Details
-
Type:
Bug
-
Status: Done
-
Resolution: Done
-
Fix Version/s: None
-
Component/s: ip_diffim
-
Labels:
-
Story Points:1
-
Epic Link:
-
Sprint:AP S20-4 (March)
-
Team:Alert Production
-
Urgent?:No
Description
The DCR templates for image differencing incorrectly set the variance using only the variance plane of the first subfilter that is loaded. The final variance plane is too low by a factor equal to the actual number of subfilters, resulting in an incorrect threshold for detecting sources in image differencing.
Attachments
Activity
| Field | Original Value | New Value |
|---|---|---|
| Epic Link |
|
| Status | To Do [ 10001 ] | In Progress [ 3 ] |
| Story Points | 2 | 1 |
| Reviewers | Meredith Rawls [ mrawls ] | |
| Status | In Progress [ 3 ] | In Review [ 10004 ] |
Pull request is here:
Good catch. In my brief review, I am taking it as a given that it is "algorithmically correct" to have the variance be equal to the variance for one sub-band multiplied by the total number of sub-bands. As best as I can tell, your one-line change implements that correctly. I'm impressed you noticed the difference between 5- and 4.69-sigma source detection threshold!
| Status | In Review [ 10004 ] | Reviewed [ 10101 ] |
| Resolution | Done [ 10000 ] | |
| Status | Reviewed [ 10101 ] | Done [ 10002 ] |
This is a simple fix, but the bug has been complicating my comparisons of deep vs dcr coadds. It's not a large effect, since the variance of the science image usually dominates over the variance of the coadd, but it roughly translates to having used a 4.69 sigma threshold for the dcr coadds, instead of 5.