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Volume 11, issue 7 | Copyright
Atmos. Meas. Tech., 11, 4545-4566, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 31 Jul 2018

Research article | 31 Jul 2018

Simulation study for the Stratospheric Inferred Winds (SIW) sub-millimeter limb sounder

Philippe Baron1, Donal Murtagh2, Patrick Eriksson2, Jana Mendrok2, Satoshi Ochiai1, Kristell Pérot2, Hideo Sagawa3, and Makoto Suzuki4 Philippe Baron et al.
  • 1National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184-8795, Japan
  • 2Department of Space, Earth and Environment, Chalmers University of Technology, 41296 Gothenburg, Sweden
  • 3Division of Science, Kyoto Sangyo University, Kyoto, Japan
  • 4Japan Aerospace Exploration Agency, Tsukuba, 305-8505 Japan

Abstract. Stratospheric Inferred Winds (SIW) is a Swedish mini sub-millimeter limb sounder selected for the 2nd InnoSat platform, with launch planned for around 2022. It is intended to fill the altitude gap between 30 and 70km in atmospheric wind measurements and also aims at pursuing the limb observations of temperature and key atmospheric constituents between 10 and 90km when current satellite missions will probably come to an end. Line-of-sight winds are retrieved from the Doppler shift of molecular emission lines introduced by the wind field. Observations will be performed with two antennas pointing toward the limb in perpendicular directions in order to reconstruct the 2-D horizontal wind vector. Each antenna has a vertical field of view (FOV) of 5km. The chosen spectral band, near 655GHz, contains a dense group of strong O3 lines suitable for exploiting the small amount of wind information in stratospheric spectra. Using both sidebands of the heterodyne receiver, a large number of chemical species will be measured, including O3 isotopologues, H2O, HDO, HCl, ClO, N2O, HNO3, NO, NO2, HCN, CH3CN and HO2. This paper presents a simulation study that assesses measurement performance. The line-of-sight winds are retrieved between 30 and 90km with the best sensitivity between 35 and 70km, where the precision (1σ) is 5–10m s−1 for a single scan. Similar performance can be obtained during day and night conditions except in the lower mesosphere, where the photo-dissociation of O3 in daytime reduces the sensitivity by 50% near 70km. Profiles of O3, H2O and temperature are retrieved with high precision up to 50km ( < 1%,  < 2%, 1K, respectively). Systematic errors due to uncertainties in spectroscopic parameters, in the radiometer sideband ratio and in the radiance calibration process are investigated. A large wind retrieval bias of 10–30m s−1 between 30 and 40km could be induced by the air-broadening parameter uncertainties of O3 lines. This highlights the need for good knowledge of these parameters and for studying methods to mitigate the retrieval bias.

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This paper investigates with computer simulations the measurement performances of the satellite Stratospheric Inferred Winds (SIW) in the altitude range 10–90 km. SIW is a Swedish mission that will be launched close to 2022. It is intended to fill the current altitude gap between 30 and 70 km in wind measurements and to pursue the monitoring of temperature and key stratospheric constituents for better understanding climate change effects.
This paper investigates with computer simulations the measurement performances of the satellite...