  Context. Inner cavities, accretion arms and density waves are characteristic
structures in the density distribution of circumbinary disks. They are the
result of the tidal interaction of the non-axisymmetric gravitational forces of
the central binary with the surrounding disk and are most prominent in the
inner region, where the asymmetry is most pronounced.
  Aims. The goal of this study is to test the feasibility of reconstructing the
gas density distribution and quantifying properties of structures in the inner
regions of edge-on circumbinary disks using multiple molecular line
observations.
  Methods. The density distribution in circumbinary disks is calculated with
two-dimensional hydrodynamic simulations. Subsequently, molecular line emission
maps are generated with 3D radiative transfer simulations. Based on these, we
investigate the observability of characteristic circumbinary structures located
in the innermost region for spatially resolved and unresolved disks.
  Results. We find that it is possible to reconstruct the inner cavity,
accretion arms and density waves from spatially resolved multi-wavelength
molecular line observation of circumbinary disks seen edge-on. For the
spatially unresolved observation only an estimate for the density gradient in
the transition area from cavity to inner disk rim can be derived.
