The authors found the effect of changes in the transmissivity through the adjoint-state equations. The locations that are most influential on the data were selected as the pilot points. Kriging was used to condition on all real or pilot-points transmissivity observations. This interesting method of solving the inverse problem appears quite general, not limited by small-perturbation or probabilistic assumptions. It is not clear in what sense the mean square estimation errors computed in this method are realistic.
Most studies use hydrogeologic data obtained in wells or in laboratory tests.
However, geophysical exploration methods hold promise as valuable tools for site characterization. Geophysical exploration data, such as seismic data, must somehow be integrated with other data to yield better estimates of the parameters that affect groundwater flow and mass transport. Geostatistics provides an ideal framework and some important steps have already been made. Rubin et al. Copty et al.