  During a quarter of a century, the main characteristics of the
horizontal-to-vertical spectral ratio of ambient noise HVSRN have been
extensively used for site effect assessment. In spite of the uncertainties
about the optimum theoretical model to describe these observations, several
schemes for inversion of the full HVSRN curve for near surface surveying have
been developed over the last decade.
  In this work, a computer code for forward calculation of H/V spectra based on
the diffuse field assumption (DFA) is presented and tested.It takes advantage
of the recently stated connection between the HVSRN and the elastodynamic
Green's function which arises from the ambient noise interferometry theory.
  The algorithm allows for (1) a natural calculation of the Green's functions
imaginary parts by using suitable contour integrals in the complex wavenumber
plane, and (2) separate calculation of the contributions of Rayleigh, Love,
P-SV and SH waves as well. The stability of the algorithm at high frequencies
is preserved by means of an adaptation of the Wang's orthonormalization method
to the calculation of dispersion curves, surface-waves medium responses and
contributions of body waves.
  This code has been combined with a variety of inversion methods to make up a
powerful tool for passive seismic surveying.
