Method for online solar calibration of digital phased array weather radar

Abstract

The present application relates to the technical field of weather radar calibration, and discloses a method for online solar calibration of a digital phased array weather radar. The method comprises: determining a real-time position of the sun on the basis of a geographical position of a digital phased array weather radar and a detection time of a current detection cycle; and by means of temporal continuity of solar radiation and digital beamforming technology of the digital phased array weather radar, performing digital beamforming on full-array IQ data of a range bin at the real-time position of the sun in the current detection cycle during a scanning detection process, so as to image the sun to obtain solar radiation data. The method can achieve synchronization between a detection process of a digital phased array weather radar and an online solar calibration process, thereby reducing additional time consumption caused by calibration, and facilitating the increase of the calibration frequency; and a calibration result can be used for real-time estimation and correction of performance parameters of the digital phased array weather radar, thereby effectively improving the observation performance of the digital phased array weather radar.

Description

A Method for Online Solar Calibration of Digital Phased Array Weather Radar Technical Field

[0001] This application relates to the field of weather radar calibration technology, and in particular to an online solar calibration method for digital phased array weather radar. Background Technology

[0002] Digital phased array weather radars employing digital beamforming have advantages such as flexible beamforming and the ability to simultaneously generate multiple beams. Compared to traditional mechanically scanned weather radars, they improve data rates and shorten radar scanning cycles, and are gradually being used for meteorological detection.

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

[0004] Because the sun has a wide spectral coverage, known polarization characteristics, and a strong solar energy flux density, it can meet the signal-to-noise ratio requirements of most radars with high-sensitivity receiving systems. Furthermore, the sun's position can be accurately calculated, allowing the radar antenna to be precisely aligned with it. Therefore, the solar calibration method, which uses the sun as an ideal external signal source, is 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. The antenna pointing of the weather radar is calibrated based on its spatial position. The antenna gain and beamwidth of the weather radar are calibrated based on solar radiation energy flux density data provided by radio astronomy observatories. The consistency of the dual-polarization receiving channels of the weather radar is calibrated based on the random polarization characteristics of solar radiation.

[0005] Regardless of whether it is a mechanically scanned or digitally phased array weather radar, the current practice for measuring and calibrating the performance parameters of weather radar using the solar calibration method is to control the weather radar to shut down the transmitter, and then perform a sector volume scan near the calculated theoretical position of the sun in a passive manner to receive the microwave energy continuously emitted by the sun, thereby obtaining solar radiation data to achieve the measurement and calibration of performance parameters. Technical issues

[0006] Existing methods all require calibration to be performed when the weather radar is not in detection mode, i.e., offline. The time spent on the calibration process will affect the continuous detection work of the weather radar, and this also results in the existing weather radar calibration frequency being low and the real-time performance of calibration being less than ideal. Technical solutions

[0007] This application addresses the aforementioned problems and technical requirements by proposing an online solar calibration method for digital phased array weather radar. The technical solution of this application is as follows:

[0008] An online solar calibration method for a digital phased array weather radar, comprising the following steps in each detection cycle of the digital phased array weather radar:

[0009] The real-time position of the sun is determined based on the geographical location of the digital phased array weather radar and the detection time of the current detection cycle.

[0010] During the scanning process of the digital phased array weather radar in the current detection cycle, both the azimuth-up mechanical scan and the elevation-up electronic scan are performed. Multiple beam composite data of all range databases after digital beamforming are acquired, as well as the full array IQ data of one range database. Based on the continuous characteristics of solar radiation over time, digital beamforming is performed on the full array IQ data of one range database at the real-time position of the sun in the current detection cycle, so as to obtain solar radiation data during the scanning process of the current detection cycle.

[0011] The detection results for the current detection cycle are obtained by combining multiple beams of all range data acquired during the scanning process, and the digital phased array weather radar is calibrated based on the solar radiation data obtained during the scanning process.

[0012] Further technical solutions include real-time solar position (including real-time solar elevation angle ELsun); the online solar calibration method for digital phased array weather radar also includes:

[0013] When the real-time solar elevation angle ELsun is detected to be within the predetermined elevation angle range during the current detection cycle, solar radiation data is acquired and the digital phased array weather radar is calibrated during the scanning process of the digital phased array weather radar in the current detection cycle.

[0014] A further technical solution involves obtaining solar radiation data during the scanning process of a digital phased array weather radar in the current detection cycle, including the real-time position of the sun and its real-time azimuth angle (AZsun).

[0015] When the radar azimuth angle of the digital phased array weather radar is within the angle range of the real-time solar azimuth angle AZsun during the scanning process, in addition to acquiring multiple beam composite data of all range libraries after digital beamforming, it also acquires the full array IQ data of one range library, and performs digital beamforming on the acquired full array IQ data of one range library at the real-time solar elevation angle ELsun to obtain solar radiation data.

[0016] The further technical solution involves performing digital beamforming on the full-array IQ data of a range database at the real-time solar elevation angle ELsun, including:

[0017] According to the elevation angle stepping accuracy requirements, digital beamforming is performed on the full array IQ data of a range library at the real-time solar elevation angle ELsun.

[0018] The further technical solution is that the predetermined pitch angle range is 20°~50°.

[0019] A further technical solution is to acquire full-area IQ data of a distance library greater than a predetermined distance threshold during the scanning process.

[0020] The further technical solution is that the digital phased array weather radar includes 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 in each pulse. L, N and M are all integer parameters.

[0021] During the scanning process of the digital phased array weather radar in the current detection cycle, multiple beam composite data of all M range databases after digital beamforming at each radar azimuth angle are acquired. When the radar azimuth angle is within the angle interval of the real-time solar azimuth angle AZsun, the m-th IQ sampling data of each pulse is acquired to obtain the full array IQ data of a range database. 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, where the integer parameter m≤M. Beneficial effects

[0022] This application discloses an online solar calibration method for a digital phased array weather radar. This method utilizes the continuous nature of solar radiation over time and the digital beamforming technology of the digital phased array weather radar. During the scanning and detection process, digital beamforming is performed at the real-time position of the sun in the current detection cycle using full-array IQ data from a range database, thereby imaging the sun to obtain solar radiation data. This method allows the detection process of the digital phased array weather radar to be performed simultaneously with the online solar calibration process, without requiring downtime. Therefore, it reduces the additional time spent on calibration, which is beneficial for increasing the calibration frequency. The calibration results can be used to evaluate and correct radar parameters such as azimuth, elevation, receiver channel consistency, and antenna gain in real time, effectively improving the observation performance of the digital phased array weather radar. Furthermore, the method of imaging the sun using dense digital beamforming in the elevation direction from full-array IQ data of a range database requires less data and has higher accuracy. Attached Figure Description

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

[0024] Figure 2 is a flowchart of an online solar calibration method for a digital phased array weather radar according to another embodiment of this application. Embodiments of the present invention

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

[0026] This application discloses an online solar calibration method for a digital phased array weather radar. This calibration method is performed simultaneously during the detection process of the digital phased array weather radar. Referring to the flowchart shown in Figure 1, the method executed in each detection cycle of the digital phased array weather radar includes the following:

[0027] First, the real-time position of the sun for 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 patterns of the Earth and the Sun and the Gregorian calendar. Combining this 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 for the current detection cycle can be calculated. This part can be determined by referring to existing calculation methods, and will not be elaborated upon in this application. The obtained real-time solar position includes the real-time solar azimuth angle AZsun and the real-time solar elevation angle ELsun. When determining the real-time solar position, an approximate time can be used for the detection time of the current detection cycle, such as the start time of the current detection cycle.

[0028] This application targets a digital phased array weather radar that operates in the S, C, and X bands, capable of locating and receiving solar radiation signals with high sensitivity. Currently used digital phased array weather radars generally employ a mechanical azimuth scanning and an electronic elevation scanning system. In each detection cycle, the radar performs a mechanical scan of 0°–360° in the azimuth direction and an electronic elevation scan during this process. Because the azimuth scan is continuous at 360°, the digital phased array weather radar can achieve complete azimuth coverage, but it cannot achieve complete elevation coverage; only a local angular range (ELrange) is available for detection. Let α be the fixed angle between the digital phased array weather radar antenna array and the ground, and let ±β be the electronic scanning range in the elevation direction. This ±β range is the electronic scanning angle range without grating lobes, determined by the antenna element spacing during the antenna array design, and is one of the technical specifications of the digital phased array weather radar. Therefore, the range of angles that can be scanned in the elevation direction by a digital phased array weather radar is ELrange = 90 - α ± β. For example, if α = 70° and 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, a digital phased array weather radar performs an azimuth-up mechanical scan followed by an elevation-up electronic scan, acquiring IQ sampling data for each element during the scan. Define a digital phased array weather radar as having L horizontal polarization elements and L vertical polarization elements. One dwell cycle of the digital phased array weather radar has N pulses with a pulse repetition period of PRT, and M samples are taken on each pulse, where L, N, and M are integer parameters. Therefore, in each dwell cycle, there are a total of L*M*N IQ sampling data for horizontal polarization elements and L*M*N IQ sampling data for vertical polarization elements. It can be seen that the data rate of the full-array IQ sampling data for all polarization elements in the range library is very high, leading to excessive data transmission. Therefore, a digital phased array weather radar does not directly output the full-array IQ sampling data during operation. Instead, it incorporates digital beamforming technology and outputs composite data from multiple beams of the range library after digital beamforming during the scan.

[0030] Digital beamforming (DBF) is a technology that combines antenna beamforming principles with digital signal processing. Its basic principle is to use digital signal processing to weight and synthesize the signals received by a phased array antenna to form the desired signal beam. By changing the weights, the beam can be pointed in different directions, achieving beam scanning, and multiple beams can be formed simultaneously. In other words, it can form any beam within the antenna's electrical scanning range based on data from a single received antenna element. The principle of digital beamforming 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: , P≤L. Where, It is the signal vector of the P beams formed, for any , Indicates the formation of the first The signal vector of each beam. Let L represent the L signal vectors received from the L antenna elements, respectively. For any... , Let represent the signal vector of the i-th antenna element. T denotes transpose.

[0032] It is a weighted vector, arbitrary. Indicates the formation of the first Each beam requires a complex weighting coefficient for the i-th antenna element, and , It is the amplitude weighting value required to reduce antenna sidelobes. Represents an imaginary number. This represents the spatial phase difference between adjacent antenna elements. It is the spacing between adjacent antenna elements. It is the signal wavelength. It is the first The direction of each beam.

[0033] For digital phased array weather radar, during reception, it can form any number of beams pointing within the ELrange range. The number P of beams formed depends on the computing power of the digital beamforming system, and the beam pointing depends on the weighting vector. By changing the weighting vector This allows you to change the direction of each of the P generated beams.

[0034] During the normal detection cycle of a digital phased array weather radar, the data rate of the full-array IQ sampling data is too large. Therefore, the aforementioned beamforming technology is used to output multiple beam composite data from all range databases after digital beamforming, i.e., multiple beam composite data from all M range databases, based on its capabilities and the direction of the radar's transmitted beam. This application, based on this working mechanism of digital phased array weather radar, considers the continuous temporal characteristics of solar radiation. For pulse Doppler weather radar, solar radiation measurement can be performed using only the full-array IQ data from one range database. The data rate of outputting only the full-array IQ data from one range database does not impose excessive data transmission pressure, and therefore is entirely feasible.

[0035] Therefore, in the scanning process of the digital phased array weather radar during the current detection cycle, in addition to acquiring multiple beam composite data of all range databases after digital beamforming in accordance with the traditional method, this application also acquires the full array IQ data of one range database. Then, based on the characteristic of the continuous nature of solar radiation over time, digital beamforming is performed on the full array IQ data of one range database at the real-time position of the sun in the current detection cycle, so that solar radiation data can also be acquired during the scanning process of the current detection cycle.

[0036] During the scanning process, an additional range library of full-array IQ data is acquired to image the sun using digital beamforming. Therefore, in order to obtain better solar radiation data, it is necessary to ensure that the obtained full-array IQ data of the range library can well characterize the solar radiation situation.

[0037] Based on this consideration, the method of this application is not necessarily used to acquire solar radiation data and perform online calibration in every detection cycle of the digital phased array weather radar (see the flowchart in Figure 2). Instead, solar radiation data is acquired and online solar calibration is performed on the digital phased array weather radar only when the real-time solar elevation angle ELsun within the predetermined elevation angle range is detected in the current detection cycle. That is, the detection process and online solar calibration are performed simultaneously. When the real-time solar elevation angle ELsun within the current detection cycle is detected to be outside the predetermined elevation angle range, only the composite data of multiple beams from all range libraries after digital beamforming is output according to conventional methods, i.e., only the detection process is performed.

[0038] This predetermined elevation angle range is used to ensure a relatively high real-time solar elevation angle (ELsun) during online solar calibration. On the one hand, a higher solar elevation angle results in less atmospheric refraction; on the other hand, higher elevation angles also reduce the impact of ground clutter and rain cloud echoes, thus ensuring the accuracy of the results obtained from simultaneous detection and online solar calibration. Actual testing and verification have shown that the predetermined elevation angle range is 20° to 50°.

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

[0040] In addition, when it is necessary to acquire solar radiation data during the scanning process of the digital phased array weather radar in the current detection cycle, in order to reduce the amount of data transmission, the full array IQ data of a range library is not extracted at each radar azimuth angle. Instead, as shown in the flowchart of Figure 2, when the radar azimuth angle of the digital phased array weather radar is within the angle range of the real-time solar azimuth angle AZsun during the scanning process, in addition to acquiring the multiple beam composite data of all range libraries after digital beamforming, the full array IQ data of one range library is acquired.

[0041] Therefore, during the scanning process of the digital phased array weather radar in the current detection cycle, multiple beam composite data of all M range libraries after digital beamforming at each radar azimuth angle are acquired. Additionally, when the radar azimuth angle is within the angle range of the real-time solar azimuth angle AZsun, the m-th IQ sampling data of each pulse is acquired to obtain the full-array IQ data of a range library. 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, where the integer parameter m ≤ M. Considering the aforementioned long-range detection requirements, if the range library corresponding to the m-th IQ sampling data is greater than a predetermined range threshold, for example, one of the last few IQ sampling data of each pulse can be selected to correspond to one of the farthest range libraries.

[0042] Digital phased array weather radars require an elevation beam pointing within the EL range during detection, typically between 0° and 20°. This often fails to cover the real-time solar elevation angle ELsun (e.g., 20°–50° as mentioned above). Therefore, to obtain the required solar radiation signal at the elevation angle, digital beamforming is performed on the full-array IQ data from a range database 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 represented as AZsun±θ, where the angle range of θ can be customized, for example, set to 5°. When performing digital beamforming on the full-array IQ data from a range database at the real-time solar elevation angle ELsun, the beamforming angle range can be represented as ELsun±γ, where the angle range of γ can also be customized, for example, set to 5°. Even if the current digital phased array weather radar's elevation beam pointing is not within the ELsun±γ range, since the acquired full-array IQ data can generate any receiving beam pointing within the ELrange range, as long as ELsun±γ is within the ELrange range of the digital phased array weather radar, solar radiation data within the azimuth angle AZsun±θ and elevation angle ELsun±γ range can be extracted.

[0043] On the other hand, the beam spacing of the electronically scanned elevation beams in digital phased array weather radars is generally 1°, which is too sparse and cannot meet the accuracy requirements of solar calibration. Therefore, when performing digital beamforming on the full array IQ data of a range library at the real-time solar elevation angle ELsun, the digital beamforming is performed according to the elevation angle step accuracy requirement. This elevation angle step accuracy requirement is set according to the accuracy requirements of solar calibration, and is generally set to 0.1° in practice.

[0044] Based on the method provided in this application, a digital phased array weather radar can output not only multi-beam composite data of all range databases acquired during the scanning process, but also solar radiation data obtained during the scanning process within one detection cycle. The detection result for the current detection cycle can be calculated based on the multi-beam composite data of all range databases; the specific calculation method can refer to existing methods, which will not be elaborated upon here. Furthermore, the digital phased array weather radar can be calibrated based on the solar radiation data obtained during the scanning process, including: obtaining elevation angle, azimuth angle, and antenna beamwidth information by fitting echo data; obtaining the amplitude consistency of the receiving channel by the difference in solar radiation power between the horizontally polarized and vertically polarized receiving channels; and obtaining the antenna gain by the solar radiation signal intensity and radar parameters. Therefore, the digital phased array weather radar can simultaneously complete online solar calibration within one detection cycle, eliminating the need for offline operation, reducing calibration time, and facilitating increased calibration frequency. The calibration results can be used to evaluate and correct the performance parameters of the digital phased array weather radar, such as azimuth, elevation, receiving channel consistency, and antenna gain, in real time, effectively improving the observation performance of the digital phased array weather radar.

[0045] The above descriptions are merely preferred embodiments of this application, and this application is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of this application should be considered to be included within the protection scope of this application.

Claims

1. A method for online sun calibration of a digital phased array weather radar, characterized in that, The online solar calibration method for the digital phased array weather radar includes the following steps in each detection cycle of the digital phased array weather radar: The real-time position of the sun is determined based on 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 in the current detection cycle, which involves mechanical scanning in the azimuth direction and electronic scanning in the elevation direction, multiple beam composite data of all range databases after digital beamforming are acquired, as well as full array IQ data of one range database. Based on the characteristic of continuous solar radiation over time, digital beamforming is performed on the full array IQ data of one range database at the real-time position of the sun in the current detection cycle, so as to obtain solar radiation data during the scanning process of the current detection cycle. The detection results for the current detection cycle are obtained based on the composite data of multiple beams from all range databases acquired during the scanning process, and the digital phased array weather radar is calibrated based on the solar radiation data obtained during 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 includes the real-time sun elevation angle ELsun; The online solar calibration method for digital phased array weather radar also includes: When the real-time solar elevation angle ELsun is detected to be within the predetermined elevation angle range during the current detection cycle, solar radiation data is acquired and the digital phased array weather radar is calibrated during the scanning process of the current detection cycle.

3. The digital phased array weather radar on-line sun calibration method of claim 2, wherein, The real-time position of the sun also includes the real-time azimuth angle AZsun. The solar radiation data acquired by the digital phased array weather radar during the current detection cycle includes: When the radar azimuth angle of the digital phased array weather radar is within the angle range of the real-time solar azimuth angle AZsun during the scanning process, in addition to acquiring multiple beam composite data of all range libraries after digital beamforming, it also acquires the full array IQ data of one range library, and performs digital beamforming on the acquired full array IQ data of one range library at the real-time solar elevation angle ELsun to obtain solar radiation data.

4. The digital phased array weather radar on-line sun calibration method of claim 3, wherein, The digital beamforming of the full-array IQ data from the acquired range database at the real-time solar elevation angle ELsun includes: According to the elevation angle stepping accuracy requirements, digital beamforming is performed on the full array IQ data of a range library at the real-time solar elevation angle ELsun.

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

6. The digital phased array weather radar on-line sun calibration method of claim 1, wherein, During the scanning process, acquire full-area IQ data from a distance library that is greater than a predetermined distance threshold.

7. The digital phased array weather radar on-line sun calibration method of claim 3, wherein, The digital phased array weather radar includes 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 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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