Multiple-Scattering Cloud Lidar: Past, Present, Future, and Extensions

I will describe the genesis of a new kind of lidar technique that is NOT
predicated on the classic lidar equation, which de facto is the
single-scattering approximation in radiative transfer (RT).  In that case
only can one connect 1D space along the pulsed laser beam one-to-one with
time, thus enabling the “ranging” aspect of lidar.  In contrast, the novel
technique targets opaque clouds and is based on the full solution of the
time-dependent monochromatic RT equation for dense scattering media, which
has 6 independent variables: 3D space, time, and all possible directions.
Here, the productive approximation is in fact the diffusion limit obtained
when the mean-free-path (a measure of direct penetration depth) is much
smaller than the outer dimensions of the cloud. RT Green function
theory—the real progenitor of the new technique—tells us that (beyond the
usual “on-beam” ceilometry product) the “off-beam” lidar data can be used
to infer the cloud’s physical and optical thicknesses, hence mean
extinction, at scales relevant to climate studies.

Armed with classic transmitters but new receivers and a new lidar
equation, we have probed several cloud layers during field campaigns, one
at the Oklahoma ARM site where standard cloud observational capability
(mm-radar, microwave, etc.) is consentrated.  The new approach performed
as well as expected under far-from-ideal circumstances from ground.  Two
airborne incarnations of multiple-scattering lidar will be described.
Furthemore, LITE (LIdar-in-space Technology Experiment) returns from a
dense marine stratocumulus deck will be re-interpreted in terms of
multiple-scattering. Finally, we will show that there is a perfect
complementarity between multiple-scattering cloud lidar and
high-resolution oxygen A-band spectroscopy from ground or from space (cf.
future Orbiting Carbon Observatory mission) in the presence of clouds.




15:15 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Anthony Davis, Los Alamos National Laboratory


Back to listing