Boundary Layer Pressurized Balloons are small balloons that keep a constant volume and thus fly at a nearly constant density level, acting as Lagrangian tracers of air particles and meteorological platforms. Their envelopes are manufactured by ZODIAC Int. under CNES supervision; with a 2.5 m diameter, they are made of three-laminated polyethylene of 120 microns thickness. Balloons are inflated with Helium at a nominal surpressure of 120 hPa at flight level. Total mass is around 9 Kg.
The BLPB can fly between the surface and 830 hPa, depending of its ballast. As long as the surpressure is maintained the volume remains constant; except for small thermal fluctuations, mainly due the diurnal cycle, inducing small altitude oscillations. Historically, the most serious problem encountered by these balloons is due to the water loading under heavy rain or when the envelope temperature is below the dew point temperature, specially by radiative cooling during night. To prevent this the BLPB envelope is treated with a hydrophobic coating. Also the metallic band attached to the equator of some of the balloons serve to difficult more the adherence of water in case the balloon land in the ocean due to rain.
Scientific instrumentation onboard includes pressure, humidity and temperature sensors and a 3D GPS from witch the balloon velocity can be deduced. This gondola is located in the top of the balloon. Helium pressure and temperature are also monitored. Meteorological data are recorded on board every 10 seconds then averaged on a time interval between 10 seconds and a few minutes. Data are transmitted periodically (at flight level every 20 minutes) by means of the Iridium communication system located in the control gondola attached to the lower pole of the balloon. The balloon flight can be stopped either automatically if the balloon approaches a specific zone or by a remote command. Both gondolas are connected each other by a radio link to avoid wiring the balloon envelope.
This balloon flight was part of a campaign denominated BAMED (Balloons over the Mediterranean sea), part of the HYMEX scientific program aimed to obtain a better understanding, quantification and modelling of the hydrological cycle in the Mediterranean, with emphasis on the predictability and evolution of extreme weather events, inter-annual to decadal variability of the Mediterranean coupled system, and associated trends in the context of global change. This particular balloon differed from the ones launched during the rest of the campaign as it was a technological test to prepare the future CHARMEX campaign. Designed to fly at an altitude of 2400m, the balloon has been launched depressurized.
Balloon launched on: 2/20/2013 at 14:18 utc
Launch site: Candillargues, France
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Super Pressure Balloon
End of flight (L for landing time, W for last contact, otherwise termination time): 2/20/2013 at 21:00 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 6 h 40 m
Landing site: Between Corsica and France, Mediterranean Sea
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