height_to_pressure_std has limited validity

[joernu76]

The height_to_pressure_std and pressure_std_to_height routines are valid only up to 11km. Above 11km, according to the ICAO standard atmosphere, the temperature structure changes and thus pressure calculation is increasingly off.

The routine should take the full ISA atmosphere into account (or at least document the valid region).
We have a rather complicated solution in MSS
https://github.com/Open-MSS/MSS/blob/5c47796f98fedbab4d76d8ec283e5432b7574d23/mslib/thermolib.py#L923
in the flightlevel2pressure_a routine (which I'd actually like to replace with something from metpy...).
Due to our gravity wave research, we are interested in the altitude range up to 60km. Beyond it gets even trickier.
I could prepare a merge request based on our code, but I am not really happy with how the conversion is solved for arrays there either...

[dopplershift]

I'd be happy to see those functions improved. I should note that our functions aren't trying to fit the ICAO standard atmosphere, but instead the 1976 U.S. Standard Atmosphere. I'm not sure how they differ.

[joernu76]

They should be the same, but I'll double check. We come (partially) from aviation so have a different first stop :-)
I'll prepare a merge request for further discussion.