Statistical models for the desert aerosol size distributions and comparison to MODTRAN models

Predictions of atmospheric transmittance in desert aerosol environments using MODTRAN code diverge significantly from measured data. Good prediction of the desert particulate size distribution is required in order to predict atmospheric scattering and absorption parameters. It is also essential to the prediction of the aerosol atmospheric modulation transfer function which is often the dominant component of the overall atmospheric MTF. Recently, an effort to predict statistics but not size distribution according to simple weather parameters has been made for coarse desert aerosols. A quantitative analysis of the desert particulate size distribution models was also performed. In this research the size distribution parameters measured by optical counters are related to weather parameters. Known statistical and analytical models such as MODTRAN relate the size distribution parameters only to relative humidity for continental atmospheres. Although humidity has a significant role in the prediction of aerosol size statistics, other weather parameters are seen here to strongly influence also the size distribution parameters. Comparisons such as the above can be used to predict under which conditions the MODTRAN aerosol models have good or poor accuracy. It is also hoped that they will lead to improvements in MODTRAN, improving the accuracy of the humidity dependence as well as by incorporating other meteorological parameters into the MODTRAN prediction models.