Understanding upper troposphere humidity is important in the context of radiative forcing and climate. We present a detailed statistic comparison of upper troposphere water vapor retrieval profiles derived from the Atmospheric Infrared Sounder (AIRS) and in-situ measurements. The in-situ measurements are based on a recently compiled database of "best estimate" atmospheric state profiles, obtained from a careful selection of RS-90 radiosondes at Department of Energy Atmospheric Radiation Measurement (ARM) sites, during AIRS overpasses. The aim of this research is to improve the skill and accuracy of the retrieval algorithms in order to understand and quantify the biases between AIRS and RS-90 radiosondes.
Multiple-scattering effects sometime bias the ground-based lidar measurements, in particular for density aerosol and cirrus cloud. Both analytical and Montecarlo methods are very useful tools to study this influence. However, for analytical solution, it needs to make some hypotheses and the Montecarlo simulation is only a forward method. In this paper, an itinerative method is introduced based on Montecarlo simulation. Both extinction and backscattering coefficients, obtained by Raman lidar, are corrected for the multiple-scattering influence. For the typical cirrus cloud, the error of the multiple-scattering influence on extinction can be as large as 100%. However, it is negligible of the influence on backscattering coefficient. Therefore, the lidar ratio is also sensitive to the multiple-scattering effect.