# MeLa: A Programming Language for a New Multidisciplinary Oceanographic Float
## 1 Introduction  
### Context  
Scientists all over the globe are permanently monitoring how our planet is changing. Knowing how much heat is stored in the ocean, how fast the sea levels are rising, and sea ice is melting, where living ecosystems are migrating in response to anthropic activity, are only a very few of the many essential questions to understanding the current state and changes in the ocean and climate. This information is critical for assessing and confronting oceanic and atmospheric changes that are associated with global warming and they can be used by decision-makers, environmental agencies, the general public, and in measuring our responses to environmental directives.  
Oceans have been monitored since the 19 th century [1]. The first oceanographic campaigns were done from ships with manually handled instruments. When electronics and batteries were emerging,instruments started to become autonomous [2]. For moored instruments, like moored lines [3; 4] or Ocean Bottom Seismometers (OBS) [5], they can now be deployed at sea for periods up to several months or years. However, the elevated costs of maintenance reduce our ability to deploy them globally. Alternatively, remote sensing based on satellites [6] allows for working at a global scale, but only has access to the ocean's surface and has relatively low spatial and temporal resolutions in comparison to _in-situ_ sensors.  
Nevertheless, satellite communication systems provide the necessary technology to locate and transmit in near real-time data that were collected by autonomous underwater vehicles. Such vehicles include profiling floats [7; 8] and wave gliders [9]. Both have different advantages and drawbacks, depending on the usage. Profiling floats are widely used in the Argo ([[https://argo.ucsd.edu/about/](https://argo.ucsd.edu/about/)]([https://argo.ucsd.edu/about/](https://argo.ucsd.edu/about/))) program with thousands of floats deployed world-wide [10]. They monitor the temperature and salinity from the surface to a depth of 2000 m to study the climate.  
Most of the floats follow the same operational cycle: (1) they descent to a depth programmed by the operator, (2) they park at this depth during several days or weeks and drift with currents, (3) they ascent to the surface, and (4) they measure their position with a Global Positioning System (GPS) receiver and send their data through a satellite link. One operational cycle is called a dive. The depth is regulated by changing the float density using an external bladder that was filled with oil. Measurements are done during any step of the dive by sensors integrated into the float to measure conductivity, temperature, depth, chlorophyll, nitrate, as well as acoustic signals and others.  
In more recent works, Underwater Passive Acoustic (UPA) measurements have been integrated into profiling floats for different monitoring applications, such as whale tracking in marine ecology [11] and above-surface wind speed or rainfall estimations in marine meteorology [12; 13]. In this field, a breakthrough has recently been obtained by seismologists with the Mobile Earthquake Recording Device in Marine Areas by Independent Divers (Mermaid), an autonomous float equipped with a hydrophone and a smart acquisition board able to recognize seismic sounds [14]. The recognition of seismic sounds allows it 1) to trigger the ascent of the float in order to obtain a precise estimation of the recording position and 2) to transmit only relevant seismogram data through the low bandwidth satellite link. So far, 60 floats have been deployed to image mantle plumes beneath hotspots in the Pacific Ocean.