A method for measuring UTC UT1 based on SXK three-frequency VLBI joint measurement
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-15
- Publication Date
- 2026-08-11
AI Technical Summary
但该技术存在一定局限性：一是双频组合对电离层残差的抑制能力有限，电离层活跃期会影响时延拟合精度；二是双频段模式无法有效规避低频段射电源的源结构效应带来的影响，进一步制约测量精度提升
本发明提出的基于SXK三频VLBI联合测量世界时UT1的方法，采用S/X/K三频联合反演电离层残余总电子含量，相比双频模式可有效降低电离层活跃期的残差干扰，实现电离层时延的高精度修正；利用X频段稳定的相位修正K频段的相位，基于对流层时延的频率无关性，精准扣除K频段的对流层相位贡献，以降低相位波动对测量结果的影响；结合K频段受射电源结构影响小的特性，减少射电源的源结构效应对UT1解算的干扰，进一步提升测量精度；用两轮解算与结果融合的策略，提升了天顶湿大气时延修正精度，最终将世界时UT1测量精度提升5%~15%，以满足深空探测、卫星定轨等高端领域的高精度需求。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of Universal Time (UT1) measurement technology, specifically relating to a method for measuring Universal Time (UT1) based on SXK three-frequency VLBI joint measurement. Background Technology
[0002] Very Long Baseline Interferometry (VLBI) technology, with its ultra-high resolution and measurement accuracy, has become the core technology for Universal Time (UT1) measurement. As a key component of the Earth's rotation parameters, the measurement accuracy of UT1 directly affects the performance of high-precision applications such as deep space tracking and control, and satellite orbit determination.
[0003] Current VLBI techniques for measuring UTC UT1 mostly employ the S / X dual-band observation mode, using combined dual-frequency data to correct ionospheric time delay errors. However, this technique has certain limitations: firstly, the dual-frequency combination has limited ability to suppress ionospheric residuals, and periods of ionospheric activity can affect the accuracy of time delay fitting; secondly, the dual-band mode cannot effectively avoid the influence of source structure effects from low-frequency radio sources, further restricting the improvement of measurement accuracy. Some improved techniques attempt to use ultra-wideband observations or time synchronization constraints between observation stations, but these still suffer from poor source structure effects from radio sources, and ultra-wideband observations suffer from large data volumes and poor timeliness.
[0004] Therefore, there is an urgent need for a VLBI measurement method that can effectively separate multi-source errors and improve the accuracy and stability of UTC UT1 calculation. Summary of the Invention
[0005] To address the aforementioned problems in the existing technology, this invention provides a method for jointly measuring Universal Time (UT1) based on SXK three-frequency VLBI. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a method for measuring Universal Time UT1 based on SXK three-frequency VLBI joint measurement, the method comprising: Construct a joint S / X / K frequency VLBI measurement system; Radio sources are selected as observation targets. Based on the S / X / K three-frequency VLBI joint measurement system, the three-frequency signals corresponding to the observation targets are received synchronously. The three-frequency signals are preprocessed to generate observation data for the corresponding frequency bands. Cross-correlation calculations are performed on the observation data to obtain the cross-power spectrum of the corresponding frequency band. The phase information of the cross-power spectrum of the X-band is used to correct the phase information of the cross-power spectrum of the K-band. The ionospheric time delay is obtained by inverting the total residual electron content of the ionosphere based on the cross-power spectrum of each frequency band and fitting it. The observation time delay of the corresponding frequency band is also obtained by fitting it. After removing the ionospheric delay from the observation delay, the first new observation delays corresponding to the X-band and K-band are obtained. The first new observation delays corresponding to the X-band and K-band are calculated in the first round to obtain the corresponding zenith moist atmospheric delay correction values. The zenith moist atmospheric delay correction values corresponding to the X-band and K-band are weighted and fused. The second new observation delays corresponding to the X-band and K-band are calculated based on the fused zenith moist atmospheric delay correction values. The second new observation delays corresponding to the X-band and K-band are calculated in the second round to obtain the corresponding UTC UT1 estimates. The UTC UT1 estimates corresponding to the X-band and K-band are weighted and fused to obtain the final UTC UT1 measurement result.
[0006] The beneficial effects of this invention are: This invention proposes a method for measuring Universal Time (UT1) based on SXK three-frequency VLBI joint measurement. It employs a three-frequency (S / X / K) joint inversion to retrieve the residual total electron content of the ionosphere. Compared to a dual-frequency mode, this method effectively reduces residual interference during periods of ionospheric activity, achieving high-precision correction of ionospheric time delay. By utilizing the stable phase correction of the X-band, the phase of the K-band is corrected. Based on the frequency independence of tropospheric time delay, the tropospheric phase contribution of the K-band is accurately subtracted, reducing the impact of phase fluctuations on the measurement results. Furthermore, by combining the characteristic of the K-band being less affected by the structure of radio sources, the interference of radio source structure effects on UT1 calculation is reduced, further improving measurement accuracy. A two-round calculation and result fusion strategy improves the accuracy of zenith wet atmospheric time delay correction, ultimately increasing the accuracy of UTC UT1 measurement by 5% to 15%, meeting the high-precision requirements of advanced fields such as deep space exploration and satellite orbit determination.
[0007] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0008] Figure 1 This is a flowchart illustrating a method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the distribution of radio sources and source flux applicable to the K-band provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the relationship between observation delay, ionospheric delay, and cross-power spectrum phase provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the UTC UT1 calculation process provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the two-round solution and result fusion strategy provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of a system for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the residuals of the UT1 measurement in the X-band throughout the year at the Jilin-Kashgar station in 2025; Figure 8 This is a schematic diagram of the sky distribution of the radio source at Jilin Station, obtained from a simulation on January 1, 2025. Figure 9 This is a schematic diagram of the sky distribution of the radio source at Kashgar station, obtained from a simulation on January 1, 2025. Figure 10 This is a schematic diagram of the measurement results of UTC UT1 under different measurement errors provided in the embodiments of the present invention. Detailed Implementation
[0009] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.
[0010] To address the issues of multiple error source coupling and insufficient calculation accuracy in existing dual-frequency VLBI measurement UT1 technology, please refer to [link to relevant documentation]. Figure 1 This invention provides a method for measuring Universal Time UT1 based on SXK three-frequency VLBI joint measurement, specifically including the following steps: S10. Construct a joint measurement system for S / X / K three-frequency VLBI.
[0011] Unlike existing dual-frequency UT1 measurement schemes, this invention proposes a tri-frequency (S / X / K) UT1 measurement scheme. First, a tri-frequency VLBI joint measurement system is constructed. Within this system, at least two observation stations form an interferometric network, and each station is equipped with tri-band receiving equipment (S-band, X-band, and K-band). For example, the interferometric network consisting of the Jilin and Kashgar stations of the National Time Service Center is used as an example. Both stations are equipped with S / X / K tri-band receiving equipment, capable of operating simultaneously in the S-band, X-band, and K-band. Specifically, the S-band can be 2.2 GHz to 2.3 GHz, the X-band can be 7.5 GHz to 9.0 GHz, and the K-band can be 21 GHz to 23 GHz.
[0012] S20. Select the radio source as the observation target, and synchronously receive the three-frequency signals corresponding to the observation target based on the S / X / K three-frequency VLBI joint measurement system. Preprocess the three-frequency signals to generate observation data for the corresponding frequency band.
[0013] In this embodiment of the invention, multiple radio sources with stable flow density can be selected, preferably dense point sources with a source flow rate greater than 0.25 Jy.
[0014] Each observatory conducts time-series observations of the selected radio sources according to the pre-set observation plan, ensuring that there are sufficient sources for VLBI measurements throughout the day. For example... Figure 2 As shown, Figure 2 The paper shows the spatial distribution of 64 compact radio sources suitable for the K-band on the celestial sphere, as well as the source flux characteristics of each radio source. The distribution of radio sources covers the celestial region from right ascension 0 to 24 hours and declination from -30 degrees to +90 degrees, which can meet the synchronous observation needs of the two observation stations in Jilin and Kashgar.
[0015] Based on the S / X / K tri-frequency VLBI joint measurement system, during the observation data acquisition phase, each observation station simultaneously receives radio source signals across the three frequencies: S-band, X-band, and K-band. After being acquired by a large-aperture antenna, the radio source signals undergo preprocessing, specifically low-noise amplification, down-conversion to intermediate frequency, and then digitization via an A / D sampling module with a bandwidth exceeding 100MHz. This generates and stores the observation data corresponding to each frequency band. The sampling rate and quantization bit depth of the observation data are optimized according to the signal characteristics of each frequency band. For example, the S-band can use 2-bit quantization and a 256MHz sampling rate, the X-band can use 2-bit quantization and a 1024MHz sampling rate, and the K-band can use 2-bit quantization and a 1024MHz sampling rate to ensure sufficient signal bandwidth and dynamic range.
[0016] Before preprocessing the captured radio source signals, the process includes: each observatory using a hydrogen clock as the frequency standard to achieve high-precision time synchronization of the three-frequency signals. Cryogenic receiving components and superconducting filters can be integrated into the receiving link to reduce system noise temperature and improve the ability to receive weak signals.
[0017] S30. Perform cross-correlation calculation on the observation data to obtain the cross-power spectrum of the corresponding frequency band. Use the phase information of the cross-power spectrum of the X band to correct the phase information of the cross-power spectrum of the K band. Based on the cross-power spectrum of each frequency band, invert the total residual electron content of the ionosphere and fit it to obtain the ionospheric time delay. Then, fit it to obtain the observation time delay of the corresponding frequency band.
[0018] In this embodiment of the invention, DiFX software is used to perform cross-correlation operations on the observation data to obtain the cross-power spectrum of the corresponding frequency bands. Specifically, cross-correlation operations are performed on the observation data of the S-band, X-band, and K-band respectively to obtain the cross-power spectra of the S-band, X-band, and K-band between each observation station. After the cross-correlation operation is completed, complex power spectrum data containing amplitude and phase information is obtained, which is used for subsequent time delay estimation and parameter calculation.
[0019] Tropospheric time delay (especially zenith moist atmosphere time delay, caused by water vapor fluctuations) has a phase interference intensity several times greater in the K-band than in the X-band. To reduce the phase changes and subsequent time delay errors introduced by tropospheric time delay in the K-band, this invention employs multi-frequency phase transfer technology. Utilizing the frequency independence of tropospheric time delay, it transfers stable phase information from the X-band to the K-band, correcting its phase fluctuations. Specifically, this invention uses the phase information of the cross-power spectrum of the X-band to correct the phase information of the cross-power spectrum of the K-band, including: calculating the tropospheric phase contribution value of the K-band based on the phase information of the cross-power spectrum of the X-band, and subtracting the tropospheric phase contribution value of the K-band from the phase information of the cross-power spectrum of the K-band. The formula for calculating the tropospheric phase contribution value of the K-band is expressed as: ; in, This represents the tropospheric phase contribution value of the K-band. Indicates the frequency of the K-band. Indicates the frequency of the X band. This represents the phase information of the cross-power spectrum in the X-band. It can be seen that, based on the measured phase information of the cross-power spectrum in the X-band, the tropospheric phase contribution value of the K-band is calculated according to the frequency ratio, and then subtracted from the original phase information of the K-band to obtain the corrected phase information, thus improving the measurement accuracy of the observation delay in the K-band.
[0020] Figure 3 This diagram illustrates the relationship between observation delay, ionospheric delay, and cross-power spectrum phase. Figure 3 The document also shows the positional relationship of the S-band, X-band, and K-band on the total phase curve. Figure 3 The slope of each line reflects the corresponding time delay effect. Specifically, the slope of the total potential curve reflects the effect of observation time delay, the slope of the non-dispersive phase curve reflects the effect of theoretical time delay, and the slope of the ionospheric introduction phase curve reflects the effect of ionospheric time delay. From Figure 3 It can be seen that the ionosphere's physical property of being inversely proportional to frequency means that low-frequency bands (such as the X-band) are more affected by the ionosphere, while high-frequency bands (such as the K-band) are less affected. This embodiment of the invention uses cross-power spectrum inversion to fit the ionospheric delay and the corresponding observation delay for each frequency band, expressed by the formula:
[0021] in, This refers to the phase information of the cross power spectrum for the corresponding frequency band. For the corresponding frequency band, For the observation delay of the corresponding frequency band, For reference frequency, For the initial phase, The estimated residual total electron content of the ionosphere, i.e., the ionospheric delay, is characterized by the residual total electron content. The ionospheric delay and observation delay for each frequency band can be calculated using the above formula.
[0022] By employing a three-frequency joint inversion method, the redundancy information from observation data across the three frequency bands is utilized to improve the estimation accuracy of the residual total electron content in the ionosphere, thereby achieving precise correction of ionospheric time delay. During periods of ionospheric activity, the three-frequency joint inversion method can further reduce ionospheric residual interference and improve the accuracy of observation time delay fitting compared to the traditional dual-frequency model.
[0023] After the above processing, the embodiments of the present invention accurately deduct the influence of the ionosphere, correct the disturbance of the troposphere to the K-band, reduce the error influence in the subsequent UT1 solution, and thus improve the solution accuracy of UTC UT1.
[0024] S40. After removing the ionospheric delay from the observation delay, the first new observation delays corresponding to the X-band and K-band are obtained. The first round of calculation is performed on the first new observation delays corresponding to the X-band and K-band to obtain the corresponding zenith moist atmospheric delay correction values. The zenith moist atmospheric delay correction values corresponding to the X-band and K-band are weighted and averaged and fused. The second new observation delays corresponding to the X-band and K-band are calculated based on the fused zenith moist atmospheric delay correction values. The second round of calculation is performed on the second new observation delays corresponding to the X-band and K-band to obtain the corresponding UTC UT1 estimates. The UTC UT1 estimates corresponding to the X-band and K-band are weighted and averaged and fused to obtain the final UTC UT1 measurement result.
[0025] The construction of theoretical time delay models is the foundation for solving world time parameters, such as... Figure 4 This demonstrates the UT1 covariance calculation process, which can be applied to both the X and K bands. Figure 4 The UT1 calculation process shown generates the corresponding estimated UT1 value. The signal is affected by various factors during its journey from the radio source to the VLBI antenna, such as planetary gravity, the ionosphere, the troposphere, clock errors between antenna systems, and instrumentation. Therefore, the observation delay between the signal arrival points at the VLBI antenna is significant. for: ; ; in, For theoretical time delay, The theoretical geometric time delay is mainly related to the relative position of the VLBI antenna, the location of the radio source, and the orientation of the Earth. The ionospheric delay has been accurately subtracted during the data fitting and inversion process. The tropospheric time delay is mainly related to the temperature, pressure, and humidity along the propagation path, and varies with the direction and time of the observation point. It is divided into dry time delay and zenith moist atmospheric time delay. The former can be calculated based on the Saastamoinen model. The clock difference between the two VLBI antennas is mainly related to the oscillation rate of the hydrogen clock at the observation station. The antenna deformation delay is mainly related to structural deformation caused by temperature, wind load, and gravity, and can be modeled and corrected. Equipment delay, primarily the time delay introduced by the equipment between signal reception from the feed source and data recording, can be corrected through corresponding signal calibration. The time delay introduced by the source structure effect has a very low impact on the K-band. Other time delays are mainly due to time delays introduced by relativistic effects, etc.
[0026] Calculate the theoretical delay using the model protocol published by IERS. Simultaneously, the observation delay is calculated using least squares to obtain the required parameter estimates. The UT1 calculation formula in this embodiment is: ; in, For Universal Time UT1, For observation delay The partial derivative relative to UT1, The correction value is calculated for UTC 1. Baseline clock bias, For observation delay relatively The partial derivative, This is the baseline clock bias correction value. This is the time delay of the zenith moist atmosphere. For observation delay relatively The partial derivative, This is the correction value for the zenith moist atmospheric time delay. To simplify the calculation of partial derivatives for the parameters to be estimated, the effects of relativistic effects are not considered in the calculation, because the estimated values obtained under this condition are not significantly different from those obtained by complex models. Therefore, for the UT1 parameter estimation, its partial derivative is: ; in: ; ; in, Let be the position vector of the radio source. To observe the baseline vector, This represents the celestial reference frame representing the center of mass of the solar system. This represents the geocentric celestial sphere reference frame. Let be the precession nutation rotation matrix. The angle of Earth's rotation. For observation delay relatively The partial derivative, for The partial derivative relative to UT1, It is a polar shift rotation matrix.
[0027] Based on the above analysis, it can be seen that the parameters to be estimated during the UT1 solution process include the UT1 solution correction value, the baseline clock error correction value, and the zenith moist atmospheric time delay correction value. This invention provides, for example... Figure 5 The strategy for fusing the two rounds of calculations and results is as follows: In the first round of calculation, the zenith moist atmospheric delay correction value is calculated; in the second round of calculation, the UT1 calculation correction value and the baseline clock error correction value are calculated, with the zenith moist atmospheric delay correction value used as a known fixed value; the UT1 estimates corresponding to the X and K bands in the second round of calculation are then fused. More specifically: This embodiment of the invention performs a first round of calculations on the first new observation delay to obtain the zenith moist atmospheric delay correction values for the X-band and K-band, including: calculating the first delay residual between the first new observation delay and the theoretical delay for the X-band and K-band respectively; and using the least squares method to calculate the zenith moist atmospheric delay correction values for the X-band and K-band. Since the X-band and K-band are observed simultaneously, the zenith moist atmospheric delay should be basically the same. To improve the accuracy of the zenith moist atmospheric delay, a weighted average fusion process is performed on the two. This embodiment of the invention performs a weighted average fusion of the zenith moist atmospheric delay correction values for the X-band and K-band, expressed by the following formula: ; in, This represents the zenith moist atmospheric time delay correction value after fusion. This indicates the accuracy of the zenith wet atmospheric delay correction for the X-band. This indicates the accuracy of the zenith wet atmospheric delay correction for the K-band. This represents the zenith wet atmospheric delay correction value for the X-band. This represents the zenith wet atmospheric delay correction value for the K-band.
[0028] Next, using the fused zenith wet atmospheric time delay as the initial value, this embodiment of the invention performs a second round of calculations on the second new observation time delays corresponding to the X-band and K-band to obtain the corresponding UTC UT1 estimates, including: calculating the second time delay residuals between the second new observation time delays and theoretical time delays corresponding to the X-band and K-band respectively; and using the least squares method to calculate the second time delay residuals to obtain the UTC UT1 estimates corresponding to the X-band and K-band.
[0029] Finally, the weighted average of the UT1 estimates corresponding to the X-band and K-band is used to obtain the final UT1 measurement result. The weighted average of the UT1 estimates corresponding to the X-band and K-band is expressed by the following formula: ; in, This represents the final world time UT1 measurement after merging. This indicates the accuracy of the world time estimate for the X-band. This indicates the accuracy of the K-band world time estimation. This represents the estimated UT1 value for the X-band. This represents the estimated UTC UT1 value for the K-band.
[0030] The embodiments of the present invention effectively improve the accuracy of zenith wet atmospheric time delay correction by fusing the above two rounds of calculations and results, thereby improving the calculation accuracy of UTC UT1.
[0031] Figure 6 A system based on SXK three-frequency VLBI joint measurement of UTC UT1 was demonstrated. The observation data is transmitted in real time between the two observation stations through a high-speed network. The data center and analysis center are equipped with high-performance computing clusters for subsequent cross-correlation calculations and UTC UT1 solution.
[0032] To verify the effectiveness of the method for measuring Universal Time UT1 based on SXK three-frequency VLBI joint measurement provided in this embodiment of the invention, the following experiments were conducted.
[0033] As can be seen from the above analysis, the time delay error caused by the ionosphere and radio source structural effects can be converted into measurement error, which can then be analyzed through simulation. Typically, the measurement error introduced by the ionosphere and radio source structural effects is 5ps to 15ps. Therefore, the impact of the measurement error on the UT1 measurement accuracy can be reflected by simulation analysis to reflect the impact of the S / X / K three-frequency observation method on the UT1 solution accuracy.
[0034] Analysis and research were conducted using daily UTC simulation data for 2025. Based on the VLBI antenna characteristics of the Jilin and Kashgar observation stations of the National Time Service Center, the two observation stations will be equipped with S / X / K tri-band receiving equipment, combined with... Figure 2 Simulation analysis of K-band UTC observations was conducted on 64 radio sources to verify the degree of accuracy improvement. Figure 7 The diagram illustrates the UTC UT1 measurement residuals in the X-band throughout 2025 at the Jilin-Kashgar station. The average measurement residual is 88 ps. This average residual of 88 ps reflects the measurement level of the existing dual-frequency VLBI system and is also an important benchmark for evaluating the accuracy improvement effect of the three-frequency joint observation of this invention. The simulation will be carried out based on this.
[0035] The sky distribution of the radio source at the observatory directly affects the accuracy of tropospheric time delay fitting, and thus the measurement accuracy of UTC UT1. Figure 8 This is a simulation of the sky distribution of the radio source at Jilin station, obtained on January 1, 2025. Figure 9 This is a simulation of the sky distribution of the radio source at the Kashgar station, obtained on January 1, 2025. Figure 8 and Figure 9 It can be seen that the overall distribution is good, and the radio source covers the 2-hour observation period.
[0036] Observational data will be generated daily in 2025. 1000 simulation analyses will be performed on the generated data to statistically analyze the accuracy of UTC (Universal Time 1) measurements. Due to the influence of the source structure, a time delay error of 5ps to 15ps will be introduced. Therefore, analyses will be conducted separately for the -5ps, -10ps, and -15ps cases. Figure 10 The diagram illustrates the UT1 measurement results under different measurement errors, from... Figure 10 It can be seen that as the source structure error is subtracted (i.e., the measurement error is reduced), the accuracy of UTC UT1 measurement is improved.
[0037] Table 1 presents the statistical values of the accuracy of UTC UT1 calculation under different measurement errors.
[0038] Table 1. Influence of measurement error on the accuracy of UT1 solution
[0039] As shown in Table 1, by using the S / X / K three-frequency joint measurement mode, as the measurement error decreased from 88ps to 73ps, the RMS accuracy of the UT1 solution decreased from 64.7μs to 55.4μs, with an accuracy improvement of 14.4%. This means that the accuracy of UT measurement has been improved by 5% to 15%, which is of great significance for China's independent measurement of UT, and can meet the high-precision requirements of high-end fields such as deep space exploration and satellite orbit determination.
[0040] In summary, the method for measuring Universal Time (UT1) based on the SXK three-frequency VLBI joint measurement proposed in this invention employs the joint inversion of the total residual electron content in the ionosphere using S / X / K frequencies. Compared to the dual-frequency mode, this method effectively reduces residual interference during periods of ionospheric activity, achieving high-precision correction of ionospheric time delay. It utilizes the stable phase correction of the X-band to correct the phase of the K-band, accurately subtracting the tropospheric phase contribution of the K-band based on the frequency independence of tropospheric time delay, thereby reducing the impact of phase fluctuations on the measurement results. Furthermore, by combining the characteristic of the K-band being less affected by the structure of the radio source, the interference of the radio source structure effect on UT1 calculation is reduced, further improving measurement accuracy. The strategy of two-round calculation and result fusion improves the accuracy of zenith wet atmospheric time delay correction, ultimately increasing the accuracy of UTC UT1 measurement by 5% to 15%, meeting the high-precision requirements of advanced fields such as deep space exploration and satellite orbit determination.
[0041] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.
[0042] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the specification and accompanying drawings, will understand and implement other variations of the disclosed embodiments in carrying out the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. While certain measures are described in different embodiments, this does not mean that these measures cannot be combined to produce good results.
[0043] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.
Claims
1. A method for measuring universal time UT1 based on SXK three-frequency VLBI joint measurement, characterized in that, The method for measuring Universal Time UT1 based on SXK three-frequency VLBI joint measurement includes: Construct a joint S / X / K frequency VLBI measurement system; Radio sources are selected as observation targets. Based on the S / X / K three-frequency VLBI joint measurement system, the three-frequency signals corresponding to the observation targets are received synchronously. The three-frequency signals are preprocessed to generate observation data for the corresponding frequency bands. Cross-correlation calculations are performed on the observation data to obtain the cross-power spectrum of the corresponding frequency band. The phase information of the cross-power spectrum of the X-band is used to correct the phase information of the cross-power spectrum of the K-band. The ionospheric time delay is obtained by inverting the total residual electron content of the ionosphere based on the cross-power spectrum of each frequency band and fitting it. The observation time delay of the corresponding frequency band is also obtained by fitting it. After removing the ionospheric delay from the observation delay, the first new observation delays corresponding to the X-band and K-band are obtained. The first new observation delays corresponding to the X-band and K-band are calculated in the first round to obtain the corresponding zenith moist atmospheric delay correction values. The zenith moist atmospheric delay correction values corresponding to the X-band and K-band are weighted and fused. The second new observation delays corresponding to the X-band and K-band are calculated based on the fused zenith moist atmospheric delay correction values. The second new observation delays corresponding to the X-band and K-band are calculated in the second round to obtain the corresponding UTC UT1 estimates. The UTC UT1 estimates corresponding to the X-band and K-band are weighted and fused to obtain the final UTC UT1 measurement result.
2. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The S / X / K tri-frequency VLBI joint measurement system consists of at least two observation stations forming an interferometric measurement network, and each observation station is equipped with tri-band receiving equipment including S-band, X-band, and K-band.
3. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The radio source is a compact point source with a source flux greater than 0.25 Jy.
4. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The phase information of the cross power spectrum in the K band is corrected using the phase information of the cross power spectrum in the X band, including: The tropospheric phase contribution value of the K-band is calculated based on the phase information of the cross power spectrum of the X-band, and the tropospheric phase contribution value of the K-band is subtracted from the phase information of the cross power spectrum of the K-band.
5. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 4, characterized in that, The formula for calculating the tropospheric phase contribution value of the K-band is as follows: ； in, This represents the tropospheric phase contribution value of the K-band. Indicates the frequency of the K-band. Indicates the frequency of the X band. This represents the phase information of the cross power spectrum in the X-band.
6. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The formula for inverting and fitting the ionospheric delay and the observation delay of the corresponding frequency band is expressed as: in, This refers to the phase information of the cross power spectrum for the corresponding frequency band. For the corresponding frequency band, For the observation delay of the corresponding frequency band, For reference frequency, For the initial phase, This is the estimated total residual electron content of the ionosphere, also known as the ionospheric delay.
7. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The first round of calculations is performed on the first new observation delay to obtain the zenith wet atmospheric delay correction values for the X-band and K-band, respectively, including: Calculate the first time delay residual between the first new observation time delay and the theoretical time delay for the X-band and K-band respectively; The least squares method is used to solve the first time delay residual to obtain the zenith wet atmospheric time delay correction values for the X and K bands.
8. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The weighted average of the zenith wet atmospheric time delay correction values corresponding to the X-band and K-band is fused, as expressed by the formula: ； in, This represents the zenith moist atmospheric time delay correction value after fusion. This indicates the accuracy of the zenith wet atmospheric delay correction for the X-band. This indicates the accuracy of the zenith wet atmospheric delay correction for the K-band. This represents the zenith wet atmospheric delay correction value for the X-band. This represents the zenith wet atmospheric delay correction value for the K-band.
9. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The second round of calculations was performed on the second new observation delays corresponding to the X-band and K-band to obtain the corresponding UTC UT1 estimates, including: Calculate the second time delay residuals between the second new observation time delay and the theoretical time delay for the X-band and K-band respectively; The least squares method is used to solve the second time delay residual to obtain the estimated values of UTC UT1 for the X and K bands.
10. The method for jointly measuring Universal Time UT1 based on SXK three-frequency VLBI according to claim 1, characterized in that, The weighted average of the estimated UT1 values corresponding to the X and K bands is expressed by the following formula: ； in, This represents the final world time UT1 measurement after merging. This indicates the accuracy of the world time estimation for the X-band. Indicates the accuracy of the K-band world time estimation. This represents the estimated UT1 value for the X-band. This represents the estimated UTC UT1 value for the K-band.