MTEM data formats

1. MTEM data formats What data do we store

2. Outline • Images of the MTEM dictionary – a dialect of the SEGY. • Comments on data files.

3. Dictionary – header definition • We use many header spaces to describe things that are not normally associated with seismic data. • The coordinates for SRC and REC midpoints would ideally also have some space for each electrode position – or spatial data in the a header that we can cross reference with the ‘peg names’ • We store some ASCII text in the headers. – ‘peg’ names. • There are some filter frequencies that we would like to include in the header definition but haven’t got round to putting that in yet. – ie we still require some flexibility!

4. Dictionary to read in segy(ish) files as provided by the observer machine.

5. The second part of the dictionary

6. Comments on Data files • They are not really segy files – although they do have quite a lot in common. • Start with an XML header with a whole bunch of stuff, taking advantage of the extended textual header option in SEGYrev1. • We use a lot of floating point headers. • Data sample rates vary quite a bit inside one EP (shot gather) a source in one position may transmit to receivers in different positions • Trace lengths can be between a few thousand and 300,000(ish) samples. But looking at the data quite a bit is less than 100,000 • After deconvolution the data trace are reduced in size by an enormous amount, the output traces many have only a few hundred data points in them.

7. Comments on Data volumes • We don’t write much data to tapes, we use hard disks, sometimes ones we share with the acquisition system.