Characterizing Surface Water from Space with Microwave Remote Sensing: Advancing Conventional and Emerging Approaches
The extent and dynamics of land surface inundation vary tremendously across the globe. Accurate spatial representation of terrestrial surface water is of critical importance for management and conservation of biodiversity and other ecosystem services associated with freshwater. Furthermore, surface water maps representing dynamic characteristics of inundated areas are also valuable for the development of wetland inventories and to assess the role of wetlands as major natural sources of methane to the atmosphere. Despite the importance of these environments in global processes and to current and future climate, the extent and dynamics of global wetlands remain poorly characterized and modeled. The objective of this research is to extend the capabilities of satellite microwave remote sensing techniques to map hydrodynamic ecosystems and investigate related Earth-science questions. This thesis examines inundation detection using three independent approaches: (1) a combination of coarse-resolution active and passive sensors, (2) synthetic aperture radar (SAR), and (3) bistatic Global Navigation Satellite System reflectometry (GNSS-R). Advancements in each method are presented along with discussion on the associated trade-offs in temporal and spatial scales and sensor sensitivities. A series of coarse-resolution radiometer and scatterometer records have been re-assembled to construct the Surface Water Microwave Product Series version 3 (SWAMPSv3), a consistent long-term, global record suitable for large-scale hydrological assessments in addition to v retrospective local investigations. This relied on improved filtering and grid posting of swath-level microwave observations, updated ancillary data sets, and refined end-member calibration over arid and semi-arid regions. Large scale trends across the 25-year record are presented, along with a focused case-study on surface inundation patterns and historical malaria occurrence in East Africa. Regional-scale assessments were performed with SAR imagery across a variety of hydrodynamic regions that are conventionally very challenging to map due to a lack of historical inventories and vegetation cover. Field measurements supported an investigation of multitemporal L-band SAR and classification of inundation patterns across a dense and remote wetlands complex in the Peruvian Amazon. A novel approach using harmonic analysis of dual frequency (C-band and L-band) backscatter time series is introduced and tested over a variety of tropical wetlands sites across South America, Africa, and Southeast Asia. GNSS-R is a bistatic radar concept that takes advantage of GNSS transmitting satellites to yield observations with global coverage and rapid revisit time. Compared to coarse-resolution sensors and SAR, this technology offers a new and complementary approach to monitoring surface hydrology. Exploratory analyses test the capability of spaceborne GNSS reflections to characterize surface inundation and optimal data preparation methods. Experimental sensitivity assessments were performed to characterize the relationships of GNSS-R signals to variable surface water coverage and vegetation cover. Preliminary efforts at large-scale surface water delineation based on GNSS-R are presented. This dissertation research seeks to advance current capabilities of these conventional and emerging approaches, with the overarching goal of a collective improvement in characterization of hydrodynamics across the globe.
Environmental Monitoring, Fresh Water Studies, Hydrology, Water Resource Management, microwave remote sensing, synthetic aperture radar, wetlands, flooding, GNSS reflectometry
City University of New York - Graduate Center
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The Graduate School and University Center of The City University of New York