Analysis of cirrus cloud spectral signatures in the far infrared

Year: 2014

Authors: Maestri T., Rizzi R., Tosi E., Veglio P., Palchetti L., Bianchini G., Di Girolamo P., Masiello G., Serio C., Summa D.

Autors Affiliation: Dipartimento di Fisica e Astronomia, Università di Bologna, viale Berti-Pichat 6/2, 40127 Bologna, Italy; Istituto Nazionale di Ottica – CNR, largo E. Fermi 6, 50125 Firenze, Italy; Scuola di Ingegneria, Università degli Studi della Basilicata, Viale dell\’Ateneo Lucano 10, 85100 Potenza, Italy; Space Science and Engineering Center, University of Wisconsin-Madison, 1225 W. Dayton St., Madison, WI 53706, USA

Abstract: This paper analyses high spectral resolution downwelling radiance measurements in the far infrared in the presence of cirrus clouds taken by the REFIR-PAD interferometer, deployed at 3500 m above the sea level at the Testa Grigia station (Italy), during the Earth COoling by WAter vapouR emission (ECOWAR) campaign. Atmospheric state and cloud geometry are characterised by the co-located millimeter-wave spectrometer GBMS and by radiosonde profile data, an interferometer (I-BEST) and a Raman lidar system deployed at a nearby location (Cervinia). Cloud optical depth and effective diameter are retrieved from REFIR-PAD data using a limited number of channels in the 820-960 cm(-1) interval. The retrieved cloud parameters are the input data for simulations covering the 250-1100 cm(-1) band in order to test our ability to reproduce the REFIR-PAD spectra in the presence of ice clouds. Inverse and forward simulations are based on the same radiative transfer code. A priori information concerning cloud ice vertical distribution is used to better constrain the simulation scheme and an analysis of the degree of approximation of the phase function within the radiative transfer codes is performed to define the accuracy of computations. Simulation-data residuals over the REFIR-PAD spectral interval show an excellent agreement in the window region, but values are larger than total measurement uncertainties in the far infrared. Possible causes are investigated. It is shown that the uncertainties related to the water vapour and temperature profiles are of the same order as the sensitivity to the a priori assumption on particle habits for an up-looking configuration. In case of a down-looking configuration, errors due to possible incorrect description of the water vapour profile would be drastically reduced. (C) 2014 Elsevier Ltd. All rights reserved.


Volume: 141      Pages from: 49  to: 62

KeyWords: Interferometers; Radiative transfer; Remote sensing; Sea level; Spectral resolution; Uncertainty analysis; Water vapor, Cirrus clouds; Degree of approximation; Far infrared; Ground based measurement; High spectral resolution; Millimeter-wave spectrometers; Radiative transfer codes; Total Measurement Uncertainty, Clouds, cirrus; ground-based measurement; infrared radiation; radiative transfer; remote sensing; spectral analysis, Cervinia
DOI: 10.1016/j.jqsrt.2014.02.030

Citations: 21
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