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An overview of the flight launch, balloon burst and landing. Watch the epic landing in a river and recovery of the flight payloads using a boat:

Flight launch preparations (filmed by Martti OH1ON), audio in Finnish only:

The idea behind choosing the flight transmitters was to make tracking of the flight a community effort, where anyone — with suitable, cheap radio receiver hardware — could participate in tracking the flight. This time we also included a transmitter for photographs, as while it is great to be able to track the flight of a high-altitude balloon on a map, it is even more interesting to be able to see photos taken from the balloon — in real time, during the flight!

In addition to transmitting photos from the flight, we included a radiation sensor in the flight as an experiment to measure the level of ionizing radiation at high altitudes. Measuring radiation intensity on a high-altitude balloon flight is particularly interesting, because the intensity is considerably higher at high altitudes than at ground level where the atmosphere absorbs much of the radiation. The sensor readings could be monitored by anyone tracking the flight.

The transmitter devices were a Vaisala RS41 radiosonde transmitting the balloon GPS position and sensor telemetry data, and a special image transmitter sending photographs taken during the flight.

An important detail regarding the way the receiver software for both the position data and the images work is that they send the received data to centralized services, which then make the data available on the Internet for anyone to view.

These centralized services are:

We wrote down detailed instructions on how to set up a receiver station for each type of transmission and also provided links to the different websites that could be used to follow the flight even without a radio receiver. We advertised the flight on several different social media platforms, mailing lists and instant messaging groups, so that as many people as possible would know about the flight and could participate in tracking it.

In the end we had 25 Horus 4FSK stations in Finland tracking the balloon position, which is a great achievement, and a couple of Wenet image receiver stations! There were also some APRS stations tracking the flight.

The weather forecast for the launch weekend was quite challenging, because there were a lot of rain areas nearby and the winds in the upper atmosphere were strong. However, Saturday morning September 2nd was sunny and calm, so we agreed to launch the balloon at 9:00 AM local time. We were at the launch site already before 8:00 to start preparations for the flight. The next rain area would reach the launch site around 11:00 AM, so we didn’t have time to waste!

We calculated the required lift for the balloon using the Sondehub burst calculator tool. We used a Hwoyee 600g latex balloon for the flight, and the weight of the flight payload (transmitters and parachute) was also about 600g. We chose the desired ascent rate to be 5 m/s, so that the flight would not take too long and the balloon would not fly too far from the launch site. Our goal was also to reach an altitude of about 30 km — by using more hydrogen gas the balloon would burst at a lower altitude.

The burst calculator tool (above) showed an altitude forecast of about 29 kilometers and a required lift of 1431 grams. We weighed the required amount of water with a regular kitchen scale in a container and filled the balloon until it was able to lift the container.

We launched the balloon from the Miemala area in Hämeenlinna, next to the OH3AA clubhouse. The core team responsible for the launch was Jari OH3UW, Sami OH3EYZ and Mikael OH3BHX. Martti OH1ON arrived to film the launch. Club members Harri OH3YG and Timo OH3CT were also watching the launch.

The approaching rain front produced some beautiful cloud formations. There is no accurate information about the altitude and location of the images, because the GPS receiver of the Wenet image transmitter did not work.

You can click a photo to display a larger version of it.

It is worth noting that the Raspberry Pi v2 camera does not distort the horizon much, because it is not a wide-angle camera, so the curvature of the horizon in the images is quite realistic!

The flight path forecasts from the predict.sondehub.org flight prediction service were again quite reliable. The prediction indicated that the maximum altitude for a 600g latex balloon and a payload of about 600g with an ascent rate of 5 m/s would be just over 30 kilometers. The upper atmosphere winds on the morning of the launch day would take the balloon to the northwest direction, towards the city of Tampere. The final forecast on Saturday morning showed the northwest part of the city of Nokia as the landing site, while earlier in the week the forecasts predicted the Kulju area as the landing site. The challenge in landing in the Nokia area is the large number of water bodies, which would make it more likely for the balloon payloads to fall into the water.

The balloon reached an altitude of 32.6 kilometers above Lempäälä and continued its descent towards Nokia. The flight payload fell into the river Nokianvirta, west of the Melo hydropower plant, contrary to the predictions and our expectations. However, the transmitters did not turn off when the payloads fell into the water, as the styrofoam enclosures caused them to float well.

The flight payloads were recovered from the river Nokianvirta by Mikael OH3BHX (from Hämeenlinna), Jouni OH3CUF (from Tampere), Jarmo OH3BSG (from Ylöjärvi) and Jari OH4NDU (form Lempäälä).

With help of the GPS position data, we ended up driving to a road near the river bank, west from the Melo hydropower plant. However, the shore was mostly steep and wooded terrain, so we walked to the nearest cottage we spotted. Near the cottage we met Tommi Lahdenperä, the resident of the house nearby, who immediately agreed to help us. We were able to look out to the river from his pier, from where we saw the balloon payloads floating a few hundred meters away.

Tommi took us with his motorboat to the other side of the river where the balloon payloads were floating, and we were able to recover the devices and the parachute intact. The devices were not damaged at all, only the Raspberry Pi camera of the Wenet transmitter was slightly wet.

Amateur radio club OH3AA would like to thank everyone tracking the flight and especially those who helped in the recovery of the flight payloads!

The RS41 radiosonde had two additional sensors attached: a Bosch BME280 sensor for temperature, air pressure and humidity, and a RadSens v2 radiation meter based on a Geiger tube. The radiation meter provided readings on the "micro-Roentgens per hour" (µR/h) scale.

The following graphs visualize the sensor data from the flight. The graphs are available on the SondeHub Grafana dashboard for the flight for anyone to view.

The OH3AA club receiver was a long cross-yagi antenna with a preamplifier. We used the same yagi to receive both the Horus and the Wenet transmissions. The technical specifications of the yagi were excellent for receiving Wenet images, but for some unknown reason the Wenet receiver station did not work at all. There was a problem with the receiving equipment or some possible local transmission was interfering with the Wenet reception.

Below are statistics from the stations that participated in tracking of the OH3HAB #7 flight.

You can also follow me on Twitter/X at @mikaelnou and on Mastodon mikaelnou@mastodon.online where I will publish content about radiosondes, high-altitude balloons and amateur radio in general!