A method for detecting the D layer in the lower ionosphere based on dual-station signal inversion

Abstract

The invention discloses a method for detecting the D layer of the lower ionosphere based on dual-station signal inversion, and specifically relates to the technical field of low ionosphere detection. A magnetic loop antenna is used to receive VLF signals from dual communication stations, and the sampling frequency is 1 MHz. S2. After filtering and amplifying 8000 times, the received electrical signal is converted into a magnetic signal according to the law of electromagnetic induction, and then the magnetic signal is converted into an electrical signal in dBμ by using Maxwell's equations. S3. The angle and height of the transmitting antenna and the path information are used to obtain an arrival phase difference information table corresponding to each sharpness β and a virtual high H' value. S4. The sharpness β and the virtual high H' value of the point where the phase of the actual measured signal is closest to that of the simulated signal are obtained by looking up the table, and the path low ionosphere information is obtained. The invention can realize accurate detection of the D layer of the ionosphere at any time, solve the multi-value problem in amplitude positioning, and further improve the detection accuracy of the D layer of the ionosphere.

Description

Technical Field

[0001] The present invention relates to the field of low ionosphere detection, and in particular to a low ionosphere D layer detection method based on dual-station signal inversion. Background Art

[0002] The Earth's space environment is divided into the troposphere, stratosphere, mesosphere, thermosphere, ionosphere, plasmasphere, magnetosphere, and magnetopause, in order from the distance from the Earth's surface to the top of the magnetosphere, which is about 10 Earth radii from the Earth's center, according to the order from low to high distance from the Earth's surface and the atmospheric properties of each region. Among them, the ionosphere is an important region embedded in the Earth's neutral atmosphere and is an important link between the Sun and Earth's space environment. The formation of the ionosphere is mainly the result of the interaction between cosmic rays and high-energy particles and the atomic nuclei and molecules of the Earth's upper atmosphere, which ionizes the atmosphere. The altitude range is about 60-1000km from the ground (Liu Xuanmou, 1994). In this region of the ionosphere, there are electrons, ions, and neutral particles that are sufficient to reflect electromagnetic waves. Different electron concentrations will have different degrees of impact on the propagation of radio waves. According to the electron concentration, the ionosphere can be divided into three regions: D layer, E layer and F layer, with corresponding altitudes of 60-90km, 90-130km and 130-1000km respectively. Common detection methods include rocket on-site detection and very low frequency wave remote sensing detection.

[0003] The D layer is located at the bottom 60-90km of the ionosphere. The main ionization source is solar radiation, so it has obvious daily and seasonal variations. The electron collision frequency of this layer is approximately equal to the electron magnetic rotation frequency. It absorbs radio electromagnetic waves severely during the day and disappears at night as solar radiation weakens. The electron concentration in this layer is low, and it is difficult to detect with traditional high-frequency vertical survey instruments. The electron collision frequency of this layer is approximately equal to the electron magnetic rotation frequency. It absorbs radio electromagnetic waves severely during the day and disappears at night as solar radiation weakens. The electron concentration in this layer is low, and it is difficult to detect with traditional high-frequency vertical survey instruments. Common detection methods include rocket on-site detection and very low frequency wave remote sensing detection. In rocket detection, Langmuir probes and other methods are used to conduct field detection of the ionosphere. In remote sensing detection, the frequency band of very low frequency waves (VLF) is 3-30kHz, which can be propagated over long distances in a waveguide composed of the ground and the ionosphere. It has the characteristics of low loss and stable phase, and is suitable as a detection signal for inversion of the D region of the ionosphere.

[0004] In very low frequency communication systems, the technical difficulty or executable difficulty is the transmitting antenna. The size of the antenna radiating VLF must be designed according to the wavelength of VLF. The wavelength of VLF is 3kHz-30kHz, and the corresponding wavelength range is between 100km-10km. Most very low frequency artificial station transmitters use vertical monopole antenna arrays, and large transmission towers are built on large valleys or plains to construct antenna arrays for installation; at the same time, due to the long wavelength, even if a large antenna array is built, the radiation efficiency of the antenna is still very low. In order to obtain greater power and radiation efficiency, the transmitting antenna array used for very low frequency communications is usually large and the construction cost is extremely high.

[0005] At present, there are many transmitting stations in the world that transmit and study the properties of VLF transmission through the ionosphere, and a series of inversion studies have been conducted. Some of these studies explore the impact of the lower ionosphere D layer on signal (VLF / LF) propagation. This method uses the received VLF transmitting station signal to compare with the simulated signal to invert the ionosphere D layer information.

[0006] When lightning occurs, most of the very low frequency electromagnetic waves radiated are propagated to all parts of the world through the Earth-ionosphere waveguide. In the data processing of the receiver, it is called "skylightning" signal. It is also possible to use the signal of the lightning source to first determine the location of the lightning, and then measure the time delay of the received lightning signal to determine the height of the reflection point, and then obtain ionospheric information.

[0007] The application document with patent number CN106646477B discloses a D-layer ionospheric detection system and method based on multi-station lightning low-frequency pulse signals. The system includes: at least two lightning low-frequency pulse signal detection and collection devices connected in communication and a central processing device; each lightning low-frequency pulse signal detection and collection device is used to detect and collect lightning low-frequency pulse signals and process them to obtain sky wave ground wave pulse pairs and their time and arrival time difference; the central processing device is used to invert the height of the D-layer ionospheric layer according to the relationship between the arrival time difference and the path difference of the sky wave and the ground wave. The present invention uses lightning discharge as a radiation source, and there is no need to artificially generate high-power VLF / LF electromagnetic waves, which greatly saves energy. In addition, since lightning discharges can occur in different locations around the world, the height of the ionosphere at different locations can be measured by reasonably adjusting the position of the lightning low-frequency pulse signal detection and collection device, which can be widely promoted and applied, and improve the adaptability and utilization rate of the D-layer ionospheric detection system.

[0008] The prior art solution of directly launching a sounding rocket is costly and cannot detect for a long time. The indirect detection using a VLF transmitter is costly and cannot solve the multi-value problem of parameters. Summary of the invention

[0009] The object of the present invention is to provide a method for detecting the D layer of the lower ionosphere based on dual-station signal inversion to solve the problems raised in the above-mentioned background technology.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The lower ionosphere D layer detection method based on dual-station signal inversion is as follows:

[0012] S1. Use magnetic loop antenna to receive VLF signals from dual communication stations, with a sampling frequency of 1MHz;

[0013] S2. After filtering and amplifying 8000 times, the received electrical signal is converted into a magnetic signal according to the law of electromagnetic induction, and then the magnetic signal is converted into an electrical signal in dBμ using Maxwell's equations;

[0014] S3. The transmitting antenna angle, height, and path information are used to obtain the arrival phase difference information table corresponding to each sharpness β and virtual high H' value;

[0015] S4. Look up the table to obtain the sharpness β and the virtual height H' value of the point where the phase of the measured and simulated signals is closest, and obtain the path low ionosphere information.

[0016] The path information is described using the sharpness β and the false height H'.

[0017] The electron density model of the lower ionosphere is expressed as: n e (h) = 1.43 × 10 7 ×exp(-0.15H)×exp[(β-0.15)(hH)], where h is the ionosphere height, sharpness β and virtual height H' are the required parameters.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention uses the amplitude information of a dual-station transmission signal source with mature technology, known site locations, and continuous and stable transmission time. Compared with natural sources (lightning sources, etc.), the present invention has the characteristics of stable transmission signals and known transmission source locations. It can realize accurate detection of the ionospheric D layer at any time, solve the multi-value problem in amplitude positioning, and further improve the detection accuracy of the ionospheric D layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the present invention;

[0021] Figure 2 A screenshot of a dual-station amplitude forward table of a receiving position in an embodiment of the present invention; DETAILED DESCRIPTION

[0022] Example

[0023] like Figure 1-2 As shown, a magnetic loop antenna is used to receive VLF signals from dual communication stations with a sampling frequency of 1MHz. After filtering and amplifying 8000 times, the received electrical signal is converted into a magnetic signal according to the law of electromagnetic induction, and then the magnetic signal is converted into an electrical signal in dBμ using Maxwell's equations. The transmitting antenna angle, height, and path information (described by sharpness β and virtual height H') are used to obtain the arrival phase difference information table corresponding to each sharpness β and virtual height H' value. Then, the sharpness β and virtual height H' values ​​of the points where the phases of the measured and simulated signals are closest are obtained by looking up the table to obtain the path low ionosphere information.

[0024] The LWPC model is used to forward model the arrival sky wave phase difference under different parameters, and the path ionospheric information is obtained by comparing it with the measured signal phase.

[0025] The ionosphere model used by LWPC is the ionosphere model proposed by (Wait, 1964) to describe the ionosphere state through the horizontal conductivity at different altitudes. v(h) represents the collision frequency of electrons and neutral particles at different altitudes (considering the ionosphere D layer). According to the research of (Belrose, 1964) and (Kane, 1961), the electron density in the lower ionosphere is: n e (h) = 1.43 × 10 7 ×exp(-0.15H')×exp[(β-0.15)(hH')], where h is the ionosphere height, sharpness β and virtual height H' are the required parameters.

[0026] The LWPC program can calculate the forward table of the dual-station amplitude at the receiving position by inputting the path information, sharpness β and virtual height H'. From this figure, it can be found that the amplitude does not change monotonically with the ionospheric parameters, which is also one of the main characteristics of waveguide mode propagation. Therefore, using only the amplitude information of a single station will inevitably encounter the problem of corresponding multiple values. Then find the parameter value that is closest to the phase of the measured signal simulated by the LWPC program to invert the ionospheric information, and you can get the information on the propagation path; similarly, when there is an ionospheric disturbance, the dual-station inversion can effectively solve the distinction between anomalies and errors. This method can also be extended to the multi-station inversion of the ionosphere.

Claims

1. The D-layer detection method of the lower ionosphere based on the inversion of dual-station signals, It is characterized in that Here are the steps: S1. Use magnetic loop antenna to receive VLF signals from dual communication stations with a sampling frequency of 1MHz; S2. After filtering and amplification, the received electrical signal is converted into a magnetic signal according to the law of electromagnetic induction, and then the magnetic signal is converted into an electrical signal using Maxwell's equations; S3. The transmitting antenna angle, height, and path information are used to obtain the arrival phase difference information table corresponding to each sharpness β and virtual high H' value; S4. Look up the table to obtain the sharpness β and the virtual height H' value of the point where the phase of the measured and simulated signals is closest, and obtain the path low ionosphere information.

2. The path information according to claim 1 is based on the dual-station signal inversion method for detecting the lower ionosphere D layer, It is characterized in that The path information is described using the sharpness β and the false height H'.

3. The method for detecting the lower ionosphere D layer based on the dual-station signal inversion of the path information according to claim 1, It is characterized in that The electron density model of the lower ionosphere is expressed as: n e (h) = 1.43 × 10 7 ×exp(-0.15H')×exp[(β-0.15)(h-H')], where h is the ionosphere height, sharpness β and virtual height H' are the required parameters.

4. The method for detecting the lower ionosphere D layer based on the dual-station signal inversion of the path information according to claim 1, It is characterized in that The VLF signal amplification factor is 8000 times.

5. The method for detecting the lower ionosphere D layer based on the dual-station signal inversion of the path information according to claim 1, It is characterized in that Convert magnetic signals into electrical signals in dBμ.

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