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The two-LAyered snow Radiative Transfer (LART) model has been proposed for snow remote sensing applications. It is based on analytical approximations of the radiative transfer theory. The geometrical optics approximation has been used to derive the local snow optical parameters, such as the probability of photon absorption by ice grains and the average cosine of single light scattering in a given direction in a snowpack. The application of the model to the selected area in Antarctica has shown that the technique is capable of retrieving the snow grain size both in the upper and lower snow layers, with grains larger in the lower snow layer as one might expect due to the metamorphism processes. Such a conclusion is confirmed by ground measurements of the vertical snow grain size variability in Antarctica. [ABSTRACT FROM AUTHOR]

The Radiation Explorer in the Far Infrared - Prototype for Applications and Development (REFIR-PAD) is a Fourier transform spectroradiometer that has been designed to operate both from stratospheric balloon platform and from ground. It has been successfully deployed in a stratospheric balloon flight and several ground based campaigns from high altitude sites, including the current installation in the Concordia Italian-French Antarctic station. The instrument is capable to operate autonomously with only a limited need of remote control and monitoring, and is providing a multi-year dataset of spectrally resolved atmospheric downwelling radiances, measured in the 100-1500cm-1 spectral range with 0.4cm-1 resolution and a radiometric uncertainty better than 0.85mW/m2srcm-1. [ABSTRACT FROM AUTHOR]

Optical and microphysical cloud properties are retrieved from measurements acquired in 2013 and 2014 at the Concordia base station in the Antarctic Plateau. Two sensors are used synergistically: a Fourier transform spectroradiometer named REFIR-PAD (Radiation Explorer in Far Infrared-Prototype for Applications and Developments) and a backscattering-depolarization LiDAR. First, in order to identify the cloudy scenes and assess the cloud thermodynamic phase, the REFIR-PAD spectral radiances are ingested by a machine learning algorithm called Cloud Identification and Classification (CIC). For each of the identified cloudy scenes, the nearest (in time) LiDAR backscattering profile is processed by the Polar Threshold (PT) algorithm that allows derivation of the cloud top and bottom heights. Subsequently, using the CIC and PT results as external constraints, the Simultaneous Atmospheric and Clouds Retrieval (SACR) code is applied to the REFIR-PAD spectral radiances. SACR simultaneously retrieves cloud optical depth and effective dimensions and atmospheric vertical profiles of water vapor and temperature. The analysis determines an average effective diameter of 28 μ m with an optical depth of 0.76 for the ice clouds. Water clouds are only detected during the austral Summer, and the retrieved properties provide an average droplet diameter of 9 μ m and average optical depth equal to four. The estimated retrieval error is about 1% for the ice crystal/droplet size and 2% for the cloud optical depth. The sensitivity of the retrieved parameters to the assumed crystal shape is also assessed. New parametrizations of the optical depth and the longwave downwelling forcing for Antarctic ice and water clouds, as a function of the ice/liquid water path, are presented. The longwave downwelling flux, computed from the top of the atmosphere to the surface, ranges between 70 and 220 W/m 2 . The estimated cloud longwave forcing at the surface is (31 ± 7) W/m 2 and (29 ± 6) W/m 2 for ice clouds and (64 ± 12) and (62 ± 11) W/m 2 for water clouds, in 2013 and 2014, respectively. The total average cloud forcing for the two years investigated is (46 ± 9) W/m 2 . [ABSTRACT FROM AUTHOR]

Ice and mixed phase clouds play a key role in the Earth's radiation budget but there is a large uncertainty about their infrared radiative impact due to the high variability in the size/shape distribution of ice particles. Their radiative effect is very strong in the mid and far infrared (FIR) spectrum, between 200-1000 cm−1 (10-50 μm). In particular the FIR part of the spectrum (under 600 cm-1) shows a strong sensitivity to the ice particle properties, such as crystal habits, and allows the discrimination of the clouds phase, since in this spectral region the refractive index of ice is very different from the water ones. Despite this, only few measurements exist in the FIR that could be used to improve the characterisation of polar clouds radiative effect.The present work describes the synergy of different instruments deployed at Concordia base, Dome C (Antarctica, 3230 m a.s.l.), to study the optical and micro-physical properties of the ice and mixed phase clouds. Currently at Italian-French base Concordia, there are different instruments devoted to the measurements of the Antarctic clouds properties, such as the Fourier transform spectroradiometer REFIR-PAD (Radiation Explorer Far Infrared – Prototype for Applications and Development), operating in the FIR spectral region, a backscattering/depolarization lidar, which allows to monitor the passage of clouds, an ice camera for the estimate of the size distribution of ice particles and, finally, a micro rain radar (MRR) operating at 24 GHz, installed during this last summer campaign in order to estimate the Ice Water Content (IWC) of the clouds. REFIR-PAD spectroradiometer is operating in ground-base zenith-looking observation geometry in continuous mode at Dome-C since December 2011, allowing to collect a very large database of the spectral radiances of the Antarctic atmosphere both in clear and cloudy sky conditions. The retrieval of the clouds parameters is performed by using the spectral measurements of REFIR-PAD and the Simultaneous Atmospheric and Clouds Retrieval (SACR) code, which is based on the optimal estimation approach. This code allows to perform the retrieval of the atmospheric variables, such as the vertical profiles of water vapour and temperature, and the clouds properties simultaneously, by using the single scattering coefficients of different ice crystal habits, provided by specific databases.The SACR algorithm allows to retrieve the effective diameter of the ice crystals and water droplets, the optical depth/ice water content and the ice fraction of the clouds. The comparison of the effective diameters and the ice water content with the measurement given by the ice camera and the radar represents one of the aims of the FIRCLOUDS (Far Infrared Radiative CLOUDS) project selected by the Italian PNRA (Programma Nazionale di Ricerche in Antartide), in order to validate the current cirrus clouds model. Furthermore the analysis of the whole database collected by REFIR-PAD will allow to obtain a statistics of the Antarctic clouds properties and studying the correlations between these clouds and the other atmospheric variables. [ABSTRACT FROM AUTHOR]