Continued investigation on image blur due to aerosols and correlation to aerosol morphology and optical properties

Scattering caused by large cloud/fog water droplets and ice crystals can cause contrast reduction and blurring in images. However, prior studies in desert and maritime environments have shown that common atmospheric particles such as dust, sand, salt can also cause image blur due to small angle forward scatter. However, these researchers have argued that sensor field of view, dynamic range and spatial frequency bandwidth can limit the image blur. The conditions (aerosol loading/ morphology, imaging range) under which ambient aerosols can contribute significantly to image blur have not been well studied. This work aims to fill the knowledge gap by taking simultaneous field measurements of aerosol number concentration and size distribution along with images of edge targets. Turbulence induced blur is calculated from independent field measurements of turbulence strength using differential motion of image features. By dividing out the blur due to turbulence from the total blur in the field images, the aerosol contribution to image blur can be analyzed. An imaging experiment conducted at Wright Patterson Air Force Base in Dayton, Ohio across a 1.78km slant path over six summer days at different times during the day with varying aerosol loading conditions showed clear evidence of aerosol contributed blur. Modulation Transfer Functions (MTFs) calculated from theory using measured aerosol loading in conjunction with an atmospheric radiative transfer code was compared against the aerosol MTFs obtained from the field images. Although the present experiment used imagery in visible wavelengths, we will extend the analysis to infrared wavelengths in the future.