home » about nssl » research divisions » radar r&d » radar engineering
Phased Array Radar
Phased Array radar has a unique antenna that collects the same information as a conventional radar in about one-sixth the time. Researchers believe phased array could extend warning lead times from 10 minutes to 18-22 minutes. The radar's electronic beams can be directed independently at particular elements of a storm to give forecasters more accurate and complete data than the current NEXRAD radars. The new technology will also gather storm information not currently available, such as rapid changes in wind fields, to provide more thorough understanding of storm evolution. Researchers will be able to refine conceptual storm models and use that knowledge to evaluate and improve stormscale computer models. The phased array radar is expected to eventually replace the current network of WSR-88D radars. NSSL's National Weather Radar Testbed (NWRT) is the official facility where phased array technology will be tested and evaluated. PAR has the potential to provide revolutionary improvements in NWS tornado, severe storm, and flash flood warnings.
HOW DOES PHASED ARRAY WORK?
Current WSR-88D radars transmit one beam of energy at a time, listen for the returned energy, then mechanically tilts up a little higher, and samples another small section of the atmosphere. When it has sampled the entire volume of atmosphere, from bottom to top at a particular location, the radar goes back down, moves over a little, and starts the process over again. This continues until the radar has scanned the entire atmosphere, which takes around six or seven minutes. Phased arrays use multiple beams, sent out at one time, so the antennas never need to tilt. Scanning takes only 30 seconds, and it already has dual-polarization capabilities.
The illustration shows from left: full-volume continuous scan through a developing cumulonimbus cloud, full-volume continuous scan through the planetary boundary layer (clear air) for mapping winds, detection and tracking of aircraft including non-cooperative targets, full-volume continuous scan through a supercell storm, and long-dwell scan through a region of a potential tornado.
ADVANTAGES OF PHASED ARRAY OVER WSR-88D
- 20 to 30-second volume scan rates, compared with 5-7 minutes with the WSR-88D
- "Dwell" – the ability to repeatedly sample areas of interest
- "Adaptive scanning" – the capability to quickly go back and look again at something that draws our attention, such as a severe weather feature
- Lower failure rate
BROAD GOALS FOR PHASED ARRAY TECHNOLOGY
- Demonstrate PAR technology can be applied to the tornado detection, forecast, and warning mission in a multi-use environment.
- Demonstrate skill in probabilistic forecasts of tornadoes and other severe weather events using ensembles of models that assimilate PAR data
- Determine if there is a viable economic strategy which would permit a national PAR network to support NOAA, DOT/FAA, DOD, Homeland Security and other national missions.
CURRENT ENGINEERING RESEARCH PROJECTS
Scan Strategies
Electronic beam steering applications to maximize weather observations
- Allow a beam to follow the terrain to minimize ground clutter
- Can notch out various buildings/structures to minimize radio frequency exposure where required
- Allow a quick surveillance scan, and then a return to the targets that are most important to obtain fine-scale data with improved space and time resolution
- Could be designed to concentrate on various phenomena such as precipitation measurements and wind measurements
Radial-by-radial processing will allow more flexibility in displaying and processing the data with algorithms
Beam multiplexing will improve scanning speed by using the phased array antenna's electronic beam steering capability.
Pulse compression will combine the high energy of a long pulse with the high resolution of a short pulse to allow the radar to "see" farther
Product Development
Rotation tracker is being developed as a new product that will allow users to see the increase and decrease in shear over time
Data Quality
An automated method to keep the NWRT calibrated will ensure accuracy and data reliability.
Implementation of a ground clutter canceling and range and velocity unfolding filter
Hardware enhancements
Implement a dual-polarized sub-array to determine the feasibility of using dual-polarized active arrays for design of the Multi-function Phased Array (MPAR) system.
SUCCESSES: The engineering phase of the PAR is complete. The PAR is operationally stable and provides good estimates of reflectivity, velocity and spectrum width; The PAR collected 30 hours of data for engineering tests, weather observations and system checks in 2005; the NWRT Testbed Control Center can run the PAR remotely from the new National Weather Center.
