Flood Depth Estimation During Hurricane Harvey Using Sentinel-1 and UAVSAR Data

In August 2017, Hurricane Harvey was one of the most destructive storms to make landfall in the Houston area, causing loss of life and property. Temporal and spatial changes in the depth of floodwater and the extent of inundation form an essential part of flood studies. This work estimates the flood extent and depth from LiDAR DEM (light detection and ranging digital elevation model) using data from the Synthetic Aperture Radar (SAR)–Unmanned Aerial Vehicle Synthetic Aperture Radar (UAVSAR) and satellite sensor—Sentinel-1. The flood extent showed a decrease between 29–30 August and 5 September 2017. The flood depths estimated using the DEM were compared with the USGS gauge data and showed a correlation (R2) greater than 0.88. The use of Sentinel-1 and UAVSAR resulted in a daily temporal repeat, which helped to document the changes in the flood area and the water depth. These observations are significant for efficient disaster management and to assist relief organizations by providing spatially precise information for the affected areas

Surface freshwater storage variations in the Orinoco floodplains using multi-satellite observations

Variations in surface water extent and storage are poorly characterized from regional to global scales. In this study, a multi-satellite approach is proposed to estimate the water stored in the floodplains of the Orinoco Basin at a monthly time-scale using remotely-sensed observations of surface water from the Global Inundation Extent Multi-Satellite (GIEMS) and stages from Envisat radar altimetry. Surface water storage variations over 2003-2007 exhibit large interannual variability and a strong seasonal signal, peaking during summer, and associated with the flood pulse. The volume of surface water storage in the Orinoco Basin was highly correlated with the river discharge at Ciudad Bolivar (R = 0.95), the closest station to the mouth where discharge was estimated, although discharge lagged one month behind storage. The correlation remained high (R = 0.73) after removing seasonal effects. Mean annual variations in surface water volume represented similar to 170 km(3), contributing to similar to 45% of the Gravity Recovery and Climate Experiment (GRACE)-derived total water storage variations and representing similar to 13% of the total volume of water that flowed out of the Orinoco Basin to the Atlantic Ocean

Mapping wetlands and potential wetland restoration areas in Black Hawk County, Iowa using object-oriented classification and a GIS-based model

Wetlands are transitional lands between terrestrial and aquatic systems that provide many benefits, including: floodwater retention, non-point pollution treatment, wildlife habitat, and soil-erosion control. Wetlands in Iowa have decreased over 95% in the last 200 years. Therefore, there is a need to map and monitor these resources, as well as to determine potential sites for wetland restoration. In Black Hawk County, wetland maps are outdated, and ground surveys have proved to be too time-consuming and expensive. Traditional pixel-based automated classifiers of remotely-sensed imagery have also proven to be inaccurate in classifying wetlands because of spectral confusion. This study tests multispectral data, hybrid data, hyperspectral data, a seasonal matrix, and a new object-oriented classifier. These are tested against traditional multispectral, pixelbased (ISODATA and Maximum-Likelihood) classifiers both to see if wetland classification accuracies from remotely-sensed imagery can be increased and to produce an updated wetlands map for Black Hawk County. A hyperspectral image of Eddyville, Iowa is tested to evaluate how well wetlands are classified when a hyperspectral image is used with an object-oriented classifier and a hyperspectral pixel-based (Spectral Angle Mapper or SAM) classifier. A GIS-based wetland restoration model is developed to identify potential wetland restoration sites in Black Hawk County. This study shows that the object-oriented classifier is more accurate in identifying wetlands and overall land-cover than pixel-based ones (ISODATA, Maximum-Likelihood, SAM) in both multispectral, hybrid-multispectral, and hyperspectral imagery. The summer/fall seasonal matrix produced unacceptable accuracies. Wetlands in Black Hawk County decreased by 1500 acres (plus or minus an error margin of 375 acres) from 1983 to 2003. The restoration model identified 2,971 acres in Black Hawk County as being highly suitable, 34,307 acres as being moderately suitable, and 121,271 acres as having low suitability for wetland restoration. The results are available at http://gisrl-9.geog.uni.edu/wetland. Limitations of the study include file size when using the object-oriented classifier, image availability for the seasonal matrix, and the number of variables employed in the GIS-based restoration model. The future direction of the study lies in obtaining hyperspectral data for Black Hawk County, more current Landsat multispectral imagery for the seasonal matrix, and testing of more non-parametric classifiers, such as the CART algorithm

Estado da Arte do Sensoriamento Remoto de Radar: Fundamentos, Sensores, Processamento de Imagens e Aplicações.

Este artigo aborda o estado da arte do sensoriamento remoto por radar e foi elaborado para fazer parte da edição especial de comemoração dos 50 anos desta revista. Neste estudo, é apresentada uma breve introdução sobre os fundamentos do sensoriamento remoto por radar, com destaque para os parâmetros mais importantes de imageamento e da superfície terrestre envolvidos no processo de obtenção de imagens de radar. Ênfase é dada para o comprimento de onda, polarização das ondas eletromagnéticas e geometria de obtenção de imagens (parâmetros de imageamento) e para a umidade de solos e da vegetação, rugosidade do terreno e estrutura da vegetação (parâmetros da superfície terrestre). Em seguida, são apresentados os principais sensores orbitais de radar de abertura sintética que estão atualmente em operação e os principais processamentos digitais de imagens de radar, destacando-se a conversão dos valores digitais para coeficientes de retroespalhamento, os filtros espaciais para redução do ruído speckle, as técnicas de decomposição de imagens e o processamento InSAR. Finalmente, é apresentada uma breve discussão sobre algumas aplicações potenciais, com especial atenção para o monitoramento de derrame de óleo em plataformas continentais, estimativa de biomassa aérea, monitoramento de desmatamento em coberturas florestais tropicais, detecção de áreas de plantio de arroz irrigado e estimativa de umidade de solos

Remote Sensing of River Discharge: A Review and a Framing for the Discipline

Remote sensing of river discharge (RSQ) is a burgeoning field rife with innovation. This innovation has resulted in a highly non-cohesive subfield of hydrology advancing at a rapid pace, and as a result misconceptions, mis-citations, and confusion are apparent among authors, readers, editors, and reviewers. While the intellectually diverse subfield of RSQ practitioners can parse this confusion, the broader hydrology community views RSQ as a monolith and such confusion can be damaging. RSQ has not been comprehensively summarized over the past decade, and we believe that a summary of the recent literature has a potential to provide clarity to practitioners and general hydrologists alike. Therefore, we here summarize a broad swath of the literature, and find after our reading that the most appropriate way to summarize this literature is first by application area (into methods appropriate for gauged, semi-gauged, regionally gauged, politically ungauged, and totally ungauged basins) and next by methodology. We do not find categorizing by sensor useful, and everything from un-crewed aerial vehicles (UAVs) to satellites are considered here. Perhaps the most cogent theme to emerge from our reading is the need for context. All RSQ is employed in the service of furthering hydrologic understanding, and we argue that nearly all RSQ is useful in this pursuit provided it is properly contextualized. We argue that if authors place each new work into the correct application context, much confusion can be avoided, and we suggest a framework for such context here. Specifically, we define which RSQ techniques are and are not appropriate for ungauged basins, and further define what it means to be ‘ungauged’ in the context of RSQ. We also include political and economic realities of RSQ, as the objective of the field is sometimes to provide data purposefully cloistered by specific political decisions. This framing can enable RSQ to respond to hydrology at large with confidence and cohesion even in the face of methodological and application diversity evident within the literature. Finally, we embrace the intellectual diversity of RSQ and suggest the field is best served by a continuation of methodological proliferation rather than by a move toward orthodoxy and standardization

Identificação de áreas inundáveis na porção sul de Roraima com auxílio de imagens de radar

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Humanas, Departamento de Geografia, Programa de Pós-graduação, 2018.As áreas úmidas são de extrema importância para o equilíbrio da vida na Terra, compreender o seu comportamento é crucial para a preservação destes ecossistemas. Muitas dessas áreas, como as inseridas em domínio amazônico, são de difícil acesso para um estudo em campo. As técnicas de Sensoriamento Remoto têm evoluído muito, aliadas aos avanços da inteligência artificial, contribuindo para o desenvolvimento de estudos em locais de difícil acesso, possibilitando bons resultados de acordo com o tipo de dado utilizado. O presente estudo utilizou a técnica de aprendizado de máquina Random Forest, e limiar de retroespalhamento em imagens SAR do satélite Sentinel 1, da Agência Espacial Europeia, para identificar áreas úmidas no sul do estado de Roraima ao longo do ano de 2017. O trabalho identificou o comportamento típico de áreas inundáveis nas margens dos rios e feições adjacentes ao principal rio do estado (rio Branco). O pico de cheia foi encontrado no mês de Julho, cobrindo mais de 72.000 hectares da área de estudo (11,9% da área total da cena), e o de seca no mês de Dezembro, cobrindo mais de 37.000 hectares (6,1% da área total da cena).Wetlands are of extreme importance for the balance of life on Earth, understanding their behavior is crucial to the preservation of these ecosystems. Many of these areas, such as those in the Amazonian domain, are difficult to access for field study. The techniques of Remote Sensing have evolved a lot, combined with the advances of artificial intelligence, contributing to the development of studies in places of difficult access, allowing good results according to the type of data used. The present study used the Random Forest machine learning technique and backscatter threshold in SAR images of the Sentinel 1 satellite of the European Space Agency to identify wetlands in the south of the state of Roraima throughout 2017. The work identified the typical behavior of flooded areas on the banks of the rivers and features adjacent to the main river of the state (Rio Branco). The flood peak was found in July, covering more than 72,000 hectares of the study area (11.9% of the total area of the scene), and the dry season in December, covering more than 37,000 hectares (6.1 % of the total area of the scene)

Monitoramento hidrológico da Bacia do Rio Madeira por altimetria espacial

The objective of this work was to monitor the hydrological stations t the border of the Amazon Basin, specifically the Madeira Basin. Radar altimetry from the Envisat and Jason-2 missions was used to provide observations of water height from 2002 to 2016. From the results obtained, the basin rivers were characterized in a hydrological way, identifying periods and beginnings of flood-spate-ebb-drought and making estimates. Finally, the observations of the altimetric satellites were used to understand the flood of 2014, which occurred in international rivers, taking into account the start of operations of the new hydroelectric power plants. The results, in general, indicate that there is influence of transboundary rivers in relation to the Madeira River, even if some of them have more seasonal, cyclical or independent behavior. The flood event in 2014 stated that there is a propagation in the maximum and minimum, upstream downstream, with significant day intervals, and the virtual stations located before the hydroelectric dams had no influence on the hydrological behavior. However, the ones located after the dams suffered from the alteration of the hydrological period, the intensity and the modification of the profile of the river.Este trabalho teve como objetivo monitorar estações hidrológicas fronteiriças pertencentes à Bacia Amazônica, especificamente a Bacia do Madeira. Foi utilizada a altimetria espacial através dos satélites Envisat e Jason-2, que fornecem observações de altura d’água no período de 2002 a 2016. A partir dos resultados obtidos, foram caracterizados os rios da bacia, de forma hidrológica, identificando períodos e inícios de enchentes-cheias-vazantes-secas e realizando estimativas. Finalmente, as observações dos satélites altimétricos foram aproveitadas para compreender a cheia de 2014, ocorrida em rios internacionais, tendo em perspectiva o início das operações das novas hidrelétricas. Os resultados, de forma geral, indicaram que há influência dos rios transfronteiriços em relação ao Rio Madeira, mesmo que alguns deles tenham comportamentos mais sazonais, cíclicos ou independentes. O evento de cheia em 2014, ratificou que há uma propagação nas máximas e mínimas, de montante a jusante, com intervalos de dias significativos, e as estações virtuais localizadas antes das hidrelétricas não sofreram influência em seu comportamento hídrico. Contudo, as posteriores sofreram com a alteração do período hidrológico, a intensidade e a modificação da assinatura do rio