-
With the advent of Doppler weather radar, not only the detection of echo intensity (reflectivity factor), but also the detection of radial velocity is realized. Although the radial velocity contains only one component of the precipitation particle motion, which is projected along the direction of radar electromagnetic waves, it provides meteorologists with atmospheric kinematic information for understanding the development of weather systems. However, to fully describe the atmospheric dynamics, wind fields at different heights in the precipitation clouds are needed, with which the internal development and evolution of weather systems can be monitored and more accurate early warning of severe storms would be possible. Since a single radar only detects one radial velocity for a given point in space, an accurate detection of the 3D motion of precipitation particles in a concerned area requires two conditions to be met: 1) at least three non-coplanar radial velocities are detected; and 2) the DTD among these radial velocities must be small enough or negligible so that the full motion vector can be composed. The AWR focuses on satisfying these two conditions: detecting three non-coplanar radial velocities, while keeping the DTD among the radial velocities smallest.
-
An AWR is comprised of one radar back-end and three or more phased-array radar front-ends. In order to obtain, for example, three non-coplanar radial velocities, three front-ends of the AWR are deployed as a group in a triangular placement and operate in the SAS mode. While an equilateral triangle is the ideal deployment for maximum FDA and minimum DTD, an acute triangular placement is more common and practical due to limitations of physical locations. Nevertheless, the equilateral triangular placement is used in most of the discussions herein, which can be easily extended to an acute triangular placement. The DTD among the front-ends is reduced by the SAS mode and a phased-array fast scanning technology. The AWR consisting of one back-end and three or more phased-array front-ends is a complete weather radar system. Even though multiple phased-array front-ends are deployed at different locations, they are controlled by only one back-end.
In brief, AWR is not a phased-array radar (PAR) network comprising several independent PARs and a central control site, of which the latter is built as an additional component to accomplish the coordination of each individual PAR. At the same time, it is also not a regular PAR, if the AWR comprises one radar back-end and only one radar front-end, then this AWR is actually the regular PAR.
The block diagram of the AWR comprising one back-end and three or more phased-array front-ends at different locations is shown in Fig. 1. The primary technical specifications of a single-polarized three-front-end AWR system are given in Table 1.
Figure 1. The block diagram of an AWR. The AWR consists of one radar back-end (left) and more than three radar front-ends (right) at locations different from the back-end. The back-end of the AWR comprises a data server, a monitor server, and a process server; and every front-end comprises 64 channel processors, 64 channel TR modules, a 64-channel antenna array, an azimuth rotation servo, and a power supply. Three front-ends of the AWR are deployed as a group in a triangular placement and operate in the SAS mode. The communication between the back-end and the front-ends mainly includes SAS controlling and radar data transmitting.
Specifications Technical indicators Technology Distributed phased-array, phase-coherent, and one dimensional, active phased-array Frequency Range 9.3–9.5 GHz (the frequency differences among the
front-ends are 10 MHz)Deployment distance between every two radar front-ends/
Maximum detection range of one radar front-end~20 km AWR product grid size 100 m × 100 m × 100 m The horizontal range of the FDA product Approximately triangular area with a baseline of ~20 km* Volume-scan data update time 12 s Maximum data time difference (Max DTD) in the FDA 2 s Synchronized azimuthal scanning (SAS) error 0.05 s Basic products Reflectivity, wind field * Actually, the horizontal FDA of the three-front-end AWR is larger than a triangle. It is actually a scalene Reuleaux triangle (an irregular triangle with the sides of arcs instead of straight lines). More discussions are found in section 4. Table 1. The primary technical specifications of an X-band single-polarized three-front-end AWR.
The AWR back-end (Fig. 1) comprises a data server, a monitor server, and a process server. The data server is used for collecting, storing, and managing radar products and equipment status data from the radar front-ends; the monitor server monitors the operational status of the radar front-ends, dispatches control commands to the radar front-ends for completing the SAS, analyzes the status data, and displays radar error warnings and various radar products; and the process server processes the radar products from the radar front-ends and completes data quality control processes. The outputs from the process server comprise various radar products such as wind fields, intensity fusion products, and other physical data.
Each radar front-end comprises 64 channel signal processors (Fig. 2), 64 channel transmit-receive (TR) modules (Fig. 3), a 64-channel antenna array, a servo, and a power supply. The antenna array (1.45 m × 1.2 m) uses an array of slot waveguides. The waveguide array is composed of 64 slot waveguides, which are wire-connected to the 64 channel TR modules. The azimuth rotation servo drives the antenna to rotate mechanically in horizontal directions for completing azimuthal scanning. The power supply powers all components in each front-end. Figure 4 is a picture showing the five main components of the phased-array front-end discussed above.
Figure 2. The detailed block diagram of the 64-channel signal processors. As shown in the figure, multiple signal processing procedures are finished in an A/D acquisition unit, an FPGA unit and multiple DSP units in sequence.
Figure 3. The detailed block and functional diagram of one-channel transmit-receive (TR) module. The basic components and part of the technical specifications are given in the figure.
Figure 4. Picture showing five main components of one front-end of the first X-band single-polarized AWR deployed at the Huanghua International Airport, Changsha, China. The five components include (1) phased-array antenna and radome, (2) TR modules, (3) power supply, (4) signal processors, and (5) servo.
The communication between the back-end and the distributed radar front-ends at different locations are completed via optical fibers, wherein the SAS controlling commands and basic physical products such as reflectivity factor, radial velocity, and spectrum width from the multiple radar front-ends are transmitted during the communication.
Figure 3 shows one channel TR module block and functional diagram. Each 64-channel transmitter sends signals to the antenna and sequentially forms four wide beams with an elevation width of 22.5° and an azimuth width of 1.6° covering the 0°–90° elevation by controlling the phases of the 64 channels. During receiving, the 64-channel receiver receives target echo signals. The echo signals are processed through a low-noise amplifier, a mixer, and an intermediate frequency amplifier firstly; secondly, they are converted into digital signals through a 64-channel analog-to-digital converter (ADC); then they are fed into the 64 channel signal processors. As shown in Fig. 2, in the 64 channel signal processors, the digital signals are processed through down-conversion, extraction, filtering, digital beamforming, linear pulse compression, ground clutter suppression, spectrum analysis, parameter estimation, and other algorithms. Part of the outputs from the signal processor, which include the reflectivity, the radial velocity, and the spectrum width are finally fed to the radar back-end. The primary technical specifications of every front-end of the X-band single-polarized AWR are shown in Table 2.
Specifications Technical indicators Range resolution 50 m Number of subarrays / elements 64 / 4096 Sensitivity 15 dBZ at 20 km Radial velocity −52−52 m s−1 Spectrum width 0−16 m s−1 Antenna scanning range and scanning mode Azimuth: 0°–360° (mechanical scanning mode);
Elevation: 0°–90° (electronic scanning mode)Antenna/Radome size 1.45 m × 1.2 m Radome transmission loss 0.4 dB Antenna beamwidth (horizontal, vertical) 1.6° Antenna Gain (Tx, Rx) 26 dB, 38 dB Transmitted pulse compression waveform Linear frequency modulation Range sidelobe levels ≤−40 dB Beam sidelobe levels (azimuth) ≤−25 dB System phase noise (frequency source phase noise) ≤−110 dBc/Hz @ 1 KHz Element spacing λ/2 Pulse widths /pulse compression ratio 4 μs /20; 20 μs /100 Pulse repetition frequencies 20 KHz, 7 KHz FFT points 64 Transmitted peak power 320 W Table 2. The primary technical specifications of every front-end of the X-band single-polarized AWR.
-
A new weather radar system (AWR) which consists of one radar back-end and distributed phased-array radar front-ends has been developed, inspired by both existing weather radar networks and the phased-array technology. Different from other weather radar systems, the AWR uses the phased-array technology and the SAS to achieve 12 s rapid volume scan with 3D fine detection of microscale features of convection events. With the unique SAS rule for three to seven front-ends, the AWR achieves < 2 s DTD while completing the full regional volume scan within 12 s.
Considering the small FDA limitation of the three-front-end AWR, we discuss the generalized AWR deployment solution below and the DTD for this deployment. As mentioned in section 4, an AWR can be built with more front-ends to cover a large region, yet still one AWR system with only one radar back-end. Based on the seven-front-end AWR discussed in section 5.4, a simple arrangement as shown in Fig. 12 can be realized for larger coverage. Figure 12 shows a 37-front-end AWR, with the center front-end of each group of seven AWRs (F, H, Q, S, U, D1, F1) rotating clockwise and the others rotating counter-clockwise. From the above discussion of the seven-front-end AWR in section 5.4, the DTD in each group of the seven front-ends is still smaller than 2 s, as shown by the darker yellow FDAs. In the light-yellow-colored FDAs, the maximum DTD is 10 s and the minimum is 2 s. This is determined by the seven-front-end AWR scanning scheme and the fact that the three front-ends surrounding these FDAs are all rotating in the same counter-clockwise direction. Taking the FDA G-L-M as an example, the front-end G starts scanning this FDA at second 6, L starts at second 2, and M starts at second 10. In this 37-front-end AWR, scanning of the entire region is still completed in one volume-scan time (12 s) with every front-end starting and ending one volume scan at the same times. The DTD is less than 2 s in 75% of the region, and 2–10 s in the remaining 25% of the region. In this way, 37 radar front-ends can form 42 FDAs, which can solve the small FDA limitation, meanwhile, the DTD of the 75% of the AWR coverage region can be less can 2 s. The AWR can cover a city which has the area similar to the region covered by the AWR with this kind of deployment solution in the future.
Figure 12. Layout of a 37-front-end AWR and the synchronized azimuthal scanning (SAS) scheme (labels are the same as in Fig. 9). In the darker yellow FDAs, the DTD in each group of seven front-ends is less than or equal to 2 s; and in the light-yellow-colored FDAs, the maximum DTD is 10 s and the minimum is 2 s.
In order to improve the speed of complex computations, suitable server configurations should be provided for the three-front-end AWR. Taking the three-front-end AWR in actual operation for example, nine servers including one control server, four normal product servers, three GPU product servers, and one data storage server are configured for one three-front-end AWR; the detailed server configurations are given in Table 3. In order to avoid data stacking, the control server controls the three-front-end AWR to complete one volume scan within 12 s, the volume-scan data is transmitted to and stored in the data storage server by using the optical fiber communication at the speed of 10 G s−1 within 12 s, and the radar products are generated in the GPU product servers and displayed in the normal product servers within 12 s. The volume-scan data quantity and the actual computational complexity are different under different weather conditions. Considering the huge amount of computation, most product computation algorithms are completed in the three GPU product servers. For the seven-front-end AWR, there are more challenges for the server configurations.
Server name Main configurations Model Quantity Control server CPU: Silver 4210
DDR: 32GB
HDD: 300G*4DELL R440 1 Product server (normal) CPU: Silver 4210
DDR: 64GB
HDD: 300G*4DELL PowerEdge R740 4 Product server (GPU) CPU: Silver 4210
DDR: 64GB
HDD: 300G*4
GPU: RTX5000 16G/384 bit/CUDA core 3072/4* DP/Power interface 6pin + 8pin/ Maximum power consumption: 265WDELL PowerEdge R740 3 Data storage server CPU: 4 cores
DDR: 16GBQNAP TS-1673U-RP-8-CN 1 Table 3. Server configurations used for the three-front-end AWR.
With the small DTD achievement, wind field synthesis and/or retrieval at different heights has been achieved from the field experiments of the first X-band single-polarized three-front-end AWR deployed at the Changsha Huanghua International Airport, China. Synthesized 100 m × 100 m × 100 m gridded wind fields at 12 s temporal resolution reveals fine structural and evolutional features inside convective clouds.
However, it should be noted that in-depth wind field comparison and the reflectivity comparison are not considered in this paper; in addition, attenuation in the convective precipitation areas is problematic, because of the X-band limitations. Our future work will focus on these aspects. Moreover, future work could also focus on some advanced PAR scanning techniques which can be used to enhance azimuth resolution (Bluestein et al., 2010; Schvartzman et al., 2021b).
Upon further refining of the wind field retrieval, this new radar system offers new capabilities for detecting fine-scale wind and intensity fields of severe convective events, which is promising to advance our understanding and nowcasting of severe storms, as well as the development of numerical weather prediction models.
Acknowledgements. Thanks are due to Professor Zhenhui WANG from Nanjing University of Information Science and Technology and Professor Xiaoyang LIU from Peking University for valuable suggestions; to Eastone Washon Science and Technology Ltd. for providing the AWR for field experiments; to graduate students Fangping LI, Wanyi WEI, and Yu LI from Chengdu University of Information Technology for their dedicated work on data collection and graphic production; and to Chuan LUO, Caiwen REN, Jingyi SUN, Shuyu ZHANG, Siwei LV, Wen YANG and others from Eastone Washon Science and Technology Ltd. for their dedicated work on AWR data collection and processing. This work is supported by Natural Science Foundation of China (NSFC) (Grant No. 31727901).
Specifications | Technical indicators |
Technology | Distributed phased-array, phase-coherent, and one dimensional, active phased-array |
Frequency Range | 9.3–9.5 GHz (the frequency differences among the front-ends are 10 MHz) |
Deployment distance between every two radar front-ends/ Maximum detection range of one radar front-end | ~20 km |
AWR product grid size | 100 m × 100 m × 100 m |
The horizontal range of the FDA product | Approximately triangular area with a baseline of ~20 km* |
Volume-scan data update time | 12 s |
Maximum data time difference (Max DTD) in the FDA | 2 s |
Synchronized azimuthal scanning (SAS) error | 0.05 s |
Basic products | Reflectivity, wind field |
* Actually, the horizontal FDA of the three-front-end AWR is larger than a triangle. It is actually a scalene Reuleaux triangle (an irregular triangle with the sides of arcs instead of straight lines). More discussions are found in section 4. |