Far-infrared spectrally resolved broadband emission of the atmosphere from Morello and Gomito mountains near Florence

Abstract

The spectrally-resolved characterization of the atmospheric emission has a fundamental role in the study of the Earth radiation balance, and only a measurement performed in a wide spectral range enables us to separate the contributions to the radiative balance due to the different altitudes, constituents and physical phases. The REFIR-PAD (Radiation Explorer in the Far InfraRed -Prototype for Application and Development) Fourier transform spectroradiometer can perform a characterization of the broadband radiative signature of clouds and aerosols, with the only limitation of the need of low levels of water vapour like those that are obtainable in high altitude stations during winter. The capabilities of this kind of measurement have been assessed in a series of test campaign performed in Tuscany during the winter of 2006/2007 when atmospheric emission spectra have been acquired in various transparency conditions and the evidence of transparency in the far-infrared region below 600 cm −1 has been demonstrated. REFIR-PAD operates in the spectral range extending from 100 to 1400 cm −1 with a resolution of 0.5 cm −1 , using room-temperature detectors and optics and a compact, misalignmentcompensated design. The instrument, developed at IFAC-CNR, Florence, has been successfully deployed in several campaigns, both in the ground based zenith-looking geometry and in the nadir-looking balloon borne configuration. The operating spectral range of the REFIR-PAD spectroradiometer encompasses great part of the atmospheric emission spectrum, from the relatively unexplored far-infrared region below 400 cm −1 , dominated by water vapour rotational band, to the atmospheric transparency window, where a number of atmospheric instruments are already operating and can provide intercomparison data.

Measurements of low amounts of precipitable water vapor by millimeter wave spectroscopy: An intercomparison with radiosonde, Raman lidar, and Fourier transform infrared data

“…It is a prototype developed as a field demonstrator of a spaceborne instrument designed for the characterization of the Earth's radiation budget in the far infrared region [ Palchetti et al , 2005; Bianchini et al , 2006]. REFIR‐PAD was specifically designed with the requirements of reliability, light weight (55 kg) and low power consumption (about 50 W average) to fly on board stratospheric balloons [ Palchetti et al , 2006], but its extremely flexible design makes it suitable also for ground‐based observations with only minor changes required [ Bianchini et al , 2007].…”

“…Measured DLR spectra are analyzed through a retrieval code based on the ARTS forward model [ Buehler et al , 2005] and a χ 2 minimization algorithm based on the MINUIT function minimization routines supplied by CERN [ James , 1994]. The number of degrees of freedom (DOF) in the acquired data is determined through the analysis of the Jacobian of water vapor and temperature observations [ Bianchini et al , 2007]. To this purpose, first of all the Jacobian matrix is calculated as a function of wave number and altitude.…”

A Fourier transform spectroradiometer for ground-based remote sensing of the atmospheric downwelling long-wave radiance

“…The REFIR-PAD spectroradiometer has been operated in several campaigns in different environments (tropical, midlatitude, polar), and at different working altitudes, from about sea level to over 5000 m a.s.l. (Bianchini, 2007;Bhawar, 2008;Turner, 2012;Palchetti, 2015).…”

Water vapor sounding with the far infrared REFIR-PAD spectroradiometer from a high-altitude ground-based station during the ECOWAR campaign

“…Among the atmospheric variables showing signatures in the REFIR‐PAD operating range, we concentrated our attention on water vapor and temperature, so the actual spectral range that is used in the analysis is a subinterval of the REFIR‐PAD operating band, range which extends from about 400 to 850 cm −1 . In this spectral region the retrieval is sensitive to water vapor vertical distribution from the rotational band in the far‐infrared [ Bianchini et al , 2007], temperature vertical profile from the CO 2 v2 band and information on water vapor continuum and thin cirrus clouds from the transparent atmospheric window above 750 cm −1 .…”

“…The REFIR‐PAD instrument is a Fourier transform spectroradiometer designed to operate both from balloon platform, in the nadir and limb view observation geometries [ Palchetti et al , 2006, 2007], and from the ground in the zenith looking geometry [ Bianchini et al , 2007]. The instrument is characterized by a compact, uncooled design, with a misalignment‐compensated optical scheme that can provide wideband (100–1100 cm −1 ) atmospheric emission spectra with a 0.5 cm −1 spectral resolution (unapodized).…”