Astronomy and Meteorology III

Sensors mounting and powering up

F. Buffa, G.C. Cocco, I. Porceddu and M. Serrau

Stazione Astronomica di Cagliari

Foreword

In the two previous reports (TNG Newsletter no. 8 and 9) of the Galileo telescope Astronomical Weather team - a branch of the Site Testing Group - we discussed about the TNG approach and the interdisciplinary activity we were starting. This progress report wants to be a short communication concerning the successful installation of the meteorological instrumentation on the meteo tower, a positive step ahead towards the site monitoring. A forthcoming Technical Report will follow, carefully describing the data collection and handling status. Here we shortly report about hardware operations (sensor mounting and cabling) and data logging procedure.

Introduction

Meteorological conditions are a de facto constraint on the telescope observational capabilities: relative high wind speed and relative humidity values can actually limit or halt the telescope. Therefore a set of reliable basic meteorological parameters must be available in order to support the observational facilities. Additional sensors may also be installed, near by and inside the dome, if dome and local seeing conditions are to be monitored.
The TNG project decided, in Phase 1, to build a robust meteo tower which would be able to resist to the harsh conditions which are not uncommon in winter at the Roque de Los Muchachos Observatory. The meteo tower of the TNG is an iron-made structure, designed by Dario Mancini, from the Capodimonte Astronomical Observatory (Naples). The total height is 15 meters, which is the approximate height above the ground of the TNG M1 mirror. The meteo tower, which is about 30 meters far away from the DIMM, did not suffer any damage during last winter, when lighter and less expensive structures crashed.

Sensors

The foreseen and now available initial set of sensors will provide these basic meteorological measurements:

Data logging and realtime transmission

Sensor sampling and data logging is driven by a Vaisala QLC50 datalogger, a fully programmable system with a onboard PCMCIA memory card for data storage: the QLC50 can actually store up to 20 megabytes of data. The memory card is only used as a local backup, where up to six months of data can be stored with the actual data sampling setup.
Due to the close interaction between meteo and seeing measurements and the need for dataflow optimization, realtime data communication from the telescope to the meteo tower is done by mean of a software routine which is part of the DIMM controller. The physical connection between meteo tower and DIMM is accomplished through an optical fiber link.

Power supply

The Astronomical Weather Station (AWS) will not be connected to the TNG power supply network but will be powered by a solar panel, with a backup pack of batteries. They should allow the AWS being able to collect and send data without solar panel contribution for about one month. The solar power supply choice should avoid most of the problems which are related to the lightning features, and it will guarantee a continuous monitoring of the data. The solar panel has been located at about 6 meters above ground.

Mounting the instrumentation

The present safety regulations do not allow the meteo tower being lowered down for maintenance operations. Therefore, the whole set of mounting operations has been accomplished with the tower in vertical position, as can easily seen from the enclosed photos. Special tools, normally used for climbing, have been used in order to guarantee the maximum level of working security for our team.
Operations have started on Monday, 7th of April, and the instrumentation was finally mounted on Thursday, 17th of april. A few days have been lost due to the extremely bad weather conditions we found. Drill and other tools have been powered from the chillers section, which is about 40 meters away from the tower. Due to the constraints we had on our back trip to Italy, we did not able to perform any test on the batteries charge/discharge duty cicle. Nevertheless, we had the opportunity to verify the correct behaviour of the whole instrumentation and to check the data logging.

Final remarks

The TNG meteo tower, will be finally tested soon. After checking the power supply facilities, we will start the commissioning phase and, hopefully, the TNG meteo data series will begin.

Meteo Tower Image


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