CASPER: Concordia Atmospheric SPectroscopy of Emitted Radiation

¹ Dipartimento di Fisica, Università ”La Sapienza”, P.le A. Moro 2, 00185 Rome, Italy
² Instituto de Astrofisica de Canarias C/ Via Lactea, s/n 38200 La Laguna, Tenerife, Spain
³ CNR/IASF-Sezione di Bologna, via P. Gobetti 101, 40129 Bologna, Italy
⁴ School of Physics and Astronomy, University of Wales, Cardiff, UK
⁵ LERMA, Observatoire de Paris, Paris, France
⁶ Inst. Estructura de la Materia, Dpto. Fisica Molecular, Madrid, Spain

Corresponding author: marco.depetris@roma1.infn.it

Abstract

CASPER (Concordia Atmospheric SPectroscopy of Emitted Radiation) is a spectrometer proposed for installation at Dome C, devoted to measurements of atmospheric emission in the spectral region between 180 μm and 3 mm (3–55 cm^-1). This instrument will be able to perform continuous spectral sampling at different altitudes at angular scales of ~1°. From the recorded data it is possible to extract atmospheric transmittance within 1% in the whole wide operating band, together with water vapour content and O₂ and O₃ concentrations. CASPER will allow us to characterize the site for future FIR/mm telescopes. Atmospheric data recorded by CASPER will allow for correction of astrophysical and cosmological observations without the need for telescope-specific procedures and further loss of observation time with more precision in the observations themselves. Calibration of ground-based telescopes on known sky sources is strongly affected by atmospheric absorption. CASPER has this as its primary goal. The spectrometer is based on a Martin-Puplett interferometer. Two data sampling solutions will be performed: phase modulation & fast scan strategy. Sky radiation is collected towards the interferometer by an optical setup that allows the field of view, to explore the full 0° ÷ 90° range of elevation angles. With a low spurious polarization instrument, monitoring of polarized atmospheric contribution will be possible.