470 research outputs found
Investigating the dynamics of Greenland's glacier-fjord systems
Over the past two decades, Greenland’s tidewater glaciers have dramatically retreated, thinned and accelerated, contributing significantly to sea level rise. This change in glacier behaviour is thought to have been triggered by increasing atmospheric and ocean temperatures, and mass loss from Greenland’s tidewater glaciers is predicted to continue this century. Substantial research during this period of rapid glacier change has improved our understanding of Greenland’s glacier-fjord systems. However, many of the processes operating in these systems that ultimately control the response of tidewater glaciers to changing atmospheric and oceanic conditions are poorly understood. This thesis combines modelling and remote sensing to investigate two particularly poorly-understood components of glacier-fjord systems, with the ultimate aim of improving understanding of recent glacier behaviour and constraining the stability of the ice sheet in a changing climate.
The research presented in this thesis begins with an investigation into the dominant controls on the seasonal dynamics of contrasting tidewater glaciers draining the Greenland Ice Sheet. To do this, high resolution estimates of ice velocity were generated and compared with detailed observations and modelling of the principal controls on seasonal glacier flow, including terminus position, ice mélange presence or absence, ice sheet surface melting and runoff, and plume presence or absence. These data revealed characteristic seasonal and shorter-term changes in ice velocity at each of the study glaciers in more detail than was available from previous remote sensing studies. Of all the environmental controls examined, seasonal evolution of subglacial hydrology (as inferred from plume observations and modelling) was best able to explain the observed ice flow variations, despite differences in geometry and flow of the study glaciers. The inferred relationships between subglacial hydrology and ice dynamics were furthermore entirely consistent with process-understanding developed at land-terminating sectors of the ice sheet. This investigation provides a more detailed understanding of tidewater glacier subglacial hydrology and its interaction with ice dynamics than was previously available and suggests that interannual variations in meltwater supply may have limited influence on annually averaged ice velocity.
The thesis then shifts its attention from the glacier part of the system into the fjords, focusing on the interaction between icebergs, fjord circulation and fjord water properties. This focus on icebergs is motivated by recent research revealing that freshwater produced by iceberg melting constitutes an important component of fjord freshwater budgets, yet the impact of this freshwater on fjords was unknown. To investigate this, a new model for iceberg-ocean interaction is developed and incorporated into an ocean circulation model.
This new model is first applied to Sermilik Fjord — a large fjord in east Greenland that hosts Helheim Glacier, one of the largest tidewater glaciers draining the ice sheet — to further constrain iceberg freshwater production and to quantify the influence of iceberg melting on fjord circulation and water properties. These investigations reveal that iceberg freshwater flux increases with ice sheet runoff raised to the power ~0.1 and ranges from ~500-2500 m³ s⁻¹ during summer, with ~40% of that produced below the pycnocline. It is also shown that icebergs substantially modify the temperature and velocity structure of Sermilik Fjord, causing 1-5°C cooling in the upper ~100 m and invigorating fjord circulation, which in turn causes a 10-40% increase in oceanic heat flux towards Helheim Glacier. This research highlights the important role of icebergs in Greenland’s iceberg congested fjords and therefore the need to include them in future studies examining ice sheet – ocean interaction.
Having investigated the effect of icebergs on fjord circulation in a realistic setting, this thesis then characterises the effect of submarine iceberg melting on water properties near the ice sheet – ocean interface by applying the new model to a range of idealised scenarios. This near-glacier region is one which is crucial for constraining ocean-driven retreat of tidewater glaciers, but which is poorly-understood. The simulations show that icebergs are important modifiers of glacier-adjacent water properties, generally acting to reduce vertical variations in water temperature. The iceberg-induced temperature changes will generally increase submarine melt rates at mid-depth and decrease rates at the surface, with less pronounced effects at greater depth. This highlights another mechanism by which iceberg melting can affect ice sheet – ocean interaction and emphasises the need to account for iceberg-ocean interaction when simulating ocean-driven retreat of Greenland’s tidewater glaciers.
In summary, this thesis has helped to provide a deeper understanding of two poorly-understood components of Greenland’s tidewater glacier-fjord systems: (i) interactions between subglacial hydrology and ice velocity, and; (ii) iceberg-ocean interaction. This research has enabled more precise interpretations of past glacier behaviour and can be used to inform model development that will help constrain future ice sheet mass loss in response to a changing climate."I must express my gratitude to the University of St Andrews and to the Scottish Alliance for Geoscience, Environment and Society (SAGES) for funding and supporting me as a research student."-- Fundin
Flood dynamics derived from video remote sensing
Flooding is by far the most pervasive natural hazard, with the human impacts of floods expected to worsen in the coming decades due to climate change. Hydraulic models are a key tool for understanding flood dynamics and play a pivotal role in unravelling the processes that occur during a flood event, including inundation flow patterns and velocities. In the realm of river basin dynamics, video remote sensing is emerging as a transformative tool that can offer insights into flow dynamics and thus, together with other remotely sensed data, has the potential to be deployed to estimate discharge. Moreover, the integration of video remote sensing data with hydraulic models offers a pivotal opportunity to enhance the predictive capacity of these models.
Hydraulic models are traditionally built with accurate terrain, flow and bathymetric data and are often calibrated and validated using observed data to obtain meaningful and actionable model predictions. Data for accurately calibrating and validating hydraulic models are not always available, leaving the assessment of the predictive capabilities of some models deployed in flood risk management in question. Recent advances in remote sensing have heralded the availability of vast video datasets of high resolution. The parallel evolution of computing capabilities, coupled with advancements in artificial intelligence are enabling the processing of data at unprecedented scales and complexities, allowing us to glean meaningful insights into datasets that can be integrated with hydraulic models. The aims of the research presented in this thesis were twofold. The first aim was to evaluate and explore the potential applications of video from air- and space-borne platforms to comprehensively calibrate and validate two-dimensional hydraulic models. The second aim was to estimate river discharge using satellite video combined with high resolution topographic data. In the first of three empirical chapters, non-intrusive image velocimetry techniques were employed to estimate river surface velocities in a rural catchment. For the first time, a 2D hydraulicvmodel was fully calibrated and validated using velocities derived from Unpiloted Aerial Vehicle (UAV) image velocimetry approaches. This highlighted the value of these data in mitigating the limitations associated with traditional data sources used in parameterizing two-dimensional hydraulic models. This finding inspired the subsequent chapter where river surface velocities, derived using Large Scale Particle Image Velocimetry (LSPIV), and flood extents, derived using deep neural network-based segmentation, were extracted from satellite video and used to rigorously assess the skill of a two-dimensional hydraulic model. Harnessing the ability of deep neural networks to learn complex features and deliver accurate and contextually informed flood segmentation, the potential value of satellite video for validating two dimensional hydraulic model simulations is exhibited. In the final empirical chapter, the convergence of satellite video imagery and high-resolution topographical data bridges the gap between visual observations and quantitative measurements by enabling the direct extraction of velocities from video imagery, which is used to estimate river discharge. Overall, this thesis demonstrates the significant potential of emerging video-based remote sensing datasets and offers approaches for integrating these data into hydraulic modelling and discharge estimation practice. The incorporation of LSPIV techniques into flood modelling workflows signifies a methodological progression, especially in areas lacking robust data collection infrastructure. Satellite video remote sensing heralds a major step forward in our ability to observe river dynamics in real time, with potentially significant implications in the domain of flood modelling science
A long-term monthly surface water storage dataset for the Congo basin from 1992 to 2015
The spatio-temporal variation of surface water storage (SWS) in
the Congo River basin (CRB), the second-largest watershed in the world,
remains widely unknown. In this study, satellite-derived observations are
combined to estimate SWS dynamics at the CRB and sub-basin scales over
1992–2015. Two methods are employed. The first one combines surface water
extent (SWE) from the Global Inundation Extent from Multi-Satellite
(GIEMS-2) dataset and the long-term satellite-derived surface water height
from multi-mission radar altimetry. The second one, based on the hypsometric
curve approach, combines SWE from GIEMS-2 with topographic data from four
global digital elevation models (DEMs), namely the Terra Advanced Spaceborne
Thermal Emission and Reflection Radiometer (ASTER), Advanced Land Observing
Satellite (ALOS), Multi-Error-Removed Improved Terrain (MERIT), and Forest
And Buildings removed Copernicus DEM (FABDEM). The results provide SWS
variations at monthly time steps from 1992 to 2015 characterized by a strong
seasonal and interannual variability with an annual mean amplitude of
∼101±23 km3. The Middle Congo sub-basin shows a higher
mean annual amplitude (∼71±15 km3). The
comparison of SWS derived from the two methods and four DEMs shows an
overall fair agreement. The SWS estimates are assessed against satellite
precipitation data and in situ river discharge and, in general, a relatively
fair agreement is found between the three hydrological variables at the
basin and sub-basin scales (linear correlation coefficient >0.5). We further characterize the spatial distribution of the major drought
that occurred across the basin at the end of 2005 and in early 2006. The SWS
estimates clearly reveal the widespread spatial distribution of this severe
event (∼40 % deficit as compared to their long-term
average), in accordance with the large negative anomaly observed in
precipitation over that period. This new SWS long-term dataset over the
Congo River basin is an unprecedented new source of information for improving our
comprehension of hydrological and biogeochemical cycles in the basin. As the
datasets used in our study are available globally, our study opens
opportunities to further develop satellite-derived SWS estimates at the
global scale. The dataset of the CRB's SWS and the related Python code to
run the reproducibility of the hypsometric curve approach dataset of SWS are
respectively available for download at https://doi.org/10.5281/zenodo. 7299823 and https://doi.org/10.5281/zenodo.8011607 (Kitambo et al., 2022b, 2023).</p
Evaluation of Multi-frequency Synthetic Aperture Radar for Subsurface Archaeological Prospection in Arid Environments
The discovery of the subsurface paleochannels in the Saharan Desert with the 1981 Shuttle Imaging Radar (SIR-A) sensor was hugely significant in the field of synthetic aperture radar (SAR) remote sensing. Although previous studies had indicated the ability of microwaves to penetrate the earth’s surface in arid environments, this was the first applicable instance of subsurface imaging using a spaceborne sensor. And the discovery of the ‘radar rivers’ with associated archaeological evidence in this inhospitable environment proved the existence of an earlier less arid paleoclimate that supported past populations.
Since the 1980’s SAR subsurface prospection in arid environments has progressed, albeit primarily in the fields of hydrology and geology, with archaeology being investigated to a lesser extent. Currently there is a lack of standardised methods for data acquisition and processing regarding subsurface imaging, difficulties in image interpretation and insufficient supporting quantitative verification. These barriers keep SAR technology from becoming as integral as other remote sensing techniques in archaeological practice
The main objective of this thesis is to undertake a multi-frequency SAR analysis across different site types in arid landscapes to evaluate and enhance techniques for analysing SAR within the context of archaeological subsurface prospection. The analysis and associated fieldwork aim to address the gap in the literature regarding field verification of SAR image interpretation and contribute to the understanding of SAR microwave penetration in arid environments.
The results presented in this thesis demonstrate successful subsurface imaging of subtle feature(s) at the site of ‘Uqdat al-Bakrah, Oman with X-band data. Because shorter wavelengths are often ignored due to their limited penetration depths as compared to the C-band or L-band data, the effectiveness of X-band sensors in archaeological prospection at this site is significant. In addition, the associated ground penetrating radar and excavation fieldwork undertaken at ‘Uqdat al-Bakrah confirm the image interpretation and support the quantitative information regarding microwave penetration
BDS GNSS for Earth Observation
For millennia, human communities have wondered about the possibility of observing
phenomena in their surroundings, and in particular those affecting the Earth on which they live.
More generally, it can be conceptually defined as Earth observation (EO) and is the collection of
information about the biological, chemical and physical systems of planet Earth. It can be undertaken
through sensors in direct contact with the ground or airborne platforms (such as weather balloons and
stations) or remote-sensing technologies. However, the definition of EO has only become significant
in the last 50 years, since it has been possible to send artificial satellites out of Earth’s orbit.
Referring strictly to civil applications, satellites of this type were initially designed to provide
satellite images; later, their purpose expanded to include the study of information on land
characteristics, growing vegetation, crops, and environmental pollution. The data collected are used
for several purposes, including the identification of natural resources and the production of accurate
cartography. Satellite observations can cover the land, the atmosphere, and the oceans.
Remote-sensing satellites may be equipped with passive instrumentation such as infrared or
cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are
non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the
Earth’s equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and
Medium Earth Orbit (MEO), thus covering the entire Earth’s surface in a certain scan time (properly
called ’temporal resolution’), i.e., in a certain number of orbits around the Earth.
The first remote-sensing satellites were the American NASA/USGS Landsat Program;
subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing
satellite), RapidEye, the French SPOT (Satellite Pour l’Observation de laTerre), and the Canadian
RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were
dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed
system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the
Chinese BuFeng-1 and Fengyun-3 series.
Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers
worldwide for a multitude of Earth monitoring and exploration applications. On the other hand,
over the past 40 years, GNSSs have become an essential part of many human activities. As is widely
noted, there are currently four fully operational GNSSs; two of these were developed for military
purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for
civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European
Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning
System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation
Satellite System (IRNSS/NavIC), will become available in the next few years, which will have
enormous potential for scientific applications and geomatics professionals.
In addition to their traditional role of providing global positioning, navigation, and timing (PNT)
information, GNSS navigation signals are now being used in new and innovative ways. Across the
globe, new fields of scientific study are opening up to examine how signals can provide information
about the characteristics of the atmosphere and even the surfaces from which they are reflected before
being collected by a receiver.
EO researchers monitor global environmental systems using in situ and remote monitoring tools.
Their findings provide tools to support decision makers in various areas of interest, from security
to the natural environment. GNSS signals are considered an important new source of information
because they are a free, real-time, and globally available resource for the EO community
Навчальний посібник з дисципліни «Іноземна мова за професійним спрямуванням (англійська)» для здобувачів вищої освіти зі спеціальності 193 «Геодезія та землеустрій»
Навчальний посібник призначено для вивчення курсу
«Іноземна мова (англійська) за професійним спрямуванням»
здобувачами вищої освіти зі спеціальності 193 «Геодезія та
землеустрій». Посібник створено з метою розвитку граматичних
та лексичних навичок, практичних умінь (говоріння та письма)
та навичок розуміння професійно спрямованої літератури
англійською мовою. Рекомендовано як для проведення
аудиторної, так і для позааудиторної, самостійної роботи, у тому
числі під час дистанційної та змішаної форми навчання у
закладах вищої та передвищої освіти
Advancing the Monitoring Capabilities of Mountain Snowpack Fluctuations at Various Spatial and Temporal Scales
Snow is a critical water resource for the western US and many regions across the globe. However, our ability to accurately monitor changes in snow mass from satellite remote sensing, specifically its water equivalent, remains a challenge in mountain regions. No single sensor currently has the ability to directly measure snow water equivalent (SWE) from space at a spatial scale suitable for water supply forecasting in mountain environments. This knowledge gap calls for the innovative use of remote sensing techniques, computational tools, and data science methods to advance our ability to estimate mountain snowpacks across a range of spatial and temporal scales. The goal of this dissertation is to advance our capabilities for understanding snowpack across watershed-relevant spatial and temporal scales. Two research approaches were used to accomplish this goal: quantifying the physiographic controls and sensitivities of hydrologically important snow metrics and progressing our ability to use L-band interferometric synthetic aperture radar (InSAR) to measure SWE changes. First, we quantify the physiographic controls and various snowpack metrics in the Sierra Nevada using a novel gridded SWE reanalysis dataset. Such work demonstrates the complexity of snowpack processes and the need for fine-resolution snowpack information. Next, using L-band Interferometric Synthetic Aperture Radar (InSAR) from the NASA SnowEx campaign, both snow ablation and accumulation are estimated in the Jemez Mountains, NM. The radar-derived retrievals are evaluated utilizing a combination of optical snow-cover data, snow pits, meteorological station data, in situ snow depth sensors, and ground-penetrating radar (GPR). Lastly, we compare multisensor optical-radar approaches for SWE retrievals and find that moderate-resolution legacy satellite products provide sufficient results. The results of this work show that L-band InSAR is a suitable technique for global SWE monitoring when used synergistically with optical SCA data and snowpack modeling. While two distinctive methods are present in this research, they both work towards advancing our ability to understand the dynamics of mountain snowpack
Urban development induced subsidence in deltaic environments: a case study in Hanoi, Vietnam
Hanoi has experienced rapid urbanisation over the last few decades, putting intense pressure on its natural resources, such as groundwater, but also on the local authorities to meet demand for infrastructure, housing and public amenities. Recent studies using Interferometric Synthetic Aperture Radar (InSAR) measured rates of subsidence in Hanoi documenting the evolution of the subsiding areas. These studies have primally attributed the high rates of subsidence to the increased extraction of groundwater. In this study we use Sentinel 1 InSAR data for six years between July 2015 and January 2021 to examine subsidence patterns across Hanoi and link them to the development of urban areas. We find that although groundwater extraction undoubtedly plays a significant role, there is a clear spatial and temporal link between new development and the areas of subsidence. The use of historical optical satellite imagery allows the evolution of the development to be linked to the InSAR ground motion time series. A correlation exists between subsidence and the reclamation of agricultural land, often flooded rice fields, for building via the dumping of aggregate to create dry, raised areas on which to build. We illustrate our findings with examples where newly developed areas are co-incident with areas of subsidence, we show the relationships between the stages of the ground loading and the rate of the resulting subsidence. Ultimately, we extract rates of motion for each year following ground loading. The collected rates of subsidence for over 40 locations of new development allows us to determine the rates of subsidence due to the consolidation process. This relationship enables an understanding of subsidence rate with time which has clear applications in the planning of future developments on thick superficial geological deposits
Advances in Methane Production from Coal, Shale and Other Tight Rocks
This collection reports on the state of the art in fundamental discipline application in hydrocarbon production and associated challenges in geoengineering activities. Zheng et al. (2022) report an NMR-based method for multiphase methane characterization in coals. Wang et al. (2022) studied the genesis of bedding fractures in Ordovician to Silurian marine shale in the Sichuan basin. Kang et al. (2022) proposed research focusing on the prediction of shale gas production from horizontal wells. Liang et al. (2022) studied the pore structure of marine shale by adsorption method in terms of molecular interaction. Zhang et al. (2022) focus on the coal measures sandstones in the Xishanyao Formation, southern Junggar Basin, and the sandstone diagenetic characteristics are fully revealed. Yao et al. (2022) report the source-to-sink system in the Ledong submarine channel and the Dongfang submarine fan in the Yinggehai Basin, South China Sea. There are four papers focusing on the technologies associated with hydrocarbon productions. Wang et al. (2022) reported the analysis of pre-stack inversion in a carbonate karst reservoir. Chen et al. (2022) conducted an inversion study on the parameters of cascade coexisting gas-bearing reservoirs in coal measures in Huainan. To ensure the safety CCS, Zhang et al (2022) report their analysis of available conditions for InSAR surface deformation monitoring. Additionally, to ensure production safety in coal mines, Zhang et al. (2022) report the properties and application of gel materials for coal gangue control
Characterizing the Dynamics of Otto Glacier, Ellesmere Island, Canadian High Arctic: 1992-2020
The mass loss observed from glaciers in the Canadian Arctic is unprecedented over recent decades (Hugonnet et al., 2021) and is the third largest contributor to global sea level rise (Derksen et al., 2019). One way in which glaciers lose mass to the ocean is through dynamic discharge, which involves the calving of icebergs to the ocean. Glacier dynamics in the Canadian Arctic have undergone limited study, especially surge-type glaciers, which oscillate between periods of fast flow and slow flow. Detailed studies of individual surge-type glaciers can enhance knowledge of how and why glaciers surge. As such, this thesis analyzed the surge cycle of Otto Glacier on northern Ellesmere Island in Nunavut, Canada, from 1992-2020. The analysis included velocity measurements from 1992-2020, which used data from optical and radar imagery. Three phases were identified for the study period: the fast flow phase (1992-2008), the deceleration phase (2009-2017), and the quiescent phase (2018-2020). Maximum velocities occurred within the lowermost ~6 km of the glacier during the fast flow phase (700-1300 m/yr), and minimum velocities (1-80 m/yr) were noted along the entire glacier during the quiescent phase. Terminus extent, analyzed with optical and radar imagery, advanced by 1545 m during the fast flow phase, and retreated by 1408 m by the end of the quiescent phase. Rates of glacier surface elevation change, obtained from pre-generated elevation products by Hugonnet et al. (2021), showed surface elevation lowering in the lowermost ~6 km of the glacier and thickening upglacier that was progressive over the study period. Analysis of bedrock topography found a v-shaped sill spanning ~4-8 km upglacier from the terminus, which was inferred to have influenced terminus retreat, glacier thickness, and subsequently velocity variability. The findings provide a detailed characterization of the surge cycle phases for Otto Glacier and suggest a possible surge mechanism, which has not previously been explored in depth
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