Weather Radar Research in Australia
Addressing the need for faster, more accurate weather warnings
Current weather monitoring radar systems are large, high-powered and expensive. They are designed to provide long-range surveillance over large areas. Terrain blockage and sighting limitations, including those due to the Earth's curvature, result in less than complete spatial coverage (Figure 1). In addition, radar images in conventional, mechanically rotating, systems are updated only every six to 10 minutes. This can be a problem because the life cycle of a convective weather cell is around 30 minutes and its severe components, such as microbursts, can develop and dissipate between scans. This limits the accuracy and timeliness of weather forecasts and warnings. Raytheon and its partners are investigating alternative networks of smaller, less expensive radars to fill these gaps.
Raytheon has been working with the University of Massachusetts Collaborative Adaptive Sensing of the Atmosphere (CASA) center for the past 10 years to eliminate this gap. In addition, Raytheon has recently started a research relationship with the University of Adelaide in South Australia to expand this research and to address weather and hydrology needs around the globe.
The team in South Australia — which includes Raytheon Australia, the University of Adelaide, the University of Melbourne, the Bureau of Meteorology (BoM), the Defence Science and Technology Organisation (DSTO) and the Defence Systems Innovation Center (DSIC) — in conjunction with the University of Massachusetts, has won a three-year Australian Research Council (ARC) linkage grant to develop and distribute a network of X-band*phased array radars to explore real-time, multi-observation weather and weather-related events. This grant focuses on establishing an experimental network of three fully polarimetric** digital X-band radars (described below) in Adelaide. The radars being demonstrated are separated by 10 to 20 kilometers. They will overcome the limited vertical coverage (i.e., fill the gap) of current weather radar systems, and be able to electronically scan their beams in order to revisit events much faster than conventional mechanically scanned parabolic dish radars. The Adelaide network (Figure 2) is located in the vicinity of Adelaide city within the gap of two long-range weather radars to the north and south.
The ability to multitask such systems, and to potentially integrate them with air traffic control or other similar systems, is an area of interest for research and development. The benefits of multitasking could greatly affect the architecture and efficiency of new systems. These include the ability to maintain broad and persistent spatial coverage to detect and track precipitation and other atmospheric phenomena (e.g., smoke and insects), while simultaneously providing narrow time resolution data on critical weather events such as tornadoes and localized areas of dangerous precipitation. This would be interleaved with information about aircraft close to these events and potentially in harm's way.
The Phase-Tilt Radar
The phased array radar being developed for this purpose is shown in Figure 3. This radar, designed for cost and performance, is called a phase-tilt radar because it scans electronically in azimuth (horizontal plane) and it scans mechanically (tilts) for elevation (vertical plane). The one square meter array has the capacity for 4,096 transmit/receive channels if it were fully populated, but to reduce cost (while still meeting performance goals), this array employs only 64 transmit/receive channels along the center horizontal axis of the aperture, feeding 64 strips of vertical antenna elements.
Figure 4 shows the radar mounted on a truck for mobile weather observation, as well as a plan position indicator (PPI) plot generated from the mobile radar during a severe storm in Western Massachusetts on August 10, 2012. This radar will be deployed to Adelaide and integrated into the radar network for a 2013 demonstration.
Improving System Performance
Raytheon's small phased array radars fill the gaps in radar coverage. This new technology also provides advanced digital signal processing techniques to improve performance.
For example, the investigation of weather effects is enhanced by the simultaneous allocation of phased array beams to different volumetric regions, as well as the adaptive allocation of these beams to track and delineate weather effects on spatial and temporal scales with resolutions greater than those in current use. The benefits of improved spatial resolution can be seen in Figure 5, with the higher resolution display on the right allowing improved geographical localization of weather patterns as compared to the lower resolution results on the left. The proposed new approach significantly augments existing systems by providing high temporal and spatial resolution and faster scanning at key locations such as airports and areas where the views of large radars are obstructed.
While weather monitoring services remain a prime application for the proposed system, another important application is meteorological research. Rapid updates provided by the phased array antennas will give new insights into cloud processes. Polarimetric functionality provides more detailed information on cloud microphysics, including the shape of particles, which can differentiate rain from hail. Observations supplied by the proposed system will enable robust testing and high spatial resolution meteorological research models.
Such testing is critical for understanding and monitoring the effects of climate change and the processes that affect it.
A network of distributed phased array radars provides not only greater multitasking flexibility, but it also allows for greater spatial coverage. While there have been some limited demonstrations in the use of a single phased array for weather monitoring, there has never been a practical demonstration of the coordinated use of networked phased arrays for monitoring weather phenomena. The system being developed places the current Adelaide facility at the forefront in the development of practical weather radar system technology. This radar system will provide strategic guidance to the Australian Bureau of Meteorology for future networked radar systems with regard to monitoring weather events, extreme phenomena and multitasking.
Christopher McCarroll and David McLaughlin
Contributors: Robert Palumbo and Ken Wood
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