On the estimation of temporal changes of snow water equivalent by spaceborne SAR interferometry : a new application for the Sentinel-1 mission

In this work we present a methodology for the mapping of Snow Water Equivalent (SWE) temporal variations based on the Synthetic Aperture Radar (SAR) Interferometry technique and Sentinel-1 data. The shift in the interferometric phase caused by the refraction of the microwave signal penetrating the snow layer is isolated and exploited to generate maps of temporal variation of SWE from coherent SAR interferograms. The main advantage of the proposed methodology with respect to those based on the inversion of microwave SAR backscattering models is its simplicity and the reduced number of required in-situ SWE measurements. The maps, updated up to every 6 days, can attain a spatial resolution up to 20 m with sub-centimetre ASWE measurement accuracy in any weather and sun illumination condition. We present results obtained using the proposed methodology over a study area in Finland. These results are compared with in-situ measurements of ASWE, showing a reasonable match with a mean accuracy of about 6 mm.Peer reviewe

Iterative atmospheric phase screen compensation for near-real-time ground-based InSAR measurements over a mountainous slope

In this article, an atmospheric phase screen (APS) compensation algorithm for a near real-time ground-based interferometry synthetic aperture radar (GB-InSAR) over a mountainous area is investigated. A novel APS compensation scheme is proposed to compensate the fluctuated APS caused by a spatial 3-D inhomogeneous refractivity index distribution without any a priori knowledge of moving location. The proposed method simultaneously addresses to identify moving pixels by a criterion of absolute velocity estimated by the coherent pixels technique (CPT). The proposed method consists mainly of three steps: 1) the stratified APS compensation; 2) identification of moving pixel candidate; and 3) the residual APS [remained APS after 1)] compensation by Kriging interpolation. The steps mentioned above are iteratively applied in order to increase the accuracy of the whole process. In this framework, we develop the 2-D quadratic polynomial model of the refractivity index with respect to slant range and topographic height for modeling the stratified APS. Furthermore, a prediction of the residual APS is achieved by applying the intrinsic random function of order k (IRF-k) Kriging interpolation, taking into account the nonstationarity of the residual APS. We evaluate the proposed method using zero-baseline GB-differential InSAR (GB-DInSAR) data over a mountainous area located in Minami-Aso, Kumamoto, Japan, through the near real-time post-landslide measurement campaign

Data Assimilation in high resolution Numerical Weather Prediction models to improve forecast skill of extreme hydrometeorological events.

The complex orography typical of the Mediterranean area supports the formation, mainly during the fall season, of the so-called back-building Mesoscale Convective Systems (MCS) producing torrential rainfall often resulting into flash floods. These events are hardly predictable from a hydrometeorological standpoint and may cause significant amount of fatalities and socio-economic damages. Liguria region is characterized by small catchments with very short hydrological response time, and it has been proven to be very exposed to back-building MCSs occurrence. Indeed this region between 2011 and 2014 has been hit by three intense back-building MCSs causing a total death toll of 20 people and several hundred million of euros of damages. Building on the existing relationship between significant lightning activity and deep convection and precipitation, the first part of this work assesses the performance of the Lightning Potential Index, as a measure of the potential for charge generation and separation that leads to lightning occurrence in clouds, for the back-building Mesoscale Convective System which hit Genoa city (Italy) in 2014. An ensemble of Weather Research and Forecasting simulations at cloud-permitting grid spacing (1 km) with different microphysical parameterizations is performed and compared to the available observational radar and lightning data. The results allow gaining a deeper understanding of the role of lightning phenomena in the predictability of back-building Mesoscale Convective Systems often producing flash flood over western Mediterranean complex topography areas. Despite these positive and promising outcomes for the understanding highly-impacting MCS, the main forecasting issue, namely the uncertainty in the correct reproduction of the convective field (location, timing, and intensity) for this kind of events still remains open. Thus, the second part of the work assesses the predictive capability, for a set of back-building Liguria MCS episodes (including Genoa 2014), of a hydro-meteorological forecasting chain composed by a km-scale cloud resolving WRF model, including a 6 hour cycling 3DVAR assimilation of radar reflectivity and conventional ground sensors data, by the Rainfall Filtered Autoregressive Model (RainFARM) and the fully distributed hydrological model Continuum. A rich portfolio of WRF 3DVAR direct and indirect reflectivity operators, has been explored to drive the meteorological component of the proposed forecasting chain. The results confirm the importance of rapidly refreshing and data intensive 3DVAR for improving first quantitative precipitation forecast, and, subsequently flash-floods occurrence prediction in case of back-building MCSs events. The third part of this work devoted the improvement of severe hydrometeorological events prediction has been undertaken in the framework of the European Space Agency (ESA) STEAM (SaTellite Earth observation for Atmospheric Modelling) project aiming at investigating, new areas of synergy between high-resolution numerical atmosphere models and data from spaceborne remote sensing sensors, with focus on Copernicus Sentinels 1, 2 and 3 satellites and Global Positioning System stations. In this context, the Copernicus Sentinel satellites represent an important source of data, because they provide a set of high-resolution observations of physical variables (e.g. soil moisture, land/sea surface temperature, wind speed, columnar water vapor) to be used in NWP models runs operated at cloud resolving grid spacing . For this project two different use cases are analyzed: the Livorno flash flood of 9 Sept 2017, with a death tool of 9 people, and the Silvi Marina flood of 15 November 2017. Overall the results show an improvement of the forecast accuracy by assimilating the Sentinel-1 derived wind and soil moisture products as well as the Zenith Total Delay assimilation both from GPS stations and SAR Interferometry technique applied to Sentinel-1 data

Satellite Positioning

Satellite positioning techniques, particularly global navigation satellite systems (GNSS), are capable of measuring small changes of the Earths shape and atmosphere, as well as surface characteristics with an unprecedented accuracy. This book is devoted to presenting recent results and development in satellite positioning technique and applications, including GNSS positioning methods, models, atmospheric sounding, and reflectometry as well their applications in the atmosphere, land, oceans and cryosphere. This book provides a good reference for satellite positioning techniques, engineers, scientists as well as user community

Novel and Emerging Strategies for Sustainable Mine Tailings and Acid Mine Drainage Management

Renewable energy and clean storage technologies are at the forefront of the world’s fight against climate change, including the UN-led move towards a carbon-neutral society. Because these complex technologies require more ‘critical’ metals and elements than fossil fuel-based technologies, the demands for raw materials in their manufacturing are skyrocketing and are projected to continue to increase into the foreseeable future.With ore grades on a steep decline, huge amounts of low-grade ores will have to be mined and processed to satisfy the world’s current and future demands for ‘critical’ metals and elements. Expansion of mining and mineral processing operations would mean more mining-related wastes—tailings, waste rocks and acid mine drainage (AMD)—notorious for their devastating and long-term destructive impacts on the environment. This Special Issue explored repurposing/reprocessing of tailings and AMD treatment cost reduction as promising alternatives to manage mine wastes more sustainably. It also includes articles on the critical roles of redox conditions and galvanic interactions on mine waste stability, hydrogeochemical controls on waste rock weathering, and climate change impacts on AMD formation in closed mines

Reducing the Burden of Bacterial Meningitis in the African Meningitis Belt After MenAfriVac

The African meningitis belt - a semi-arid region stretching from Senegal to Ethiopia - experiences the highest incidence of bacterial meningitis in the world, characterised by seasonal fluctuations in endemic disease, localized outbreaks, and multiennial epidemics. MenAfriVac, a serogroup A meningococcal conjugate vaccine, was introduced in mass campaigns in 2010 and has significantly reduced carriage and incidence of group A disease across the meningitis belt. However, other meningococcal serogroups and Streptococcus pneumoniae continue to cause outbreaks of meningitis in the region. A new pentavalent meningococcal conjugate vaccine protecting against serogroups A, C, W, Y, and X is in development and promises to help eliminate outbreaks of meningococcal meningitis by 2030. However, questions remain as to how best to respond to outbreaks of pneumococcal meningitis and non-A meningococcal meningitis and how to use the pentavalent meningococcal conjugate vaccine when it becomes available. This thesis aims to evaluate the remaining challenges to control of bacterial meningitis in the African meningitis belt and assess the relative effectiveness and efficiency of various responses. The first research chapter describes patterns in bacterial meningitis incidence before and after the introduction of MenAfriVac and compares outbreaks where NmA, NmC, NmW, and S. pneumoniae are predominant. The second chapter describes in detail an outbreak of pneumococcal meningitis in Ghana and models the potential impact of reactive vaccination using pneumococcal conjugate vaccine. In the third chapter I present a systematic review and meta-analysis of meningococcal carriage patterns by age and season in the African meningitis belt and propose ways in which it might inform the use of the pentavalent meningococcal conjugate vaccine. In the fourth chapter, I analyse the results of a longitudinal household study to identify behavioural and environmental risk factors for meningococcal carriage acquisition. The final chapter examines the spatio-temporal spread of the novel NmC strain which emerged in Nigeria in 2013, estimates the impact of reactive vaccination campaigns that occurred in the region between 2015 and 2017, and models the effects of alternative outbreak response strategies, including targeting neighbouring districts

Optimal GPS/GALILEO GBAS methodologies with an application to troposphere

In the Civil Aviation domain, research activities aim to improve airspace capacity and efficiency whilst meeting stringent safety targets. These goals are met by improving performance of existing services whilst also expanding the services provided through the development of new Navigation Aids. One such developmental axe is the provision of safer, more reliable approach and landing operations in all weather conditions. The Global Navigation Satellite System (GNSS) has been identified as a key technology in providing navigation services to civil aviation users [1] [2] thanks to its global coverage and accuracy. The GNSS concept includes the provision of an integrity monitoring function by an augmentation system to the core constellations. This is needed to meet the required performances which cannot be met by the stand-alone constellations. One of the three augmentation systems developed within civil aviation is the GBAS (Ground Based Augmentation System) and is currently standardized by the ICAO to provide precision approach navigation services down to Cat I using the GPS or GLONASS constellations [3]. Studies on-going with the objective to extend the GBAS concept to support Cat II/III precision approach operations with GPS L1 C/A, however some difficulties have arisen regarding ionospheric monitoring. With the deployment of Galileo and Beidou alongside the modernization of GPS and GLONASS, it is envisaged that the GNSS future will be multi-constellation (MC) and multi-frequency (MF). European research activities have focused on the use of GPS and Galileo. The MC/MF GBAS concept should lead to many improvements such as a better modelling of atmospheric effects but several challenges must be resolved before the potential benefits may be realized. Indeed, this PhD has addressed two key topics relating to GBAS, the provision of corrections data within the MC/MF GBAS concept and the impact of tropospheric biases on both the SC/SF and MC/MF GBAS concepts. Due to the tight constraints on GBAS ground to air communications link, the VDB unit, a novel approach is needed. One of the proposals discussed in the PhD project for an updated GBAS VDB message structure is to separate message types for corrections with different transmission rates. Then, this PhD argues that atmospheric modelling with regards to the troposphere has been neglected in light of the ionospheric monitoring difficulties and must be revisited for both nominal and anomalous scenarios. The thesis focuses on how to compute the worst case differential tropospheric delay offline in order to characterize the threat model before extending previous work on bounding this threat in order to protect the airborne GBAS user. In the scope of MC/MF GBAS development, an alternative approach was needed. Therefore, in this PhD project, Numerical Weather Models (NWMs) are used to assess fully the worst case horizontal component of the troposphere. An innovative worst case horizontal tropospheric gradient search methodology is used to determine the induced ranging biases impacting aircraft performing Cat II/III precision approaches with GBAS. This provides as an output a worst case bias as a function of elevation for two European regions.The vertical component is also modelled by statistical analysis by comparing the truth data to the GBAS standardized model for vertical tropospheric correction up to the height of the aircraft. A model of the total uncorrected differential bias is generated which must be incorporated within the nominal GBAS protection levels. In order to bound the impact of the troposphere on the positioning error and by maintaining the goal of low data transmission, different solutions have been developed which remain conservative by assuming that ranging biases conspire in the worst possible way. Through these techniques, it has been shown that a minimum of 3 parameters may be used to characterize a region’s model

Nitrate isotope anomaly as a tracer of biogeochemical processes

The general aim of the thesis is testing the potential of the nitrate MIF (massindependent fractionation) signature as a tracer of biogeochemical processes. Nitrate δ15N, δ17O and δ18O of water samples collected at the Marano lagoon (Italy) have been analysed, by combining the denitrifier method with the N2O thermal decomposition in a gold furnace. No clear correlation between the magnitude of the capital delta (Δ17O=δ17O+0.5*δ18O) and the local atmospheric deposition has been found. Moreover, sewage treatments with ozone might be responsible for some high Δ17O values associated to sampling points close to populated areas. Overall, the signal is low (0.6‰ on average, which would correspond to roughly 2% of atmospheric nitrate in sample water) and the error associated to the measure is no less than 75%. To test the assumption that the atmosphere is the only source of a MIF signature, a set of nitrate minerals of different origin was analysed. The capital delta in a specimen of buttgenbachite (with formula Cu36(NO3)2Cl8(OH)62*4−10H2O) from Likasi mine (Congo, 4‰±1) and in a sample of nitromagnesite (Mg(NO3)2*6H2O) collected at Pozalagua Cave (Spain, 10.3‰±0.4) would indicate the possibility that a significant isotope anomaly could be generated due to geochemical processes. So far the MIF in atmospheric nitrate has been interpreted as the result of chemical reactions only, but it could be demonstrated that a series of mass dependent processes might generate an apparent Δ17O. The study of the MIF is a relatively new field and the present work underlined some limits of this novel tracer. Further work should be focused on identifying the systems and the conditions for what the nitrate MIF can be considered as a conservative tracer. Particularly, attention should be paid to the effects of biological processes involved in the nitrogen cycle, such as nitrification and denitrification, and transport processes

Enhancing Precise Point Positioning with global and regional ionospheric models

In the last two decades Precise Point Positioning (PPP) has become a well-established stand-alone positioning method by means of Global Navigation Satellite Systems (GNSSs) for a wide range of applications. By using code and phase measurements from a single GNSS receiver and precise orbit and clock information derived from global or regional GNSS networks, highly precise positions can be obtained. One critical problem of the PPP technique is that a typical period of about 30 minutes is required to reach decimeter-level under normal conditions. In order to shorten the convergence time and improve the positioning accuracy, several PPP integer ambiguity resolution methods have been developed in the last decades. The common approach is to provide additional corrections on the existing PPP (clock) products. Although improvement in positioning accuracy is achieved by fixing ambiguities, the initialization time of PPP is not significantly reduced. Rapid convergence and ambiguity resolution in PPP is still a challenge. The key to instantaneous ambiguity resolution in relative positioning for short baselines lies in the a priori knowledge of the ionosphere. Therefore, the primary objective of this thesis is to investigate the introduction of global and regional ionospheric models as external constraints for enhancing PPP ambiguity resolution. The main work and contributions of this thesis are specified as follows: a. Mathematical modeling aspects for PPP are investigated. The procedures of estimating FCBs for integer ambiguity resolution in PPP based on standard ionosphere-free model and uncombined model are derived. The compatibility of FCBs estimated from both models are validated by comparing their wide-lane and narrow-lane float ambiguities as well as estimated FCBs using real data sets. b. The equivalence of three extended PPP integer ambiguity resolution models with capabilities of constraining external ionosphere information is derived. The method equivalence is demonstrated in three aspects: the ionospheric parameter, integer property recovery and the system redundancies. It is shown that all three models permit strengthening solutions by constraining ionospheric parameter from global and regional ionospheric models. The positioning results indicate that PPP can be further improved if external ionospheric information is available. c. Accuracies of regional atmospheric corrections for PPP ambiguity resolution are assessed. The focus is on the achievable accuracies of interpolated tropospheric and ionospheric delays derived from a typical regional network from ambiguity-fixed PPP solutions. The results indicate that centimeter level accuracies can be obtained for both tropospheric and ionospheric corrections and fast ambiguity resolution can be achieved after applying the regional atmospheric corrections. d. Ambiguity-fixing approaches based on uncombined PPP model are investigated, the one-step approach, in which L1 and L2 ambiguities are simultaneously fixed, and the two-step approach which involves sequentially fixing wide-lane and N1 ambiguities such that the fixed wide-lane ambiguities are applied as constraints to update remaining unknown parameters. Experiment results demonstrate that ambiguity-fixing time can be reduced using the two-step approach as compared to the one-step approach. e. Software system is developed to estimate satellite FCBs from global and regional GNSS network using both ionosphere-free and uncombined model. A PPP software package is developed to validate the contribution of global and regional ionospheric information on PPP ambiguity resolution