The Variance Maps have patterns.

We investigated the variance maps for different stages/processing:

 * chip (md)
 * warp (md)
 * stack (md and sas)

There are periodic patterns associated with warp and stack, which are not associated with chip.  

Here is a zoom of one of the unconv.wt.fits for SAS footprint: (stack_Id= 336346). You can see an odd periodic background. The yellow circles are the false detections.


Here is a zoom of one of the unconv.wt.fit stacks for a recent MD refstack, it not quite as strange, but still, there is an underlying odd, periodic background.


Chip stage does not have this background (click to zoom in)

|| chip   || chip.wt ||


Warp stage (for the same chip) has a very strange background for the weight map (click to zoom in)


|| warp  || warp.wt ||