Near-nadir interferometric imaging SAR (Synthetic Aperture Radar) techniques are\npromising in measuring global water extent and surface height at fine spatial and temporal resolutions.\nThe concept of near-nadir interferometric measurements was implemented in the experimental\nInterferometric Imaging Radar Altimeters (InIRA) mounted on Chinese Tian Gong 2 (TG-2) space\nlaboratory. This study is focused on mapping the extent of high mountain lakes in the remote\nQinghaiâ??Tibet Plateau (QTP) areas using the InIRA observations. Theoretical simulations were first\nconducted to understand the scattering mechanisms under near-nadir observation geometry. It was\nfound that water and surrounding land pixels are generally distinguishable depending on the degree\nof their difference in dielectric properties and surface roughness. The observed radar backscatter is\nalso greatly influenced by incidence angles. A dynamic threshold method was then developed to\ndetect water pixels based on the theoretical analysis and ancillary data. As assessed by the LandSat\nresults, the overall classification accuracy is higher than 90%, though the classifications are affected\nby low backscatter possibly from very smooth water surface. The algorithms developed from this\nstudy can be extended to all InIRA land measurements and provide support for the similar space\nmissions in the future.
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