  The Mars Orbiter Laser Altimeter (MOLA) on board Mars Global Surveyor (MGS)
made $> 10^{8}$ measurements of the reflectivity of Mars at 1064 nm
($R_{1064}$) by both active sounding and passive radiometry. Past studies of
$R_{1064}$ neglected the effects of atmospheric opacity and viewing geometry on
both active and passive measurements and also identified a potential
calibration issue with passive radiometry. Therefore, as yet, there exists no
acceptable reference $R_{1064}$ to derive a column opacity product for
atmospheric studies and planning future orbital lidar observations. Here, such
a reference $R_{1064}$ is derived by seeking $R^{M,N}_{1064}$: a
Minnaert-corrected normal albedo under clear conditions and assuming minimal
phase angle dependence. Over darker surfaces, $R^{M,N}_{1064}$ and the absolute
level of atmospheric opacity were estimated from active sounding. Over all
surfaces, the opacity derived from active sounding was used to exclude passive
radiometry measurements made under opaque conditions and estimate
$R^{M,N}_{1064}$. These latter estimates then were re-calibrated by comparison
with $R^{M,N}$ derived from Hubble Space Telescope (HST) observations over
areas of approximately uniform reflectivity. Estimates of $R^{M,N}_{1064}$ from
re-calibrated passive radiometry typically agree with HST observations within
10%. The resulting $R^{M,N}_{1064}$ is then used to derive and quantify the
uncertainties of a column opacity product, which can be applied to
meteorological and climatological studies of Mars, particularly to detect and
measure mesoscale cloud/aerosol structures.
