Derivation of High Spatial Resolution Albedo from UAV Digital Imagery:Application over the Greenland Ice Sheet

Measurements of albedo are a prerequisite for modeling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimeter resolution albedo products with accuracies of ?5% using consumer-grade digital camera and unmanned aerial vehicle (UAV) technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique could become increasingly common in field studies and used for a wide range of applications. These include the mapping of debris, dust, cryoconite and bioalbedo, and directly constraining surface energy balance models.publishersversionPeer reviewe

Subglacial lake drainage detected beneath the Greenland ice sheet

The contribution of the Greenland ice sheet to sea-level rise has accelerated in recent decades. Subglacial lake drainage events can induce an ice sheet dynamic response—a process that has been observed in Antarctica, but not yet in Greenland, where the presence of subglacial lakes has only recently been discovered. Here we investigate the water flow paths from a subglacial lake, which drained beneath the Greenland ice sheet in 2011. Our observations suggest that the lake was fed by surface meltwater flowing down a nearby moulin, and that the draining water reached the ice margin via a subglacial tunnel. Interferometric synthetic aperture radar-derived measurements of ice surface motion acquired in 1995 suggest that a similar event may have occurred 16 years earlier, and we propose that, as the climate warms, increasing volumes of surface meltwater routed to the bed will cause such events to become more common in the future

SCABBARD: single-node fault-tolerant stream processing

Single-node multi-core stream processing engines (SPEs) can process hundreds of millions of tuples per second. Yet making them fault-tolerant with exactly-once semantics while retaining this performance is an open challenge: due to the limited I/O bandwidth of a single-node, it becomes infeasible to persist all stream data and operator state during execution. Instead, single-node SPEs rely on upstream distributed systems, such as Apache Kafka, to recover stream data after failure, necessitating complex cluster-based deployments. This lack of built-in fault-tolerance features has hindered the adoption of single-node SPEs.We describe Scabbard, the first single-node SPE that supports exactly-once fault-tolerance semantics despite limited local I/O bandwidth. Scabbard achieves this by integrating persistence operations with the query workload. Within the operator graph, Scabbard determines when to persist streams based on the selectivity of operators: by persisting streams after operators that discard data, it can substantially reduce the required I/O bandwidth. As part of the operator graph, Scabbard supports parallel persistence operations and uses markers to decide when to discard persisted data. The persisted data volume is further reduced using workload-specific compression: Scabbard monitors stream statistics and dynamically generates computationally efficient compression operators. Our experiments show that Scabbard can execute stream queries that process over 200 million tuples per second while recovering from failures with sub-second latencies

Evaluation of the suitability of Skylab data for the purpose of petroleum exploration

There are no author-identified significant results in this report

Dynamic re-optimization techniques for stream processing engines and object stores

Large scale data storage and processing systems are strongly motivated by the need to store and analyze massive datasets. The complexity of a large class of these systems is rooted in their distributed nature, extreme scale, need for real-time response, and streaming nature. The use of these systems on multi-tenant, cloud environments with potential resource interference necessitates fine-grained monitoring and control. In this dissertation, we present efficient, dynamic techniques for re-optimizing stream-processing systems and transactional object-storage systems.^ In the context of stream-processing systems, we present VAYU, a per-topology controller. VAYU uses novel methods and protocols for dynamic, network-aware tuple-routing in the dataflow. We show that the feedback-driven controller in VAYU helps achieve high pipeline throughput over long execution periods, as it dynamically detects and diagnoses any pipeline-bottlenecks. We present novel heuristics to optimize overlays for group communication operations in the streaming model.^ In the context of object-storage systems, we present M-Lock, a novel lock-localization service for distributed transaction protocols on scale-out object stores to increase transaction throughput. Lock localization refers to dynamic migration and partitioning of locks across nodes in the scale-out store to reduce cross-partition acquisition of locks. The service leverages the observed object-access patterns to achieve lock-clustering and deliver high performance. We also present TransMR, a framework that uses distributed, transactional object stores to orchestrate and execute asynchronous components in amorphous data-parallel applications on scale-out architectures

Requirement analysis and sensor specifications – First version

In this first version of the deliverable, we make the following contributions: to design the WEKIT capturing platform and the associated experience capturing API, we use a methodology for system engineering that is relevant for different domains such as: aviation, space, and medical and different professions such as: technicians, astronauts, and medical staff. Furthermore, in the methodology, we explore the system engineering process and how it can be used in the project to support the different work packages and more importantly the different deliverables that will follow the current. Next, we provide a mapping of high level functions or tasks (associated with experience transfer from expert to trainee) to low level functions such as: gaze, voice, video, body posture, hand gestures, bio-signals, fatigue levels, and location of the user in the environment. In addition, we link the low level functions to their associated sensors. Moreover, we provide a brief overview of the state-of-the-art sensors in terms of their technical specifications, possible limitations, standards, and platforms. We outline a set of recommendations pertaining to the sensors that are most relevant for the WEKIT project taking into consideration the environmental, technical and human factors described in other deliverables. We recommend Microsoft Hololens (for Augmented reality glasses), MyndBand and Neurosky chipset (for EEG), Microsoft Kinect and Lumo Lift (for body posture tracking), and Leapmotion, Intel RealSense and Myo armband (for hand gesture tracking). For eye tracking, an existing eye-tracking system can be customised to complement the augmented reality glasses, and built-in microphone of the augmented reality glasses can capture the expert’s voice. We propose a modular approach for the design of the WEKIT experience capturing system, and recommend that the capturing system should have sufficient storage or transmission capabilities. Finally, we highlight common issues associated with the use of different sensors. We consider that the set of recommendations can be useful for the design and integration of the WEKIT capturing platform and the WEKIT experience capturing API to expedite the time required to select the combination of sensors which will be used in the first prototype.WEKI

Cloud-based system for IoT data acquisition

IoT permite-nos trazer o mundo físico para o mundo virtual, dando o poder de o controlar e monitorizar. Isto tem encorajado um aumento no interesse em IoT, devido às múltiplas aplicações nos mais variados contextos. Ainda assim sistemas de IoT enfrentam desafios tais como o suporte de altos volume de conexões ou a baixa capacidade de computação face a algoritmos para segurança dos dados. O objectivo desta dissertação é criar um sistema de recolha de dados de sensor de qualidade do ar que resolva esses desafios usando tecnologias de estado de arte, dando preferência a ferramentas de código aberto. O sistema foi implementado em volta Apache Kafka, com Spring Boot e VerneMQ responsáveis por receber dados e PostgreSQL, com plugin Timescale, encarregue de os guardar. Um protótipo do sistema foi implementado usando contentores Docker, mas não foi possível organiza-los com Kubernetes; Abstract: Cloud-based system for IoT data acquisition The purpose of IoT is to bring the physical world into a digital one and allowing it to be controlled and monitored from a virtual standpoint. The interest in IoT has increased due to its many applications in various fields, but IoT systems still deal with challenges such as the support of a high volume of connections or the low processing capacity of devices faced with data security algorithms. The objective of this dissertation is to create a data collection for air quality sensors system, that solves those challenges based on state of the art technologies, giving preference to open-source tools. Implementation was done around Apache Kafka, with Spring Boot and VerneMQ receiving data, HMAC granting a level security on data transport and PostgreSQL with the plugin Timescale storing the data. A prototype of the system was implemented in Docker containers, but we were unable to orchestrate them through Kubernetes

Ice-water dynamics over a land-terminating sector of western Greenland

In this dissertation I investigate the dynamics of a land-terminating reach of the west Greenland ice sheet through three projects utilizing unique field data and modeling experiments. In Chapter 1 I use in-situ water pressure data and numerical modeling to elucidate the conceptual model of subglacial hydrologic drainage beneath Greenland. Measurements in boreholes drilled to the ice sheet bed along a transect in the ablation zone reveal water pressures that question the stability of water-draining conduits. I apply numerical techniques to model transient evolution of subglacial conduits and show that seasonal growth of such features is unsupported in the ice sheet interior. Low potential gradients that drive energy availability to melt channel walls limit conduit growth. This elucidates the importance of other processes in facilitating seasonal development of the subglacial hydrologic system in the interior setting. In Chapter 2 I investigate the effect of thermal boundary conditions on the thermo-mechanical state of western Greenland. I propose new boundary fields from measurements of temperature near the surface and basal heat flux beneath the ice sheet. Comparison of these observation-based fields with model-driven datasets suggests that model-derived basal heat flux is too high, and surface temperatures too low in the study area. By applying different boundary conditions to a thermo-mechanically coupled ice sheet model I show that thermal conditions at the ice/bedrock interface critically depend on the boundary conditions at both the surface and bed. Unrealistically cold conditions are induced if basal heat flux alone is driven by observations. Warmer surface conditions consistent with observations are sufficient to reintroduce melted conditions at the bed, elucidating the importance of the surface boundary in thermo-mechanical model exploration. In Chapter 3 I address the processes responsible for inducing a region of anomalously low driving stress that is evident in west-southwest Greenland. I show that the feature corresponds to a consistent reduction in surface slope rather than a strong bedrock topographic expression. Kinematic wave experiments show that the diffusive nature of the ice sheet renders the development of such a feature infeasible from surface mass balance perturbations. Low driving stress necessitates a change in dynamics and I surmise it is this variation in basal sliding that is an important factor in inducing changes in the surface slope, and thus the driving stress