If the user supplies a profile grid of N levels (specified by
the first profile in the first file of the
*ATM section), then this flag
adds an extra N-1 levels at the intermediate points, specified in
altitude on ln(p), according to which type of grid is used.
The main purpose of this flag is as a quick test to see if the
altitude grid-spacing on the user-supplied profiles
is sufficiently fine to support the assumptions
used in equating atmospheric paths to equivalent homogeneous paths for
the Curtis-Godson approximation and Planck-function variation
(see also
BFX flag for Planck-variation).
If the results with/without the LAY flag are significantly different
then the layering is too coarse.
The PRF Flag can be used to write out
the new profiles that are actually used
