Applying Bandpass Filter in Time variant fashion

Theory

Applying Bandpass filter in a different flavor. In this we design the time windows and different frequency bands based our requirements and apply the filters. Time Varying Bandpass filter is also known as (TVF). This procedure is used because the higher frequencies tend to be attenuated by the earth more quickly than lower frequencies, so higher frequency data at the top of the section may be valid, while the same frequencies would be noise (ambient noise) lower in the section.

Care must be taken while applying TVF in the case of merging two seismic surveys. The frequency bandwidth should match between the two surveys. TVF is applied mostly on the stack section.

Input data

Input DataItem

Input gather

connect/reference to output gather. Input should any common shot/receiver/depth point gather. Also, time variant band pass filter can be applied on post stack gather as well.

Parameters

Time-frequency table - design appropriate Time-Frequency windows. In the frequency column, provide different band pass filter values. In the shallower parts, we've both high and low frequencies however the low frequencies mask the higher frequencies. As we know, frequencies getting absorbed as they travel through the earth. So higher frequencies attenuate faster than the lower frequencies. As the seismic waves travel deeper into the earth, higher frequencies get attenuated. Design a time variant frequency values as per the data requirements.

Percent overlapping taper - provide taper value for the overlapping time windows. Tapering allows smooth transitioning between the time windows and avoids any gaps or artifacts. By default, 25%.

Settings

Auto-connection

By default, TRUE(Checked).It will automatically connects to the next module. To avoid auto-connect, the user should uncheck this option.

Bad data values option { Fix, Notify, Continue }

This is applicable whenever there is a bad value or NaN (Not a Number) in the data. By default, Notify. While testing, it is good to opt as Notify option. Once we understand the root cause of it, the user can either choose the option Fix or Continue. In this way, the job won't stop/fail during the production.

Notify

It will notify the issue if there are any bad values or NaN. This will halt the workflow execution.

Fix

It will fix the bad values and continue executing the workflow.

Continue

This option will continue the execution of the workflow however if there are any bad values or NaN, it won't fix it.

Calculate difference

This option creates the difference display gather between input and output gathers. By default Unchecked. To create a difference, check the option.

Number of threads

One less than total no of nodes/threads to execute a job in multi-thread mode. Limit number of threads on main machine.

Skip

By default, FALSE(Unchecked). This option helps to bypass the module from the workflow.

Output data

Output DataItem

Output gather

generates the time variant band pass filtered output.

Gather of difference

generates the difference gather before and after applying the time variant band pass filter.

Information

There is no information available for this module so the user can ignore it.

Examples

Let's see step by step process of applying time-variant band pass filter. Just like normal band-pass filter, we've lower pass cut off, pass band and high pass cut off filter parameters. In this example, we would like to preserve the higher frequencies so we designed a filter such that all low frequencies are filtered.

As we know that the higher frequencies get attenuated at the deeper part of the seismic section. So we design a time-variant filter that filters the lower frequencies in the shallow and higher frequencies at the deep. Higher frequencies in the shallow gives a high resolution image.

Actions

There are no action items available for this module so the user can ignore it.

Video lesson

YouTube video lesson, click here to open [VIDEO IN PROCESS...]

Related articles

Yilmaz. O., 1987, Seismic data processing: Society of Exploration Geophysicist

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