Influence of Interrogators’ Design on DAS Directional Sensitivity

Summary With the rapid increase of use of Distributed Acoustic Sensing (DAS) technology for seismic acquisition, it is important to have a good understanding of the nature of DAS measurements. It is little known that the measurement characteristics of a DAS interrogator can be significantly altered by the design principles used to measure optical phase. In this study we demonstrate that directional sensitivity of incident seismic wave can be influenced by DAS interrogator design. In this work we compare amplitudes of VSP direct wave acquired in dedicated research well using borehole geophones and two DAS systems: deformation rate based Terra15-Treble and strain rate based Fotech-Helios. Data analysis shows that the amplitude of the direct wave recorded with Terra15 DAS system is proportional to particle velocity amplitudes recorded by geophones. Meanwhile, the amplitude relationship between Fotech system and Terra15 system is proportional to cosine function of the incidence angle. It means that the directivity pattern of the deformation rate DAS system is similar to geophones.