Synthetic aperture radar (SAR) backscatter response from methane ebullition bubbles trapped by thermokarst lake ice

Engram, Melanie; Anthony, K. M. Walter; Meyer, Franz J.; Grosse, Guido

doi:10.5589/m12-054

Cited by 38 publications

(46 citation statements)

References 53 publications

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“…Therefore, the roughness must involve the high dielectric contrast of the ice-water interface which is present in floating ice and is absent in grounded ice. While Engram et al (2012) postulated that the roughness involved the ice-water interface, our results here show the substantial decrease in T 11 backscatter intensity from floating to grounded ice, which provides evidence for the first time that the roughness comes from a rough ice-water interface. A rough ice-water interface could be caused by uneven ice growth, which can be the result of uneven snow distribution on the ice surface.…”

Section: Discussionsupporting

confidence: 42%

“…Ebullition activity can cause roughness at the ice water interface in two distinct ways. First, as bubbles come to rest under the ice, they cause a rough ice-water interface by creating a pocked water surface, similar to standing waves (Engram et al, 2012). Secondly, as seen in the results of our ebullition simulation experiment at O'Grady Pond, bubbles that are frozen in the ice cause slower ice growth directly beneath the bubble column, leading to the formation of steep domes of ice that are filled with water (Fig.…”

Section: Discussionmentioning

confidence: 77%

“…Weeks (1978Weeks ( , 1981 and others (Jeffries et al, 1994;Mellor, 1982;Morris et al, 1985 have posited that the small (< 2 mm diameter) tubular bubbles formed in lake ice by the rejection of dissolved gasses during the freezing process Langson, 1977, Boereboom et al, 2012) play a role in turning radar back to the satellite. Similarly, Engram et al (2012) showed a positive correlation between L-band backscatter and the abundance of larger (usually 1-100 cm diameter) ebullition bubbles in ice-covered lakes. The same study demonstrated that this positive correlation between single-pol L-band SAR and field measurements of ebullition bubbles in frozen lakes did not exist for C-band VV SAR.…”

Section: Engram Et Al: Characterization Of L-band Synthetic Apertmentioning

confidence: 82%

“…Field data on lake-ice thickness, water depth and sediment characteristics were collected for 10 locations on four NSP thermokarst lakes in April 2009 that varied both in bathymetry (deep vs. shallow) and in levels of ebullition bubbles observed previously by Engram et al (2012) in field work. We measured ice thickness in auger holes and water depth using sonar (Vexilar LPS-1 Hand-Held Depth Finder) and a weighted measuring tape.…”

Section: Methodsmentioning

confidence: 99%

“…It is furthermore important to study the driving scattering mechanism for scattering in the L-band frequency range in order to better understand the interaction of SAR with lake ice, and in order to identify observation parameters that optimize the contrast between floating and grounded ice. Finally, the magnitude of backscatter intensity decrease that suddenly occurs when lakes freeze to the lake bed is important to know in order to eliminate lakes that exhibit a backscatter drop of this magnitude from lake-ice analyses targeting methane ebullition (Engram et al, 2012).…”

Section: Engram Et Al: Characterization Of L-band Synthetic Apertmentioning

confidence: 99%

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Characterization of L-band synthetic aperture radar (SAR) backscatter from floating and grounded thermokarst lake ice in Arctic Alaska

et al. 2013

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Abstract. Radar remote sensing is a well-established method to discriminate lakes retaining liquid-phase water beneath winter ice cover from those that do not. L-band (23.6 cm wavelength) airborne radar showed great promise in the 1970s, but spaceborne synthetic aperture radar (SAR) studies have focused on C-band (5.6 cm) SAR to classify lake ice with no further attention to L-band SAR for this purpose. Here, we examined calibrated L-band single-and quadraturepolarized SAR returns from floating and grounded lake ice in two regions of Alaska: the northern Seward Peninsula (NSP) where methane ebullition is common in lakes and the Arctic Coastal Plain (ACP) where ebullition is relatively rare. We found average backscatter intensities of −13 dB and −16 dB for late winter floating ice on the NSP and ACP, respectively, and −19 dB for grounded ice in both regions. Polarimetric analysis revealed that the mechanism of L-band SAR backscatter from floating ice is primarily roughness at the ice-water interface. L-band SAR showed less contrast between floating and grounded lake ice than C-band; however, since L-band is sensitive to ebullition bubbles trapped by lake ice (bubbles increase backscatter), this study helps elucidate potential confounding factors of grounded ice in methane studies using SAR.

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Section: Discussionsupporting

confidence: 42%

Section: Discussionmentioning

confidence: 77%

Section: Engram Et Al: Characterization Of L-band Synthetic Apertmentioning

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Section: Engram Et Al: Characterization Of L-band Synthetic Apertmentioning

confidence: 99%

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Characterization of L-band synthetic aperture radar (SAR) backscatter from floating and grounded thermokarst lake ice in Arctic Alaska

et al. 2013

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Remote sensing of lake and river ice

Duguay

Bernier

Gauthier

et al. 2014

Remote Sensing of the Cryosphere

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Carbon emission from thermokarst lakes in NE European tundra

Zabelina

Shirokova

Klimov

et al. 2020

Limnology & Oceanography

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Emission of greenhouse gases (GHGs) from inland waters is recognized as highly important and an understudied part of the terrestrial carbon (C) biogeochemical cycle. These emissions are still poorly quantified in subarctic regions that contain vast amounts of surface C in permafrost peatlands. This is especially true in NE European peatlands, located within sporadic to discontinuous permafrost zones which are highly vulnerable to thaw. Initial measurements of C emissions from lentic waters of the Bolshezemelskaya Tundra (BZT; 200,000 km 2) demonstrated sizable CO 2 and CH 4 concentrations and fluxes to the atmosphere in 98 depressions, thaw ponds, and thermokarst lakes ranging from 0.5 × 10 6 to 5 × 10 6 m 2 in size. CO 2 fluxes decreased by an order of magnitude as waterbody size increased by > 3 orders of magnitude while CH 4 fluxes showed large variability unrelated to lake size. By using a combination of Landsat-8 and GeoEye-1 images, we determined lakes cover 4% of BZT and thus calculated overall C emissions from lentic waters to be 3.8 AE 0.65 Tg C yr −1 (99% C-CO 2 , 1% C-CH 4), which is two times higher than the lateral riverine export. Large lakes dominated GHG emissions whereas small thaw ponds had a minor contribution to overall water surface area and GHG emissions. These data suggest that, if permafrost thaw in NE Europe results in disappearance of large thermokarst lakes and formation of new small thaw ponds and depressions, GHG emissions from lentic waters in this region may decrease.

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Synthetic aperture radar (SAR) backscatter response from methane ebullition bubbles trapped by thermokarst lake ice

Cited by 38 publications

References 53 publications

Characterization of L-band synthetic aperture radar (SAR) backscatter from floating and grounded thermokarst lake ice in Arctic Alaska

Characterization of L-band synthetic aperture radar (SAR) backscatter from floating and grounded thermokarst lake ice in Arctic Alaska

Remote sensing of lake and river ice

Carbon emission from thermokarst lakes in NE European tundra

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