A method and system for quickly measuring radio telescope signal delay

Abstract

The present invention discloses a method and system for quickly measuring the signal delay of a radio telescope, the method comprising the following steps: setting periodic noise parameters and recording baseband data; calculating the standard deviation of the upper half of each cycle and the standard deviation of the lower half of each cycle according to the period of the noise, calculating the standard deviation ratio of M cycles, and taking the average value; increasing the start time offset until one noise cycle, respectively calculating the average standard deviation ratio of M cycles; fitting the curve of the average standard deviation and the start time offset to obtain the accurate time delay; comparing historical data, analyzing the differences and causes. The present technology can realize the accurate measurement of the signal delay of a radio telescope. Compared with the previous method using power spectrum, the present method has a very short data recording time, can be performed during the telescope source change period, and will not occupy the normal working time of the telescope; the present method is not affected by radio interference, and the measurement accuracy can be improved to 0.1 microseconds.

Description

Technical Field

[0001] The present invention relates to the field of signal time delay measurement, and in particular to a method and system for rapidly measuring the signal time delay of a radio telescope. Background Art

[0002] In the field of radio astronomy, the instructions issued need to be transmitted through optical fibers and electronic devices, which causes a time delay. For observations with high requirements for time accuracy, this time delay needs to be accurately measured.

[0003] The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a major national scientific and technological infrastructure in the 11th Five-Year Plan and the most sensitive single-aperture radio telescope in the world. The radio signals are collected by the reflector and then enter the feed and amplifier, and are transported to the receiver backend for processing through about 2 kilometers of optical fiber.

[0004] The noise tube is an important calibration component on the radio telescope. The noise tube is located at the front end of the receiver. When the noise tube is turned on, its noise power spectrum is superimposed on the signal power spectrum. The frequency-noise temperature relationship of the noise tube has been measured in the laboratory. By turning the noise tube on and off, the observed machine reading-noise temperature relationship can be matched, thereby converting the signal frequency-machine reading into a frequency-noise temperature relationship to achieve the calibration of the flow rate.

[0005] Due to the time delay caused by the signal transmission path, the switching and signal acquisition cycles of the noise tube will not match, resulting in errors in flow calibration.

[0006] The speed of light in optical fiber is about 0.7 times that in vacuum, and 2 km of optical fiber will produce a time delay of 10 microseconds. Since the noise tube is located at the front end of the receiver, the noise tube control command will first reach the noise tube through 2 km of optical fiber, and the signal after the noise tube state changes will then reach the back end of the receiver through 2 km of optical fiber. The actual time delay is about 20 microseconds, and the FAST high-frequency sampling time is about 49 microseconds. The time delay will reach 40% of the sampling time, causing significant flow calibration errors.

[0007] In order to measure this time delay, the time delay approximation method is usually used. That is, a series of time delay compensations are set, and the power spectrum ratio of the noise on and off states is calculated. When the ratio is the largest, the rough value of the time delay can be calculated. The step size of the time compensation is further adjusted, and the exact value of the time delay is calculated under the same steps.

[0008] This method has two obvious disadvantages. First, when there is interference, it will cause anomalies in the power spectrum, resulting in measurement errors and low accuracy of the calculated time delay. Second, each time delay requires about ten minutes of measurement, and a round of experiments takes several hours, which can usually only be performed when the telescope is under maintenance.

[0009] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0010] The object of the present invention is to provide a method and system for quickly measuring the delay of a radio telescope signal, which can improve the calculation accuracy of the time delay and shorten the time required for the calculation, so as to solve the above-mentioned problems existing in the prior art.

[0011] To achieve the above object, the present invention provides a method for quickly measuring the delay of a radio telescope signal, the method comprising the following steps:

[0012] S1. Set a periodic noise signal and record baseband data. The periodic noise is generated by a noise generator behind the telescope feed, and the periodic noise signal is merged into the telescope signal to form baseband data.

[0013] S2. Calculate the standard deviation of the first half of each cycle and the standard deviation of the second half of each cycle according to the cycle of the noise;

[0014] S3. Calculate the standard deviation ratio of M cycles and take the average value;

[0015] S4. Increase the start time offset until it is one noise period, and calculate the average standard deviation ratio of M periods respectively;

[0016] S5. Fit the mean standard deviation ratio curve to obtain the accurate time delay;

[0017] S6. Compare historical data and analyze differences and reasons.

[0018] Further, in step S1, the noise signal parameters are set as follows: noise period T=50 microseconds, noise intensity 10K, noise delay D=100 milliseconds, and 1 second of baseband data is recorded.

[0019] Furthermore, in step S2, the standard deviation ratio of the first cycle is calculated after removing the 100 millisecond noise delay, and within one noise cycle, the standard deviation ratio of the first half cycle and the second half cycle are calculated respectively.

[0020] Furthermore, in step S3, the same calculation method as in step S2 is used to continue calculating the standard deviation ratios of the next M-1 periods, and the average value of these M standard deviation ratios is taken, where M=1000.

[0021] Furthermore, in step S4, the start time offset Δt is increased until one noise period is 50 microseconds, and steps S2 and S3 are repeated to obtain the average standard deviation ratio of M periods corresponding to each start time offset Δt.

[0022] Further, in step S5, a first-order function is adopted to segmentally fit the curve of Δt and the average standard deviation ratio. At the inflection point of the trapezoidal curve, the corresponding Δt1 and Δt2 are calculated, and the average value of Δt1 and Δt2 is calculated to obtain the accurate time delay.

[0023] Furthermore, in step S6, the above steps are repeated for 19 beams respectively to obtain the time delay corresponding to each beam; the signal delay of each beam is accumulated, compared with historical data, and the change of signal delay is analyzed for monitoring the status of the device.

[0024] In another aspect, the present invention provides a system for rapidly measuring the delay of a radio telescope signal, wherein the system is used to implement the method for rapidly measuring the delay of a radio telescope signal according to the present invention.

[0025] Furthermore, the system includes a baseband data recording module, a baseband data processing module, a time delay calculation module and a time delay monitoring module.

[0026] Further, the baseband data recording module is used to set the period of noise according to the rough estimate of the time delay and record the baseband data;

[0027] The baseband data processing module is used to calculate the standard deviation of the upper half cycle and the standard deviation of the lower half cycle in each cycle; calculate the standard deviation ratio of M cycles and take the average value; increase the start time offset until it is one noise cycle, and calculate the average standard deviation ratio of M cycles respectively;

[0028] The time delay calculation module is used for segmentally fitting the curve of the average standard deviation ratio and the start time offset, calculating the inflection point value and the platform value, and obtaining the time delay.

[0029] By adopting the above technical solution, the present invention has the following beneficial effects:

[0030] This method can achieve accurate measurement of radio telescope signal delay. Compared with the previous method using power spectrum, this method greatly shortens the time of recording data, and can be performed during the telescope source change, without occupying the normal working time of the telescope; this method is not affected by radio interference, and the measurement accuracy can be improved to 0.1 microsecond; the time required for measurement will be reduced from several hours to 0.1 second, and can be performed during the telescope source change without affecting normal observation. The method of the present invention can also become a means of monitoring telescope state changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The overall architecture flow chart of the method and system for rapidly measuring the time delay of radio telescope signals of the present invention;

[0032] Figure 2 This is a data schematic diagram of the first 10 noise cycles (500 microseconds) in an embodiment of the present invention;

[0033] Figure 3 is a curve diagram of different average standard deviation ratios ratio_ave corresponding to different Δt of beam M01 in an embodiment of the present invention;

[0034] Figure 4 is a piecewise fitting curve diagram of beam M01 in an embodiment of the present invention;

[0035] Figure 5 It is a piecewise fitting curve diagram of beam M02 in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] The following combination Figure 1-Figure 5 The specific embodiments of the present invention are described in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0040] like Figure 1 As shown, the present invention provides a method for quickly measuring the delay of a radio telescope signal, the method comprising the following steps:

[0041] S1. Set a periodic noise signal and record the baseband data. Periodic noise is generated by a noise generator behind the telescope feed, and the periodic noise signal is merged into the telescope signal. The baseband data is the telescope signal merged with the periodic noise signal. The specific signal acquisition process is as follows: the astronomical signal in the form of electromagnetic waves is collected to the feed bin through the reflecting surface of the radio telescope. After passing through the feed, the electromagnetic waves are converted into voltage signals, which are merged with the periodic signal generated by the noise generator behind the feed to form an analog signal. The merged analog signal is then connected to the sampling terminal through an optical fiber. The ADC in the sampling terminal converts the analog signal into a digital signal through high-speed sampling. The digital signal is called baseband data.

[0042] In a specific embodiment, the noise signal parameters are set as follows: noise period T = 50 microseconds, noise intensity 10K, noise delay D = 100 milliseconds, and 1 second of baseband data is recorded. The noise period should be selected to be greater than the noise delay value, and the average value of the time offset Δt1 and Δt2 is calculated, which is the actual signal delay. If the noise period is less than the noise delay value, the signal delay needs to be calculated in combination with the artificially set noise delay D.

[0043] Δt1 and Δt2 are the time offsets (Δt) corresponding to the inflection points of the curve in step S5. Since the instrument has a response time when the noise injection is turned on or off, it is manifested as a maximum standard deviation ratio in the range of Δt1 to Δt2. In S5, the curve is a trapezoidal platform. Assuming that the instrument response is similar when the noise is turned on and off, the average of Δt1 and Δt2 is the noise delay.

[0044] When the noise period is smaller than the signal delay value, the calculated average values ​​of Δt1 and Δt2 need to be added with an integer multiple of the noise period N to obtain the true signal delay value. N can be estimated by the artificially set noise delay amount D and the standard deviation curve of the previous noise periods.

[0045] For example, when D=100 milliseconds and the noise period is set to 10 milliseconds, the average value of Δt1 and Δt2 is 5 milliseconds. By observing the standard deviation curve of the first 200 milliseconds, it is found that the noise starts from more than 120 milliseconds, so N is 2. The actual signal delay should be: millisecond.

[0046] If the noise period is set to 30 milliseconds, the average value of Δt1 and Δt2 is 25 milliseconds. By observing the standard deviation curve of the first 200 milliseconds, it is found that the noise also starts from more than 120 milliseconds, so N=0. The actual signal delay should be: millisecond.

[0047] S2. According to the period of the noise, calculate the standard deviation of the upper half period and the standard deviation of the lower half period in each period.

[0048] After removing the 100 millisecond noise delay, the standard deviation ratio of the upper half cycle and the lower half cycle is calculated in one noise cycle. Choosing high temperature noise can increase the value of the standard deviation ratio, thereby improving the measurement accuracy.

[0049] The FAST telescope uses 1K and 10K noise, and 10K is considered high temperature noise. Relative to the telescope system temperature of about 25K, the power ratio of the signal with noise (35K) and the signal without noise (25K) is 1.2, and the single polarization is 1.18. For other radio telescopes, the selected noise can make the power ratio of the single polarization with noise and without noise exceed 1.1, which can meet the needs.

[0050] The artificially set noise delay D in the first 100 milliseconds needs to be skipped during calculation. The higher the noise intensity, the larger the standard deviation ratio, which is conducive to improving the calculation accuracy. Therefore, if the telescope noise has 1K and 10K noise, choose 10K noise.

[0051] The standard deviation is calculated using the std function in the numpy package in Python, using the following calculation formula:

[0052]

[0053] in It is a sample The average value of The number of samples.

[0054] S3. Calculate the standard deviation ratio of M cycles and take the average value. Where M is equal to 1000. If M is too large, it will increase the program running time, and if it is too small, it will affect the calculation accuracy. It is preferred that M is equal to 1000.

[0055] In the same manner as step S2, continue to calculate the standard deviation ratios of the next M-1 periods, and take the average of these M standard deviation ratios.

[0056] S4. Increase the start time offset until it is one noise period, and calculate the average standard deviation ratio of M periods respectively.

[0057] The start time offset plus the 100 millisecond noise delay D is skipped during calculation. The cycle in S2 starts after skipping Δt+D. Different start time offsets Δt correspond to different standard deviation ratios. The signal delay value is obtained by the time offset corresponding to the maximum value of the standard deviation ratio.

[0058] Increase the start time offset (Δt) until one noise cycle is 50 microseconds, repeat steps S2 and S3, and obtain the average standard deviation ratio of M cycles corresponding to each Δt. The step size of Δt can be selected according to the accuracy of the noise cycle. Too large a Δt step size will affect the measurement accuracy. When calculating the inflection point of the trapezoidal curve in sections, the inflection point of the trapezoid where the standard deviation ratio is the largest should be selected.

[0059] The step size of the start time offset Δt, i.e., the increment value dt, is an integer multiple of the sampling period and is less than or equal to one tenth of the desired accuracy. If the desired accuracy is 0.1 microseconds and the sampling period is 1 nanosecond, then the step size dt should be 1 to 10 nanoseconds.

[0060] S5. Fit the mean-standard deviation ratio curve to obtain the accurate time delay.

[0061] Take the first-order function and fit the curve of Δt and the average standard deviation ratio in sections. At the inflection point of the trapezoidal curve, calculate the corresponding Δt1 and Δt2, calculate the average value of Δt1 and Δt2, and get the accurate time delay. The data of 19 beams can be processed in parallel to improve the efficiency of program operation. Use multiprocessing in python to process the data of different beams in parallel using different CPU threads.

[0062] The first-order function is y=a*x+b, where x is different Δt values ​​and y is the average standard deviation ratio corresponding to Δt. Through first-order function fitting, the values ​​of coefficients a and b are determined and a curve is drawn. This process is first-order function fitting.

[0063] S6. Compare historical data and analyze differences and reasons.

[0064] Repeat the above steps S1-S5 for 19 beams respectively to obtain the time delay corresponding to each beam. Accumulate the signal delay of each beam, compare with historical data, analyze the change of signal delay, which can be used to monitor the status of the equipment.

[0065] Steps S1-S5 are the process of processing data for one beam, and the same processing steps are performed for other beams.

[0066] In summary, the method of the present invention can improve the measurement accuracy of the signal delay of the radio telescope from several microseconds to 0.1 microseconds; the time required for measurement will be reduced from several hours to 0.1 seconds, and it can be performed during the telescope source change without affecting normal observation. The method of the present invention can also become a means of monitoring changes in the state of the telescope.

[0067] On the other hand, the present invention also provides a system for rapidly measuring the delay of a radio telescope signal, the system comprising a baseband data recording module, a baseband data processing module, a time delay calculation module, and a time delay monitoring module.

[0068] The baseband data recording module is used to set the noise period according to a rough estimate of the time delay and record the baseband data; that is, the baseband data recording module is used to implement step S1.

[0069] The baseband data processing module is used to calculate the standard deviation of the upper half cycle and the standard deviation of the lower half cycle in each cycle; calculate the standard deviation ratio of 1000 cycles and take the average value; increase the start time offset until one noise cycle, and calculate the average standard deviation ratio of 1000 cycles respectively; that is, the baseband data processing module is used to implement steps S2-S4.

[0070] The time delay calculation module is used to segmentally fit the curve of the average standard deviation ratio and the start time offset, calculate the inflection point value and the platform value, and obtain the time delay; that is, the time delay calculation module is used to implement step S5.

[0071] Example: Processing of beam M01 data:

[0072] S1: Set the noise delay D = 100 microseconds, the noise period T = 50 microseconds, the noise temperature 10K, and record the baseband data.

[0073] Figure 2 Data from the first 10 noise cycles (500 microseconds) are shown, with standard deviations at 100 nanosecond intervals.

[0074] S2: Start with time offset Δt=0, skip the data of D+Δt=100 microseconds, calculate the standard deviation std_p1 of the data from 101 microseconds to 125 microseconds and the standard deviation std_p2 of the data from 126 microseconds to 150 microseconds, and obtain the standard deviation ratio ratio_1 of the first cycle.

[0075] S3: Calculate the standard deviation std_a2 of the data from 151 microseconds to 175 microseconds and the standard deviation std_b2 of the data from 176 microseconds to 200 microseconds, and obtain the standard deviation ratio ratio_2 of the second cycle. Continue to calculate until the standard deviation ratio ratio_1000 of the 1000th cycle. Average the 1000 standard deviation ratios to obtain the average standard deviation ratio ratio_ave.

[0076] S4: Increase the start time offset Δt=dt,2dt,3dt,…,50us, and obtain different ratio_ave through S2-S3 method. Figure 3 It shows that different Δt of beam M01 corresponds to different average standard deviation ratios ratio_ave.

[0077] M01 and M02 represent the first and second beams in the FAST 19-beam receiver, respectively.

[0078] S5: Draw the curves of different Δt and ratio_ave. By observation, the maximum value of the standard deviation ratio is around 26.1 microseconds. Use three segments of data from 25.6 to 26 microseconds, 26.1 to 26.2 microseconds, and 26.4 to 26.8 microseconds to fit the first-order function to obtain f1, f2, and f3. Calculate the corresponding Δt_1 and Δt_2 when f1=f2 and f2=f3, and use the average value as the precise time delay. Figure 4 shows the piecewise fit of beam M01, Figure 5 A piecewise fit of beam M02 is shown. Figure 4 In Figure 5, the two lines represent the results of the two polarizations, and the vertical line marks the inflection point calculated after the segmented fitting. The average value of the two inflection points is taken as the time delay of this beam and this polarization. It can also be seen from the figure that beam M01 ( Figure 4 ) and M02 (Figure 5) have different time delays.

[0079] The time delay monitoring module is used to call previous measurement results and compare the changes in time delay, platform value, and standard deviation ratio; that is, the time delay monitoring module is used to implement step S6.

[0080] The present invention is based on the following principle: the noise temperature can be superimposed on the signal temperature received by the telescope, and the signal temperature is reflected in the baseband data as the size of the standard deviation. Thus, the exact time of the noise switch can be inferred by the change of the standard deviation. In the field of radio astronomy, temperature is used to characterize power, such as the system temperature of the telescope, the temperature of the radio source, and the temperature of the noise.

[0081] One of the technical effects of the present invention is to greatly shorten the time for recording data, which is mainly achieved by the following technical means:

[0082] High time resolution of baseband data is achieved. The time resolution of baseband data is determined by the high-speed sampling of the ADC in the acquisition terminal. The time resolution of baseband data with a sampling rate of 1GHz can reach 1 nanosecond. Accurate results can be obtained with 1000 noise cycles (50 microseconds).

[0083] The noise generator can be set to a precise period. The noise period can be accurate to 4 nanoseconds, and the increase or decrease of the telescope signal temperature can be controlled by switching the noise.

[0084] Another technical effect is the high measurement accuracy. One reason is that the time resolution of the baseband data is high (nanosecond level). The second reason is that the total time of the experiment is short. 1000 noise cycles correspond to 50 milliseconds. In such a short time, the radio interference can be considered stable. Stable interference will only affect the value of the average standard deviation ratio, but will not affect the trend of the average standard deviation ratio, and will not affect the finding of the extreme value of the average standard deviation ratio.

[0085] Any process or method description in the flowchart of the present invention or described in other ways herein can be understood as a module, segment or part of a code including one or more executable instructions for implementing the steps of a specific logical function or process, which can be implemented in any computer-readable medium for use by an instruction execution system, device or equipment, and the computer-readable medium can be any medium containing storage, communication, propagation or transmission programs for use by execution systems, devices or equipment, including read-only memories, magnetic disks or optical disks, etc.

[0086] In the description of this specification, the description with reference to the terms "embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. In addition, those skilled in the art can combine or combine different embodiments or examples described in this specification and the features therein without causing any contradiction.

[0087] Although the above content has shown and described the embodiments of the present invention, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in the field can change, modify, replace, modify and other update operations on the above embodiments within the scope of the present invention.

Claims

1. A method for rapidly measuring the delay of a radio telescope signal, characterized in that: The method comprises the following steps: S1. Set a periodic noise signal and record baseband data. The periodic noise is generated by a noise generator behind the telescope feed, and the periodic noise signal is merged into the telescope signal to form baseband data. S2. Calculate the standard deviation of the first half of each cycle and the standard deviation of the second half of each cycle according to the cycle of the noise; S3. Calculate the standard deviation ratio of M cycles and take the average value; S4. Increase the start time offset until it is one noise period, and calculate the average standard deviation ratio of M periods respectively; S5. Fit the mean standard deviation ratio curve to obtain the accurate time delay; S6. Compare historical data and analyze differences and reasons; In step S2, the standard deviation is calculated using the std function in the numpy package in python, and the calculation formula used is: in It is a sample The average value of The number of samples; In step S5, a first-order function is used for piecewise fitting and the curve of the mean standard deviation ratio; at the inflection point of the trapezoidal curve, calculate the corresponding and ,calculate and The average value of , obtains the accurate time delay.

2. The method for rapidly measuring radio telescope signal delay according to claim 1, characterized in that: In step S1, the noise signal parameters are set as follows: noise period T=50 microseconds, noise intensity 10K, noise delay D=100 milliseconds, and 1 second of baseband data is recorded.

3. The method for rapidly measuring radio telescope signal delay according to claim 1, characterized in that: In step S2, the standard deviation ratio of the first cycle is calculated after removing the 100 millisecond noise delay, and within one noise cycle, the standard deviation ratio of the first half cycle and the second half cycle are calculated respectively.

4. The method for rapidly measuring radio telescope signal delay according to claim 1, characterized in that: In step S3, the same calculation method as in step S2 is used to continue calculating the standard deviation ratios of the next M-1 periods, and the average value of these M standard deviation ratios is taken, where M=1000.

5. The method for rapidly measuring radio telescope signal delay according to claim 4, characterized in that: In step S4, the start time offset Δt is increased until one noise period is 50 microseconds, and steps S2 and S3 are repeated to obtain the average standard deviation ratio of M periods corresponding to each start time offset Δt.

6. The method for rapidly measuring radio telescope signal delay according to claim 1, characterized in that: In step S6, the above steps are repeated for 19 beams respectively to obtain the time delay corresponding to each beam; the signal delay of each beam is accumulated, compared with historical data, and the change of signal delay is analyzed for monitoring the status of the device.

7. A system for rapidly measuring the delay of radio telescope signals, characterized in that: The system is used to implement the method for rapidly measuring radio telescope signal delay according to any one of claims 1-6.

8. The system for rapidly measuring radio telescope signal delay according to claim 7, characterized in that: The system comprises a baseband data recording module, a baseband data processing module, a time delay calculation module and a time delay monitoring module.

9. The system for rapidly measuring radio telescope signal delay according to claim 8, characterized in that: The baseband data recording module is used to set the period of noise according to the rough estimation of time delay and record the baseband data; The baseband data processing module is used to calculate the standard deviation of the upper half cycle and the standard deviation of the lower half cycle in each cycle; Calculate the standard deviation ratio of M cycles and take the average value; increase the start time offset until it is one noise cycle, and calculate the average standard deviation ratio of M cycles respectively; The time delay calculation module is used for segmentally fitting the curve of the average standard deviation ratio and the start time offset, calculating the inflection point value and the platform value, and obtaining the time delay.

Images