Coherent backscatter enhancement in bistatic Ku-/X-band radar observations of dry snow
- 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.
- 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.
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Marcel Stefko et al.
Status: closed
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RC1: 'Comment on tc-2021-358', Henning Loewe, 31 Jan 2022
- AC1: 'Reply on RC1', Marcel Stefko, 30 Mar 2022
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RC2: 'Comment on tc-2021-358', Anonymous Referee #2, 27 Feb 2022
Coherent Backscattering enhancement for volume scattering and rough surface scattering have been known for a long time. The experiments for volume scattering were first observed in Kuga and Ishimaru ( JOSA 1984), and for rough surface by Phu etal, Radio Science (1994)
The enhancement has a maximum of 3dB which is significant for remote sensing applications. The validations have been exclusively from laboratory optical and microwave experiments where accurate bistatic measurements can be made within a fraction of a degree from the backscattering direction. However, it has largely been neglected in applications in microwave remote sensing of snow because of the difficulty of bistatics measurements to within a fraction of a degree from the backscattering direction
The authors in this experiment have made a good effort in measuring accurate bistatic measurements with Ku band for ground measurements and Tandem X of X band for satellites. The paper is a good step towards experiment validation of CBOE in remote sensing applications and the possible inclusion in modeling X band and Ku band volume scattering in snow. I have a few minor comments
- For Ku bad for volume scattering of snow, cross polarizations are usually strong. In laboratory experiments cross polarization enhancement are more conspicuous than co-polarization for both volume scattering (Kuga etal JOSA A, 1985) and surface scattering ( Johnson etal IEEE Transactions on Antennas and Propagation 1994) . What are the reasons for non-observations in this paper. How about deeper snow?
- The optical thickness can indicate the order of multiple scattering. Please discuss the optical thicknesses tau in the measurements at X band and Ku band
- For X band at Tandem X, the soil surface below the snow have significant contributions. What is the magnitude of surface scattering of the snow/soil interface below the snow layer?
- Will there be coherent backscattering due to rough soil surface below the snow at X band?
- AC2: 'Reply on RC2', Marcel Stefko, 30 Mar 2022
Status: closed
-
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
Coherent Backscattering enhancement for volume scattering and rough surface scattering have been known for a long time. The experiments for volume scattering were first observed in Kuga and Ishimaru ( JOSA 1984), and for rough surface by Phu etal, Radio Science (1994)
The enhancement has a maximum of 3dB which is significant for remote sensing applications. The validations have been exclusively from laboratory optical and microwave experiments where accurate bistatic measurements can be made within a fraction of a degree from the backscattering direction. However, it has largely been neglected in applications in microwave remote sensing of snow because of the difficulty of bistatics measurements to within a fraction of a degree from the backscattering direction
The authors in this experiment have made a good effort in measuring accurate bistatic measurements with Ku band for ground measurements and Tandem X of X band for satellites. The paper is a good step towards experiment validation of CBOE in remote sensing applications and the possible inclusion in modeling X band and Ku band volume scattering in snow. I have a few minor comments
- For Ku bad for volume scattering of snow, cross polarizations are usually strong. In laboratory experiments cross polarization enhancement are more conspicuous than co-polarization for both volume scattering (Kuga etal JOSA A, 1985) and surface scattering ( Johnson etal IEEE Transactions on Antennas and Propagation 1994) . What are the reasons for non-observations in this paper. How about deeper snow?
- The optical thickness can indicate the order of multiple scattering. Please discuss the optical thicknesses tau in the measurements at X band and Ku band
- For X band at Tandem X, the soil surface below the snow have significant contributions. What is the magnitude of surface scattering of the snow/soil interface below the snow layer?
- Will there be coherent backscattering due to rough soil surface below the snow at X band?
- AC2: 'Reply on RC2', Marcel Stefko, 30 Mar 2022
Marcel Stefko et al.
Marcel Stefko et al.
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