get_dist for VERTISSURFACE

[hkershaw-brown]

Moved from #756

location_mod get_dist "! Vert distance can only be done for like vertical locations units" why can you not calculate vertical distance between two points one with VERTISSURFACE(m) and one with VERTISHEIGHT(m)?

https://github.com/NCAR/DART/blob/e2188646b97573f198c66f7ea63482ebc34afa11/assimilation_code/location/threed_sphere/location_mod.f90#L507-L509

Originally posted by @hkershaw-brown in https://github.com/NCAR/DART/issues/756#issuecomment-2435532825

[hkershaw-brown]

copied comments over:

nancycollins commented 1 hour ago it's because the vertical conversion is almost always model-dependent. the location mod expects the model mod to do the conversion before calling get_dist.

@nancycollins Member nancycollins commented 1 hour ago p.s. in this case the location mod can't know the height of the surface to do the calculation.

@hkershaw-brown Member Author hkershaw-brown commented 35 minutes ago VERTISSURFACE is defined as surface value (value is surface elevation in m) so no conversion needed between VERTISSURFACE and VERTISHEIGHT

https://docs.dart.ucar.edu/en/latest/guide/creating-obs-seq-real.html#observation-locations

[hkershaw-brown]

this text in the docs:

https://github.com/NCAR/DART/blob/e2188646b97573f198c66f7ea63482ebc34afa11/guide/creating-obs-seq-real.rst?plain=1#L333-L337

Is this true for VERTISSURFACE? That you would want want anything surface to impact the whole column? This is not what the code is doing.

https://github.com/NCAR/DART/blob/e2188646b97573f198c66f7ea63482ebc34afa11/assimilation_code/location/threed_sphere/location_mod.f90#L501-L520

[hkershaw-brown]

mpas example https://github.com/hkershaw-brown/DART/tree/mpas_surf_height

[nancycollins]

i don't believe that DART itself requires that the vertical value for VERTISSURFACE be in meters. i think it's ignored. WRF and then MPAS were then free to require that observations set the value to be the elevation of the observing station so they could do rejections of obs at too different elevations. you might want to grep the code because i may be confused, but i don't think we require that the vertical value be anything when the vertical type is VERTISSURFACE. that doesn't mean we can't change it if that's useful.