A short diversion from the discussions of the atmosphere! Bjorn asked Karen and I to put together a short email to summarise how we plan to use our Seaglider and Autonaut to take ocean observations during the EUREC4A field campaign next year, so I thought I would summarise our involvement in the project, the two vehicles we will deploy, what they measure, and what we hope to study.
Our involvement in EUREC4a is due to a chance meeting at EGU last year. We were looking for an opportunity to trial a prototype mechanism that would enable a surface robotic vehicle (Autonaut) to tow a subsurface robotic ocean glider (Seaglider) to a region of interest and then release it. The goal is that these two vehicles could then be sent to remote parts of the world to take simultaneous surface and subsurface ocean measurements. A long term goal is to use this system in the oceans around Antarctica, but a tropical campaign seemed like a more friendly starting point, and the opportunity to collaborate on EUREC4A was perfect. We are grateful for the opportunity to be involved, and hope that we can provide useful oceanographic observations to complement what is already being done during the campaign.
The Autonaut is a robotic surface vehicle, around 5 m long, with a 1 m high mast. It has solar panels to recharge the scientific instruments, and its propulsion is generated by waves acting on horizontal fins. It can move at around 1-3 knots, depending on the wave height. Our Autonaut will be equipped to measure shortwave and longwave radiative fluxes, along with wind speed & direction, atmospheric temperature and humidity (all at ~ 1 m above sea level), and sea surface temperature (around 0.3 m below sea level). From these, we plan to calculate net heat flux. One of our goals for this mission is to validate these measurements against other observations from nearby ships.
The Seaglider is a small robotic submarine, around 2 m long, that is powered by buoyancy, and has wings to enable it to glide (at a slope of around 20-30° from horizontal). Our Seaglider will most likely dive to around 250 m every hour or so, but can take measurements to 1000 m. It is a bit slower than Autonaut (maximum speed < 1 knot). It is powered by lithium batteries that should last around 3 months, depending on how much we use the sensors and how frequently we take profiles. The Seaglider will take subsurface temperature and salinity measurements, and we may also measure subsurface photosynthetically active radiation (PAR), dissolved oxygen and chlorophyll fluorescence.
We are interested in studying how variability in surface fluxes and boundary layer meteorology influence the ocean surface mixed layer. As a result, we plan to keep the two vehicles close together, possibly with Autonaut going in circles around the Seaglider. We will deploy the two vehicles from Barbados at the start of January 2020, and will recover the Seaglider from one of the ships (most likely METEOR, I think) at the end of the campaign. We expect to send the Autonaut back to Barbados. We hope to spend some time near to a ship to calibrate and verify our measurements, but other than that, we are flexible with where we deploy, and what we do. If you have suggestions or ideas for where we send these platforms or what to study, please let us know - Karen will be at the meeting in Hamburg next week, so you can talk to her there, or you can email us.