Antarctic Ice Cloud Identification and Properties Using Downwelling Spectral Radiance From 100 to 1,400 cm⁻¹

Abstract

One year (2013) of high spectral resolution measurements of downwelling radiance in the 100–1,400 cm−1 range, taken by the Fourier Transform Spectrometer REFIR‐PAD at the research station Concordia (Antarctic Plateau), is analyzed. Optically thin ice clouds are identified by means of a new identification/classification tool based on a Support Vector Machine algorithm. The use of transparent microwindow channels in the Far InfraRed (FIR) spectral region (100–667 cm−1) is shown to be of great importance in the identification and classification of cloud type. In particular, the channels between 380 and 575 cm−1 are key channels for the clear/cloud and phase identification due to their sensitivity to cloud properties; in addition, FIR channels down to 238 cm−1 are exploited for the selection of precipitating or nonprecipitating cases because of their sensitivity also to water vapor content. A subset of 26 cases of nonprecipitating ice clouds is selected based on the presence of colocated LIDAR and radiosonde data. REFIR‐PAD channel in the 800–1,000 cm−1 are used to derived optical and microphysical properties for four different assumptions concerning the crystal habits. Results, showing a correlation between cloud base temperature, optical depth, and particle size distribution effective dimensions, are compared with what found in literature. Based on the retrievals, forward simulations are also run over the whole sensor spectral interval, and results are compared to data. The simulation‐data residuals in the FIR are evaluated for selected “window” channels and analyzed in relation to crystal's habit assumption, cloud retrieved features, and atmospheric water vapor content.

Cloud identification and classification from high spectral resolution data in the far infrared and mid-infrared

“…Moreover, in Palchetti et al (2016) it is shown that by using the full infrared emission spectrum more information may be retrieved about cirrus cloud microphysical properties. In Maestri et al (2019), it is shown that the Radiation Explorer in the "Far InfraRed: Prototype for Applications and Development" (REFIR-PAD) channels hold additional information for cloud detection and cloudphase classification from ground-based measurements.…”

FORUM: Unique Far-Infrared Satellite Observations to Better Understand How Earth Radiates Energy to Space

“…OD =0.5 and OD= 5). This suggests that the analysis of combined observations in the FIR and MIR part of the spectrum, acquired with a brightness temperature accuracy of 0.1 K as required for the FSI measurements, might be sufficient to allow an identification of the crystal habits, as recently shown Maestri et al (2019a).…”

Cirrus Cloud Identification from Airborne Far-Infrared and Mid-Infrared Spectra

“…Despite this, their role for cloud feedback is not yet completely understood [9]. Recently, simulations have been used to show that FIR can contribute to improve the detection of thin cirrus cloud [4,10] and that FIR and MIR measurements can be combined to efficiently retrieve the cloud properties and the atmospheric state (water vapor and temperature profiles) [11,12]. The detection of thin cirrus clouds and the derivation of some of their features have been improved by using active satellite sensors [13][14][15].…”