Method for Detecting the Presence of a Gas in an Atmosphere.
DEPARTMENT OF THE ARMY WASHINGTON DC
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Near real time remote sensing of atmospheric gases is performed using differential absorption lidar or transmission techniques. The wedge absorption remote sensor WARS utilizes an emission spike train of short time duration as is found in the long pulse output mode of a solid-state laser to define the on and off line absorption of an atmospheric gas and hence its concentration. The laser beam is split into a reference beam and a transmission beam which passes through the atmosphere being tested. The two beams are detected and amplified, and then digitized. Comparing the ratio of the digitized reference signal to transmitted signal for each spike in the spike train yields a set of transmittance values as a function of wavelength. When the digitized reference and transmitted signals are plotted, a wedge of data points results. The ratio of the upper and lower slopes of the wedge yields the absorption coefficient and concentration of the absorbing gas.
- Atmospheric Physics
- Test Facilities, Equipment and Methods