Weather balloons

Twice a day, every day of the year, weather balloons are released simultaneously from almost 900 locations worldwide. The balloon flights last for around 2 hours, can drift as far as 200 km away, and rise up to over 100,000 ft. (about 30 km) in the atmosphere! Weather balloons, which are made of latex or synthetic rubber (neoprene), are filled with either hydrogen or helium. An instrument called a radiosonde is attached to the balloon to measure pressure, temperature and relative humidity as it ascends up into the atmosphere. 
By tracking the position of the radiosonde, we can also calculate wind speed and wind direction.
The radiosonde is powered by a small battery. A parachute, attached to the end of the balloon, allows the radiosonde to fall slowly to the ground at speeds less than 35 km/ph after the balloon bursts. Each radiosonde contains a mailing bag and instructions on what to do if you find one. About 20% of the 657,000 radiosondes sent up each year worldwide are found and returned. That's a lot of litter that can potentially kill previous wildlife. 
Pic: Mandy Beaumont, April 2019, Terrey Hills