Changes between Version 7 and Version 8 of MOPS_diff_false_positives

Timestamp:

Nov 13, 2012, 4:04:51 PM (14 years ago)

Author:

watersc1

Comment:

--

MOPS_diff_false_positives

@@ -33 +33 @@
 The first thing to note is that the MOPS cut does a reasonable job of isolating the large "tail" of asteroid detections.  In this projection, the majority of asteroids have a positive source close (often less than 1 pixel, with some up to ~3 pixels away), and the S/N of that source is less than 10x the S/N of the difference detection.  Therefore, relaxing the MOPS cut to allow these lower significance diffs to be accepted seems reasonable.  This tail also has a large number of "star" associations.  This is reasonable, as the positive object is likely found in the warp image as well.  However, the bulk of the star population falls at larger S/N ratios (as the positive source is far more significant than the source after subtraction) and at larger radii (as the residual is not necessarily going to be symmetric for a star, resulting in a shift between the center between the positive source and the subtracted source). 
 
+The bifurcation of the S/N values shown above is visible in this plot as well, suggesting that the split is due to some issue in the difference process.
+
 || Positive || Original || Updated || 
 || WW ||[[Image(original_WW_P.png)]]  || [[Image(updated_WW_P.png)]] ||
@@ -39 +41 @@
 
 
-These plots are the same, but showing the relations between diff_rm/diff_sn_m for the different diff images (the plot labels are incorrect; these are the M versions).
+These plots are the same, but showing the relations between diff_rm/diff_sn_m for the different diff images (the plot labels are incorrect; these are the M versions).  These measurements are somewhat less obvious than for the P versions.  Although the signal to noise ratios (diff_sn_p / mops_sn and diff_sn_m / mops_sn) are similar for the warp-warp diff detections of asteroids, the diff_rm is not as small as for diff_rp.  This is reasonable, as the minus source is assumed to have moved between exposures.  The stellar sources occupy the same SNR/R space as in the P version, as the same residual issues create the matches.  
+
+Warp-stack diffs are far less likely to have a correct minus source associated, as any objects moving through the warp field is unlikely to have been there during the frames used for the stack.  As a result, the S/N ratio for known asteroid objects has a large amount of scatter, indicating that a random minus source is being associated with these objects.
 
 || Minus    || Original || Updated ||