CN113093189B - Ionospheric tomography method for improving iteration initial value precision - Google Patents
Ionospheric tomography method for improving iteration initial value precision Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
- G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/42—Determining position
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
- G01T1/2914—Measurement of spatial distribution of radiation
- G01T1/2985—In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis)
Abstract
The invention relates to an ionospheric tomography method, computer equipment and a computer-readable storage medium for improving the accuracy of an iterative initial value, wherein the method comprises the following steps: dividing the ionization layer area into a plurality of grids, and determining the coordinates and the initial value of electron density of each grid; a plurality of vertical measuring instruments are arranged below the ionized layer area at intervals, and the vertical electron density of a plurality of different points is determined by utilizing the vertical measuring instruments and combining satellite-borne full-polarization SAR data; updating the electron density initial value of the corresponding grid; acquiring a plurality of rays of different paths by using a GPS (global positioning system) and inverting the TEC value corresponding to each ray; calculating the projection length of each ray in each grid; and carrying out tomography iterative inversion based on a multiplicative algebraic reconstruction method, and obtaining the electron density distribution in the ionization layer region after multiple iterations. The ionosphere IRI empirical model data is corrected by using the vertical measuring instrument and the satellite-borne full-polarization SAR data, so that the authenticity of an iteration initial value is improved, and the ionosphere tomography precision can be improved.
Description
Technical Field
The invention relates to the technical field of radar detection, in particular to an ionosphere tomography method, computer equipment and a computer readable storage medium for improving iteration initial value precision.
Background
The ionosphere is an important component of the world-space environment and can contribute significantly to low frequency signals passing through it, such as global navigation system (GPS) signals. Meanwhile, because signals contain abundant ionospheric information, ionospheric sounding based on GPS signals is the most widely used ionospheric sounding technique at present. The ionosphere tomography (CIT) based on GPS signals can receive echo information through a receiving station positioned on the ground, invert the Total Electron Content (TEC) of a path, and further solve the electron density distribution condition in an ionosphere region through iterative calculation.
The accuracy of CIT is determined to a large extent by iterative initial values, which are determined based on an ionosphere IRI empirical model in the currently common method. However, the ionosphere IRI empirical model is obtained based on a large amount of historical data, and cannot well reflect the current and future spatial electron density distribution conditions, so that the large error affects the CIT reconstruction accuracy, and a more real and accurate electron density value is difficult to obtain.
Disclosure of Invention
Technical problem to be solved
The invention aims to solve the technical problem that the reliability of an iteration initial value determined by an ionosphere tomography method based on an ionosphere IRI empirical model is poor, so that the electron density measurement accuracy is low in the prior art.
(II) technical scheme
In order to solve the technical problem, the invention provides an ionosphere tomography method for improving the accuracy of an iteration initial value, which comprises the following steps:
s1, dividing an ionized layer region into a plurality of grids, determining the coordinate of each grid, and determining the initial value of the electron density of each grid based on an ionized layer IRI empirical model;
s2, arranging a plurality of vertical measuring instruments at intervals below the ionosphere area, and determining the vertical electron density of a plurality of different points by using the vertical measuring instruments in combination with satellite-borne full-polarization SAR data;
s3, updating the initial electron density value of the corresponding grid according to the vertical electron density determined by combining the vertical measuring instrument with the satellite-borne fully-polarized SAR data;
s4, acquiring a plurality of rays of different paths by using the GPS, inverting TEC values corresponding to the rays, and respectively recording GPS satellite coordinates and receiving station coordinates during GPS detection;
s5, calculating the projection length of each ray in each grid;
and S6, carrying out tomography iterative inversion based on a multiplicative algebraic reconstruction method by utilizing the initial electron density value of each grid, the projection length of each ray in each grid and the TEC value corresponding to each ray, and obtaining the electron density distribution of the ionization layer region after multiple iterations.
Preferably, in step S2, when the vertical measuring instrument is used to determine the vertical electron densities of multiple different points in combination with the satellite-borne fully-polarized SAR data, the vertical measuring instrument directly measures the electron density information below the ionospheric peak height to obtain the corresponding vertical electron density, and the alpha-Chapman model is used to calculate the corresponding vertical electron density in combination with the vertical measuring instrument and the satellite-borne fully-polarized SAR data for the electron density information at and above the ionospheric peak height.
Preferably, in step S2, the α -Chapman model includes:
wherein N (h) represents the electron density at height h, z represents the virtual height, N m F 2 Is the peak height h m F 2 Electron density of (b), H T The elevation is indicated.
Preferably, in the step S2, when the corresponding vertical electron density is calculated by combining the α -Chapman model with the vertical meter and the satellite-borne fully-polarized SAR data, the elevation H is calculated by combining the vertical meter with the satellite-borne fully-polarized SAR data T The method comprises the following steps:
firstly, detecting each vertical measuring instrument on the ground by using a satellite-borne full-polarization SAR, determining a plurality of rays corresponding to the SAR by using satellite-borne full-polarization SAR data, and determining a total TEC value TEC corresponding to each ray SAR ；
Secondly, determining total electron content TEC from the upper section of the ionization layer region to the height of the SAR satellite T ，TEC T Equal to the corresponding total TEC value TEC SAR Subtracting the TEC value of the lower section of the ionized layer region measured by the vertical measuring instrument;
finally, according to the elevation H T Total electron content TEC from upper section of ionization layer region to height of SAR satellite T The altitude H is calculated according to the relation between the altitude H and the altitude H T 。
Preferably, in step S2, for the ray corresponding to the SAR, the total TEC value TEC corresponding to each ray is determined by the following formula SAR ：
Wherein f represents the carrier frequency of the satellite-borne fully-polarized SAR, B represents the geomagnetic field intensity in an ionization layer region, theta represents the included angle between the geomagnetic field in the ionization layer region and the satellite-borne fully-polarized SAR signal, and omega represents the Faraday rotation angle offset caused by the ionization layer region.
Preferably, in the step S2, the altitude H is determined according to T Total electron content TEC from upper section of ionization layer region to height of SAR satellite T The elevation H is calculated by the relation between T When, the relation is:
wherein H s Is the SAR satellite altitude.
Preferably, in step S6, when tomographic iterative inversion is performed based on a multiplicative algebraic reconstruction method, an iterative formula is as follows:
wherein N is ej k+1 Represents the electron density of the jth grid at the (k + 1) th iteration，TEC m Indicating the TEC value corresponding to the m-th ray,<·>represents the inner product, | | · | | | represents the norm,
is A m Transpose of (A) m Is represented by a matrix { A } mj The vector formed by the m-th row elements, the matrix { A } mj Element A of the mth row and jth column mj Represents the projection length of the mth ray in the jth grid, N e k Represents the electron density distribution, λ, of all n grids obtained at the k-th iteration k Is an iterative relaxation factor with the value range of 0 to lambda k ≤1。
Preferably, in step S6, after at least 5 iterations, the electron density distribution in the ionization region is obtained.
The invention also provides computer equipment which comprises a memory and a processor, wherein the memory stores a computer program, and the processor realizes the steps of the ionospheric tomography method for improving the accuracy of the initial iteration value when executing the computer program.
The present invention also provides a computer readable storage medium having stored thereon a computer program which, when being executed by a processor, implements the steps of any of the above-mentioned methods for ionospheric tomography with improved accuracy of initial values for iteration.
(III) advantageous effects
The technical scheme of the invention has the following advantages: the invention provides an ionosphere tomography method, computer equipment and a computer readable storage medium for improving the accuracy of an iterative initial value. The ionosphere IRI empirical model data is corrected by using the vertical measuring instrument and the satellite-borne full-polarization SAR data, so that the authenticity and the accuracy of an iterative initial value are improved, the ionosphere tomography precision can be improved, and a more accurate space electron density distribution condition is obtained.
Drawings
FIG. 1 is a schematic diagram of a step of an ionospheric tomography method with improved iteration initial value accuracy according to an embodiment of the present invention;
FIG. 2 is a schematic illustration of the electron concentration profile of the ionosphere;
FIG. 3 is a schematic diagram of ionosphere regions and rays in an embodiment of the present invention;
fig. 4 (a) to 4 (c) are simulation image results; wherein, fig. 4 (a) is ionospheric tomography under the real distribution condition, and fig. 4 (b) is ionospheric tomography of the method provided by the present invention; FIG. 4 (c) is an ionospheric tomography image with an initial electron density determined for a conventional empirical model of ionospheric IRI.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
As shown in fig. 1 to fig. 3, an ionospheric tomography method for improving accuracy of an initial iteration value according to an embodiment of the present invention includes the following steps:
s1, dividing an ionosphere region to be detected into a plurality of grids, determining the coordinates of each grid, and determining an initial electron density value (namely an iteration initial value) of each grid based on an ionosphere IRI empirical model.
As shown in fig. 3, in step S1, it is preferable to perform average segmentation to obtain each grid, where the total number of the segmented grids is n, n is a positive integer, and a specific value of n may be selected according to the size of the ionization region to be detected and the required detection accuracy, which is not further limited herein.
And S2, arranging a plurality of vertical measuring instruments at intervals below the ionosphere region, and determining the vertical electron density of a plurality of different points by using the vertical measuring instruments in combination with satellite-borne full-polarization SAR data.
Ideally, one vertical measuring instrument is arranged below each grid distributed in the horizontal direction, cost is considered in practical situations, a large number of vertical measuring instruments cannot be arranged on the ground, no less than 4 vertical measuring instruments are preferably arranged in step S2 and are arranged right below the central part of the ionosphere area as far as possible, the interval between the vertical measuring instruments is preferably consistent with the interval between the grids distributed in the horizontal direction, if the interval between the centers of the grids distributed in the horizontal direction is 10km, the interval between two vertical measuring instruments is also set to be 10km, and one vertical measuring instrument corresponds to a series of grids in the vertical direction.
And S3, updating the initial electronic density value of the corresponding grid determined based on the ionosphere IRI empirical model in the step S1 according to the vertical electronic density determined by combining the vertical measuring instrument with the satellite-borne full-polarization SAR data in the step S2 to obtain the updated initial electronic density value.
The threshold is preferably set in step S3, for example, the threshold may be set to 1e 9 /m 3 And if the difference between the vertical electron density determined by combining the vertical measuring instrument with the satellite-borne fully-polarized SAR data and the initial electron density value determined based on the ionosphere IRI empirical model is larger than a set threshold value, correcting the initial electron density value of the corresponding grid by using the vertical electron density determined by combining the vertical measuring instrument with the satellite-borne fully-polarized SAR data. Theoretically, the more grids are iterated, the closer the corrected initial electron density value is to the actual condition distribution. In practical situations, cost is considered, each grid iteration initial value of the central part of the ionized layer region is updated by using the finite table vertical measuring instrument, and the ionosphere tomography precision can be effectively improved.
And S4, acquiring a plurality of rays of different paths by using the GPS, inverting the TEC value corresponding to each ray, and respectively recording the GPS satellite coordinate and the receiving station coordinate during GPS detection.
In step S4, as shown in fig. 3, if the ground includes L receiving stations, L rays in different paths can be obtained in each GPS detection, and a total of M × L rays in different paths can be obtained when a GPS satellite detects in M different positions, where each ray has a corresponding TEC value according to a different specific path through the ionization region. Preferably, the value of M should be as large as or equal to the number of horizontal grids after the ionosphere region is segmented, so as to ensure the imaging accuracy of the ionosphere tomography method.
And S5, calculating the projection length of each ray in each grid.
In step S5, as shown in fig. 3, after determining the coordinates of each receiving station and the coordinates of the GPS satellite during detection, the path position of each ray can be determined, and the projection length a of each ray in each grid can be calculated according to the geometric relationship mj I.e. the projection length of the mth ray (path) on the jth grid.
S6, carrying out tomography iterative inversion based on a multiplicative algebraic reconstruction method by using the (updated) initial electron density value of each grid, the projection length of each ray in each grid and the TEC value corresponding to each ray, and obtaining the electron density distribution of the ionization region after multiple iterations.
The electron concentration of the spatial ionosphere is generally distributed as shown in fig. 2, with the electron density value being maximum around 300km, and decreasing in the upward and downward electron concentrations. The ground vertical measurer continuously emits a group of electromagnetic waves vertically upwards, and the critical frequency of the ionized layer with different heights can be calculated as follows because the electron density of the ionized layer changes along with the height:
wherein the critical frequency f 0 Expressed as the frequency at which the electron concentration returns to the ground when the electromagnetic wave is projected perpendicularly, the electromagnetic wave penetrates the layer when the frequency of the emitted electromagnetic wave exceeds a critical frequency. As shown in FIG. 2, the peak value of the electron density of the ionized layer is about 300km in height, i.e. the critical frequency is the maximum point, and when the electromagnetic wave is greater than the maximum critical frequency, the electromagnetic wave is greater than the maximum critical frequencyThe whole ionosphere can be penetrated, and the echo information can not be received by the ground vertical measuring instrument.
Preferably, in step S2, when the vertical measuring instrument is used to determine the vertical electron density of a plurality of different points in combination with the satellite-borne fully-polarized SAR data, the vertical measuring instrument directly measures the electron density information below the ionospheric peak height to obtain the corresponding vertical electron density, and the alpha-Chapman model is used to calculate the corresponding vertical electron density in combination with the vertical measuring instrument and the satellite-borne fully-polarized SAR data for the electron density information at the ionospheric peak height and above.
Because the ground vertical measuring instrument can only directly measure echo information below the ionosphere peak height, the one-dimensional electron density distribution condition above the ionosphere peak height needs to be reversely deduced, and for the electron density above the peak, a commonly used deduction model is an alpha-Chapman model.
Further, in step S2, the α -Chapman model includes:
wherein N (h) represents the electron density at height h, z represents the virtual height, N m F 2 Is the peak height h m F 2 Electron density of (i) h m F 2 Denotes the peak height, N m F 2 Represents the peak electron density, N m F 2 、h m F 2 All can be directly measured by a plumb measuring instrument, H T The elevation is indicated.
Height mark H in traditional method T The method is obtained by calculating the electronic density data of the lower section of the vertical measuring instrument, but the method does not use any upper section information and is difficult to ensure the precision, so the method introduces the upper section information of the ionization layer region by fusing satellite-borne fully-polarized SAR data.
Preferably, in step S2, when the corresponding vertical electron density is calculated by combining the α -Chapman model with the plumb bob instrument and the satellite-borne fully-polarized SAR data, the elevation H is calculated by combining the plumb bob instrument with the satellite-borne fully-polarized SAR data T 。
Specifically, firstly, detecting each vertical measuring instrument on the ground by using satellite-borne full-polarization SAR, determining a plurality of rays corresponding to SAR by using satellite-borne full-polarization SAR data, and determining a total TEC value TEC corresponding to each ray SAR (ii) a Each ray determined by satellite-borne complete polarization SAR data corresponds to each vertical measuring instrument on the ground one by one; preferably, the elevation angle range of the ray formed by the satellite-borne fully polarized SAR and the vertical measuring instrument on the ground is 87-90 degrees, more preferably 88.77-89.59 degrees, namely the deviation angle of the ray formed by the SAR satellite and the vertical measuring instrument relative to the vertical direction does not exceed 3 degrees
Secondly, determining total electron content TEC from the upper section of the ionization layer region to the height of the SAR satellite T TEC for total electron content from upper section of ionization layer region to SAR satellite height T TEC equal to corresponding ray corresponding total TEC value SAR Subtracting TEC value TEC of a profile under an ionized layer region measured by a vertical measuring instrument B ；
Finally, according to the elevation H T Total electron content TEC from upper section of ionization layer region to height of SAR satellite T The relationship between them, calculate the elevation H T 。
Preferably, in step S2, for the ray corresponding to the SAR, the total TEC value TEC corresponding to each ray is determined by the following formula SAR ：
Wherein f represents the carrier frequency of the satellite-borne fully-polarized SAR, B represents the geomagnetic field intensity in an ionization layer region, theta represents the included angle between the geomagnetic field in the ionization layer region and the satellite-borne fully-polarized SAR signal, and omega represents the Faraday rotation angle offset caused by the ionization layer region.
The Faraday rotation angle offset omega caused by the ionization layer region can be obtained through satellite-borne fully-polarized SAR scattering matrix information, and the inversion expression is as follows:
wherein the content of the first and second substances,
arg (. Cndot.) denotes argument of complex element, Z 11 、Z 12 、Z 21 And Z 22 Respectively representing echo information received by four polarization channels of the satellite-borne complete polarization SAR to form a satellite-borne complete polarization SAR echo scattering matrix
Is Z 21 Conjugation of (1); s hh 、S vv The scattered waves are H-polarized waves scattered from the ground, V-polarized waves scattered from the ground, and omega real Representing the magnitude of the faraday rotation angle that is actually experienced. i represents an imaginary unit. For the ray corresponding to the SAR, when the total TEC value TEC corresponding to the ray is obtained SAR Then, the total electron content of the upper section can be obtained, and the expression is as follows:
TEC T ＝TEC SAR -TEC B
wherein, the TEC B Representing the TEC value, TEC, of the lower profile of the ionosphere region measured by a vertical measuring instrument T The total electron content of the section above the ionization region to the height of the SAR satellite is shown.
Further, in step S2, according to the altitude H T Total electron content TEC from upper section of ionization layer region to SAR satellite height T The altitude H is calculated by the relation between T Hour, TEC T And H T The (approximate) relationship between:
wherein H s Is the SAR satellite altitude. When calculating, the approximate relation is regarded as an equation, and the elevation H is calculated and determined T 。
The elevation H is calculated by combining a vertical measuring instrument and satellite-borne full-polarization SAR data T Then at an elevation H T And substituting the vertical electron density into an alpha-Chapman model to finally determine the vertical electron density of a plurality of different points so as to correct the iterative initial value of the corresponding grid, and the method integrates the vertical measuring instrument and satellite-borne full-polarization SAR data, and utilizes the information of the upper section and the lower section of the ionization layer region, so that the method is more accurate and closer to the actual electron distribution condition.
Preferably, in step S4, when a plurality of rays of different paths are obtained by using the GPS and the TEC value corresponding to each ray is inverted, the TEC value of each ray is determined by the following formula:
wherein, f 1 、f 2 Representing two different frequencies, L, of the GPS 1 、L 2 Respectively represent f 1 、f 2 Corresponding carrier pseudoranges, or L 1 、L 2 Respectively represent f 1 、f 2 The corresponding carrier phase value. TEC (thermoelectric cooler) GPS A TEC value representing a ray acquired based on GPS.
Preferably, in step S6, when performing tomographic iterative inversion based on a multiplicative algebraic reconstruction method, the iterative formula is:
wherein, N ej k+1 Represents the electron density of the jth grid in the k +1 th iteration, j = epsilon {1, 2.. N }, TEC m Indicating the TEC value corresponding to the m ray, wherein the m ray is a ray determined based on GPS,<·>represents the inner product, | | · | | | represents the norm,
is A m Transpose of (A) m Is represented by a matrix { A } mj The vector formed by the m-th row elements, the matrix { A } mj Element A of the mth row and jth column mj Represents the projection length of the mth ray in the jth grid, N e k Representing the electron density distribution obtained for all N grids at the k-th iteration, i.e. N e k Is { N ej k J =1, 2.. N } of a vector, λ k Is an iterative relaxation factor with the value range of 0 to lambda k ≤1。
Preferably, in step S6, the electron density distribution in the ionization region is determined after at least 5 iterations.
In one specific embodiment, as shown in fig. 3, assuming that the horizontal range of the ionospheric region is 200km and the height range is 100km to 500km, the entire ionospheric region is equally divided into n grids to obtain spatial coordinates of each grid. And (3) bringing the ionosphere IRI empirical model data into each grid to obtain an iteration initial value, wherein the size of each grid is 10km multiplied by 10km, namely, 800 grids exist. The circles in fig. 3 represent the measurement points of the vertical measuring instrument on the ground, and a plurality of measurement points of the vertical measuring instrument are arranged on the ground and fused with the satellite-borne fully-polarized SAR data, so that the vertical electron density above the plurality of measurement points can be obtained. At this time, the initial iteration value of the grid can be compared with the region where the measuring points of the vertical measuring instrument coincide with each other, if the difference between the initial iteration value and the measuring points of the vertical measuring instrument is larger than a set threshold value, the initial iteration value is updated to be the result calculated by fusing the vertical measuring instrument and the satellite-borne full-polarization SAR data, then the tomography iterative inversion is carried out through a multiplicative algebraic reconstruction method, and finally the electron density distribution condition of the ionization layer region is obtained.
Fig. 4 (a) to 4 (c) show the iterative simulation results, where fig. 4 (a) shows the real space electron density distribution, fig. 4 (b) shows the inversion result obtained by combining the vertical measurement instrument and the satellite-borne fully-polarized SAR data and correcting the initial iteration value, and the root mean square value of the difference between the inversion result and the real situation is 3.0828e 9 /m 3 FIG. 4 (c) shows the determination of the initial iteration value using only the empirical model of the ionosphere IRIThe root mean square value of the difference between the inversion result of (1) and the real situation is 5.8394e 9 /m 3 . It can be seen that the ionospheric tomography reconstruction accuracy can be effectively improved by improving the authenticity of the iteration initial value.
In particular, in some preferred embodiments of the present invention, there is further provided a computer device, including a memory and a processor, where the memory stores a computer program, and the processor, when executing the computer program, implements the steps of the ionospheric tomography method with improved iteration initial value accuracy in any of the above embodiments.
In other preferred embodiments of the present invention, a computer-readable storage medium is further provided, on which a computer program is stored, and the computer program is executed by a processor to implement the steps of the ionospheric tomography method with improved accuracy of iterative initial values described in any of the above embodiments.
It will be understood by those skilled in the art that all or part of the processes of the method of the above embodiments may be implemented by a computer program, which may be stored in a non-volatile computer-readable storage medium, and when executed, the computer program may include the processes of the above embodiments of the ionospheric tomography method for improving the accuracy of the initial iteration value, and the description thereof will not be repeated here.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. An ionospheric tomography method for improving the accuracy of an iterative initial value, characterized by comprising the following steps:
s1, dividing an ionized layer area into a plurality of grids, determining the coordinate of each grid, and determining the initial electron density value of each grid based on an ionized layer IRI empirical model;
s2, arranging a plurality of vertical measuring instruments at intervals below the ionosphere area, and determining the vertical electron density of a plurality of different points by using the vertical measuring instruments in combination with satellite-borne full-polarization SAR data;
s3, updating the initial electronic density value of the corresponding grid according to the vertical electronic density determined by combining the vertical measuring instrument with the satellite-borne full-polarization SAR data;
s4, acquiring a plurality of rays of different paths by using the GPS, inverting TEC values corresponding to the rays, and respectively recording GPS satellite coordinates and receiving station coordinates during GPS detection;
s5, calculating the projection length of each ray in each grid;
s6, carrying out tomography iterative inversion based on a multiplicative algebraic reconstruction method by using the initial electron density value of each grid, the projection length of each ray in each grid and the TEC value corresponding to each ray, and obtaining the electron density distribution of an ionization layer region after multiple iterations.
2. The ionospheric tomography method with improved iterative initial-value accuracy of claim 1, wherein:
in the step S2, when the vertical electron density of a plurality of different points is determined by combining the vertical measuring instrument with the satellite-borne full-polarization SAR data, the corresponding vertical electron density is directly obtained by measuring the electron density information below the ionosphere peak height through the vertical measuring instrument, and the corresponding vertical electron density is obtained by calculating the electron density information at the ionosphere peak height and above through an alpha-Chapman model combining the vertical measuring instrument with the satellite-borne full-polarization SAR data.
3. The ionospheric tomography method with improved iterative initial-value accuracy of claim 2, wherein:
in step S2, the α -Chapman model includes:
wherein N (h) represents the electron density at height h, z represents the virtual height, N m F 2 Is the peak height h m F 2 Electron density of (b), H T The elevation is indicated.
4. The ionospheric tomography method with improved iterative initial-value accuracy of claim 3, wherein:
in the step S2, when the corresponding vertical electron density is obtained by combining the alpha-Chapman model with the vertical measuring instrument and the satellite-borne full-polarization SAR data calculation, the elevation H is calculated by combining the vertical measuring instrument with the satellite-borne full-polarization SAR data T The method comprises the following steps:
firstly, detecting each vertical measuring instrument on the ground by using a satellite-borne full-polarization SAR, determining a plurality of rays corresponding to the SAR by using satellite-borne full-polarization SAR data, and determining a total TEC value TEC corresponding to each ray SAR ；
Secondly, determining total electron content TEC from the upper section of the ionization layer region to the height of the SAR satellite T ，TEC T Equal to the corresponding total TEC value TEC SAR Subtracting the TEC value of the lower section of the ionized layer area measured by the vertical measuring instrument;
finally, according to the elevation H T Total electron content TEC from upper section of ionization layer region to SAR satellite height T The altitude H is calculated according to the relation between the altitude H and the altitude H T 。
5. The ionospheric tomography method with improved iterative initial-value accuracy of claim 4, wherein:
in the step S2, for the ray corresponding to the SAR, the total TEC value TEC corresponding to each ray is determined by the following formula SAR ：
Wherein f represents the carrier frequency of the satellite-borne fully-polarized SAR, B represents the geomagnetic field intensity in an ionization layer region, theta represents the included angle between the geomagnetic field in the ionization layer region and the satellite-borne fully-polarized SAR signal, and omega represents the Faraday rotation angle offset caused by the ionization layer region.
6. The ionospheric tomography method with improved iterative initial-value accuracy of claim 4, wherein:
in the step S2, according to the elevation H T Total electron content TEC from upper section of ionization layer region to height of SAR satellite T The altitude H is calculated by the relation between T The relation is:
wherein H s Is the SAR satellite altitude.
7. The ionospheric tomography method with improved iterative initial-value accuracy of claim 1, wherein:
in step S6, when tomographic iterative inversion is performed based on a multiplicative algebraic reconstruction method, an iterative formula is as follows:
wherein N is ej k+1 Represents the electron density, TEC, of the jth grid at the (k + 1) th iteration m Indicating the TEC value corresponding to the m-th ray,<·>represents the inner product, | | · | | | represents the norm,
is A m Transpose of (A) m Is represented by a matrix { A } mj The vector formed by the m-th row elements, the matrix { A } mj Element A of the mth row and jth column mj Represents the projection length of the mth ray in the jth grid, N e k Indicating that all n meshes are inElectron density distribution, λ, obtained by k iterations k Is an iterative relaxation factor with the value range of 0 to lambda k ≤1。
8. The ionospheric tomography method with improved iterative initial-value accuracy of claim 1, wherein:
in step S6, after at least 5 iterations, the electron density distribution in the ionization layer region is obtained.
9. A computer arrangement comprising a memory and a processor, said memory storing a computer program, wherein said processor when executing said computer program performs the steps of the method for ionospheric tomography with improved iterative initial value accuracy of any of claims 1 to 8.
10. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method for ionospheric tomography with improved accuracy of initial values for iteration of any of claims 1 to 8.
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