Abstract:The Louisiana coast is among the most productive coastal areas in the US and home to the largest coastal wetland area in the nation. However, Louisiana coastal wetlands have been disappearing at an alarming rate due to natural and anthropogenic processes, including sea level rise, land subsidence and infrastructure development. Wetland loss occurs mainly along the tidal zone, which varies in width and morphology along the Louisiana shoreline. In this study, we use Interferometric Synthetic Aperture Radar (InSAR) observations to detect the extent of the tidal inundation zone and evaluate the interaction between tidal currents and coastal wetlands. Our data consist of ALOS and Radarsat-1 observations acquired between 2006-2011 and 2003-2008, respectively. Interferometric processing of the data provides detailed maps of water level changes in the tidal zone, which are validated using sea level data from a tide gauge station. Our results indicate vertical tidal changes up to 30 cm and horizontal tidal flow limited to 5-15 km from open waters. The results also show that the tidal inundation is disrupted by various man-made structures, such as canals and roads, which change the natural tidal flow interaction with the coast.

ABSTRACT:During Hurricane Irma's passage over Florida in September 2017, many sections of the state experienced heavy rain and sequent flooding. In order to drain water out of potential flooding zones and assess property damage, it is important to map the extent and magnitude of the flooded areas at various stages of the storm. We use Synthetic Aperture Radar (SAR) and Interferometric SAR (InSAR) observations, acquired by Sentinel-1 before, during and after the hurricane passage, which enable us to evaluate surface condition during different stages of the hurricane. This study uses multi-temporal images acquired under dry condition before the hurricane to constrain the background backscattering signature. Flooded areas are detected when the backscattering during the hurricane is statistically significantly different from the average dry conditions. The detected changes can be either an increase or decrease of the backscattering, which depends on the scattering characteristics of the surface. In addition, water level change information in Palmdale, South Florida is extracted from an interferogram with the aid of a local water gauge as the reference. The results of our flooding analysis revealed that the majority of the study area in South Florida was flooded during Hurricane Irma.

The Karapinar basin, located in the Central Anatolian part of Turkey, is subjected to land subsidence and sinkhole activity due to extensive groundwater withdrawal that began in the early 2000s. In this study, we use Interferometric Synthetic Aperture Radar (InSAR), Global Navigation Satellite System (GNSS), and groundwater level data to monitor and better understand the relations between groundwater extraction, land subsidence, and sinkhole formation in the Karapinar basin. The main observations used in the study are InSAR-derived subsidence velocity maps calculated from both Sentinel-1 (2014–2018) and COSMO-SkyMed (2016–2017) SAR data. Our analysis reveals broad areas of subsidence with rates exceeding 70 mm/yr. The InSAR-derived subsidence was compared with GNSS data acquired by a continuously operating GNSS station located in the study area, which show a similar rate of subsidence. The temporal characteristic of both InSAR and GNSS time series indicate a long-term subsidence signal superimposed by seasonal variability, which follows the overall groundwater level changes, with over 80% cross-correlation consistency. Our results also indicate that sinkhole activity is limited to slow subsidence areas, reflecting strong cohesion of near-surface rock layers that resist subsidence but yield to collapse in response to aquifer system deformation induced by groundwater extraction.

MotivationWhile subsidence has affected Mexico City for over a century, other cities in central Mexico have been subjected to ground subsidence since the 1980's, as a result of their large urban expansion, population increase and aggressive groundwater extraction rates. The continuous ground subsidence results in severe damage to urban infrastructure and civil structures. Unfortunately the damage cost assessment and vulnerability are difficult to evaluate, because of the variable geographic extent and the time-continuous nature of the process, which have different characteristics than other phenomena characterized by localized, short duration events such as earthquakes or floodings with better media coverage.A recent SBAS survey based on ALOS-1 PALSAR data along central Mexico (Chaussard et al., 2014) indicates that this process is rapidly becoming a widespread phenomenon that potentially affects a population over 25 million inhabitants. InSAR-derived information and its cartographic products from geodetic imaging will be key to develop a better groundwater extraction strategy in areas that undergo extreme subsidence rates, propose better mitigation strategies and ultimately improve water resource management.In Mexico, subsidence induced damage to houses or other urban infrastructure is not eligible for federal emergency relief funds, because it is not considered a naturally occurring process but rather an anthropogenically induced one. Furthermore, this phenomenon is localized and usually managed only at the local city or county-level administrations, while most other large impact natural hazards, as earthquakes, volcano eruptions, or flooding events, are usually managed by federal agencies. This work is aimed towards a better recognition of subsidence as a major hazard in Mexico, assess the number of inhabitants affected and the spatial extent of the subsiding areas affected by this process. The space-based subsidence imaging can be used to improve water resources management (e.g. Hernández-Espriú et al., 2014) in an area that comprises a number of rapidly growing urban areas and assess its associated surface faulting geological hazard.We envision that this work will serve as a test case where water-usage policy makers can have access to custom cartographic products suitable for data fusion and data mining from third party regional water management agencies databases and include satellite geodesy imaging techniques as a routine monitoring technique for aquifer assessment and its sustainable management. Within this context, space geodetic techniques, most notably InSAR complemented by GPS are quite suitable for this task. InSAR provides an unsurpassed synoptic view of the earth's dynamic surface; for Published by Copernicus Publications on behalf of the International Association of Hydrological Sciences.

Here, we present an enhanced algorithm to correct interferometric synthetic aperture radar (InSAR) phase unwrapping errors by incorporating iterative spatial bridging between islands and phase closure among interferograms. We use rapid repeat airborne synthetic aperture radar acquisitions from NASA's airborne uninhabited aerial vehicle synthetic aperture radar (UAVSAR) instrument to estimate short-term changes in water level within coastal wetlands from a stack of consecutive interferograms acquired with very short temporal separation (∼30 min). The algorithm is applied to six consecutive UAVSAR images collected in tidal wetlands of the Wax Lake Delta, Louisiana, USA. Validation of our water level change retrievals with in situ field observations was conclusive with high correlation and an RMSE generally smaller than 3 cm. Comparison of our algorithm with other phase unwrapping error correction methods shows significant improvement (30%-35% increase in the number of correctly unwrapped pixels) when applied to rapid changes in water level. The set of corrections presented in this work enables measurement of water level change in deltas and other areas where tides drive highly dynamic flooding of inland vegetated areas. Although demonstrated for water level change, the method is applicable to other InSAR datasets with large spatial gradients or observed discontinuities between coherent but spatially isolated areas.