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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 4 | Copyright

Special issue: NETCARE (Network on Aerosols and Climate: Addressing Key Uncertainties...

Atmos. Meas. Tech., 9, 1817-1832, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Apr 2016

Research article | 27 Apr 2016

A microbolometer-based far infrared radiometer to study thin ice clouds in the Arctic

Quentin Libois1, Christian Proulx2, Liviu Ivanescu1, Laurence Coursol1, Ludovick S. Pelletier1, Yacine Bouzid1, Francesco Barbero1, Éric Girard1, and Jean-Pierre Blanchet1 Quentin Libois et al.
  • 1ESCER Centre, Department of Earth and Atmospheric Sciences, Université du Québec à Montréal (UQAM), Montréal, Canada
  • 2Institut National d'Optique (INO), 2740 Einstein Street, Québec City, QC G1P 4S4, Canada

Abstract. A far infrared radiometer (FIRR) dedicated to measuring radiation emitted by clear and cloudy atmospheres was developed in the framework of the Thin Ice Clouds in Far InfraRed Experiment (TICFIRE) technology demonstration satellite project. The FIRR detector is an array of 80 × 60 uncooled microbolometers coated with gold black to enhance the absorptivity and responsivity. A filter wheel is used to select atmospheric radiation in nine spectral bands ranging from 8 to 50µm. Calibrated radiances are obtained using two well-calibrated blackbodies. Images are acquired at a frame rate of 120Hz, and temporally averaged to reduce electronic noise. A complete measurement sequence takes about 120s. With a field of view of 6°, the FIRR is not intended to be an imager. Hence spatial average is computed over 193 illuminated pixels to increase the signal-to-noise ratio and consequently the detector resolution. This results in an improvement by a factor of 5 compared to individual pixel measurements. Another threefold increase in resolution is obtained using 193 non-illuminated pixels to remove correlated electronic noise, leading an overall resolution of approximately 0.015Wm−2sr−1. Laboratory measurements performed on well-known targets suggest an absolute accuracy close to 0.02Wm−2sr−1, which ensures atmospheric radiance is retrieved with an accuracy better than 1%. Preliminary in situ experiments performed from the ground in winter and in summer on clear and cloudy atmospheres are compared to radiative transfer simulations. They point out the FIRR ability to detect clouds and changes in relative humidity of a few percent in various atmospheric conditions, paving the way for the development of new algorithms dedicated to ice cloud characterization and water vapor retrieval.

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Short summary
Here we present a radiometer, FIRR, aimed at measuring atmospheric radiation in the far infrared, an underexplored region of the Earth spectrum. The FIRR is a prototype for the planned TICFIRE satellite mission dedicated to studying thin ice clouds in polar regions. Preliminary in situ measurements compare well with radiative transfer simulations. This highlights the high sensitivity of the FIRR to water vapor content and cloud physical properties, paving the way for new retrieval algorithms.
Here we present a radiometer, FIRR, aimed at measuring atmospheric radiation in the far...