tutorials:processing_gpr
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tutorials:processing_gpr [2019/07/21 15:20] – dominique | tutorials:processing_gpr [2019/07/25 10:43] – [Examples] dominique | ||
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====== Processing GPR data with SU ====== | ====== Processing GPR data with SU ====== | ||
- | Yes ! It is possible to process GPR data wit SU to apply all the power of seismic processing tools to GPR data. | + | Yes ! It is possible to process GPR data wit SU to use all the power of seismic processing tools to GPR data. |
- | The basic trick is to fool SU by using micro second as the time unit and centimeters | + | The basic trick is to fool SU by using micro second as the time unit and centimeter |
* frequencies are in MHz | * frequencies are in MHz | ||
* velocities range from 3330 cm/micro sec (water) to 30000 cm/microsec (air) | * velocities range from 3330 cm/micro sec (water) to 30000 cm/microsec (air) | ||
- | * offset | + | * offset |
- | ===== Importing GPR data ===== | + | Note : this is sufficient for low frequency GPR used for geological applications (25-1000 MHz) but may be adapted for higher frequency GPR. |
+ | |||
+ | ===== General presentation ===== | ||
+ | ==== Importing GPR data ==== | ||
There is no unified GPR data format and each manufacturer produces its own files. GPR data need to be imported from the manufacturer' | There is no unified GPR data format and each manufacturer produces its own files. GPR data need to be imported from the manufacturer' | ||
- | * For [[https:// | + | * For [[https:// |
- | * For [[https:// | + | * For [[https:// |
* For other manufacturers, | * For other manufacturers, | ||
Once the data are converted to SU format, you will probably need to adjust the geometry using tools like '' | Once the data are converted to SU format, you will probably need to adjust the geometry using tools like '' | ||
- | ===== Initial processing ===== | + | ==== Initial processing |
+ | |||
+ | Compared to seismic data (apart from the recording or sampling time and size of the survey) GPR data exhibit a few differences. | ||
+ | |||
+ | * Absolute propagation time is generally unknown. Actually, GPR propagation is so fast that the receiver can't start diitizin when receiving a trigger signal from the transmitter, | ||
+ | * GPR signal is generally strongly polarized and affected by some very low frequencies caused by electronic noise. This is easily corrected by removing the mean of the trace ('' | ||
+ | * The direct wave in the air (even with shielded antennas) and in the ground is very strong. It often saturates the analog to digital converter. They must be muted prior applying bandpass filters. This can be done using '' | ||
+ | * The intrinsic attenuation of GPR signal is much faster (with respect to the wavelength) that for seismic signal and require the early application of a strong gain (with '' | ||
+ | |||
+ | ==== Final processing ==== | ||
+ | Like in seismics, there is no such thing as //standard processing// | ||
+ | |||
+ | === Band pass filtering === | ||
+ | The dominant frequencies of the antennas are well known in the air, but for geological applications, | ||
+ | The best way is to locate the low and high frequencies where the recorded signal contains no or little geologic information by low or high pass filtering the data. | ||
+ | |||
+ | === Ringing removal === | ||
+ | Sometimes, GPR signal is affected by ringing. For single trace processing, you can try predictive deconvolution ('' | ||
+ | |||
+ | === Time migration === | ||
+ | Once the signal is clean, if the goal of the survey is not to evidence diffraction hyperbolas, it is often fine to migrate the data. GPR velocities tend to vary less that seismic velocities et a simple Stolt migration ('' | ||
+ | |||
+ | === Depth conversion === | ||
+ | A time to depth correction ('' | ||
+ | |||
+ | ===== Examples | ||
+ | <WRAP center round todo 60%> | ||
+ | Later... Be patient ! | ||
+ | </ | ||
+ | |||
+ | |||
+ | |||
+ | --- // | ||
+ | --- // |
tutorials/processing_gpr.txt · Last modified: 2019/07/25 10:44 by dominique