Sizing and Ranging Aerosol Distributions using combined Lidar and

Sizing and Ranging of Aerosol Distributions using combined Lidar and
Skyradiometer (AERONET) observations.
Ben Hermann, Marco Vargas, Fred Moshary, Barry Gross, and Sam Ahmed
Monitoring of tropospheric aerosols is of fundamental importance in air quality
monitoring and its impact on health, where both the amount and sizes of aerosols are
important. On one hand, sky radiometers provide column-integrated optical depth
information and can be processed to obtain column averaged particle size distribution
(PSD) under a homogeneous atmosphere assumption. On the other hand, since
tropospheric aerosols are highly variable, range dependant information using lidars are
usually obtained from vertical profiling of the backscatter signals but this approach
requires calibration and assumptions concerning the extinction/backscatter (S) ratio.
Under homogeneous atmosphere assumption, typical S values for local conditions are
used. Similarly, S values derived from sky-radiometry can be employed for inversions
To probe inhomogeneous (variable S-Ratio) profiles, a technique based on an
iterative multiwavelength approach which combines elastic backscatter signals at several
wavelengths along with an improved first estimate of single channel properties using a
CIMEL path averaged particle size distribution (PSD) is presented. In particular,
necessary conditions are obtained which determine the convergence properties of this
algorithm and examples illustrating this approach are given using two channel lidar data.
On the other hand, raman Lidars are the most direct method for probing
inhomogeneous atmospheres, although their range is limited under daylight conditions.
We present a study to compare inversion uncertainties between the standard three channel
elastic lidar and the augmentation of this system with the addition of both extinction at
355 and 532 nm (from raman returns). In particular, we show that while significant
improvement is found when a single extinction measurement is added, no additional
benefit is obtained when adding two raman extinction measurements.