MTEM data formats What data do we store

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

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!

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

The second part of the dictionary

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.

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