Multiframe comparisons between v4 (with old dynacal) and v6 (new dynacal)
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Notes:

* all plots below pertain to multiframe extractions from tile 3306m561_wppm41 

* fops = processed with v4 with frames calibrated using dynacal version
         that introduced a "false mode" in pixel distributions.

* As a reminder, this "false mode" is one of the causes for the "big" 
  photometric bias seen in the All-Sky Source Catalog.

* pops = processed with v6 where frames were reprocessed using new
         dynacal software that corrected for the "false mode", and cleaned
         up some other bugs, e.g., over-masking of bad (transient pixels).

* filtering performed in fops and pops for band of interest: 0.5<w?rchi2<2.3;
  no upper limits; na=0; nb=1. 

* goal: are there significant differences between source metrics (e.g.,
        photometric uncertainties) between these versions to warrant recreating
	frame masks and uncertainty products when reprocessing cryo data with
	the fixed (v6) dynacal?

* conclusion (answer to previous question): there does not seem to be a
              significant difference in source metrics.


Plots:

In the following, note the flux-underestimation bias in fops (v4) relative to
pops (v6). Vertical lines are s/n=5 (multiframe) limits for v6 for this tile,
deduced from the w?sigmpro vs mag plots below.
W1mpro_fops_vs_pops
W2mpro_fops_vs_pops
W3mpro_fops_vs_pops
W4mpro_fops_vs_pops

The following show differences in the single-exposure RMS repeatability. The
rational here is that if more pixels were masked in fops (v4), then fewer pixels
were being used in profile-fit photometry in general. This should manifest itself
as an inflation in the w?sigP1 values - i.e., more uncertain single-exposure
photometry in fops. This does not appear to be the case. Vertical lines are s/n=5
(single-exposure) limits for v6 for this tile, deduced from the w?sigP1 vs mag
plots below.
W1sigP1_fops_vs_pops
W2sigP1_fops_vs_pops
W3sigP1_fops_vs_pops
W4sigP1_fops_vs_pops

Same as previous set, but as scatter plots:
W1sigP1_fops_vs_pops
W2sigP1_fops_vs_pops
W3sigP1_fops_vs_pops
W4sigP1_fops_vs_pops

Vertical lines in following plots are s/n=5 (multiframe) limits for v6,
for this tile, deduced from the w?sigmpro vs mag plots below. Note the upturn
towards faint magnitudes. This is a consequence of the flux-underestimation bias
in fops (v4) since w?sigmpro ~ sigma(flux)/flux and the action here is all in
the flux, not sigma(flux). Hence for a given (faint) magnitude, the reported
photometric (mag) uncertainties are overestimated in the All-Sky release.
W1sigmpro_fops_vs_pops
W2sigmpro_fops_vs_pops
W3sigmpro_fops_vs_pops
W4sigmpro_fops_vs_pops

Same as previous set, but as scatter plots:
W1sigmpro_fops_vs_pops
W2sigmpro_fops_vs_pops
W3sigmpro_fops_vs_pops
W4sigmpro_fops_vs_pops

Following were used to estimate approximate s/n=5 (multiframe) limits for v6
for this tile (vertical lines). Assumption here is that the "model-based"
w?sigmpro values reflect the actual photometric uncertainty.
W1sigmpro_pops_vs_mag
W2sigmpro_pops_vs_mag
W3sigmpro_pops_vs_mag
W4sigmpro_pops_vs_mag

Following were used to estimate approximate s/n=5 (single-exposure) limits for v6
for this tile (vertical lines). These are based on the single-exposure RMS
repeatability and are not sensitive to confusion noise like the w?sigmpro values.
W1sigP1_pops_vs_mag
W2sigP1_pops_vs_mag
W3sigP1_pops_vs_mag
W4sigP1_pops_vs_mag

--
F. Masci, 12/13/2012