# 8.1.1. NSEM: From raw EDI files to GIF formatted data¶

Here we provide a recipe for creating GIF formatted natural source electromagnetic (NSEM) data objects from EDI files. Depending on the forward model/inversion code the user intends to run, additional steps may be required once the data are loaded. The additional steps are explained in the content below.

• Import data from EDI files: The raw EDI data files contain a combination of impedance, apparent resistivity, phase, ZTEM and other data which can all be loaded. The resulting data object can be an IMPdata or APPdata object.

• Create different data type (optional): Let us assume the EDI files contain impedance, apparent resistivity, phase and ZTEM data and that an IMPdata (impedance data) object was created upon loading. This functionality can be used to create a ZTEMdata or IMPdata object if those data are found in the IMPdata object.

• Correct units: GIFtools makes assumptions regarding the units of data within EDI files and converts data to standard units used by GIFtools. See data units in EDI files and GIF data units.

• Correct imaginary and/or phase data: If the time-dependence ($$\pm i\omega t$$) differs between the data being loaded and the code being used, then imaginary data and phases must be multiplied by -1 using the calculator. The details of this step are explained further for MT data and ZTEM data.

• Assign uncertainties

Important

Before writing data files and attempting to invert MT data, it strongly advised that the data are viewed in terms of apparent resistivity. This information can be used to determine how resistivity changes with respect to depth, determine which frequencies are sensitive to your target and design an appropriate mesh.