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On 29.07.2019, on my way back from the Tomorrowland Festival in Belgium, I organized a trip to the KMI in Uccle to bring back my two Belgian ozone sondes and visit the institute and attend an ozone sonde launch.

The KMI has now had a continuous ozone measurement series of radiosonde ascents for almost exactly 50 years. Launches are always Mon, Wed and Fri at 11:30 UTC. ECC ozone sondes are used, since the middle of the 90s, before Brewer-Mast sondes were used.

In general a normal radiosonde, here a Vaisala RS41, is used for ozone sounding. The ozone measuring device is connected to this sonde, which consists of an electrochemical reaction cell, a sampling pump, a control board and the necessary batteries, and is connected in a polystyrene box. If you don’t already know it, take a look at the Vaisala Ozone Sounding Guide, which is very good and detailed.

The preparations on the launch day start with the electrochemical testing of the cell starting at 7:30 UTC. We reached the institute at 9:00 UTC and were immediately taken into the balloon hangar to inflate the balloon. 1200 g balloons from Totex are used, which are filled with hydrogen to a counterweight of 2400 g. The hydrogen storage is located about 30 m away from the balloon hangar and is connected to it via underground piping. When the takeoff volume has been reached (the balloon is a  considerable bit larger than a normal helium balloon from the automatic launch system despite the hydrogen filling), the balloon is tied up with cord and attached to the parachute. The balloon is removed from the filling device and attached to a weight, the cord between parachute and probe is measured and attached to the parachute.

Then we went on to the laboratory where the electrochemical preparations take place and which is located in the basement of the institute. This is where the ozone sonde supplies and the test station are located. During the preliminary examination for the next but one ascent, my sondes were handed over. For the staff in Uccle, it is okay if the finder opens the sonde to reduce the packing volume and to remove the batteries. The air intake hose is also replaced each time the sonde is launched.

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The tour continued in the attic, where the receiving station and the ground check station are located. Here I got the opportunity to program the sondes I brought with me to a different frequency.

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About 1 hour before the launch the ozone sonde is brought up for the groundcheck. The heating battery is attached and the motor battery is fixed in the battery compartment. Since Vaisala no longer distributes water activated batteries, Uccle switched to lithium batteries in spring as one of the last stations in western europe. Vaisala now supplies 2 9V lithium batteries instead of the water activated battery, which are already connected in series, fitted with the correct plug and glued shut.

A radiosonde is unpacked and placed on the groundcheck device. After the ground check has been completed and the correction values for the ozone sonde have been entered in MW41, the radiosonde is attached to the ozone sonde. The motor is switched on and the motor current is controlled. Now ozone is flown into the sonde again and the measurement is checked before the motor is switched off again. The probe is then placed on the roof to obtain the GPS fix. The paper documentation of the sonde is entered into an online form and stapled together. The sonde is completely glued shut using tape.

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15 minutes prior to launch, the values of the ground-based weather station are entered in MW41 and supplemented in the documentation. The sonde is brought into the balloon hangar and fastened with both cords (one serves for the improvement of the flight stability) to the long cord leading to the parachute.

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A second employee now exits the hangar with the sonde, and the assembly as a whole is brought to a nearby meadow. The balloon is risen gradually. Now was my moment: I was allowed to hold the sonde and wait until the time for the launch had come. Then I released the sonde on its journey, which took it west of Antwerp.

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I would like to thank Roger Ameloot, Roeland van Malderen and the whole KMI team for giving me this great insight into their work!

I had been waiting for my first hat-trick for quite some time, but until now there had only been two consecutive sondes. That changed when I was awakened on Wednesday morning by manoeuvre sonde from Baumholder who were just approaching my QTH. I quickly got out of bed and took the next train to Marienheide, where the first 0630Z sonde had just landed in the forest near Listringhausen. While I was waiting for the bus there, the next sonde already landed behind Marienheide.

After the position of the first sonde had been decoded at the bus stop, I went 2 km into the forest in the best weather, only to find out that the chute was hanging on the edge of the forest at a height of about 7.5 m, and the sonde was not visible. So the parachute was quickly caught and pulled down, and lo and behold – the robust DFM could be pulled over the treetops, and eventually abseiled.

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Further on to the second sonde, this time by bus to the Bruchertalsperre, there across the dam wall and this time about 3 km into the forest, beforehand the position was decoded. This time the parachute was hanging on a high spruce, which bordered on a spruce conservation, and I had to climb along the slope to the landing site. Again the parachute was just within reach of my pole, again the sonde could be abseiled. But this time I had to extend it’s string with the string of the previous one. New tool in the sonde backpack: DFM string.

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In the meantime the following sonde had gone down faster and had only made it to Nümbrecht. Short investigation on the way back revealed that the landing site could be reached by foot from the central “bus station” aka road with many branches and bus shelters, Homburg-Bröl in the southern county past Wiehl. Therefore quickly into the TH in Gummersbach to empty the now full backpack in my lab and refill my water bottle. The new “express bus” 302 took me there. The sonde had already stopped transmitting and was not visible in the clearing where the forecast saw it. I stomped a few steps into the high undergrowth, which was full of ferns, and saw the sonde as ready to be picked up on the ground. The hat trick was complete. So quickly back to the bus stop, where I could also stop three ticks from getting too comfortable on my calves… and another tool for the sonde backpack: tick card.

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When the way home was waiting for us on Monday, the forecast for the midday probe from Idar gave us reason to take a look over Koblenz, especially as we wanted to see the stream of the WWDC keynote at flynamic in Bonn in the evening.

While the sonde was on its way, the forecast predicted a landing south of Koblenz, we stationed at Vapiano and then took a short walk to the Deutsches Eck. Meanwhile the sonde fell very fast and didn’t even make it across the Rhine and landed near the A61 at Boppard.

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The last position was reached quickly, but the signal of the sonde could hardly be heard, let alone decoded. An apparently nearby BOS-Funk station also littered the spectrum with TETRA, which didn’t make things any easier. Only with a mobile Yagi increased to six directors it was possible to achieve anything. When the sonde was found, it was clear why: the antenna had buried itself in the soft forest soil and the sonde body was on top of it. The small red parachute and the big balloon remains hung in a nearby tree out of reach of the pole and could not be pulled down either.

Flynamic, nikcani and myself drove to the GPN19 in Karlsruhe over Ascension Day holidays. Of course the sonde hunting equipment was aloon board, one doesn’t know what might happens. And indeed, the Sunday midday sonde from Stuttgart landed at a reasonable distance southeast of Bietigheim-Bissingen, on a paddock behind a farm.

I was afraid that the on-time recovery of the sonde would be harder in the more fought-over Baden-Württemberg area than at my regular QTH, and therefore also registered the planned recovery at radiosondy. Unfortunately we didn’t met anybody spontaneously at the sonde. When we arrived about 90 minutes after landing, the sonde was active and was quite easy to salvage.

The sonde was on a path behind a farm, the big balloon remainings and the unopened parachute were situated behind an electric fence on a paddock, but could be pulled over.

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On 23.04. Jason, his dad and I went to Essen to watch a sonde launch live at the AutoSonde container. And we were not disappointed during the launch. After a visit to the nearby airfield and lunch we followed the sonde towards Gelsenkirchen Buir. The sonde fell very slowly and we could see the parachute during the landing approach. Unfortunately the sonde landed in a high deciduous tree above a dog school. On the way back we stopped at the landing site of the previous night sonde, whose finders happened to be in the garden. So Jason came to his first own sonde.