Spaceborne lidar aerosol retrieval approaches based on aerosol model constraints

In the absence of auxiliary optical depth or transmittance information, or self-determination of same for specialized observing situations, aerosol backscatter and extinction profiles cannot be retrieved from lidar observations along a single direction without an assumption linking aerosol extinction and backscatter (i.e., the aerosol extinction-to-backscatter ratio, or aerosol lidar ratio, S_a). Aerosol retrievals at 532 nm for the current GLAS and upcoming CALIPSO satellite lidar missions employ/can employ a look-up table approach to select climatologically based S_a model values for these retrievals when alternate, less uncertain methods for either defining S _a or providing the needed auxiliary information are unavailable. This paper addresses a revised table look-up approach that incorporates two notable revisions for improved S_a selection which, as a consequence, enable more bounded aerosol retrievals. One is a refined, more bounded set of S_a values, both for 532 nm and 1064 nm, representative of a definitive set of aerosol types/models determined from an extensive analysis of the global aerosol solar radiometer network, AERONET, data base. The other is an accompanying set of key spectral ratio parameters (i.e., dual wavelength, 532 nm to 1064 nm, ratios of backscatter, extinction and S_a) also derived from the AERONET data which offer additional ways to bound the lidar aerosol retrievals. Thus, aerosol retrievals can be obtained subject to the constraints that the lidar data yield retrievals with spectral ratio parameters consistent with a given aerosol model (or models), to confirm the model choice and better bound the retrievals. Examples of retrievals make subject to these constraints are included as a part of the paper