Abstract
Abstract. Use of a compact, low power commercial lidar onboard a small aircraft for aerosol studies is demonstrated. A Micro Pulse Lidar fitted upside down in a Beech Superking aircraft is used to measure the vertical distribution of aerosols in and around Hyderabad, an urban location in the central India. Two sorties were made, one on 17 February 2004 evening hours and the other on 18 February 2004 morning hours for a total flight duration of four hours. Three different algorithms, proposed by Klett (1985), Stephens et al. (2001) and Palm et al. (2002) for deriving the aerosol extinction coefficient profile from lidar data are studied and is shown that the results obtained from the three methods compare within 2%. The result obtained from the airborne lidar is shown more useful to study the aerosol distribution in the free troposphere than that obtained by using the same lidar from ground. Using standard radiative transfer model the aerosol radiative forcing is calculated and is shown that knowledge on the vertical distribution of aerosols is very important to get more realistic values than using model vertical profiles of aerosols. We show that for the same aerosol optical depth, single scattering albedo and asymmetry parameter but for different vertical profiles of aerosol extinction the computed forcing values differ with increasing altitude and improper selection of the vertical profile can even flip the sign of the forcing at tropopause level.
Highlights
Aerosols play a major role in determining the regional scale radiation budget of the earth’s atmosphere by directly scat-tering and absorbing the incoming and outgoing radiations as well as through modifying cloud properties, such as the cloud droplet size distribution and cloud lifetime (e.g. Twomey, 1974; Albrecht, 1989; Pincus and Baker, 1994; Haywood and Boucher, 2000; Kaufman et al, 2005; Ramanathan el al., 2005)
For the first time feasibility of using a commercial lidar of Micro Pulse Lidar (MPL) type on a small aircraft is established for the study of boundary layer height and aerosol vertical profile over urban locations
The study made over Hyderabad, an urban location in the central India proves the possibility of making low cost airborne lidar observations elsewhere
Summary
Aerosols play a major role in determining the regional scale radiation budget of the earth’s atmosphere by directly scat-. During LC-1, for the first time in India, airborne lidar measurements were carried out over Hyderabad, one of the major industrialized cities located in the central India. Results obtained from this airborne lidar experiment are discussed in the present paper in the context of their implication to radiative forcing calculations. Measured backscattered signal strength data are summed for 15 s, which corresponds to a total of 37 500 profiles and averaged before storing as a single profile This results into 1.3 km resolution in the horizontal direction for the typical aircraft speed of 320 km/h. Aerosol extinction profile from the measured backscatter intensity is retrieved in two steps.
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