Many years ago, I did a radiosonde chase down in Mt Gambier to recover one of the then-new (to us, anyway) Vaisala RS92-SGPA radiosondes. These were being launched by a Vaisala AUTOSONDE station, installed as part of the Bureau of Meteorology's (BOM) effort to make the Mt Gambier site mostly unmanned. Back in 2011, Adelaide Airport was still launching the old 'analog' RS92-K radiosondes, so these newfangled digital radiosondes were a rare thing to us!

Nearly seven years later the RS92-SGPA radiosondes are obsolete, and the new and exciting thing is the Vaisala RS41, which as a friend put it, is 'the STM32 devboard that falls from the sky'. The Bureau of Meteorology are currently in the process of transitioning to the new model, however at the time of writing this post only the Autosonde launch stations (generally in regional areas) had been cut over. Our interest in these sondes is in the potential for re-using them as Project Horus telemetry payloads, particularly if we can reverse engineer the various onboard weather sensors.

So, almost seven years after recovering a shiny new RS92-SGP, a few friends and I decided to head to Mt Gambier over the New-Year break and try and get ourselves a shiny new Vaisala RS41! I was joined by Michael Wheeler and Geordie Millar, both fellow radiosonde hunting enthusiasts, making the trip over from Melbourne. Mt Gambier is about a 5 hour drive away for home for all of us, so this was a fairly serious effort to get one radiosonde!

Originally we had planned to spend a week down at Mt Gambier chasing as many sondes as we could. Unfortunately, a discussion with an engineer at the BOM confirmed that regular launches only occurred twice a week, on Mondays and Thursdays. So, we targeted the sonde launch on Monday the 1st of January 2018 - New Years Day.

In the week leading up to the launch the predictions were looking at bleak, with a landing in the Grampians National Park a real possibility. Thankfully by the day before the launch the weather models had settled for a landing somewhere near Dunkeld, just to the South of the Grampians. Still, this was a 160km drive from Mt Gambier, across state boundaries, making this possibly the longest radiosonde chase we'd done in some time.

We departed Mt Gambier around 9:30AM, and had crossed the border into Victoria by the time we first detected the radiosonde signal on 402.3 MHz - just a few minutes after launch. Using the radiosonde_auto_rx software, the payload position was uploaded into both APRS-IS (visible on aprs.fi), and the Habitat High-Altitude Balloon tracker, allowing members of the local South East Radio Group to follow along with the chase.

The radiosonde flight was fairly standard - 5 m/s ascent rate, and a burst around 27km altitude (actually 26.776 km) while over Hamilton, Victoria. The payload descended (much slower than we were used to, likely due to the lighter payload weight) to a gentle landing 10km to the South-East of a small town called Glenthompson. Unfortunately we were not close enough to watch this one land, but did receive data all the way down to the local ground level of 223 metres.

After a brief chat with the property owners, who were quite surprised that a balloon had landed on their property, we were given a lift to the landing site. A short walk through a field and the payload was found!

A few stats on the flight:

First Received Signal: -37.74643, 140.78701, 723m ASL

-37.74643, 140.78701, 723m ASL Flight Duration: 2 hours, 42 minutes

2 hours, 42 minutes Maximum Altitude: 26776 metres ASL

26776 metres ASL Landing Location: -37.71748, 142.64814

-37.71748, 142.64814 Total Distance Driven: 392 km

We now eagerly await the cut-over to these sondes at our home launch locations (Adelaide & Melbourne), apparently occurring sometime early in 2018.

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