Characterizing Near Nadir Ka-band Backscatter for Mapping Water Surfaces With InSAR

To gain an empirical understanding of the utility of near-nadir Ka-band for mapping surface changes, particularly with respect to water and wet surfaces, this dissertation demonstrates the utility for mapping water surface elevation (WSE) and inundation as observed by the airborne complement of the upcoming Surface Water and Ocean Topography (SWOT), AirSWOT. To produce high-resolution WSE and extents, SWOT and AirSWOT rely on strong backscatter signal returns using the Ka-band radar frequency. However, despite having many theoretical assessments of Ka-band scattering for water surfaces, observation-based knowledge of high-resolution Ka-band scattering for small inland water bodies is limited, consequently limiting the understanding of signal errors and resultant elevation errors. AirSWOT has provided the first Ka-band InSAR observations over diverse land cover and under changing hydrologic conditions by flying through Alaska and Canada during July and August 2017, allowing an unprecedented assessment of Ka-band scattering dynamics. These flights revealed bright radar returns, akin to a theoretical open water return, over vegetation and moist, bare soils, complicating open water classification, a necessary task for the SWOT mission. AirSWOT WSE errors relative to in-situ GPS showed an average bias of -58 cm. After correcting for biases, centimeter-level seasonal hydrologic changes are identified across the study region for the period July-August 2017. Following bias correction, residual errors may be explained by the prevalence of mixed water-vegetation pixels, which may occur in 5% of observations on average, and by wind speeds below 3 m/s (6.7 mph), which reduce water surface roughness. This dissertation uses airborne AirSWOT, LiDAR, model, and in-situ data to (1) demonstrate the utility of the 2017 Ka-band AirSWOT observations, showing that the error-prone dataset can nonetheless observe cm-scale hydrologic spatial and temporal gradients across the ABoVE domain; (2) identify differences and similarities in backscattering values between water and land cover types to assess the likelihood of misclassification, additionally enabling the characterization of vegetation densities alongside the heights estimated from InSAR; and (3) assess atmospheric influences from the wind on Ka-band scattering changes due to water surface roughening, creating a path for assessments at the water-air interface for small water bodies