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Abstract

The acronym EMERALD was supposed to stand for ElectroMagnetic Equipment, Raw data And Locations Database. What survived over the years was the EMERALD processing, a set of computer programs to analyse MT time series data, and the EMERALD file format for storing MT data. This document describes the EMERALD file format and how to use it with the C++, C and FORTRAN programming languages. Interface functions also exist for Matlab and Powershell but they are not described here. EMERALD data files typically come in pairs of two files with the same name but differing file name extensions, sometimes called RAW and XTR files. XTR (extract) files are plain ASCII files, which can be read and modified with text editors. RAW files or more generally, EMERALD ‐type data files are in most cases binary and used to store all kind of magnetotelluric (MT) data such as time series, cross‐ and auto spectra and calibration data. The EMERALD ‐type data files store any number of channels of data in matrix form, but do not contain any description of the data. This information is stored in the according XTR file. In 2015 the original XTR files were replaced by a modernized version based on the Extensible Markup Language (XML). The new files have the extension .XTRX.