Search results for "Time-series"
showing 10 items of 32 documents
Long-Term Hydrological Regime Monitoring of a Mediterranean Agro-Ecological Wetland Using Landsat Imagery: Correlation with the Water Renewal Rate of…
2021
The Natural Park of Albufera (Valencia, Spain) is one of the Spanish Mediterranean wetlands where rice is cultivated intensively. The hydrology of the Albufera Lake, located in the center, combines natural contributions with complex human management. The aim of our study was to develop a new methodology to accurately detect the volume of flood water in complex natural environments which experience significant seasonal changes due to climate and agriculture. The study included 132 Landsat images, covering a 15-year period. The algorithm was adjusted using the NDWI index and simultaneous measurements of water levels in the rice fields. The NDVI index was applied to monitor the cultivated area…
Testing Equality of Multiple Power Spectral Density Matrices
2018
This paper studies the existence of optimal invariant detectors for determining whether P multivariate processes have the same power spectral density. This problem finds application in multiple fields, including physical layer security and cognitive radio. For Gaussian observations, we prove that the optimal invariant detector, i.e., the uniformly most powerful invariant test, does not exist. Additionally, we consider the challenging case of close hypotheses, where we study the existence of the locally most powerful invariant test (LMPIT). The LMPIT is obtained in the closed form only for univariate signals. In the multivariate case, it is shown that the LMPIT does not exist. However, the c…
Information decomposition in the frequency domain: a new framework to study cardiovascular and cardiorespiratory oscillations
2021
While cross-spectral and information-theoretic approaches are widely used for the multivariate analysis of physiological time series, their combined utilization is far less developed in the literature. This study introduces a framework for the spectral decomposition of multivariate information measures, which provides frequency-specific quantifications of the information shared between a target and two source time series and of its expansion into amounts related to how the sources contribute to the target dynamics with unique, redundant and synergistic information. The framework is illustrated in simulations of linearly interacting stochastic processes, showing how it allows us to retrieve …
Specialization and herding behavior of trading firms in a financial market
2008
Agent-based models of financial markets usually make assumptions about agent’s preferred stylized strategies. Empirical validations of these assumptions have not been performed so far on a full-market scale. Here we present a comprehensive study of the resulting strategies followed by the firms which are members of the Spanish Stock Exchange. We are able to show that they can be characterized by a resulting strategy and classified in three well- defined groups of firms. Firms of the first group have a change of inventory of the traded stock which is positively correlated with the synchronous stock return whereas firms of the second group show a negative correlation. Firms of the third group…
Cyclic influences on the heavy metal chronology in a Central Mediterranean area (Palermo Gulf, Italy)
2010
PurposeThe evaluation of long-term heavy metal concentrations in the Gulf of Palermo (Italy) has been carried out in order to investigate how changes of pollution levels in the last 50 years can be reflected in marine sediments. Measurements of Cr, Cu, Hg, Pb, and Zn concentrations were performed on dated fractions of a sediment core. Time series analysis has allowed to obtain information on the chronology of the heavy metal pollution of the area and to identify seasonal components and trends.Materials and methodsHeavy metal concentrations in the <63 μm fraction of core sections were obtained by Atomic Absorption Spectrophotometry, after wet sieving, drying, and digestion procedures. Dating…
Do Saharan Dust Days Carry a Risk of Hospitalization From Respiratory Diseases for Citizens of the Canary Islands (Spain)?
2021
Background: Saharan dust meets the Canary Islands at the beginning of its westward path across the North Atlantic, exceeding the European daily levels for PM10; for this reason, their two provincial capital cities, constitute optimal sites where to evaluate the health effects of this natural event. Objectives: To assess the short-term association between Saharan Dust Days (SDDs) and respiratory morbidity in the two capital cities. Methods: We carried out a time-series analysis with daily emergency hospital admissions due to all respiratory system diseases, chronic obstructive pulmonary disease (COPD) and asthma between 2001 and 2005, assessing the independent effect of SDDs, defined accordi…
Semi-blind Independent Component Analysis of functional MRI elicited by continuous listening to music
2013
This study presents a method to analyze blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (tMRI) signals associated with listening to continuous music. Semi-blind independent component analysis (ICA) was applied to decompose the tMRI data to source level activation maps and their respective temporal courses. The unmixing matrix in the source separation process of ICA was constrained by a variety of acoustic features derived from the piece of music used as the stimulus in the experiment. This allowed more stable estimation and extraction of more activation maps of interest compared to conventional ICA methods.
Quantifying Irrigated Winter Wheat LAI in Argentina Using Multiple Sentinel-1 Incidence Angles
2022
Synthetic aperture radar (SAR) data provides an appealing opportunity for all-weather day or night Earth surface monitoring. The European constellation Sentinel-1 (S1) consisting of S1-A and S1-B satellites offers a suitable revisit time and spatial resolution for the observation of croplands from space. The C-band radar backscatter is sensitive to vegetation structure changes and phenology as well as soil moisture and roughness. It also varies depending on the local incidence angle (LIA) of the SAR acquisition’s geometry. The LIA backscatter dependency could therefore be exploited to improve the retrieval of the crop biophysical variables. The availability of S1 radar time-series data at d…
Monitoring the invasion of an exotic tree (Ailanthus altissima) (Mill.) Swingle with Landsat satellite time series imagery in urban forest.
2015
In the Mediterranean area, one the most threat tree to various ecosystems is Ailanthus altissima (Mill.) Swingle. This is an aggressive invasive species common in natural and semi-natural habitat. Monitoring and mapping of invasive species is an important information for the conservation and management of ecosystems. The study of distribution and diffusion of invasive species are useful to assess their environmental impacts, formulate effective control strategies, and forecast potential spread. The main target of this work is to examine the feasibility of mapping the expansion of A. altissima using remote sensing techniques in a highly complex urban forest setting. Remote sensing has been a…