Nowcasting Astronomical Seeing and Forecasting Telescope Environment for the Eso Vlt

TELESCOPE ENVIRONMENT FOR THE ESO VLT Fionn Murtagh Space Telescope { European Coordinating Facility { European Southern Observatory (A liated to Astrophysics Division, Space Science Department, European Space Agency) and Marc Sarazin European Southern Observatory, D-85748 Garching, Germany November 21, 1995 ABSTRACT We use extensive seeing and low-atmosphere meteorological data obtained at the European Southern Observatory's La Silla complex in Chile, and at the site of the Very Large Telescope at Cerro Paranal which is currently under construction. Predictability of good seeing would allow appropriate instrumentation to be mounted in time, to make best use of the observing conditions. In line with aviationrelated prediction, we have been led in the short-term to cast this problem into nowcasting terms, rather than forecasting. A prototype system is set up to nowcast seeing values, given knowledge of the low-atmosphere meteorological environment. Correspondence analysis is used to investigate seasonal variation: in particular we seek to know what environmental variables are most important for determining seeing. Following this, a system based on fuzzy set theory (used in order to facilitate interpretation of the results) is used to determine possibilities of good seeing. Temperature prediction would permit air conditioning in the telescope enclosure to be preset as a function of the next night's minimum expected temperature. We report results of prediction of univariate temperature measurements. These were obtained using a nonparametric (nearest neighbor) method, which we contrast to another non-parametric model (multilayer perceptron) and to an autoregressive model with exogenous inputs. KEYWORDSAstronomy,Meteorology, Seeing, Prediction 1 The VLT Astronomical Weather Station The VLT Astronomical Weather Station is an automatic unit operated 24 hours a day to gather informaREMOTE USERS