Question regarding Huygens surface video Options

[sittingduck]

Recently I found a short animation of several of the images taken of the Titan surface by Huygens after it landed:

Link to animation.

I see that several objects appear to move in and out of frame, which I have read is attributed to fluffy aerosols kicked up from the surface settling down again.

My question is, what is the explanation for the object which appears to move horizontally from left to right? If it is in fact the same object in all 3 frames from frame 11-13, it appears at (x,y) pixel coordinates (74,290), (119,291), and (212,297). Is it something on the lens, drifting to the side perhaps?

Because I do not know how this sequence of images has been combined, and whether or not they are chronological or in reverse order, or whether there are missing intermediate frames, I cannot estimate the time that passes during the movement of this small blob.

Finally, is there a table somewhere with timestamps of all the Huygens triplets?

Regards,
Nick

[algorimancer]

The Huygens descent imager (DISR) utilized a custom hardware solution to implement jpeg-like compression of the images. Is anyone aware of a software emulator of this compression tool? Or even an equivalent and clearly defined algorithm? I've sketched-out a statistical and simulation approach to attempt to extract additional information about the uncompressed images, but I really need some means of taking a simulated uncompressed image and then compressing it as the Huygens system did. My goal is, following compression, to be able to exactly reproduce the compression artifacts from the side-looking imager produced by DISR.

The closest I've come to an answer is the papers:

THE DESCENT IMAGER/SPECTRAL RADIOMETER (DISR) EXPERIMENT ON THE HUYGENS ENTRY PROBE OF TITAN, by Tomasko et al, Space Science Reviews 104:469-551, 2002.
https://www.researchgate.net/publication/22..._Probe_of_Titan

Comparison of the Lossy Image Data Compressions for the MESU Pathfinder and for the Huygens Titan Probe, by Ruffer et al, NASA, 1994.
https://ntrs.nasa.gov/archive/nasa/casi.ntr...19940023751.pdf

So far as archived imagery, this resource seems helpful:
CASSINI PROJECT, IMAGING SCIENCE SUBSYSTEM (ISS), ARCHIVE VOLUME SOFTWARE INTERFACE SPECIFICATION (SIS)
http://pds-imaging.jpl.nasa.gov/documentat...ini_archsis.pdf

A concern I have with simply implementing an algorithm is that it likely would not completely account for the hardware limitations of the solution used on Huygens, such as floating point arithmetic with hardware-specific byte limitations. Plus, if I did implement an algorithm I would still want to be able to validate it on a known pair of uncompressed and Huygens-compressed images.

[rlorenz]

The Huygens descent imager (DISR) utilized a custom hardware solution to implement jpeg-like compression of the images.
Is anyone aware of a software emulator of this compression tool? Or even an equivalent and clearly defined algorithm? I would still want to be able to validate it on a known pair of uncompressed and Huygens-compressed images.

To respond to this thread more generally......

In the last few years Erich Karkoschka at U. Arizona has extensively reprocessed the images with revised flatfields, and improved implementation
of the DCT (de)compression. There are several papers in Icarus and Planetary and Space Science that go into the details. Different image versions are
archived on the PDS. But THE MOST IMPORTANT THING is to read the very detailed DISR Users Guide (which hasn't actually been on the PDS for terribly long)

http://atmos.pds.nasa.gov/data_and_service...gens/disr1.html

Someone mentioned battery dimming - I doubt it. The probe power bus was regulated, and there was probably DISR-internal regulation of the lamp
current anyway. However, the auto-exposure algorithm did change the exposure times, so looking at raw pixel numbers might show a decline.
The Appendix to the user guide has a table with the image numbers, exposure times, compression level etc.

Erich analyzed the little spots and determined they were all radiation hits on the detector, except for the one feature in the bottom left of image 897, which seems
to be a dewdrop from methane sweated out of the ground by the lamp. (Note they may be hits from neutrons from the RHUs - the rate of cosmic rays should
be very low in Titan's thick atmosphere).

There was a publication a few months ago purporting to detect a fog bank, but Erich says while one can't exclude it, it's at the noise level.

Ralph

[Stefan]

Erich analyzed the little spots and determined they were all radiation hits on the detector, except for the one feature in the bottom left of image 897, which seems to be a dewdrop from methane sweated out of the ground by the lamp. (Note they may be hits from neutrons from the RHUs - the rate of cosmic rays should be very low in Titan's thick atmosphere).

That's this paper.

The DISR lamp flux was constant after landing. The brightness distribution over the images slowly changed, however, most likely because of charge build-up on the CCD.

If there was a fog, Erich would have found it.