We have developed a new forward model for all sky radiative transfer calculations in the spectral range 10 to 2760 cm−1 . This new code, which we call σ-IASI/F2N, allows us to calculate in all-sky based on an original parametrization of the optical depth of atmospheric gases and clouds. Clouds are represented through the atmospheric profiles of Liquid Water Content (LWC), Ice Water Content (IWC), and effective radii of both water droplets (re) and ice crystals (De). The cloud parametrization relies on suitable scaling laws, which make the radiative transfer equations for a cloudy atmosphere identical to those for a clear atmosphere. Therefore, the difficulties in applying a multiple-scattering algorithm to a partly cloudy atmosphere are avoided, and the computational efficiency is practically the same as that for a clear atmosphere. The new radiative transfer code has been coupled with an inverse scheme based on the Optimal Estimation methodology. The problem of dimensionality of the data and parameter space is handled by considering suitable transforms, which allow the representation of the radiances (data space) and the atmospheric state vector (parameter space) through a set of reduced components. The dimensionality is diminished through the random Projections transform for the radiance space, whereas we use the usual Principal Component Analysis for the parameter space. The scheme’s performance has been evaluated using the Infrared Atmospheric Sounder Interferometer (IASI) spectral radiances. The soundings are collocated with analyses from the European Centre for Medium-Range Forecasts (ECMWF) model. The ECMWF analyses provide the basic information, i.e., the first guess state vector to initialize the inverse scheme. The forward/inverse technique uses the whole IASI spectral coverage (645 to 2760 cm−1 ). As such, it is the first scheme for all sky using the full IASI spectrum to retrieve clouds and atmospheric parameters simultaneously. This new forward/inverse model is exemplified through the analysis of a set of IASI soundings over the Antarctica continent on 9 September 2021 at the onset of the ozone hole. We will show that infrared retrievals add information to assess ozone’s spatial extent and depletion.
The international experiment EAQUATE (European AQUA Thermodynamic Experiment) was held in September 2004 in Italy and in the United Kingdom. The Italian phase, performed in the period 6-10 September 2004, was mainly devoted to assessment and validation of performances of new IR hyperspectral sensors and benefits from data and results of measurements of AQUA and in particular of AIRS. It is also connected with the preparatory actions of MetOp mission with particular attention to calibration and validation of IASI products (as water vapour and temperature profiles), characterization of semitransparent clouds and study of radiative balance, demonstrating the role of ground-based and airborne systems in validation operations.
The Italian phase of the campaign was carried out within a cooperation between NASA Langley Research Center, University of Wisconsin, the Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA), the Mediterranean Agency for Remote Sensing (MARS) and the Universities of Basilicata, Bologna and Napoli. It involved the participation of the Scaled Composites Proteus aircraft (with NAST thermal infrared interferometer and microwave radiometer, the Scanning HIS infrared interferometer, the FIRSC far-IR interferometer), an Earth Observing System-Direct Readout Station and several ground based instruments: four lidar systems, a microwave radiometer, two infrared spectrometers, and a ceilometer. Radiosonde launches for measurements of PTU and wind velocity and direction were also performed as ancillary observations. Four flights were successfully completed with two different AQUA overpasses. The aircraft flew over the Napoli, Potenza and Tito Scalo ground stations several times allowing the collection of coincident aircraft and in- situ observations.
The clear sky radiative energy balance in the infrared spectrum is investigated with particular attention to the role of water vapor pure rotational band in the spectral range 10-600 cm-1. Main results for Tropical and Sub Arctic Winter atmospheres are in good agreement with those previously reported by other authors. Multiple scattering layers, simulating the presence of cirrus clouds, are used in Tropical atmosphere. The cloudy tropospheric heat balance is studied by the introduction of spectral power densities instead of spectral heating rates. Distribution of radiant energy between air molecules and cloud ice crystals is taken into account and the effects of cirrus absorption and scattering are distinguished. Finally a comparison between Mie and Fu parameterization is performed to understand the effects of more realistically shaped cirrus particles.
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