The wind blew in north-easterly direction which placed the predicted landing point of the ozone probe near Memmingen. Near to Stuttgart would have been something else but I do not think the probes launched from Peißenberg will get much closer.
I got up really early and went to Memmingen. The timing was good, I was in the predicted landing area in time. The prediction shifted a little bit, and I followed. When the probe landed next to Niederrieder Strasse, I entered the position into google maps and realized that I was 700 meters away.
[11515] (L4743762) (2018-09-03) Mo 07:41:51.500 lat: 48.02857 lon: 10.24924 alt: 663.5 (d:1.0) vH: 0.2 D: 146.0° vV: 0.2 DOP[31,29,16,4] 3.8
I assumed it to be an easy catch and drove over. When I arrived I saw to my disbelief already somebody winding up the thread and collecting the probe. This is how I met Rolf (DF9DQ). We chatted a little bit and he showed me his impressively small gear that has the maturity of a product solution: His receivers have the size of a USB sticks and are connected via Bluetooth to his mobile phone. Using the received positions with a navigation program on his mobile gives him a high situational awareness. As antenna he uses moxon antennas that are directly hooked up to the receiver (without cables). That makes his solution mechanically very robust. And the moxon antenna has enough directional sensitivity to also use it for direction finding. The details of his project can be found here:
https://github.com/einergehtnochrein/ra-hardware/wiki
And I learned that Rolf had also had located the probe in Munich on August 13th about 2 hours earlier than myself and collected the probe at Kröbelbauer on August 20th.
Rolf was kind enough to give the probe to me as he had already collected in the order of 50. When I came back, the sight of the probe put a big smile into Felix’s face…
We dismantled the probe and looked up the measurement principle: To measure the ozone, the probe pumps in air through potassium iodide solution. The ozone splits the potassium iodide which generates a current between 2 electrodes, one made from silver and the other from one platinum. The strength of the current reflects the ozone concentration and is transmitted via an RS92 probe attached on the outside of the probe. For a description of the measurement principle see also http://www.wetterklima.de/umwelt/ozon/profil.htm (the article is in German).
