During the nightside campaign focused on Venus (click
here for further informations), in the images, beyond the
topographic details, there are also some darker regions changing
aspect from one day to another. It is known that thermal radiation,
at 1.01 microns does not escape unaltered from the thick atmopshere
of Venus. Actually, much of the light
coming from the surface is scattered and partly abdorbed by low layers
of clouds at 30-35 km of altitude. These clouds have different
densities and tickness, so they don't adsord uniformly the thermal
radiation. As a result, I thought it would be possible to show the
change in the atmosphere opacity by dividing two images taken on
consecutives (or close) days, so that the rotation of surface
features would be invisible at spatial resolution of 2.6", while the
fast moving clouds should leave some kind of pattern.
I took two raw images, normalized, alligned and divided. The results are visible in the images below. No processing was applied, they are just the result of the division. As expected, details associated with surface structures disappeared totally, leaving place to some brightness gradients.
This is the first amateur image showing low clouds pattern, revealed only by professional equipment with digital devices sensitive to wavelengths greater than 1 micron (unfortunately, silicon based devices are not sensitive to vavelengths greater than 1.1 microns)