Surface deployment of DAS systems: Coupling strategies and comparisons to geophone data
Surface deployment of DAS systems: Coupling strategies and comparisons to geophone data
复制标题
DAS 系统的地面部署：耦合策略以及与地震检波器数据的比较
DOI：
10.1002/nsg.12232
复制
发表时间：
2022
影响因子：
1.6
通讯作者：
Harmon N
中科院分区：
文献类型：
--
作者：
Harmon N
分布式声学传感 (DAS) 系统是一项最新技术发展，用于在广泛的频率范围内进行地震观测，具有多种应用。通常，光纤电缆埋在地下或用水泥固定在井套管中，电缆与地面良好耦合。在需要快速测量和最小化地下干扰的区域中，快速和临时的地面部署电缆具有巨大的潜在用途。然而，光纤与地面之间的适当机械耦合对于临时表面部署仍然是一个挑战。在这里，我们测试了部署在草地上的 DAS 系统的四种不同的耦合策略，包括未耦合、在张力下固定在地面、通过地毯施加压力以及通过沙袋施加压力。我们将 DAS 数据与垂直分量检波器数据和估计的水平检波器数据进行比较，以评估 DAS 地面运动记录的保真度。我们发现完全解耦的光纤能够记录距震源约 10 m 的地震能量，而固定和加权的光纤则记录数十米以外的信号。 DAS 记录与多道地震系统估计的水平位移记录相比具有优势。 DAS 系统采集的信号相位与地震检波器采集的信号相位非常一致，但某些频率下的绝对幅度存在高达两倍的不匹配。我们对耦合 DAS 数据执行多种标准分析技术，包括表面波的折射和多通道分析。最后，使用多道地震系统估计的水平分量确定耦合 DAS 数据对地面运动的仪器响应。例如，如果多组件地震检波器不可用，DAS 系统的地面部署可为标准垂直地震检波器部署提供一组补充观测。此外，与地震检波器相比，DAS 在部署速度和易用性方面也有一些优势，具体取决于所使用的耦合策略。
Distributed acoustic sensing (DAS) systems are a recent technological development for seismic observations over a broad range of frequencies with a wide variety of applications. Typically, fibre‐optic cables are buried underground or cemented into well casings where the cables are well‐coupled to the ground. Quick and temporary surface deployment of cables has great potential utility in areas where rapid surveying and minimal disturbance of the subsurface are desired. However, proper mechanical coupling between the fibre and the ground is still a challenge for temporary surface deployments. Here we test four different coupling strategies for a DAS system deployed in a grassy field, including uncoupled, pinned under tension to the ground, weighted down by carpeting, and weighted down by a sandbag. We compare the DAS data to vertical component geophone data and estimated horizontal geophone data to assess the fidelity of DAS ground motion recordings. We find a completely uncoupled fibre is capable of recording seismic energy up to ∼10 m away from the source, while the pinned and weighted fibre record signals over several tens of metres. The DAS recordings compare favourably with the estimated horizontal displacement records from the multi‐channel seismic system. There is a good agreement between the phase of the signals acquired by the DAS system with that of the geophones, but there is a mismatch of up to a factor of two in the absolute amplitude at some frequencies. We perform several standard analysis techniques, including refraction and multi‐channel analysis of surface waves, on the coupled DAS data. Finally, the instrument response of the coupled DAS data to ground motions is determined using the estimated horizontal component from the multi‐channel seismic system. Surface deployments of DAS systems provide a complementary set of observations to standard vertical geophone deployments, for instance, if multi‐component geophones are not available. Also, there are some advantages in speed and ease of deployment of DAS in comparison to geophones depending on the coupling strategy used.