20 Nov 2021

20 Nov 2021

Review status: this preprint is currently under review for the journal AMT.

VELOX – A new thermal infrared imager for airborne remote sensing of cloud and surface properties

Michael Schäfer1, Kevin Wolf1,a, André Ehrlich1, Christoph Hallbauer2, Evelyn Jäkel1, Friedhelm Jansen3, Anna Elizabeth Luebke1, Joshua Müller1, Jakob Thoböll1, Timo Röschenthaler2, Bjorn Stevens3, and Manfred Wendisch1 Michael Schäfer et al.
  • 1Leipzig Institute for Meteorology, University of Leipzig, Germany
  • 2enviscope GmbH, Frankfurt am Main, Germany
  • 3Max Planck Institute for Meteorology, Hamburg, Germany
  • anow at: Institut Pierre-Simon Laplace, Sorbonne Université, Paris, France

Abstract. The new airborne thermal infrared (TIR) imager VELOX (Video airbornE Longwave Observations within siX channels) is introduced. The commercial camera system of VELOX covers six spectral bands with center wavelengths between 7.7 µm and 12 µm. VELOX is currently applied on board the German High Altitude and Long Range Research Aircraft (HALO). It observes two-dimensional fields of upward terrestrial spectral radiance with a horizontal spatial resolution of approximately 10 m by 10 m at a target distance of 10 km. Atmospheric temperature values are rather low compared to the original application of the TIR imager system and range close to the detection limit of the sensor. This challenge requires additional calibration efforts to reduce the measurement uncertainties of VELOX. These calibration and correction procedures, including radiometric calibrations, non-uniform corrections, bad-pixel replacements, and window corrections for data collected by VELOX, are presented. First measurements acquired by VELOX during the EUREC4A (ElUcidating the RolE of Cloud-Circulation Coupling in ClimAte) campaign are presented, including an analyses of the cloud top brightness temperature, cloud mask/fraction, and cloud top altitude data. They reveal that the cloud top temperature can be resolved with a resolution of better than 0.1 K, which translates into a resolution of approximately 40 m with respect to cloud top altitude.

Michael Schäfer et al.

Status: open (until 13 Jan 2022)

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Michael Schäfer et al.

Michael Schäfer et al.


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Short summary
The new airborne thermal infrared imager VELOX is introduced. It measures two-dimensional fields of spectral thermal infrared radiance or brightness temperature within the large atmospheric window. The technical specifications as well as necessary calibration and correction procedures are presented. Example measurements from the first field deployment are analyzed with respect to cloud coverage and cloud top altitude.