Changes between Version 26 and Version 27 of Stack_Sky_Levels

Timestamp:

Sep 19, 2014, 4:37:16 PM (12 years ago)

Author:

watersc1

Comment:

--

Stack_Sky_Levels

@@ -5 +5 @@
 From the DRAVG page, Peter reports that his manual psphot SKY distribution is centered around 1 count, while the SAS static sky distribution is centered around ~0.3.  I cannot reproduce the SAS distribution either.  The current trunk, the current PV3 processing tag (ipp-pv3-20140717), the ipp-pv3-cr-20140614 processing tag that was used for the SAS processing, and that same tag reverted back to r36878 to match the log file entry for the original static sky run all agree with Peter's distribution:
 
-[[Image(staticsky_comp-3365975.png)]]
+[[Image(staticsky_comp-3365975.png,400px)]]
 
 I don't know what went wrong with the SAS reduction, as I can not reproduce the values previously published.  I believe the ~1 count offset from zero in the stack is consistent with the remaining small background bias that leaves a small amount of background on the input warps.  This test also confirms that with a fixed seed value, psphot and psphotStack produce identical background models.  This is expected, as they both make an identical call to the psImageBackground function.
@@ -11 +11 @@
 Moving on to Peter's analysis of warp/stack SKY levels, I first confirmed that the ppStack code does not subtract any values from the input warps.  The images are scaled by a multiplicative factor, individual pixels are rejected, and the remainder are summed.  Because of this, the pixel distributions of the stack and the input warps must agree to within a scaling factor.  Looking at histograms of all warps and the stack (which I constructed from the warps listed on Peter's analysis, and adopting the factor of 14 between an individual warp and the stack listed there):
 
-[[Image(warp_stack_comparison.png)]]
+[[Image(warp_stack_comparison.png,400px)]]
 
 Fitting Gaussians to the populated bins from that histogram yield "true" mean and sigma values, with warp "4" being the outlier Peter identified.
@@ -38 +38 @@
 On the stacks, we seem to be getting a better estimate of the true sky level, but there is still some variation depending on which set of pixels is examined.  Below I show the CMF sky values for multiple photometry runs with psphot and psphotStack that I ran with my stack.  The mean of this distribution (which samples the background model realization) shifts by about 1 count between these runs, due to this pixel selection.  Also plotted is a fixed seed comparison between psphot and psphotStack, again confirming that they produce the same models. 
 
-[[Image(multiple_stack_runs.png)]]
+[[Image(multiple_stack_runs.png,400px)]]
 
 Finally, plotting all the warp and stack background models as a function of pixel index (index 0 is image(0,0), and index 256 is image(16,16), it is clear that the warp background models all cluster around values ~0.3.  The stack realizations (different psphot/psphotStack runs) match the expected value around zero.  
 
-[[Image(warp_stack_pixel_comp.png)]]
+[[Image(warp_stack_pixel_comp.png,400px)]]
 
 == 2014-05-21 ==