@article{imhof_calvo_2003,  title={A variational formulation to image inclusions in 2D travel time cross hole tomography},  volume={21},  ISSN={0102-261X},  url={https://doi.org/10.1590/S0102-261X2003000300006},  DOI={10.1590/S0102-261X2003000300006},  number={3},  journal={Revista Brasileira de Geofísica},  publisher={Sociedade Brasileira de Geofísica},  author={Imhof, Armando Luis and Calvo, Carlos Adolfo},  year={2003},  month={Aug},  pages={269–274} }