21 Dec 2021
21 Dec 2021
Status: a revised version of this preprint is currently under review for the journal TC.

Coherent backscatter enhancement in bistatic Ku-/X-band radar observations of dry snow

Marcel Stefko1,, Silvan Leinss1,2,, Othmar Frey1,3, and Irena Hajnsek1,4 Marcel Stefko et al.
  • 1ETH Zurich, Institute of Environmental Engineering, 8093 Zurich, Switzerland
  • 2Université Savoie Mont Blanc, LISTIC, 74000 Annecy, France
  • 3Gamma Remote Sensing, 3073 Gümligen, Switzerland
  • 4German Aerospace Center, Microwaves and Radar Institute, 82234 Wessling, Germany
  • These authors contributed equally to this work.

Abstract. The coherent backscatter opposition effect (CBOE) enhances the backscatter intensity of electromagnetic waves by up to a factor of two in a very narrow cone around the direct return direction when multiple scattering occurs in a weakly absorbing, disordered medium. So far, this effect has not been investigated in terrestrial snow in the microwave spectrum. It has also received little attention in scattering models. We present the first characterization of the CBOE in dry snow using ground-based and space-borne bistatic radar systems. For a seasonal snow pack in Ku-band (17.2 GHz), we found backscatter enhancement of 50–60 % (+1.8–2.0 dB) at zero bistatic angle and a peak half-width-at-half-maximum (HWHM) of 0.25°. In X-band (9.65 GHz), we found backscatter enhancement of at least 35 % (+1.3 dB) and an estimated HWHM of 0.12° in the accumulation areas of glaciers in the Jungfrau-Aletsch region, Switzerland. Sampling of the peak shape at different bistatic angles allows estimating the scattering and absorption mean free paths, ΛT and ΛA. In the VV polarization, we obtained ΛT = 0.4 ± 0.1 m and ΛA = 19 ± 12 m at Ku-band, and ΛT = 2.1 ± 0.4 m, ΛA = 21.8 ± 2.7 m at X-band. The HH polarization yielded similar results. The observed backscatter enhancement is thus significant enough to require consideration in backscatter models describing monostatic and bistatic radar experiments. Enhanced backscattering beyond the Earth, on the surface of solar system bodies, has been interpreted as being caused by the presence of water ice. In agreement with this interpretation, our results confirm the presence of the CBOE at X- and Ku-band frequencies in terrestrial snow.

Marcel Stefko et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-358', Henning Loewe, 31 Jan 2022
    • AC1: 'Reply on RC1', Marcel Stefko, 30 Mar 2022
  • RC2: 'Comment on tc-2021-358', Anonymous Referee #2, 27 Feb 2022
    • AC2: 'Reply on RC2', Marcel Stefko, 30 Mar 2022

Marcel Stefko et al.

Marcel Stefko et al.


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Short summary
The coherent backscatter opposition effect can enhance the intensity of radar backscatter from dry snow by up to a factor of two. Despite widespread use of radar backscatter data by snow scientists, this effect has received notably little attention. For the first time, we characterize this effect for the Earth's snow cover with bistatic radar experiments from ground and from space. We are also able to retrieve scattering and absorbing lengths of snow at Ku- and X-band frequencies.