Technical flights at the Meteorological Ob- Ob-servatory Lindenberg

The first test flights with the new sonde were carried out at the Meteorological Observatory (MO) of the Deutscher Wetterdienst (DWD, german weather ser-vice) in Lindenberg, Germany. The prototype of the sonde PIOS A was started in January 2004 in order to check the overall functionality. After that flight, some technical details were changed and two improved sondes were launched in May 2004, PIOS B and C.

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6.1 Technical flights at the Meteorological Observatory Lindenberg 71

Figure 6.1: The balloon-preparation hall at the Meteorological Observatory Lin-denberg. The balloon to the right carries the PIOS sensor. The left balloon carries the ECC-sonde.

6.1.1 Meteorological Observatory Lindenberg

The village of Lindenberg is located about 60 km South-East of Berlin at 52.18^◦ North and 14.06^◦ East. The Meteorological Observatory Lindenberg (MOL) was founded in 1905. At that time systematic measurements of vertical profiles of wind, temperature and humidity were carried out with tethered balloons and kites. These measurements and their scientific analyses contributed to a descrip-tion of the vertical structure and the processes in the troposphere and lower stratosphere. Today, Lindenberg is an aerological station, with four regular ra-diosonde launches per day. Once a week, an electrochemical ozone sensor is started. The measurement programme is extended by numerous instruments de-tecting various atmospheric parameters. Lindenberg is also a reference station for worldwide radiation measurements and provides cloud- and radiation data for satellite validation.

6.1.2 Technical status and improvements

The controlling unit of the prototype sonde complied mainly with the description given in section 4.1.3. The communication rate between the spectrometer and the controlling unit was set to 38.4 Mbaud. The integration time of the spectrometer was reduced stepwise from 1000 to 20 ms.

A major difference to the current version of the sonde was the power supply.

The prototype (PIOS A, 21.1.2004) was equipped with one battery pack (10.5 V), connected to the controlling unit. The energy was distributed further to the spectrometer and to the radiosonde. In the second sonde (PIOS B, 12.5.2004), the battery pack (10.5 V) was connected to the radiosonde unit instead. From there power was distributed to the controlling unit and the spectrometer. The PIOS B solution resulted in a more stable voltage at the GPS-receiver. The GPS-receiver reacts very sensitive on short-time power oscillations. In the third sonde (PIOS C, 13.5.2005), the power was provided by two battery packs: (1) The radiosonde was supplied by three parallel connected 9 V batteries. (2) A 10.5 V battery pack supplied the controlling unit and the spectrometer.

To avoid electromagnetical interferences between the controlling unit and the GPS-receiver of the radiosonde, a shielding of the controlling unit was realised with some aluminium foil between the two styrofoam boxes for PIOS A. For the second and third flight, the polystyrene box containing the spectrometer and controlling unit was wrapped totally in aluminium foil.

For the first flight, the data were received by the Vaisala antenna of the MOL.

The antenna has eight poles, covering different directions. The best available element for signal reception is selected automatically by the telemetry receiver.

For all following flights, a yagi antenna was used, which needed to be directed manually towards the sonde.

Two of the sondes (PIOS A and B) were equipped with SD memory cards.

6.1.3 Technical aspects of the flights

PIOS A, 21.1.2004

The ground test of the sonde showed a very instable GPS-signal. Therefore, a provisorily shielding was applied by using an aluminium foil between the two polystyrene boxes. Meteolabor, the producer of the radiosonde, recommended to reduce the sending power of the sonde to 13 Dbm, instead of 20 Dbm (full power).

Before the launch, the data transmission worked and a GPS-signal was received.

During the ascent, the quality of the received radio signal decreased rapidly and ended in a total signal loss at 16.8 km altitude, about 70 minutes after launch.

Possible reasons for the telemetry problems may be the reduced sending power, as well as the power distribution in the sonde. The size of the power supply was calculated sufficiently for the entire system and should last for several hours under normal conditions. However, the hypsometer heating device may have temporary peaks of very high power consumption, thus reducing the available power for the radio transmitter, which needs a minimum voltage of 5 V.

For the next start the power supply was connected directly to the radio trans-mitter of the radio sonde. The power connection of the spectrometer was realised through the controlling unit. That guaranteed stable power supply of the

trans-6.2 Measurement campaign at Koldewey-Station, Ny-˚Alesund 73

mitter, independent from the hypsometer behaviour.

After the flights, PIOS A and B were recovered and the SD-cards could be read out. It became apparent that due to a software failure in the controlling unit, only the transmitted data sets were stored on the SD-card and not all measured spectra.

PIOS B, 12.5.2004

Before the launch, the data transmission worked and a GPS-signal was received.

During the entire ascent up to 32 km altitude and parts of the descent, a radio signal could be received. For the highest altitudes a small decrease in the data quality was observed.

Right after the launch, the GPS signal dropped out, but was received again with changing quality until 5 km altitude. From that no further GPS signal was received.

PIOS C, 13.5.2004

Tests on ground with the third sonde, gave some evidence that one reason for the unstable GPS-signal could be due to unstable power supply, caused by power consumption peaks in one of the other components. Therefore, two separated power supplies were realised in the PIOS C sonde: one for the controlling unit and spectrometer, the other supplying the radiosonde.

No GPS signal was received during the flight. The data transmission quality decreased very rapidly and total signal loss was reported in 12 km altitude, 35 minutes after the launch. No reason could be identified for the early signal loss.

6.2 Measurement campaign at Koldewey-Station,