Characterization of tropical atmosphere through wide-band emission spectra acquired with a balloon-borne uncooled FTS spectroradiometer
Authors: Bianchini G., Palchetti L., Carli B., Cortesi U., Del Bianco S.
Autors Affiliation: Istituto di Fisica Applicata Nello Carrara CNR-IFAC, Via Madonna del Piano 10, Florence, Italy
Abstract: On June 30th, 2005 the REFIR-PAD (Radiation Explorer in the Far InfraRed-Prototype for Application and Development) Fourier transform spectroradiometer performed the first wide-band spectral characterization of the top-of-atmosphere emitted radiation in the far-infrared with an uncooled instrument. The nadir emitted radiance has been measured down to 100 cm -1, thus covering a spectral interval that, until now, was nearly unexplored, and up to 1400 cm-1, including the well characterized atmospheric window region, in which it is possible to perform comparison and intercalibration with operative instruments. The measurements were performed at an altitude of 34 km, from a stratospheric balloon launched in tropical region, near Teresina (Brazil). The acquired spectra have a spectral resolution of 0.5 cm-1. It should be noted that despite the operating spectral range extending to the far-infrared region, REFIR-PAD does not require any cooled components, thanks to the use of pyroelectric detectors and an optical scheme that compensates for the instrument self-emission. This work shows the results of the analysis of the spectra, focusing on the far infrared portion of the atmospheric emitted radiance. The retrieval of the vertical profiles of water vapour and temperature during the flight is presented. The vertical resolution of the retrieval is 2 km in the upper troposphere-lower stratosphere (UTLS) region, and lower at higher altitudes. The comparison with ECMWF for validation is also shown. Besides the characterization of temperature and water vapour, from the analysis of the emitted radiance useful information can be gathered about cloud and aerosol contribution to radiation budget.
KeyWords: Emission spectroscopy; Fourier transforms; Infrared spectroscopy; Water vapor, Emission sounding; Outgoing long-wave radiation, Tropical engineering