Tropospheric O-3 measurement by simultaneous differential absorption lidarand null profiling and comparison with sonde measurement

A differential absorption lidar (DIAL) system consisting of two identical t unable laser systems and a single optical receiver is applied to measuremen t of O-3 concentration profiles in the lower troposphere. Each laser is cap able of emitting two wavelengths on alternate pulses, so the system is capa ble of simultaneous measurement of two species in the same wavelength regio n. We set the two lasers to emit at identical wavelength pairs consisting o f on wavelength 285.0 nm and off wavelength 290.1 nm for simultaneous measu rement of two null profiles, one at each wavelength, and two DIAL profiles, or O-3 concentration profiles. Null profiles are useful in estimating inst rumental error and checking the vertical range interval in which the DIAL p rofiles are accurate. Null and DIAL profiles are obtained for vertical rang e 1000 to 4000 m using neutral density filters of different transmissions t o prevent the strong return signals from close range from saturating the ph otodetector. The obtained O-3 concentration profiles agree with simultaneou s O-3 sonde measurements. An evaluation of the measurement error shows that the average O-3 measurement error for vertical range 1000 to 4000 m was 3. 4 ppb, or 8% relative to the average O-3 concentration of 42.3 ppb, most of which is due to statistical error. The error due to differential Mie atten uation and differential backscatter gradient was found to be 0.5 ppb. (C) 2 001 Society of Photo-Optical Instrumentation Engineers.