Comparison of 2D filters for suppressing noise in common shot gathers

From the point of view of reflection signal fidelity, the best way of removing strong regular noise from a common shot gather is to estimate the noise and then subtract it from the data. This minimizes the distortion of the signal. The Karhunen±Loeive (K±L) transform is the basis of such a method, and may be used to extract high-amplitude coherent noise from common shot gathers acquired in seismic reflection surveys on land. In this paper we compare the results of filtering synthetic and real data examples in the frequency±wavenumber (f±k) domain, by hyperbolic velocity filtering in the intercept-slowness (tau-p) domain, and by extracting the noise using the K±L transform. The f±k and hyperbolic velocity filters cause serious distortion of the reflection signals, especially when the difference between the apparent velocities of signal and noise is small. In contrast, the K±L transform enables the noise to be extracted with minimal distortion of the reflection signals. It is a common experience in processing land seismic reflection data to be confronted with data containing weak reflection signals submerged by strong, regular noise such as groundroll or air waves. Although the stack-array approach to the choice of acquisition parameters is a powerful technique for suppressing these types of noise in processed sections, applications such as AVO analysis of the prestack data require that the noise be suppressed with minimum distortion of the reflection signals. For such prestack applications, the choice of filtering method to remove the noise is very important. Other types of source-generated noise, commonly observed in land data, are reverberant refraction events parallel to the first breaks. They are even more difficult to suppress than groundroll and airwaves because their apparent velocities are close to the apparent velocities of the reflection events at far offsets. We show synthetic examples to evaluate the performance of the three filtering methods when the apparent velocities of strong, regular noise are similar to, and different from, the apparent velocities of reflection signals. We then show a real data example which illustrates the superiority of the K±L transform method of noise extraction for suppressing the reverberant refracted arrivals.