Radars on the Storm
Military tech could help forecasters improve weather predictions
Weather forecasters can now predict dangerous tornadoes and thunderstorms in a flash.
Advanced computer models, more precise satellite observations and radar upgrades allow meteorologists to issue storm warnings much earlier than in the past, giving the public more lead time to prepare and seek refuge. Yet they could be even faster: a military-grade radar system called Active Electronically Scanned Array, or AESA, could spot a severe storm in seconds rather than minutes.
“Adding AESA radar, we could go from ‘warn on’ detection to ‘warn on’ forecasting,” said Charlie French, a Raytheon weather programs senior manager. “Instead of saying, ‘Take cover immediately, there’s a tornado here,’ we’d be able to say “Find a shelter. there’s a tornado that will be heading in our direction.”
Of the country’s 600-plus ground radars, about a third belong to the National Oceanic and Atmospheric Administration. About 160 are Weather Surveillance Radar-1988 Doppler, or WSR-88D. NOAA and the National Weather Service could upgrade to the faster, higher-fidelity and more-accurate AESA radar when the government auctions off part of the radio spectrum and uses the proceeds to recapitalize the country’s aging radar systems.
The FAA, DoD, DHS and NOAA have formed a cross-agency team called SENSR, for Spectrum Efficient National Surveillance Radar. The goal: Decrease the number and types of radars across the country and replace them with advanced, highly sophisticated multi-purpose radars for air traffic control, air defense and air surveillance, border and critical infrastructure protection and weather forecasting.
“AESA radar is more effective, more efficient and degrades gracefully versus simply shutting down,” said Mark Thompson, Raytheon SENSR capture executive. “By the way, having four agencies share radars will result in a significant reduction in operations and sustainment through efficiency; it won’t be a burden on any one single agency’s operations and maintenance budget.”
Weather radar works by beaming out radio waves that reflect off particles in the atmosphere, such as raindrops, drizzle, snow or even dust. By measuring the strength of the waves that return to the radar and how long the round-trip takes, forecasters can see the location and intensity of precipitation.
“Ground-based weather radar is the most critical pieces in the weather data chain,” Thompson said. “Satellites give you the big picture but ground radar gets you up-close and personal.”
Doppler radars scan one elevation angle at a time, with a parabolic dish that is mechanically turned. Once the dish completes a full 360-degree slice, it tilts up, sampling one small sector of the atmosphere at a time. After sampling from lowest to highest elevation, which during severe weather equates to 14 individual slices, the radar returns to the lowest angle and begins the process all over again.
“Scanning the entire atmosphere during severe weather takes Doppler radar about four to six minutes,” said Nick Powell, a Raytheon SENSR principal meteorologist. “In contrast, AESA radar is a stationary panel with no moving parts. It sends out multiple beams simultaneously, eliminating the need to tilt the antennas, decreasing the time between scans of storms. Operators will be able to steer its beams electronically to concentrate on areas of interest, resulting in more data about the worst parts of the storm.”
The SENSR team couldn’t discuss the specifics of AESA’s range resolution, but they said it was an order of magnitude better.
“It’s going to be like going from a cathode-ray-tube television to a 70-inch, 4K, curved HDTV,” Thompson said.
Because AESA’s scan rate is so fast, it will be able to serve all of the needs of National Weather Service while executing the missions of the Department of Defense, FAA and Homeland Security.
“Using AESA technology is an elegant solution for combining multiple missions,” Powell said. “None of the agencies’ missions will be compromised or degraded, but markedly improved instead.”
Another AESA benefit, according to the team, is that nothing new will have to be invented or created, which means it could be deployed quickly.
“We’ll be amalgamating today’s technology for tomorrow’s radar,” Powell said. “The technology will be a game-changer, decreasing scans of storms to less than a minute and gathering storm information currently not available. The improvement will allow meteorologists to identify rapidly evolving changes in thunderstorm circulations and, ultimately, be able to more quickly detect the changes that cause tornadoes.”