Comparisons of aerosol backscatter using satellite and ground lidars: implications for calibrating and validating spaceborne lidar.

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on the polar orbiter Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is an elastic backscatter lidar that produces a global uniformly-calibrated aerosol data set. Several Calibration/Validation (Cal/Val) studies for CALIOP conducted with ground-based lidars and CALIOP data showed large aerosol profile disagreements, both random and systematic. In an attempt to better understand these problems, we undertook a series of ground-based lidar measurements in Atlanta, Georgia, which did not provide better agreement with CALIOP data than the earlier efforts, but rather prompted us to investigate the statistical limitations of such comparisons.

Infrared lidar observations of stratospheric aerosols.

We observed the stratospheric aerosol layer at 34° north latitude with a photon-counting 1574 nm lidar on three occasions in 2011. During all of the observations, we also operated a nearby 523.5 nm micropulse lidar and acquired National Weather Service upper air data.

Reexamination of depolarization in lidar measurements.

Almost all of the depolarization papers in the lidar literature employ a physically inappropriate notation and they use a definition of the depolarization ratio that is not linear in the quantity of interest. This depolarization lidar legacy is misleading and confusing. In particular, subscripts meaning parallel and perpendicular do not apply to atmospheric parameters, such as the volume backscatter coefficient, because (for linear polarization) the two components of the backscattered light are polarized in the transmitted sense and completely unpolarized; the unpolarized component is not "perpendicular.

Comment on two-wavelength lidar inversion techniques.

In a critique of two-wavelength lidar inversion techniques, Kunz [Appl. Opt. 38, 1015 (1999)] presented mathematical arguments that such techniques cannot yield unique solutions for extinction profiles.

Experimental validation of the differential image motion lidar concept.

We have experimentally validated the concept of a differential image motion (DIM) lidar for measuring vertical profiles of the refractive-index structure characteristic C(n)(2) by building a hard-target analog of the DIM lidar and testing it against a conventional scintillometer on a 300-m horizontal path throughout a range of turbulent conditions. The test results supported the concept and confirmed that structure characteristic C(n)(2) can be accurately measured with this method.