Design and Development of a Mini Ultralight Radioprobe System for Atmospheric Measurements

Clouds play a crucial role in the climate system of Earth and the climate change, by directly influencing the environmental temperature and the radiative energy balance of the planet. However, they are still considered as a major source of uncertainty in current climate models due to their complex characteristics, influenced by physical processes spanning from sub-meter to tens of kilometer in scales, making them difficult to study with both mathematical models and in-situ and laboratory measurements. Recently, several studies have underscored the important role of turbulence in cloud formation processes, enhancing the growth of water droplets within warm clouds. The development of new models and the advancing of computational capabilities paved the way for new methods of sounding atmosphere to validate those models. However, obtaining in-situ measurements inside warm clouds is exceptionally challenging due to the high variability in cloud properties. Among the existing instruments for in-situ atmospheric sounding, radiosondes have proven effective for particle tracking and sensing of physical quantities: specialised radiosondes, mounted on Lagrangian balloons, are able to track trajectories of air particles by taking advantage of the Lagrangian description of fluid flow. A novel radiosonde system designed to track small-scale turbulence was recently developed in Politecnico di Torino: this mini ultralight radioprobe is engineered to passively float within warm clouds and collect data on trajectory and thermodynamic quantities of its surrounding. Featuring a compact form factor (5mm x 5mm) and a low weight (9g without batteries), the radioprobe operates as part of a Wireless Sensor Network comprising multiple probes, communicating with a prearranged receiving station by using the physical layer of the LoRa communication protocol. This work presents a redesign and optimisation effort on the Radioprobe system, with a focus on the enhancing of both electronic architecture and firmware while reducing the physical board's overall size and weight. Starting from an accurate analysis of the previous design, the device was then developed by retaining all the successful features of the initial version of the Radioprobe. Key areas of improvements included interconnections and power consumption, as well as rearrangement of components and optimisation of the space on the board. The final system includes a set of sensors capable of measuring temperature, pressure and relative humidity of its surrounding. Addiationally, it features a highly integrated positioning system composed of a GNSS module and and an Inertial Measurement Unit. Data collection and preliminary processing are handled by a 32-bit microcontroller, and then transmitted by using the LoRa protocol managed by a specialized module, enabling data transmission to ground stations placed at distances in the order of few kilometers. The resulting prototype is both smaller and lighter, featuring a custom shape with maximum physical dimensions of 4mm x 3mm and a weight of just 3 g, excluding the battery. The final test campaign successfully validated the new Radioprobe's capabilities in terms of mission duration, power consumption, performance of RF sections and sensing capabilities. These enhancements make it well-suited for the mission its intended mission, thus opening the door to new and more embedded architectures for this type of radioprobes.