The Mountain Meteorology Group at the University of Utah is evaluating Windsond for their meteorology research. During one test, the sonde failed to detach from the balloon. They continued to track the balloon to an altitude of 9700 m MSL, at which point the sonde battery was drained. This is close to the altitude of the tropopause, the important point where the temperature reaches a local low point.
The last message before the sonde shut down was transmitted at a distance of 49 km, where the sonde was still rising at 1.5 m/s and travelling at 17 m/s. This is a great result for the basic whip receiver antenna. The reception was becoming increasingly spotty towards the end and the contact wouldn’t be possible without the error-correcting code used in the radio link. The range could easily be improved a lot by using a directional antenna.
To reaching high altitudes on purpose, a bigger balloon would be used to gain a higher vertical speed and to allow the contained helium to expand the balloon further before the balloons bursts. A high-altitude radiosonde commonly use a balloon weighing 100 g, compared to the 8 g balloon commonly used for Windsond. Officially supporting high altitudes would also require proper testing of all components in a climate chamber.
I’m now doing all I can to avoid the mishap from repeating:
- Cut-down is done by heating a thin metal wire until it melts the wire tethering the sonde to the balloon. The duration of the heating will get progressively longer if the detaching fails.
- Before launch, the sonde will detect if the mechanism is broken to alert the user.
- There’s now support for backup cut-down hardware.
- If the sonde still continues to fail to detach it will eventually stop trying. That will save the battery from draining as it did this time. The balloon will eventually pop and with battery to spare it’s still possible to recover the sonde.