AMTCLAB: A MATLAB ® -based program for traveltime analysis and velocity tuning in 2D elliptical anisotropic media

In this paper we present the program AMTCLAB, a MATLAB^(R)-based computer code that analyzes the traveltime distribution and performs quality analysis at the pre-inversion stage for elliptically anisotropic media explored via 2D transmission experiments. This software generalizes the program MTCLAB presented in the past for the case of layered isotropic media, and makes use of traditional and robust traveltime distribution descriptors (mean, standard deviation, median, lower and upper quartiles, inter-quartile range and minimum absolute deviation), which are valid for all kinds of recording geometries. A guided user interface leads the modeller through the algorithm steps using the same data MTCLAB-structures. This methodology offers better understanding of the data variability prior to inversion, and provides the geophysicist with a macroscopic elliptical anisotropic velocity model, which is valid at the experiment scale, and matches the experimental mean traveltime distribution. To solve the inverse problems involved, program AMTCLAB uses the particle swarm optimisation algorithm, which allows the use of different norms and sampling the region of equivalent anisotropic velocity models in order to perform posterior sample statistics in each individual model parameter. The approximated velocity model issued from this analysis can serve in the traveltime inverse problem as an initial guess, or as a reference model in the subsequent inversion.