RESUMEN
A novel aerosol lidar inversion method based on the use of multiple-scattering contributions measured by a multiple-field-of-view receiver is proposed. The method requires assumptions that restrict applications to aerosol particles large enough to give rise to measurable multiple scattering and depends on parameters that must be specified empirically but that have an uncertainty range of much less than the boundary value and the backscatter-to-extinction ratio of the conventional single-scattering inversion methods. The proposed method is applied to cloud measurements. The solutions obtained are the profiles of the scattering coefficient and the effective diameter of the cloud droplets. With mild assumptions on the form of the function, the full-size distribution is estimated at each range position from which the extinction coefficient at any visible and infrared wavelength and the liquid water content can be determined. Typical results on slant-path-integrated optical depth, vertical extinction profiles, and fluctuation statistics are compared with in situ data obtained in two field experiments. The inversion works well in all cases reported here, i.e., for water clouds at optical depths between ~0.1 and ~4.
RESUMEN
As a laser pulse propagates into the atmosphere, it becomes broader in the lateral direction as a result of scattering by aerosols. The laser pulse may be described as the superposition of a central, unscattered component of reduced intensity and a surrounding scattered component. A multiple field of view lidar has been developed that makes simultaneous measurements of the backscattered power from the central pulse and multiply scattered power arising from the scattered component. Measurements from various types of atmospheric aerosols and precipitation are presented and compared with simulated returns. The results show how the multiply scattered signals are influenced by the distribution of the aerosols along the lidar path, the characteristic size of the aerosols, and the optical depth. It is shown that the multiple field of view lidar can provide meaningful, additional information about the aerosols that is not available from a conventional single field of view lidar.
RESUMEN
Classical optics holds that the extinction cross of particles should be equal to twice their geometric cross section, in the limit where the particles are much larger than the wavelength. It follows that the extinction coefficient of such large scatterers should be independent of wavelength. Snowflakes are much larger than the wavelengths of visible and infrared radiation, yet many investigators have found that the visible and infrared extinction coefficient of falling snow measured with transmissometers is wavelength dependent. This dependency is known to be a result of the scattering contribution to the transmissometer signal. Furthermore, many measurements in the visible and infrared show that extinction values measured simultaneously with two transmissometers are linearly related up to at least 12 km(-1). The slope depends on the wavelengths and optical characteristics of the transmissometers. We show that for small values of extinction, the observations can be explained by taking into account single-scattering contributions to transmissometer signals. For high values of extinction, a multiplescattering model gives good agreement with measurements.