New Horizon Cameras |
New Horizon Cameras |
Sep 14 2005, 01:18 PM
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#16
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Interplanetary Dumpster Diver Group: Admin Posts: 4404 Joined: 17-February 04 From: Powell, TN Member No.: 33 |
QUOTE (edstrick @ Sep 14 2005, 09:58 AM) Sadly, the noise added to the Deep Impact images will probably render multispectral imaging of the nucleus useless due to noise amplification during the deconvolution process. There may well be no usable color information with the original s/n of the camera, but all we may now see is the brownish overall color described in postings from the DPS meeting. What did MRI get? I don't think I've seem images from it pre-impact near closest approach. Perhaps its data could be used to look for large scale variations. -------------------- |
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Sep 14 2005, 01:23 PM
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#17
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
I think the MRI, as with the impactor camera ( they were exact copies I believe) were sans-filters, the Cometary equiv of Navcam.
Doug |
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Sep 14 2005, 03:34 PM
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#18
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Member Group: Members Posts: 345 Joined: 2-May 05 Member No.: 372 |
QUOTE (djellison @ Sep 14 2005, 09:23 AM) I think the MRI, as with the impactor camera ( they were exact copies I believe) were sans-filters, the Cometary equiv of Navcam. Doug No, the MRI has filters: http://deepimpact.jpl.nasa.gov/tech/mri.html |
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Sep 14 2005, 03:47 PM
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#19
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
Oo - my bad, thought it was a straight copy. Perhaps it was just a copy of the electronics and optics - but had the filter wheel dropped in for the flyby.
Doug |
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Guest_BruceMoomaw_* |
Sep 14 2005, 07:55 PM
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#20
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Guests |
I've heard nothing to suggest that they didn't get color-filter images through MRI. I may recheck that recent article in "Space Science Reviews", which mentiones among other things what kinds of geological color observations they had hoped to make.
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Sep 14 2005, 08:32 PM
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#21
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Interplanetary Dumpster Diver Group: Admin Posts: 4404 Joined: 17-February 04 From: Powell, TN Member No.: 33 |
In addition, if they can get what appear to be color variations in the HRI pics, then MRI could be used perhaps to verify that they aren't artifacts. If they are not artifacts, HRI might be able to tell us more precise positions of regional boundaries given the MRI "ground truth."
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Sep 14 2005, 08:40 PM
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#22
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Senior Member Group: Members Posts: 1636 Joined: 9-May 05 From: Lima, Peru Member No.: 385 |
QUOTE (edstrick @ Sep 12 2005, 03:44 PM) Does the photograph camera wear an automatic focus in order to solve the problem of out of focus? Every modern camera has an automatic focus. Here, I am naive with the images...You can correct me if I am wrong. Rodolfo |
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Guest_BruceMoomaw_* |
Sep 15 2005, 06:16 AM
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#23
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Guests |
The article on Deep Impact imaging of geological features on Tempel's unimpacted surface is at http://www.beltonspace.com/bsei_web_page_g000000.pdf . Specific references to color imaging are on pages 2, 3, 6 and 9. The impression I get is that they could still get quite a bit of useful color data -- if, of course, there are any significant color differences to be found.
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Sep 15 2005, 07:11 AM
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#24
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
Well - I saw a reasonable colour image at the BAA conference - it showed a general brown colour, but there were different shades across the surface, some brighter areas etc.
Doug |
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Sep 15 2005, 08:02 AM
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#25
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Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
Bruce Moomaw: ".... -- if, of course, there are any significant color differences to be found."
That's the rub. Small bodies tend to have vanishingly small color variations and it's very easy to go from noisy but usable data to unusable data on small scale features. While overall color or spectral properties tell you about bulk composition, variations tell about chemical variations, or to a lesser extent physical property variations...they tell you about processes that made the surface, distinct from what you're told by feature morphology. |
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May 26 2015, 05:48 PM
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#26
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Member Group: Members Posts: 148 Joined: 9-August 11 From: Mason, TX Member No.: 6108 |
At risk of reopening what appears to be a dead thread (and mods may want to move this post for that reason), my search for LORRI optical characteristics led to this thread where the original question about Ralph and LORRI focal lengths was never answered. That information has been published elsewhere but the thread needs closure for the sake of other seekers who arrive here, and I have a follow-on question that is not answered anywhere else, so this thread may yet be useful.
The optical characteristics of the Ralph visible/NIR/IR camera are described in this paper, principally in Table 2 on page 6: http://www.boulder.swri.edu/pkb/ssr/ssr-ralph.pdf (TL;DR: an unobscurred, off-axis, three-mirror anastigmat design; Telescope Aperture: 75 mm Focal Length: 657.5 mm f/#: 8.7) The optical design of the LORRI camera is described in these slightly variant resources, in Table 6 on page 10 and in section 3.1.2 Optical Design on page 12: http://lanl.arxiv.org/ftp/arxiv/papers/0709/0709.4278.pdf http://www.boulder.swri.edu/pkb/ssr/ssr-lorri.pdf (TL;DR from the abstract: a narrow angle (field of view=0.29°), high resolution (4.95 µrad pixels), Ritchey-Chrétien telescope with a 20.8 cm diameter primary mirror, a focal length of 263 cm, and a three lens field-flattening assembly) I gathered that the LORRI primary and secondary mirrors are made from low thermal expansion silicon-impregnated silicon carbide. The field-flattening lenses are of fused silica. This design was based on monochromatic imaging (color via filters) therefore the refractive components are not achromatic (they can't be, being all of the same refractive index). This goes a long way in explaining some of the transmissive properties of the system. Yet two details don't seem to be mentioned anywhere: 1. What reflective coating was used on the mirrors (aluminum? something more exotic?)? Was the reflective coating hardened or overcoated in any way (such as silicon monoxide commonly applied to terrestrial mirrors)? Is deep space tarnishing even an issue? 2. Were the optical components coated in any manner? In a monochromatic environment, I suppose that spectral multicoating may be meaningless, but how durable are fused silica surfaces? And aren't internal reflections (ghosts) still a design problem for a multiple element field group? The papers are otherwise helpful about nearly all other questions one might have about these camera systems. But even if coatings were not needed, that design point was not clear to me in the papers. Thanks for any... erm... illumination on this. -------------------- --
Don |
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May 26 2015, 06:20 PM
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#27
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
1. What reflective coating was used on the mirrors (aluminum? something more exotic?)? 2. Were the optical components coated in any manner? I can't speak to the specifics of these instruments but generically: 1) Typically the most reflective stuff available is used. Formulations may be proprietary but "protected silver" is typical for the visible. 2) The best possible AR coatings are used. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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May 26 2015, 08:41 PM
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#28
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
...http://lanl.arxiv.org/ftp/arxiv/papers/0709/0709.4278.pdf .. 2. ... And aren't internal reflections (ghosts) still a design problem for a multiple element field group? P.24: QUOTE The ghosts are dominated by out-of-field illumination at the red extreme of the LORRI passband, depending on the radiance distribution over field angles just outside the FOV up to approximately 0.37° off-axis. The ghosts are strongly dependent on source spectrum and will be characterized extensively with Jupiter observations An application I've been pondering has been, whether this effect could be used to retrieve color information from LORRI images. |
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May 27 2015, 07:52 PM
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#29
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Member Group: Members Posts: 148 Joined: 9-August 11 From: Mason, TX Member No.: 6108 |
Thanks, all. I had read this on p. 12 and somehow inferred that baffles were the primary mitigation for ghost suppression. It makes sense that AR coatings were still involved.
QUOTE All baffle design features were optimized through TracePro ray tracing analysis. This analysis shows that out-of-field stray light is adequately suppressed and that ghosting is acceptable.
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Don |
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May 27 2015, 08:02 PM
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#30
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Member Group: Members Posts: 148 Joined: 9-August 11 From: Mason, TX Member No.: 6108 |
An application I've been pondering has been, whether this effect could be used to retrieve color information from LORRI images. If each image is filtered, won't any out-of-band ghost artifacts likewise be removed? Moreover, if they are off-FOV, isn't that the same as "not imaged?" I'm not sure where in the recorded field this unfiltered color information could get in. -------------------- --
Don |
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