Description
The OBS will record continuously ground motion and pressure variations at 250 Hz sampling rate to allow for the recording of the wider set of signals as possible, from low frequency infragravity waves to whale vocalizations up to 100 Hz. This frequency range includes several typical notes produced by fin whales, blue whales and sei whales, all species that have been observed in the Azores.
Since DAS is a directional sensor it is important that the orientation of the seismometer on the seafloor is acknowledged. The orientation can be inferred from the location of frequent earthquakes in the area that are to be expected to be recorded over the 12 months recording period. Time synchronization is also critical, and this will be performed by comparing the sensor clocks with a time reference before and after deployment. The true ground motion and true pressure variations will be recovered since the system response is well known.
The preprocessing of the data after instrument recovery comprises data conversion to daily files in miniseed format, one file for each channel, and evaluation to recover sensor orientation on the seafloor.
will analyse data obtained in Tasks 1 and 2 to determine the most important sources of variability in fin whale vocal behaviour, estimate context-specific vocalization rates (i.e. number of calls per unit time) and calculate the relationship between whale density (number of whales present in the area) and call density (total number of calls recorded). Conversion of sound density .
Expected results
This task will provide 12-month data recorded by two Ocean Bottom Seismometers (OBS) equipped with one 3 component seismometer and one broadband hydrophone. The OBS will be deployed close to the DAS submarine cable so that ground motion and pressure data recorded by the sensors can be compared to DAS data with the objective to calibrate (task 5) and fine tuning the processing routines (task 4). The deployment period will overlap the DAS recording period.