During mid March 2009, I followed the nightside of Venus at 1 micron
wavelengths with my 235 mm Schmidt-Cassegrain telescope. Some good amateur astronomers, like Christophe Pellier
(2004, the first amateur to have spot the faint infrared glow of the
dark emisphere of Venus) succeeded to image this faint and curious
detail, but no one could detect clear surface patterns in the
thermal glow of Venus.
Unlike other amateur astronomers, I used a cooled 16 bit CCD camera (SBIG ST-7XME) and acquired images only when the background became enough dark, after the sunset. As expected, the nightside of the planet was quite easy to detect, with just 0.5 seconds exposure (thanks to the high sensitivity of the CCD camera). Exposures bewteen 4 and 10 seconds were the best compromise between the increasing glow of the dayside (about 20000 times brighter) and the signal of the much fainter nightside.
Any processing software and filters (walevets, unsharp masks or
deconvolution) showed exactly the same small scale and high contrast
features on the nightside.
In order to have an image with only surface features, I
took the images taken on March 16-17-18 and made the median. This
mathematical operation tends to erase the contribution of changing
details (i.e. fast moving clouds) while the much slower surface
features stay unaltered. The resulting image has a better S/N ratio,
so it was possible to enphatize some low scale and low temperature
Conclusion: Amateur equipment can produce high quality images of the nightside
of Venus and give a good topographic view of the planet. The details
are in perfect agrement with altimetric data. A good and new
topographic global map is very useful in order to compare with the
older Magellan, finding some possible modifications due to volcanism
or other large scale phenomena that modify the thermal emission of
the soil (modulated by temperature but influenced also by chemical
composition). Amateur equipment might spot volcanic eruption as
large as 25 Kmē (as amall bright dots in the nightside) and be a valid support for the knowledge of this
still misterious planet.