A method for measuring universal time

Abstract

The present invention provides a method for measuring world time, wherein a digital zenith telescope is installed on an observation pedestal with known astronomical longitude and latitude to observe stars, and the astronomical longitude and latitude of the station are calculated according to the astronomical positioning principle, and the deviation between the atomic clock time of the station and the UT1 time is calculated by comparing with the known astronomical longitude and latitude, and the output time of the atomic clock is adjusted to obtain the UT1 time signal. UT1 is measured and obtained in extraordinary times (when UTC cannot be obtained) to meet application needs. The present invention only needs to connect an external atomic clock that can be controlled to obtain the shooting time of each picture, and no longer relies on the UTC time provided by the GNSS receiver. At special times, only the instrument needs to be set up at a site with known station coordinates for astronomical observation, and UT1 can be quickly obtained. The equipment has a simple structure and mobile observation, and real-time measurement results can be obtained through observation.

Description

Technical Field

[0001] The invention relates to a time measurement method and belongs to the technical field of astrometry. Background Art

[0002] UT1 is the time quantity defined by the Earth's rotation angle. It is part of the Earth Orientation Parameters (EOP) and is also an important broadcast content in the shortwave timing system of my country's National Time Service Center. The Earth Orientation Parameters (EOP) represent the Earth's rotation rate and the spatial orientation of the rotation axis and its changes. It is an important conversion parameter connecting the Geocentric Celestial Reference System (GCRS) and the International Terrestrial Reference System (ITRS). Since the Earth's rotation rate is affected by tides, oceans, atmosphere and other factors, its change rate is uneven. UT1 parameters cannot be predicted long-term and with high precision through models and can only be obtained through observations. UT1 data services are essential basic services in the fields of astrometry, geodesy, satellite navigation and orbit determination.

[0003] At present, the main ways to measure UT1 are satellite / Lunar Laser Ranging (SLR / LLR), Very Long Baseline Interferometry (VLBI), Global Navigation Satellite System (GNSS) and digital zenith telescope measurement to obtain UT1 parameters. The paper "UT1 Measurement System Based on Multi-station Digital Zenith Telescope" describes the UT1 measurement principle, which measures the local mean sidereal time of the station, and then converts the Greenwich Mean Sidereal Time and the longitude of the station to obtain the universal time UT1.

[0004] Whether it is GPS, VLBI and SLR / LLR technology based on radio measurement or digital zenith telescope (also called digital zenith tube) based on optical measurement, the method of measuring UT1 is based on UTC as a reference, measuring the difference between UT1 and UTC (UT1-UTC), marked as DUT1, and using DUT1 to correct UTC time to obtain UT1, that is, UT1 = UTC + DUT1. At present, the maintenance of UTC time is obtained by processing the atomic time provided by cooperative institutions of various countries. If UTC cannot be obtained under special circumstances, UT1 cannot be measured by the above method. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a method for measuring world time, wherein a digital zenith telescope is installed on an observation pier with known astronomical longitude and latitude to observe stars, and the astronomical longitude and latitude of the station are calculated according to the astronomical positioning principle, and the deviation between the atomic clock time of the station and the UT1 time is calculated by comparing with the known astronomical longitude and latitude, and the output time of the atomic clock is adjusted to obtain the UT1 time signal. UT1 is measured in extraordinary times (when UTC cannot be obtained) to meet application needs.

[0006] The technical solution adopted by the present invention to solve the technical problem comprises the following steps:

[0007] Step 1: Set up a digital zenith telescope on an observation pier with known coordinates λ0 and φ0 of the observation station;

[0008] Step 2: Set an initial time value UT1 for the controllable atomic clock according to the local clock time r ; Use the digital zenith telescope to collect star CCD images, extract star images and center them, and match the star images with the stars in the working star catalog to obtain the coordinates of the zenith point; According to the tilt correction value of the digital zenith telescope at the moment of observation and the polar motion correction value of the corresponding epoch, the coordinates of the zenith point are corrected to obtain the astronomical longitude, latitude λ,

[0009] Step 3: Calculate the astronomical longitude and latitude λ of the observatory station. With the known coordinates λ0 of the observation station, There is a difference, which includes the effect of polar motion and the initial UT1 of the station atomic clock. r The inaccurate impact of

[0010] For the case of only one observation station, the influence of polar motion is eliminated by constructing a prediction model for polar motion, and then the initial value UT1 of the setting station clock time is calculated. r The difference DT from UT1 time is used to adjust the output time of the atomic clock through the atomic clock control system. At this time, the output time of the atomic clock of the measuring station is UT1.

[0011] When the number of observation stations is greater than two, the astronomical latitude obtained by the observation station is used to solve the polar shift value by least squares to eliminate the influence of polar shift on the station coordinates, and then the initial value of the station clock time UT1 is obtained. r The difference DT from the real UT1 is used to adjust the output time of the atomic clock through the atomic clock control system. At this time, the output time of the atomic clock of the measuring station is UT1.

[0012] Step 4: Continue to observe and solve the station coordinates and compare them with the known station coordinates to check the accuracy of the universal time UT1. If the solution of UT1 is inaccurate, repeat step 3 to solve the difference DT again, use the atomic clock control system to control the station atomic clock time, and then output UT1.

[0013] In the step 2, for the case where there is only one observation station, the polar motion correction value of the corresponding epoch is obtained by the polar motion prediction model; for the case where the number of observation stations is greater than two, the polar motion correction value of the corresponding epoch is obtained by least squares solution.

[0014] Step 3: Obtain the initial value UT1 for setting the station clock time. r The time difference DT from UT1,

[0015]

[0016]

[0017] The beneficial effects of the present invention are:

[0018] (1) The present invention only needs to connect an external atomic clock to obtain the shooting time of each picture, and no longer relies on the UTC time provided by the GNSS receiver.

[0019] (2) The coordinates of the observation station in the agreed earth coordinate system are known. The coordinates of the observation station are observed, and the difference between the atomic clock time of the observation station and the UT1 time can be quickly determined. According to the difference, the atomic clock control system is used to control and adjust the atomic clock time of the observation station so that the atomic clock outputs UT1 time to meet the application needs in extraordinary times (when UTC cannot be obtained).

[0020] (3) At present, the methods for measuring the universal time UT1 are mainly based on VLBI, GNSS and digital zenith telescopes. VLBI requires the use of large-aperture radio antennas and the organization and coordination of joint observations of multiple stations. The large amount of data requires a special data transmission system for related processing of the stations, and the observation results have a lag. Since the right ascension of the ascending node of the satellite orbit is the same as UT1 and the longitude of the station in GNSS measurement, only the length of day LOD (LOD) can be obtained, and UT1 cannot be obtained. The digital zenith telescope has a simple structure, is easy to build, has strong anti-electromagnetic interference ability, and can quickly obtain measurement results. However, the results of the above measurements are all expressed in the form of UT1-UTC. In order to obtain UT1, UTC must be known. The method for measuring the universal time proposed in the present invention no longer relies on UTC, and UT1 is directly obtained through measurement. After the atomic clock of the station is driven, it can continuously output UT1 time.

[0021] (4) Based on the existing digital zenith telescope observation equipment, the present invention is connected to an external station atomic clock and atomic clock control system. At special moments, it is only necessary to set up the instrument at a site with known station coordinates for astronomical observation to quickly obtain UT1. The equipment has a simple structure and can be used for mobile observation. Real-time measurement results can be obtained through observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a composition diagram of a device for measuring the universal time UT1 of the present invention;

[0023] Figure 2 It is a data processing flow chart of the universal time UT1 measurement method of the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The present invention includes but is not limited to the following embodiments.

[0025] like Figure 1 As shown, the equipment required by the present invention includes a digital zenith telescope, an astronomical observation data processing system, a steerable atomic clock, an atomic clock control system and an observation pier. With the atomic clock time of the observation station as a reference, a digital zenith telescope installed on a pier with known astronomical longitude and latitude is used to observe stars, and the astronomical longitude and latitude of the observation station are calculated according to the astronomical positioning principle, and compared with the known astronomical longitude and latitude, the relative deviation of the observation station clock time and UT1 is calculated, and the output time of the atomic clock is adjusted accordingly to achieve the generation of UT1 time signal.

[0026] The digital zenith telescope is used to observe stars and obtain the star images in the zenith direction of the observation station;

[0027] The station atomic clock is used to provide reference time for digital zenith telescope observations, and outputs UT1 time after being controlled by the atomic clock control system;

[0028] The function of the astronomical observation data processing system is to process the star map of the zenith direction taken by the digital zenith telescope, and use the obtained positions of the stars in the image plane coordinate system and the reference star visual positions calculated by the reference star catalog to obtain the astronomical longitude and latitude of the observation station at the moment of observation by using the astronomical positioning algorithm, and compare with the known astronomical longitude and latitude to calculate the relative deviation between the station clock time and UT1 time;

[0029] The function of the atomic clock control system is to adjust the atomic clock output UT1 time according to the relative deviation between the station atomic clock time and UT1 time calculated by the data processing system;

[0030] The function of the observation pier is to set up instruments and provide a position reference for observation.

[0031] like Figure 2 As shown, the present invention comprises the following steps:

[0032] Step 1: At the measuring station coordinate λ0, (correspond Figure 2 A digital zenith telescope is set up on a known observation pier (known astronomical longitude and latitude of a known observation station);

[0033] Step 2: When UT1 is unknown or UTC cannot be obtained, an initial time is obtained by checking the time on the local clock before observation, and the controllable atomic clock is used to set an initial time value UT1 r ; Use the digital zenith telescope to collect star CCD images, extract star images, center, and match the stars in the working star catalog published by the International Astronomical Union (IAU) to obtain the coordinates of the zenith point. According to the tilt correction value at the moment of observation provided by the electronic inclinometer and the polar motion correction value of the corresponding epoch, the astronomical longitude and latitude of the zenith point of the station are obtained after correction (corresponding to Figure 2 The astronomical longitude and latitude of the station under the condition of unknown UTC (degrees);

[0034] Step 3: According to the principle of geodetic astronomical measurement, the relationship between the astronomical longitude and latitude of observation station i at observation epoch t and the astronomical longitude and latitude in the agreed geocentric reference system is shown in the following formula (1):

[0035]

[0036]

[0037] Where: i0 , is the astronomical coordinate of station i in the agreed geocentric reference system, λ i (t), is the astronomical longitude and latitude measured by the i-station at the t-epoch, x p ,y p is the polar motion parameter corresponding to the t observation epoch;

[0038] At the observation epoch t, ​​the observed local sidereal time S i (t) and the corresponding Greenwich sidereal time S G The relationship between them is as follows:

[0039] S G =S i (t)-λ i (t) (2)

[0040] Substituting formula (2) into formula (1) yields:

[0041]

[0042]

[0043] Where: S G (UT10 h ) is the Greenwich sidereal time corresponding to UT 0, k is the scaling factor for converting UT to sidereal time, the value of k is 1.00273791, and UT1(t) is the UT corresponding to time t.

[0044] Let UT1-UT1 r =DT, the above formula (3) becomes:

[0045]

[0046]

[0047] Step 4: Since there is a deviation between the observation station clock time and the universal time UT1, the astronomical longitude and latitude λ and With the known coordinates λ0 of the observation station, There is a difference, which includes two aspects: ① the influence of polar motion ② the initial UT1 of the atomic clock of the station r inaccuracy;

[0048] There are two solutions:

[0049] a: When there is only one observation station, the influence of polar motion can be calculated by building a prediction model for polar motion, and then the initial value UT1 of the setting station clock time can be calculated. r The difference DT with the UT1 time is controlled and adjusted by the atomic clock control system to adjust the output time of the atomic clock. At this time, the output time of the atomic clock of the measuring station is UT1.

[0050] b: When the number of stations is greater than two, the astronomical latitude obtained from the station observation is used to solve the polar shift value using the least square method to eliminate the part of the polar shift that affects the station coordinates, and then the initial value of the station clock time UT1 is calculated. r The difference DT from the real UT1 is controlled and adjusted by the atomic clock control system to adjust the output time of the atomic clock. At this time, the output time of the atomic clock of the measuring station is UT1.

[0051] Step 5: According to the difference DT solved above, use the atomic control system to steer the station atomic clock time to output the correct UT1, continue to observe and solve the station coordinates and check the accuracy of the world time UT1. If UT1 is not solved accurately, solve the difference again according to the formula (5) for solving the difference DT above, use the atomic clock control system to steer the station atomic clock time, and then output UT1.

[0052] The astronomical observation data solution process is as follows:

[0053] (1) CCD image acquisition, star image extraction, centering

[0054] Due to the influence of background noise, atmospheric disturbance and other factors, the images taken by CCD have noise. Before star image extraction, the images taken by CCD are denoised. After denoising, star image extraction is performed. First, the edge of the star image is extracted using the edge detection algorithm, and then the center of mass of the star captured is extracted using the star point center of mass extraction algorithm.

[0055] (2) Select stars from star catalog and calculate apparent position

[0056] A star catalog is a parameter catalog that records various information about stars. It publishes the coordinate position information of stars in the equatorial coordinate system at a certain reference epoch. Some also contain each star's proper motion, parallax, magnitude, spectral information, etc. In astronomical observations, it is necessary to determine the coordinates of the zenith direction at the time of observation. The position in the star catalog is the position at a certain reference epoch, so it needs to be converted to the position at the time of observation through translation and rotation changes.

[0057] (3) Star Image Matching

[0058] Star image matching is to match the star points photographed by CCD with the star points in the star catalog, and use the principle of astronomical positioning to obtain the astronomical longitude and latitude in the zenith direction of the instrument at the time of observation.

[0059] (4) Tilt correction

[0060] Digital zenith tube observation is based on the plumb line. However, due to the influence of external temperature changes, electromagnetic interference and other factors, it is difficult to ensure that the instrument's rotation axis is strictly orthogonal to the horizontal axis during the observation process. The electronic inclinometer measures the tilt correction of the instrument's rotation axis relative to the plumb line of the survey station during the observation period, and performs tilt correction on the observation results.

[0061] (5) Calculate the astronomical longitude and latitude of the station

[0062] The astronomical longitude and latitude of the station are calculated based on the results of star map matching and the tilt correction value.

[0063] (6) Calculate the difference between the station clock and UT1 and control the station clock to output UT1

[0064] According to the obtained astronomical longitude and latitude, the difference DT between the station clock time and the universal time UT1 is solved using formula (4). According to the obtained difference DT, the atomic clock is controlled by the atomic clock control system to output the universal time UT1. The observation is continued to solve the station coordinates to check the accuracy of the universal time UT1.

[0065] An embodiment of the present invention comprises the following steps:

[0066] Step 1: First, we need to determine the coordinate λ0 of the observation pier in the agreed earth reference system. The traditional measurement method can be used to use the theodolite to measure the zenith distance of the star and record the observation time to obtain the clock error to determine the astronomical longitude and latitude of the observation base in the protocol reference system; then at the station coordinate λ0, A digital zenith telescope is installed on the known observation pier;

[0067] Step 2: Before observation, check the time on the local clock to get an initial time as the initial time value UT1 set by the controllable atomic clock. r ; Use the digital zenith telescope to collect star CCD images, extract star images and center them, and match the star images with the stars in the working star catalog published by the International Astronomical Union to obtain the coordinates of the zenith point;

[0068] Step 3: During the instrument observation process, due to the influence of external temperature changes, electromagnetic interference and other factors, the instrument's rotation axis is difficult to be strictly orthogonal to the horizontal axis. Therefore, the observation results must be tilt corrected according to the tilt correction value provided by the electronic inclinometer at the moment of observation to obtain the corrected astronomical longitude and latitude of the station.

[0069] Step 4: Due to the continuous change of the position of the earth's rotation axis in the earth, the position of the ground point also changes accordingly. The result obtained in step 3 is the astronomical longitude and latitude based on the instantaneous rotation axis of the earth and the instantaneous earth pole. The International Earth Reference System is a protocol coordinate system, so the observation results must be corrected for polar shift. When there is only one measuring station, the polar shift correction value of the corresponding epoch is obtained by the polar shift prediction model; the polar shift correction value of the corresponding epoch obtained by the least squares solution of multiple measuring stations is corrected to obtain the astronomical longitude and latitude of the zenith of the measuring station;

[0070] Step 5: Since there is a deviation between the observation station clock time and the universal time UT1, the astronomical longitude and latitude λ and With the known coordinates λ0 of the observation station, There is a difference. The reason for the difference is that the initial UT1 of the atomic clock of the measuring station r inaccurate.

[0071] Let UT1-UT1 r =DT:

[0072]

[0073]

[0074] The initial value UT1 of the station clock time is obtained by the above formula. rThe difference DT from UT1 time is used to adjust the output time of the atomic clock through the atomic clock control system. At this time, the output time of the atomic clock of the measuring station is UT1.

[0075] Step six, continue to observe and solve the station coordinates and compare them with the known station coordinates to check the accuracy of the universal time UT1. If the solution of UT1 is inaccurate, solve the difference again according to the above formula for solving the difference DT, use the atomic clock control system to control the station atomic clock time, and then output UT1.

Claims

1. A method for measuring universal time, characterized in that The following steps are involved: Step 1: At the observation station coordinates λ0, A digital zenith telescope is set up on the known observation pier; the observation station coordinates λ0, are astronomical longitude and latitude coordinates; Step 2: Set an initial time value UT1 for the drivable atomic clock according to the local clock time r ; Use the digital zenith telescope to collect star CCD images, extract star images and center them, and match the star images with the stars in the working star catalog to obtain the astronomical longitude and latitude coordinates of the zenith point of the observatory; According to the tilt correction value of the digital zenith telescope at the moment of observation and the polar motion correction value of the corresponding epoch, the coordinates of the zenith point are corrected to obtain the astronomical longitude and latitude λ of the zenith point of the observation station. Step 3: Calculate the astronomical longitude and latitude λ of the observatory station. With the known coordinates λ0 of the observation station, There is a difference, which includes the effect of polar motion and the initial UT1 of the atomic clock of the observatory. r The impact of inaccuracy; In the case of only one observation station, the influence of polar motion is eliminated by constructing a prediction model for polar motion, and then the initial value UT1 of the atomic clock time of the setting observation station is calculated. r The difference DT from UT1 time is controlled by the atomic clock control system to adjust the output time of the atomic clock. At this time, the output time of the atomic clock of the observatory is UT1. When the number of observation stations is greater than two, the astronomical latitude obtained by the observation station is used to solve the polar shift value by least squares to eliminate the influence of polar shift on the station coordinates, and then the initial value of the atomic clock time UT1 of the set observation station is obtained. r The difference DT from the real UT1 is used to adjust the output time of the atomic clock through the atomic clock control system. At this time, the output time of the atomic clock of the observation station is UT1. Step 4: Continue to observe and solve the station coordinates and compare them with the known station coordinates to check the accuracy of the universal time UT1. If the solution of UT1 is inaccurate, repeat step 3 to solve the difference DT again, use the atomic clock control system to control the atomic clock time of the observation station, and then output UT1.

2. The method for measuring universal time according to claim 1, characterized in that: In the step 2, for the case where there is only one observation station, the polar motion correction value of the corresponding epoch is obtained by the polar motion prediction model; for the case where the number of observation stations is greater than two, the polar motion correction value of the corresponding epoch is obtained by least squares solution.

3. The method for measuring universal time according to claim 1, characterized in that: Step 3 is to obtain the initial value UT1 of the atomic clock time of the observation station. r The time difference DT from UT1, Among them, S i (t) is the local sidereal time observed at epoch t, ​​S G (UT10 h ) is the Greenwich sidereal time corresponding to 0 o'clock in the universal time, k is the ratio coefficient of converting the universal time to the sidereal time, λ i0 , is the astronomical coordinate of observation station i in the agreed geocentric reference system; x p ,y p is the polar motion parameter corresponding to the t observation epoch.

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