Changes between Version 8 and Version 9 of Stack_Rejection_Discussion

Timestamp:

Aug 29, 2012, 1:52:08 PM (14 years ago)

Author:

watersc1

Comment:

--

Stack_Rejection_Discussion

@@ -5 +5 @@
 Nigel pointed me to a number of remaining linear structures in the SAS data, and I scanned through a number of them.  These seem to be almost entirely features due to burntool issues, as shown in the images below.  For all images, the first 19 panels show input warps (of 20 total inputs.  One was removed for space issues), with the final (bottom right) panel showing the unconvolved SAS8 stack for the same position.  The green region markers are linear features that have a detection along them, as supplied by Nigel.
 
+[[Image(btA.png,800px)]]
 
-[[Image(btA.png,800px)]]
+This set shows that the faint linear feature with a detection is caused by a single burntool trail from input 19.  Other burntool trails (from inputs 7, 9, 10, and 17) visibly print through onto the final stack as well.
 
 [[Image(btB.png,800px)]]
 
+A pair of parallel features are visible in the stack, the result of a burntool trail that has had the core subtracted well, but the edges still remain.
+
 [[Image(btC.png,800px)]]
+
+Two inputs create the burntool trail.  Note that only the fainter end of the trail is printing through into the stack
 
 [[Image(btD.png,800px)]]
 
+Two inputs cause the burntool trail.  Note the absence of the bright BT trail from inputs 7 and 9.
+
 [[Image(btE.png,800px)]]
+
+Two inputs again.
+
+
+Given that all of these structures are caused by burntool, there are two obvious strategies to remove them:
+
+1. Improve burntool fitting.  The structures that print through are close (within tens of pixels) from the edge of the cell.  Burntool has known problems detecting and correcting stars near the cell edges, so it is likely that this is the reason that they aren't subtracted better.  The split trail (image two) shows that the brightest burns are not being fit with the correct width, another issue that can hopefully be resolved by burntool.  The downside of any such change is that it would require new burntool processing for all exposures, which could slow down reprocessing.  The development time for burntool fixes is also not likely to be fast.
+
+2. Improve stack pixel rejection.  The fact that the brightest portions of these trails are removed suggests that the current stack rejection is correctly identifying these outliers and rejecting them.  However, as the trails become faint (and therefore more consistent with the sky level), they are less likely to be removed from the pixel array.  The large variance values clearly let larger outliers remain that is desirable, but without further algorithm tests, it's unclear how to fix this.
 == July 31, 2012 ==