FW-NA is a package of Fortran programs based on a Monte Carlo approach for solving a waveform inversion and thus defining the 1-D physical properties of small-scale structures.
FW-NA is a package of Fortran programs based on a Monte Carlo approach for solving a waveform inversion and thus defining the 1-D physical properties (e.g., shear wave-speed, compressional wave-speed, shear dissipation factor) of small-scale (i.e., from millimetres to few meters) structures.
It consists of three main ingredients:
- The programs for solving the inverse problem using the Neighbourhood Algorithm (NA), a Monte Carlo technique developed by Sambridge,  and  (rses.anu.edu.au/~malcolm/NA/).
- The programs for solving the forward modelling using the package GEMINI II.
- Fortran codes to connect the input/output files of NA and GEMINI with each other.
From a theoretical point of view, the NA samples the entire model space and attributes a misfit function to each solution compatible with the data (top panel of Figure). For each sampled model the algorithm solves a forward problem which in the present case is given by the approach of Friederich & Dalkomo . Then, all the models are expressed in terms of (Gaussian or non-Gaussian) probability density functions (pdfs) which represent all the possible information gained from the data (bottom panel of Figure).
 W. Friederich & J. Dalkolmo (1995). Complete synthetic seismograms for a spherically earth by a numerical computation of the Green's function in the frequency domain - Geophys. J. Int., 122, 537-550
 M. Sambridge (1999a). Geophysical inversion with a neighbourhood algorithms I - Searching a parameter space - Geophys. J. Int., 138, 479-494.
 M. Sambridge (1999b). Geophysical inversion with a neighbourhood algorithms II - Appraising the ensemble - Geophys. J. Int., 138, 727-746.