208 research outputs found
Synthetic Aperture Radar (SAR) Meets Deep Learning
This reprint focuses on the application of the combination of synthetic aperture radars and depth learning technology. It aims to further promote the development of SAR image intelligent interpretation technology. A synthetic aperture radar (SAR) is an important active microwave imaging sensor, whose all-day and all-weather working capacity give it an important place in the remote sensing community. Since the United States launched the first SAR satellite, SAR has received much attention in the remote sensing community, e.g., in geological exploration, topographic mapping, disaster forecast, and traffic monitoring. It is valuable and meaningful, therefore, to study SAR-based remote sensing applications. In recent years, deep learning represented by convolution neural networks has promoted significant progress in the computer vision community, e.g., in face recognition, the driverless field and Internet of things (IoT). Deep learning can enable computational models with multiple processing layers to learn data representations with multiple-level abstractions. This can greatly improve the performance of various applications. This reprint provides a platform for researchers to handle the above significant challenges and present their innovative and cutting-edge research results when applying deep learning to SAR in various manuscript types, e.g., articles, letters, reviews and technical reports
The Role of Synthetic Data in Improving Supervised Learning Methods: The Case of Land Use/Land Cover Classification
A thesis submitted in partial fulfillment of the requirements for the degree of Doctor in Information ManagementIn remote sensing, Land Use/Land Cover (LULC) maps constitute important assets for
various applications, promoting environmental sustainability and good resource management.
Although, their production continues to be a challenging task. There are various factors
that contribute towards the difficulty of generating accurate, timely updated LULC maps,
both via automatic or photo-interpreted LULC mapping. Data preprocessing, being a
crucial step for any Machine Learning task, is particularly important in the remote sensing
domain due to the overwhelming amount of raw, unlabeled data continuously gathered
from multiple remote sensing missions. However a significant part of the state-of-the-art
focuses on scenarios with full access to labeled training data with relatively balanced class
distributions. This thesis focuses on the challenges found in automatic LULC classification
tasks, specifically in data preprocessing tasks. We focus on the development of novel
Active Learning (AL) and imbalanced learning techniques, to improve ML performance in
situations with limited training data and/or the existence of rare classes. We also show
that much of the contributions presented are not only successful in remote sensing problems,
but also in various other multidisciplinary classification problems. The work presented
in this thesis used open access datasets to test the contributions made in imbalanced
learning and AL. All the data pulling, preprocessing and experiments are made available at
https://github.com/joaopfonseca/publications. The algorithmic implementations are made
available in the Python package ml-research at https://github.com/joaopfonseca/ml-research
A Survey on Deep Learning based Time Series Analysis with Frequency Transformation
Recently, frequency transformation (FT) has been increasingly incorporated
into deep learning models to significantly enhance state-of-the-art accuracy
and efficiency in time series analysis. The advantages of FT, such as high
efficiency and a global view, have been rapidly explored and exploited in
various time series tasks and applications, demonstrating the promising
potential of FT as a new deep learning paradigm for time series analysis.
Despite the growing attention and the proliferation of research in this
emerging field, there is currently a lack of a systematic review and in-depth
analysis of deep learning-based time series models with FT. It is also unclear
why FT can enhance time series analysis and what its limitations in the field
are. To address these gaps, we present a comprehensive review that
systematically investigates and summarizes the recent research advancements in
deep learning-based time series analysis with FT. Specifically, we explore the
primary approaches used in current models that incorporate FT, the types of
neural networks that leverage FT, and the representative FT-equipped models in
deep time series analysis. We propose a novel taxonomy to categorize the
existing methods in this field, providing a structured overview of the diverse
approaches employed in incorporating FT into deep learning models for time
series analysis. Finally, we highlight the advantages and limitations of FT for
time series modeling and identify potential future research directions that can
further contribute to the community of time series analysis
Real-time Ultrasound Signals Processing: Denoising and Super-resolution
Ultrasound acquisition is widespread in the biomedical field, due to its properties of low cost, portability, and non-invasiveness for the patient. The processing and analysis of US signals, such as images, 2D videos, and volumetric images, allows the physician to monitor the evolution of the patient's disease, and support diagnosis, and treatments (e.g., surgery). US images are affected by speckle noise, generated by the overlap of US waves. Furthermore, low-resolution images are acquired when a high acquisition frequency is applied to accurately characterise the behaviour of anatomical features that quickly change over time. Denoising and super-resolution of US signals are relevant to improve the visual evaluation of the physician and the performance and accuracy of processing methods, such as segmentation and classification. The main requirements for the processing and analysis of US signals are real-time execution, preservation of anatomical features, and reduction of artefacts. In this context, we present a novel framework for the real-time denoising of US 2D images based on deep learning and high-performance computing, which reduces noise while preserving anatomical features in real-time execution. We extend our framework to the denoise of arbitrary US signals, such as 2D videos and 3D images, and we apply denoising algorithms that account for spatio-temporal signal properties into an image-to-image deep learning model. As a building block of this framework, we propose a novel denoising method belonging to the class of low-rank approximations, which learns and predicts the optimal thresholds of the Singular Value Decomposition. While previous denoise work compromises the computational cost and effectiveness of the method, the proposed framework achieves the results of the best denoising algorithms in terms of noise removal, anatomical feature preservation, and geometric and texture properties conservation, in a real-time execution that respects industrial constraints. The framework reduces the artefacts (e.g., blurring) and preserves the spatio-temporal consistency among frames/slices; also, it is general to the denoising algorithm, anatomical district, and noise intensity. Then, we introduce a novel framework for the real-time reconstruction of the non-acquired scan lines through an interpolating method; a deep learning model improves the results of the interpolation to match the target image (i.e., the high-resolution image). We improve the accuracy of the prediction of the reconstructed lines through the design of the network architecture and the loss function. %The design of the deep learning architecture and the loss function allow the network to improve the accuracy of the prediction of the reconstructed lines. In the context of signal approximation, we introduce our kernel-based sampling method for the reconstruction of 2D and 3D signals defined on regular and irregular grids, with an application to US 2D and 3D images. Our method improves previous work in terms of sampling quality, approximation accuracy, and geometry reconstruction with a slightly higher computational cost. For both denoising and super-resolution, we evaluate the compliance with the real-time requirement of US applications in the medical domain and provide a quantitative evaluation of denoising and super-resolution methods on US and synthetic images. Finally, we discuss the role of denoising and super-resolution as pre-processing steps for segmentation and predictive analysis of breast pathologies
Flexible estimation of temporal point processes and graphs
Handling complex data types with spatial structures, temporal dependencies, or discrete values, is generally a challenge in statistics and machine learning. In the recent years, there has been an increasing need of methodological and theoretical work to analyse non-standard data types, for instance, data collected on protein structures, genes interactions, social networks or physical sensors. In this thesis, I will propose a methodology and provide theoretical guarantees for analysing two general types of discrete data emerging from interactive phenomena, namely temporal point processes and graphs.
On the one hand, temporal point processes are stochastic processes used to model event data, i.e., data that comes as discrete points in time or space where some phenomenon occurs. Some of the most successful applications of these discrete processes include online messages, financial transactions, earthquake strikes, and neuronal spikes. The popularity of these processes notably comes from their ability to model unobserved interactions and dependencies between temporally and spatially distant events. However, statistical methods for point processes generally rely on estimating a latent, unobserved, stochastic intensity process. In this context, designing flexible models and consistent estimation methods is often a challenging task.
On the other hand, graphs are structures made of nodes (or agents) and edges (or links), where an edge represents an interaction or relationship between two nodes. Graphs are ubiquitous to model real-world social, transport, and mobility networks, where edges can correspond to virtual exchanges, physical connections between places, or migrations across geographical areas. Besides, graphs are used to represent correlations and lead-lag relationships between time series, and local dependence between random objects. Graphs are typical examples of non-Euclidean data, where adequate distance measures, similarity functions, and generative models need to be formalised. In the deep learning community, graphs have become particularly popular within the field of geometric deep learning.
Structure and dependence can both be modelled by temporal point processes and graphs, although predominantly, the former act on the temporal domain while the latter conceptualise spatial interactions. Nonetheless, some statistical models combine graphs and point processes in order to account for both spatial and temporal dependencies. For instance, temporal point processes have been used to model the birth times of edges and nodes in temporal graphs. Moreover, some multivariate point processes models have a latent graph parameter governing the pairwise causal relationships between the components of
the process. In this thesis, I will notably study such a model, called the Hawkes model, as well as graphs evolving in time.
This thesis aims at designing inference methods that provide flexibility in the contexts of temporal point processes and graphs. This manuscript is presented in an integrated format, with four main chapters and two appendices. Chapters 2 and 3 are dedicated to the study of Bayesian nonparametric inference methods in the generalised Hawkes point process model. While Chapter 2 provides theoretical guarantees for existing methods, Chapter 3 also proposes, analyses, and evaluates a novel variational Bayes methodology. The other main chapters introduce and study model-free inference approaches for two estimation problems on graphs, namely spectral methods for the signed graph clustering problem in Chapter 4, and a deep learning algorithm for the network change point detection task on temporal graphs in Chapter 5.
Additionally, Chapter 1 provides an introduction and background preliminaries on point processes and graphs. Chapter 6 concludes this thesis with a summary and critical thinking on the works in this manuscript, and proposals for future research. Finally, the appendices contain two supplementary papers. The first one, in Appendix A, initiated after the COVID-19 outbreak in March 2020, is an application of a discrete-time Hawkes model to COVID-related deaths counts during the first wave of the pandemic. The second work, in Appendix B, was conducted during an internship at Amazon Research in 2021, and proposes an explainability method for anomaly detection models acting on multivariate time series
Exploring Numerical Priors for Low-Rank Tensor Completion with Generalized CP Decomposition
Tensor completion is important to many areas such as computer vision, data
analysis, and signal processing. Enforcing low-rank structures on completed
tensors, a category of methods known as low-rank tensor completion has recently
been studied extensively. While such methods attained great success, none
considered exploiting numerical priors of tensor elements. Ignoring numerical
priors causes loss of important information regarding the data, and therefore
prevents the algorithms from reaching optimal accuracy. This work attempts to
construct a new methodological framework called GCDTC (Generalized CP
Decomposition Tensor Completion) for leveraging numerical priors and achieving
higher accuracy in tensor completion. In this newly introduced framework, a
generalized form of CP Decomposition is applied to low-rank tensor completion.
This paper also proposes an algorithm known as SPTC (Smooth Poisson Tensor
Completion) for nonnegative integer tensor completion as an instantiation of
the GCDTC framework. A series of experiments on real-world data indicated that
SPTC could produce results superior in completion accuracy to current
state-of-the-arts.Comment: 11 pages, 4 figures, 3 pseudocode algorithms, and 1 tabl
Towards Artificial General Intelligence (AGI) in the Internet of Things (IoT): Opportunities and Challenges
Artificial General Intelligence (AGI), possessing the capacity to comprehend,
learn, and execute tasks with human cognitive abilities, engenders significant
anticipation and intrigue across scientific, commercial, and societal arenas.
This fascination extends particularly to the Internet of Things (IoT), a
landscape characterized by the interconnection of countless devices, sensors,
and systems, collectively gathering and sharing data to enable intelligent
decision-making and automation. This research embarks on an exploration of the
opportunities and challenges towards achieving AGI in the context of the IoT.
Specifically, it starts by outlining the fundamental principles of IoT and the
critical role of Artificial Intelligence (AI) in IoT systems. Subsequently, it
delves into AGI fundamentals, culminating in the formulation of a conceptual
framework for AGI's seamless integration within IoT. The application spectrum
for AGI-infused IoT is broad, encompassing domains ranging from smart grids,
residential environments, manufacturing, and transportation to environmental
monitoring, agriculture, healthcare, and education. However, adapting AGI to
resource-constrained IoT settings necessitates dedicated research efforts.
Furthermore, the paper addresses constraints imposed by limited computing
resources, intricacies associated with large-scale IoT communication, as well
as the critical concerns pertaining to security and privacy
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