PORTLAND, Ore. The blimp with the 23-foot-long sensor-studded tether that is now hovering over the Pentagon is about to conduct novel tests of simulated airborne toxins. As the blimp releases a faux poison over the course of the next two weeks, a real-time system designed for first responders will gauge how much of the toxin has been discharged and where, and then predict where the plume will drift and how it will disperse.
Results of the effort, which is sponsored by the Defense Advanced Research Projects Agency, will be incorporated into an umbrella protection regime against chemical, biological and radiological toxins that can be adapted to all Defense Department facilities and foreign embassies.
"What we think is really novel about this system, making it the only one in the world, is that it uses what we call multiscale forecasting," said project leader Scott Swerdlin, a software engineer at the National Center for Atmospheric Research (NCAR).
The system infuses weather-forecasting models with specialized knowledge about the plume and dispersion patterns for various toxic agents, as well as venue-specific data such as the local temperature inversions at night, which could allow an airborne hazard to spread below rooftop height.
The plume-and-dispersion model spans four concentric airspaces, somewhat in the manner of a Russian nesting doll, with resolutions of a few kilometers down to 2 meters, respectively.
Meanwhile, a real-time monitoring system integrates streaming sensor data from fixed sites with at-a-distance measures such as Doppler and laser-based radars. The result is a virtual 3-D hemisphere around the protected site in this case, the grounds of the Pentagon with varying resolutions, from coarser to finer.
The air composition is known anywhere inside the hemisphere; turbulence measures enable the model to predict the near future and to self-correct for surprises in real-time.
At its widest reach, with a resolution of a few kilometers, the model gets updated every few hours from conventional weather-forecasting sources. At the next layer the resolution becomes finer, less than 1 km, by virtue of real-time data from fixed-sensor locations and from radar scans that are updated every 6 minutes.
At the next-finest scale, laser-based radars (lidars) bring the resolution down to about 75 meters. Finally, the finest scale brings the innermost layer's resolution down to 7 feet (2 meters), by virtue of on-site high-resolution meteorological sensors and fine-scale models that simulate the airspace around the forecast area and verify their predictions with finely focused local lidars.
Tests were scheduled to begin on Saturday and will run until May 15. The National Oceanic and Atmospheric Administration in cooperation with the U.S. Army's Dugway Proving Ground will release a simulated toxic gas called sulfur hexafluoride.Following this inert, invisible, nontoxic gas will enable Swerdlin's NCAR team to verify the accuracy of the computer models they have constructed.
The controlled releases will be monitored by thousands of passive ground-based meteorological instruments dubbed "pigs" (for program integrated ground-based samplers). The pigs will take second-by-second readings, time-stamp them and record them onto a fixed media for analysis after the last test on May 15.
Measuring in the air above the Pentagon enables the normal circular weather forecasts to be extended upward to create a model that is a true 3-D hemisphere. The blimp's sensor-studded tether, made from Kevlar, can be hoisted hundreds of feet high to make measurements that rival the accuracy of the ground-based pigs.
"One of the stars of the show is our 30 x 10-foot blimp," said Swerdlin. "The idea there is to fly it through what's called the boundary layer"the lowest part of the atmosphere from the surface up that is still affected by conditions on the ground."
Measurements taken by the blimp's tether will be correlated with simultaneous measurements from the lidar currently atop the Pentagon, "so that we can come to understand the atmosphere from the lidar [alone]," said Swerdlin. After May 15, the lidars alone will take over.
Coherent Technologies Inc. is providing the Doppler lidars for the test period.