Digital phased array weather radar on-line sun calibration method

Abstract

The invention discloses an online sun calibration method for a digital phased array weather radar, and relates to the technical field of weather radar calibration, and the method comprises the steps: determining the real-time position of the sun according to the geographic position of the digital phased array weather radar in combination with the detection time of a current detection period, and then carrying out the calibration of the sun through employing the continuous characteristics of solar radiation in time; and a digital beam forming technology of a digital phased array weather radar is adopted, and digital beam forming is carried out on full-array-plane IQ data of a distance library at the real-time position of the sun in the current detection period in the scanning detection process, so that sun imaging is carried out to obtain solar radiation data. According to the method, the detection process of the digital phased array weather radar and the online sun calibration process can be synchronously carried out, extra time consumption caused by calibration is reduced, the calibration frequency can be increased, the calibration result can be used for evaluating and correcting performance parameters of the digital phased array weather radar in real time, and the calibration efficiency is improved. And the observation performance of the digital phased array weather radar is effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of weather radar calibration, and in particular to an online solar calibration method for a digital phased array weather radar. Background Art

[0002] Digital phased array weather radar using digital beamforming system has the advantages of flexible beamforming and simultaneous multi-beam. Compared with traditional mechanical scanning weather radar, it improves the data rate and shortens the radar scanning cycle. It has been gradually used for meteorological detection.

[0003] The performance parameters of weather radar, such as antenna pointing, antenna gain, beam width, and consistency of dual-polarization receiving channels, are important indicators for measuring weather radar and data quality. Therefore, measuring and calibrating these performance parameters is an important part of the weather radar application process.

[0004] Since the spectrum of the sun covers a wide range, its polarization characteristics are known, and its solar flux density is strong, it can meet the signal-to-noise ratio requirements of most radars with high-sensitivity receiving systems. At the same time, there is an accurate calculation method for the position of the sun, which can enable the radar antenna to be accurately aligned with the sun. Therefore, the solar calibration method, which uses the sun as an ideal external signal source, is currently a commonly used calibration method for weather radars. In the application of the solar calibration method, the sun is used as a microwave radiation source, and the antenna pointing of the weather radar is calibrated according to its spatial position. The antenna gain and beam width of the weather radar are calibrated according to the solar radiation energy flux density data provided by the radio astronomy observatory, and the consistency of the dual-polarization receiving channel of the weather radar is calibrated according to the random polarization characteristics of solar radiation.

[0005] Whether it is a mechanical scanning type or a digital phased array type weather radar, when using the solar calibration method to measure and calibrate the performance parameters of the weather radar, the existing practice is to control the weather radar to turn off the transmitter, and then perform a fan-shaped volume scan near the calculated theoretical position of the sun, passively receiving the microwave energy continuously emitted by the sun, thereby obtaining solar radiation data to achieve performance parameter measurement and calibration. That is, the existing implementation methods all need to be carried out when the weather radar is not detecting, that is, offline. The time-consuming calibration process will affect the continuous detection work of the weather radar, and this also leads to the fact that the calibration frequency of existing weather radars is often low, and the real-time performance of the calibration is not ideal. Summary of the invention

[0006] In view of the above problems and technical requirements, this application proposes an online solar calibration method for digital phased array weather radar. The technical solution of this application is as follows:

[0007] A digital phased array weather radar online solar calibration method, the digital phased array weather radar online solar calibration method comprising:

[0008] Determine the real-time position of the sun based on the geographical location of the digital phased array weather radar and the detection time of the current detection cycle;

[0009] During the scanning process of the digital phased array weather radar performing mechanical scanning in azimuth and electrical scanning in elevation in the current detection cycle, multiple beam synthesis data of all distance libraries after digital beamforming and full-array IQ data of one distance library are obtained, and digital beamforming is performed on the obtained full-array IQ data of one distance library at the real-time position of the sun in the current detection cycle based on the temporal continuity characteristics of solar radiation, so as to obtain solar radiation data during the scanning process of the current detection cycle;

[0010] The detection result of the current detection cycle is obtained according to the multiple beam synthesis data of all distance libraries obtained during the scanning process, and the digital phased array weather radar is calibrated according to the solar radiation data obtained during the scanning process.

[0011] A further technical solution is that the real-time position of the sun includes the real-time elevation angle of the sun ELsun; and the online solar 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 cycle is within the predetermined elevation angle range, solar radiation data is acquired during the scanning process of the digital phased array weather radar in the current detection cycle and the digital phased array weather radar is calibrated.

[0013] A further technical solution is that the real-time position of the sun also includes the real-time azimuth of the sun AZsun. The solar radiation data obtained during the scanning process of the digital phased array weather radar in the current detection cycle includes:

[0014] When the radar azimuth of the digital phased array weather radar is within the angle interval of the real-time sun azimuth AZsun during the scanning process, in addition to obtaining multiple beam synthesis data of all distance libraries after digital beamforming, the full-array IQ data of one of the distance libraries is also obtained, and digital beamforming is performed on the full-array IQ data of one distance library at the real-time sun elevation angle ELsun to obtain solar radiation data.

[0015] A further technical solution is to perform digital beamforming on the acquired full array IQ data of a distance library at the real-time sun elevation angle ELsun, including:

[0016] According to the pitch angle step accuracy requirement, digital beamforming is performed on the full-array IQ data of a distance library at the real-time sun pitch angle ELsun.

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

[0018] A further technical solution is to obtain full-array IQ data of a distance library greater than a predetermined distance threshold during the scanning process.

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

[0020] During the scanning process of the digital phased array weather radar in the current detection cycle, multiple beam synthesis data of all M range bins after digital beam forming at each radar azimuth are obtained, and when the radar azimuth is located within the angle interval where the real-time azimuth of the sun AZsun is located, the mth IQ sampling data of each pulse is obtained to obtain the full-array IQ data of a range bin, and the full-array IQ data includes the IQ sampling data of L*N horizontal polarization units and the IQ sampling data of L*N vertical polarization units, and the integer parameter m≤M.

[0021] The beneficial technical effects of this application are:

[0022] The present application discloses an online solar calibration method for a digital phased array weather radar. The method utilizes the temporal persistence of solar radiation and the digital beamforming technology of a digital phased array weather radar. During the scanning detection process, digital beamforming is performed at the real-time position of the sun in the current detection cycle through the full array IQ data of a distance library, thereby imaging the sun to obtain solar radiation data. The method can realize the detection process of the digital phased array weather radar and the online solar calibration process synchronously without stopping the operation, thereby reducing the extra time consumption caused by calibration, which is conducive to increasing the calibration frequency. The calibration results can be used for real-time evaluation and correction of radar azimuth, elevation, receiving channel consistency, antenna gain and other parameters, effectively improving the observation performance of the digital phased array weather radar. The method of imaging the sun using dense digital beamforming in the elevation direction for the full array IQ data of a distance library has a small amount of data and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a method flow chart of an online solar calibration method for a digital phased array weather radar according to an embodiment of the present application.

[0024] Figure 2 It is a method flow chart of an online solar calibration method for a digital phased array weather radar according to another embodiment of the present application. DETAILED DESCRIPTION

[0025] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0026] This application discloses an online solar calibration method for digital phased array weather radar. The calibration method is performed simultaneously during the detection process of the digital phased array weather radar. Please refer to Figure 1 The flowchart shown in the figure shows that the method executed in each detection cycle of the digital phased array weather radar includes the following contents:

[0027] First, the real-time position of the sun in the current detection cycle is determined based on the geographical location of the digital phased array weather radar and the detection time of the current detection cycle. The solar declination and time difference can be calculated based on the celestial motion laws of the earth and the sun and the Gregorian calendar. Combined with the geographical location of the digital phased array weather radar and the detection time of the current detection cycle, the real-time position of the sun in the current detection cycle can be calculated. This part can be determined with reference to the existing solution method, and this application will not go into details. The obtained real-time position of the sun includes the real-time azimuth angle AZsun and the real-time elevation angle ELsun of the sun. When determining the real-time position of the sun, an approximate time can be used for the detection time of the current detection cycle, such as the start detection time of the current detection cycle.

[0028] The digital phased array weather radar targeted by this application operates in the S, C, and X frequency bands, can locate and receive solar radiation signals, and has high sensitivity. The digital phased array weather radars currently used generally adopt the technical system of mechanical scanning in azimuth and electronic scanning in elevation. In each detection cycle, the digital phased array weather radar will perform mechanical scanning of 0° to 360° in azimuth, and perform electronic scanning in elevation during the mechanical scanning in azimuth. Since the digital phased array weather radar is 360° continuous scanning in azimuth, it can achieve complete coverage in azimuth, but it cannot achieve complete coverage in elevation, and only the local angle range ELrange can be used for detection. The fixed angle between the antenna array of the digital phased array weather radar and the ground is defined as α, and the electronic scanning range of the digital phased array weather radar in elevation is ±β. The electronic scanning range ±β is the electronic scanning angle range that does not exceed the grating lobe determined by the antenna unit spacing when the antenna array of the digital phased array weather radar is designed. It is one of the technical indicators of the digital phased array weather radar. It can be determined that the angle range that can be used for scanning in the elevation direction of the digital phased array weather radar is ELrange = 90-α±β. For example, α = 70°, β = 30°, then ELrange = [-10, 50]. Considering that negative elevation angles have no practical significance for detection, ELrange = [0, 50] is actually taken.

[0029] In each detection cycle, the digital phased array weather radar will perform an electrical scan in the pitch direction while performing a mechanical scan in the azimuth direction, and obtain the IQ sampling data of each unit during the scanning process. The digital phased array weather radar is defined as L horizontal polarization units and L vertical polarization units. There are N pulses in one dwell cycle of the digital phased array weather radar, and the pulse repetition period is PRT. M sampling is performed in each pulse, and L, N and M are all integer parameters. In each dwell cycle, there are a total of L*M*N IQ sampling data of horizontal polarization units and L*M*N IQ sampling data of vertical polarization units. It can be seen that the data rate of the IQ sampling data of the entire array of all polarization units in all range libraries is very high, which will result in excessive data transmission. Therefore, the digital phased array weather radar does not directly output the IQ sampling data of the entire array when working, but will introduce digital beamforming technology and output multiple beam synthesis data of all range libraries after digital beamforming during the scanning process.

[0030] Digital beam forming (DBF) is a technology that combines antenna beam forming principles with digital signal processing technology. Its basic principle is to use digital signal processing technology to perform weighted synthesis on the signals received by the phased array antenna to form the required signal beam. By changing the weights, the beam can be pointed in different directions to achieve beam scanning, and multiple beams can be formed at the same time. That is, any beam within the antenna electronic scanning range can be formed based on the antenna unit data received once. The principle of digital beam forming is as follows:

[0031] For a one-dimensional linear phased array, when a digital phased array weather radar includes L antenna elements and needs to form P beams, its output can be expressed as Y = W T X, P≤L. Where 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 received by the L antenna units in turn. For any 1≤i≤L, x q represents the signal vector of the ith antenna element. T represents the transpose.

[0032] is a weight vector, any w ik represents the coefficients of complex weighting of the i-th antenna element required to form the k-th 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 units, d is the spacing between adjacent antenna units, λ is the signal wavelength, is the pointing direction of the kth beam.

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

[0034] During the normal detection cycle of the digital phased array weather radar, since the data rate of the IQ sampling data of the entire array is too large, the above-mentioned beamforming technology will be used according to its capabilities and the radar transmission beam pointing to output multiple beam synthesis data of all distance libraries after digital beamforming, that is, multiple beam synthesis data of all M distance libraries. Based on this working mechanism of the digital phased array weather radar, the present application takes into account the continuous characteristics of solar radiation in time. For the pulse Doppler weather radar, solar radiation can be measured only through the full array IQ data of one distance library, and the data rate of outputting only the full array IQ data of one distance library does not bring too much data transmission pressure, so it is completely feasible.

[0035] Therefore, during the scanning process of the digital phased array weather radar in the current detection cycle, in addition to obtaining multiple beam synthesis data of all distance libraries after digital beamforming according to traditional practices, the present application also obtains the full-array IQ data of one of the distance libraries, and then performs digital beamforming on the obtained full-array IQ data of one distance library at the real-time position of the sun in the current detection cycle based on the temporal continuity characteristics of solar radiation, so that solar radiation data can also be obtained during the scanning process of the current detection cycle.

[0036] The full-array IQ data of a distance library additionally obtained during the scanning process is used to image the sun using digital beamforming. Therefore, in order to better obtain solar radiation data, it is necessary to ensure that the full-array IQ data of a distance library obtained can better represent the solar radiation situation.

[0037] Based on this consideration, it is not necessary to use the method of this application to obtain solar radiation data and perform online calibration in every detection cycle of the digital phased array weather radar. Please refer to Figure 2The flowchart shown in the figure is that only when it is detected that the real-time pitch angle ELsun of the sun in the current detection cycle is within the predetermined pitch angle range, the solar radiation data is acquired during the scanning process of the current detection cycle of the digital phased array weather radar and the digital phased array weather radar is calibrated online, that is, the detection process and the online solar calibration are carried out simultaneously. When it is detected that the real-time pitch angle ELsun of the sun in the current detection cycle is not within the predetermined pitch angle range, only multiple beam synthesis data of all distance libraries after digital beamforming are output according to the conventional method, that is, only the detection process is carried out.

[0038] The preset pitch angle range is used to ensure that the real-time solar pitch angle ELsun is relatively high when online solar calibration is performed. On the one hand, when the solar pitch angle is relatively high, it is less affected by atmospheric refraction. On the other hand, the received data at a high pitch angle can also reduce the influence of ground clutter and rain cloud echoes, thereby ensuring the accuracy of the results of simultaneous detection and online solar calibration. After actual testing and verification, the preset pitch angle range is 20° to 50°.

[0039] In another embodiment, full array IQ data of a distance library greater than a predetermined distance threshold is obtained during the scanning process, that is, full array IQ data of long-distance sampling is obtained. The long-distance received data can further reduce the influence of ground clutter and rain cloud echoes, thereby further improving the accuracy of the results. The predetermined distance threshold can be customized.

[0040] In addition, when it is necessary to obtain solar radiation data during the scanning process of the current detection cycle of the digital phased array weather radar, in order to reduce the amount of data transmission, the full-array IQ data of a range library will not be extracted at each radar azimuth, but Figure 2 As shown in the flowchart, when the radar azimuth of the digital phased array weather radar during the scanning process is located within the angle interval where the real-time azimuth of the sun AZsun is located, in addition to obtaining multiple beam synthesis data of all distance libraries after digital beam forming, full-array IQ data of one of the distance libraries is obtained.

[0041] Therefore, during the scanning process of the digital phased array weather radar in the current detection cycle, multiple beam synthesis data of all M distance libraries after digital beam forming at each radar azimuth are obtained, and when the radar azimuth is within the angle interval where the real-time azimuth of the sun AZsun is located, the mth IQ sampling data of each pulse is obtained to obtain the full array IQ data of a distance library. The obtained full array IQ data includes the IQ sampling data of L*N horizontal polarization units and the IQ sampling data of L*N vertical polarization units, and the integer parameter m≤M. In combination with the above-mentioned long-distance detection requirements, the distance library corresponding to the mth IQ sampling data is greater than the predetermined distance threshold, for example, one of the last several IQ sampling data of each pulse is selected to correspond to one of the farthest several distance libraries.

[0042] The required elevation beam pointing of the digital phased array weather radar during detection is within ELrange and is generally between 0° and 20°. It often cannot cover the real-time solar elevation angle ELsun (such as the above-mentioned 20° to 50°) with a higher elevation angle. Therefore, in order to obtain the required elevation solar radiation signal, the full array IQ data of a distance library is digitally beamformed at the real-time solar elevation angle ELsun to obtain solar radiation data. The angle range of the real-time solar azimuth angle AZsun can be expressed as AZsun±θ, and the angle range of θ can be customized, such as 5°. When digital beamforming is performed on the full array IQ data of a distance library at the real-time solar elevation angle ELsun, the beamforming angle range can be expressed as ELsun±γ, and the angle range of γ can also be customized, 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 acquired full array IQ data can generate any receiving beam pointing within the range of ELrange, as long as ELsun±γ is within the range of ELrange of the digital phased array weather radar, the solar radiation data within the range of azimuth angle AZsun±θ and elevation angle ELsun±γ can be extracted.

[0043] On the other hand, the pitch electronic scanning beam interval of the digital phased array weather radar is generally 1°, which is too sparse to meet the accuracy requirements of solar calibration. Therefore, when the digital beamforming is performed on the full array IQ data of a range library at the real-time solar pitch angle ELsun, the digital beamforming is performed according to the pitch angle step accuracy requirements. The pitch angle step accuracy requirements are set according to the accuracy requirements of solar calibration, and are generally set to 0.1° in practice.

[0044] Based on the method provided by the present application, the digital phased array weather radar can not only output multiple beam synthesis data of all distance libraries obtained during the scanning process in one detection cycle, but also output the solar radiation data obtained during the scanning process. According to the multiple beam synthesis data of all distance libraries, the detection result of the current detection cycle can be solved. The specific solution method can refer to the existing solution method, and the present application will not repeat it. According to the solar radiation data obtained during 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 amplitude consistency of the receiving channel by the difference of solar radiation power of the horizontal polarization receiving channel and the vertical polarization receiving channel; obtaining the antenna gain by the solar radiation signal strength and radar parameters. Therefore, the digital phased array weather radar can synchronously complete the online solar calibration in one detection cycle without offline operation, which reduces the calibration time consumption and is conducive to increasing the calibration frequency. The calibration results can be used to evaluate and correct the performance parameters such as the azimuth, pitch, receiving channel consistency, antenna gain, etc. of the digital phased array weather radar in real time, effectively improving the observation performance of the digital phased array weather radar.

[0045] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated 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 digital phased array weather radar online solar calibration method, characterized in that: The digital phased array weather radar online solar calibration method comprises the following steps in each detection cycle of the digital phased array weather radar: Determine the real-time position of the sun according to the geographical location of the digital phased array weather radar and the detection time of the current detection cycle; During the scanning process of the digital phased array weather radar performing mechanical scanning in azimuth and electrical scanning in elevation in the current detection cycle, multiple beam synthesis data of all distance libraries after digital beamforming and full-array IQ data of one distance library are obtained, and digital beamforming is performed on the obtained full-array IQ data of one distance library at the real-time position of the sun in the current detection cycle based on the temporal continuity feature of solar radiation, so as to obtain solar radiation data during the scanning process of the current detection cycle; The detection result of the current detection cycle is obtained according to the multiple beam synthesis data of all distance libraries obtained during the scanning process, and the digital phased array weather radar is calibrated according to the solar radiation data obtained during the scanning process.

2. The online solar calibration method for digital phased array weather radar according to claim 1, characterized in that: The real-time position of the sun includes the real-time pitch angle ELsun of the sun; The digital phased array weather radar online solar calibration method also includes: When it is detected that the real-time pitch angle ELsun of the sun in the current detection cycle is within the predetermined pitch angle range, solar radiation data is acquired during the scanning process of the digital phased array weather radar in the current detection cycle and the digital phased array weather radar is calibrated.

3. The online solar calibration method for digital phased array weather radar according to claim 2, characterized in that: The real-time position of the sun also includes the real-time azimuth of the sun AZsun. Acquiring solar radiation data during the scanning process of the digital phased array weather radar in the current detection cycle includes: When the radar azimuth of the digital phased array weather radar during the scanning process is within the angle interval where the real-time azimuth angle AZsun of the sun is located, in addition to obtaining multiple beam synthesis data of all distance libraries after digital beamforming, full-array IQ data of one of the distance libraries is also obtained, and digital beamforming is performed on the obtained full-array IQ data of one distance library at the real-time elevation angle ELsun of the sun to obtain solar radiation data.

4. The online solar calibration method for digital phased array weather radar according to claim 3 is characterized in that: The digital beamforming of the acquired full-array IQ data of a distance library at the real-time sun elevation angle ELsun comprises: According to the pitch angle step accuracy requirement, digital beamforming is performed on the full-array IQ data of a distance library at the real-time sun pitch angle ELsun.

5. The online solar calibration method for digital phased array weather radar according to claim 2, characterized in that: The preset pitch angle range is 20° to 50°.

6. The online solar calibration method for digital phased array weather radar according to claim 1, characterized in that: During the scanning process, full-array IQ data of a distance library greater than a predetermined distance threshold is acquired.

7. The online solar calibration method for digital phased array weather radar according to claim 3, characterized in that: The digital phased array weather radar comprises L horizontal polarization units and L vertical polarization units. The digital phased array weather radar has N pulses in one dwell period and performs M samplings on each pulse. L, N and M are all integer parameters. During the scanning process of the digital phased array weather radar in the current detection cycle, multiple beam synthesis data of all M distance libraries after digital beamforming at each radar azimuth are obtained, and when the radar azimuth is located within the angle interval where the real-time azimuth of the sun AZsun is located, the mth IQ sampling data of each pulse is obtained to obtain the full-array IQ data of a corresponding distance library, wherein the 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.

Images