value M2(i) is constructed, wherein i=1, 2, 3, …, N, the relationship among the three exists in the form of a multipath modeling table, and the data test process is not less than one week; The format of the multipath modeling table is as follows: The column is the GNSS signal waveguide exit angle θ.

2. The GNSS occultation-based low-altitude coastal atmospheric duct multipath processing method according to claim 1, characterized in that: In step S1, the GNSS observation data is read, comprising: S11, the GNSS signal receiving device receives the GNSS signal and generates a GNSS observation event; S12, the time sequence, dual-frequency signal-to-noise ratio, dual-frequency carrier phase and dual-frequency pseudorange information of the GNSS observation event are obtained.

3. The GNSS occultation-based low-altitude coastal atmospheric duct multipath processing method according to claim 1, characterized in that: In step S2, the GNSS signal waveguide exit angle is calculated, comprising: S21, defining the GNSS signal waveguide exit angle as θ; S22, estimating the gain size G1 by using the GNSS signal intensity; S23, define the GNSS antenna gain pattern, the horizontal axis x is the angle, the vertical axis y is the gain size, make y=G1 parallel to the horizontal axis x straight line l , straight line l Intersect with the GNSS antenna gain pattern at A, B two points, draw a horizontal axis x vertical line through A point and intersect with the horizontal axis x at C point, draw a horizontal axis x vertical line through B point and intersect with the horizontal axis x at D point, the horizontal axis x value corresponding to C point, D point is the two estimated values of GNSS signal waveguide exit angle θ.

4. The GNSS occultation-based low-altitude coastal atmospheric duct multipath processing method according to claim 1, characterized in that: In step S3, the GNSS occultation event near the sea is extracted, comprising: S31, defining the GNSS occultation event judgment threshold R: -2°~+2°; S32, judging whether the GNSS observation event is a GNSS occultation event: if the GNSS signal waveguide exit angle θ of the GNSS observation event is within the range of the occultation event judgment threshold R, it is determined as a GNSS occultation event, otherwise, it is determined as a non-GNSS occultation event and is not processed.

5. The GNSS occultation-based low-altitude coastal atmospheric duct multipath processing method according to claim 1, characterized in that: The GNSS signal waveguide exit angle θ ranges from -2° to +2°, and there is a point every 0.2°; The GNSS signal waveguide exit angle θ is rounded to determine the column position.

6. The GNSS occultation-based low-altitude coastal atmospheric duct multipath processing method according to claim 2, characterized in that: The GNSS signal receiving device comprises a GNSS antenna, a GNSS near-sea low-altitude occultation receiver, and corresponding power supply and cables.

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