Title :
Supraglacial Streams on the Greenland Ice Sheet Delineated From Combined Spectral–Shape Information in High-Resolution Satellite Imagery
Author :
Kang Yang ; Smith, L.C.
Author_Institution :
Dept. of Geographic Inf. Sci., Nanjing Univ., Nanjing, China
Abstract :
Supraglacial meltwater streams and lakes that form each summer across large expanses of the Greenland Ice Sheet (GrIS) ablation zone have global implications for sea level rise but remain one of the least studied hydrologic systems on Earth. Remote sensing of supraglacial streams is challenging owing to their narrow width (~1-30 m) and proximity to other features having similar visible/near-infrared reflectance (lakes and slush) or shape (dry stream channels, crevasses, and fractures). This letter presents a new automated “spectral-shape” procedure for delineating actively flowing streams in high-resolution satellite imagery, utilizing both spectral and pattern information. First, a modified normalized difference water index adapted for ice ( NDWIice) enhances the spectral contrast between open water and drier snow/ice surfaces. Next, three NDWIice thresholds are used to mask deep-water lakes and discern open water from slush, in concert with a multipoints fast marching method to rejoin resulting stream fragments. Comparison of this procedure with manual digitization for six WorldView-2 images in southwestern Greenland demonstrates its value for detecting actively flowing supraglacial streams, particularly in slushy areas where classification performance dramatically improves (85.2% success) versus simple threshold methods (52.9% and 59.4% success for low and moderate thresholds, respectively). While a simple threshold approach is satisfactory for areas known to be slush free, the procedure outlined here enables comprehensive stream mapping across the GrIS ablation zone, regardless of slush conditions and/or the presence of similarly shaped glaciological features.
Keywords :
fracture; geophysical image processing; glaciology; hydrological techniques; lakes; remote sensing; sea level; snow; GrIS ablation zone; Greenland Ice Sheet ablation zone; WorldView-2 images; actively flowing streams; classification performance; crevasses; deep-water lakes; drier ice surfaces; drier snow surfaces; dry stream channels; fractures; glaciological features; high-resolution satellite imagery; hydrologic systems; manual digitization; modified normalized difference water index; multipoint fast marching method; near-infrared reflectance; open water; pattern information; remote sensing; sea level rise; slush conditions; slushy areas; southwestern Greenland; spectral contrast; spectral information; spectral-shape information; spectral-shape procedure; stream fragments; stream mapping; supraglacial meltwater streams; threshold methods; visible reflectance; Accuracy; Green products; Ice; Image edge detection; Lakes; Shape; Streaming media; Fast marching method; Greenland Ice Sheet (GrIS); WorldView-2; mathematical morphology; normalized difference water index (NDWI); supraglacial stream hydrology;
Journal_Title :
Geoscience and Remote Sensing Letters, IEEE
DOI :
10.1109/LGRS.2012.2224316