I’ve had an interest in weather balloons since the 1970’s. I couldn’t have imagined back then the amazing resources that are now available to monitor and track them and that I would so easily set up a monitoring station.
Why would you want to monitor radiosondes? I have found it is surprisingly interesting and it combines radio, electronics, meteorology, GPS, and a real-world treasure hunt. If you are persistent you could find a radiosonde that you can keep. Finally, it is not very expensive and you don’t need a huge amount of equipment.
In this post I will cover some basic information about weather balloons / radiosondes. I’ll also cover the amazing sondehub.org site that lets anyone view flight details using information provided by amateurs.
Weather balloons / Radiosondes
A radiosonde is a small, battery-powered instrument package attached to a weather balloon. They usually contain sensors to measure temperature, pressure and relative humidity. A GPS/GNSS receiver gets the balloon’s location, including altitude and this information is transmitted by radio back to a ground station. The balloons can reach altitudes of 16–35 km in the upper atmosphere before the balloon bursts and then it falls back to Earth on a parachute or a foil-coated cardboard target.
The onboard transmitter is very low powered. According to the Vaisala RS41-SG datasheet the ones us in our location have an output power of at least 60 mW although I think they can go as high as 100mW. Either way this is very low power, similar to home WiFi.
This is an AI generated image. It gives an idea of the different parts. After launch the radiosonde hangs further down below the balloon as a winder unspools.
Worldwide, weather balloons are released from about 1,300 locations each day. According to the Bureau of Meteorology, Australian releases about 42 weather balloons a day from 38 locations. That’s about 15,000 launches per year from Australia and its offshore territories, including Antarctica.
I’m not sure if it is the same in every country, but in Australia and probably many other countries you are allowed to keep the radiosondes if you find them. According to the Australian Bureau of Meteorology (BoM) They have a safety warning about inflated balloons as they can contain hydrogen gas, but otherwise, they ask that you let them know details of where it was found and that you can then dispose of it in your household garbage and recycling.
Monitoring balloons online – SondeHub
There are quite a lot of hobbyists interested in tracking and attempting to retrieve the radiosondes. A popular website sondehub.org is run by a group of hobbyists. It displays a map of the world and lets you monitor current and recent launches.
Icons
There are a few different icons shown. The main ones are:
- Grey circle: This is a known launch location. Click on it to see a list of launch times and historical launch details.
- Green circle: The location of a receiver that is sending data to Sondehub.
- Balloon: A balloon on its way. At this point it is not believed to have popped as it is not descending.
- Burst icon: These appear along the flight path and indicate when the balloon is expected to or has burst.
- Parachute: It is on it’s way down so it is assumed the balloon has burst and is floating down.
- Car: Someone is hunting for a radiosonde.
- Grey barrel: The radiosonde has been found
- Grey barrel with cross: A hunt for the radiosonde was ended without finding or recovering it.
The radiosonde balloons and parachutes
Clicking on a balloon expands its name in the lefthand list to show the balloons data. It shows the current vertical and horizontal speed, current and maximum altitude. At higher altitudes the temperate drops and often goes down to -60C. The transmission frequency, sonde type and details of last received stations are also shown.
The info is sometimes quite interesting. In this case this balloon was travelling at 320 km/h. This was over Melbourne, Australia and as its altitude is 12 km, I presume it was in the jet stream.
The Plot button on the left leads to a lot of details with graphs and logs of the balloon.
Chasers
The radiosondes only have limited batteries. The ones used here only transmit for around 5 hours. If their last recorded location is at altitude getting nearby with a receiver before the battery stops can help get its actual location.
The site encourages you to upload details of your hunt. Chasers appear with a car icon. Here we have Ferris Bueller doing some chasing on his day off.
Radiosondes that have been recovered display with a grey topped container. Clicking on them displays details with a note added by the finder.
Some just can’t be recovered. These have a red cross. The notes show some of the challenges of the hunt.
Historical data
As well as data about current flights, info about previous flights is also available. To see old flight details from a launch site, click on nearby launch sites and click Historical > Year: current one > Month: All to see historical activity.
Missing information
Remember this site and data is provided by enthusiasts. It’s easy to forget this as it is all so well presented. However, only information is available from non official receiving stations, so there is information missing. The info for this balloon demonstrates it. It was launched from Cobar NSW. There are no receiving stations in the area for monitoring. Looking at it’s path can appear as though it was tracked all the way, but until the balloon was at the point of the first arrow did it appear on the map. Once the balloon had burst and it had dropped to 9251m it went out of range again. The map shows projections of where it came from and is expected to land, but being 9000m in the air it could have deviated significantly from the projected path before it hit the ground.
This is the same balloon zoomed in further. Notice the line above is actually two lines. One is the monitored path and the other darker one is projected path.
Looking at all of Australia we can see there are fewer radiosondes on the map than launching sites (the grey circles). This is particularly noticeable in Western Australia. It’s not that those sites didn’t launch any, most launch each day, it just that monitoring stations are few and far between. What does this mean for you? If there are no existing monitoring stations near you, then adding one may show balloons that would otherwise not be monitored.
Monitoring station
It’s easier to set up a monoitoring station than I expecte. I found two main ways. The first one uses an SDR radio, commonly the RTL-SDR dongle, along with a Linux computer and the sondehub_auto_rx software. radio, commonly the RTL-SDR dongle, along with a Linux computer and the sondehub_auto_rx software. Another option uses a 433MHz LILLYGO TTGO ESP32‑based microcontroller board with rdz_ttgo_sonde software.
Setting up my own monitoring station
I’ve set up a station using an old laptop running Linux and a RTL-SDR monitoring.. You can read more about it in my next post.
Wrapping it up
It has been a very enjoyable project. Even my wife has enjoyed hearing the updates I’ve provided whenever there is a pause in conversation.
If you are interested the place to start is to look at sondehub.org and see what is going on in your area. Click on nearby launch sites and have a look at the historical activity.
There are lot’s of good posts about setting up a receiving station, but if you would like to read mine instead, check out my next post Track Weather Balloons: Monitoring with an RTL-SDR and Old Laptop
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