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Posted by: Arnaud Nov 8 2007, 08:00 AM

Hi all,

I was wondering if anyone could help me obtain the spectral transmission curves for the Pioneer Orbiter, Galileo and Mariner 10 UV-filters. Especially the Galileo VLT (violet filter) is of interest.

I'm am currently imaging Venus and found that there is a lack of good commercial filters for imaging Venus' clouds in the amateur world. Most commerical filters have transmissions too deep in the UV to give optimal results because the AR coatings on amateur optics block most of the UV. I made some advancement in constructing better filters which include the violet, allowing me to make more detailed images of the planet than I could before, like these:

http://www.farhorizons.nl/images/astronomie/Venus/VEX/AVK%20Venus%2023oct2007.jpg

http://www.farhorizons.nl/images/astronomie/Venus/VEX/Venus%2006%20oktober%20AVK%200620%201020%20UT.jpg

http://img211.imageshack.us/img211/4650/beginningwesternelongatki8.jpg

But I feel I could do better. I have turned to the spacecraft that have photographed Venus from space. I already know the spectra curve of the filter used in the VEX mission, but I would also like to know the spectral curves of the Pioneer Venus Orbiter, the Mariner 10 and the Galileo probe, who all took images through slightly different filters. Especially the Galileo filter is very interesting, because the optics were AR coated, limiting the UV transparancy to about 375 nm, like most amateur equipment. To analyze the properties of the Galileo Violet filter may contribute significantly to getting a new and better filter.

I have heard that this data is made available by JPL, but I am not very used to search to their images formats and databases. I would be very grateful if anyone could help obtain the transmission curves.

Thank you,

Arnaud van Kranenburg,
The Netherlands

Posted by: Bjorn Jonsson Nov 10 2007, 10:18 PM

There is a lot of information scattered across various threads here. A search using the search string "+Galileo +filters" is particularly interesting if you want Galileo related stuff.

As a result of this search I found http://www.unmannedspaceflight.com/index.php?showtopic=4059. There is some interesting information in http://www.unmannedspaceflight.com/index.php?showtopic=4059&view=findpost&p=87791 but I recommend reading the entire thread if you are interested in image processing and color.

http://www.unmannedspaceflight.com/index.php?showtopic=2223 may be interesting as well.

Posted by: Arnaud Nov 12 2007, 08:16 PM

QUOTE (Bjorn Jonsson @ Nov 10 2007, 11:18 PM)

There is a lot of information scattered across various threads here. A search using the search string "+Galileo +filters" is particularly interesting if you want Galileo related stuff.

As a result of this search I found http://www.unmannedspaceflight.com/index.php?showtopic=4059. There is some interesting information in http://www.unmannedspaceflight.com/index.php?showtopic=4059&view=findpost&p=87791 but I recommend reading the entire thread if you are interested in image processing and color.

http://www.unmannedspaceflight.com/index.php?showtopic=2223 may be interesting as well.

Thanks,

I had seen the thread, but didn't advance enough in reading it to notice the transmission curves of the Galileo. On the internet, I read that the Galileo SSI is really a modified Voyager camera with similar filters. Only the AR coatings block the deeper UV part of the spectrum in Galileo's case. Fortunately Voyagers transmission curves were easy to find. I'll compare that transmission curve to the one you pointed out in the thread above to see if this is true.

Thanks again for your assistance!

Regards,

Arnaud

Posted by: Del Palmer Nov 12 2007, 09:31 PM

QUOTE (Arnaud @ Nov 12 2007, 08:16 PM)

I had seen the thread, but didn't advance enough in reading it to notice the transmission curves of the Galileo. On the internet, I read that the Galileo SSI is really a modified Voyager camera with similar filters.

Only the telescope and filters are similar. Galileo used a CCD in contrast to Voyager's videcon tube.

Posted by: Bjorn Jonsson Nov 12 2007, 09:54 PM

QUOTE (Del Palmer @ Nov 12 2007, 09:31 PM)

Only the telescope and filters are similar. Galileo used a CCD in contrast to Voyager's videcon tube.

The optics were almost identical - the filters were different. From the top of my head the Voyagers (narrow angle) had CL, UV, V, B, G1, G2 and O. Galileo had CL, V, G, R, IR7270, IR7560, IR8890 and IR9680.

Posted by: Arnaud Nov 13 2007, 07:55 PM

QUOTE (Bjorn Jonsson @ Nov 12 2007, 10:54 PM)

The optics were almost identical - the filters were different. From the top of my head the Voyagers (narrow angle) had CL, UV, V, B, G1, G2 and O. Galileo had CL, V, G, R, IR7270, IR7560, IR8890 and IR9680.

Hi Bjorn,

It seems that the Galileo violet filter from the info you sent me is a bit narrower bandpass than the one from Voyager. So it is very useful to know. I'm trying to make a filter with about the same properties, I hope it works!

Again, thank you for the info!

Regards,

Arnaud

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