FDEM and TDEM data files

[mariosgeo]

Hi Florian,

Is it possible to provide a Time Domain and Frequency Domain input data file, landbased (say ABEM WalkTEM and DualEM) and airborne (say Resolve and SkyTEM)?

I can't see to find or I am searching correctly.

Best

[florian-wagner]

Hi @mariosgeo,

there is not much to see here yet. We started this recently to use external data files, meshes, etc. within the documentation (e.g., here) without cluttering the main repository.

I personally don't have any EM data sets, but everyone is happy to contribute example data sets here. @halbmy probably has some data sets, but I guess you are looking for an example how to invert such data rather than the data itself?

Best wishes
Florian

[halbmy]

Generally, the EM stuff is not very well developed yet but it will be in the future as we have several TDEM (mostly central loop and some fixed loop) and FDEM (mainly Resolve, but also CSEM). We have a lot of routines in a separate project that will be merged into pyGIMLi soon.

That's what we have in pygimli.physics.em (https://github.com/gimli-org/gimli/tree/master/python/pygimli/physics/em)

TDEM

There is a TDEM data managing class that can read

• USF
• SiroTEM
• TEMfast
  data and invert them. The underlying modelling class VMDmodelling (simulating the reverse case) is only valid for circular loops with central dB/dt receiver.

FDEM

There are two forward operators for arbitrary frequency/offset pairs: an internal (pg.core) FDEMModelling mainly made for ground-based (MaxMin) EM data and a HEMmodelling made for airborne data (made for the Resolve system). Similar but not identical physics, both relying on inphase/outphase data.

The FDEM class is for reading and managing the data (flight lines, or single soundings) and running single inversions or laterally constrained 1D inversions.

There is no example yet but there will be some once we are done with the pyGIMLi redesign (v1.1) and a lot of things will change. You are highly welcome to contribute in the EM part.

[halbmy]

I just started adding some data for FDEM (ground and airborne) and TDEM (only ground) data with different types of instruments that have been documented in literature. I will keep digging and contribute other kinds of data and instruments. So far I don't have any SkyTEM data by hand but I will ask some colleagues for published data.

[mariosgeo]

I have, HEM data from BGR and TEM data from SKYTEM. Also data from ABEM WalkTEM and DualEM.
I have some scripts that I convert them and process with Aarhus Workbech. I would like to use pygmli for some fun projects, but i don't know how the input should look like.

If that helps you, I can send them to you .

[erickvilla24]

Do you have any code that allows you to invert the data like in a WalkTEM device, but with its arrangement in a square and with two receiving antennas? Since pygimli does not have those types of arrangements.

The other question is how to calculate or look at the waveform of a TDEM from a WalkTEM device

[halbmy]

The TDEM operator currently supports only central-loop configuration (the transmitter shape does not matter, just the area) and a point-like receiver in the middle. But as we are using apparent resistivity, it will be working well also for coincident loop data.

For everything else, I suggest using a forward operator like empymod in conjunction with pyGIMLi as inverse solver.

As far as I know, you cannot save the full wave train with the WalkTEM, only the gated (and stacked) data. But this is beyond the scope of pyGIMLi.