FDNA  (Frequency Dependent Noise Attenuation) module uses frequency-dependent and time-variant algorithm where an amplitude threshold values are defined in a trace neighbor area (T-X) for detecting and noise attenuation according to different frequencies and different time windows. The attenuation process consists of two steps – First prepare the etalon (model) and noise attenuation data sets. The etalon should contain only the signal zones, with the noise zone muted. The module estimates the median value of the amplitude spectrum in the sliding windows of the etalon data set, and for each window computes an operator using the threshold value. The procedure attenuates amplitudes whose values exceed the specified threshold.

Let's have a look at the example:

Input data – Two seismic data sets are input to the FDNA module.

The Input gather are 2D/3D seismic gathers in source or receiver sort order. It is better if they are NMO corrected and static corrections have been applied, but for this step we can apply denoise sequence in a soft mode without NMO correction.

The Model gather is the etalon of 2D/3D seismic gathers in source or receiver sort order. The same idea: it is better if they are NMO corrected and static corrections have been applied, but for this step we can apply denoise sequence in a soft mode without NMO correction.

Seismic loop makes automatic connections between all modules in a sequence under that seismic loop and the user cannot disconnect them. In this case, we need to use an additional Flow module inside of the Seismic loop for etalon preparation. Put the mute modules into a Flow inserted into the Seismic loop and then connect the output muted data to the Model gather field of the Input data tab of the FDNA module. The Input gather on the Input data tab will be automatically connected to the previous module in the Seismic loop processing flow.

Firstly, we need to create an etalon for FDNA by using Mute by velocity module:

Next, we need to connect input Model gather (etalon) with output from the Mute by velocity module:

Input data is taken from Despike:

FDNA parameters:

Collection frequency time windows:

Parameter definition:

Trace window type: one window or multi-window;

Trace window[-1 - all traces]

Number of traces to use for the sliding window. This window is used for local attenuation.

Default: -1 (all traces)

Range: from 1 to max traces in the input gather

Time window

Time in milliseconds for sliding window. This window used for local attenuation. The taper zone between sliding windows is ¼ of time window length default 200ms.

Sliding time window - Amount to advance the sliding time window each shift

Iteration number - Define the number of iterations to perform. The more number of iterations, more run time.

Collection frequency time windows

Three parameters of basic control noise attenuation:

• Frequency– frequency for attenuation;

• Time– time value for threshold;

• Threshold– the limiting parameter for calculating threshold values to attenuate excessive amplitudes.

Carefully prepare the etalon (model) data, try to mute the high amplitude zones and include the signal zones.

Control the noise attenuation by using the threshold parameters and the ability to specify the thresholds in a time variant manner and frequency.

This procedure is more effective in the first steps of the seismic data processing flow when noise zones still have high amplitudes. The input seismic data should not be amplitude normalized.

Execute FDNA and check the results, source gathers before - after - difference: