Method for constructing ionospheric scintillation index based on GNSS doppler observations

Abstract

The application discloses a method for constructing an ionospheric scintillation index based on GNSS Doppler observation values, and belongs to the field of space weather monitoring. The method first acquires GNSS Doppler observation values from sites such as IGS / MGEX monitoring stations, then extracts ionospheric scintillation information from the Doppler observation values, and constructs ionospheric scintillation indexes DI one by one epoch by using a sliding window method. The availability of the scintillation indexes constructed by ionospheric scintillation receiver products and geodetic GNSS receivers is analyzed, and finally the threshold values of DI indexes of different types of GNSS receivers are given. The method can reduce the cost of ionospheric scintillation monitoring, and has the characteristics of simplicity, reliability and practicality by constructing the scintillation indexes based on the Doppler observation values of the globally widely distributed ordinary geodetic receivers for ionospheric scintillation monitoring.

Description

Technical Field

[0001] This invention belongs to the field of GNSS space weather monitoring technology, and relates to a method for monitoring ionospheric scintillation using Global Navigation Satellite System (GNSS), and particularly to a method for constructing an ionospheric scintillation index based on GNSS Doppler observations. Background Technology

[0002] Ionospheric scintillation refers to the phenomenon of rapid, random fluctuations in the amplitude and phase of radio signals passing through irregularities in the ionosphere. It affects GNSS high-precision positioning, navigation, and timing services. With the arrival of the solar activity peak of the 25th solar cycle, the probability and intensity of ionospheric scintillation, which is closely related to solar activity, will also increase. Therefore, conducting ionospheric scintillation monitoring and early warning is of significant practical importance.

[0003] The ionospheric scintillation monitoring receiver (ISMR) provides the amplitude scintillation index S4 and the phase scintillation index through 50Hz sampling. However, due to its high deployment cost, there are only about a hundred units worldwide. With the development of GNSS technology and the continuous construction of ground monitoring stations, international and regional organizations, represented by IGS / MGEX, can provide GNSS measurement data from nearly 2,000 stations worldwide, providing rich observational information for ionospheric scintillation monitoring.

[0004] In 1997, Pi proposed the concept of the rate of change of total electron content in the ionosphere (ROTI). Building upon this, numerous scholars have proposed various ionospheric scintillation indices based on GNSS phase observations. Mendillo proposed f[…] in 2000. p Index; proposed by Forte in 2005 The index; Sanz proposed the AATR index in 2014 and Juan proposed the σ index in 2017. IF In addition, Luo constructed the amplitude scintillation index S in 2020 using carrier noise density observations from a 1Hz geodesic GNSS receiver. 4c The construction of these indices demonstrates the feasibility of using data from globally distributed geodesic receivers for ionospheric scintillation monitoring.

[0005] Currently, the ROTI index is widely used in ionospheric scintillation monitoring. However, during data preprocessing, the ROTI index needs to be constructed based on correctly detected and repaired cycle slip carrier phase observations. Incorrect cycle slip handling can lead to an overestimation of the ROTI value, affecting the reliability of the corresponding ionospheric scintillation monitoring. Furthermore, unsuccessful cycle slip repair may result in the rejection of ROTI observations, which is detrimental to the continuity of ionospheric scintillation monitoring. Effectively handling cycle slips remains one of the challenges in the GNSS field. Summary of the Invention

[0006] In the context of strong ionospheric scintillation environments, frequent cycle slips can affect the usability of the ROTI index. This invention utilizes the characteristic that Doppler observations are unaffected by cycle slips to provide a method for constructing the ionospheric scintillation index based on GNSS Doppler observations.

[0007] To achieve the above objectives, this invention provides a method for constructing the ionospheric scintillation index based on GNSS Doppler observations, comprising:

[0008] (1) Obtain GNSS observations from regions at different latitudes;

[0009] (2) Perform data preprocessing on the acquired GNSS observations to obtain the elevation angles of all satellites over the station, and set the cutoff satellite elevation angles;

[0010] (3) Extract ionospheric scintillation information from GNSS Doppler observations above the cutoff satellite elevation angle, and construct the ionospheric scintillation index DI for each epoch using the sliding window method;

[0011] (4) The availability of the ionospheric scintillation index DI was analyzed using the scintillation index constructed by ionospheric scintillation receiver products and geodesic GNSS receivers, and the threshold values ​​of the DI index for different types of GNSS receivers were given.

[0012] In some alternative implementations, step (2) includes:

[0013] (2.1) Complete the merging and reading of GNSS high sampling rate observation data;

[0014] (2.2) Read the broadcast ephemeris parameters and calculate the approximate position of the satellite in the observed epoch using the broadcast ephemeris parameters;

[0015] (2.3) Obtain the precise WGS-84 coordinates of the station using precise single-point positioning technology;

[0016] (2.4) Based on the approximate position of the satellite and the precise coordinates of WGS-84, calculate the elevation angle of all satellites above the station, set the cutoff satellite elevation angle, and extract the GNSS Doppler observations above the cutoff satellite elevation angle.

[0017] In some alternative implementations, the mathematical expression for GNSS Doppler observations is: λ1 and λ2 are the wavelengths of the GNSS signal frequencies f1 and f2, respectively; D1 is the Doppler observation value of the GNSS signal frequency f1; and D2 is the Doppler observation value of the GNSS signal frequency f2. The rate of change of the geometric distance between the satellite and the receiver at GNSS signal frequency f1. This represents the rate of change of the geometric distance between the satellite and the receiver at the GNSS signal frequency f2. and These represent the rates of change of GNSS receiver clock bias and satellite clock bias, respectively. The rate of change of ionospheric delay error at GNSS signal frequency f1. This represents the rate of change of ionospheric delay error at GNSS signal frequency f2. ε1 represents the rate of change of tropospheric delay error, ε2 represents the multipath effect and error at GNSS signal frequency f1, and c represents the speed of light in vacuum.

[0018] In some alternative implementations, step (3) includes:

[0019] (3.1) The GNSS Doppler observations above the cutoff satellite elevation angle are combined into a dual-frequency Doppler observation combination ΔD;

[0020] (3.2) Select the length of the sliding window and the time limit of 5 minutes;

[0021] (3.3) Based on the sliding window, the scintillation index DI is calculated epoch by epoch from the combination of dual-frequency Doppler observations ΔD.

[0022] In some alternative implementations, ΔD = λ1D1 - λ2D2.

[0023] In some alternative implementations, <> represents the average operation.

[0024] In some alternative implementations, step (4) includes:

[0025] (4.1) Calculate the DI and ROTI indices of the geodesic receiver;

[0026] (4.2) Calculate the DI of the scintillation receiver and obtain the scintillation index S4.

[0027] (4.3) Conduct comparative analysis of the scintillation indices of different types of receivers and statistically analyze the DI on non-scintillation days;

[0028] (4.4) Construct empirical thresholds for DI under different types of receivers.

[0029] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0030] 1. A new ionospheric scintillation index (DI) based on dual-frequency Doppler observations was constructed using GNSS Doppler observations unaffected by cycle slips, which has significant practical value. Compared to ROTI, this index avoids the overestimation or discontinuity of the ROTI index caused by frequent cycle slips in strong scintillation environments.

[0031] 2. Compared with professional scintillation receivers, the ionospheric scintillation index DI constructed based on Doppler observations from ordinary geodesic GNSS receivers can reduce the cost of ionospheric scintillation monitoring and has certain practical value. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the construction of a scintillation index (DI) according to an embodiment of the present invention.

[0033] Figure 2 This is a time series of Doppler observations, ΔD, and DI provided in an embodiment of the present invention;

[0034] Figure 3 This invention provides a flicker index DI and S4. Comparison chart of ROTI;

[0035] Figure 4 This invention provides a flicker index DI and S4. The correlation of ROTI. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The specific process of the implementation scheme of the present invention is as follows: Figure 1 As shown, the processing steps include the following:

[0038] Step 1: Collect GNSS tracking station data from different latitude regions around the world based on reference station networks such as IGS network, MGEX network, BeiDou ground-based augmentation network or land-based network;

[0039] Step 2: Data preprocessing, which can be implemented in the following ways:

[0040] (2.1) Complete the merging and reading of GNSS high sampling rate observation data;

[0041] (2.2) Read the broadcast ephemeris parameters and calculate the approximate position of the satellite in the observed epoch using the broadcast ephemeris parameters;

[0042] (2.3) Obtain the precise WGS-84 coordinates of the station using precise single-point positioning technology;

[0043] (2.4) Based on the approximate position of the satellite and the precise coordinates of WGS-84, calculate the elevation angle of all satellites above the station, set the cutoff satellite elevation angle, and extract the GNSS Doppler observations above the cutoff satellite elevation angle.

[0044] The mathematical expression for the Doppler observations is as follows:

[0045]

[0046] In equation (1), λ1 and λ2 are the wavelengths of the GNSS signal frequencies f1 and f2, respectively. D is the Doppler observation value. This represents the rate of change of the geometric distance between the satellite and the receiver. and These represent the rates of change of GNSS receiver clock bias and satellite clock bias, respectively. and ε represents the rate of change of ionospheric delay error and tropospheric delay error, respectively. ε represents the multipath effect and error.

[0047] Step 3: Constructing the flicker index DI, which can be achieved in the following way:

[0048] (3.1) The GNSS Doppler observations above the cutoff satellite elevation angle are combined to form a dual-frequency Doppler observation combination ΔD, the mathematical expression of which is:

[0049] ΔD=λ1D1-λ2D2 (2)

[0050] (3.2) Select a sliding window length of 5 minutes;

[0051] (3.3) Calculate the scintillation index DI epoch by epoch. The mathematical expression for DI is:

[0052]

[0053] In the formula, <> represents the average value operation.

[0054] Step 4: Analyze the availability of the DI index and establish empirical thresholds for DI based on different types of receivers. This can be achieved in the following ways:

[0055] (4.1) Calculate the DI and ROTI indices for the geodesic receiver, where the mathematical expression for ROTI is:

[0056]

[0057]

[0058] In the formula, Δt represents the GNSS carrier phase observation. i is the observation epoch. Δt is the epoch difference.

[0059] (4.2) Calculate the DI of the scintillation receiver and obtain the scintillation index S4. S4 and The mathematical expressions are as follows:

[0060]

[0061]

[0062] In the formula, SI det , These are the observed signal strength and carrier phase values ​​after detrending, respectively.

[0063] (4.3) Comparative analysis of various scintillation indices for different types of receivers (e.g.) Figure 2 and Figure 3 (As shown), the DI for non-scintillation days is statistically analyzed;

[0064] (4.4) Construct empirical thresholds for DI under different types of receivers.

[0065] Step 5: Analyze the DI index and the commonly used flicker index S4. and the correlation of ROTI (e.g.) Figure 4 (As shown).

[0066] The present invention constructs the ionospheric scintillation index DI using Doppler observations that are unaffected by cycle slips through the above-mentioned technical solution. Compared with the commonly used scintillation index ROTI, the DI index avoids the situation where the ROTI index is overestimated or becomes discontinuous due to frequent cycle slips in strong scintillation environments.

[0067] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0068] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing an ionospheric scintillation index based on GNSS Doppler observations, characterized in that, Comprise: (1) Obtain GNSS observation values in different latitude regions; (2) Data preprocessing is carried out on the obtained GNSS observation values to obtain the elevation angles of all satellites above the station, and the cut-off satellite elevation angle is set; (3) Extract ionospheric scintillation information from GNSS Doppler observations above the cut-off satellite elevation angle, and construct ionospheric scintillation index by sliding window method epoch by epoch DI ; (4) The availability of ionospheric scintillation index is analyzed by using scintillation index of ionospheric scintillation receiver products and geodetic GNSS receivers, and the threshold values of different types of GNSS receiver index are given. DI DI index is analyzed by using scintillation index of ionospheric scintillation receiver products and geodetic GNSS receivers, and the threshold values of different types of GNSS receiver index are given.​ wherein the construction of the flicker index in step (3) is achieved by the following way: (3.1) form a dual-frequency Doppler observation combination from the GNSS Doppler observations above the cut-off satellite elevation angle , , and are the wavelengths of the GNSS signal frequencies and , is the Doppler observation for the GNSS signal frequency , is the Doppler observation for the GNSS signal frequency ; (3.2) Select the length of the sliding window; (3.3) Calculate the flicker index per epoch , , < > is the averaging operation; Step (4) is realized by the following way: (4.1) Computing a Geodetic Receiver with the ROTI index, where, , , is a GNSS carrier phase observation, is an observation epoch, is an epoch difference; (4.2) Computing a flicker receiver , obtaining a flicker index with , , , , are the detrended signal strength and carrier phase observations, respectively. (4.3) Comparison and analysis of the different types of receiver each flicker index, statistics of non-flickering day ; (4.4) The empirical threshold values are constructed for different types of receivers under the assumption that the receiver is not in the vicinity of a jammer.

2. The method of claim 1, wherein, Step (2) comprises: (2.1) Complete the merging and reading of GNSS high sampling rate observation data; (2.2) Read the broadcast ephemeris parameters, and calculate the approximate position of the satellite at the observation epoch through the broadcast ephemeris parameters; (2.3) Obtain the WGS-84 precise coordinates of the station through precise point positioning technology; (2.4) Based on the approximate position of the satellite and the WGS-84 precise coordinates, the elevation angles of all satellites above the station are calculated, the cut-off satellite elevation angle is set, and the GNSS Doppler observation values above the cut-off satellite elevation angle are intercepted.

3. The method of claim 2, wherein, The mathematical expression of GNSS Doppler observations is: , and are the wavelengths of GNSS signal frequencies and respectively, is the Doppler observation of GNSS signal frequency , is the Doppler observation of GNSS signal frequency , is the rate of change of the geometric distance between the satellite and the receiver at GNSS signal frequency , is the rate of change of the geometric distance between the satellite and the receiver at GNSS signal frequency , and are the rates of change of GNSS receiver clock error and satellite clock error respectively, is the rate of change of ionospheric delay error at GNSS signal frequency , is the rate of change of ionospheric delay error at GNSS signal frequency , is the rate of change of tropospheric delay error, is the multipath effect and error at GNSS signal frequency , is the multipath effect and error at GNSS signal frequency , is the propagation speed of light in vacuum.

Images