Astronomy Picture of the Day
April 28, 2012

Venusian Surface and Sky, from Venera 13
Venusian Surface and Sky, from Venera 13

Credits: Soviet Space Agency - Credits for the additional process. and color.: Dr Don P. Mitchell and Dr Paolo C. Fienga/Lunar Explorer Italia/IPF

Following yesterday's APOD, we have decided to take you once again on the Surface of the Planet Venus (as imaged by the Soviet Lander Venera 13) and we are proud to show you the result of a combined effort: the perspective imaging of the Venusian Surface as seen from the the Lander (a work carried out by the American Researcher Dr Don P. Mitchell) with the Absolute Natural Colorization of the landscape and Sky (this job carried out by the Italian Researcher Dr Paolo C. Fienga). The result, as you can see, is a deeply suggestive (and, maybe, even a little scary...) vision of what has been called by many Scientists and Researchers, "The Venusian Inferno": such as a World that, from every point of view, seems to be completely hostile to the human concept of Life itself.

And here is a brief story of what happened that day, such as March 1st, 1982, when the Descent Module of the Venera 13 Spacecraft landed on Venus, as told us by Dr Don P. Mitchell himself:"...Two optical-mechanical cameras repeatedly scanned 180° or 60° through Clear and Colored Filters and at higher resolution than the Venera 9/10 System. The camera system was developed by Dr A.S. Selivanov's Team at the Institute of Space Device Engineering. The main Spacecraft, flying on a Fly-By Trajectory, remained in radio contact with the Lander for 127 minutes. It relayed the video to Earth as a phase-modulated digital signal, at 9 bits per pixel. The Venera 13 (and Venera 14 too) Lander/s transmitted digital images with a depth of 9 bits and an approximately logarithmic encoding of photometric brightness. Multiple panoramas were scanned by the camera, including some with red, green or blue glass filters in place. The entire transmission was relayed to Earth in real time, and also replayed from digtal tape recordings onboard the Venera 13 Spacecraft. This peculiar tecnique permitted the reconstruction of an almost noiseless version from the multiple transmissions. An accurate conversion of that encoding to linear brightness has also been derived, using calibration information included with the images (to be noted is the improved rendering of shape and details in very dark and very light portions of the image). The original Soviet versions of this frame included a full panorama from Clear-Filter images, and color panoramas from the red, green and blue-filter images. The signal to noise was poorer for the color images, because they were much darker. I (meaning Dr Don P. Mitchell) combined the two types of panoramas by adding the Chroma Signal (in CIE Lab Color Space) from the color images with the luminance from the clear images, thus obtaining simply spectacular results. Furthermore, the Venera 13 panoramas were just spherical projections and therefore they had to be remapped to perspective projections and overlayed (using Adobe Photoshop CS2) to produce views that were good enough to give us a better subjective impression of the Venusian Surface. In the overhead view, notice the subtle shadowing existing around the Lander. The Surface illumination is from the uniformly bright hemisphere of the Sky, but the Lander (as you can better see in the spherical projections) blocks part of the Sky from nearby Ground. In addition to the above, please notice that in this frame the thick yellow-orange color of the Sky is due to Rayleigh Scattering of the Sunlight by the thick Venusian Atmosphere and, possibly, by an additional (still) unknown blue-absorbing Gas Component. Brightness has been normalized. Please remember that the variations in the color of the Surface and Sky that you may certainly notice once you will have compared different color images taken by the different Soviet Venera Class Landers that made it to the Venusian Surface, are due to differing Atmospheric Depths and Opacities, as well as to the differing Sun Angles existing at the different Landing Sites...".

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