## 1 Introduction  
Following the indications of the European Commission in the context of the Integrated Maritime Policy inaugurated by the Blue Book (COM2007(575)), in the coming years, it is desirable to arrive at a system of integrated sea observation and forecasting systems for intermediate and end users (COM2009(544)) that provides data, products, and services to facilitate the management of coastal and marine environments, intervene in the presence of risks, implement security in sensitive areas, and provide visibility on the quality of the coastal and marine environment (EMODNET--European Marine Observation and Data Network). Therefore, expanding and optimizing the communication capabilities between oceanographic measurement instruments can bring significant improvements in the monitoring of ocean currents and search-and-rescue activities in the MediterraneanSea. In the specific case of research on marine currents, passive buoys (drifters: [1; 2; 3]) are transported by the surface movements of water or currents within the first few meters. The main types of research drifters are the SVP drifter [4], the CODE drifter ([5; 6]), and the CARTHE drifter [7]. They are designed for the study of ocean circulation, plankton dispersion, runoff dispersion, and oil spill modeling. They attempt to minimize Stokes drift and direct wind force (windage) while following the near-surface (from about 0.5 m to 10 m-deep) flow. There are also some drifters, such as the ARGOSPHERE type, designed for hydrocarbon spills that follow the currents in the first few centimeters of water. The usual communication method of these drifters is by satellite (IRIDIUM, Globalstar-SPOT, ARGOS), justified by the fact that they are designed to follow real-time large-scale marine currents, often very far from the coastline. Drifter designs that focus on the transport and dispersion of pollutants such as floating marine debris or oil spills typically have a lower drag area ratio and target the transport of material in the upper meter of water, taking into account wind- and wave-induced motions that primarily influence the transport, for example, of \"macro\"-plastics [8]. Recent developments of software and hardware technologies in the field of Internet of Things (IoT), pattern recognition, and sensing, offer the possibility to explore new ways to study Lagrangian ocean currents. The basic idea is to create an integrated system for the remote acquisition of marine data using a new conception of \"drifters\" that are much cheaper and logistically simpler than the current ones by exploiting the latest software and hardware consumer technologies. Very simple types of these drifters are marine litter trackers (MLTs) [9]. In effect, MLTs are objects representing different types of real \"marine litter\", such as wooden boards and plastic bottles of different shapes and volumes. The MLTs do not have the capacity to communicate with each other: they just contain optimized electronics/devices for GSM/LoRa (long-range) communication to land. The cost of MLTs is particularly low (some tens of euros) and they are especially suitable for monitoring marine litter discharged from rivers into the sea, which normally follows paths close to the coastline. Among the innovations introduced with MLTs, compared to other similar systems previously tested [10; 11; 12; 13], is the ability to record data so that, when connected to the GSM/LoRa network, data tracked offline can also be sent. Another key feature of these devices is that they are completely energy independent, with virtually unlimited autonomy, thanks to an appropriate onboard photovoltaic system, which is very small in size due to the very low power consumption of MLTs. The readily available technologies used for MLTs allow for the direct involvement of citizens in the acquisition process in this field as well as raising awareness of related issues (pollution dispersion and marine debris).