Possible misunderstanding in the tutorial

[wilhem]

Hi Emanuel,

according to the output of the function str(), you should get the parameter dz, which is the sampling rate of the radar

> str(A)
Formal class 'GPR' [package "RGPR"] with 29 slots

  ..@ dz          : num 0.00893   # Sampling rate

But in the migration section dz is the vertical resolution and its unit is "m"

Topographic Kirchhoff migration. Vertical resolution of the migrated data, we set dz = 0.01m.

Is it just a coincidence and dz means two different things? Or they are the same thing and dz is the sampling rate even in the second case?

[emanuelhuber]

Hello wilhem

It is intentionally that dz can be in time unit or in depth unit. That is maybe not very elegant. The challenge I faced was that a GPR trace can be a signal amplitude as a function of time (the recorded signal) or a signal as a function of depth for migrated GPR data. I did not want to handle two different slots for a GPR object (one for the sampling rate in time unit (e.g., dt) and another one for the sampling rate in depth unit dz). That's the explanation. Note that the standard user should not notice that because the slot dz has no setter/getter. In the develop version of RGPR, the slot dz as well as depthunit() will disappear and unit conversion will be supported.

In your data, dz is most likely in time unit (check the output of depthunit(A)). In the migration function, dz correspond to the vertical resolution in depth unit (e.g., meters) you want to obtain (because the output of migrate() in a signal as a function of depth).

Does it answer your questions?

[wilhem]

Thank for your reply. That's clear the question.

But I found another possible misunderstanding regarding the function dewow() In the wiki it is reported that:

Dewow

Remove the low-frequency components (the so-called “wow”) of the GPR record using:

a running median filter (type = "runnmed")
a running mean filter (type = "runmean")
a Gaussian filter (type = "Gaussian")

For the two first cases, the argument w is the length of the filter in time units.

But looking at the help

?dewow

I get:

w [numeric(1)] If type = runmed, MAD or runmean, window length of the filter in trace unit; If type = Gaussian, standard deviation in trace unit. If w = NULL, w is estimated as five times the wavelength corresponding to the maximum frequency of x (estimated with spec)

Now it is not clear to me what w should be.

Let's say I have in my function w = 5 (time unit [ns]). Does it mean that the window length of the filter goes from 0 ns to 5 ns all over the traces? Or does it mean, that the window length of the filter for every n trace [n-5, n-4, n-3, ...0, n+1, n+2,.., n+5] goes from 0 ns till the end of the vertical time windows?

Regards