A correlation-based approach to modeling interferometric radar observations of the Greenland ice sheet
Stanford University, 2001 - Technology & Engineering - 330 pages
"Interferometric synthetic aperture radar (InSAR) phase observations have greatly increased our understanding of the topography and motion of ice sheets, but yield little information on the sub-surface structure, a needed description for mass-balance estimates. Inversion of a diffuse volume scatter model shows that InSAR correlation values, p, can be related to radiowave penetration depths, d, which depend on characteristics of the snow/ice volume. Application to European Research Satellite (ERS) images (VV, 5.6 cm, 23 ̊incidence angle) of the Greenland ice sheet imply C-band d of 0 m along the rocky coast, 10-20 m in the bare ice zone, and 20-35 m in the percolation zone and dry snow zone, consistent with in situ results. Moreover, volume scattering reduces the ERS critical baseline from about 1100 m to 300 m. Correlation and backscatter power (ơ0) observations can be combined for further understanding of the snow/ice volume. In particular, p and ơ0 data of 15 km-long, 50 m-high topographic undulations in the dry snow zone arc minimum on the windward side and maximum on the lee side, with 1 to 3 dB variation typical. These spatial variations in the scattering medium appear to follow from differences in snow accumulation due to prevailing winds. Assuming that snow-grains are the dominant source of backscatter, the classical independent-scatterer model is physically implausible at firn densities; a second-order dense-medium radiative transfer model also is unable to explain both the observed d and ơ0. A modified Born approach provides a better match to ơ0 and p separately, but leads to different grain size solutions for each measurement type. A buried layer model based on the incoherent addition of echoes from hoar layer interfaces, in which scattering from a single layer is derived from small-perturbation methods, reconciles the ERS ơ0 and p data, with variations in hoar layer spacing of 12-17 cm providing the needed structural fluctuations for the observed range of ơ0 and p. Translation of layer spacing into accumulation rates predicts a 40% variability in accumulation rate from the windward to lee side and, more importantly, addresses high-resolution mapping of continental accumulation rates"--Leaves iv-v.
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Remote Sensing of Ice Sheets
SAR and InSAR
5 other sections not shown
accumulation rates antenna assume average azimuth backscatter power image C-band calculate coast correlation coefficient correlation data correlation images decrease derived discussed in Chap discussed in Sec DMRT model dry snow zone ERS data Figure function geometry Greenland firn Greenland ice sheet ice pipes ice stream impulse response incidence angle increases InSAR InSAR data interfaces interferograms interferometric phase Jezek Joughin Kaiser window mass balance Matzler measured meters microwave noise number of looks parameters penetration depth percolation zone permittivity perpendicular baseline pixel plot polar firn power and correlation radar cross section radiowave region remote sensing resolution cell resolution element return echo return power rocky Rott Ryder Glacier SAR image SAR observations satellite scattering coefficient scattering medium scattering models shown in Fig signal snow grain spatial correlation spatial frequency surface scatter temporal baseline temporal decorrelation terrain thermal topography variations vertical volume correlation volume scatter wavelength Zebker