Tomographic analysis is used to provide a correction to low-pressure s
toichiometric premixed CH4/O-2 flame temperatures measured with tunabl
e diode laser absorption spectroscopy employing CO two-line thermometr
y. It is shown that flame temperatures measured with line-of-sight-bas
ed two-line thermometry are always too low and that the correction to
the observed temperature is a nonlinear function of the height above t
he burner surface. It is also shown that, at a given height in the fla
me, a constant temperature across the flame does not imply that vibrat
ional populations are constant and that, at low pressures (<20 Torr),
the flame spreads radially beyond the burner diameter and so may no lo
nger be approximated by a one-dimensional model.