An iterative background subtraction algorithm has been implemented starting with version 3.0 of sharp_combine.

This was tested using polarization data on M82 from the January 2006 observing run. As an extreme test I artificially introduced a large DC offset into one of 40 polarization cycles. The results below show multiple iterations of the background subtraction algorithm.

The upper left image is for no background subtraction followed by 1, 2, 3, 4, 5, 7, 10, and 15 iterations (left-to-right and top-to-bottom).