@article{PAR00008559,
  title = {{C}haracterizing aquifers when using magnetic resonance sounding in a heterogeneous geomagnetic field},
  author = {{V}ouillamoz, {J}.{M}. and {L}egchenko, {A}natoli and {N}andagiri, {L}.},
  editor = {},
  language = {{ENG}},
  abstract = {{I}t has previously been reported that the heterogeneity of the geomagnetic field disturbs the currently-measured free induction decay signal of magnetic resonance sounding ({MRS}). {T}o overcome the limitation of {MRS} in a non-homogeneous geomagnetic field, we adapted the spin-echo methodology usually used at the laboratory scale and in boreholes. {W}e present examples of measurements carried out in a sandy aquifer in southern {I}ndia. {T}he 15-25 m thick sand deposit overlays a gneissic basement. {T}wo sources of geomagnetic field heterogeneity have been identified at this site, both affecting the geomagnetic field within the sandy aquifer: the gneissic bedrock and an intruded dyke into the bedrock. {S}pin-echo and free induction decay signals have been recorded at six locations. {W}e found that the groundwater content, the thickness of the saturated aquifer and its transmissivity calculated with free induction decay measurements are underestimated compared to those derived from spin-echo measurements. {T}he closer to the dyke the higher the underestimation. {T}ime-domain electromagnetic measurements indicate that the aquifer is rather homogeneous at the site scale, as suggested by spin-echo results. {W}e also found that a small heterogeneity of the geomagnetic field can go unnoticed, thus leading to an unknown mis-estimate of aquifer properties when using free induction decay measurements. {T}hus spin-echo measurements can be used to improve the accuracy of aquifer characterization when using {MRS} in geological contexts where geomagnetic field heterogeneity exists.},
  keywords = {},
  booktitle = {},
  journal = {{N}ear {S}urface {G}eophysics},
  volume = {9},
  numero = {2},
  pages = {135--144},
  ISSN = {1569-4445},
  year = {2011},
  DOI = {10.3997/1873-0604.2010053},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00008559},
}