Measurement of the droplet size distribution of fog using multi-wavelength lidar: A feasibility study

The extinction and backscatter coefficients of an aerosol are determined in part by the aerosol size distribution. If specified at more than one wavelength these optical data can be used to infer the aerosol size distribution if the relationship between the optical data and the size distribution is well defined. In the case of fog the index of refraction is known and the fog droplets are spherical so that the relationship between the optical data and the droplet distribution is given by Mie theory. The inversion procedure of Twomey (1977) is adapted to derive the size distribution of an example fog using the extinction and backscatter coefficients at wavelengths between 0.53 μm and 10.6 μm. Such measurements could be made using a multi-wavelength lidar. The accuracy of the solution as a function of intrinsic inversion error and measurement error is discussed.