Articles | Volume 10, issue 2
Atmos. Meas. Tech., 10, 477–490, 2017
Atmos. Meas. Tech., 10, 477–490, 2017

Research article 08 Feb 2017

Research article | 08 Feb 2017

ISMAR: an airborne submillimetre radiometer

Stuart Fox1, Clare Lee1, Brian Moyna2, Martin Philipp3, Ian Rule1, Stuart Rogers1, Robert King1, Matthew Oldfield2, Simon Rea2, Manju Henry2, Hui Wang2, and R. Chawn Harlow1 Stuart Fox et al.
  • 1Met Office, FitzRoy Road, Exeter, EX1 3PB, UK
  • 2Rutherford Appleton Laboratory, Harwell Campus, Didcot, OX11 0QX, UK
  • 3RPG Radiometer Physics GmbH, Werner-von-Siemens-Str. 4, 53340 Meckenheim, Germany

Abstract. The International Submillimetre Airborne Radiometer (ISMAR) has been developed as an airborne demonstrator for the Ice Cloud Imager (ICI) that will be launched on board the next generation of European polar-orbiting weather satellites in the 2020s. It currently has 15 channels at frequencies between 118 and 664 GHz which are sensitive to scattering by cloud ice, and additional channels at 874 GHz are being developed. This paper presents an overview of ISMAR and describes the algorithms used for calibration. The main sources of bias in the measurements are evaluated, as well as the radiometric sensitivity in different measurement scenarios. It is shown that for downward views from high altitude, representative of a satellite viewing geometry, the bias in most channels is less than ±1 K and the NEΔT is less than 2 K, with many channels having an NEΔT less than 1 K. In-flight calibration accuracy is also evaluated by comparison of high-altitude zenith views with radiative-transfer simulations.

Short summary
In this paper we present the ISMAR instrument, a new airborne submillimetre radiometer designed for cloud ice remote sensing. We discuss the instrument calibration and evaluate the main sources of bias and the radiometric sensitivity in different measurement scenarios. We also compare clear-sky zenith measurements from high altitude with radiative transfer simulations to demonstrate the performance of ISMAR in flight.