We launch four of these each day. The balloons are filled with helium and attached to a sensor that records the pressure, humidity and temperature in the atmosphere on their way up. In addition, the sensor has GPS, and therefore the wind speed can be calculated based on the drift. The sensor sends the data back to the ship, and the data is used to improve global weather and climate forecasting models. The balloons can reach an altitude of 20 km before they explode and fall down.
PS: Can you spot the sun dogs on each side of the sun in the background (which I incorrectly called sun halos some days ago)? More pictures here. We got an explanation about how they form from, Ian Brooks, head of the meteorology work package on board, some days ago. According to him, sun dogs are commonly caused by the refraction of light from plate-shaped hexagonal ice crystals either in high and cold cirrus or cirrostratus clouds or, during very cold weather, drifting in the air at low levels, in which case they are called diamond dust. Diamond dust how beautiful is that!?