Near real-time flood detection in urban and rural areas using high resolution Synthetic Aperture Radar images

A near real-time flood detection algorithm giving a synoptic overview of the extent of flooding in both urban and rural areas, and capable of working during night-time and day-time even if cloud was present, could be a useful tool for operational flood relief management. The paper describes an automatic algorithm using high resolution Synthetic Aperture Radar (SAR) satellite data that builds on existing approaches, including the use of image segmentation techniques prior to object classification to cope with the very large number of pixels in these scenes. Flood detection in urban areas is guided by the flood extent derived in adjacent rural areas. The algorithm assumes that high resolution topographic height data are available for at least the urban areas of the scene, in order that a SAR simulator may be used to estimate areas of radar shadow and layover. The algorithm proved capable of detecting flooding in rural areas using TerraSAR-X with good accuracy, classifying 89% of flooded pixels correctly, with an associated false positive rate of 6%. Of the urban water pixels visible to TerraSAR-X, 75% were correctly detected, with a false positive rate of 24%. If all urban water pixels were considered, including those in shadow and layover regions, these figures fell to 57% and 18% respectively

On the use of COSMO/SkyMed data and Weather Models for interferometric DEM generation

AbstractThis work experiments the potentialities of COSMO/SkyMed (CSK) data in providing interferometric Digital Elevation Model (DEM). We processed a stack of CSK data for measuring with meter accuracy the ground elevation on the available coherent targets, and used these values to check the accuracy of DEMs derived from 5 tandem-like CSK pairs. In order to suppress the atmospheric signal we experimented a classical spatial filtering of the differential phase as well as the use of numerical weather prediction (NWP) model RAMS. Tandem-like pairs with normal baselines higher than 300 m allows to derive DEMs fulfilling the HRTI Level 3 specifications on the relative vertical accuracy, while the use of NWP models still seems unfeasible especially for X-band

Evolução hidro geomorfológica da zona proglacial da Geleira Collins, Ilha Rei George, Antártica

As geleiras são indicadores sensíveis às mudanças climáticas, aquelas áreas marginais à geleira e proglaciais apresentam várias mudanças decorrentes da retração das geleiras. Dessa forma, esta tese propõe um modelo de desenvolvimento hidrológico e geomorfológico da zona proglacial de uma geleira no sul da ilha Rei George, ilhas Shetland do Sul, Antártica no período desde a Pequena Idade do Gelo até 2017. A compartimentação do relevo e mapeamento geomorfológico proglacial foi feito a partir de Modelo Digital de Elevação gerado a partir de imagens TanDEM-X e de uma imagem QuickBird de 2008, além de coletas de sedimentos em campo. Já para a caracterização da fenologia de gelo da superfície de lagos proglaciais, foi feita uma correlação da área de superfície líquida, obtida em imagens TerraSAR X de 2011, com as variáveis temperatura, precipitação e vento. O cenário de evolução da geleira (chamada localmente de geleira Collins) até 2070 foi elaborado a partir de metodologia de Ruckamp et al. (2011). Os compartimentos na península onde encontra-se a geleira (península Fildes) são planaltos e depressões que possuem como principais formas associadas paleovales em U e vales em anfiteatro que foram posteriormente retrabalhados por canais de degelo e processos intempéricos. A área proglacial não é homogênea e a frente da geleira apresentou distintos ambientes que foram mapeados nessa tese em setores. Os setores do lado leste são os mais dinâmicos da geleira, pois além de apresentar vários canais de água de degelo, tem feições como flutings e morainas de recessão. No cenário do comportamento da geleira para o futuro, são justamente essas áreas que deverão ser as primeiras a apresentarem retração, até 2030 É provável que no futuro, com a retração da geleira, devido a configuração do relevo subglacial, haverá formação de lagos, alagados e canais nas suas porções mais côncavas e mais tempo de atuação dos processos paraglaciais. Os setores voltados para a passagem de Drake indicam um sistema glacial ativo com capacidade de transporte de material de diferentes tamanhos e quantidade. No futuro essa área, devido ao relevo subglacial e hidrologia, provavelmente não terá a formação de lagos e feições como flutings ou morainas de recessão, se caracterizando como mais estável. Quanto a formação atual dos lagos, 7 dos 15 lagos analisados para o verão de 2011 apresentaram correlação significativa (ρ maior que 0,4) com a temperatura, enquanto 11 lagos responderam significativamente para precipitação. Os lagos atingem a área máxima de superfície líquida no final de fevereiro e congelam completamente no início de abril. O cenário de variação espacial da frente da geleira Collins revela a continuidade do processo de retração para as próximas décadas, com perda de 35% de sua área até 2070. No primeiro momento, a retração na zona proglacial formará uma área instável com alta quantidade de sedimentos nos canais. A fixação da vegetação contribuirá nessa fase para aumento da infiltração de água de degelo no solo (formação de alagados), aumento da força e cisalhamento do solo até que a paisagem atinja uma fase estável, com indícios de atividade periglacial entre 2050 e 2070.Glaciers are sensitive indicators of climate change, those marginal and proglacial areas show several changes due to glaciers retraction. Having this in mind, this thesis proposes a hydrological and geomorphological development model for the proglacial zone of a glacier in the south of the King George island, South Shetland Islands, Antarctica in the period between the Little Ice Age and 2017. The relief compartmentation and proglacial geomorphological mapping was done using a Digital Elevation Model generated from TanDEM-X images and a QuickBird image from 2008, in addition to field sediment samples. For the characterization of the ice phenology of the proglacial lakes surface, a correlation of the net surface area, obtained from 2011 TerraSAR X images, was made with temperature, precipitation and wind variables. The evolution of the glacier (locally called Collins Glacier) until 2070 was elaborated using the methodology by Ruckamp et al. (2011). The compartments in the peninsula where the glacier is located (Fildes Peninsula) are plateaus and depressions that have U paleovalley sand amphitheatre valleys as main forms later reworked by melting channels and intemperic processes. The proglacial area is not homogeneous and the glacier front has different environments that were mapped in this thesis in sectors. The glacier eastern sectors are the most dynamic ones, as they have several melting water channels, features like flutings and moraines of recession. In the scenario for the future behaviour of the glacier, it is possible that these areas that will be the first ones to present retraction, until 2030 It is probable that in the future, with the retraction of the glacier, due to the configuration of the subglacial relief, there will be formation of lakes, flooded areas and channels in their more concave portions and more time for operation of the paraglacial processes. The sectors orientated to the Drake Passage indicate an active glacial system with capacity to transport material of different sizes and quantity. In the future this area, due to subglacial relief and hydrology, probably will not have the formation of lakes and features like flutings or moraines of recession, characterizing itself as more stable. Regarding the current lake formation, 7 of the 15 lakes analysed for the 2011 summer presented a significant correlation (ρ greater than 0.4) with temperature, while 11 lakes responded significantly to precipitation. The lakes reached the maximum net surface area at the end of February and frozen completely at the beginning of April. The spatial variation scenario of the Collins Glacier front reveals the continuity of the retraction process for the coming decades, with a loss of 35% of its area by 2070. At the first moment, the retraction in the proglacial zone will form an unstable area with a high amount of sediments in the channels. In this phase, vegetation fixation will increase the infiltration of melting water into the soil (formation of floodwaters), increase of soil strength and shear until the landscape reaches a stable phase, with indications of periglacial activity between 2050 and 2070

High-accuracy digital elevation model generation and ship monitoring from synthetic aperture radar images: innovative techniques and experimental results.

In this Thesis several state-of-the-art and innovative techniques for Digital Elevation Model (DEM) generation from Synthetic Aperture Radar (SAR) images are deeply analyzed, with a special focus on the methods which allow the improvement of the accuracy of the DEM product, which is directly related to the geolocation accuracy of geocoded images and is considered as an enabling factor for a large series of civilian and Defence applications. Furthermore, some of the proposed techniques, which are based both on phase and amplitude information, are experimented on real data, i.e. COSMO-SkyMed (CSK) data, assessing the achievable performances compared with the state-of-the-art, and pointing out and quantitatively highlighting the acquisition and processing strategies which would allow to maximize the quality of the results. Moreover, a critical analysis is performed about the main errors affecting the applied techniques, as well as the limitations of the orbital configurations, identifying several complementary techniques which would allow to overcome or mitigate the observed drawbacks. An innovative procedure for on-demand DEM production from CSK SAR data is elaborated and proposed, as well as an auto-validation technique which would enable the validation of the produced DEM also where vertical ground truths are not available. Based on the obtained results and on the consequent critical analysis, several interferometric specifications for new generation SAR satellites are identified. Finally, a literature review is proposed about the main state-of-the-art ship monitoring techniques, considered as one of the main fields of application which takes benefit from SAR data, based on single/multi-platform multi-channel SAR data, with a focus on TanDEM-X (TDX). In particular, in Chapter 1 the main concepts concerning SAR operating principles are introduced and the main characteristics and performances of CSK and TDX satellite systems are described; in Chapter 2 a review is proposed about the state-of-the-art SAR interferometric techniques for DEM generation, analyzing all the relevant processing steps and deepening the study of the main solutions recently proposed in the literature to increase the accuracy of the interferometric processing; in Chapter 3 complementary and innovative techniques respect to the interferometric processing are analyzed to mitigate disadvantages and to improve performances; in Chapter 4 experimental results are presented, obtained in the generation of high accuracy DEM by applying to a dataset of CSK images properly selected state-of-the-art interferometric techniques and innovative methods to improve DEM accuracy, exploring relevant limitations, and pointing out innovative acquisition and processing strategies. In Chapter 5, the basic principles of Ground Moving Target Indication (GMTI) are described, focusing on Displaced Phase Center Antenna (DPCA) and Along-Track Interferometry (ATI) techniques