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TitleSnow water equivalent change mapping from slope-correlated synthetic aperture radar interferometry (InSAR) phase variations
AuthorEppler, J; Rabus, B; Morse, PORCID logo
SourceThe Cryosphere vol. 16, 2022 p. 1497-1521, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20210443
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
Lat/Long WENS-136.0000 -132.0000 69.0000 68.0000
SubjectsScience and Technology; surficial geology/geomorphology; snow; mapping techniques; infrared surveys; radar imagery; synthetic aperture radar surveys (SAR)
Illustrationssatellite images; graphs; plots; tables
ProgramClimate Change Geoscience Permafrost
Released2022 06 02
AbstractArea-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. Another method is repeat-pass synthetic aperture radar interferometry (InSAR) that 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 repeatpass 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 (C-band, 5.405 GHz) spotlight-mode dataset near Inuvik, Northwest Territories (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, thus providing complementary coverage to passive-microwave-based SWE estimation. Further, our method has the advantage of requiring only a single wavelength band and thus can utilize existing spaceborne synthetic aperture radar systems.
Summary(Plain Language Summary, not published)
Snow Water Equivalent (SWE) is a measure of the amount of water contained in a cross-section of the snow cover. This is the first method developed to provide a direct estimate of SWE from space-borne synthetic aperture radar systems. We test the method with satellite images over Inuvik, NT, where we have field measurements of snow properties to compare with the results. Our method performs well in high-relief areas and in areas with high SWE (>150 mm), thus providing complementary coverage to other radar-based SWE estimation methods. Our method also has the advantage of requiring only a single wavelength band and thus can utilize existing space-borne synthetic aperture radar systems.

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