On a good night with a Sky Quality Meter (SQM) reading of the sky background at 21.4 mag/[arcsec.sup.2], I estimate the faintest visible portions of the M81/M82 cirrus are 25.5 mag/[arcsec.sup.2], offering a contrast of a scant several percent in terms of
field brightness.
OMA is the difference between the observed
field brightness temperature and the analysis
field brightness temperature value, and OMB is the difference between the observed
field brightness temperature value and the background
field brightness temperature value.