IPB

Welcome Guest ( Log In | Register )

3 Pages V  < 1 2 3 >  
Reply to this topicStart new topic
New Horizon Cameras
tedstryk
post Sep 14 2005, 01:18 PM
Post #16


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.


--------------------
Go to the top of the page
 
+Quote Post
djellison
post Sep 14 2005, 01:23 PM
Post #17


Founder
****

Group: Chairman
Posts: 14431
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
Go to the top of the page
 
+Quote Post
um3k
post Sep 14 2005, 03:34 PM
Post #18


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
Go to the top of the page
 
+Quote Post
djellison
post Sep 14 2005, 03:47 PM
Post #19


Founder
****

Group: Chairman
Posts: 14431
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
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Sep 14 2005, 07:55 PM
Post #20





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.
Go to the top of the page
 
+Quote Post
tedstryk
post Sep 14 2005, 08:32 PM
Post #21


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."


--------------------
Go to the top of the page
 
+Quote Post
RNeuhaus
post Sep 14 2005, 08:40 PM
Post #22


Senior Member
****

Group: Members
Posts: 1636
Joined: 9-May 05
From: Lima, Peru
Member No.: 385



QUOTE (edstrick @ Sep 12 2005, 03:44 PM)
...be the other problem-of-the-decade, besides out of focus cameras.
*

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
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Sep 15 2005, 06:16 AM
Post #23





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.
Go to the top of the page
 
+Quote Post
djellison
post Sep 15 2005, 07:11 AM
Post #24


Founder
****

Group: Chairman
Posts: 14431
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
Go to the top of the page
 
+Quote Post
edstrick
post Sep 15 2005, 08:02 AM
Post #25


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.
Go to the top of the page
 
+Quote Post
MarsInMyLifetime
post May 26 2015, 05:48 PM
Post #26


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
Go to the top of the page
 
+Quote Post
mcaplinger
post May 26 2015, 06:20 PM
Post #27


Senior Member
****

Group: Members
Posts: 2502
Joined: 13-September 05
Member No.: 497



QUOTE (MarsInMyLifetime @ May 26 2015, 10:48 AM) *
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.
Go to the top of the page
 
+Quote Post
Gerald
post May 26 2015, 08:41 PM
Post #28


Senior Member
****

Group: Members
Posts: 2346
Joined: 7-December 12
Member No.: 6780



QUOTE (MarsInMyLifetime @ May 26 2015, 07:48 PM) *
...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.
Go to the top of the page
 
+Quote Post
MarsInMyLifetime
post May 27 2015, 07:52 PM
Post #29


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.


--------------------
--
Don
Go to the top of the page
 
+Quote Post
MarsInMyLifetime
post May 27 2015, 08:02 PM
Post #30


Member
***

Group: Members
Posts: 148
Joined: 9-August 11
From: Mason, TX
Member No.: 6108



QUOTE (Gerald @ May 26 2015, 03:41 PM) *
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
Go to the top of the page
 
+Quote Post

3 Pages V  < 1 2 3 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 19th March 2024 - 09:10 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.