Smooths map before making SNR mask SSN.ZERO_SNR_LOPASS
"
ssn.zero_snr"
to be based
on a copy of the SNR map that has been low-pass filtering (i.e smoothed) to remove noise and other
features smaller than the number of map pixels given by ssn.zero_snr_lopass. This may
help to prevent pixels oscillating in and out of the mask on successive iterations, and thus
aid smoother convergence. [0.0]