EMTF XML: New data interchange format and conversion tools for electromagnetic transfer functions

Initial processing of magnetotelluric (MT) data collected at a site results in a small data file that defines the MT transfer functions (MT TFs) or variants at a discrete set of frequencies. Although not data intensive, the TF represents almost all of the information about earth’s conductivity found in the raw data and provides a key input to geophysical inversion and to geomagnetic hazard-mitigation procedures. However, to be useful for scientific interpretation, MT TFs must be accompanied by carefully recorded metadata. The value of these data is amplified if they are collected into a common database in a discoverable fashion; to achieve this, the metadata must also be searchable. We have developed a new format for MT and related electromagnetic transfer function extensible markup language (EMTF XML), which is a novel, self-describing, searchable, and extensible way to store the data. We also evaluate our open-source, highly capable conversion tools that implement format conversion between historical MT TF formats (electrical data interchange [EDI], EDI SPECTRA, Z-files, and potentially others) and EMTF XML and we examine the associated issues of data rotation. We have paired our work with the open-source format conversion tools, EMTF FCU v4.0, with a user guide and a set of use case examples. We hope that this effort will assist the MT community in creating a more open data-sharing culture and practices.