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TAPAS, a web-based service of atmospheric transmission computation for astronomy

Abstract : We have developed a web-based service, TAPAS ( "Transmissions Atmosphriques Personnalise pour lAStronomie" or Transmissions of the AtmosPhere for AStronomical data, Bertaux et al., Astronomy and Astrophysics, 564,A46, 2014). This service, hosted at ETHER/IPSL in Paris, computes the atmospheric transmission in the line-of-sight (LOS) to the target indicated by the user. The user files a request indicating the time, ground location, and RA/DEC of the target or the Zenith Angle of the LOS. The actual atmospheric profile (temperature, pressure, humidity, ozone content) at that time and place is retrieved from the ETHER atmospheric data base (from a combination of ECMWF meteorological field and other information), and the atmospheric transmission is computed from LBLRTM software and HITRAN data base for a number of gases O2,H2O,O3,CO2,CH4,N2O, and Rayleigh extinction. The first purpose of TAPAS output is to allow identification of observed spectral features as being from atmospheric or astrophysics origin. The returned transmission may also serve for characterizing the spectrometer in wavelength scale and Instrument Line Spectral Function (ILSF) by comparing one observed spectrum of an atmospheric feature to the transmission. Finally, the TOA (Top Of Atmosphere) spectrum is obtained by division of the observed spectrum by the computed atmospheric transmission. We describe briefly the mechanism of computation of the atmospheric transmissions, and we show some results for O2 and H2O atmospheric absorption in the range 0.5-1.5 µm. The wavelength range is 5002500 nm, but may be extended in the future. It is hoped that this service will help many astronomers in their research. The user may also contribute to general knowledge of the atmospheric transmission, if he/she finds systematic discrepancies between synthetic transmissions and the observed spectra. We show an extreme case of a water line at 1507.26 nm whose intensity predicted by HITRAN 2008 is overestimated by a factor 5, while much better estimated with HITRAN 2012. The TAPAS address is `100
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Jean-Loup Bertaux, Rosine Lallement, Stéphane Ferron, Cathy Boonne. TAPAS, a web-based service of atmospheric transmission computation for astronomy. 13th International HITRAN Conference, Jun 2014, Cambridge, United States. ⟨hal-01119177⟩



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