[KIDS] Crosstalk on CCD96 exceeds bias level

[Ewout M. Helmich]

Hi Koen,

Well, what's what with the crosstalk correction I've put on our wiki:

http://wiki.astro-wise.org/projects:kids:crosstalk

The plan is to implement essentially what you did during commissioning. 
I have functional code (see results on the wiki) but not yet a proper 
way to store what was done in the database, which is what I'm working on.

It became clear during yesterdays KIDS telecon that masking will result 
in gaps/holes in the coverage, because the masked pixels are at the same 
RA,DEC position for all exposures of a dither.

Regards,
Ewout

On 04/19/2012 11:15 AM, Konrad Kuijken wrote:
> Indeed, no option now but to mask the pixels where the information is lost. I did not see this behaviour in the commissioning data I looked at last year, the signal remained above zero.
>
> Regarding the effect of changing the bias level: indeed, a higher bias level reduces the level of saturation.
> But I do not believe bias level gives Poisson noise, it is purely a dial in the video chain I think, designed to hit the most linear part of the amplifier response.
> It is not clear to me that we have much freedom in setting the bias level - all CCDs talk to each other and I do not think Olaf can control them individually.
>
> How are you doing the correction? Previously I showed that also unsaturated pixels can cause electronic ghosts (see commissioning reports).
>
> K
>
> On Apr 19, 2012, at 8:42, Massimo Dall'Ora wrote:
>
>> Hi Ewout,
>>
>> interesting plot....
>>
>>>  From the stellar photometry point of view (that is my point of view), to
>> increase the bias level has no scientific effects, apart of to slightly reduce
>> the dynamical range, and to increase the noise of the measurements at high
>> magnitudes.
>>
>> Probably some issue could arise for the extended sources, since an increase of
>> the bias level of ~600 counts introduces an additional noise of  ~25 counts,
>> that could mask faint features.
>>
>> Regards
>> massimo
>>
>> On Wednesday 18 April 2012 12:22:30 Ewout M. Helmich wrote:
>>> Hi everyone,
>>>
>>> We're investigating correcting the crosstalk of OmegaCAM. One issue that
>>> may require action on Paranal is that the crosstalk on CCD#96 (upto -600
>>> ADU from CCD#95) exceeds the bias level of ~400 ADU in CCD#96. See the
>>> attached plot. Pixels exceeding ~50000ADU in CCD#95 will put that pixel
>>> to 0 in CCD#96, destroying the information there (this in the absense of
>>> sky background, the background in the attached example is about 100 ADU,
>>> in g'). I see two ways to address this:
>>>
>>> 1) We can mask pixels with value 0 in CCD #96 (will have to for existing
>>> data).
>>> 2) The bias level of CCD #96 can be increased by e.g. 300-600 ADU.
>>>
>>> The question is if there are objections from a scientific point of view
>>> to this bias level increase.
>>>
>>> Regards,
>>> Ewout
>> _______________________________________________
>> KiDS mailing list
>> KiDS at astro-wise.org
>> http://listman.astro-wise.org/mailman/listinfo/kids
>>
> _______________________________________________
> KiDS mailing list
> KiDS at astro-wise.org
> http://listman.astro-wise.org/mailman/listinfo/kids