  We retrieve vertical and meridional variations of methane mole fraction in
Titan's lower troposphere by re-analyzing near-infrared ground-based
observations from 17 July 2014 UT (Adamkovics et al., 2016). We generate
synthetic spectra using atmospheric methane profiles that do not contain
supersaturation or discontinuities to fit the observations, and thereby
retrieve minimum saturation altitudes and corresponding specific humidities in
the boundary layer. We relate these in turn to surface-level relative
humidities using independent surface temperature measurements. We also compare
our results with general circulation model simulations to interpret and
constrain the relationship between humidities and surface liquids. The results
show that Titan's lower troposphere is undersaturated at latitudes south of
60N, consistent with a dry surface there, but increases in humidity toward the
north pole indicate appreciable surface liquid coverage. While our observations
are consistent with considerably more liquid methane existing at the north pole
than is present in observed lakes, a degeneracy between low-level methane and
haze leads to substantial uncertainty in determining the extent of the source
region.
