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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-226
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-226
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  24 Aug 2020

24 Aug 2020

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A revised version of this preprint is currently under review for the journal TC.

Mapping potential signs of gas emissions in ice of lake Neyto, Yamal, Russia using synthetic aperture radar and multispectral remote sensing data

Georg Pointner1,2, Annett Bartsch1,2, Yury A. Dvornikov3, and Alexei V. Kouraev4,5 Georg Pointner et al.
  • 1b.geos, Korneuburg, Austria
  • 2Austrian Polar Research Institute, Vienna, Austria
  • 3Agrarian-Technological Institute, Peoples' Friendship University of Russia, Moscow, Russia
  • 4LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS Toulouse, France
  • 5Tomsk State University, Tomsk, Russia

Abstract. Regions of anomalously low backscatter in C-band Synthetic Aperture Radar (SAR) imagery of lake ice of lake Neyto in northwestern Siberia have been suggested to be caused by emissions of gas (methane from hydrocarbon reservoirs) through the lake's sediments before. However, to assess this connection, only analyses of data from boreholes in the vicinity of lake Neyto and visual comparisons to medium-resolution optical imagery have been provided so far due to lack of in situ observations of the lake ice itself. These observations are impeded due to accessibility and safety issues. Geospatial analyses and innovative combinations of satellite data sources are therefore proposed to advance our understanding of this phenomenon. In this study, we assess the nature of the backscatter anomalies in Sentinel-1 C-band SAR images in combination with Very High Resolution (VHR) WorldView-2 optical imagery. We present methods to automatically map backscatter anomaly regions from the C-band SAR data (40 m pixel-spacing) and holes in lake ice from the VHR data (0.5 m pixel-spacing), and examine their spatial relationships. The reliability of the SAR method is evaluated through comparison between different acquisition modes. The results show that the majority of mapped holes in the VHR data are clearly related to anomalies in SAR imagery acquired a few days earlier and also more than a month before, supporting the hypothesis of gas emissions as the cause of the backscatter anomalies. Further, a significant expansion of backscatter anomaly regions in spring is documented and quantified in all analysed years 2015 to 2019. Our study suggests that the backscatter anomalies might be caused by expanding cavities in the lake ice, formed by strong emissions of gas, which could also explain outcomes of polarimetric analyses of auxiliary L-band ALOS PALSAR-2 data. C-band SAR data is considered to be valuable for the identification of lakes showing similar phenomena across larger areas in the Arctic in future studies.

Georg Pointner et al.

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Georg Pointner et al.

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Short summary
This study presents new strong indications that regions of anomalously low backscatter in C-band synthetic aperture radar (SAR) imagery of ice of lake Neyto in northwestern Siberia are caused by strong emissions of natural gas. Spatio-temporal dynamics and potential scattering and formation mechanisms are assessed. It is suggested that exploiting the spatial and temporal properties of Sentinel-1 SAR data may be beneficial for the identification of similar phenomena in other Arctic lakes.
This study presents new strong indications that regions of anomalously low backscatter in C-band...
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