Multiwavelength And Triple CO2 Lidars For Trace Gas Detection

SRI International has developed two infrared differential absorption lidar (IR DIAL) systems to detect infrared-absorbing trace gases and environmental monitoring applications. The multiwavelength DIAL system operates at 10.6 μm and performs both path-integrated (column-content) and range-resolved measurements. This van-mounted system contains four grating-tuned Tachisto 555-G (custom) TEA CO2 lasers, with a nominal 1 J of transmitted energy at 10P(20). The lasers are typically fired with a 100 μs spacing to freeze the atmosphere. The IR receiver uses a 16-in. f/2.5 telescope and a liquid-nitrogen-cooled HgCdTe quadrant detector. The scanner allows pointing over a full hemisphere. The lidar data system features two DEC PDP-11/73 microcomputers and a computer automated measurement and control (CAMAC) data acquisition system for real-time data collection, signal averaging, data analysis, color graphics display, and storage on magnetic tape. The multiwavelength DIAL system has demonstrated path-integrated measurements to a range of 9 km and range-resolved measurements to 4 km. The triple CO2 DIAL system operates at 3.4 μm and utilizes three mini-TEA CO2 lasers and nonlinear crystals in a novel frequency-mixing technique to detect and discriminate selective hydrocarbons.