 # Input data in SimPEG EM

Hello, How should be the input data in SimPEG EM? always dbdt? has to be normalized? Which kind of normalization? by Tx and Rx area? by the current?

Hi @jcbarreto,

you can define type of the data when initiating receiver class.
For instance,

rx = EM.TDEM.Rx.Point_dbdt(rxloc, time, ‘z’)

Here, we are say our receiver measures dbdt in z-direction, and measured time channels are defined in `time`

but how about the normalization? if I have the data in V/A, and I divide by the Tx and Rx area, so I have V/[A.m^4] is that enough?

This depends upon what source type you use. If you are using magnetic dipole then yes you can divide the measured V/A data by rx area and tx area. But if you use a circular loop then, tx area is already taken account, so you don’t have to divide V/A with tx area, so only with rx area.

Ok, I have a square loop that I put in SimPEG as a circular one, so I just need to divide by the Rx. Thanks In this case, where SimPEG asks for the current, should I put 1./area or the equipment current? Why in the Bookpurnong example is 1./area?

I guess you are mentioning skytem case. For that the unit of the skytem data was v/Am^4, but the source type that we used was circular loop, so we put 1./area to compensate. Actually, bit confusing …, but correct.

Yes, it is the Skytem case. To compensate what? Why the moment has to be equal 1?
So in my case, that I have V/A, and I have divided by the Rx area, [V/Am^2], should I put the equipment current in this place (3.5A)?

Hmm… I am now looking at `plot_booky_1D_time_freq_inv.py` not sure where you have got 1./area?

May be your comment was about: `skytem["data"][rxind_skytem, :-3] * area`?

If then, the unit of the skytem data was V/Am^4, so I multiplied area to make it as V/Am^2.

For your case, you need to put effective radius for your rectangular loop, then dividing your data [V/A] with Rx area resulting [V/Am^2] is correct. So, no need to put the current, since your data is normalized by the current.

To summarize, for the circularloop with db/dt receiver, the unit of the predicted data is [V/Am^2], so you need to normalize your data (assuming it’s unit is [V]) with the current [A] and Rx area [m^2], but not Tx area [m^2].

Hope this helps.

It helps a lot! Thank you. I was talking about this notebook, the one we did the EM Tutorial on Hangouts

Ah, got it. that `1./area` was to have output of [V/Am^4], which could be potentially bit confusing. So, you need to be careful about the unit of the observed data, and also what simpeg outputs.