VSP wavefield separation using the gray-scale Hough transform: synthetic data
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ARABGU2016
VSP wavefield separation using the gray-scale Hough transform: synthetic data Asma Hadjadj 1 & Zahia Benaissa 1 & Abdelkader Benaissa 1 & Amar Boudella 1
Received: 6 December 2016 / Accepted: 18 April 2017 / Published online: 8 May 2017 # Saudi Society for Geosciences 2017
Abstract The principal objective in Vertical Seismic Profile (VSP) processing is the separation of the downgoing and upgoing wavefields. Several methods have been suggested in this area. This paper presents a new approach based on the gray-scale Hough transform (GSHT) which is an extension of the conventional Hough transform used to detect straight lines and other curves. The technique, we suggest here, directly maps the gray-scale VSP image, including the downgoing and upgoing linear events, in image coordinate space (x,t,g) to the gray Hough parameter counting space (θ,ρ,g), where θ and ρ are the polar parameters and g is the gray-scale value. In this new space, the downgoing events appear in the negative angles θ quadrant and the upgoing in the positive quadrant, owning to their opposite apparent velocities. The inverse GSHT algorithm, we developed in this study, is performed for extracting separately these two wavefields by considering the straight lines that satisfy the corresponding filtering conditions. The experimental results on synthetic VSP datasets are convincing. The wave separation is well performed, even in the presence of loud noise levels, with signal to noise ratio improvement and amplitude preservation, in contrast to median filtering.
This article is part of the Topical Collection on Current Advances in Geology of North Africa * Asma Hadjadj [email protected] * Zahia Benaissa [email protected]
1
Laboratory of Geophysics, Faculty of Earth Sciences, Geographical and Territorial Amenagement, Laboratory of Geophysics, Houari Boumediene University of Sciences and Technology (USTHB), BP 32, El Alia, 16111 Bab-Ezzouar, Algiers, Algeria
Keywords Gray-scale Hough transform . Seismic wave . VSP . Upgoing wavefield . Downgoing wavefield
Introduction In a Vertical Seismic Profile (VSP) recording, the useful signal is composed of the superposition of two wavefields: (1) a downgoing wavefield with positive apparent velocities and (2) an upgoing wavefield with negative apparent velocities (Hardage 2000). To make best use of them, they need to be separated. Several methods involving different mathematical tools (2D Fourier transform, median filter, singular value decomposition, spectral matrix, etc.) exist to perform this separation, each with its advantages and disadvantages (Seeman and Horowicz 1983; Freire and Ulrych 1988; Kommedal and TJostheim 1989; Glangeaud and Mari 1990; Chopra et al. 2004; Mars et al. 2004; Gao et al. 2014). The most frequently used in the industry are (f-k) and median filtering techniques. However, the first one requires a large number of traces with uniform depth sampling interval, and the second one remains unsuitable when amplitude preservation is critical (Kommedal and TJostheim 1989; Glange
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