Method and system for determining current time using radio observations of multiple pulsars

Abstract

This invention discloses a method and system for determining the current time using radio observations of multiple pulsars, comprising the following steps: S1. Correcting the deviation between the local clock time and the absolute time to within a set threshold; S2. Selecting N radio pulsars, where N is greater than or equal to 4, and continuously observing the selected radio pulsars using a radio telescope to obtain observation data; S3. Processing the observation data to generate the observed pulse profile; calculating the pulsar pulse phase φ. i S4. Calculate the standard pulse profile P k With the observed pulse profile P' k The relative phase deviation δφ between i Calculate the relative phase deviation δφ with error S5. i With phase φ i deviation Δφ i S6. The deviation δT between the telescope's local clock time and absolute time is calculated, thereby determining the absolute time. This invention eliminates the need to synchronize the local clock with the absolute time of a certain time standard. It can obtain absolute time with an accuracy on the order of tens of microseconds by analyzing observed pulsars, and significantly reduces calculation time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of astronomy and computer communication, in particular to a method and system for determining current time by radio observation of multiple pulsars. BACKGROUND

[0002] Currently, there is a corresponding technology for determining accurate time by radio observation of pulsars. The current method is to observe pulsars with known rotation rules, determine the number of whole rotation periods of the pulsar from the reference time point in the ephemeris to the current time point by the local clock time of the telescope, determine the decimal part of the number of rotation periods of the pulsar by the phase of the observation data, and combine the two to obtain the total number of rotation periods of the pulsar. Then, the time difference from the reference time point in the ephemeris to the observation start time point is calculated using the rotation rule of the pulsar, which is the prediction deviation of the absolute time.

[0003] The existing technical means include: 1) determining time with an accuracy of within 2 minutes by a star sensor or a sun sensor without absolute time; 2) processing radio pulsar data to obtain a radio pulse profile with known absolute time; 3) comparing the radio pulse profile with a standard profile to obtain the difference between the pulse phase of the current observation pulse profile and the theoretical pulse phase.

[0004] In the above calculation method, an observation station clock with an absolute time accuracy of within 1 millisecond is needed to compare its time indication with the rotation phase of the pulsar to obtain the number of whole rotation periods of the pulsar. If the observation station itself does not have a precise clock, or the time of the observation station is lost and cannot be accurately synchronized, the above time determination method cannot be performed. SUMMARY

[0005] In view of the problems existing in the prior art, the purpose of the present application is to provide a method and system for determining current time by radio observation of multiple pulsars, which can obtain absolute time with an accuracy of up to ten microseconds without synchronizing the local clock with the absolute time of a certain time standard by analyzing the observed pulsars.

[0006] To achieve the above purpose, the present application provides a method for determining current time by radio observation of multiple pulsars, which comprises the following steps:

[0007] S1. correcting the deviation between the local clock time of the telescope and the absolute time to within a set threshold;

[0008] S2. selecting N radio pulsars in right ascension, N being greater than or equal to 4, and using a radio telescope to continuously observe the selected radio pulsars respectively to obtain observation data;

[0009] S3. Fold the observed data with the pulsar ephemeris and the observed start time within the set threshold to remove the dispersion and polarization calibration; and correct the time to the pulsar barycenter using the solar system ephemeris and the binary orbit model and parameters in the pulsar ephemeris, and calculate the pulsar pulse phase φ i ;

[0010] S4. Compare the standard pulse profile P k with the observed pulse profile P' k , where the subscript k represents the intensity value corresponding to the kth point of the discretized pulse profile; and calculate the relative phase deviation δφ k between the standard pulse profile P k and the observed pulse profile P' i and the error

[0011] S5. The decimal part of the relative phase deviation δφ i and the phase φ i corresponds to the measured value and the theoretical value, respectively, and the deviation Δφ i between the two is calculated.

[0012] S6. The deviation δT between the local clock time of the telescope and the absolute time is calculated by the period of different pulsars and the deviation Δφ i between the observed pulse phase and the theoretical pulse phase, and the absolute time is determined.

[0013] Further, in step S1, first, the deviation between the local clock time of the telescope and the absolute time is corrected using the sun sensor and the star sensor according to whether the time is during the day or at night, so that the deviation is within a set threshold, and the set threshold is 2 minutes, to ensure that the specified celestial body coordinates can be captured within the beam of the radio telescope.

[0014] Further, in step S2, four or more radio pulsars with a timing residual lower than 10 microseconds and a timing red noise intensity lower than 5 times the timing white noise intensity in the allowed right ascension range of the observable sky area of the telescope are selected, and the selected radio pulsars are observed continuously using the radio telescope, each for 1 minute, and the signal intensity data of the pulsar radiation processed by the back end of the telescope and the local clock time T' i of the telescope at the start of each observation are recorded, where the subscript i corresponds to different pulsars.

[0015] Further, in step S3, the following sub-steps are further included:

[0016] S31. Obtain the pulsar ephemeris including the pulsar rotation frequency f i , the first derivative of the pulsar rotation frequency with respect to time and the second derivative of the pulsar rotation frequency and the time reference point T of higher-order derivatives and pulsar rotation frequency derivatives. 0i pulsar dispersion DM i Parameters of the elliptical orbit of a pulsar binary;

[0017] S32. Using the binary star orbit model and parameters from the solar system ephemeris and pulsar ephemeris, the time is corrected to the pulsar barycenter to obtain the abstract reference time T'. ai ;

[0018] S33. Using T' ai Calculate the pulse phase φ of a pulsar i .

[0019] Furthermore, in step S32, the abstract reference time T' is obtained. ai The calculation formula is as follows:

[0020]

[0021] The first term is the dispersion time delay, v GHz The first term represents the pulsar radio observation frequency in GHz, and s represents the parameter in seconds; the second and third terms represent the time delay caused by the Earth's revolution around the solar system's center of mass and the pulsar's radiation position's revolution around the binary star system's center of mass, Δx. pi Let Δx be the sum of the lengths of the projections of the pulsar's position relative to the center of mass of the binary system along the line of sight and the lengths of the projections of the telescope relative to the center of mass of the solar system along the line of sight. ai The length of the projection of the vector of the pulsar radiation beam relative to the center of the pulsar onto the line of sight, where c is the speed of light; the fourth term Δt Si This is the time delay caused by the gravitational field of the companion star on the propagation of pulsar radiation.

[0022] Furthermore, in step S33, T' is used ai Calculate the pulse phase φ of a pulsar i The formula is as follows:

[0023]

[0024] Furthermore, in step S6, the periods of different pulsars and the deviations between the observed pulse phase and the theoretical pulse phase can form a system of linear congruent equations {δT≡P}. i Δφ i (mod P i )}.

[0025] Furthermore, in Δφ i The error is Under the given conditions, solve the above system of linear congruence equations to obtain the deviation δT between the local time of the telescope and the absolute time of the observation station clock, and determine the absolute time.

[0026] On the other hand, the present invention provides a system for determining the current time using radio observations of multiple pulsars, the system being used to implement the method for determining the current time using radio observations of multiple pulsars as described in the present invention.

[0027] Furthermore, the system includes an observation module and a calculation module. The observation module is used to observe N pulsars to obtain observation data, and the calculation module is used to calculate absolute time based on the observation data.

[0028] The beneficial effects of this invention are as follows: This invention utilizes a method and system for determining the current time through radio observations of multiple pulsars. It eliminates the need to synchronize a local clock with the absolute time of a specific time standard, allowing for the acquisition of absolute time with an accuracy on the order of tens of microseconds through pulsar observation and analysis. The brute-force search problem of calculating time deviations using the period and phase deviations of different pulsars is transformed into a linear congruence problem, significantly reducing computation time. Attached Figure Description

[0029] Figure 1 A flowchart illustrating the method for determining the current time using radio observations of multiple pulsars according to the present invention;

[0030] Figure 2 The standard pulse profile and observed pulse profile of pulsar J0751+1807 are shown in a specific embodiment of the present invention; where the horizontal axis is the pulse phase and the vertical axis is the normalized relative flux intensity.

[0031] Figure 3 As shown in the specific embodiments of the present invention Figure 1 A schematic diagram of the phase difference between the Fourier transform results of two pulse profiles; where the horizontal axis represents the frequency count of the Fourier transform, and the vertical axis represents the aforementioned phase difference;

[0032] Figure 4 This is an example of the coarse screening results of solving a system of linear congruence equations in a specific embodiment of the present invention; where the horizontal axis is the test value (unit: seconds) of the difference between the local clock time and the absolute time used for testing, and the vertical axis is the likelihood function corresponding to the test value;

[0033] Figure 5 This is an example of the fine screening results of solving a system of linear congruence equations in a specific embodiment of the present invention; where the horizontal axis is the test value (unit: seconds) of the difference between the local clock time and the absolute time used for testing, and the vertical axis is the likelihood function corresponding to the test value;

[0034] Figure 6The experimental statistical result diagram of the method and system for determining the current time by using the radio observation of multiple pulsars according to the present application; wherein the horizontal axis is the difference between the calculation result and the preset result (unit: microsecond), and the vertical axis is the experimental number falling in a certain grid. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0036] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0037] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0038] The specific embodiments of the present application will be described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. Figures 1-6 The specific embodiments of the present application will be described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0039] The embodiment of the present application provides a method and system for determining current time by using radio observation of multiple pulsars, and the basic concept is to determine absolute time based on radio observation of multiple pulsars and local clock time of a telescope. The radio observation process of the pulsar needs to record and observe the radio pulsar signal based on the radio telescope and its back-end equipment, and fold and disperse the signal according to the pulsar ephemeris to obtain distinguishable pulse profile data. The absolute time is a certain time defined at a certain reference point of time, and is also the time used for analyzing the pulsar ephemeris. The local clock time of the telescope refers to the time recorded by the clock located at the observation station, and the time recorded by the clock has a comparable time flow rate compared with the absolute time, but there is a certain deviation between the values of the two.

[0040] As shown in the figure, the method for determining current time by using radio observation of multiple pulsars in the embodiment comprises the following steps: Figure 1

[0041] S1. Correct the deviation between the local clock time of the telescope and the absolute time to within a set threshold. Specifically, first, according to whether the time is in the daytime or at night, use optical devices such as a sun sensor and a star sensor to observe visible light celestial bodies. If it is at night, use the star sensor to measure the sidereal time angle (Note: the star sensor can obtain the direction parameters of the stars in the device in real time, including the sidereal time angle), and the sidereal time angle and the right ascension of the stars are added to obtain the local sidereal time. Since the local sidereal time is equal to the local mean time plus the sidereal time of the zero time of the world time of the day plus the Greenwich mean time divided by 365.2422, the local mean time can be solved through this relationship; if it is in the daytime, the local mean time can be directly measured by using the sun sensor. Since the angular accuracy of the current star sensor is more than 0.5 degrees, the maximum time angle is 2 minutes. Since the current star sensor has different specifications, the angular accuracy is about 0.01 degrees to 0.5 degrees. If the star sensor with an angular accuracy of 0.01 degrees is used, the time angle deviation should be within 2.5 seconds. Therefore, the time deviation determined by the star sensor is within 2 minutes. Correcting the deviation between the local clock time of the telescope and the absolute time to within 2 minutes can ensure that the specified celestial body coordinates can be captured in the beam of the radio telescope.

[0042] S2. Select four or more radio pulsars in the allowed right ascension range of the observable sky area of the telescope, which have a timing residual less than 10 microseconds and a timing red noise intensity less than 5 times the timing white noise intensity, and use the radio telescope to continuously observe the selected radio pulsars respectively, each pulsar is observed for 1 minute, and the signal intensity data of the pulsar radiated after being processed by the back-end of the telescope and the local clock time T' of the telescope at the beginning of each observation are recorded. i Wherein the subscript i corresponds to different pulsars. The local clock time T' of the telescope i ​The time recorded by the station local clock has a time flow rate that differs from the absolute time flow rate by less than 1 microsecond / day. i The recorded time differs from the absolute time T i by a difference δT i Due to the operation in step S1, the time difference |δT i | is less than 2 minutes. Since the different pulsar observations are continuous and each pulsar observation lasts only 1 minute, δT i differs by less than 1 microsecond for different indices i. For the present technology, the final error precision is only on the order of ten microseconds, so δT i may be considered as the same value, which is denoted as δT

[0043] S3. Processing the observation data using the pulsar ephemeris and the observation start time within 2 minutes to obtain the pulsar pulse phase and the observation pulse profile. Specifically, step S3 includes the following sub-steps:

[0044] S31. The pulsar ephemeris includes the pulsar rotation frequency f i , the derivative of the pulsar rotation frequency with respect to time , the second derivative of the pulsar rotation frequency that can exist , and higher-order derivatives, the time reference point T 0i of the derivative of the pulsar rotation frequency, the pulsar dispersion measure DM i , and the binary elliptical orbit parameters of the pulsar. T i is considered as T i , and the coordinates of the solar system barycenter at each time point of the observation data are calculated. si .

[0045] S32. Using the solar system ephemeris and the binary orbit model and parameters in the pulsar ephemeris, the time is corrected to the pulsar barycenter to obtain the abstract reference time T ai (Note: This time represents the time at which the pulsar radiation is emitted from the beam position in the solar system barycenter reference system, plus the calculation result of the time difference of the virtual radiation propagating from the pulsar binary system barycenter to the solar system barycenter), and the formula is as follows,

[0046]

[0047] where the first term is the dispersion time delay, v GHz is the pulsar radio observation frequency in GHz, and s represents the unit of this parameter in seconds; the second and third terms are the time delays generated by the revolution of the Earth around the solar system barycenter and the revolution of the pulsar radiation position around the binary system barycenter, Δx piLet Δx be the sum of the lengths of the projections of the pulsar's position relative to the center of mass of the binary system along the line of sight and the lengths of the projections of the telescope relative to the center of mass of the solar system along the line of sight. ai The length of the projection of the vector of the pulsar radiation beam relative to the center of the pulsar onto the line of sight, where c is the speed of light; the fourth term Δt Si This is the time delay caused by the gravitational field of the companion star on the propagation of pulsar radiation.

[0048] S33. Using T' ai Calculate the pulse phase φ of a pulsar i The formula is as follows:

[0049]

[0050] Since the time deviation is within 2 minutes and the observation duration for each pulsar is only 1 minute, folding within the observation duration will not result in significant profile widening.

[0051] S4. Through pulse phase φ i The observation data from each period of the pulsar are superimposed according to phase to obtain the observed pulse profile. The standard pulse profile P of each pulsar is then used. k With the observed pulse profile P' k A comparison is performed, where the subscript k represents the intensity value corresponding to the k-th point of the discretized pulse profile. The Fourier transform arrays of the two are then obtained. and The subscript j represents the value at the j-th frequency point of the Fourier transform array. The argument of the two Fourier transform arrays is... and The difference between the two is Based on the time-shift property of the Fourier transform, array translation leads to... There is a linear homogeneous relationship between j and j. Where δφ i This represents the morphological shift of the original array, and is also the linear coefficient of this linear relationship. In the above linear relationships... Since both j and are known quantities, the standard pulse profile P is obtained by fitting the homogeneous linear relationship using the least squares method. k With the observed pulse profile P' k The relative phase deviation δφ between i With error Yes, it can be obtained.

[0052] S5. Relative phase deviation δφ i With phase φ i The decimal parts correspond to the measured value and the theoretical value, respectively, and the deviation Δφ between the two is calculated. i .

[0053] S6. Due to the period P of the pulsar i Since they are naturally formed, the periods of different pulsars are coprime. Furthermore, because the observation period is only one minute, the variation in the pulsar period can be ignored during the observation period. Therefore, the periods of different pulsars and the deviations between the observed pulse phase and the theoretical pulse phase can constitute a system of linear congruence equations {δT≡P}. i Δφ i (modP i )}。 In Δφ i The error is Under the given conditions, solving this system of linear congruence equations yields the deviation δT between the telescope's local clock time and absolute time, thus determining the absolute time. The method for solving the system of linear congruence equations includes the following steps:

[0054] S61. Based on the linear congruence equations, coarsely screen the range of δT within the time interval from -2 minutes to +2 minutes. The coarse screening process involves selecting an array between -2 minutes and +2 minutes and calculating δT for each point in the array. test Likelihood function satisfying a system of linear congruence equations Among them Π i This represents calculating and multiplying all pulsars, with % representing the modulo operation. The δT value with the highest likelihood function is selected from the initial coarse screening. test To proceed with the next fine screening calculation. The spacing between the coarse screening arrays should be less than or equal to... The time scale represented.

[0055] S62. Further fine screening is performed based on the coarse screening. The spacing of the fine screening is on the order of nanoseconds to obtain the predicted value of δT.

[0056] The final time error is determined by the accuracy of the pulsar ephemeris and the telescope aperture. If the world's largest radio telescope, FAST, is used, the final determined time deviation can be limited to the order of ten microseconds.

[0057] In one specific embodiment, the present invention used the FAST telescope to test observation data of four pulsars. The specific method is as follows:

[0058] Since the relevant thresholds for step S1 can be directly determined using commercial equipment parameters and related theories, this step does not require testing and is skipped in this data test. In the actual data test, the data is pre-observed and stored in the telescope database, which cannot be modified. However, the deviation between the local clock time at the start of each observation and the absolute time can be preset during data processing (for example, we advance the start time of all data by 10 seconds). If a large number of preset deviation values ​​can be determined through data processing, it indicates that time can be corrected through data analysis.

[0059] In the test, the deviation between the local clock time and the absolute time is corrected to be less than a set threshold (preferably the threshold is set to 2 minutes). The Earth Time is used as the standard of absolute time. The FAST telescope local clock has a time link of tracing back to the Earth Time from the station clock-GPS satellite group-UTC-TT (TAI)-TT (BIPM), and the tracing back parameters of the station clock-GPS satellite group are provided by the telescope local time server, and the other parameters are provided by the International Bureau of Weights and Measures BIPM. At the same time, the mass and motion information of each celestial body in the solar system can be calculated and obtained using DE438 ephemeris, and the Earth Time can be corrected to the barycentric coordinate time of the solar system using the corresponding formula of relativity.

[0060] Corresponding to step S2, four millisecond pulsars J0645+5158, J0621+1002, J0751+1807 and J1022+1001 are selected as test pulsars in this embodiment, and the historical timing data of the observation of the four pulsars by the FAST telescope is analyzed, and the ephemeris parameters of the four pulsars provided by other telescopes can be obtained. The ephemeris parameters and standard pulse profile of the four stars can be obtained. After the observation duration of the data used for ephemeris analysis, one day (the actual experimental date is March 14, 2022, i.e. MJD = 59652) is selected for continuous observation of the four stars, and the observation starting time is 12:04, 12:36, 14:45 and 15:49 Greenwich time respectively. The observation duration is 15 minutes each time, and the data of the first minute of each observation is selected for actual data processing. The reason for observing for 15 minutes each time is to avoid the invalidation of data caused by possible radio frequency interference and to observe for a longer time.

[0061] Taking one of the calculations as an example: the FAST telescope started observing pulsar J0751+1807 at local time 14:45 on March 14, 2022, which is 59652.6145833333333333 in MJD time, which is T i In this test, the time deviation is assumed to be 1 second, which is δT i . Since this value is an experimental preset and not the true deviation, it can be marked as t fact . The starting time used in the test is Greenwich time 14:45:01 on March 14, 2022, which corresponds to MJD time 59652.6145949074074074, which is T' iThe time difference between the local clock and GPS time provided on the FAST telescope server is found to be 0.0001177173 seconds. Therefore, the corresponding GPS time at this moment is 59652.6145949087698763. The time difference between GPS and UTC conversions provided by BIPM, the time difference between UTC and TT (TAI) conversions, and the time difference between TT (TAI) and TT (BIPM) conversions are then determined. Finally, the starting time is corrected to BIPM Earth time 59652.6153956498308427, which is T' in step T2. i Values ​​in Earth time.

[0062] A random deviation δT within 2 minutes is added to the telescope's local clock time in the data recording. The ephemeris of each pulsar is used to fold, achromatic, and polarization-calibrate the data for the four pulsars. The processed data is compared with the standard pulse profile to obtain the observed pulse phase of different pulsars, and the difference is calculated with the theoretical pulse phase. Solving the linear congruence equation composed of the pulse period and observed pulse phase of the four pulsars yields δT and the relationship with a preset absolute time t. fact The predicted value t pred (Note: For the same reason as in the previous paragraph, since this value is a prediction of the experimental preset value rather than a prediction of the actual deviation, it is labeled as t in this experiment.) pred ), and the actual absolute time t fact Compare them.

[0063] Continuing with the example of pulsar J0751+1807, using Equation 10.4 of the IERS 2010 Convention, the BIPM Earth time 59652.6153956498308427 can be corrected to the solar system's barycenter time, yielding 59652.6156516378886339, which is T' in step S3. si The ephemeris provides a dispersion time delay of 0.08029688898430966 seconds for this moment, the time delay caused by the positions of Earth and the pulsar is 270.6085164014867 seconds, and the time delay caused by the binary star gravitational field is 8.678125765486764e-08 seconds. Therefore, T' in step S3 can be calculated. ai The value is 59652.618784610264681. The frequency of this star in the ephemeris is f = 287.457853995101 seconds × 86400 seconds per day, and the frequency derivative is... Second frequency derivative =0, time reference point T 0i Since the value is 55000, the pulse phase φ at this point in step S4 can be calculated. iThe value is 115554108442.7179281654396803. The standard pulse profile and the observed pulse profile are as follows: Figure 2 As shown, the phase difference between the Fourier transform results of the two is obtained. like Figure 3 As shown. Fitting is performed using the leastsq program from Python's scipy.optimize library. Figure 3 The linear relationship in the equation can be used to obtain δφ. i =0.179, with an error of According to step S5, Δφ i =0.179-0.7179281654396803≡0.461mod 1), with an error of 0.002. According to step S6, since the period of this pulsar is 0.0034787708392794254 seconds, the above values ​​form a linear congruence equation δT≡0.001604(mod 0.0034787708392794254). Similarly, under the same δT preset, the linear congruence equations corresponding to the other three stars J0645+5158, J0621+1002, and J1022+1001 can be obtained as follows: δT≡0.008433 (mod 0.008853496823689886), δT≡0.018991 (mod 0.028853861194057407), and δT≡0.012844 (mod 0.016452929958449262), respectively. The units of the values ​​in the equations are all seconds. The errors of the four equations are 7 microseconds, 8 microseconds, 2 microseconds, and 11 microseconds, respectively. Using the characteristics of linear congruence equations, a data coarse screening of values ​​between -120 and 120 is performed with a data interval of 20 microseconds. The results are as follows: Figure 4 As shown (δT on the horizontal axis in the figure) test (This represents a guessed value for δT). The maximum peak in the figure is located at 1.00002. Based on this, the values ​​between 1.00001 and 1.00003 were finely screened at intervals of 0.2 nanoseconds, and the results are as follows. Figure 5 As shown. The result of the fine sieve is 1.0000220912, which is the result for t. fact The prediction result t pred . t pred With t fact The difference is 22.0912 microseconds.

[0064] Step S4 is repeated 5000 times, with a different preset t each time. fact And obtain different t pred . Figure 6 t is obtained for each experiment pred With t factThe average of the statistical data in the figure is the system deviation of 22.5 microseconds between the prediction result of the prediction and the absolute time, and the standard deviation of the statistical data in the figure is the measurement error of 0.2 microseconds of the prediction. The system error is caused by the timing red noise of the pulsar.

[0065] In addition, the application also provides a system for determining current time by radio observation of multiple pulsars, which is used to realize the method for determining current time by radio observation of multiple pulsars according to the application. The system comprises an observation module and a calculation module. The observation module is used to observe N pulsars to obtain observation data, and the calculation module is used to calculate absolute time according to the observation data.

[0066] The advantages of the present technology are:

[0067] The application does not need to synchronize the local clock with the absolute time of a certain time standard, but can obtain the corresponding absolute time by analyzing the observation of the pulsar;

[0068] The time information used in the application has an error of the order of minutes, but the error can be eliminated through data processing, and finally the absolute time with an accuracy of the order of ten microseconds is obtained;

[0069] The application limits the observation duration of the pulsar to less than 1 minute, reduces the deviation caused by pulsar folding and dispersion, and also reduces the total working time required to determine the absolute time;

[0070] The application converts the brute force search problem of using the period and phase deviation of different pulsars to obtain time deviation into a linear congruence problem, greatly reducing the calculation time;

[0071] The application combines the rough time positioning of the star sensor with the high-precision observation analysis of the pulsar observation analysis, and finally obtains high-precision absolute time.

[0072] The object of the application is to find back the time by observing the pulsar by using the radio telescope in the case that the local time is lost and cannot be obtained from the outside world through real-time tracing. The present scheme has the following technical advantages:

[0073] 1) In the case that the absolute time is lost, the absolute time is obtained by observing the radio pulsar. This point is to abandon the absolute time parameter in the prior art, and to use the existing parameters and data to inversely calculate it, and the feasibility is ensured by the stability of the known pulsar ephemeris;

[0074] 2) The linear congruence relationship between the pulsar phases in 4 minutes is used to simplify the pure brute force search to a linear congruence equation. Through the design of the updated calculation model, the two-step process of coarse screening and fine screening in the above is shown, and its establishment is guaranteed by the mathematical calculation process;

[0075] 3) The absolute time with 10 microseconds accuracy is obtained by combining optical timing and pulsar timing. The high accuracy of pulsar timing is used to improve the accuracy of optical timing. The feasibility is guaranteed by the pulsar flux and the sensitivity of the telescope, i.e. the telescope needs to select the pulsar that can be observed by itself.

[0076] Any procedural or methodological descriptions in the flowcharts of the present application or otherwise described herein can be understood as representing modules, segments or portions of code that include one or more executable instructions for implementing specific logic functions or steps, which can be carried out in any computer-readable medium for execution by an instruction execution system, apparatus or device. The computer-readable medium can be any medium including a storage medium, a communication medium, a propagation medium, or a transmission medium that includes a program for use by or in connection with an instruction execution system, apparatus or device.

[0077] In the description of the present application, the description of the terms "embodiment", "example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms is not necessarily directed to the same embodiment or example. In addition, those skilled in the art can combine or combine different embodiments or features described in the present specification without producing contradictions.

[0078] Although the above has shown and described the embodiments of the present application, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and modifications of the above embodiments within the scope of the present application.

Claims

1. A method of determining the current time using radio observations of a plurality of pulsars, characterized in that, The method comprises the following steps: S1. Correcting the deviation between the local clock time of the telescope and the absolute time to within a set threshold; S2. Selecting N radio pulsars, N greater than or equal to 4, and using a radio telescope to continuously observe the selected radio pulsars respectively to obtain observation data; S3. Using the pulsar ephemeris and the observation start time within the set threshold, the observation data is processed to generate the observed pulse profile and the pulsar pulse phase ; S4. Utilize the standard pulse profile of each pulsar with the observed pulse profile to perform a comparison, where the subscript represents the intensity value corresponding to the point of the discretized pulse profile The standard pulse profile is calculated The relative phase deviation between the observed pulse profile and the standard pulse profile is calculated The error ; S5. Relative phase deviation The decimal part of the phase corresponds to the measured value and the theoretical value, respectively, and the deviation between the two is calculated; S6. The period of different pulsars and the deviation between the observed pulse phase and the theoretical pulse phase The deviation between the local clock time of the telescope and the absolute time is calculated The absolute time is thus determined; In step S3, the following sub-steps are further included: S31. Obtain a pulsar ephemeris comprising a pulsar rotational frequency , a derivative of the pulsar rotational frequency over time , a second derivative of the pulsar rotational frequency , higher order derivatives, a time reference point for the pulsar rotational frequency derivative , a pulsar dispersion measure , pulsar binary elliptical orbit parameters; S32. The time is corrected to the pulsar barycenter using the binary orbit model and parameters in the solar system ephemeris and the pulsar ephemeris, and an abstract reference time is obtained ; S33. Utilizing Computing pulsar pulse phase ; In step S32, the abstract reference time is obtained The calculation formula is as follows: where the first term on the right is the dispersion time delay, is the pulsar's radio observation frequency in GHz; the second and third terms are the time delays caused by the Earth's revolution around the solar system barycenter and the pulsar's radiation position's revolution around the binary system barycenter, is the sum of the length of the projection of the pulsar's position relative to the binary system barycenter position in the line-of-sight direction and the projection length of the telescope relative to the solar system barycenter position in the line-of-sight direction, is the projection length of the vector of the pulsar's radiation beam relative to the pulsar's center position in the line-of-sight direction, is the speed of light; the fourth term is the time delay caused by the companion's gravitational field to the pulsar's radiation propagation, is the solar system barycenter coordinate time; The formula used in step S33 is The formula for calculating the pulse phase of the pulsar is The formula is as follows: 。 2. The method for determining current time using radio observations of multiple pulsars according to claim 1, characterized in that, In step S1, first, according to whether the time is in the daytime or at night, the deviation between the local clock time of the telescope and the absolute time is corrected using a sun sensor and a star sensor, so that the deviation is less than a set threshold, and the set threshold is 2 minutes, to ensure that the specified celestial body coordinates source can be captured within the beam of the radio telescope.

3. The method for determining current time using radio observations of multiple pulsars according to claim 2, characterized in that, In step S2, more than four radio pulsars with timing residuals less than 10 microseconds and timing red noise intensity less than 5 times the timing white noise intensity in the allowed RA range of the observable sky area of the telescope are selected, and the selected radio pulsars are continuously observed by the radio telescope respectively, each pulsar is observed for 1 minute, and the signal intensity data of the radiation of the pulsar processed by the back end of the telescope and the local clock time of the telescope at the start of each observation are recorded wherein the subscript corresponds to different pulsars.

4. The method for determining current time using radio observations of multiple pulsars according to claim 1, wherein, In step S6, the periods of different pulsars and the deviations between the observed pulse phases and the theoretical pulse phases can constitute a system of linear congruence equations .

5. A method of determining current time using radio observations of a plurality of pulsars as claimed in claim 4, wherein, In the error is solving the above linear congruence equations under the condition that the deviation between the local clock time of the telescope and the absolute time is obtained , and the absolute time is determined.

6. A system for determining current time using radio observations of a plurality of pulsars, characterized in that, The system is used to implement the method for determining the current time by using radio observation of multiple pulsars according to any one of claims 1-5.

7. A system for determining current time using radio observations of a plurality of pulsars as claimed in claim 6, wherein, The system comprises an observation module and a calculation module, the observation module is used to observe N pulsars to obtain observation data, and the calculation module is used to calculate the absolute time according to the observation data.

Images