I’ve been interested in radiosondes since I learned about them years ago while watching a teardown of one online. Twice a day, NOAA in the US (and other weather bureaus across the world) launches high-altitude balloons with devices called radiosondes attached. These radiosondes report temperature, humidity, altitude, and GPS coordinates. Using this data, the weather service can get a profile of the winds aloft, as well as important data about temperature and humidity levels which help predict the weather. As these radiosondes transmit their data openly, you can track and receive the data yourself using this Radiosonde Tracker, which can lead you right to the radiosonde after it lands!
Why would you want to do this? Well, the thrill of the chase is a big part of it. By using the location of the balloon and the estimated winds, websites like sondehub can help predict where it might land. The landing spot changes based on how long the balloon stays aloft — they are designed to burst when they reach a particular altitude, but there is a lot of variance, and even a difference of a minute can make a large difference in the landing location. So it takes practice and persistence to locate one.
Secondly, you are helping recover what is essentially litter. Some weather bureaus request that you return it, but it’s up to you. Many can’t or don’t re-use radiosondes, so you’re free to tinker with it. They just generally ask that you properly recycle the battery. The batteries in radiosondes are interesting in themselves. They are in a very narrow niche: a product that needs to be shipped with a battery, but that might sit around for long periods of time, and have to be ready to go and reliable for launch time. In many cases, radiosondes use water-activated batteries. Simply add the required amount of water, let it soak into the cells, and you get a battery that will output a few tens of milliamps at just under 3V.
This device comes with firmware that will help you track nearby balloons, showing their GPS coordinates. Optionally, you can flash (or ask the seller to flash) a firmware called MySonde Go, which enables Bluetooth connectivity so your phone can display the coordinates on a map and give you more information. With the included antenna, you can track radiosondes that are over 100 miles away! It has a built-in 18650 rechargeable battery, and comes with a nice 3D printed case to protect it.
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