Pentagon tests breakthrough system to detect airborne toxins

A breakthrough blend of high-tech instruments and weather forecasting models is being tested at the Pentagon April 15-May 15. Coordinated by scientists at the National Center for Atmospheric Research (NCAR), the tests scan for potential airborne toxins near the Pentagon and predict their motion and impact on the building. The knowledge gained from the tests will allow the development of improved systems for protecting Department of Defense facilities.

Partners from academia and the public and private sector are joining NCAR in the effort, sponsored by the Defense Advanced Research Projects Agency (DARPA). NCAR brings to the test years of experience in developing systems that detect and warn for wind shear and turbulence at airports and protect against terrorism at high-profile events, such as the Olympic Games.

"Knowing how to properly respond to an attack or a toxic industrial incident requires the best modeling tools and sensors available today, and these must all work in a coordinated fashion in real time," says NCAR project leader Scott Swerdlin.

Understanding air circulation around the Pentagon is a unique challenge, says Swerdlin. The air circulations are very complex because of the building's size and unusual geometry. Temperature inversions, especially at night, could allow an airborne hazard to spread below rooftop height, which adds to the complexity of a monitoring system.

To tackle the problem, NCAR and partners built a nest of concentric computer models--each with a different strength--that predict weather conditions from the entire Washington region inward to the Pentagon itself. Information is routed among them every 15 minutes.

"The weather modeling system tested here is one of the most complex ever constructed," says NCAR's Thomas Warner, lead scientist on the project.

DARPA program manager Paul Benda adds, "The weather modeling system being tested will greatly improve our understanding of how to best protect the occupants of the Pentagon from a chemical or biological attack."

This spring's testing

Tests will occur between April 15 and May 15. In addition to the system's standard equipment (below), these tests will include

• A 23-foot-long instrumented balloon tethered above the Pentagon. Deployed by the University of Colorado, the setup includes sensors studded along the balloon's tethering wire. As the balloon rises and falls, the sensors sample air flow and turbulence.

• Periodic releases of sulfur hexafluoride (SF6). This inert, invisible, nontoxic gas helps scientists verify the accuracy of the computer models and sensors that track dispersal of airborne material. The releases are coordinated by the National Oceanic and Atmospheric Administration with assistance from the U.S. Army's Dugway Proving Ground.

The dates of the SF6 releases hinge on day-to-day weather conditions. Scientists are taking advantage of wind directions and speeds that allow SF6 to be tracked from a release point directly toward the Pentagon.

"It's a very challenging exercise," says Swerdlin. "We're calling on a lot of experienced players and advanced weather forecasting systems in order to precisely time the releases."

What's in the system

Most modern weather forecasts target areas the size of a county, not a single building. NCAR and colleagues are developing a unique, fine-scale weather monitoring and forecasting system. It includes

• A multiscale weather forecast model. Every 15 minutes, this software pulls information from a high-resolution regional weather analysis and generates a set of wind forecasts with increasingly finer detail at smaller scales. The forecasts draw on data from Doppler radars as well as lidars (see below). At its finest scale, the system charts air flow every 7 feet (2 meters) immediately around the Pentagon.

• Lidars (laser-based radars). With a beam narrower than that of conventional radar, a lidar is ideal for tracking tiny particles at short distances in clear air. Coherent Technologies, Inc., is providing a Doppler lidar for monitoring winds, while NCAR tests its new lidar suitable for tracking toxic clouds at very fine scales.

• Other sensors. Local weather stations and sensors are designed to spot airborne toxins as they pass a single point.

NCAR's portion of this research is nonclassified. NCAR's primary sponsor is the National Science Foundation. Opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of the National Science Foundation.