An Object-Based Classification Method to Detect Methane Ebullition Bubbles in Early Winter Lake Ice

Remote Sensing

卷:11

Guido Grosse¹  Prajna Lindgren²  FranzJ. Meyer²  KateyWalter Anthony³ 

[1] Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany;

[2] Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, USA;

[3] Water and Environmental Research Center, University of Alaska Fairbanks, Fairbanks, AK 99775, USA;

关键词: methane ebullition mapping;    lake ice;    object-based image classification;    aerial photography;    thermokarst lake;    permafrost carbon feedback;   

DOI  :  10.3390/rs11070822

来源: DOAJ

【 摘 要 】

Thermokarst lakes in the Arctic and Subarctic release carbon from thawing permafrost in the form of methane and carbon dioxide with important implications for regional and global carbon cycles. Lake ice impedes the release of gas during the winter. For instance, bubbles released from lake sediments become trapped in downward growing lake ice, resulting in vertically-oriented bubble columns in the ice that are visible on the lake surface. We here describe a classification technique using an object-based image analysis (OBIA) framework to successfully map ebullition bubbles in airborne imagery of early winter ice on an interior Alaska thermokarst lake. Ebullition bubbles appear as white patches in high-resolution optical remote sensing images of snow-free lake ice acquired in early winter and, thus, can be mapped across whole lake areas. We used high-resolution (9–11 cm) aerial images acquired two and four days following freeze-up in the years 2011 and 2012, respectively. The design of multiresolution segmentation and region-specific classification rulesets allowed the identification of bubble features and separation from other confounding factors such as snow, submerged and floating vegetation, shadows, and open water. The OBIA technique had an accuracy of >95% for mapping ebullition bubble patches in early winter lake ice. Overall, we mapped 1195 and 1860 ebullition bubble patches in the 2011 and 2012 images, respectively. The percent surface area of lake ice covered with ebullition bubble patches for 2011 was 2.14% and for 2012 was 2.67%, representing a conservative whole lake estimate of bubble patches compared to ground surveys usually conducted on thicker ice 10 or more days after freeze-up. Our findings suggest that the information derived from high-resolution optical images of lake ice can supplement spatially limited field sampling methods to better estimate methane flux from individual lakes. The method can also be used to improve estimates of methane ebullition from numerous lakes within larger regions.

【 授权许可】

Unknown