Method for baseline measurement and signal synchronization of a full sky radio imaging array

Abstract

The present disclosure provides a method for baseline measurement and signal synchronization of a full-sky radio imaging array, relates to the field of radio observation, and comprises determining two satellite antennas to be measured and N known radio sources; establishing a three-dimensional coordinate system with one of the satellite antennas as the origin, and obtaining a first elevation angle and a first azimuth angle of the N radio sources relative to the coordinate origin; calculating the time difference of the signals emitted by each radio source at the two satellite antennas according to a first correlation operation; and calculating the baseline vector between the two satellite antennas to be measured according to the first elevation angle, the first azimuth angle and the time difference based on a second correlation operation; wherein the baseline vector comprises the distance between the two satellite antennas, a second elevation angle and a second azimuth angle. The present disclosure has the advantages of not requiring additional equipment in the determination of the baseline vector of the two satellites, and greatly reducing the effect of satellite load.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of radio observation, and particularly relates to a baseline measurement and signal synchronization method of a full-sky radio imaging array. BACKGROUND

[0002] In radio astronomy observation, in order to perform synthetic aperture imaging, the signals of different antennas in a radio array need to be correlated, and the correlated signals must be synchronized in time and phase, which requires that the relative positions between antenna units be known exactly during observation, so that the time delay of signals between different antennas can be compensated accurately. In addition, the sampling clocks of signals of different antennas must also be synchronized.

[0003] For a space very low frequency radio array, the antennas of the array are installed on different satellites. After the antennas are deployed, the positions of each satellite antenna in space are different, and the distribution range is large, which can be tens to hundreds of kilometers at most. Due to the different relative positions and distances between different antennas, and the different synchronization of signal clocks of different antenna units, the signal links between different antennas and a center reference antenna are very different. In order to perform accurate radio synthetic aperture imaging observation, the accurate measurement of three-dimensional baseline vectors between distributed antennas in space and the signal synchronization between different antennas are one of the key technologies.

[0004] The traditional measurement of baseline vectors between satellites (including range and angle) is performed by laser or microwave. Laser technology is suitable for point-to-point communication, and is not suitable for a space satellite formation composed of a main satellite and several sub-satellites. Microwave technology can be used for one-to-many communication, and is suitable for the needs of a space very low frequency radio array, but this technology is mainly used for range measurement and signal synchronization, and cannot realize the measurement of antenna positions and angles. If the angle is to be measured, additional equipment such as a star sensor device is needed to cooperate, which greatly increases the load weight of the satellite. SUMMARY

[0005] In view of the above problems, the present disclosure provides a baseline measurement and signal synchronization method of a full-sky radio imaging array to improve the problem of additional equipment needed for baseline vector measurement, which increases the load weight of the satellite.

[0006] The baseline measurement and signal synchronization method of the full-sky radio imaging array provided by the present disclosure comprises: determining two satellite antennas to be measured and N known radio sources; establishing a three-dimensional coordinate system with one of the satellite antennas as the origin, and obtaining a first elevation angle and a first azimuth angle of the N radio sources relative to the coordinate origin; calculating the time difference of the signal emitted by each radio source at the two satellite antennas based on a first correlation operation; and calculating the baseline vector between the two satellite antennas to be measured based on a second correlation operation according to the first elevation angle, the first azimuth angle and the time difference; wherein the baseline vector comprises the distance between the two satellite antennas, a second elevation angle and a second azimuth angle.

[0007] Optionally, the calculation of the time difference of the signal emitted by each radio source at the two satellite antennas based on the first correlation operation comprises: under the condition that the clocks between the two satellite antennas are the same, calculating the path geometry difference between the two satellite antennas as the time difference, and constructing the following first relationship formula according to the path geometry difference and the time difference obtained by the first correlation operation:

[0008]

[0009] wherein ΔT is the time difference, Δτ is the path geometry difference, c is the value of the speed of light, θ s is the first elevation angle, is the first elevation angle, d is the distance between the two satellite antennas to be measured, θ is the second elevation angle, is the second azimuth angle.

[0010] Optionally, the calculation of the time difference of the signal emitted by each radio source at the two satellite antennas based on the first correlation operation comprises: under the condition that the clocks between the two satellite antennas are not the same, calculating the sum of the path geometry difference between the signals of the two satellite antennas and the clock difference of the receiving systems of the two satellite antennas as the time difference, and constructing a second relationship formula according to the time difference, the path geometry difference and the clock difference:

[0011] ΔT = Δτ + Δt

[0012] wherein Δt is the clock difference of the receiving systems of the two satellite antennas.

[0013] Optionally, the calculation of the time difference of the signal emitted by each radio source at the two satellite antennas based on the first correlation operation further comprises: performing a cross-correlation operation on the time data sequences of the radio source signals at the two satellite antennas, obtaining a cross-correlation function, and obtaining the correlation results of different time displacements; obtaining the maximum value in the correlation results, and determining the corresponding time difference of the signal emitted by each radio source at the two satellite antennas according to the data sequence shift corresponding to the maximum value.

[0014] Optionally, the maximum value in the correlation result is obtained, and the time difference corresponding to the signal emitted by each radio source on the two satellite antennas is determined according to the time sequence shift corresponding to the maximum value, and the time difference corresponding to the signal emitted by each radio source on the two satellite antennas is determined by performing Gaussian fitting on the time sequence shift near each maximum value to obtain a fitting curve, and taking the time shift corresponding to the amplitude maximum value of the fitting curve as the time difference corresponding to the signal emitted by each radio source on the two satellite antennas.

[0015] Optionally, the baseline vector between the two satellite antennas to be measured is calculated according to the first elevation angle, the first azimuth angle, and the time difference based on the second correlation operation, and the baseline vector between the two satellite antennas to be measured is calculated by constructing the following relationship as the second correlation operation according to the first elevation angle, the first azimuth angle, the second elevation angle, the second azimuth angle, the time difference, and the clock difference:

[0016]

[0017] wherein c is the speed of light, is the first elevation angle of the Nth radio source, is the first azimuth angle of the Nth radio source, and ΔT n is the time difference of the Nth radio source, and Δt is the clock difference of the two satellite antenna receiving systems.

[0018] Optionally, the baseline vector between the two satellite antennas to be measured is calculated according to the first elevation angle, the first azimuth angle, and the time difference based on the second correlation operation, and the baseline vector between the two satellite antennas to be measured is calculated by substituting the first relationship or the second relationship into the second correlation operation.

[0019] Optionally, the sampling rate of the satellite antenna is 90-120MHz.

[0020] Optionally, the satellite antenna is a subarray antenna.

[0021] Optionally, the satellite antenna is an electrically small antenna.

[0022] The above at least one technical solution adopted by the embodiments of the present disclosure at least has the following beneficial effects:

[0023] Compared with the related art, the baseline vector between the two satellite antennas is measured by using the satellite antennas to be measured and the known radio sources without additional satellite-borne devices, and the baseline vector between the two satellite antennas is determined by passive observation, which greatly reduces the complexity of measuring the baseline vector between the two satellite antennas, significantly reduces the load weight of the satellite, reduces the research cost, and has better economy.

[0024] By using the first correlation operation and the second correlation operation, the clock difference between the two satellite antennas can be obtained synchronously while the baseline vector is obtained, signal synchronization is ensured, and accurate measurement of the baseline vector is realized.

[0025] By using a low-frequency electrically small antenna to simultaneously observe multiple radio sources, signal synchronization between the two satellite antennas and measurement of the baseline vector can be quickly realized using millisecond-level raw sampling data, and the measurement can be completed at one time without multiple switching measurement modes, and the real-time performance of the measurement is better.

[0026] In the related art, the baseline vector measurement or signal synchronization using microwave or laser technology reflects the parameters of the satellite platform and the measurement link, compared with the related art, the present disclosure uses the satellite antenna system for scientific observation to measure, and the measurement result also reflects the parameter characteristics of the scientific satellite antenna system and the signal link itself, so that the observation data is more accurate.

[0027] The method can achieve a measurement distance between the two satellite antennas with an accuracy of less than 0.5 meters, and a measurement accuracy of the azimuth angle and the elevation angle of less than 0.1 degrees under the condition of a signal-to-noise ratio of less than or equal to -10 dB by using millisecond-level raw sampling data.

[0028] The method provided by the present disclosure is not only suitable for measurement of the baseline vector and signal synchronization between satellites in a radio imaging array, but also suitable for measurement of the baseline vector in a space satellite formation and a ground large-field-of-view radio array, and has high promotion and application value. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more completely understand the present disclosure and its advantages, reference will now be made to the following description taken together with the accompanying drawings, in which:

[0030] Figure 1 A flowchart of a baseline measurement and signal synchronization method of a full-sky radio imaging array is schematically shown;

[0031] Figure 2 A schematic diagram of a radio source and a satellite antenna in the baseline measurement and signal synchronization method of the full-sky radio imaging array is schematically shown;

[0032] Figure 3 A schematic diagram of a radio source and a satellite antenna in the baseline measurement and signal synchronization method of the full-sky radio imaging array is schematically shown; DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application with reference to the specific embodiments and accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0034] The terms used herein are only used to describe specific embodiments, and are not intended to limit the present application. The terms "comprise", "include", and the like used herein indicate the presence of the stated features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0035] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection or can communicate with each other; can be direct connection, or indirect connection through intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0036] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "length", "circumferential", "front", "back", "left", "right", "top", "bottom", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the subsystems or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0037] Throughout the drawings, the same elements are denoted by the same or similar reference numerals. When it may cause confusion in understanding the present application, the conventional structure or configuration will be omitted. And the shape, size, positional relationship of each component in the drawing does not reflect the true size, proportion and actual positional relationship. In addition, in the claims, any reference symbol located between parentheses should not be construed as a limitation on the claims.

[0038] Similarly, to the extent that the foregoing description contains example of the invention, also describe or show various aspects of the invention, it is to be understood that the same can be applicable to any of the many alternatives or equivalents of the various aspects of the invention. And, mutually exclusive alternatives are not mutually exclusive unless explicitly stated. For example, any of the aspects of the invention described or shown can be implemented in either hardware or software, or a combination of both. Also, any of the aspects of the invention described or shown can be implemented in a single device or in multiple devices.

[0039] Furthermore, the terms "first", "second", and the like, do not denote any

[0040] The baseline measurement and signal synchronization method of the full-sky radio imaging array provided by the embodiments of the present disclosure comprises the following steps.

[0041] Figure 1 The baseline measurement and signal synchronization method of the full-sky radio imaging array provided by the embodiments of the present disclosure comprises the following steps.

[0042] Referring to Figure 1 The baseline measurement and signal synchronization method of the full-sky radio imaging array may, for example, comprise operations S100-S400.

[0043] In operation S100, two satellite antennas to be measured and N known radio sources are determined.

[0044] In operation S200, a three-dimensional coordinate system is established with one of the satellite antennas as the origin, and the first elevation angle and the first azimuth angle of the N radio sources relative to the coordinate origin are obtained.

[0045] In operation S300, the time difference of the signals emitted by each radio source at the two satellite antennas is calculated based on the first correlation operation.

[0046] In operation S400, the baseline vector between the two satellite antennas to be measured is calculated based on the second correlation operation according to the first elevation angle, the first azimuth angle, and the time difference.

[0047] The baseline vector comprises the distance between the two satellite antennas, the second elevation angle, and the second azimuth angle.

[0048] Figure 2 Fig. 1 schematically shows a diagram of a radio source and a satellite antenna in a baseline measurement and signal synchronization method of a full-sky radio imaging array provided by an embodiment of the present disclosure.

[0049] With reference to Figure 2 According to an embodiment of the present disclosure, in operation S100, two satellite antennas to be measured and N known radio sources are determined.

[0050] Wherein, N≥4, since the unknown parameters in the present disclosure include three parameters of the baseline vector and one parameter of the clock difference, information of at least four radio sources is required for correlation calculation. It should be noted that this method can be calculated by information of no less than four radio sources, and as the number N increases, the length of the original sampling data can be increased to obtain more accurate baseline vector measurement and clock difference data.

[0051] For example, an embodiment of the present disclosure takes two satellite antennas to be measured and five known radio sources as an example for observation calculation, and the satellite antenna uses an electrically small antenna in the array antenna.

[0052] According to an embodiment of the present disclosure, in operation S200, a three-dimensional coordinate system is established with one of the satellite antennas as the origin, and the first elevation angle and the first azimuth angle of the N radio sources relative to the coordinate origin are obtained.

[0053] Wherein, the line connecting the radio source and the origin is referred to as the first line, the orthogonal projection of the radio source in the X and Z axis plane and the origin is referred to as the second line, the included angle between the first line and the second line is the first elevation angle, and the included angle between the second line and the X axis is the first azimuth angle. It should be noted that the definition of the second line is not limited to the orthogonal projection of the radio source in the X and Z axis plane and the origin, and researchers can redefine it according to their own coordinate system design. The first azimuth angle is also not limited to the included angle between the second line and the X axis, and researchers can redefine it according to the measurement requirements.

[0054] According to an embodiment of the present disclosure, in operation S300, the time difference of the signal emitted by each radio source on the two satellite antennas is calculated based on the first correlation operation, including operations S301-S303.

[0055] In operation S301, the time data sequence of the radio source signal on the two satellite antennas is cross-correlated to obtain a cross-correlation function and obtain the correlation results of different time displacements.

[0056] Wherein, the sampling rate of the satellite antenna is 90-120MHz, and the sampling rate in the present embodiment is 100MHz.

[0057] Specifically, the time data sequences of the radio source signals on the two satellite antennas are shifted and multiplied to obtain different correlation results.

[0058] In operation S302, a maximum value in the correlation result is obtained, and a time difference of the signal emitted by each radio source on the two satellite antennas is determined according to the data sequence shift corresponding to the maximum value.

[0059] In operation S303, two cases are divided:

[0060] Case one: under the condition that the clocks between the two satellite antennas are the same, a path geometry difference between the two satellite antennas is calculated as the time difference, and a first relationship is constructed according to the path geometry difference and the time difference:

[0061]

[0062] wherein ΔT is the time difference, Δτ is the path geometry difference, c is the value of the speed of light, θ s is the first elevation angle, is the first elevation angle, d is the distance between the two satellite antennas to be measured, θ is the second elevation angle, is the second azimuth angle.

[0063] Case two: under the condition that the clocks between the two satellite antennas are not the same, the sum of the path geometry difference between the signals of the two satellite antennas and the clock difference of the receiving systems of the two satellite antennas is calculated as the time difference, and a second relationship is constructed according to the time difference, the path geometry difference and the clock difference:

[0064] ΔT=Δτ+Δt

[0065]

[0066] wherein Δt is the clock difference of the receiving systems of the two satellite antennas.

[0067] Figure 3 A schematic diagram of Gaussian fitting of multiple maximum values in a baseline measurement and signal synchronization method of a full-sky radio imaging array is schematically shown.

[0068] Referring to Figure 3 According to the embodiment of the present disclosure, in order to obtain a higher precision time difference, in operation S302:

[0069] The maximum value in the correlation result is obtained, and since the amplitude of the maximum value can reflect the intensity of the signal emitted by the radio source, the maximum value corresponding to each radio source can be determined according to the amplitude of the maximum value.

[0070] The time shift sequence near each maximum value is Gaussian fitted to obtain a fitting curve.

[0071] The time displacement corresponding to the amplitude maximum of the fitted curve is taken as the time difference corresponding to the signals emitted by each radio source on the two satellite antennas.

[0072] Where, since the signals emitted by the radio sources have been digitally sampled when received by the satellite antennas, the time difference is an integer multiple of the sampling interval, that is, the error of the time difference can be up to one sampling interval, so that the time difference obtained through Gaussian fitting can have a time precision of less than one tenth of the sampling interval at most.

[0073] According to an embodiment of the present disclosure, in operation S400, the baseline vector between the two satellite antennas to be measured is calculated based on the second correlation operation according to the first elevation angle, the first azimuth angle, and the time difference, including operations S401-S402.

[0074] In operation S401, the following relationship is constructed as the second correlation operation according to the first elevation angle, the first azimuth angle, the second elevation angle, the second azimuth angle, the time difference, and the clock difference:

[0075]

[0076] Where, c is the value of the speed of light, is the first elevation angle of the Nth radio source, is the first azimuth angle of the Nth radio source, ΔT n is the time difference of the Nth radio source, and Δt is the clock difference of the two satellite antenna receiving systems.

[0077] In operation S402, the first relationship or the second relationship is substituted into the second correlation operation to calculate the baseline vector between the two satellite antennas to be measured.

[0078] For example, five radio sources are used for calculation in an embodiment of the present disclosure, and the second correlation calculation is:

[0079]

[0080] The time differences of the five radio sources obtained in operation S300 are respectively denoted as ΔT1, ΔT2, ΔT3, ΔT4, and ΔT5.

[0081] Under the condition that the clocks of the two satellite antennas are the same, Δt is 0, where,

[0082]

[0083] Since It is known that, by analogy, the relationship of ΔT2, ΔT3, ΔT4, and ΔT5 is obtained respectively, and substituted into the matrix of the second correlation calculation to obtain d, θ, and

[0084] Under the condition that the clocks between two satellite antennas are not the same, Δt = ΔT - Δτ,

[0085] According to ΔT1= Δτ1+ Δt

[0086] Wherein The relationship of Δt about d, θ and The relationship of Δt about d, θ and The relationship of Δt about d, θ and

[0087] In the present disclosure, the four parameters of baseline vector and clock difference between two satellite antennas are not necessarily unknown at the same time. When one or two parameters are known, the unknown parameters can be calculated with fewer radio sources, and the calculation is more efficient.

[0088] The above-described specific embodiments further illustrate the technical solutions of the present application. It should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of baseline measurement and signal synchronization for a full sky radio imaging array, characterized by, The method comprises the following steps: determining two satellite antennas to be measured and N known radio sources; establishing a three-dimensional coordinate system with one of the satellite antennas as the origin, and obtaining a first elevation angle and a first azimuth angle of the N radio sources relative to the coordinate origin; calculating a time difference of a signal emitted by each radio source at the two satellite antennas based on a first correlation operation, including: under the condition that the clocks between the two satellite antennas are the same, calculating a path geometry difference between the two satellite antennas as the time difference, and constructing a first relationship as follows based on the path geometry difference and the time difference obtained by the first correlation operation: wherein ΔT is the time difference, Δτ is the path geometry difference, c is the value of light speed, θ s is the first elevation angle, φ s is the first elevation angle, d is the distance between two satellite antennas to be measured, θ is the second elevation angle, and φ is the second azimuth angle; under the condition that the clocks of the two satellite antennas are not the same, the path geometry difference between the two satellite antenna signals and the sum of the clock differences of the two satellite antenna receiving systems are calculated as the time difference, and a second relational expression is constructed according to the time difference, the path geometry difference, and the clock difference: ΔT = Δτ + Δt, wherein Δt is the clock difference of the two satellite antenna receiving systems; calculating a baseline vector between the two satellite antennas to be measured based on the first elevation angle, the first azimuth angle, and the time difference based on a second correlation operation, including: constructing a relationship as follows based on the first elevation angle, the first azimuth angle, the second elevation angle, the second azimuth angle, the time difference, and the clock difference as the second correlation operation: wherein c is the value of the speed of light, is the first elevation angle of the Nth radio source, is the first azimuth angle of the Nth radio source, ΔT n is the time difference of the Nth radio source, Δt is the clock difference of the two satellite antenna receiving systems; wherein the baseline vector includes a distance between the two satellite antennas, a second elevation angle, and a second azimuth angle.

2. The method for baseline measurement and signal synchronization of a full sky radio imaging array according to claim 1, wherein, The calculation of the time difference of the signal emitted by each radio source at the two satellite antennas based on the first correlation operation further comprises: performing a cross-correlation operation on the time data sequences of the radio source signals at the two satellite antennas to obtain a cross-correlation function and obtain correlation results of different time displacements; obtaining a maximum value in the correlation results, and determining the corresponding time difference of the signal emitted by each radio source at the two satellite antennas based on the time displacement corresponding to the maximum value.

3. The method for baseline measurement and signal synchronization of a full sky radio imaging array according to claim 2, wherein, The determination of the corresponding time difference of the signal emitted by each radio source at the two satellite antennas based on the time displacement corresponding to the maximum value comprises: performing Gaussian fitting on the time displacement sequence near each maximum value to obtain a fitting curve; taking the time displacement corresponding to the amplitude maximum value of the fitting curve as the corresponding time difference of the signal emitted by each radio source at the two satellite antennas.

4. The method for baseline measurement and signal synchronization of a full sky radio imaging array according to claim 1, wherein, The calculation of the baseline vector between the two satellite antennas to be measured based on the second correlation operation comprises: substituting the first relationship or the second relationship into the second correlation operation to calculate the baseline vector between the two satellite antennas to be measured.

5. The method for baseline measurement and signal synchronization of a full sky radio imaging array according to claim 1, wherein, The sampling rate of the satellite antenna is 90-120 MHz.

6. The method for baseline measurement and signal synchronization of a full sky radio imaging array according to claim 1, wherein, The satellite antenna is an array antenna.

7. The method for baseline measurement and signal synchronization of a full sky radio imaging array according to claim 1, wherein, The satellite antenna is an electrically small antenna.

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