;+
; NAME:
; vt3d_skindepth
; PURPOSE: (one line)
;  Return vt3d_skindepth
; DESCRIPTION:
;  Return vt3d_skindepth
; CATEGORY:
;  Volatile Transport
; CALLING SEQUENCE:
;  z_skin = vt3d_skindepth(dens, specheat, thermcond, freq)
; INPUTS:
;  dens : density of the substrate (g/cm^3)
;  specheat : specific heat (erg/(g K))
;  thermcond : thermal conductivity of the substrate (erg/(cm s K))
;  freq : frequency of the solar forcing, 2 pi/period (1/(s))
; OUTPUTS:
;  z_skin : skin depth (cm)
; RESTRICTIONS:
; PROCEDURE:
;  Young, L. A. 2016, Volatile transport on inhomogeneous surfaces: II. Numerical calculations (VT3D)
;   Resubmitted to Icarus.
;   Eq 3.2-6
; MODIFICATION HISTORY:
;  Written 2011 Aug 10, by Leslie Young, SwRI
;  2016 Mar 24 LAY. Modified for inclusion in vt3d library.
;-

function vt3d_skindepth, dens, specheat, thermcond, freq

    return, sqrt( thermcond / (dens *specheat * freq) )

end