Day 9: Loads of data!

Nine days of the cruise are done and we managed to do 10 different seismic surveys – excellent progress! Since our last update we have continued with our range of seismic sources, including a DuraSpark surface sparker, deep tow sparker and GI airguns. We were careful to follow the protocol for marine mammal observation before and during the survey.

Three survey designs for GI airguns

GI gun deployment

Ship crew deploying streamer into the water for recording seismic signals

Careful planning and a super-efficient crew are making this cruise a big success. Following the GI gun survey we completed a Deep Towed Sparker (DTS) survey, which is high frequency seismic sparker system that can be towed to a depth of c. 500m from the sea surface. In our surveys, we limited the depth to c. 125m as we have a maximum water depth of around 160 m.

Deep towed Sparker

After the seismic reflection surveys we headed to the Mini-lander location to recover it from the water. On the lander we had fixed a passive acoustic recorder floating at a depth of c. 20 m above the seafloor. The aim of the acoustic recorder was to record all the signals that we had generated using different seismic sources. A big well done to University of Southampton undergraduate student Dan Ellis for successful programming the recorder to operate properly. The data look great. The lander signals are going to be very useful in processing of the seismic data (in technical language we have recorded what is known as the far field signature). The recorded data from lander shows echoes from seismic sources, ship noises, and noise from other sources in water – it records any sound in the vicinity!

Signal detected on the acoustic recorder showing Deep Towed Sparker signal and other ship signals. Top panel shows sound detected on the acoustic recorder, the bottom panel shows the frequencies of different arrivals.

After lander recovery, we started with the Airgun grid, but we had to halt the survey due to poor weather on 4th September.

Airguns into the water

Next on the cards is Ocean Bottom Seismometer recovery (hoping to recover all OBSs without losing none). The recording of swath bathymetry (seafloor topography), sub-bottom profiles (30m below sea bed) and echosounder (water column) have been going on throughout all the surveys. The profiles from the three recordings show very clearly the gas flares emitting from pockmarks and chimney structures into the water!

Echo sounder (EK60) showing gas flare (yellowish) from pockmark– each panel shows a different signal range

See you later with more updates 🙂

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