Quote:
Originally Posted by bird
Thanks Lester.
Tervor - one more random thought... on Jupiter I use 1 min per channel, ie 3 mins total, and that seems to work pretty well. Saturn's roughly half the size as seen from here and so I'd have guessed that 2 mins per channel would work nicely, ie 6 mins total. Have you tried that sort of run time?
regards, Bird
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Hi Bird,
No, have never used that sort of run time. Although Saturn is about double the distance of Jupiter and it's disk appears about half the diameter, its rotation rate is very similar, 9hs 50mins to 10hr 14min at the equator. As the rotation rate is so similar, to resolve storm structure within the atmosphere really requires similar treatment to Jupiter.
I have experimented with various configurations, using 2 x and 3 x.
I find that the image scale I get at 2 x works best for storm detection with Saturn.
Obviously I get a bigger image scale at 3 x and I have produced some very nice images of Jupiter at 3 x. However at 2 x with Saturn and the image scale of a 16" scope, I can capture a lot of data in well under 3 minutes, enough to eek out any storm structure that is present.
Early in 2008 the storm on Saturn was massive very bright and initially easy to image. However as it evolved it changed significantly and broke up into multiple smaller features that were very difficult to detect. I was able to successfully detect them at 2 x with the imaging and processing regime that sort of developed over the 7 1/2 months of the life of that storm.
The storm I detected on 15/12/08 was very difficult to confirm. The shorter RGB's make such structure more or less point source and taken at 10 min intervals clearly shows the movement of the storm across the disk of the planet. I posted an animation of that storm on this forum, three RGB's in which the storm is very difficult to detect, and an animation of seven R channel images from the RGB's. The movement in the 10 mins intervals is clearly demonstrated. I think that capturing the data over 6 mins would tend to smear such structure.
I have found that 30 fps at 1/30 sec works well and I use the same gain for the R and G channel, enough to give a histogram of about 190. For the B channel I increase the gain to get the histogram up around 150. Since the majority of the data for the storms is in the R and G channels I don't worry about trying to maintain the histogram of the B channel to that of the R and G.
Dr Georg Fischer, the guy I send my data to is interested in the storm structure and how it's morphology changes over time, not with the colour balance of the image or how heavily I have to process to reveal it. He receives radio data from his RPWS instrument on board the Cassini space craft but that is just radio data, to do his scientific analysis he needs to have optical images to compare with his radio data. That said I would like to have a crack at longer captures, as you have done but at the moment I am committed to supplying data to Georg.
This particular storm showed up much better in the R channel, I think the B channel really tends to smear the detail at the moment due to the low altitude of Saturn and the obvious scattering effect of the blue part of the spectrum by our atmosphere at that altitude.
Regards
Trevor