A Comprehensive Survey of Deep Learning in Remote Sensing: Theories, Tools and Challenges for the Community

In recent years, deep learning (DL), a re-branding of neural networks (NNs), has risen to the top in numerous areas, namely computer vision (CV), speech recognition, natural language processing, etc. Whereas remote sensing (RS) possesses a number of unique challenges, primarily related to sensors and applications, inevitably RS draws from many of the same theories as CV; e.g., statistics, fusion, and machine learning, to name a few. This means that the RS community should be aware of, if not at the leading edge of, of advancements like DL. Herein, we provide the most comprehensive survey of state-of-the-art RS DL research. We also review recent new developments in the DL field that can be used in DL for RS. Namely, we focus on theories, tools and challenges for the RS community. Specifically, we focus on unsolved challenges and opportunities as it relates to (i) inadequate data sets, (ii) human-understandable solutions for modelling physical phenomena, (iii) Big Data, (iv) non-traditional heterogeneous data sources, (v) DL architectures and learning algorithms for spectral, spatial and temporal data, (vi) transfer learning, (vii) an improved theoretical understanding of DL systems, (viii) high barriers to entry, and (ix) training and optimizing the DL.Comment: 64 pages, 411 references. To appear in Journal of Applied Remote Sensin

Survey of deep representation learning for speech emotion recognition

Traditionally, speech emotion recognition (SER) research has relied on manually handcrafted acoustic features using feature engineering. However, the design of handcrafted features for complex SER tasks requires significant manual eort, which impedes generalisability and slows the pace of innovation. This has motivated the adoption of representation learning techniques that can automatically learn an intermediate representation of the input signal without any manual feature engineering. Representation learning has led to improved SER performance and enabled rapid innovation. Its effectiveness has further increased with advances in deep learning (DL), which has facilitated \textit{deep representation learning} where hierarchical representations are automatically learned in a data-driven manner. This paper presents the first comprehensive survey on the important topic of deep representation learning for SER. We highlight various techniques, related challenges and identify important future areas of research. Our survey bridges the gap in the literature since existing surveys either focus on SER with hand-engineered features or representation learning in the general setting without focusing on SER

Joint Energy-based Model for Remote Sensing Image Processing

The peta-scale, continuously increasing amount of publicly available remote sensing information forms an unprecedented archive of Earth observation data. Although advances in deep learning provide tools to exploit big amounts of digital information, most supervised methods rely on accurately annotated sets to train models. Access to large amounts of high-quality annotations proves costly due to the human labor involved. Such limitations have been studied in semi-supervised learning where unlabeled samples aid the generalization of models trained with limited amounts of labeled data. The Joint Energy-based Model (JEM) is a recent, physics-inspired approach simultaneously optimizing a supervised task along with a generative process to train a sampler approximating a data distribution. Although a promising formulation of such models, current JEM implementations are predominantly applied to classification tasks. Their potential improving semantic segmentation tasks remains locked. Our work investigates JEM training behavior from a conceptual perspective, studying mechanisms of loss function divergences that numerically destabilizes the model optimization. We explore three regularization terms imposed on energy values and optimization gradients to alleviate the training complexity. Our experiments indicate that the proposed regularization mitigates loss function divergences for remote sensing imagery classification. Regularization on energy values of real samples performed the best. Additionally, we present an extended definition of JEM for image segmentation, sJEM. In our experiments, the generation branch did not perform as expected. sJEM was unable to generate realistic remote-sensing-like samples. Correspondingly performance is biased for the sJEM segmentation branch. Initial model optimization runs demand additional research to stabilize the methodology given spatial auto-correlations in remote sensing multi-spectral imagery. Our insights pave the way for the design of follow-up research to advance sJEM for Earth observation