Airborne CO_2 coherent lidar for measurements of atmospheric aerosol and cloud backscatter

Abstract

An airborne CO(2) coherent lidar has been developed and flown on over 30 flights of the NASA DC-8 research aircraft to obtain aerosol and cloud backscatter and extinction data at a wavelength near 9µm. Designed to operate in either zenith- or nadir-directed modes, the lidar can be used to measure vertical profiles of backscatter throughout the vertical extent of the troposphere and the lower stratosphere. Backscatter measurements in absolute units are obtained through a hard-target calibration methodology. The use of coherent detection results in high sensitivity and narrow field of view, the latter property greatly reducing multiple-scattering effects. Aerosol backscatter profile intercomparisons with other airborne and ground-based CO(2) lidars were conducted during instrument checkout flights over the NASA Ames Research Center before extended depolyment over the Pacific Ocean. Selected results from data taken during the flights over the Pacific Ocean are presented, emphasizing intercom arisons with backscatter profile data obtained at 1.06 µm with a NASA Goddard Space Flight Center Nd:YAG lidar on the same flights.

Retrieval of aerosol backscatter and extinction from airborne coherent Doppler wind lidar measurements

“…Quantitative aerosol optical properties derived from airborne coherent DWLs, like backscatter and extinction coefficient, are rarely reported (Menzies and Tratt, 1994).…”

“…Most of these techniques rely on the use of the return signals from targets with known optical properties, including ground-based hard targets (Menzies and Tratt, 1994), sea surface (Bufton et al, 1983) and ground return (Cutten et al, 2002).…”

“…The main problems associated with the calibration of a coherent DWL at ground using calibrated targets (Menzies and Tratt, 1994) are the variability in the optical transmission of the boundary layer, the effect of the turbulence in the heterodyning efficiency, the limitations of the calibration range due to target size restrictions and the necessity of a wellcharacterized system heterodyne efficiency. This last problem is related to practical limitations in the distance at which the target can be placed.…”

Aerosol Backscatter and Extinction Retrieval from Airborne Coherent Doppler Wind Lidar Measurements

“…Up to now, different approaches where applied to retrieve calibrated backscatter coefficient from lidars to which calibration methods based on molecular return cannot be applied, including the use of ground based hard targets (Menzies and Tratt, 1994), ground return (Cutten et al, 2002), sea return (Bufton et al, 1983) and clouds (O' Connor et al, 2003).…”

Design and Implementation of Vibration Isolation System for Mobile Doppler Wind LIDAR

“…All these measurements were performed with the LIDAR system stationary, level-adjusted and stable, as the exact direction of the laser beam was critical for its good performance in elevation-over-azimuth scans [5]. Without an appropriate vibration isolation system, shock and vibration from the vehicle engine rotation, pumping exhaust and uneven road surface affect the LIDAR directly and were found to be the cause for system failures such as optical path misalignment and optical component damage [6,7]. These failures severely limited LIDAR operation.…”