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RE: Quick note on Disk 18a
> -----Original Message-----
> From: Stupendous Man [mailto:richmond@a188-l009.rit.edu]
> Sent: Sunday, May 20, 2001 10:00 AM
<snip>
>
> If one makes a histogram of the pixel values in the raw images
> on Disk 18a, one finds
>
> - the distribution of pixel values in I-band images shows
> a small peak every 8'th value, and a very large
> peak every 64'th value
>
> - the distribution of pixel values in V-band images shows
> a small peak every 2'nd or 4'th value; the amplitude of
> the variations is smaller than those in the I-band images
>
> Perhaps some sticky bits in the ADC?
It looks like each ADC has it's own "signature". Is this
how you'd fix it?
Normally you interpret a positive binary integer by doing
SUM( b[i] * 2^^i )
where b[i] is the value of the bit (0 or 1) at location i.
I wonder if you could histogram some random noise and determine
values for c[i] and then replace the above by
SUM( b[i] * c[i] )
So far so good. But how to compute c[i]? Is it based on just
the difference between the observed fraction of 1s vs. the
expected 0.5? So we'd get values for C like 0.9998, 2.0003,
3.9996, ...
If what we are seeing really is an artifact of the ADC which
remains constant over time we could built a hardware white
noise source and spend a mount taking 10^10 samples in day light
hours. I've heard of people using a white hot lamp filament
as a white noise source, so it could be cheap.
If tom is right about this being a 0.03% problem it's still
worth fixing if you want to look for stuff like transits.
Those 0.03% fixes add up.
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