MFOV lidar retrieval of cloud microphysical parameters: Monte Carlo and field validation

A multiple-field-of-view (MFOV) lidar measurement and solution technique has been developed to exploit the retrievable particle extinction and size information contained in the multiple scattering contributions of measured aerosol lidar returns. The paper describes the proposed solution algorithm. The method draws on empirical modeling and many approximations but what it lacks in mathematical rigor, it gains in speed and robustness. The primary retrieved parameters are the extinction coefficient at the lidar wavelength and the effective particle diameter. The coupling between the size and extinction solutions is handled by iterations and direct multiple scattering calculations based on the solutions obtained at the preceding iteration step are required. Under the technical constraints of our current MFOV lidar system, the inversion method is applicable to precipitation and water droplet clouds viewed from a distance of similar to200 m to similar to3 km, and the lower and upper limits for the effective droplet diameter are similar to3 and similar to20 mum, respectively. For precipitation, the upper limit extends to 200-300 mum because the forward scatterings originate from distance zero. Solution time for typical cloud penetration depths of similar to200m at a resolution of 3 m and using our semi-empirical direct multiple scattering calculation algorithm is 2-3 s on a Pentium II computer. From the primary extinction and size solutions, secondary products like the extinction at other wavelengths and the liquid water content (LWC) of liquid phase clouds can be derived.