Description
The methods that will be applied to obtain information from earthquakes, infragravity waves, sea state (wave height and period), surface currents, ship noise and whale vocalizations were detailed in the workplan and methods section and will not be detailed here. Worth mentioning is that MODAS will expect the unexpected and “strange” signals identified on spectrograms will be investigated using the full power of DAS dense array of sensors. In the Azores fluid flow from sediments or volcanic activity might be at the origin of the unexpected signals.
Open source DAS analysis packages will be investigated and taken as benchmark for base comparison of system performance. Cloud based industry tested fast prototyping processing flows on python basis will be investigated and adapted to the geophysics use case in the MODAS project, as will be open software developed and tested in DAS monitoring and profiling applications.
From a general perspective, comparing DAS and subsea optical fiber communication, a stronger overlap of technology and methodology, and eventually convergence, would be desirable. This would allow for better economy of scale of sensing systems and better integration and networking with commercial communication systems. In order to pave the way towards convergence, we will apply numerical signal propagation methods and investigate to what extent these could support and improve the DAS data analysis. Based on open source technology, we will investigate and adapt a digital signal processing chain for optical communication signals, typically used for simulation and equalization of signals from optical communication transmissions, designed for high performance numerical computation and simulation of equalization of advanced data encoding and a variety of signal impairments. For signal equalization the package contains for example phase recovery using Viterbi-Viterbi algorithms, frequency offset compensation, and pilot-based equalization routines, including frame synchronization, frequency offset estimation, and adaptive equalization. Regarding impairments, it can simulate frequency offset, SNR, PMD, phase noise and transceiver impairments.
Expected results
This task will provide 1-year analysis of the DAS recorded signals that are relevant for the project: i) ground motion caused by earthquakes; ii) infragravity waves as proxy to tsunami waves; iii) sea state conditions (wave height and period); iv) whale vocalizations; v) natural and anthropogenic soundscape; vi) other phenomena. DAS strain data will be converted to ground motion and pressure and then compared to the OBS recordings (deployed and recovered in task 3) and to the land recordings on ADH seismic station operated by IPMA. Wave characteristics will be compared to the sea-level buoys data collected by CLIMAAT project. Surface currents will be compared to the ocean wave models run at IPMA.
Instrumental signals will be analyzed with respect to contribution of modeled traces of instrumental (emitter and detector) noise. Additionally, numerical optical fiber propagation models will be employed to investigate causal contributions to the seismic signal patterns and event signatures. Results are fed back to refine calibration and data analysis procedures.