Radiosondes are a combination of a balloon and a small package of instruments. They are used to measure the atmosphere. When released, the radiosonde travels way up into the air, measuring as it goes and sending the information (height, pressure, temperature, humidity, horizontal wind speed, horizontal wind direction and vertical wind speed--at different heights) back to the ship. In areas where there are not very many weather obsevations (such as at sea), the information that radiosondes collect can improve the forecast and our understanding of the weather systems.
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