Low-atmosphere drifting balloons: Platforms for environment monitoring and forecast improvement

Low-atmosphere constant-volume balloons offer unique observing capabilities, such as Lagrangian sampling of air masses and data collection for weather prediction. CNES, the French Space Agency, uses planetary boundary layer (PBL) balloons to serve as vehicles to carry potentially heavy scientific payload. The spherical envelope of BLPBs is made of a semirigid, multilayer plastic that was chosen to withstand the internal pressure of the balloon and limit the leaks of the carrier gas. The typical diameter of the BLPB is 2.5 or 2.6 m. The latter is used to reach higher altitudes and to carry potentially heavier weights. The carrier gas is a mixture of helium and ambient air that is tuned to achieve a predefined buoyancy corresponding to a f light level to carry potentially heavier weights. The carrier gas is a mixture of helium and ambient air that is tuned to achieve a predefined buoyancy corresponding to a flight level. The buoyancy of CNES BLPBs is set before launch thanks to precise tuning of the helium and air mixture that fills the balloon. BLPBs are almost ideal observational platforms for Lagrangian studies of chemicals and dust transport, especially as the scientific approach requires calm and dry weather conditions. It is worth emphasizing the balloons' ability to last for several weeks when their flight domain is sufficiently wide enough and when optimized power consumption allows for such a duration. BLPBs also proved able to cope with a variety of weather conditions and nonquiet weather situations, sometimes leading to an anticipated end of flight.