I would recommend Ground Penetrating Radar (if surface and soil conditions permit) or electromagnetic imaging. An slower alternative would be electrical resistance tomography. The choice of methods depends on the site that you would like to investigate, on the desired depth of investigation, on the resolution and the physical conrtast between the infiltrating medium. What type of infiltration are you interested in?

I advise you to read the international standard ISO 22282 : Geotechnical investigation and testing - geohydraulic testing which specifies requirements for dtermination of the local permeability in soils and rocks