Odd trails in Darks

[Earl]

I have been building up my darks and noticed I have what look like worms of noise in my darks.

Any thoughts

https://dl.dropboxusercontent.com/u/43788925/Dark600s_024.fit

[Earl]

A stretched JPG

[Earl]

My reply from QSI

Earl,

Are you talking about the short, bright tracks that appear in the dark frames?

Those are the tracks of energetic particles, commonly called cosmic rays, although most have terrestrial origins. One of the "problems" with CCDs is that they are exceptionally good at recording energetic events including light, heat and stray high energy particles.

The most common way of managing the effects of energetic particles is to use a statistical combine method. In MaxIm, you can select Sigma Clip or SD Mask. I use Sigma Clip with a factor of 3. After combining 5 or more dark frames (I recommend at least 15) using Sigma Clip, your master dark will be completely free of the effect of these random events.

Best regards.

I must say that is a first for me. but does make sense

[ollypenrice]

Yes, it does make sense but you had a lot. Could there be any kind of source near you? Or maybe the sun did something exciting eight minutes earlier!

Olly

[swag72]

Interesting as I did consider this, but discounted it almost immediately as there were so many on a new camera that I think hadn't even been outside or used in anger. I know that cosmic ray hits are not fussy about where or when they strike, but I was surprised to see this many.

[IanL]

Interesting as I did consider this, but discounted it almost immediately as there were so many on a new camera that I think hadn't even been outside or used in anger. I know that cosmic ray hits are not fussy about where or when they strike, but I was surprised to see this many.

There are two different types of energetic particle issues:

- Permanent damage to an individual sensor element or part of a row/column.  These will result in a hot or cold pixel or a line of them aligned with the pixel matrix (horizontal or vertical depending on the sensor and the type of damage).  Since they appear in every frame, they can't be removed by using darks and you need to us a defect map or cosmetic correction process to fix them.

- Transient events like these, where you get streaks (generally) not aligned with the pixel rows or columns.  These are caused by high energy particle shooting through a whole bunch of sensor elements and merrily dislodging lots of electrons as they go.  These should stack out with an appropriate pixel rejection method since they are in different places in every image.

Permanent damage could be expected to increase with the age of the sensor, but it can occur at any time.  High energy particles do not really care about things like shutters or even walls, which is why they put sensitive detectors for things like neutrinos and WIMPs at the bottom of mines so that they have a lot of rock to shield them.

The particles are usually caused by a high energy cosmic ray striking the upper atmosphere, which creates a shower of secondary particles (still pretty high energy) that cascade to the ground (and your camera sensor).  It is not that surprising to see a whole bunch of them on a single image because of this process.

[swag72]

- Transient events like these, where you get streaks (generally) not aligned with the pixel rows or columns.  These are caused by high energy particle shooting through a whole bunch of sensor elements and merrily dislodging lots of electrons as they go.  These should stack out with an appropriate pixel rejection method since they are in different places in every image.

A great explanation Ian

@Earl - Do these appear in each dark? Or just the one?

[Earl]

Most Darks have them to one degree or another.

[Earl]

Hopefully tonight ill get some lights and see how it all calibrates etc.

[FraserClarke]

Looks pretty clean to me... certainly most professional detectors I've ever used would have at least this number of cosmic hits in 600 seconds.

I'd expect even more than this on our ST8 camera -- but the observatory does sit on top a former nuclear physics building... maybe I should be getting the Geiger counters out

I wouldn't worry about it at all. As IanL says, it'll clean up with even the most basic stacking algorithms. I've never seen a cosmic damage a CCD, though I'm sure it could happen. It is an issue with electronics in space for sure, but not something to worry much about on the ground.

[opticalpath]

I just had a look at a series of my own 600s darks taken with a QSI583 (binned 2x2).  Every one had at least 5 strikes; one had 15.  I don't think what you're seeing is too unusual.

Adrian

[Earl]

I just had a look at a series of my own 600s darks taken with a QSI583 (binned 2x2).  Every one had at least 5 strikes; one had 15.  I don't think what you're seeing is too unusual.

Adrian

Thank you for taking the time to check yours.

I wonder why I never noticed this with my QHY8L and my Atik 383?

Regardless the darks work well on my lights.

[msh1]

i get the same been wondering what they are now i know