Preprints
https://doi.org/10.5194/tc-2021-359
https://doi.org/10.5194/tc-2021-359

  15 Dec 2021

15 Dec 2021

Review status: this preprint is currently under review for the journal TC.

Snow Water Equivalent Change Mapping from Slope Correlated InSAR Phase Variations

Jayson Eppler1, Bernhard T. Rabus1, and Peter Morse2 Jayson Eppler et al.
  • 1School of Engineering Science, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
  • 2Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, K1A 0E8, Canada

Abstract. Area-based measurements of snow water equivalent (SWE) are important for understanding earth system processes such as glacier mass balance, winter hydrological storage in drainage basins and ground thermal regimes. Remote sensing techniques are ideally suited for wide-scale area-based mapping with the most commonly used technique to measure SWE being passive-microwave, which is limited to coarse spatial resolutions of 25 km or greater, and to areas without significant topographic variation. Passive-microwave also has a negative bias for large SWE. Repeat-pass synthetic aperture radar interferometry (InSAR) as an alternate technique allows measurement of SWE change at much higher spatial resolution. However, it has not been widely adopted because: (1) the phase unwrapping problem has not been robustly addressed, especially for interferograms with poor coherence and; (2) SWE change maps scaled directly from repeat-pass interferograms are not an absolute measurement but contain unknown offsets for each contiguous coherent area. We develop and test a novel method for repeat-pass InSAR based dry-snow SWE estimation that exploits the sensitivity of the dry-snow refraction-induced InSAR phase to topographic variations. The method robustly estimates absolute SWE change at spatial resolutions of < 1 km, without the need for phase unwrapping. We derive a quantitative signal model for this new SWE change estimator and identify the relevant sources of bias. The method is demonstrated using both simulated SWE distributions and a 9-year RADARSAT-2 spotlight-mode dataset near Inuvik, NWT, Canada. SWE results are compared to in situ snow survey measurements and estimates from ERA5 reanalysis. Our method performs well in high-relief areas and in areas with high SWE (> 150 mm), thus providing complementary coverage to other passive- and active-microwave based SWE estimation methods. Further, our method has the advantage of requiring only a single wavelength band and thus can utilize existing spaceborne synthetic aperture radar systems. In application, a first order analysis of SWE trends within three drainage basins suggests that differences between basin-level accumulations are a function of major landcover types, and that re-vegetation following a forest-tundra fire that occurred over 50 years ago continues to affect the spatial distribution of SWE accumulation in the study area.

Jayson Eppler et al.

Status: open (until 10 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-359', Silvan Leinss, 14 Jan 2022 reply

Jayson Eppler et al.

Jayson Eppler et al.

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Short summary
We introduce a new method for mapping changes in the snow water-equivalent (SWE) of dry snow based on differences between time-repeated synthetic aperture radar (SAR) images. It correlates phase differences with variations in the topographic slope which allows the method to work without any ‘reference’ targets within the imaged area and without having to numerically ‘unwrap’ the spatial phase maps. This overcomes the key challenges faced in using SAR interferometry for SWE change mapping.