Cloud recognition system watching over Pentagon.

• Author: Pappalardo, Joe

A laser system designed to identify and track chemical or biological attacks on the Pentagon is providing a glimpse into the future of long-range threat detection equipment.

Perched on top of a raised elevator shaft on the roof of the Pentagon's Navy annex, one kilometer from the main building, a pencil-thin laser beam constantly sweeps the air. The light waves bounce off particles, which arc analyzed based on changes in the frequency of the returning waves.

The light detection and ranging (LIDAR) system, called "Wind-Tracer," was developed by CLR Photonics. It is used internationally in airports and atmospheric research laboratories.

Across the highway, CLR technicians ensconced in a hotel room near the Pentagon examine real-time displays of wind direction and speed. Another monitor displays a shimmering white mist--the usual pattern of background dust, pollution and water normally found in the D.C. air. The goal is to create computer models in determine the direction a toxic plume could drift if released near the Defense Department's headquarters.

LIDAR is one of many sensors contributing to the wind-modeling program. More standard weather forecasting equipment is also being used, including battery-powered wind sensors mounted on light poles and buildings, a 100-foot tower mourned with sensors planted on Arlington Cemetery property, and a 30- by 10-foot blimp to measure the winds at various heights.

The LIDAR system is also on the lookout for anomalous clouds that could indicate the presence of a biological weapon or other toxin. Scientists can detect a release, chart wind speed and direction, and calibrate the size and likely movement of a possible threat. The $1 million WindTracer will remain permanently on the annex roof.

"LIDAR can do initial detection and tracking, but it needs other systems to verify what [substance] it's looking at," said CLR business unit manager Jerry Pelk, one of the on-site supervisors of the project. "There's a lot of research going on in that area, but the technology is not there yet."

During a May exercise, researchers released a non-toxic, colorless gas over a three-day period, simulating how chemical or biological agents would flow around and into the Pentagon. The scientists used sulfur hexafluoride, commonly used in airflow testing, for the test release. The Food and Drug Administration considers the gas safe enough to permit its injection into the human body.

When an agent is released, the laser picks...