An online sun calibration method for digital phased array weather radar

Abstract

The application discloses an online sun calibration method for a digital phased array weather radar, and relates to the technical field of weather radar calibration. The method determines the real-time position of the sun according to the geographical position of the digital phased array weather radar and the detection time of the current detection period, and then uses the time persistence of solar radiation and the digital beam forming technology of the digital phased array weather radar to perform digital beam forming on the full-array IQ data of a distance bank at the real-time position of the sun in the current detection period during the scanning detection process, so as to image the sun and obtain solar radiation data. The method can realize the synchronization of the detection process and the online sun calibration process of the digital phased array weather radar, reduces the additional time consumption caused by calibration, is beneficial to increasing the calibration frequency, and the calibration result can be used for real-time evaluation and correction of the performance parameters of the digital phased array weather radar, thereby effectively improving the observation performance of the digital phased array weather radar.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weather radar calibration, and particularly relates to an online sun calibration method for digital phased array weather radar. BACKGROUND

[0002] The digital phased array weather radar adopting the digital beam forming system has the advantages of beam forming flexibility and simultaneous multi-beam realization, and compared with the traditional mechanical scanning type weather radar, the data rate is improved and the radar scanning period is shortened, and the digital phased array weather radar has been gradually used for meteorological detection.

[0003] The antenna pointing, antenna gain, beam width and consistency of dual-polarized receiving channels of the weather radar are important performance parameters for measuring the weather radar and data quality, and therefore, measurement and calibration of these performance parameters are important links in the application process of the weather radar.

[0004] Since the sun has a wide spectral coverage, known polarization characteristics and strong solar energy flow density, the sun can meet the requirements of most radars with high sensitivity receiving systems for signal-to-noise ratio, and the position of the sun can be accurately calculated to enable the radar antenna to be accurately aligned with the sun. Therefore, the sun calibration method using the sun as an ideal external signal source is a commonly used calibration method for weather radars. In the application process of the sun calibration method, the sun is taken as a microwave radiation source, the spatial position of the sun is used to calibrate the antenna pointing of the weather radar, the solar radiation energy flow density data provided by the radio astronomy observatory is used to calibrate the antenna gain and beam width of the weather radar, and the random polarization characteristics of the solar radiation are used to calibrate the consistency of the dual-polarized receiving channels of the weather radar.

[0005] Irrespective of the mechanical scanning type or the digital phased array type, in the process of measuring and calibrating the performance parameters of the weather radar by using the sun calibration method, the existing method is to control the weather radar to turn off the transmitter, then perform a fan volume scanning around the calculated theoretical position of the sun, and passively receive the continuous microwave energy emitted by the sun to obtain the solar radiation data and realize the measurement and calibration of the performance parameters. That is, the existing implementation method needs to be performed in the non-detection state of the weather radar, that is, in the offline state, and the time consumption of the calibration process will affect the continuous detection work of the weather radar, and this also leads to the fact that the calibration frequency of the existing weather radar is often low and the real-time performance of the calibration is not ideal. SUMMARY

[0006] In view of the above problems and technical requirements, the present application provides an online sun calibration method for digital phased array weather radar, and the technical scheme of the present application is as follows.

[0007] The online sun calibration method for digital phased array weather radar comprises the following steps in each detection cycle of the digital phased array weather radar:

[0008] The real-time position of the sun is determined according to the geographical position of the digital phased array weather radar and the detection time of the current detection period.

[0009] In the scanning process of the digital phased array weather radar in the current detection period, the mechanical scanning in the azimuth direction and the electrical scanning in the elevation direction, the multiple beam synthesis data of all the range bins after digital beam forming and the full-array IQ data of one of the range bins are obtained, the full-array IQ data of one of the range bins obtained is subjected to digital beam forming at the real-time position of the sun in the current detection period based on the time-continuous characteristic of the sun radiation, and the sun radiation data is obtained in the scanning process of the current detection period.

[0010] The detection result of the current detection period is obtained according to the multiple beam synthesis data of all the range bins obtained in the scanning process, and the digital phased array weather radar is calibrated according to the sun radiation data obtained in the scanning process.

[0011] Further, the real-time position of the sun includes a real-time elevation angle ELsun of the sun, and the online sun calibration method of the digital phased array weather radar further includes:

[0012] When it is detected that the real-time elevation angle ELsun of the sun in the current detection period is within a predetermined elevation angle range, the sun radiation data is obtained in the scanning process of the digital phased array weather radar in the current detection period, and the digital phased array weather radar is calibrated.

[0013] Further, the real-time position of the sun further includes a real-time azimuth angle AZsun of the sun, and the obtaining of the sun radiation data in the scanning process of the digital phased array weather radar in the current detection period includes:

[0014] When the radar azimuth angle of the digital phased array weather radar in the scanning process is within the angle interval of the real-time azimuth angle AZsun of the sun, the full-array IQ data of one of the range bins is obtained in addition to the multiple beam synthesis data of all the range bins after digital beam forming, and the full-array IQ data of one of the range bins obtained is subjected to digital beam forming at the real-time elevation angle ELsun of the sun to obtain the sun radiation data.

[0015] Further, the digital beam forming of the full-array IQ data of one of the range bins obtained at the real-time elevation angle ELsun of the sun includes:

[0016] The digital beam forming of the full-array IQ data of one of the range bins obtained at the real-time elevation angle ELsun of the sun is performed according to the elevation angle stepping accuracy requirement.

[0017] The further technical solution is that the predetermined pitch angle range is 20°-50°.

[0018] The further technical solution is that the full-array IQ data of a distance bin greater than the predetermined distance threshold is acquired in the scanning process.

[0019] The further technical solution is that the digital phased array weather radar includes L horizontal polarization units and L vertical polarization units, and there are N pulses in one dwell period of the digital phased array weather radar and M times of sampling are performed in each pulse, L, N and M are integer parameters.

[0020] In the scanning process of the digital phased array weather radar in the current detection period, the full-array IQ data of a distance bin is obtained by performing the mth time of IQ sampling data acquisition of each pulse when the radar azimuth angle is located in the angle interval of the real-time azimuth angle of the sun AZsun, and the full-array IQ data includes the IQ sampling data of the L*N horizontal polarization units and the IQ sampling data of the L*N vertical polarization units, and the integer parameter m≤M.

[0021] The beneficial technical effects of the present application are:

[0022] The present application discloses an online sun calibration method for a digital phased array weather radar, which utilizes the time persistence of solar radiation and the digital beam forming technology of the digital phased array weather radar to perform digital beam forming at the real-time position of the sun in the current detection period through the full-array IQ data of a distance bin in the scanning detection process, so as to image the sun and obtain solar radiation data. The method can realize the synchronization of the detection process and the online sun calibration process of the digital phased array weather radar, and does not need to stop running, so that the additional time consumption caused by calibration can be reduced, the calibration frequency can be increased, and the calibration results can be used for real-time evaluation and correction of the radar azimuth, pitch, receiving channel consistency, antenna gain and other parameters, thereby effectively improving the observation performance of the digital phased array weather radar. The method of imaging the sun by using the full-array IQ data of a distance bin through dense digital beam forming in the pitch direction has small data volume and high precision. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FIG. 1 is a method flowchart of the online sun calibration method for the digital phased array weather radar according to an embodiment of the present application.

[0024] Figure 2 FIG. 2 is a method flowchart of the online sun calibration method for the digital phased array weather radar according to another embodiment of the present application. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application will be further described below with reference to the accompanying drawings.

[0026] The present application discloses a kind of digital phased array weather radar online sun calibration method, the calibration method is carried out simultaneously in the detection process of digital phased array weather radar, please refer to Figure 1 The method executed in each detection cycle of digital phased array weather radar includes the following contents as shown in the flow chart:

[0027] First, according to the geographical position of the digital phased array weather radar is combined with the detection time of current detection cycle to determine the real-time position of the sun of current detection cycle.According to the celestial motion law of earth and sun and Gregorian calendar, the sun declination and time difference can be solved, combined with the geographical position of the digital phased array weather radar and the detection time of current detection cycle, the real-time position of the sun of current detection cycle can be solved, this part can refer to the existing solving method to determine, this application will not repeat here.The obtained real-time position of the sun includes real-time azimuth angle AZsun and real-time elevation angle ELsun.In determining the real-time position of the sun, the detection time of current detection cycle uses a general time, for example, the starting detection time of current detection cycle can be used.

[0028] The digital phased array weather radar worked in S, C, X frequency band can be positioned and received solar radiation signal in the present application, and the sensitivity is high.Currently used digital phased array weather radar generally adopts the technical system of azimuth mechanical scanning and elevation electric scanning, and the digital phased array weather radar will be mechanically scanned in 0°-360° in azimuth direction in each detection cycle, and electrically scanned in elevation direction during the mechanical scanning in azimuth direction.The digital phased array weather radar is continuously scanned in 360° in azimuth direction, so that complete coverage in azimuth direction can be realized, and complete coverage in elevation direction cannot be realized, only in the local angle range ELrange can be used for detection.The fixed angle between the antenna array surface of digital phased array weather radar and the ground is defined as α, and the electric scanning range of digital phased array weather radar in elevation direction is ± β, and the electric scanning range ± β is the electric scanning angle range determined by the distance between antenna elements without grating lobe when the antenna array surface of digital phased array weather radar is designed, which is one of the technical indexes of digital phased array weather radar.From this, it can be determined that the angle range that can be used for scanning in elevation direction of digital phased array weather radar is ELrange=90-α±β.For example, α=70°, β=30°, then ELrange=[-10, 50], considering that negative elevation angle has no practical significance for detection, therefore, ELrange=[0, 50] is actually taken.

[0029] In each detection cycle, the digital phased array weather radar performs electrical scanning in the elevation direction during mechanical scanning in the azimuth direction, and obtains the IQ sampling data of each unit during the scanning process. A digital phased array weather radar is defined to include L horizontal polarization units and L vertical polarization units, and there are N pulses in one dwell cycle of the digital phased array weather radar, the pulse repetition period is PRT, and M sampling is performed in each pulse, L, N and M are all integer parameters. In each dwell cycle, there are L*M*N IQ sampling data of the horizontal polarization units and L*M*N IQ sampling data of the vertical polarization units in total, and it can be seen that the data rate of the full array IQ sampling data of all polarization units on all range bins is very high, which will cause the data transmission to be too large. Therefore, the digital phased array weather radar does not directly output the full array IQ sampling data when working, but introduces a digital beam forming technology, and outputs the beam synthesis data of all range bins after digital beam forming during scanning.

[0030] Digital beam forming (DBF) is a technology combining antenna beam forming principle and digital signal processing technology, the basic principle of which is to perform weighted synthesis on the signals received by the phased array antenna through digital signal processing technology to form the required signal beam, and by changing the weight value, the beam can be directed to different directions to realize beam scanning, and multiple beams can be formed at the same time. That is, an arbitrary beam in the antenna electrical scanning range can be formed according to the once-received antenna unit data. The principle of digital beam forming is as follows:

[0031] For a one-dimensional linear phased array, when the digital phased array weather radar includes L antenna units and needs to form P beams, the output can be represented as Y = W T X, P≤L. Wherein, Y = (y1, y2, …, y P ) T is the signal vector of the P beams formed, for any 1≤k≤P, y k represents the signal vector of the kth beam formed. X = (x1, x2, …, x L ) T represents the L signal vectors of the L antenna units received in turn, for any 1≤i≤L, x q represents the signal vector of the ith antenna unit. T represents transposition.

[0032] is a weight vector, and any w ik represents the coefficient of complex weighting of the ith antenna unit required for forming the kth beam, and w ik = a ik exp(-jiΔφ k ), aik is the amplitude weighting value required to reduce the antenna sidelobe. j represents an imaginary number. represents the spatial phase difference between adjacent antenna elements, d is the spacing between adjacent antenna elements, and λ is the signal wavelength, is the pointing direction of the kth beam.

[0033] For a digital phased array weather radar, it can form any number of beams pointing in any direction within the ELrange during reception. The number of beams P formed depends on the computing power of the digital beam forming system, and the beam pointing direction depends on the weighting vector W. By changing the weighting vector W, the pointing direction of each of the P beams formed can be changed.

[0034] During the normal detection period of a digital phased array weather radar, the data rate of the IQ sampling data of the full array is too large, so the beam forming technology described above is used to output the beam synthesis data of all distance bins after digital beam forming according to its ability and the pointing direction of the radar transmit beam, that is, the beam synthesis data of all M distance bins. Based on this working mechanism of the digital phased array weather radar, considering that the solar radiation has a continuous characteristic in time, for a pulse Doppler weather radar, solar radiation measurement can be performed only by using the full array IQ data of one distance bin, and the data rate of outputting the full array IQ data of only one distance bin does not bring too much data transmission pressure, so it is completely possible to realize.

[0035] Therefore, in addition to obtaining the beam synthesis data of all distance bins after digital beam forming according to the traditional method during the scanning process of the current detection period of the digital phased array weather radar, the full array IQ data of one distance bin is also obtained, and then the full array IQ data of the distance bin obtained is subjected to digital beam forming at the real-time position of the sun during the current detection period based on the continuous characteristic of the solar radiation in time, so that solar radiation data can also be obtained during the scanning process of the current detection period.

[0036] The full array IQ data of one distance bin obtained additionally during the scanning process is used to image the sun by using digital beam forming, so in order to better obtain solar radiation data, it is necessary to ensure that the full array IQ data of one distance bin obtained can better represent the solar radiation condition.

[0037] Based on this consideration, the method of the present application is not necessarily used to obtain solar radiation data and perform online calibration in every detection period of the digital phased array weather radar, please refer to Figure 2Instead of acquiring the sun radiation data and performing the online sun calibration of the digital phased array weather radar in the scanning process of the current detection cycle of the digital phased array weather radar as shown in the flow chart, the sun radiation data is acquired and the online sun calibration of the digital phased array weather radar is performed in the scanning process of the current detection cycle of the digital phased array weather radar when the real-time sun elevation angle ELsun in the current detection cycle is detected to be within the predetermined elevation angle range, that is, the detection process and the online sun calibration are performed simultaneously. When the real-time sun elevation angle ELsun in the current detection cycle is detected to be not within the predetermined elevation angle range, only the multiple beam synthesis data of all the range bins after the digital beam forming is output according to the conventional method, that is, only the detection process is performed.

[0038] The predetermined elevation angle range is used to ensure that the real-time sun elevation angle ELsun is relatively high when the online sun calibration is performed. On the one hand, the sun elevation angle is relatively high, and the influence of atmospheric refraction is small. On the other hand, the reception data at the high elevation angle can reduce the influence of ground clutter and rain cloud echo, so as to ensure the accuracy of the results of the simultaneous detection and online sun calibration. Through actual testing and verification, the predetermined elevation angle range is 20°-50°.

[0039] In another embodiment, the full-array IQ data of one range bin greater than a predetermined distance threshold is acquired in the scanning process, that is, the full-array IQ data of the far distance sampling is acquired. The reception data of the far distance can further reduce the influence of ground clutter and rain cloud echo, so as to further improve the accuracy of the results. The predetermined distance threshold can be self-defined.

[0040] In addition, when the sun radiation data needs to be acquired in the scanning process of the current detection cycle of the digital phased array weather radar, in order to reduce the data transmission amount, the full-array IQ data of one range bin is not extracted at each radar azimuth, but as shown in the flow chart of Figure 2 the full-array IQ data of one range bin is acquired in addition to the multiple beam synthesis data of all the range bins after the digital beam forming when the radar azimuth in the scanning process of the digital phased array weather radar is within the angle interval of the real-time sun azimuth AZsun.

[0041] Therefore, in the scanning process of the digital phased array weather radar in the current detection cycle, a plurality of beam synthesis data of all M range bins after digital beam forming at each radar azimuth angle is obtained, and the full-array IQ data of a range bin is obtained by acquiring the mth IQ sampling data of each pulse when the radar azimuth angle is located in the angle interval of the real-time azimuth angle of the sun AZsun. The obtained full-array IQ data includes IQ sampling data of L*N horizontal polarization units and IQ sampling data of L*N vertical polarization units, and the integer parameter m≤M. In combination with the above requirement for long-distance detection, the range bin corresponding to the mth IQ sampling data is greater than a predetermined distance threshold, such as selecting one of the IQ sampling data of the last several times of each pulse to correspond to one of the last several range bins.

[0042] The required elevation beam pointing of the digital phased array weather radar in detection is within ELrange and generally within 0°-20°, and cannot cover the real-time elevation angle of the sun ELsun (such as 20°-50°) with a high elevation angle. Therefore, in order to obtain the required elevation sun radiation signal, digital beam forming is performed on the full-array IQ data of a range bin obtained at the real-time elevation angle of the sun ELsun to obtain sun radiation data. The angle interval of the real-time azimuth angle of the sun AZsun can be represented as AZsun±θ, and the angle range of θ can be set by the user, such as 5°. When digital beam forming is performed on the full-array IQ data of a range bin obtained at the real-time elevation angle of the sun ELsun, the beam forming angle range can be represented as ELsun±γ, and the angle range of γ can also be set by the user, such as 5°. In this way, even if the current digital phased array weather radar detection elevation beam pointing is not within the range of ELsun±γ, since the full-array IQ data obtained can generate any receiving beam pointing within the range of ELrange, as long as ELsun±γ is within the ELrange of the digital phased array weather radar, the sun radiation data within the range of azimuth angle AZsun±θ and elevation angle ELsun±γ can be extracted.

[0043] On the other hand, the interval of the elevation electric scanning beam of the digital phased array weather radar is generally 1°, which is too sparse and cannot meet the accuracy requirement of sun calibration. Therefore, when digital beam forming is performed on the full-array IQ data of a range bin obtained at the real-time elevation angle of the sun ELsun, digital beam forming is performed according to the elevation angle stepping accuracy requirement, which is set according to the accuracy requirement of sun calibration, and is generally set to 0.1° in practice.

[0044] Based on the method provided in the present application, the digital phased array weather radar can output not only the multiple beam synthesis data of all range bins obtained in the scanning process in a detection period, but also the solar radiation data obtained in the scanning process. The detection result of the current detection period can be calculated according to the multiple beam synthesis data of all range bins, and the specific calculation method can refer to the existing calculation method, which will not be described here. According to the solar radiation data obtained in the scanning process, the digital phased array weather radar can be calibrated, including: obtaining the pitch angle, azimuth angle and antenna beam width information by fitting the echo data; obtaining the receiving channel amplitude consistency by the difference of solar radiation power of the horizontal polarization receiving channel and the vertical polarization receiving channel; and obtaining the antenna gain by the solar radiation signal strength and the radar parameters. Therefore, the digital phased array weather radar can complete the online solar calibration synchronously in a detection period without offline operation, which reduces the calibration time, is beneficial to increase the calibration frequency, and the calibration result can be used for real-time evaluation and correction of the performance parameters of the digital phased array weather radar, such as azimuth, pitch, receiving channel consistency and antenna gain, thereby effectively improving the observation performance of the digital phased array weather radar.

[0045] The above is only the preferred embodiment of the present application, and the present application is not limited to the above embodiments. It can be understood that other improvements and changes directly derived or thought by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A method for online sun calibration of a digital phased array weather radar, characterized in that, The online sun calibration method of the digital phased array weather radar comprises the following steps: determining a real-time position of the sun according to a geographical position of the digital phased array weather radar and a detection time of a current detection cycle; acquiring a plurality of beam synthesis data of all range bins after digital beam forming and full-array IQ data of one range bin during a scanning process of mechanical scanning in the azimuth direction and electrical scanning in the elevation direction of the digital phased array weather radar in the current detection cycle, performing digital beam forming on the acquired full-array IQ data of one range bin at the real-time position of the sun in the current detection cycle based on the time-continuous characteristic of the sun radiation, and acquiring sun radiation data in the scanning process of the current detection cycle; acquiring a detection result of the current detection cycle according to the plurality of beam synthesis data of all range bins, and calibrating the digital phased array weather radar according to the sun radiation data acquired in the scanning process.

2. The digital phased array weather radar on-line sun calibration method of claim 1, wherein, The real-time position of the sun comprises a real-time elevation angle ELsun of the sun. The online sun calibration method of the digital phased array weather radar further comprises the following steps: when it is detected that the real-time elevation angle ELsun of the sun in the current detection cycle is within a predetermined elevation angle range, acquiring sun radiation data in the scanning process of the digital phased array weather radar in the current detection cycle and calibrating the digital phased array weather radar.

3. The digital phased array weather radar on-line sun calibration method of claim 2, wherein, The real-time position of the sun further comprises a real-time azimuth angle AZsun of the sun, and the acquiring of the sun radiation data in the scanning process of the digital phased array weather radar in the current detection cycle comprises the following steps: when a radar azimuth angle of the digital phased array weather radar in the scanning process is within an angle interval of the real-time azimuth angle AZsun of the sun, acquiring full-array IQ data of one range bin in addition to the plurality of beam synthesis data of all range bins after digital beam forming, and performing digital beam forming on the acquired full-array IQ data of one range bin at the real-time elevation angle ELsun of the sun to obtain the sun radiation data.

4. The digital phased array weather radar on-line sun calibration method of claim 3, wherein, The digital beam forming on the acquired full-array IQ data of one range bin at the real-time elevation angle ELsun of the sun comprises the following steps: performing digital beam forming on the acquired full-array IQ data of one range bin at the real-time elevation angle ELsun of the sun according to the elevation angle stepping accuracy requirement.

5. The digital phased array weather radar on-line sun calibration method of claim 2, wherein, The predetermined elevation angle range is 20°-50°.

6. The digital phased array weather radar on-line sun calibration method of claim 1, wherein, The full-array IQ data of one range bin greater than a predetermined distance threshold is acquired in the scanning process.

7. The digital phased array weather radar on-line sun calibration method of claim 3, wherein, The digital phased array weather radar comprises L horizontal polarization units and L vertical polarization units, and there are N pulses in one dwell cycle of the digital phased array weather radar and M samplings are performed in each pulse, L, N and M are all integer parameters. In the scanning process of the digital phased array weather radar in the current detection cycle, a plurality of beam synthesis data of all M distance banks after digital beam forming at each radar azimuth angle are acquired, and full-array IQ data of a corresponding distance bank is obtained by acquiring mth IQ sampling data of each pulse when the radar azimuth angle is located in the angle interval in which the real-time azimuth angle AZsun of the sun is located, the full-array IQ data including IQ sampling data of L*N horizontal polarization units and IQ sampling data of L*N vertical polarization units, and an integer parameter m≤M.

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