INTDP     Default interpolation type for vertical interpolation to pressure
           surfaces (*VPRS) (one INTEGER value, default is INTDP = 2).  This
           interpolation type is used for all fields not named in the except-
           ions list <PINTXL>.  Specifying a value for this ICP nullifies the
           default for <PINTXL>.  See <PINTXL> for examples.  The valid interp-
           olation type codes are as follows.

           INTDP = 0  - no interpolation
           INTDP = 1  - linear in pressure
           INTDP = 2  - linear in natural log of pressure(default).
           INTDP = 3  - linear in natural log of natural log of pressure.