Mermaids - Mobile Earthquake Recording in Marine Areas by Independent Divers - to Mariscope.

Abstract:

Mermaids are floating seismometers. The first generation used Argo floats developed for oceanographers to measure temperature and salinity. The Mermaids drift under water at about the speed of USArray and share with USArray the ability to cover a large surface. They record teleseismic P waves for events above magnitude 6.5 under noisy conditions (Indian Ocean), well below magnitude 6 under mild conditions (Mediterranean, Pacific). There are occasional recordings of PKP and PP waves. Local events can be seen down to magnitude 2. They are a perfect, low expensive and maintainable modern tool to fill the gap for monitoring the ocean. Ten mermaids have been launched May 2014 near the Galapagos to provide seismic information for deep tomography of the plume, whereas three of the Mermaids in the Mediterranean are currently being deployed/redeployed in the Ligurian Sea. These are the first launches with a purely scientific goal (as opposed to 8 earlier test deployments). Using the experience with the first fleet of prototypes, a new version is being developed. These are long-lived (five years), reach deeper (3000 m), multidisciplinary (up to eight instruments). The basic model also provides temperature and salinity data to facilitate co-financing with oceanography. In a more advanced version, it will be fully programmable by the scientist using them, and will have the ability to adapt software during missions using two-way satellite communication. If deployed in a dense array (e.g. rapid response) they obtain relative locations by sending out chirp signals between each other, surfacing from time to time for data transmission and to obtain a location and drift via GPS. They will have a "landing" capability to stay at location and monitor aftershocks while surfacing regularly for data transmission. For solo drifters, a magnetometer and a bathymetry sounder will assist in constraining the trajectory at depth.
The first tests of seaworthiness of this second generation Mermaid have taken place, and a version for seismologists will be available early in 2016. Software development of the more advanced features is still under way.