Temperature and humidity environmental conditions in the VLTI

Knowledge of the environmental conditions in the Very Large Telescope Interferometer (VLTI) is fundamental for assessing the performance of the scientific instruments and sub-systems of the VLTI, as well as for the calibration of measurement biases (e.g. in astrometry). Therefore, four temperature and humidity sensors were installed in the VLTI delay line tunnel and in the VLTI laboratory in September 2004. First results from the analysis of the long-term (18 months) humidity and temperature data measured by this network will be presented, along with a comparison of the temperatures monitored by the VLTI temperature sensors network and correlations with the external data of the Paranal weather station.