The ast.zero_snr parameter will mask the map after each iteration
based on the the signal to noise ratio within each map pixel. For example, if it is set to 5, after each
iteration all map pixels with an SNR below this threshold will be forced to zero. the mask is
re-evaluated on each iteration. An ast.zero_snr value of zero means no SNR mask is used. See also
parameter
"
ast.zero_snr_ffclean"
. [0.0]