In Situ Cloud Lidar

We are developing a new in situ technique for sensing cloud properties averaged over volumes of millions of cubic meters. In this technique pulses of light are emitted from a high powered laser on an aircraft flying inside clouds. The light pulses multiply scatter in optically thick clouds, and the amount of light returned as a function of time is measured by upward and downward viewing wide field of view detectors. From these time series the extinction averaged over diameters of hundreds of meters can be accurately retrieved. The distance of the airplane from the cloud boundaries, the cloud geometrical thickness, and the area averaged optical depth can also be obtained.

This project was funded by a NASA Small Business Innovative Research contract to SPEC, Inc. of Boulder (Paul Lawson, PI).

A sketch shows an artist rendition of the in situ lidar on the SPEC operated Learjet aircraft

A paper (764 kB PDF) was published exploring the in situ lidar technique with diffusion theory, simulating the lidar time series in inhomogeneous stratocumulus clouds with a Monte Carlo radiative transfer model, estimating the accuracy of the technique with retrieval simulations, and showing results from a prototype ground-based demonstration. (Evans, K. F., R. P. Lawson, P. Zmarzly, D. O'Connor, and W. J. Wiscombe, 2003: In situ cloud sensing with multiple scattering lidar: Simulations and demonstration. J. Atmos. Ocean Tech., 20, 1505-1522.)

SPEC completed construction of the airborne in situ lidar in June 2004, and made engineering and science flights in November and early December 2004. An overview of results from the 2004 flight series describes the successful validation of the in situ lidar technique in marine stratus clouds. A paper (1660 kB PDF) was published describing the design of the airborne in situ lidar and analysis of the December 1 science flight data (Evans, K. F., D. O'Connor, P. Zmarzly, and R. P. Lawson, 2006: In situ cloud sensing with multiple scattering lidar: Design and validation of an airborne sensor. J. Atmos. Ocean Tech., 23, 1068-1081.)

Last modified: August 16, 2006

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