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why no true high resolution systems for "jetstream" seeing?
Frank Johnson wrote:
"Chris L Peterson" wrote in message ... On Sat, 07 Jan 2006 16:16:24 GMT, "Frank Johnson" wrote: While it's true that webcams are doing wonders for certain types of seeing, in many areas of the US during the Wintertime, the jetstream is constantly overhead and even a webcam cannot undo this blurring. The problem here is the scale length of the jet stream turbulence is shorter and it is moving past your aperture a lot faster. In principle if you could freeze the seeing you would eventually get some lucky frames but the problem is that a webcam isn't fast enough to do it. these new adaptive optics scopes, like the new pro scope used for solar imaging, which also incorporate speckle imaging and reconstruction- why nothing for amateurs? Couldn't blurring of frames (caused by high jetstreams) be deblurred or "reconstructed" so blurring is minimized. Speckle is only realistic on apertures of 0.5m and above and requires narrow bandpass filters to do it. It should be within the abilities of amateurs to do now on bright stars but I don't know of anyone doing it. programs that can do this or maybe jetstream effects still can't be truly nullified. It is better to get good data in the first place. Deconvolution techniques can help to reconstruct distorted images, but there is no certain way to determine just where any given photon came from. Deconvolution is a sort of educated guess, but it frequently produces invalid data- and there is no getting around that problem. It is probably better to say that deconvolution attempts to produces a representation of what the sky brightness looked like before it was convolved with your instrumental response function. It is valid in the sense that what it produces when blurred would look like your observational data to within the measurement noise. But there are many such images that meet these requirements and choosing a suitably represenative one is fraught with difficulty. Serious problems will arise if you ask the wrong question of your data. Even in a perfect world these deconvolution codes produce images with artefacts that are different and unfamiliar and that can be a problem in eg medical diagnosis. Hi, yes, I already pretty much understand the current techniques involving adaptive optics. I myself have experimented on Jupiter by using one of its moons as a PSF. Then I tried to apply max ent to Jupiter only to end up with a very noisy and artifact prone result. As you said, there simply might have not been enough signal to work with. Signal to noise was probably OK. The thing that would most likely have caused trouble is that the Galilean moons are not unresolved objects in any reasonable sized scope. You set a the program problem that had no reasonable answer. You need the instrumental psf determined from a bright field star (and it is rare to have one) or modelled from theory. Any errors in the psf determination are amplified by any of the deconvolution methods. Deconvolving with a broader psf than the true instrumental response will amplify the high frequency noise and also cause excessive ringing on sharp edges. Regards, Martin Brown |
#12
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why no true high resolution systems for "jetstream" seeing?
Frank Johnson wrote:
Couldn't blurring of frames (caused by high jetstreams) be deblurred or "reconstructed" so blurring is minimized. With computers and the power they possess these days, I'm surprised there aren't programs that can do this or maybe jetstream effects still can't be truly nullified. Frank, If you provide me with an image, I can see what SeDDaRA blind deconvolution can do for jetstream effects. Best Regards, Jim C of Quarktet |
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