3,032 research outputs found
Remote sensing of earth terrain
A systematic approach for the identification of terrain media such as vegetation canopy, forest, and snow covered fields is developed using the optimum polarimetric classifier. The covariance matrices for the various terrain cover are computed from theoretical models of random medium by evaluating the full polarimetric scattering matrix elements. The optimal classification scheme makes use of a quadratic distance measure and is applied to classify a vegetation canopy consisting of both trees and grass. Experimentally measured data are used to validate the classification scheme. Theoretical probability of classification error using the full polarimetric matrix are compared with classification based on single features including the phase difference between the VV and HH polarization returns. It is shown that the full polarimetric results are optimal and provide better classification performance than single feature measurements
Towards a cyber physical system for personalised and automatic OSA treatment
Obstructive sleep apnea (OSA) is a breathing disorder that takes place in the course of the sleep and is produced by a complete or a partial obstruction of the upper airway that manifests itself as frequent breathing stops and starts during the sleep. The real-time evaluation of whether or not a patient is undergoing OSA episode is a very important task in medicine in many scenarios, as for example for making instantaneous pressure adjustments that should take place when Automatic Positive Airway Pressure (APAP) devices are used during the treatment of OSA. In this paper the design of a possible Cyber Physical System (CPS) suited to real-time monitoring of OSA is described, and its software architecture and possible hardware sensing components are detailed. It should be emphasized here that this paper does not deal with a full CPS, rather with a software part of it under a set of assumptions on the environment. The paper also reports some preliminary experiments about the cognitive and learning capabilities of the designed CPS involving its use on a publicly available sleep apnea database
Concealed Object Detection for Passive Millimeter-Wave Security Imaging Based on Task-Aligned Detection Transformer
Passive millimeter-wave (PMMW) is a significant potential technique for human
security screening. Several popular object detection networks have been used
for PMMW images. However, restricted by the low resolution and high noise of
PMMW images, PMMW hidden object detection based on deep learning usually
suffers from low accuracy and low classification confidence. To tackle the
above problems, this paper proposes a Task-Aligned Detection Transformer
network, named PMMW-DETR. In the first stage, a Denoising Coarse-to-Fine
Transformer (DCFT) backbone is designed to extract long- and short-range
features in the different scales. In the second stage, we propose the Query
Selection module to introduce learned spatial features into the network as
prior knowledge, which enhances the semantic perception capability of the
network. In the third stage, aiming to improve the classification performance,
we perform a Task-Aligned Dual-Head block to decouple the classification and
regression tasks. Based on our self-developed PMMW security screening dataset,
experimental results including comparison with State-Of-The-Art (SOTA) methods
and ablation study demonstrate that the PMMW-DETR obtains higher accuracy and
classification confidence than previous works, and exhibits robustness to the
PMMW images of low quality
A Review of Indoor Millimeter Wave Device-based Localization and Device-free Sensing Technologies and Applications
The commercial availability of low-cost millimeter wave (mmWave)
communication and radar devices is starting to improve the penetration of such
technologies in consumer markets, paving the way for large-scale and dense
deployments in fifth-generation (5G)-and-beyond as well as 6G networks. At the
same time, pervasive mmWave access will enable device localization and
device-free sensing with unprecedented accuracy, especially with respect to
sub-6 GHz commercial-grade devices. This paper surveys the state of the art in
device-based localization and device-free sensing using mmWave communication
and radar devices, with a focus on indoor deployments. We first overview key
concepts about mmWave signal propagation and system design. Then, we provide a
detailed account of approaches and algorithms for localization and sensing
enabled by mmWaves. We consider several dimensions in our analysis, including
the main objectives, techniques, and performance of each work, whether each
research reached some degree of implementation, and which hardware platforms
were used for this purpose. We conclude by discussing that better algorithms
for consumer-grade devices, data fusion methods for dense deployments, as well
as an educated application of machine learning methods are promising, relevant
and timely research directions.Comment: 43 pages, 13 figures. Accepted in IEEE Communications Surveys &
Tutorials (IEEE COMST
Remote sensing of clouds and precipitation using active and passive microwave observations
Global observations of clouds and precipitation are of great importance for weather prediction and the monitoring of the climate. Nonetheless, the currently available record of global observations does not constrain the properties of clouds very well owing to the inherent limitations of the observation systems used to produce them. The upcoming Ice Cloud Imager (ICI) microwave radiometer, which will be launched on the next generation of European weather satellites, will improve this situation by providing observations of clouds at sub-millimeter wavelengths. ICI will be the first sensor of its kind to deliver these observations, which will significantly improve the sensitivity to small ice particles and low mass concentrations compared to currently available microwave observations.This thesis presents research aimed at developing knowledge and methodology required for the modeling and interpretation of the observations that will be provided by ICI. Two studies are presented which propose a method for measuring distributions of ice hydrometeors from ICI-type sub-millimeter observations combined with radar observations.The first study uses simulated observations to assess the potential benefits of combin- ing sub-millimeter radiometer observations with radar observations for the retrieval of ice hydrometeors. It is found that the combined observations improve the sensitivity to microphysical properties of clouds, which can help to reduce the error in the retrieved mass concentrations for specific hydrometeor types. Furthermore, improved sensitivity to supercooled liquid cloud is found as an additional synergy between the active and passive observations.The second study aims to validate the results from the first by applying the synergistic retrieval algorithm to observations from a flight campaign. The retrieval algorithm is found to show overall good agreement with in-situ measured ice concentrations taking into account the sensitivity limits of the sensors. In addition to that, indications of a signal from mixed-phase particles are found in observations of convective updrafts. In the two presented studies, a synergistic retrieval algorithm for ice hydrometeors from radar and passive sub-millimeters has been developed, characterized and vali- dated. The method can be applied in a future satellite mission to reduce uncertainties in global observations of clouds or used to study cloud microphysical properties in field campaigns. In addition to that, the presented application to field campaign data provides one of the rare validation cases for the radiative transfer modeling involving clouds at sub-millimeter wavelengths
Image Restoration
This book represents a sample of recent contributions of researchers all around the world in the field of image restoration. The book consists of 15 chapters organized in three main sections (Theory, Applications, Interdisciplinarity). Topics cover some different aspects of the theory of image restoration, but this book is also an occasion to highlight some new topics of research related to the emergence of some original imaging devices. From this arise some real challenging problems related to image reconstruction/restoration that open the way to some new fundamental scientific questions closely related with the world we interact with
Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R CrA
Models predict that in the innermost AU of the disk around Herbig Ae/Be star,
the dust disk forms a "puffed-up" inner rim, which should result in a strongly
asymmetric brightness distribution for disks seen under intermediate
inclination. Using the VLTI/AMBER long-baseline interferometer, we obtained 24
near-infrared (H- and K-band) spectro-interferometric observations on the
Herbig Ae star R CrA. In the derived visibility function, we detect the
signatures of an extended (25 mas) and a compact component (5.8 mas), with the
compact component contributing about 2/3 of the total flux. The brightness
distribution is highly asymmetric, as indicated by the strong closure phases
(up to 40 deg) and the detected position angle dependence of the visibilities
and closure phases. To interpret these asymmetries, we employ geometric as well
as physical models, including a binary model, a skewed ring model, and a
puffed-up inner rim model with a vertical or curved rim shape. Our curved
puffed-up rim model can reasonably well reproduce the interferometric
observables and the SED simultaneously and suggests a luminosity of 29 L_sun
and the presence of relatively large (> 1.2 micron) Silicate dust grains.
Perpendicular to the disk, two bow shock-like structures appear in the
associated reflection nebula NGC 6729, suggesting that the resolved sub-AU size
disk is the driving engine of a large-scale outflow. Detecting, for the first
time, strong non-localized asymmetries in the inner regions of a Herbig Ae
disk, our study supports the existence of a puffed-up inner rim in YSO disks.Comment: 17 pages; 15 figures; Accepted by A&
Cost benefit analysis of space communications technology. Volume 2: Final report
For abstract, see preceding accession
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