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    Passive Microwave Remote Sensing of Terrestrial Snow — Preparing for the Copernicus Imaging Microwave Radiometer
    (University of Waterloo, 2026-09-28) Zschenderlein, Lina
    Seasonal terrestrial snow is a crucial freshwater resource and a fundamental indicator of climate change. Spaceborne passive microwave radiometry is capable of monitoring both snow cover extent (SCE) and snow water equivalent (SWE) on a global scale, by exploiting the distinctive frequency-dependent characteristics of the microwave emission of snow. The main limitation of passive microwave approaches is the coarse spatial resolution which, amongst other reasons, causes systematic underestimation and large uncertainties of both SCE and SWE. The upcoming Copernicus Imaging Microwave Radiometer (CIMR), with its higher spatial resolution and full 360° scan promises substantial improvements—provided current methodologies and the influence of instrument geometry and topography are well understood. In preparation for CIMR, this thesis advances passive microwave snow methodologies through three studies, focused on dry snow detection and its implications for SWE retrieval on hemispheric, continental and regional scales. The first study presents the first comprehensive long-term, hemispheric evaluation of six dry snow detection algorithms for CIMR-like frequencies of SMMR, SSM/I and SSMIS, which are validated against in situ snow depth measurements and IMS snow maps. All algorithms underestimate SCE, but cumulative snow masks counteract this bias during the accumulation season. Implementing the best algorithms within the GlobSnow framework improves SWE statistics, most notably for shallow autumn snow. This highlights the impact that the algorithm choice for dry snow detection has on the quality of SWE retrieval and therefore on long-term climate data records. The second study is the first to investigate WindSat’s near-instantaneous dual-look brightness temperatures for snow mapping over Eurasia. The scan azimuth angle systematically affects detection: south-looking observations (capturing deeper, drier snow on north-facing slopes) consistently detect more snow. Spatially superimposing both looks increases mapped SCE while maintaining high agreement with reference data. Dual-look snow mapping further highlights the need for water-spillover corrections and renews the interest in relief effects. The third study then quantifies, for the first time, how topography affects brightness temperatures of snow-covered land. WindSat’s fore-aft brightness temperatures generally have a high correlation over Eurasia; however, the correlation drops over mountains and during peak winter. This drop, as demonstrated for the Greater Alpine Region in Europe, is due to subpixel rather than coarse-pixel topography and can be expressed through sensor-independent and sensor-dependent characteristics. This motivates topographic corrections on fine spatial scales as well as regionally varying incidence angles within snow retrievals. Overall, this thesis demonstrates that algorithm choice, viewing geometry, and subpixel topography each measurably affect passive microwave snow estimates. These effects and related uncertainties will persist for CIMR, despite the higher spatial resolution, making the findings directly transferable to CIMR snow product development and to global snow monitoring for enhanced climate adaptation and water resource management.
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    The Contribution of Stereoacuity to Cybersickness When Viewing 3D Films in Augmented Reality Head Mounted Displays
    (University of Waterloo, 2026-09-28) Merchant, Wasim Karim
    Cybersickness remains a barrier to the adoption of augmented reality (AR) head-mounted displays (HMDs). AR HMDs present stereoscopic 3D (S3D) graphics that decouple the vergence and accommodation responses of the eyes. This decoupling produces a vergence-accommodation mismatch (VAM) that is implicated in cybersickness and visual fatigue. Because stereoacuity determines an individual’s sensitivity to binocular disparity, it may modulate how strongly VAM is experienced. However, existing evidence on the effect of stereoacuity on cybersickness and visual fatigue is mixed. The present study examined whether stereoacuity influences subjective cybersickness and visual fatigue and whether it influences oculomotor function post S3D viewing. Twenty-six participants, classified into HIGH and LOW stereoacuity groups using the TNO stereo test, viewed the first 30 minutes of an S3D film on the Microsoft HoloLens 2 while seated with the head stabilized in a chin-rest. Cybersickness (Simulator Sickness Questionnaire; SSQ) and visual fatigue (Visual Fatigue Questionnaire; VFQ) were assessed at baseline and every five minutes. Optometric measures assessed oculomotor function before and after exposure. Cybersickness and visual fatigue did not differ between the high and low stereoacuity groups but did increase significantly over the exposure. Oculomotor change over exposure was confined to metrics of vergence, including a receded near point of convergence but was unrelated to stereoacuity. A strong, positive correlation emerged between subjective cybersickness and visual fatigue. These findings indicate that stereoacuity is not a dominant factor in cybersickness during AR HMD use, and that managing exposure duration may be more effective than screening users on stereoacuity.
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    Nd:YAG Laser Welding of NiTi-SS Wires by Creating In-Situ High Entropy Joints
    (University of Waterloo, 2026-09-28) Creaser, Aidan
    Welding of NiTi and stainless steel (SS) wires is of great importance for device fabrication within the medical industry. Devices such as implants, surgical equipment, and even orthodontic arc-wires would benefit from cost effective and efficient welding between NiTi and SS. The production of Ni-Ti and Fe-Ti based intermetallic compounds (IMCs) in the fusion zone (FZ) makes joining extremely challenging. This study aims to eliminate IMCs in the FZ by generating an in-situ high entropy alloy (HEA) FZ of NiTi-SS wires. A custom Co-Cr-Ni powder was created to target a face-center-cubic (FCC) CoCrNiFe HEA FZ. Temporal pulse shaping was investigated by using different laser power/duration during the welding process. It was discovered that long; low-power pulses were effective at obtaining a fully FCC HEA joint. However, IMC precipitation occurred at the NiTi-FZ interface. The results observed a 60% increased tensile strength and 47 % increased strain. Ultrasonic assistance was then applied under the same conditions to mechanically alter the interfacial region. Using the acoustic streaming and cavitation effects, the thickness of the interface was drastically reduced. Instead, a Ti-rich area of the FZ, with lower hardness, served as the point of failure. As a result, the mechanical properties of the joint increased and the welds came remarkably close to the target, the super-elastic plateau of the base NiTi wire. Achieving a weld capable of the functional properties of the base NiTi has rarely been reported in the literature, especially for wire joining. A chemical route was then further developed, using a CoVNi powder. It was observed that the V was successful at migrating into previously Ti-rich regions and forming more ductile IMCs which lowered hardness. However, the V could not diffuse far enough into the interface, and the results matched those observed with the CoCrNi powder.
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    Breaking Information Silos: Advancing Search System for Unified Information Seeking
    (University of Waterloo, 2026-09-28) Ma, Xueguang
    Information seeking is central to how people learn, make decisions, and advance knowledge. At the center of any search system is the retriever, the component that provides access to world knowledge: a system can surface only what its retriever can find. Retrievers, however, have traditionally been specialized, each trained for a particular task, fitted to a single language, restricted to one modality, and limited to a single retrieval pass. Each such specialization makes the retriever effective for what it was built for but walls off everything else, fragmenting the world's information into information silos: bodies of relevant information that no single search system can cohesively reach. This thesis breaks these silos by replacing traditional retrieval's specialized components, one for each task, language, and modality, with general-purpose models that learn relevance, perceive documents, and reason over information needs, lifting each underlying constraint rather than building another pipeline. The thesis then studies how to make this unified access general, efficient, verifiable, and reproducible, across three dimensions: domain and language, modality, and representation space. For domain and language silos, I show that fine-tuning a large language model (LLM) as a dense retriever yields strong generalization across retrieval tasks, even without the task-specific pretraining or data augmentation that BERT-era retrievers relied upon. I then show that this relevance-modeling capability need not remain locked inside a large model: it can be distilled into small, efficient retrievers that generalize across both tasks and languages, and it can be exploited with no relevance supervision at all by letting an LLM generate a hypothetical document that an off-the-shelf encoder grounds to the corpus. A recurring consequence is that such retrievers improve in step with the underlying language models. For modality silos, I introduce a paradigm shift from extracting text out of documents to encoding documents as they appear. Document Screenshot Embedding encodes a document's screenshot directly with a vision-language model, preserving text, images, tables, and layout in a single dense representation and outperforming parsing- and OCR-based pipelines on mixed-modality retrieval. I further argue that unifying access is only half of the goal, since a unified system must also be trustworthy: VISA extends the visual paradigm to the output side, attributing each generated answer to the specific region of the source document that supports it, and yielding a fully visual pipeline from retrieval to verifiable generation. For representation-space silos, I address the limitation that a single query embedding reaches only a local neighborhood, while the evidence for a complex, reasoning-intensive need is dispersed across the space. Crossing this silo requires an agent that can reason and search iteratively. I therefore cultivate general reasoning by scaling reinforcement learning with verifiable rewards beyond mathematics and code, bring that reasoning into the retrieval pipeline through a reranker trained to reason before ranking, and construct a benchmark over a fixed, curated corpus that, for the first time, evaluates deep-search agents fairly by disentangling the contribution of the retriever from that of the reasoning agent. This evaluation shows that, even with strong agents, retrieval quality remains pivotal. Underpinning these contributions, I develop and maintain open-source toolkits that make the unified paradigm efficient and reproducible: one for reproducible first-stage retrieval and evaluation, and one for training neural retrievers at scale and across languages and modalities. Together, these works move document retrieval from a collection of specialized pipelines toward unified, efficient, verifiable, and agentic access to world knowledge. I conclude by outlining how representations, search agents, and interaction must evolve to make such access seamless across both digital and physical worlds.
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    Microbiology of pre-saturated gap fill bentonite compacted in pressure vessels
    (University of Waterloo, 2026-09-28) Schofield, Luke
    Deep geologic repositories (DGRs) are the planned long-term management and disposal approach for used nuclear fuel in many countries. Designs include the use of multiple engineered barriers, including used fuel containers, bentonite buffer material, and the surrounding host rock. In Canada’s design, used fuel containers (UFCs) will be encased in highly compacted bentonite blocks and placed at depths of 650-800 m below ground surface in emplacement rooms excavated from crystalline rock, with spaces between bentonite blocks and the host rock filled with a granular bentonite (i.e., “gap fill material”). Past research has shown that microorganisms exist in as-received bentonites, some of which could negatively influence the longevity of a DGR, for example through microbially influenced corrosion of copper-coated UFCs particularly by sulfate-reducing bacteria (SRB). Previous research has focused on the use of pump-saturated pressure vessels to simulate early stages of groundwater infiltration in a DGR. Results showed suppression of microbial abundances in compacted bentonite after a relatively slow saturation process is completed and high swelling pressures have been established. To examine post-saturation microbial suppression, while minimizing changes that occur during slow saturation, pressure vessels were used to rapidly compress pre-wetted gap fill material to varying dry densities under oxic or anoxic conditions. This approach targeted nominal 100% saturation prior to incubation of the bentonite “plugs” for periods of up to three months. Following incubation, bentonite plugs were analyzed using cultivation and 16S rRNA gene sequencing. Results revealed decreasing abundances of culturable aerobic heterotrophs with increasing bentonite dry density. Relative to the as-received bentonite starting material, no significant increases in the abundance of culturable microorganisms were detected for the highest dry density tested (1.45 g cm-3). In contrast, all lower dry densities tested showed significantly greater abundances of culturable aerobic heterotrophs compared to as-received bentonite. These samples were associated with high relative abundances of three Bacillus-associated ASVs that were mostly undetected in 1.45 g cm-3 samples. Both cultivation and sequencing results demonstrated that a bentonite dry density of 1.45 g cm-3 limited detectable increases in culturable abundances under the tested conditions, which is a target average dry density under consideration for repository gap fill material. No significant increases in SRB counts were detected by cultivation methods for any conditions tested, and 16S rRNA gene profiles also did not reveal increases in taxa affiliated with putative SRB. This research also presents a rapid saturation and compaction method for studying microbial suppression in bentonite, while minimizing the influence of slow saturation effects, allowing for rapid testing of post-saturation microbial processes.