With a cost-to-science ratio of a few hundred rand in parts and an amateur radio licence, a hobbyist can generate months of genuine atmospheric data from the stratosphere, data that is publicly archived and can be used by researchers.
But I am putting the cart before the horse. Let me first explain what a Pico balloon is.
Pico balloons are small, super-pressure balloons that carry lightweight trackers into the stratosphere. The stratosphere is the second-lowest layer of Earth's atmosphere, located directly above the troposphere and below the mesosphere, extending from about 10 to 50 kilometres above the Earth's surface. It is distinguished by its dryness, lack of weather turbulence and the presence of the ozone layer.
These balloons can stay aloft for months, circling the Earth multiple times. They are typically filled with helium and carry a payload weighing less than 20 g. Most Pico balloons are solar-powered by a small solar panel. Batteries would be far too heavy, so the only disadvantage is that they transmit data only when in sunlight.
The Pico balloon community is essentially building a distributed, citizen-operated global sensor network, filling gaps that government weather agencies simply cannot afford to cover. Pico balloon payloads generally consist of a standard GPS receiver, altitude sensors and small radio transmitters that send data to a tracking network.
They float within jet streams. Wind speed and direction are inferred from GPS data transmitted back to Earth via WSPR telemetry, creating a continuous global picture of upper-troposphere and lower-stratosphere wind patterns that would be difficult and expensive to gather any other way.
WSPR stands for Weak Signal Propagation Reporter and is commonly pronounced "whisper". Some Pico balloons venture into the polar regions and, during the June solstice, can remain in constant sunlight while reaching extreme Arctic latitudes.
Balloons orbiting over remote oceans and polar regions are particularly valuable, since weather balloons launched by meteorological services do not consistently cover these areas. These flights traverse some of the most data-sparse regions on Earth, and their primary contribution is tracking long-duration stratospheric air movement, with additional temperature, humidity and pressure data depending on the onboard sensors.
Long-duration platform experiments
Flights lasting many months allow the study of electronics reliability in extreme cold. In these conditions, batteries degrade and solar panels age faster.
Long-duration Pico balloons are particularly useful for studying stratospheric circulation stability over extended periods because conventional weather balloons remain airborne for only a few hours. This is a unique niche where amateur experimentation can contribute meaningfully.
There are, however, realistic limitations. Despite their value, Pico balloon measurements have important constraints. Sensor calibration is often poor, payload orientation can introduce bias, such as solar heating effects, and altitude is not tightly controlled, resulting in inconsistent measurement standards.
As a result, the data is best suited to trend observation and trajectory analysis rather than precision meteorology.
Weak Signal Propagation Reporter network
The radio transmitter (WSPR beacon) is a low-power Pico PI with a temperature-controlled crystal oscillator, which must be very stable. The Pico PI is switched on only when the voltage exceeds a threshold. If it were connected directly to the solar panels, it could enter an unstable operating state.
The antenna is a half-wave dipole. WSPR is a great way to monitor the balloon because tens of thousands of amateurs have automatic WSPR receivers listening 24/7. Each time a valid WSPR message is successfully decoded, it is uploaded to the WSPRnet website.
The WSPRnet website provides a simple user interface for querying the database, a mapping facility and many other features.
Not all balloons use WSPR as a means of telemetry. Some use other systems, such as the Automatic Packet Reporting System (APRS). The key thing about WSPR is that it is extremely sensitive. It can detect signals down to -28 dB below the noise floor. The transmit power of the balloon can be as low as 20 milliwatts.
Pico balloons are more than just a hobby. Stewart Clark ZR1WT discussed their scientific value and global tracking capabilities during a presentation at the recent South African Radio League Technical Symposium. His presentation, "Telemetry via Repurposed WSPR for Pico Balloons", can be viewed on YouTube.
Email: hans@comsa.africa
