The use of pseudorandom sweeps for vibroseis surveys

Abstract

A B S T R A C TPseudorandom vibroseis sweeps have long been suggested as an alternative to standard linear sweeps due to their potential for having superior orthogonality, a lower likelihood for infrastructure damage, and increased low-frequency content. In the past, they were also attractive as they have a better autocorrelation shape, although that is less important today. Their use has been limited but the increasing popularity of simultaneous acquisition techniques has rekindled interest as they offer the ability to reduce interference noise. A wide variety of methods for generating pseudorandom sweeps have been developed over the last 45 years. This paper gives an overview of the motivations for their use before classifying and describing the different sweep types. Finally, the sweeps will be compared in terms of their major attributes including their suitability for simultaneous surveys.

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“…Originally the fleets used sweeps with different lengths, or pseudorandom sweeps (Dean 2014), but later this approach was discarded in favour of every fleet using the same sweep, which simplified acquisition with no discernible effect on data quality (Abma et al, 2015). This technique requires the system to be recording data continuously, from which each record is then extracted.…”

A seismic vertical vibrator driven by linear synchronous motors

“…With such signals, multiple seismic vibrators could work simultaneously reducing the acquisition time tremendously. Pseudorandom signals (for an overview, see Dean, 2014) can be designed to have such properties. One of the reasons why pseudorandom signals are not used that frequently is the difficulty to transmit them by (hydraulic) vibrators (Dean, 2014).…”

Research note: deblended‐data reconstruction using generalized blending and deblending models

“…Third, blended acquisition also uses signaturing, in which each source is encoded with its own signature, for example popcorn‐shooting sequences (Abma and Ross ) and near‐orthogonal firing sequences (Mueller et al . ) for marine acquisition; various sweeps (Bagaini ) and pseudo‐random sweeps (Dean ) for land. This method again yields distinguishable wavefields generated by each shot.…”

“…This method yields frequency-banded wavefields generated by each shot, thereby offers multi-scale spatial sampling, for example optimally coarser spatial sampling for a low frequency source, whereas relatively denser spatial sampling for a high frequency one in order to meet the Shannon-Nyquist sampling theorem for each frequency band. Third, blended acquisition also uses signaturing, in which each source is encoded with its own signature, for example popcorn-shooting sequences (Abma and Ross 2013) and near-orthogonal firing sequences (Mueller et al 2016) for marine acquisition; various sweeps (Bagaini 2006) and pseudo-random sweeps (Dean 2014) for land. This method again yields distinguishable wavefields generated by each shot.…”