The agricultural sector is the backbone which supports the livelihoods and the economic development of nations across the globe. In consequence, the need for robust and continuous monitoring of agricultural crops is primordial to face the interlinked challenges of growth rate population, food security and climate change. Synthetic Aperture Radar (SAR) sensors have the powerful imaging capability of operating at almost all weather conditions, independent of day and night illumination. By penetrating through clouds and into the vegetation canopy, the incident radar signal interacts with the structural and dielectric properties of the vegetation and soil, thus providing critical information of the crop state, such as height, biomass, crop yield or leaf structure, which can help devise sustainable agricultural management practices. This is achieved by means of the Polarimetric SAR Interferometry (PolInSAR) technique, which by coherently combining interferometric SAR acquisitions at different polarization states allows for the retrieval of biophysical parameters of the vegetation. In this framework, this thesis focuses on the development of crop monitoring techniques that properly exploit satellite-based PolInSAR data. All the known InSAR and PolInSAR methodologies for this purpose have been analysed. The sensitivity of these data provided by the TanDEM-X bistatic system to both the physical parameters of the scene (height and structure of the plants, moisture and roughness of the soil) and the sensor configuration (polarization modes and observation geometry) is evaluated. The effect of different simplifications made in the physical model of the scene on the crop estimates is assessed. The interferometric sensitivity requirements to monitor a crop scenario are more demanding than others, such as forests. Steep incidences associated with the largest spatial baselines provided by the available data set lead to the most accurate estimates under all the different model assumptions. Shallower incidences, on the other hand, generally yield important errors due to their characteristic shorter spatial baselines. Through the methodologies proposed in this thesis, PolInSAR data have shown potential to refine current methods for the quantitative estimation of crop parameters. Results encourage to continue further research towards the objective of achieving operational crop monitoring applications. / Work supported by the Spanish Ministry of Science and Innovation, the State Agency of Research (AEI) and the European Funds for Regional Development (EFRD) under Project TEC2017-85244-C2-1-P. Noelia Romero-Puig received a grant from the Generalitat Valenciana and the European Social Fund (ESF) [ACIF/2018/204].

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19283号 / 工博第4080号 / 新制||工||1629(附属図書館) / 32285 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 田村 正行, 教授 小池 克明, 准教授 須﨑 純一 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

In the form of images and videos, visual content has always attracted considerable interest and attention to itself since the early days of the computer era. Although, due to the high density of information in such contents, it has always been challenging to generate, process and broadcast videos and images. These challenges grew along with the demand for higher quality content and attained the research community's attention to themselves. Even though many works have been done by researchers and engineers in academic and industrial environments, the demand for high-quality content introduces new constraints on the quality, performance (speed) and energy consumption. This thesis focuses on a couple of image and video processing applications and introduces new approaches and tweaks to improve the performance and save resources while keeping the functionality intact. In the first part, we target Interferometric Synthetic Aperture Radar (InSAR), an imaging technique used by satellites to capture the earth's surface. Many algorithms have been developed to extract useful information, such as height and displacement, from such images. However, the sheer size of these images, along with the complexity of most of these algorithms, lead to very long processing time and resource utilization. In this work, we take one of the dominant algorithms used for almost every In-SAR application, Phase Unwrapping, and introduce an approach to gain up to 6.5 times speedups. We evaluated our method on InSAR images taken by the Radarsat-2 sensor and showed its impact on a real-world application. In the second part of this thesis, we look at a prevalent application, video streaming. These days video streaming dominates the internet traffic, so any slight improvement in terms of energy consumption or resource utilization will make a sizable difference. Although the streamers use various encoding techniques, the quality of experience of the clients prevents them from overplaying these techniques. On the other hand, there has been a growing interest in another venture of research which focuses on developing techniques that aim to restore the quality of the videos that have been subjected to compression. Although these techniques are used by many users on the receiver side, the streamers often ignore their capabilities. In our work, we introduce an approach that makes the streamer aware of the capabilities of the receiver and utilizes that awareness to reduce the cost of transmission without compromising the end user's quality of experience. We demonstrated the technique and proved our concept by applying it to the HEVC encoding standard and JCT-VC dataset. / Graduate

Permafrost deformation is expected to increase due to climatic perturbations such as amplified air and soil temperatures, resulting in permafrost thawing and subsequent subsidence. Palsas and peat plateaus are uplifted ice-rich peat mounds that experience permafrost subsidence. This is due to the uppermost layer of permafrost, known as the Active Layer (AL), that seasonally thaws and freezes. Interferometric Synthetic Aperture Radar (InSAR) is an interferometric stacking technique successfully applied over permafrost regions when monitoring ground subsidence. The Small Baseline Subset (SBAS) technique is based on interferograms produced by stacking Synthetic Aperture Radar (SAR) acquisitions with small normal baselines. In this study, seasonal Sentinel-1 SAR C-band data obtained during June, July, August and September (JJAS) was used to generate seasonal Line of Sight (LoS) deformation time series of palsas and peat plateaus in Tavvavuoma (Sweden) by using the SBAS technique. Chersky (Russia) has documented permafrost subsidence and was used as a reference site. Findings include that seasonal stacks with short normal baselines generated more robust results than inter-annual stacks with longer normal baselines and temporal data gaps. No instances of pronounced subsidence were reported during JJAS. Nevertheless, minor subsidence during the early season and negative development trends were identified in the Tavvavuoma 2020 andChersky 2020-2021 stacks, respectively. Increased subsidence during the mid-and late thaw season was detected. The SBAS technique performed better and resulted in less temporal and seasonal decorrelation in areas above the tree line (Tavvavuoma) compared to the lowlands in the forest-tundra (Chersky). The challenge lies in whether surface subsidence of palsas and peat plateaus in sporadic permafrost regions experience irreversible long-term changes or seasonally cyclic changes in the permafrost ground regime. Future studies are recommended to implement annual intervals, including winter images over Tavvavuoma.

Lake Mead, the largest reservoir in the United States along the Colorado River on the border between the states of Nevada and Arizona, is one of the nation's most important sources of freshwater. As reported by the U.S. drought monitor (USDM), the entire region has been experiencing recurring severe to extreme droughts since the early 2000s, which have further intensified during the past two years. The drought-driven water deficit caused Lake Mead's water volume to decrease to approximately one-third of its capacity, creating a water crisis and negatively affecting soil and groundwater storage across the region. Water deficits have further reduced the mass of water loading on the Earth's crust, causing it to elastically deform. I observe this process from the ground by recording the vertical land motion occurring at Global Navigation Satellite System (GNSS) stations, or from space via Interferometric Synthetic Aperture Radar (InSAR) technology. In this study, I analyze vertical deformation observations from GNSS sites and multi-temporal InSAR analysis of Sentinel-1A/B to investigate the contribution of water mass changes in lake, soil, and groundwater to the deformation signal. To achieve this, I remove the effects of glacial isostatic adjustment and non-tidal mass loads from GNSS/InSAR observations. Our findings indicate that recent drought periods led to a notable uplift near Lake Mead, averaging 7.3 mm/year from 2012 to 2015 and an even larger rate of 8.6 mm/year from 2020 to 2023. Further, I provide an estimate of the expected vertical crustal deformation in response to well-known changes in lake and soil moisture storage. For that, I quantify hydrological loads through two different loading models. These include the application of Green's functions for an elastic, layered, self-gravitating, spherical Earth, and the Love load numbers from the Preliminary Reference Earth Models (PREMs), as well as elastic linearly homogeneous half-space Earth models. I further test various load models against the GNSS observations. Our research further investigates the impact of local crustal properties and evaluates the output of several elastic loading models using crustal properties and different model types under non-drought and drought conditions. For future studies, I suggest a comprehensive analysis of the deformation field InSAR data. Also, rigorous monitoring of groundwater levels is essential to accurately predict changes in water masses based on deformation. In addition, for each data set, I suggest implementing an uncertainty analysis to assess the predictability of groundwater level changes based on vertical loading deformation observed by INSAR/GNSS data around the region. Obtaining such estimates will provide valuable insight into the dynamic interactions of the local aquifers with Lake Mead. / Master of Science / The drought has led to a decline of approximately 40 meters in Lake Mead since 1999. During the process of water mass loss from a lake, the crust lifts and extends from the center. However, the water mass loss seen on the lake is not sufficient to explain the movement seen at nearby GPS sites. Hence, the uplift loading of water loss in the form of other hydrological components surrounding Lake Mead needs to be estimated. Here, I analyze several models that best fit the geodetic displacements and try to fill in the gap in deformation observations.

The launch of Sentinel-1A/B satellites in 2014 and 2016 marked a pivotal moment in Synthetic Aperture Radar (SAR) technology, ushering in a golden era for SAR. With a revisit time of 6–12 days, these satellites facilitated the acquisition of extensive stacks of high-resolution SAR images, enabling advanced time series analysis. However, processing these stacks posed challenges like interferometric phase degradation and tropospheric phase delay. This study introduces an advanced Small Baseline Subset (SBAS) algorithm that optimizes interferometric pairs, addressing systematic errors through dyadic downsampling and Delaunay Triangulation. A novel statistical framework is developed for elite pixel selection, considering distributed and permanent scatterers, and a tropospheric error correction method using smooth 2D splines effectively identifies and removes error components with fractal-like structures. Beyond geodetic technique advancements, the research explores geological phenomena, detecting five significant slow slip events (SSEs) along the Southern San Andreas Fault using multitemporal SAR interferometric time series from 2015-2021. These SSEs govern aseismic slip dynamics, manifesting as avalanche-like creep rate variations. The study further investigates Managed Aquifer Recharge (MAR) as a nature-engineering-based solution in the Santa Ana Basin. Analyzing surface deformation from 2004 to 2022 demonstrates MAR's effectiveness in curbing land subsidence within Orange County, CA. Additionally, MAR has the potential to stabilize nearby faults by inducing a negative Coulomb stress change. Projecting into the future, a suggested 2% annual increase in recharge volume through 2050 could mitigate land subsidence and reduce seismic hazards in coastal cities vulnerable to relative sea level rise. This integrated approach offers a comprehensive understanding of geological processes and proposes solutions to associated risks. / Doctor of Philosophy / The launch of Sentinel-1A/B satellites in 2014 and 2016 marked a big step forward in radar technology, especially Synthetic Aperture Radar (SAR). These satellites, which revisit the same area every 6-12 days, allowed us to collect many high-quality radar images. This helped us study changes over time in a more advanced way. However, there were challenges in handling all these images, like errors in the radar signals and delays caused by the Earth's atmosphere. We devised a smart algorithm based on the Small Baseline Subset (SBAS) to tackle these challenges. It helps optimize how we use pairs of radar images, reducing errors. We also developed a new method to pick the best pixels in the images and corrected errors caused by the atmosphere using mathematical methods. Moving beyond just technology, our research also looked at interesting Earth events. We found five major slow slip events along the Southern San Andreas Fault by studying radar data from 2015 to 2021. These events are like slow-motion slips along the fault, influencing how the ground moves. We also explored Managed Aquifer Recharge (MAR) as a solution in the Santa Ana Basin. By studying ground movement from 2004 to 2022, we found that MAR helped prevent the land from sinking in Orange County, California. It even has the potential to make nearby faults more stable. Looking ahead, increasing MAR activities by 2% each year until 2050 could protect against land sinking and reduce earthquake risks in coastal cities facing rising sea levels. This combined approach gives us a better understanding of Earth's processes and suggests ways to tackle related problems.

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Many cities in Sweden are partly located on clay and because of that, some urban city centres are undergoing significant subsidence. To measure subsidence in cities, precise leveling has been the traditional technique, but the interest for the Persistent Scatter InSAR (PSI) technique has increased in the last years, in this application. With the PSI technique, a mm-accuracy can be obtained and the analyses can be done over large areas. In this study, a validation between the PSI and the precise leveling techniques was performed for a selection of buildings located in areas that are facing great subsidence. A correlation between the subsidence rate achieved in the PSI analyses and near-surface soil type was also done, to easier identify risk zones. The city of Uppsala was chosen as study area, because it is partly built on deep layers of clay and the consulting company Bjerking AB has established a leveling network with metal pegs on many buildings. One ascending and one descending PSI analysis was performed, with Sentinel-1 data from the period mid-2015 to mid-2019, and the PSI analyses were done in SARPROZ. After the PSI analyses, comparative permanent scatters (PS) points and metal pegs were identified creating validation pairs. 15 different validation pairs were identified in four different objects, which was one or two buildings. The PSI analyses showed that Uppsala is undergoing significant subsidence in some parts, with an annual rate of about 6 mm/year in the line-of-sight (LOS) direction, which corresponds to about 7.5 mm/year in the vertical direction. The areas of greatest deformation were exclusively found on postglacial clay. The standard deviation of the time series were calculated around their linear regression lines, which was a measure of how temporal coherent the points were. The mean of this standard deviation for the PS points in the 15 validation pairs was 1.5 mm. This standard deviation increased to 2.3 mm in the time series where the direction was transformed from LOS to vertical and where the movements were in respect to the benchmarks. Between the PSI and the precise leveling techniques, in the validation, the vertical subsidence rate differed less than 1 mm/year in all validation pairs and the mean of all differences was 0.56 mm/year. Based on these results, Sentinel-1 data can measure urban subsidence in a satisfactory way, when the PSI technique is applied.

An early phase continental rift is an emerging plate boundary where tectonic forces stretch and thin the continental lithosphere, shaping the Earth's surface. Continental breakup and its progression are typically driven by the interplay between repeated magmatic and tectonic activities, which have been explored through both tectonic and magma-assisted rifting models. Understanding volcano-tectonic interactions is key for evaluating the role of magmatic fluids in facilitating the initiation of continental breakup during early phase rifting. This study applies the magma-assisted rifting model to the Natron Rift and investigates volcano-tectonic interactions during early phases of continental breakup associated with observed changes in the volcanic plumbing system of the active volcano Ol Doinyo Lengai. The Natron Rift is a magma-rich rift in the southern segment of the Eastern Branch in northern Tanzania providing an ideal setting to explore the interactions between tectonic and magmatic processes in the early stages of rifting. To investigate tectonic and magmatic interactions, we began by characterizing the magmatic plumbing system of Ol Doinyo Lengai using Global Navigational Satellite System (GNSS) data from our TZVOLCANO network and Interferometric Synthetic Aperture Radar (InSAR) observations. We inverted the GNSS and InSAR data independently to identify potential deformation sources using the software dMODELS. We then conducted a joint inversion of both datasets and found results that were consistent with the independent inversions within 2-sigma uncertainty. Our findings suggest that Ol Doinyo Lengai is fed by an offset multi-tiered reservoir system, consisting of a shallow magma reservoir located east of the volcano connected to a deeper reservoir through a network of fractures. This magmatic system likely influences the nature, style, and magnitude of volcanic activity at the edifice. We also assessed temporal and spatial changes in surface motion observed with GNSS stations associated with magmatic activity to help mitigate risks to nearby communities, tourism, and air traffic. Detecting transient deformation is essential for forecasting eruptions since these signals often precede eruptive events. To detect transient signals using GNSS data from the TZVOLCANO network, we employed the Targeted Projection Operator (TPO) program which projects GNSS time-series data onto a target spatial pattern. We analyzed seven years of continuous GNSS data and divided the observations into three-year intervals. The TPO method detected rapid uplift between March 2022 and December 2022 followed by steady-state uplift through August 2023. The method also identified quiescent periods and non-eruptive inflation signals that enhance our understanding of the dynamic magma plumbing system of Ol Doinyo Lengai. When integrated with the TZVOLCANO network, which streams real-time GNSS data, this approach enables continuous monitoring and early detection of potential volcanic hazards. Ongoing monitoring is crucial for assessing volcanic risks and improving emergency response plans. Finally, we examined the role of interactions between tectonic and magmatic processes in the Natron Rift during the early stages of continental breakup, focusing on the evolution of the magma plumbing system beneath Ol Doinyo Lengai. Using the code PyLith, we developed a 3D model of the region. The modeling experiments test both homogeneous and heterogeneous medium, with and without topography to estimate surface deformation and stress changes on the Natron fault due to geodetically constrained magma source inflation and deflation. Our analysis focused on stress transfer from the magma sources to assess the likelihood of fault slip, considering the typical 0.1 MPa threshold for triggering slip in magmatic rift settings. Results indicate that during the inflation period from 2016 to 2023, slip on the Natron fault is inhibited adjacent to the volcano under all scenarios. During the magma source deflation phase that occurred from 2007 to 2008 due to explosive eruptions, slip on the Natron fault was promoted adjacent to the volcano under all scenarios. Shear stress change analyses reveal that during the magma deflation scenario, slip of the Natron fault is consistent with oblique normal fault movement that is dominated by normal faulting and has components of strike-slip motion. Finite numerical modeling results demonstrate that topography considerably influences stress changes caused by dynamic magma sources as compared to material heterogeneity highlighting the importance of incorporating topography in volcano-tectonic settings. This work suggests that the potential ongoing magmatic activity at Ol Doinyo Lengai and its proximity to the Natron Fault influence the development of the youthful Natron Rift during early phase rifting. However, this influence likely inhibits fault slip at present on the adjacent section of the Natron fault due to magma source inflation. / Doctor of Philosophy / Continental rifts in their early phases mark the initial stage of plate boundary formation, characterized by the stretching and thinning of the Earth's outer, rigid shell under tectonic forces. Rifts are a significant agent in shaping the Earth's rigid, outer shell, ultimately leading to the formation of oceanic basins and volcanoes. Rifting occurs when tectonic plates break apart, creating faults and allowing magma that formed deep in the Earth to rise to shallower depths. This process not only contributes to the geological evolution of our planet, but it also poses significant hazards in the form of earthquakes and volcanic eruptions. Understanding the interaction between tectonic activity, like slip on faults, and magmatic processes, like volcanic deformation, is essential for assessing rift behavior, particularly in the early, immature stages of rifting when volcanic and tectonic activities are closely linked. This research focuses on the Natron Rift, a magma-rich segment of the southern part of the Eastern Branch of the East African Rift System located in Northern Tanzania. This region includes the active volcano Ol Doinyo Lengai, which is known for its unique magma composition and a history of explosive eruptions. The Natron Rift is an ideal setting to study the interactions between volcanic and faulting processes since it is still in the early stages of rifting. We examined the volcanic structure beneath the active volcano Ol Doinyo Lengai and its surroundings to assess the sources of magma supplying the volcano. We analyzed the geometry and location of a magma source using Global Navigational Satellite System (GNSS) data from our TZVOLCANO monitoring network and satellite images. We used the software dMODELS to independently model the surface displacements and identify potential magma sources. We also combined both datasets and jointly modeled them to test the independent results, which suggested a shallow, deflating magma source located to the east of Ol Doinyo Lengai. The magma source we found is likely connected to a deeper one through fractures that feed Ol Doinyo Lengai. The magmatic system determined from this study influences the nature and intensity of volcanic activity. We further assessed how the surface of Ol Doinyo Lengai volcano changes over time in response to magmatic activity to better understand and reduce the risks posed by eruptions. Volcanic eruptions at Ol Doinyo Lengai pose a risk to nearby communities, tourism, and air traffic, making it crucial to detect surface changes that could indicate an impending eruption. We developed computer models that identified potential non-eruptive volcanic signals due to magma source changes using seven years of continuous GNSS data from our monitoring network. The detected transient signals include a period of rapid uplift from March 2022 to December 2022 followed by steady uplift through August 2023. When the difference between the observed data and the expected pattern three times larger, this difference indicates transient surface motion that could signal an eruption in the near future. This information provides valuable context for eruption forecasting and serves as an early-warning system for the surrounding communities. Continuous monitoring using real-time data from the GNSS network is essential for the early detection of volcanic hazards and improving emergency response efforts. Finally, we investigate the roles played by the interactions between tectonic and magmatic processes in developing the Natron Rift during early stages of continental breakup. We use advanced modeling software called PyLith to create a 3D model of the region that incorporates known magma sources and the Natron fault. We estimate the surface motions and stress changes on the Natron fault due to changes in the known magma sources (inflation or deflation). Our stress transfer analysis indicates that during magma source inflation from 2016 to 2023 the Natron fault near the volcano section is clamped and prevents fault slip. For the deflating magma source associated with 2007-2008 explosive eruptions, stress changes on the Natron fault adjacent to the volcano section indicated fault slip likely occurred with dominantly normal faulting that includes a small component of strike-slip motion. The incorporation of topography significantly affects the amount of stress transferred on the fault under all scenarios. This study suggests that current magmatic activity at Ol Doinyo Lengai along with its closeness to the Natron Fault affects how the early stage Natron Rift develops. However, this influence likely prevents fault slip currently on the volcanic section of the Natron fault because of magma source inflation inhibiting slip the fault.