2-D Seismic Data Processing Exercise

Frequency filtering

In this part of the tutorial, we will start processing the Nankai dataset by attenuating noise using frequency filtering.

1. We will design the noise attenuation filter as a muting function in the Fourier domain. Let us design the filter by focusing on one selected shot gather. The 2-D Fourier spectrum of the gather before and after filtering is shown in Figure 2. The corresponding separation of the gather into signal and noise is shown in Figure 3. Ideally, we would like to see no noise remaining in the estimated signal and no signal leaking into the estimated noise.

   To reproduce the denoising result, run

   scons signal.view
   

   To display the Fourier-domain functions, run

   scons fft.view
   scons mute.view
   scons filter.view
   

   The mute function is implemented in the attached filter.c program and is designed as a triangular wedge controlled by two command-line parameters: velocities v1 and v2. The filter passes seismic events with velocities higher than v2, attenuates those with velocities smaller than v1, and makes a smooth transition in between using a sine taper.

   

   fft,filter
   Figure 2. The 2-D Fourier spectrum of the Nankai shot before (a) and after (b) noise attenuation.

   

   
   

   

   signal
   Figure 3. Shot gather separated into signal and noise. The noise section is gained to demonstrate that it contains no useful signal.

   

   
   

   To run the noise attenuation filter on all shot gathers, run

   scons fshots.view
   

2. Your task is to try improving the quality of the noise attenuation. You can do it by selecting better parameters or by modifying the filter.c program. Test your change not only on the selected shot gather but also on other gathers to make sure you achieve an improvement. Document your processing choices and create new figures if necessary.

2-D Seismic Data Processing Exercise