Ground-Based and Balloon-Borne Characterization of the Far Infrared Atmospheric Emission Spectrum

The measurement of the Earth's atmospheric emission spectrum is fundamental for the study of the global radiation budget. Up to now, this measurement has typically been limited to the mid-infrared region because of the technological limitations of space-borne spectrometers operating in the far infrared (FIR). The uncovered region of the FIR is however very important because most of the radiative cooling of the atmosphere, due to the strong rotational band of water vapor, occurs here. The REFIR-PAD (Radiation Explorer in the Far InfraRed - Prototype for Applications and Development) instrument is a completely uncooled Fourier transform spectrometer that allows to perform the spectrally resolved measurement of the entire atmospheric emission spectrum including the FIR region with a spectral resolution of 0.5 cm(-1). REFIR-PAD was deployed in June 2005 on board a stratospheric balloon to perform the nadir-looking spectral measurement of the outgoing longwave radiation in the tropics, near Teresina (North-East Brazil), and in 2006-2007 in different ground-based campaigns in Italy to obtain zenith-looking spectral measurements of the downward longwave radiation from high-altitude. These wideband measurements have shown that the retrieval capability of atmospheric parameters is improved using the FIR portion of the emission spectrum. Moreover, both sets of measurements are important for the characterization of the spectroscopy of water vapor continuum in the relatively unexplored spectral region below 600 cm(-1).