Method for calibrating pointing of a telescope using radio spectral lines

Abstract

The present application relates to a kind of methods for telescope pointing calibration using radio spectral lines, comprising: selecting a spectral line radio source as calibration source from preset spectral line radio source table;While the radio telescope is observed in NP-ON-OFF mode, make antenna scan in preset azimuth range and elevation range according to preset method, and obtain azimuth scanning pretreatment data and elevation scanning pretreatment data;Calibration result is obtained according to azimuth scanning pretreatment data and elevation scanning pretreatment data and by model fitting and polynomial fitting cross-validation, the calibration result includes whether scanning succeeds and the pointing deviation obtained when scanning succeeds.The present application uses spectral line to calibrate the method for telescope pointing calibration, the adjacent spectral line of calibration source is used for pointing calibration, and dynamic compensation value is evaluated and calculated by cross-validation and other ways, so as to reduce the influence of weather on pointing calibration.

Description

Technical Field

[0001] The present invention relates to the field of radio telescopes, and more particularly to a method for calibrating the pointing of a telescope by using radio source spectral lines. Background Art

[0002] The Tianma Radio Telescope (TMRT), located in Sheshan, Songjiang District, Shanghai, features a 65-meter Cassegrain primary reflector, an active reflector system, a low-noise receiver system covering eight bands from 1 to 50 GHz, a high-speed data acquisition system for Very Long Baseline Interferometry (VLBI), and a highly stable hydrogen atomic clock. The TMRT is suitable for radio astronomy, single-antenna VLBI, and geodynamics. Due to its powerful performance and unique location, the TMRT is a powerful unit in the domestic and international VLBI network. Its VLBI baselines connected to Shanghai are the longest, providing the highest spatial angular resolution. With the TMRT replacing the 25-meter reflector at Sheshan, the sensitivity of the Chinese VLBI Network (CVN) has increased by 1.67 times. In addition to its primary applications for high-resolution VLBI mapping and high-precision measurements, it can also serve as a standalone unit for a wide range of single-antenna astronomical observations and research, covering many important spectral lines.

[0003] Currently, radio telescopes use methods for pointing correction, including establishing a static pointing model and dynamic real-time correction. The static pointing model involves scanning a large number of radio sources using azimuth and elevation offsets and a cross-scanning technique. The scan results are then used to fit the established model parameters, taking into account and calculating as many error terms as possible to improve pointing accuracy. The dynamic real-time correction method primarily involves acquiring scan data, preprocessing the scan data, calculating the pointing error based on a parameterized model, and correcting the pointing error based on the pointing error to eliminate it.

[0004] However, the existing method has many deficiencies. First, whether it is a static model or a dynamic pointing correction, a continuous spectrum calibration source is used, which is easily affected by water vapor, which leads to the fact that the pointing calibration of the continuous spectrum radio source can only be used in good weather, and the available continuous spectrum strong source is very rare for radio telescopes such as the Tianma telescope which can observe many spectral lines. Second, the continuous spectrum pointing source needs to be selected manually, and the source intensity is not evaluated. When the pointing calibration fails, the source needs to be selected again for scanning, which is very time-consuming. Third, the above method establishes a parameterized model (Gaussian model) to process data. In actual use, when the weather is bad and the signal-to-noise ratio decreases, the probability of model fitting failure is very high. Finally, after the fitting fails, the result is not checked, and it is easy to lose the target in a chain, such as first scanning the azimuth axis, and then scanning the elevation axis. Due to the loss of the azimuth, the elevation is also lost. SUMMARY

[0005] The purpose of the present application is to provide a method for calibrating the pointing of a radio telescope using the spectral lines of a radio source, which calibrates the pointing by using the adjacent spectral lines of the calibration source and evaluates and calculates the dynamic compensation value by cross-validation, thereby reducing the influence of weather on the pointing calibration.

[0006] In order to achieve the above purpose, the present application provides a method for calibrating the pointing of a radio telescope using the spectral lines of a radio source, comprising the steps of:

[0007] S100: selecting a spectral line radio source from a preset spectral line radio source table as a calibration source;

[0008] S200: while the radio telescope is observing in the NP-ON-OFF mode, the antenna is scanned in a preset azimuth range and elevation range according to a preset method, and azimuth scan pre-processing data and elevation scan pre-processing data are obtained, wherein the azimuth scan pre-processing data and the elevation scan pre-processing data include the relationship between the sum of the temperatures of all spectral lines in the temperature spectrum of the calibration source and the scanning time;

[0009] S300: obtaining a calibration result by cross-validation of model fitting and polynomial fitting according to the azimuth scan pre-processing data and the elevation scan pre-processing data, wherein the calibration result includes whether the scanning is successful and the pointing deviation obtained when the scanning is successful.

[0010] Step S100 further comprises:

[0011] S110: selecting a spectral line radio source closest to the radio telescope from a preset spectral line radio source table as a calibration source;

[0012] S120: making the radio telescope observe in the NP-ON-OFF mode;

[0013] S130: Obtaining signal intensity parameters of each spectral line of the calibration source according to the observed time domain signals in the four states;

[0014] S140: Determine whether the signal strength parameters of all spectral lines meet the preset conditions. If so, it is considered that the calibration source can be used for calibration; otherwise, select a spectral line radio source with stronger spectral lines from the spectral line radio source table as the calibration source, and return to step S120.

[0015] Furthermore, step S130 specifically includes:

[0016] S131: obtaining a power spectrum of the calibration source based on time domain signals when the noise tube is in an on state when pointing toward the calibration source, when the noise tube is in an off state when pointing toward the calibration source, when the noise tube is in an on state when offset from the calibration source, and when the noise tube is in an off state when offset from the calibration source, wherein the power spectrum includes a plurality of spectral lines;

[0017] S132: Performing Doppler correction on the frequency of the spectral line of the calibration source to obtain a corrected spectral line frequency;

[0018] S133: converting the power spectra of the calibration source in the four states into temperature spectra of the calibration source;

[0019] S134: Obtaining a noise-subtracted temperature spectrum of each spectral line based on the temperature spectrum of the calibration source and the corrected spectral line frequency, wherein the bandwidth of the noise-subtracted temperature spectrum of each spectral line is a preset bandwidth;

[0020] S135: Obtain a signal intensity parameter of each spectral line according to the temperature spectrum of each spectral line after subtracting the background noise when the spectral line is directed toward the calibration source.

[0021] Furthermore, the power spectrum obtained in step S131 is a plurality of power spectra with time sequence obtained with the first integration time as the integration time;

[0022] In S135, obtaining a signal strength parameter of the calibration source according to the temperature spectrum of each spectrum line after subtracting the background noise further includes:

[0023] For each spectral line when pointing to the calibration source, all sub-temperature spectra included in the noise-deducted temperature spectrum of the spectral line are added together to obtain an added temperature spectrum. The maximum temperature, standard deviation, and median temperature value of the spectral line are obtained based on the added temperature spectrum. The ratio of the difference between the maximum temperature and the median temperature value to the standard deviation is used as the signal strength parameter of the spectral line.

[0024] If the signal strength parameter of the existing spectrum line is greater than 2, the preset condition is met; otherwise, the preset condition is not met.

[0025] Step S200 further includes:

[0026] S210: while the radio telescope is observing in the NP-ON-OFF mode, causing the antenna to scan within a preset azimuth angle range and elevation angle range according to a preset method, and recording antenna position information at a preset frequency during the scanning process;

[0027] S220: Obtaining an azimuth offset value sequence and its corresponding time series, and an elevation offset value sequence and its corresponding time series according to the azimuth axis motion accuracy and elevation axis motion accuracy of the antenna and the antenna position information recorded during scanning;

[0028] S230: Acquire time domain signals observed by the antenna during azimuth scanning and elevation scanning, and obtain, based on the time domain signals, a noise-free temperature spectrum of each spectral line during azimuth scanning and a noise-free temperature spectrum of each spectral line during elevation scanning;

[0029] S240: For each spectral line, obtain an array of temperature variations over time for the spectral line during azimuth scanning based on a noise-subtracted temperature spectrum of the spectral line during azimuth scanning, and obtain an array of temperature variations over time for the spectral line during elevation scanning based on a noise-subtracted temperature spectrum of the spectral line during elevation scanning;

[0030] S250: Add up the temperature values ​​with the same time in the array of all spectral lines whose temperatures change with time during azimuth scanning to obtain azimuth scanning preprocessing data; add up the temperature values ​​with the same time in the array of all spectral lines whose temperatures change with time during elevation scanning to obtain elevation scanning preprocessing data.

[0031] Furthermore, the preset method is a cross scanning method, and the preset azimuth range and elevation range are both 5 times the half-power beam width.

[0032] Step S240 further includes:

[0033] For each spectral line, based on the noise-subtracted temperature spectrum of the spectrum line during azimuth scanning, the frequency corresponding to the maximum temperature is selected, and an array of temperature changes over time corresponding to the frequency is obtained, which is used as the array of temperature changes over time for the spectrum line during azimuth scanning; based on the noise-subtracted temperature spectrum of the spectrum line during elevation scanning, the frequency corresponding to the maximum temperature is selected, and an array of temperature changes over time corresponding to the frequency is obtained, which is used as the array of temperature changes over time for the spectrum line during elevation scanning.

[0034] Step S300 further includes:

[0035] S310: Fitting preset formulas to the azimuth scanning preprocessed data and the pitch scanning preprocessed data, respectively, to obtain a first azimuth temperature model and a first pitching temperature model; substituting the time series corresponding to the azimuth offset value series into the first azimuth temperature model to obtain a first azimuth temperature array; substituting the time series corresponding to the pitching offset value series into the first pitching temperature model to obtain a first pitching temperature array;

[0036] S320: Performing polynomial fitting on the azimuth scan preprocessed data and the elevation scan preprocessed data to obtain a second azimuth temperature model and a second pitching temperature model, substituting the time series corresponding to the azimuth offset value series into the second azimuth temperature model to obtain a second azimuth temperature array; substituting the time series corresponding to the pitching offset value series into the second pitching temperature model to obtain a second pitching temperature array;

[0037] S330: dividing the second azimuth temperature array into a first azimuth timing signal and a second azimuth timing signal, and obtaining a third azimuth timing signal based on the first azimuth temperature array, wherein the third timing signal has the same timing sequence as the first azimuth timing signal; dividing the second pitch temperature array into a first pitch timing signal and a second pitch timing signal, and obtaining a third pitch timing signal based on the first pitch temperature array, wherein the third timing signal has the same timing sequence as the first pitch timing signal;

[0038] S340: Determine whether the azimuth scan and the pitch scan are successful based on the first azimuth timing signal, the second azimuth timing signal, the third azimuth timing signal and the first pitch timing signal, the second pitch timing signal and the third pitch timing signal respectively; if both are successful, obtain the azimuth axis compensation value and the pitch axis compensation value, and update the pointing deviation of the radio telescope based on the azimuth axis compensation value and the pitch axis compensation value; if only one of the azimuth scan and the pitch scan is successful, obtain the axis compensation value corresponding to the successful scan, and update the pointing deviation of the corresponding axis; if both are unsuccessful, re-select a stronger spectral line power source with signal strength parameters that meet the requirements from the spectral line radio source table as the calibration source.

[0039] Step S330 further includes:

[0040] The second azimuth temperature array is divided into several segments, and the expected value of each segment is calculated respectively. The segment with the maximum expected value and its adjacent segments are taken as the first azimuth timing signal, and the remaining segments constitute the second azimuth timing signal; the temperature corresponding to the same timing as the first azimuth timing signal in the first azimuth temperature array is taken as the third azimuth timing signal; the second pitch temperature array is divided into several segments, and the expected value of each segment is calculated respectively. The segment with the maximum expected value and its adjacent segments are taken as the first pitch timing signal, and the remaining segments constitute the second pitch timing signal; the temperature corresponding to the same timing as the first pitch timing signal in the first pitch temperature array is taken as the third pitch timing signal.

[0041] Step S340 further includes:

[0042] Calculate the root mean square error between the third azimuth timing signal and the first azimuth timing signal, the standard deviation of the third azimuth timing signal, and the standard deviation of the second azimuth timing signal. If the root mean square error between the third azimuth timing signal and the first azimuth timing signal is less than 5 times the standard deviation of the third azimuth timing signal or the standard deviation of the first azimuth timing signal is greater than 10 times the standard deviation of the second azimuth timing signal, the azimuth scan is successful; otherwise, the azimuth scan is unsuccessful. Calculate the root mean square error between the third pitch timing signal and the first pitch timing signal, the standard deviation of the third pitch timing signal, and the standard deviation of the second pitch timing signal. If the root mean square error between the third pitch timing signal and the first pitch timing signal is less than 5 times the standard deviation of the third pitch timing signal or the standard deviation of the first pitch timing signal is greater than 10 times the standard deviation of the second pitch timing signal, the pitch scan is successful; otherwise, the pitch scan is unsuccessful.

[0043] The method of the present invention has the following beneficial effects:

[0044] First of all, compared with the pointing calibration of traditional continuous spectrum radio source, it has certain environmental adaptability and can also be calibrated under severe weather conditions.

[0045] Secondly, in the preprocessing stage, the dimensionless power spectrum is converted into a dimensional temperature spectrum, which provides physical meaning for the data, can effectively identify the rationality of the data, and provides great help for the evaluation of the results.

[0046] Thirdly, cross-validation through model fitting and polynomial fitting can avoid the situation where the correction becomes more and more distorted; moreover, logical judgment is added to give it a higher degree of autonomy.

[0047] By making an observation of about 20 seconds in the source selection stage, a preliminary judgment of the ground intensity can be made, thus reducing the significant time cost of failure in the pre-processing stage.

[0048] Finally, the traditional pointing calibration method selects radio sources as continuous spectrum intensity sources, while this method allows spectral line intensity sources to be used as available pointing calibration sources, expanding the available types of telescope pointing calibration sources in the field of radio astronomy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Flowchart of a method for performing telescope pointing calibration using radio source spectral lines according to an embodiment of the present invention;

[0050] Figure 2A is a relationship diagram between temperature and azimuth offset values ​​obtained after pointing calibration of the Tianma telescope using a method according to an embodiment of the present invention;

[0051] Figure 2B FIG. 1 is a relationship diagram between temperature and pitch offset value obtained after pointing calibration of the Tianma telescope using a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0053] When the relevant information of a radio telescope (such as the Tianma telescope) (including longitude, latitude, altitude, antenna aperture, etc.), spectrum line radio source table information, and receiver noise tube calibration file are known, the method of the present invention can be used to calibrate the pointing of the radio telescope during observation, and can correct the pointing error of a radio telescope with a half-power beamwidth (HPBW) of 5 times. (If there is a measured beam width, it is mainly based on the actual measurement), λ is the observation wavelength, and D is the aperture of the radio telescope. The spectrum line radio source table includes the equatorial coordinate system position information of the spectrum line radio source, the adjacent spectrum line frequency f of the calibration source i and its brightness temperature. Adjacent spectral lines refer to the spectral lines that can be simultaneously covered by the bandwidth of the telescope, and the molecular spectral line frequencies whose spectral lines have not been eliminated by Doppler shift. For n spectral lines, they are denoted as f1, f2...f n Typically, 2-4 spectral lines are sufficient. For example, if the radio source "R_AQR" (J2000 coordinates 23:43:49.46, -15:17:04.1) is selected as the calibration source, and the maser emission lines of silicon monoxide (SiO) molecular energy levels 1 and 2 are selected, then the spectral lines f1 = 42820 MHz and f2 = 43122 MHz are used for subsequent pointing calibration.

[0054] like Figure 1 As shown, an embodiment of the present invention provides a method for telescope pointing calibration using radio source spectral lines, including a source selection stage, a preprocessing stage, and a calibration stage (evaluation stage), which specifically includes the following steps:

[0055] S100: Source selection stage, select a suitable calibration source. S100 further includes:

[0056] S110: Selecting a spectral line radio source closest to the radio telescope from a preset spectral line radio source table as a calibration source.

[0057] A list of spectral line radio sources is known, including multiple spectral line radio sources and their associated information. These sources can be used to calibrate the pointing of radio telescopes. Since the list includes multiple spectral line radio sources, it is necessary to select a suitable one as the calibration source. When selecting a source, the spectral line intensity and distance from the radio telescope are typically considered. High spectral line intensity results in a higher signal-to-noise ratio, enabling use in harsher observing conditions; close distances reduce the time required for pointing calibration and ensure that the pointing error in the sky near the target observation source is maximized after calibration. Initially, the closest spectral line radio source is usually selected as the calibration source.

[0058] S120: Enables the radio telescope to observe in NP-ON-OFF mode. NP-ON-OFF mode involves using a noise tube to calibrate the radio flux during Position ON-OFF observations. This involves switching the noise tube on and off for a short period of time, typically one second. Position ON-OFF mode involves pointing the antenna toward the target object for a period of time, then deflecting it for the same amount of time.

[0059] During observation, the antenna will track the calibration source. Therefore, the antenna deviation from the calibration source means that the telescope is deflected from the calibration source by a certain angle while maintaining relative stillness with the calibration source in the geodetic coordinate system. During the source selection phase, the calibration source is observed using the NP-ON-OFF mode. The deviation angle here is usually greater than 10 times the beam width of the radio telescope.

[0060] Since a noise tube is used for radio flux calibration, noise ON OFF means that the noise tube in the antenna receiver alternates between the ON and OFF states, i.e., the noise tube is turned on for a period of time, then turned off for a period of time, then turned on again for a period of time, then turned off again for a period of time, and so on. In an exemplary embodiment, when pointing toward a calibration source, the noise tube is observed for 10 seconds in an alternating manner between the ON and OFF states. Then, the calibration source is deviated and the noise tube is observed for 10 seconds in an alternating manner between the ON and OFF states. For example, the noise tube is first turned on for 1 second, then turned off for 1 second, then turned on again for 1 second, and then turned off again for 1 second, and so on. In this way, the antenna can obtain four time domain signals, including the noise tube ON state signal when pointing toward the calibration source, the noise tube OFF state signal when pointing toward the calibration source, the noise tube ON state signal when deviated from the calibration source, and the noise tube OFF state signal when deviated from the calibration source.

[0061] S130: Obtaining signal intensity parameters of each spectral line of the calibration source according to the observed time domain signals in the four states.

[0062] Step S130 specifically includes:

[0063] S131: Obtain the power spectrum of the calibration source based on the time domain signals of the noise tube in the on state when pointing to the calibration source, the off state when pointing to the calibration source, the on state when offset from the calibration source, and the off state when offset from the calibration source, wherein the power spectrum includes multiple spectral lines.

[0064] After acquiring the time domain signal, it can be subjected to a fast Fourier transform to convert the voltage signal into a power spectrum. The power spectrum includes information of a certain bandwidth, including multiple spectral lines. The spectral lines are the emission lines in the power spectrum that are much larger than the noise floor. In the fast Fourier transform, the first integration time is used as the integration time. The first integration time t i The value is usually 1s or less, marking the time t of the power spectrum s =t start +t d / 2. For example, if the integrated data is from 18:09:00 to 1 second, the time stamp is 18:09:0.5 seconds. Since the calibration source flux (i.e., the time-domain signal) is recorded separately from the telescope coordinates, the absolute time will be used as the mapping / interpolation to map the time of the strongest spectral line to the offset position of the telescope during the final settlement. Therefore, the time stamp will also affect the pointing error (a calculation error). The recording interval of the radio telescope position is much smaller than the data recording time. The position record can be understood as an instant. Therefore, time and position can be equated here. The power spectrum calculation integrates 1 second of data. This 1 second is actually the offset of the radio telescope based on tracking, that is, the integration of the 1 second of time that has passed. Therefore, setting the time at the center can reduce the error during pointing calibration.

[0065] The power spectrum obtained in step S131 is a plurality of power spectra with time sequence obtained by taking the first integration time as the integration time. Since the antenna can obtain time domain signals of four states, four power spectra can be obtained after integrating the time domain signals of the four states respectively. The integration time t i Typically, the duration is 1 second. Each power spectrum contains multiple power spectra at different times (i.e., different time sequences). For example, if the time spent pointing toward the calibration source and the time spent away from the calibration source are both 10 seconds, the interval between Noise ON and Noise OFF is 1 second, and the integration time is 1 second, then the Nosie ON state when pointing toward the calibration source has a 5-second time domain signal. By Fourier transforming each 1-second time domain signal, we can obtain power spectra at five different times. Similarly, we can obtain power spectra at five different times when pointing toward the calibration source, when away from the calibration source, when away from the calibration source, and when away from the calibration source.

[0066] S132: Performing Doppler correction on the spectral line frequency of the calibration source to obtain a corrected spectral line frequency.

[0067] Due to the influence of the Earth's rotation, the Earth's revolution, the rotation of the Sun with the Milky Way, the lunar tides, etc., the radio telescope and the calibration source have a relative speed. Therefore, the spectral lines of the calibration source will have Doppler frequency shift deviation when they reach the radio telescope, and the spectral line frequency needs to be corrected.

[0068] In some embodiments, Barycentric Corrections can be performed using the coordinates of the radio telescope (including longitude, latitude, and altitude), the observation time of the radio telescope (Universal Time Coordinated, UTC) (observation station), and the equatorial coordinates (right ascension, declination) of the calibration source to obtain the station's motion velocity v0 under the Local Standard of the Rest (LSR). Then, the Doppler shift formula f obs =(1-v0 / c)f, the frequency position f of the actually observed spectral line can be calculated obs , c is the speed of light.

[0069] S133: Convert the power spectra of the calibration source in the four states into temperature spectra of the calibration source.

[0070] In this embodiment, a noise tube is used to perform radio flux calibration to convert the power spectrum of the calibration source in four states into the temperature spectrum of the calibration source. Specifically, as described above, in S120, the antenna of the radio telescope is observed in the noise tube ON state and the noise tube OFF state when pointing to and deflecting from the calibration source. Step S133 specifically includes: intercepting the power value of a frequency channel, and according to the noise tube calibration file in the receiver of the radio telescope, performing radio flux calibration on the receiver to obtain the system temperature T of the receiver of the intercepted frequency channel. sys , and perform radio flux calibration on the calibration source to obtain the calibration source temperature T of the intercepted frequency channel src (f) Then, the above operation is performed on each frequency channel to convert the power spectra of the calibration source under four different states into the temperature spectra of the calibration source under different states.

[0071] Since the power spectra in different states include a plurality of power spectra in different time sequences, the temperature spectra in different states also include a plurality of temperature spectra in different time sequences.

[0072] The noise tube calibration file in the radio telescope's receiver contains an information table that maps frequency information to noise temperature. is the power value of the noise tube in the ON state when the calibration source is offset, that is, the power value on the power spectrum of the noise tube in the ON state when the calibration source is offset; is the power value of the noise tube in the OFF state when the calibration source is offset, that is, the power value on the power spectrum of the noise tube in the OFF state when the calibration source is offset; is the power value of the noise tube in the ON state when pointing to the calibration source, that is, the power value on the power spectrum of the noise tube in the ON state when pointing to the calibration source; is the power value of the noise tube in the OFF state when pointing to the calibration source, that is, the power value on the power spectrum of the noise tube in the OFF state when pointing to the calibration source; T cal is the noise tube temperature in the noise tube calibration file, which is a constant value. The system temperature T in K (Kelvin) can be calculated by formula (1) sys Then use formula (2) through the system temperature T sys Calculate the calibration source temperature T of the intercepted frequency channel src (f). In this way, the power spectrum of each mode is calculated at each frequency point to obtain the calibration source temperature at each frequency point, so that the unit of the data at each frequency point is K, thereby obtaining the temperature spectrum of the calibration source, that is, the relationship between temperature and frequency.

[0073]

[0074]

[0075] S134: Obtain a noise-subtracted temperature spectrum of each spectral line according to the temperature spectrum of the calibration source and the corrected spectral line frequency, wherein the bandwidth of the noise-subtracted temperature spectrum of each spectral line is a preset bandwidth.

[0076] In order to remove the noise of high frequency signal in link transmission, the temperature spectrum can be flattened by removing the background noise. In some embodiments, for each spectrum line, the corrected spectrum line frequency f obs As the center, the temperature spectrum of the preset bandwidth (for example, 36MHz) is intercepted on the temperature spectrum in different states as the temperature spectrum of the spectrum line in different states; then for each of the temperature spectra in different states (for the convenience of description, it is referred to as a sub-temperature spectrum below, and all sub-temperature spectra constitute a temperature spectrum), the sub-temperature spectrum is divided into three sections, [f obs -18,f obs -6),[f obs -6,f obs +6),[f obs +6,f obs+18], a unary linear fit is performed on P = kx + P0 based on the data of the first and third segments to obtain k and P0, where P0 is the noise floor temperature of the radio telescope and k is the slope of the noise floor temperature changing with frequency. The entire 36 MHz noise floor temperature spectrum is calculated using k and P0, and then the noise floor temperature spectrum is subtracted from the 36 MHz temperature spectrum before fitting to obtain the temperature spectrum of the 36 MHz bandwidth after deducting the noise floor. The temperature spectrum of all sub-temperature spectra under different states after deducting the noise floor is the temperature spectrum of the spectrum line under different states after deducting the noise floor.

[0077] S135: Flow calibration: The signal intensity parameter of each spectrum line is obtained based on the temperature spectrum of each spectrum line after deducting the background noise when the spectrum line is directed to the calibration source.

[0078] In S135, obtaining a signal strength parameter of each spectrum line according to the temperature spectrum of each spectrum line after subtracting the background noise when the spectrum line is directed to the calibration source further includes:

[0079] For each spectral line when pointing to the calibration source (including the noise tube ON state when pointing to the calibration source and the noise tube OFF state when pointing to the calibration source), all sub-temperature spectra included in the temperature spectrum of the spectral line after deducting the background noise are added to obtain the added temperature spectrum. According to the added temperature spectrum, the maximum temperature, standard deviation and median of the temperature value of the spectral line are obtained, and the ratio of the difference between the maximum temperature and the median of the temperature value to the standard deviation is used as the signal intensity parameter of the spectral line.

[0080] S140: Determine whether the signal strength parameters of all spectral lines meet preset conditions.

[0081] The median of the temperature value represents the background noise temperature, and the difference between the maximum temperature and the median of the temperature value represents the intensity of the spectral line relative to the background noise. The standard deviation represents the average value of the data fluctuation of the added temperature spectrum. Therefore, the larger the standard deviation, the stronger the spectral line must be. On the contrary, the spectral line must be weaker, resulting in the inability to distinguish between the spectral line and the noise. If there is a spectral line that satisfies its signal strength parameter greater than 2, it is considered that it meets the preset conditions, and the calibration source can be used for calibration, and step S200 is executed; if the signal strength parameters of all spectral lines are not greater than 2, it is considered that it does not meet the preset conditions, and the calibration source cannot be used for calibration. It is necessary to select a spectral line radio source with a stronger spectral line from the spectral line radio source table as the calibration source, and return to step S120.

[0082] S200: Preprocessing stage: while the radio telescope is observing in the NP-ON-OFF mode, the antenna is scanned in a preset azimuth range and elevation range according to a preset method, and azimuth scanning preprocessing data and elevation scanning preprocessing data are obtained.

[0083] Step S200 further includes:

[0084] S210: While the radio telescope is observing in the NP-ON-OFF mode, the antenna is scanned in a preset azimuth angle range and elevation angle range according to a preset method, and the antenna position information is recorded at a preset frequency during the scanning process.

[0085] Since the calibration source is usually a celestial body and will move continuously, the antenna will always track the calibration source during observation. In some embodiments, the preset method is a cross scanning method. Specifically, an azimuth angle range and a pitch angle range are first set. For example, the azimuth angle range can be set to the range included in the azimuth angle of ±5HPBW, and the pitch angle range can be the range included in the pitch angle of ±5HPBW, and then scan within the azimuth angle range and the pitch angle range. Scanning refers to an action, which means that while a certain axis (azimuth axis or pitch axis) in the geodetic coordinate system remains relatively stationary with the target, the offset value of the pointing is from -5HPBW to 5HPBW; wherein, when deviating, the target is the deviated position, and when pointing, the target is the calibration source. In an exemplary embodiment, in NP-ON-OFF mode, the coordinates of the calibration source are (x, y), and the target that the radio telescope points to when deflected is (x+a, y+a). Then, when scanning while pointing to the calibration source, the scanning range is (x-5HPBW, x+5HPBW) and (y-5HPBW, y+5HPBW); when scanning while deflected from the calibration source, the scanning range is (x+a-5HPBW, x+a+5HPBW) and (y+a-5HPBW, y+a+5HPBW), where x is the azimuth axis and y is the pitch axis.

[0086] Specifically, after setting the azimuth range, first set the compensation value of the antenna azimuth axis to -5HPBW. After setting, increase the compensation value of the antenna azimuth axis from -5HPBW to 5HPBW in fixed steps. After the azimuth scan is completed, return the compensation value to zero. Then start setting the elevation range. The elevation range is also centered on the calibration source. The scan width is consistent with the azimuth scan width. When scanning, first set the compensation value of the antenna pitch axis to -5HPBW. After setting, increase the compensation value of the antenna pitch axis from -5HPBW to 5HPBW in fixed steps. In this way, the antenna can be scanned within the preset azimuth range and pitch range. In an exemplary embodiment, the antenna half-power beamwidth is 20 arc seconds, and the antenna's azimuth range and pitch range are both [-50", 50".

[0087] The antenna position information includes the position and offset value of the azimuth axis, the position and offset value of the pitch axis, and the time corresponding to the azimuth axis position and the pitch axis position. At the same time, the azimuth scanning time t can also be recorded. az , pitch scanning time t elFor example, when the preset frequency is 20Hz, it means recording 20 times per second, that is, once every 0.05 seconds. If the initial time is 0 seconds, then at 0.05 seconds, the antenna position at that time is recorded, at 0.1 seconds, the antenna position at that time is recorded, and so on, until the end of the scan.

[0088] S220: Obtain an azimuth offset value sequence and its corresponding time sequence, and an elevation offset value sequence and its corresponding time sequence according to the azimuth axis motion accuracy and elevation axis motion accuracy of the antenna and the antenna position information recorded during scanning.

[0089] The azimuth axis motion accuracy and the pitch axis motion accuracy are the minimum values ​​of the azimuth axis and pitch axis motion respectively. When scanning, the antenna will perform azimuth scanning with the azimuth axis motion accuracy as a fixed step size, and perform pitch scanning with the pitch axis motion accuracy as a fixed step size. Assume that the azimuth axis motion accuracy of the antenna is s az0 , the pitch axis motion accuracy is s el0 , the azimuth axis scanning range can be expanded to s az0 An array A of intervals az , that is, the azimuth offset value sequence; the pitch axis scanning range can be expanded to s el0 An array A of intervals el , which is the elevation offset value sequence. For example, if the antenna half-power beam width is 20 arc seconds, the antenna's azimuth scanning range and elevation range are both [-50", 50". If the azimuth axis motion accuracy is s az0 is 1 arc second, then the azimuth offset value sequence A az is [-50",-49",-48",...,50". Similarly, if the pitch axis motion accuracy s el0 is 1 arc second, then the pitch offset value sequence A el is [-50”,-49″,-48″,...,50”].

[0090] Since the antenna position information is recorded at a preset frequency during the scanning process, it may not correspond one-to-one with the azimuth offset value sequence and the elevation offset value sequence. Therefore, the azimuth offset value and time, and the elevation offset value and time in the antenna position information can be fitted respectively to obtain the relationship between the azimuth offset value and the elevation offset value and time. Then, the time series t corresponding to the azimuth offset value sequence can be obtained by interpolation. az And the time series t corresponding to the pitch offset value series el .

[0091] S230: Acquire time domain signals observed by the antenna during azimuth scanning and elevation scanning, and obtain, based on the time domain signals, a temperature spectrum of each spectral line during azimuth scanning and a temperature spectrum of each spectral line during elevation scanning after subtracting the background noise.

[0092] Since the radio telescope always observes in NP-ON-OFF mode during the scanning process, the time-domain signal can be divided into four states: the noise tube is ON when pointing to the calibration source, the noise tube is OFF when pointing to the calibration source, the noise tube is ON when deviating from the calibration source, and the noise tube is OFF when deviating from the calibration source.

[0093] Based on the same method of steps S131-S134, the temperature spectrum of each spectral line after subtracting the noise and the temperature spectrum of each spectral line after subtracting the noise during the elevation scan can be obtained according to the time-domain signal during the scanning.

[0094] S240: For each spectral line, obtain the array of temperature changes with time of the spectral line during the azimuth scan according to the temperature spectrum of the spectral line after subtracting the noise during the azimuth scan, and obtain the array of temperature changes with time of the spectral line during the elevation scan according to the temperature spectrum of the spectral line after subtracting the noise during the elevation scan.

[0095] For each spectral line, select the maximum temperature value and its corresponding frequency value (the strongest frequency) from the temperature spectrum of the spectral line after subtracting the noise during the azimuth scan. If the frequency value differs from the Doppler-corrected spectral line frequency by more than 1 MHz, the frequency value is rejected and the maximum temperature value is reselected. Finally, the array of temperature changes with time at the frequency value is cut from the temperature spectrum of the spectral line after subtracting the noise. As mentioned earlier, the integration time is usually used when integrating the time-domain signal, so the final power spectrum and temperature spectrum both have corresponding times. By obtaining the temperature value corresponding to the frequency value in all temperature spectra after subtracting the noise, and the time corresponding to the temperature spectrum, a two-dimensional array is formed by combining the temperature value and the time, which is the array of temperature changes with time of the spectral line during the azimuth scan. Similarly, the array of temperature changes with time of the spectral line during the elevation scan can be obtained.

[0096] S250: Add each temperature value with the same time in the array of temperature changes with time of all spectral lines during the azimuth scan to obtain the azimuth scan preprocessing data; add each temperature value with the same time in the array of temperature changes with time of all spectral lines during the elevation scan to obtain the elevation scan preprocessing data.

[0097] Because the time series of each spectral line is identical, the temperatures of each spectral line corresponding to the same ordinal number in the time series of each spectral line can be directly added together. That is, the temperature values ​​of each spectral line corresponding to the same time during the azimuth scan are added together to obtain an added temperature value, thereby obtaining an array of the added temperature changes over time, which serves as the azimuth scan preprocessing data. Similarly, the elevation scan preprocessing data can be obtained. The obtained azimuth scan preprocessing data and elevation scan preprocessing data are time domain data of the sum of the temperatures of all spectral lines in the temperature spectrum of the calibration source. Therefore, the azimuth scan preprocessing data and the elevation scan preprocessing data include the relationship between the sum of the temperatures of all spectral lines in the temperature spectrum of the calibration source and the scan time.

[0098] S300: Calibration stage: obtaining a calibration result according to the azimuth scanning pre-processed data and the elevation scanning pre-processed data.

[0099] Step S300 specifically includes:

[0100] S310: Fitting preset formulas by the azimuth scanning preprocessing data and the pitch scanning preprocessing data respectively to obtain a first azimuth temperature model and a first pitch temperature model, substituting the time series corresponding to the azimuth offset value sequence into the first azimuth temperature model to obtain a first azimuth temperature array; substituting the time series corresponding to the pitch offset value sequence into the first pitch temperature model to obtain a first pitch temperature array.

[0101] The preset formula is as follows:

[0102]

[0103] Where f(x) is temperature, x is time, b is the baseline constant, m is the delay caused by pointing deviation, n is the half-power beamwidth, and a is the Gaussian amplitude.

[0104] Substituting the temperature and time from the azimuth scan preprocessed data into equation (3) above, we can calculate the values ​​of parameters such as b, m, n, and a, thereby obtaining the first azimuth temperature model. Similarly, substituting the temperature and time from the elevation scan processed data into equation (3) above can also obtain the first elevation temperature model.

[0105] The azimuth offset value sequence A az The corresponding time series t az Substituting into the first-position model, we can get the first-position temperature array T az , the first position temperature array T az The temperature and time series t az The time value in the azimuth offset value sequence and the azimuth offset value in the azimuth offset value sequence are all in one-to-one correspondence; the pitch offset value sequence A el The corresponding time series t elSubstituting into the first pitch model, the first pitch temperature array T can be obtained el , wherein the temperature corresponds to the time sequence t el , and the time value in the time sequence t az corresponds to the pitch offset value in the pitch offset value sequence.

[0106] S320: polynomial fitting is performed on the azimuth scanning preprocessed data and the pitch scanning preprocessed data respectively to obtain a second azimuth temperature model and a second pitch temperature model reflecting the relationship between the sum of all spectral line temperatures and time, the time sequence corresponding to the azimuth offset value sequence is substituted into the second azimuth temperature model to obtain a second azimuth temperature array, and the time sequence corresponding to the pitch offset value sequence is substituted into the second pitch temperature model to obtain a second pitch temperature array.

[0107] The polynomial can be a 10th order polynomial, and the method of polynomial fitting is a conventional statistical method, which will not be described here.

[0108] The azimuth offset value sequence A az corresponds to the time sequence t az , and the pitch offset value sequence A az corresponds to the time sequence t el . Substituting into the second azimuth model, the second azimuth temperature array T' can be obtained el , wherein the temperature corresponds to the azimuth offset value in the azimuth offset value sequence; and substituting into the second pitch model, the second pitch temperature array T' can be obtained el , wherein the temperature corresponds to the pitch offset value in the pitch offset value sequence.

[0109] S330: the second azimuth temperature array is divided into a first azimuth time sequence signal and a second azimuth time sequence signal, a third azimuth time sequence signal is obtained according to the first azimuth temperature array, wherein the time sequence of the third time sequence signal is the same as that of the first azimuth time sequence signal; the second pitch temperature array is divided into a first pitch time sequence signal and a second pitch time sequence signal, and a third pitch time sequence signal is obtained according to the first pitch temperature array, wherein the time sequence of the third time sequence signal is the same as that of the first pitch time sequence signal.

[0110] Specifically, the second azimuth temperature array is evenly divided into several segments, the expected value of each segment is calculated respectively, and the segment where the maximum expected value is located and its adjacent segments are taken as the first azimuth time sequence signal T' az-beam , and the remaining segments constitute the second azimuth time sequence signal T' az-line ; the temperature corresponding to the same time sequence of the first azimuth temperature array T az and the first azimuth time sequence signal T' az-beam is taken as the third azimuth time sequence signal T az-beamSimilarly, the second pitch temperature array is divided into several segments, and the expected value of each segment is calculated respectively. The segment with the maximum expected value and its adjacent segments are taken as the first pitch timing signal T′ el-beam , the remaining segments constitute the second pitch timing signal T′ el-line ; Take the first pitch temperature array T el and the first pitch timing signal T′ el-beam The temperature corresponding to the same timing is used as the third pitch timing signal T el-beam .

[0111] The number of segments for the second azimuth and elevation temperature arrays depends on the sweep width. If the sweep width is 5 times the HPBW, the number of segments is 5. This step is primarily intended to separate the beam from the noise floor. By dividing the array into equal segments, we can avoid the beam being split across two segments during separation.

[0112] S340: Determine whether the azimuth scan and elevation scan are successful based on the first azimuth timing signal, the second azimuth timing signal, the third azimuth timing signal, and the first, second, and third elevation timing signals. If all are successful, obtain azimuth and elevation axis compensation values, and update the pointing deviation of the radio telescope based on the azimuth and elevation axis compensation values. If only one of them is successful, obtain the corresponding axis compensation value and update the pointing deviation of the corresponding axis. If all are unsuccessful, select a stronger spectral line source from the spectral line radio source table as the calibration source, and execute step S120. The first azimuth timing signal is a polynomially fitted antenna beam pattern, the second azimuth timing signal is a polynomially fitted antenna scan signal low-noise figure, and the third azimuth timing signal is a Gaussian-fitted antenna beam pattern. The polynomially fitted signal noise floor and beam pattern can be used to determine whether the antenna beam is normal, i.e., whether the signal strength within the beam is significantly higher than the noise. Since the theoretical antenna beam pattern is a standard one-dimensional Gaussian model, it is often the optimal value after successful fitting. However, the one-dimensional Gaussian model is prone to fitting failure when encountering interference (noise contributed by interference such as the electromagnetic environment, weather changes, and telescope terminal links). This results in a huge gap between the maximum signal point after fitting and the actual maximum signal point. Polynomial fitting does not have the problem of excessive gap. The Gaussian fitting data is verified by the polynomial fitting data to ensure that there is no fitting failure. If the fitting fails, the actual maximum signal point with better results is used. Therefore, cross-validation can be achieved to avoid further deviation after correction.

[0113] S340 specifically includes: first, calculating the third bit timing signal T az-beam and the first azimuth timing signal T′ az-beam The root mean square error, the third position timing signal T az-beam The standard deviation of the second azimuth timing signal T′ az-lineCalculate the standard deviation of the third pitch timing signal T el-beam and the first pitch timing signal T′ el-beam The root mean square error of the third pitch timing signal T el-beam The standard deviation of the second pitch timing signal T′ el-line The standard deviation of .

[0114] Then, if the third bit timing signal T az-beam and the first azimuth timing signal T′ az-beam The root mean square error is less than 5 times the third bit timing signal T az-beam The standard deviation of , then the azimuth scan is considered successful, take T az-beam The time corresponding to the maximum temperature in the azimuth offset value sequence is obtained according to the time as the azimuth axis compensation value; if the first azimuth timing signal T′ az-beam The standard deviation of the second azimuth timing signal T′ is greater than 10 times az-line The standard deviation of , then the azimuth scan is considered successful, take T ′ az-beam The time corresponding to the maximum temperature value in the azimuth offset value sequence is then obtained according to the time, as the azimuth axis compensation value. If none of the above conditions are met, it is considered that the azimuth axis scanning has failed. Similarly, if the third pitch timing signal T el-beam and the first pitch timing signal T′ el-beam The root mean square error is less than 5 times the third pitch timing signal T el-beam The standard deviation of , then the pitch scan is considered successful, take T el-beam The time corresponding to the maximum temperature in , and then obtain the corresponding pitch offset value from the pitch offset value sequence according to the time as the pitch axis compensation value; if T′ el-beam The standard deviation is greater than 10 times T′ el-line The standard deviation of , then the pitch scan is considered successful, take T ′ el-beam The time corresponding to the maximum temperature value in the image is then obtained from the pitch offset value sequence according to the time as the pitch axis compensation value. If none of the above conditions are met, the pitch scan is considered to have failed.

[0115] If both the azimuth scan and the elevation scan are successful, the calibration result is: azimuth and elevation compensation values ​​are obtained, which can be used to update the radio telescope's pointing deviation. Updating the pointing deviation means adding the azimuth and elevation compensation values ​​to the original pointing direction of the radio telescope. For example, if the radio telescope is originally pointed at 100° in azimuth and 50° in elevation, and the azimuth deviation is +1° and the elevation deviation is -2°, the radio telescope's pointing position is adjusted to 101° in azimuth and 48° in elevation, completing the update. If only one scan is successful, the calibration result is: only the compensation value for the successful axis is obtained. After updating the pointing direction of that axis, the process returns to the preprocessing stage and scans and calibrates the unsuccessful axis. For example, if the azimuth scan is successful, the azimuth compensation value is obtained, and the pointing deviation is updated based on the azimuth compensation value. Then, the process returns to step S210 and re-performs the elevation scan to calibrate the elevation axis. If all are unsuccessful, a stronger source needs to be selected from the spectrum line radio source list as the calibration source, and then the process returns to step S120. If there is no stronger spectrum line radio source, the calibration result is: the current environment cannot perform observations in this frequency band.

[0116] The pointing calibration method of the present invention has the following beneficial effects:

[0117] First, compared to traditional continuous spectrum radio source pointing calibration, the proposed method has a certain degree of environmental adaptability. To verify the effectiveness of the proposed method, actual tests were conducted on the Q-band of the Tianma Telescope. During the tests, red giant stars such as U_HER, W_HYA, V1111_OPH, VX_SGR, and R_AQR were observed using the SiO v=1 and v=2 emission lines under clear, rainy, overcast, and cloudy weather conditions. The comparison results between the operating conditions and the continuous spectrum source pointing calibration are shown in Table 1.

[0118] Table 1: Status of the method of the present invention and continuous spectrum source pointing calibration in different weather conditions

[0119]

[0120] As can be seen from Table 1, when the weather is clear, the results of the continuous spectrum source pointing calibration method and the method of the present invention are similar. However, as the water vapor density increases, the signal-to-noise ratio of the continuous spectrum source decreases significantly and becomes almost unusable, while the strong spectral lines of the spectral line source still have a good signal-to-noise ratio.

[0121] Secondly, during the preprocessing stage, the dimensionless power spectrum is converted into a dimensioned temperature spectrum, which provides physical meaning to the data, effectively identifying its rationality and greatly assisting in the evaluation of the results. The method of the present invention considers multiple aspects of the processing results to prevent the loss of pointing due to incorrect pointing deviation values.

[0122] Thirdly, the method of the present invention also performs cross-validation through model fitting and polynomial fitting, thus avoiding the situation where the correction becomes more distorted. Moreover, logical judgment is added to make the method of the present invention have a higher degree of autonomy.

[0123] Finally, the method proposed in this paper takes into account the time required for pointing calibration. Antenna scanning is quite time-consuming. For example, the Tianma telescope requires approximately 190 seconds to scan the azimuth axis. Due to the slower rotation speed of the elevation axis, the elevation axis scan requires even longer. The method proposed in this paper uses a single observation of approximately 20 seconds during the source selection phase to complete a preliminary assessment of ground intensity, thus reducing the significant time penalty incurred by failures in the preprocessing phase.

[0124] The following is an example of applying the method of the present invention to the Tianma telescope:

[0125] The Tianma telescope has accumulated 16 SiO spectral line calibration sources. During calibration, the v=1 and v=2 emission lines of SiO are mainly used, with frequencies at 42820MHz and 43122MHz respectively. These calibration sources are mainly used for Q-band (observation frequency at 40-50GHz) pointing calibration. On November 17, 2022 (light rain), the method of the present invention was used to calibrate the Tianma telescope. The spectral line source used was R_AQR, with a scan width of 300 arc seconds, and the following was obtained: Figure 2A The relationship between temperature and azimuth offset values ​​shown in the figure and Figure 2B The relationship between temperature and pitch offset value is shown in the figure. The two solid lines in the figure are left-handed and right-handed signals respectively, and the cross star is the fitting result (the choice of left-handed and right-handed signals does not affect the use of the method of the present invention). Figure 2A and Figure 2B It can be seen that the azimuth offset value and the pitch offset value corresponding to the maximum temperature are the azimuth axis compensation value and the pitch axis compensation value, which are -1.360 and 1.455 (arc seconds) respectively.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Various modifications are possible. In other words, any simple, equivalent changes and modifications made in accordance with the claims and description of the present invention are within the scope of protection of the patent claims. Anything not fully described in this invention constitutes conventional technology.

Claims

1. A method for telescope pointing calibration using radio source spectral lines, characterized in that: Including steps: S100: selecting a spectral line radio source from a preset spectral line radio source table as a calibration source; S200: while the radio telescope is observing in the NP-ON-OFF mode, the antenna is caused to scan within a preset azimuth range and elevation range according to a preset method, and azimuth scanning pre-processed data and elevation scanning pre-processed data are obtained, wherein the azimuth scanning pre-processed data and the elevation scanning pre-processed data include a relationship between the sum of the temperatures of all spectral lines in the temperature spectrum of a calibration source and the scanning time; when observing in the NP-ON-OFF mode, the radio telescope is pointed at the target celestial object for a period of time and then deflected for the same period of time, while maintaining the switching operation of the noise tube on and off; S300: Obtaining a calibration result by cross-validating the azimuth scanning preprocessed data and the elevation scanning preprocessed data through model fitting and polynomial fitting, wherein the calibration result includes whether the scanning is successful and the pointing deviation obtained when the scanning is successful.

2. The method for telescope pointing calibration using radio source spectral lines according to claim 1, characterized in that: Step S100 further includes: S110: Selecting a spectral line radio source closest to the radio telescope from a preset spectral line radio source table as a calibration source; S120: Make the radio telescope perform NP-ON-OFF mode observation; S130: Obtaining signal intensity parameters of each spectral line of the calibration source according to the observed time domain signals in the four states; S140: Determine whether the signal strength parameters of all spectral lines meet the preset conditions. If so, it is considered that the calibration source can be used for calibration; otherwise, select a spectral line radio source with a stronger spectral line from the spectral line radio source table as the calibration source, and return to step S120.

3. The method for telescope pointing calibration using radio source spectral lines according to claim 2, characterized in that: Step S130 specifically includes: S131: obtaining a power spectrum of the calibration source based on time domain signals when the noise tube is in an on state when pointing toward the calibration source, when the noise tube is in an off state when pointing toward the calibration source, when the noise tube is in an on state when offset from the calibration source, and when the noise tube is in an off state when offset from the calibration source, wherein the power spectrum includes a plurality of spectral lines; S132: Performing Doppler correction on the frequency of the spectral line of the calibration source to obtain a corrected spectral line frequency; S133: converting the power spectra of the calibration source in the four states into temperature spectra of the calibration source; S134: Obtaining a noise-subtracted temperature spectrum of each spectral line based on the temperature spectrum of the calibration source and the corrected spectral line frequency, wherein the bandwidth of the noise-subtracted temperature spectrum of each spectral line is a preset bandwidth; S135: Obtain a signal intensity parameter of each spectral line according to the temperature spectrum of each spectral line after subtracting the background noise when the spectral line is directed toward the calibration source.

4. The method for telescope pointing calibration using radio source spectral lines according to claim 3, characterized in that: The power spectrum obtained in step S131 is a plurality of power spectra with time sequence obtained by taking the first integration time as the integration time; In S135, obtaining a signal strength parameter of the calibration source according to the temperature spectrum of each spectrum line after subtracting the background noise further includes: For each spectral line when pointing to the calibration source, all sub-temperature spectra included in the noise-deducted temperature spectrum of the spectral line are added together to obtain an added temperature spectrum. The maximum temperature, standard deviation, and median temperature value of the spectral line are obtained based on the added temperature spectrum. The ratio of the difference between the maximum temperature and the median temperature value to the standard deviation is used as the signal strength parameter of the spectral line. If the signal strength parameter of the existing spectrum line is greater than 2, the preset condition is met; otherwise, the preset condition is not met.

5. The method for telescope pointing calibration using radio source spectral lines according to claim 1, characterized in that: Step S200 further includes: S210: while the radio telescope is observing in the NP-ON-OFF mode, causing the antenna to scan within a preset azimuth angle range and elevation angle range according to a preset method, and recording antenna position information at a preset frequency during the scanning process; S220: Obtaining an azimuth offset value sequence and its corresponding time series, and an elevation offset value sequence and its corresponding time series according to the azimuth axis motion accuracy and elevation axis motion accuracy of the antenna and the antenna position information recorded during scanning; S230: Acquire time domain signals observed by the antenna during azimuth scanning and elevation scanning, and obtain, based on the time domain signals, a noise-free temperature spectrum of each spectral line during azimuth scanning and a noise-free temperature spectrum of each spectral line during elevation scanning; S240: For each spectral line, obtain an array of temperature variations over time for the spectral line during azimuth scanning based on a noise-subtracted temperature spectrum of the spectral line during azimuth scanning, and obtain an array of temperature variations over time for the spectral line during elevation scanning based on a noise-subtracted temperature spectrum of the spectral line during elevation scanning; S250: Add up the temperature values ​​with the same time in the array of all spectral lines whose temperatures change with time during azimuth scanning to obtain azimuth scanning preprocessing data; add up the temperature values ​​with the same time in the array of all spectral lines whose temperatures change with time during elevation scanning to obtain elevation scanning preprocessing data.

6. The method for telescope pointing calibration using radio source spectral lines according to claim 5, characterized in that: The preset method is a cross scanning method, and the preset azimuth range and elevation range are both 5 times the half-power beam width.

7. The method for telescope pointing calibration using radio source spectral lines according to claim 5, characterized in that: Step S240 further includes: For each spectral line, based on the noise-subtracted temperature spectrum of the spectrum line during azimuth scanning, the frequency corresponding to the maximum temperature is selected, and an array of temperature changes over time corresponding to the frequency is obtained, which is used as the array of temperature changes over time for the spectrum line during azimuth scanning; based on the noise-subtracted temperature spectrum of the spectrum line during elevation scanning, the frequency corresponding to the maximum temperature is selected, and an array of temperature changes over time corresponding to the frequency is obtained, which is used as the array of temperature changes over time for the spectrum line during elevation scanning.

8. The method for telescope pointing calibration using radio source spectral lines according to claim 1, characterized in that: Step S300 further includes: S310: Fitting preset formulas to the azimuth scanning preprocessed data and the pitch scanning preprocessed data, respectively, to obtain a first azimuth temperature model and a first pitching temperature model; substituting the time series corresponding to the azimuth offset value series into the first azimuth temperature model to obtain a first azimuth temperature array; substituting the time series corresponding to the pitching offset value series into the first pitching temperature model to obtain a first pitching temperature array; S320: Performing polynomial fitting on the azimuth scan preprocessed data and the elevation scan preprocessed data to obtain a second azimuth temperature model and a second pitching temperature model, substituting the time series corresponding to the azimuth offset value series into the second azimuth temperature model to obtain a second azimuth temperature array; substituting the time series corresponding to the pitching offset value series into the second pitching temperature model to obtain a second pitching temperature array; S330: dividing the second azimuth temperature array into a first azimuth timing signal and a second azimuth timing signal, and obtaining a third azimuth timing signal based on the first azimuth temperature array, wherein the third timing signal has the same timing sequence as the first azimuth timing signal; dividing the second pitch temperature array into a first pitch timing signal and a second pitch timing signal, and obtaining a third pitch timing signal based on the first pitch temperature array, wherein the third timing signal has the same timing sequence as the first pitch timing signal; S340: Determine whether the azimuth scan and the pitch scan are successful based on the first azimuth timing signal, the second azimuth timing signal, the third azimuth timing signal and the first pitch timing signal, the second pitch timing signal and the third pitch timing signal respectively; if both are successful, obtain the azimuth axis compensation value and the pitch axis compensation value, and update the pointing deviation of the radio telescope based on the azimuth axis compensation value and the pitch axis compensation value; if only one of the azimuth scan and the pitch scan is successful, obtain the axis compensation value corresponding to the successful scan, and update the pointing deviation of the corresponding axis; if both are unsuccessful, re-select a stronger spectral line power source with signal strength parameters that meet the requirements from the spectral line radio source table as the calibration source.

9. The method for telescope pointing calibration using radio source spectral lines according to claim 8, characterized in that: Step S330 further includes: The second azimuth temperature array is divided into several segments, and the expected value of each segment is calculated respectively. The segment with the maximum expected value and its adjacent segments are taken as the first azimuth timing signal, and the remaining segments constitute the second azimuth timing signal; the temperature corresponding to the same timing as the first azimuth timing signal in the first azimuth temperature array is taken as the third azimuth timing signal; the second pitch temperature array is divided into several segments, and the expected value of each segment is calculated respectively. The segment with the maximum expected value and its adjacent segments are taken as the first pitch timing signal, and the remaining segments constitute the second pitch timing signal; the temperature corresponding to the same timing as the first pitch timing signal in the first pitch temperature array is taken as the third pitch timing signal.

10. The method for telescope pointing calibration using radio source spectral lines according to claim 8, characterized in that: Step S340 further includes: Calculate the root mean square error between the third azimuth timing signal and the first azimuth timing signal, the standard deviation of the third azimuth timing signal, and the standard deviation of the second azimuth timing signal. If the root mean square error between the third azimuth timing signal and the first azimuth timing signal is less than 5 times the standard deviation of the third azimuth timing signal or the standard deviation of the first azimuth timing signal is greater than 10 times the standard deviation of the second azimuth timing signal, the azimuth scan is successful; otherwise, the azimuth scan is unsuccessful. Calculate the root mean square error between the third pitch timing signal and the first pitch timing signal, the standard deviation of the third pitch timing signal, and the standard deviation of the second pitch timing signal. If the root mean square error between the third pitch timing signal and the first pitch timing signal is less than 5 times the standard deviation of the third pitch timing signal or the standard deviation of the first pitch timing signal is greater than 10 times the standard deviation of the second pitch timing signal, the pitch scan is successful; otherwise, the pitch scan is unsuccessful.

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