Sigma Clipping Settings to Reject Satellites

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
poolemarkw
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Sigma Clipping Settings to Reject Satellites

#1

Post by poolemarkw »

Hello Everyone,

In last night's live-stacking effort I was using the Sigma Clipping stacking algorithm but a satellite was not rejected in my stack. I've attached a picture showing my settings, which used the first 5 frames to compute the average. I know that the satellite occurred AFTER this because it wasn't there after 20 frames were stacked but WAS there after 35 frames were stacked. I've also attached a picture of the stack showing the satellite trail going vertically on the left side of the image. How should I change my settings to prevent this from happening again?

Thanks,

Mark
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Satellite.JPG
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SigmaClipping.JPG
SigmaClipping.JPG (38.21 KiB) Viewed 1355 times
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oopfan
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Re: Sigma Clipping Settings to Reject Satellites

#2

Post by oopfan »

Looks like the Jellyfish Nebula to me!

EDIT: What was your exposure, Mark?

Brian
poolemarkw
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Re: Sigma Clipping Settings to Reject Satellites

#3

Post by poolemarkw »

Hi Bryan, my exposure was 5 minutes and gain 150 on an ASI2600MC Pro with an L-Extreme filter.

Mark
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admin
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Re: Sigma Clipping Settings to Reject Satellites

#4

Post by admin »

Hi Mark,

you don't have the individual frames saved do you? If you do and can share them with me then I can test to see what happened. I am also on the look out generally for satellite affected frames to help develop a new idea I have for trail removal.

thanks,

Robin
poolemarkw
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Re: Sigma Clipping Settings to Reject Satellites

#5

Post by poolemarkw »

Hi Robin,

Unfortunately, I didn't keep the individual frames on this session.

Mark
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Re: Sigma Clipping Settings to Reject Satellites

#6

Post by admin »

Hi,

Ok, never mind... If you do get some satellite frames in future, please send them my way :D

Some things I can think of here that might affect the ability to reject the trail include

* The sigma low limit setting - this sets a minimum on the calculated tolerance in pixel brightness (as a percentage of full camera brightness). Setting this to somewhere around 1% is necessary for 8 bit imaging, but you can set it lower for 12/16 bit imaging (0.1%?) If the trail was relatively faint, this could have allowed it through

* The brightest part (core) of the trail might be rejected, but if the trail covers several pixels the fainter ones at the edges may get through the filtering. Not sure what can be done about that!

cheers,

Robin
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DocHighCo
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Re: Sigma Clipping Settings to Reject Satellites

#7

Post by DocHighCo »

* The brightest part (core) of the trail might be rejected, but if the trail covers several pixels the fainter ones at the edges may get through the filtering. Not sure what can be done about that!
Hello,

would it be possible to define an area around a rejected pixel that will be rejected as well with a weight proportional to the distance from the rejected pixel? That will increase the calculation demands of yourse.

Regards

Heiko
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Re: Sigma Clipping Settings to Reject Satellites

#8

Post by admin »

Hi Heiko,

yes, definitely a possibility - define a mask (0/1) of the pixels you definitely want to ignore, then blur that mask a bit and make a new mask of any pixel with a blurred value of bigger than say 0.2.

cheers,

Robin
Oberon510
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Re: Sigma Clipping Settings to Reject Satellites

#9

Post by Oberon510 »

Robin,

Per your comment "If you do get some satellite frames in future, please send them my way", are you still interested in some raw frames of a satellite - I have one with a geostationary satellite streaking as the scope tracks the sky around NGC2024?

Ken
NGC2024-Small.jpg
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Re: Sigma Clipping Settings to Reject Satellites

#10

Post by admin »

Hi Ken,

absolutely - if possible, can you send me the original frame file (in FITS or whatever) as well as another frame (the one before or after) that doesn't have the trail in it. The files will be too large to upload here, so you can either upload them to google drive/dropbox/etc and share the link or email them to me (the 'contact us' link at the bottom of the page will work).

cheers,

Robin
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