Читать книгу Distributed Acoustic Sensing in Geophysics - Группа авторов - Страница 51

The intrinsic SNR level of DAS data sets is lower than the corresponding geophone data sets because of, in part, the noise sources previously listed. However, in addition to those noise sources, there is an ambient noise floor present in the DAS recording system. One method to help improve this is to make repeated measurements and stack them together to increase the SNR. Another option is to use the increased number of data channels, which are typically every meter (although some systems record channels at less than a meter and others record every few meters). In contrast with conventional recording using widely spaced sensors, DAS data sets allow the ability to use neighboring channels to help improve the SNR by use of the redundancy of this information (Cheng et al., 2019). Typically, DAS channel spacing is considerably smaller than the seismic wavelengths to be measured; therefore, we do not expect rapid changes for the signal from channel to channel, allowing multi‐trace filters (e.g., median filters, running mean filters, etc.) to help improve the SNR. In addition, wave types (e.g. tube waves and ground roll) typically aliased in widely spaced sensor data can be more easily filtered with tools such as f‐k filtering acquired using DAS.