Artificial Interferences Research Articles

Factors influencing microtremor data collected using nested-triangular array configurations

The availability of microtremor data is potentially affected by various external factors. By combining field data and artificial interference, this work aims to determine the correlation between these factors and the dispersion curve of fundamental-mode Rayleigh waves extracted from microtremors. The first step was to obtain real, high-quality microtremor records using a triangular ten-station array of 48-m radius. Secondly, a series of artificial or semi-artificial interferences of varying type, duration, amplitude, etc., were generated and combined with the real records to imitate actual interferences. Thirdly, all the dispersion curves of the fundamental-mode Rayleigh waves of these modified microtremor records were estimated using the extended spatial autocorrelation method (ESAC). Finally, by comparing the experimental dispersion curves with the original curve, in terms of overlap ratio, we obtained useful conclusions that can be directly applied to microtremor data collection and analysis.

Convex compressive beamforming with nonconvex sparse regularization.

The convex sparse penalty based compressive beamforming technique can achieve robust high resolution in direction-of-arrival (DOA) estimation tasks, but it often leads to an insufficient sparsity-inducing problem due to its convex loose approximation to ideal ℓ0 nonconvex penalty. On the contrary, the nonconvex sparse penalty can tightly approximate ℓ0 penalty to effectively enhance DOA estimation accuracy, but it incurs an initialization sensitivity problem due to its multiple local minimas. Leveraging their individual advantages, a minimax-concave penalty (MCP) regularized DOA estimation algorithm is proposed to achieve a maximally sparse level while maintaining the convex property of the overall objective function. Moreover, an accelerated block gradient descent-ascent algorithm with convergence guarantee is developed to rapidly achieve its one optimal point. Simulation results demonstrate that MCP penalty improves DOA estimation accuracy compared with popular sparse compressive beamforming techniques in strong noise scenarios and weak source confirmation. Ocean experimental results also validate that it retains more stable DOA estimation accuracy and incurs less artificial interferences.

Approximation Algorithm-Based Prosumer Scheduling for Microgrids

Since the inherent intermittency and uncertainty of renewable energy resources complicates efficient Microgrid operations, a Demand Response (DR) scheme is implemented for customers in the grid to alter their power-usage patterns. However, for a real-time pricing model at the current DR, the automated decision on the energy price is not trustworthy because of artificial interferences to the power generation. As opposed to energy price, an operational cost-based prosumer scheduling approach would be able to protect the integrity of the power grid operations from deceptive market transactions and assist in robust energy management. To investigate the operational challenges associated with the costs and prosumers in the Microgrid, we focus on formulating the problem mathematically and designing approximation algorithms to solve the problem of how to optimally identify suppliers to minimize the total operational costs associated with providing electricity. We prove the hardness of the scheduling as one of the NP-Hard problems and propose polynomial time algorithms for approximating optimal solutions. With a proper resilience level for reliable power services, the scheduling algorithms include ways to construct not only robust supplier networks, but also group energy communities in terms of black start while minimizing the operational costs. A series of theoretical performances and experimental evaluations also demonstrates the practical effectiveness of this scheduling model for the operations.

Suppression of Mainbeam Deceptive Jammer With FDA-MIMO Radar

Suppression of radar-to-radar jammers, especially the mainbeam jammers, has been an urgent demand in vehicular sensing systems with the expected increased number of vehicles equipped with radar systems. This paper deals with the suppression of mainbeam deceptive jammers with frequency diverse array (FDA)-multiple-input multiple-output (MIMO) radar, utilizing its extra degrees-of-freedom (DOFS) in the range domain. At the modelling stage, false targets, which lag several pulses behind the true target, are considered as a typical form of mainbeam jammers. To this end the data-independent beamforming is performed to suppress false targets by nulling at the equivalent transmit beampattern with an appropriate frequency increment. However, the suppression performance degrades in the presence of transmit spatial frequency mismatch, which could be induced by quantization errors, angle estimation errors and frequency increment errors. To solve this problem, a preset broadened nulling beamformer (PBN-BF) is proposed by placing artificial interferences with appropriate powers around the nulls of the equivalent transmit beampattern. In such a way, effective suppression of deceptive jammer can be guaranteed owing to the broadened notches. At the analysis stage, numerical results in a scenario with multiple unmanned aerial vehicles (UAVs) are provided to illustrate the effectiveness of the devised data-independent BF, and the signal-to-interference-plus-noise ratio is improved compared with the conventional data-independent BF.

Elastomeric polydimethylsiloxane polymer on conductive interdigitated electrode for analyzing skin hydration dynamics

With an approach towards generating a wearable skin hydration detecting system, simple, cheap, and flexible skin hydration sensing strategy was demonstrated here using an interdigitated electrode (IDE) coated with polydimethylsiloxane (PDMS) matrix. Aluminium IDE with a 400 µm gap and 250 µm electrode sizes were fabricated using a photolithography method. Morphological characterizations were performed using a high power microscope, 3D-profilometer, and scanning electron microscope. The dimensions of electrodes and gaps measured through electron microscopic analysis affirmed the exactness of IDE and the fabrication process. After coated with PDMS polymer, the IDE/PDMS surface was examined under a high power microscope and 3D-profilometer. The optical characterization revealed the polymer was coated on IDE through the color-shade changes and smooth surface observed under an optical microscope and the respective 3D-visualization. IDE/PDMS was also analyzed by an atomic force microscope, revealing the smoothness of the IDE surface. Electrical characterizations were performed using different pH and urea solutions and the sweat to investigate the influence of real-time and artificial sweat on IDE/PDMS. As the device showed appropriate results with real-time sweat and no effect with artificial interferences, it is highly encouraged and recommended for detecting skin hydration and the related illnesses with the point-of-care concept.

Transceive Beamforming With Accurate Nulling in FDA-MIMO Radar for Imaging

Beamforming plays a crucial role in synthetic aperture radar (SAR) for interference mitigation and ambiguity unaliasing. In this article, a series of novel beamforming methods for SAR systems is proposed based on nulling the transceive beampattern accurately in frequency diverse array (FDA)-multiple-input and multiple-output (MIMO) scheme. In general, these methods are implemented by assigning artificial interferences with prescribed powers within the given rectangular regions in the joint transmit–receive spatial frequency domain. In specific, according to the predefined null depths, closed-form expressions of artificial interference powers are first formulated. Then, iteration algorithms are developed to update the interference-plus-noise covariance matrix and the designed weight vector. In such a way, a trough-like transceive beampattern with arbitrarily distributed broadened nulls is formed in the joint transmit–receive spatial frequency domain. As a result, interferences mixed in signals received by SAR can be suppressed effectively. Numerical simulations and experimental results are provided to corroborate the effectiveness of the proposed methods.

Synthesis of derivatives of complex signals based on nonlinear discrete sequences with improved correlation properties

The structure of modern information and communication systems (ICS) is characterized by considerable spatial diversity of a large number of interacting subscribers. In these conditions, technologies of processing, storage, protection, transmission and reception of information on the network under conditions of natural and artificial interferences (impacts), as well as limited frequency and energy resources of ICS play an extremely important role in ensuring the quality of service of end users. ICS, especially for critical applications, are increasingly demanding to ensure the effectiveness of their functioning (speed of information transmission, electromagnetic compatibility, noise immunity, information security, survivability, secrecy, information security). The ability to implement these requirements is largely disregarded by applicable information technology. There is a contradiction between the strict requirements for secrecy, confidentiality, integrity, authenticity of data stored and transmitted through communication lines, on the one hand, and existing models, methods and technologies for managing telecommunications networks, information security, services and quality of service, on the other hand. The main ways to resolve this contradiction is to increase the noise immunity, secrecy and information security of ICS based on the improvement of methodological bases for the construction of ICS by developing methods of information exchange, methods of synthesis of signals of physical data carriers with the necessary properties. The principles of construction of derivative signal systems are given. The requirements for output and source signals are defined. The justification of the possibility of using random (pseudorandom) processes for the production of signals is used to construct them. The results of studies of ensemble, correlation, and structural properties of the obtained systems of derivative signals are presented. It is shown that the use of this class of complex nonlinear discrete signals in modern ICS will improve such performance indicators of such systems as noise immunity, information and structural stealth.

Pattern recognition in time series for space missions: A rosetta magnetic field case study

Time series analysis is a technique widely employed in space science. In unpredictable environments like space, scientific analysis relies on large data sets to enable interpretation of observations. Artificial signal interferences caused by the spacecraft itself further impede this process. The most time consuming part of these studies is the efficient identification of recurrent pattern in observations, both of artificial and natural origin, often forcing researchers to limit their analysis to a reduced set of observations. While pattern recognition techniques for time series are well known, their application is discussed and evaluated primarily on purpose built or heavily preprocessed data sets. The aim of this paper is to evaluate the performance of state of the art pattern recognition techniques in terms of computational efficiency and validity on a real-life testcase. For this purpose the most suitable techniques for different types of pattern are discussed and subsequently evaluated on various hardware in comparison to manual identification. Using magnetic field observations of the ESA Rosetta mission as a representative example, both disturbances and natural patterns are identified. Compared to manual selection a speed-up of a factor up to 100 is achieved, with values for recall and precision above 80%. Moreover, the detection process is fully automated and reproducible. Using the presented method it was possible to detect and correct artificial interference. Finally, the feasibility of onboard deployment is briefly discussed.

$\text {A}^\text {2}\text {RC}$: An Accurate Array Response Control Algorithm for Pattern Synthesis

This paper presents a novel accurate array response control algorithm, abbreviated as A 2 RC, and its application to array pattern synthesis. The proposed A 2 RC algorithm deals with the problem of how to accurately control the array response at a given direction. Starting from the adaptive array theory, a deep analysis of the optimal weight vector is carried out. It is found that the normalized response at a given direction can be accurately adjusted to an arbitrary level, by means of making some simple modification to the initial weight vector. On this basis, all possible weight vectors, which have a specific form and can make the normalized response at the given direction equal to the prescribed value, are first figured out. Then, an effective approach to selecting the most appropriate one, which would cause the least pattern distortion, is devised. By applying the A 2 RC algorithm, a new pattern synthesis approach for arbitrary arrays is developed. In this approach, the array pattern is adjusted in a point-by-point manner by successively modifying the weight vector. Contrary to the conventional approaches that assign artificial interferences in an ad hoc way, our approach is able to obtain the weight vector without iteratively determining the powers of the artificial interferences. Extensive simulation results are provided to demonstrate the performance of the A 2 RC algorithm in array response control and the effectiveness of this algorithm in pattern synthesis under various situations.

Shoal morphodynamics of the Changjiang (Yangtze) estuary: Influences from river damming, estuarine hydraulic engineering and reclamation projects

Concerns regarding estuarine shoal morphodynamics have increased worldwide because of intensive anthropogenic activities. To explore response of estuarine shoals to possible couplings of multiple artificial interferences in river basins and within estuaries, the link between the morphodynamic processes of the Nanhui Shoal (NHS), which is located along the southern margin of the Changjiang estuary, the largest estuary in Asia, and river damming, estuarine hydraulic engineering and reclamation projects, is discerned in this study. The results reveal that the NHS exhibited secular polarization during 1998–2013, with a significant accretion of 1.8×108m3 landward from the tidal ridge and an erosion of 0.3×108m3 on the seaward edge, respectively, forming a steep slope with an elevation between −2 and −3m. Meanwhile, the NHS morphodynamics could be divided into 3 stages: mild accretion with an undisturbed tidal channel during 1998–2002, strong sedimentation with a disrupted tidal channel during 2003–2008, and large-scale landward accretion with an infilled tidal channel after 2009. Moreover, the NHS's volume variations exhibited an 18-month cycle, even though an increased area of 35km2 above −2m and a decreased area of 45km2 between −2 and −5m were observed. The primary causes of theses periodic changes in the NHS's volume are determined as the fluctuating Changjiang water discharge and cyclically altered hydrodynamics of the South Passage. The Deep Waterway Project (DWP) and reclamation projects were responsible for the polarization of seaward erosion and landward accretion, respectively. Moreover, these reclamation projects dominated the staggered changes in NHS morphodynamics by inducing continuous accretion within the tidal channel. Compared to estuarine engineering, river damming induced dramatic declines in distal sediment may have played a minor role in flat changes of NHS.

Generalized 2-D Numerical Pattern Synthesis Algorithm for Low Cross Polarization and Low Sidelobe Synthesis

Numerical pattern synthesis (NPS) algorithm based on adaptive array theory is an effective spatial power pattern synthesis method for antenna arrays. In this letter, instead of using the artificial interferences weighted on the total power pattern in the conventional NPS algorithm, a generalized two-dimensional (2-D) NPS algorithm is proposed in which two weighting functions are assigned to control the copolarization and cross-polarization patterns, respectively. The weighting functions are iteratively updated until both the sidelobe and cross-polarization levels reach their prescribed ones. Two numerical examples for synthesizing the patterns of a linearly polarized planar array and a circularly polarized cylindrical array are provided to validate effectiveness and advantages of the proposed generalized 2-D NPS algorithm.

RFI Mitigation in Aperture Synthesis Radiometers Using a Modified CLEAN Algorithm

For aperture synthesis radiometers, sparse samplings on the $u$ - $v$ frequency plane cause undesirable sidelobes in the synthesized beam. Through these sidelobes, artificial sources emitting in the protected 1400–1427 MHz band contaminate the retrievals of the soil moisture and ocean salinity (SMOS) from MIRAS measurements. One effective way to correct the artificial interferences is to create a synthetic signal to compensate for the interference’s impact. Based on the similar idea, in this letter, we describe an algorithm to compensate for the interference’s impact by constructing an artificial signal as close as possible to the Gaussian beam. Numerical studies using synthetic and real SMOS data have been carried out to demonstrate that the proposed algorithm outperforms the classical CLEAN algorithm in correcting the impact of the extended radio frequency interference source.

Determining the First-Null Mainlobe Region of an Arbitrary Pattern for 2-D Numerical Pattern Synthesis Algorithm

Determining the mainlobe region of an arbitrary pattern is a critical problem in the two-dimensional numerical pattern synthesis (2-D-NPS) method in which a number of artificial interferences with appropriate powers are distributed outside of the mainlobe region. In this communication, a novel mainlobe region determination procedure based on the seeded region growing (SRG) method is proposed. Two different stopping criterions are introduced. Several numerical synthesis examples for uniformly and nonuniformly spaced planar arrays as well as a cylindrical array with directive elements, are presented to validate the effectiveness of the 2-D-NPS with the proposed mainlobe determination procedure. The two stopping criterions are also compared with these examples.

국내 PBN 이행을 위한 대안 항법 적용 방안

한국은 성능기반항행 (PBN; performance-based navigation)으로 전환하기 위한 단계적 PBN 이행계획을 2010년에 수립하고 로드맵에 따른 새로운 비행절차를 개발 중에 있다. PBN 비행절차에는 GNSS (global navigation satellite systems), DME (distance measuring equipment), VOR (VHF omnidirectional range), INS (inertial navigation system) 등의 항행시설 (NAVAID; navigation aid)이 활용되는 것으로 되어있다. 그 중에서 GNSS를 이용한 PBN 업무제공이 중심을 이루고 있는 실정이다. 그러나 위성항법신호의 인위적, 자연적 간섭에 의한 취약성이 발견됨에 따라 세계 각국은 다양한 대안항법(APNT; alternative positioning, navigation and timing) 기술을 연구하고 있다. 본 논문에서는 GNSS 신호가 가용하지 않을 경우 기존의 항행시스템으로 지속적인 PBN 운항이 가능한지를 분석하였으며, 결과적으로 국내 일부 공항은 접근 단계 구역에서 대안항법의 구축이 필요한 것으로 나타났다. Republic of Korea has established its performance-based navigation (PBN) implementation plan in 2010 for ensuring a smooth transition to PBN operations and relevant new flight procedures are being developed in accordance with the roadmap. Various Navigation aids (NAVAIDs) like global navigation satellite systems (GNSS), distance measuring equipment (DME), VHF omnidirectional range (VOR), inertial navigation system (INS) are used to support PBN procedures. Among them, GNSS would play a central role in PBN implementation. However, vulnerability of satellite navigation signals to artificial and natural interferences has been discovered and various alternative positioning, navigation and timing (APNT) technologies are under development in many countries. In this paper, we study whether continuous PBN operations can be achievable without GNSS signals. As a result, it shows that some of the domestic airports require the construction of APNT in the approach area.

Filtering Chinese Image Spam Using Pseudo‐OCR

For image spam filtering, the Optical character recognition(OCR) based methods often achieve a better performance due to the more complex structure of recognizing corresponding text. However, applying traditional OCR techniques usually introduced shortcomings like the expensive computational cost, vulnerability to image noises and artificial interferences, especially for Chinese image spam filtering. So, by optimizing recognition procedure of traditional OCR, we propose the idea of pseudo-OCR more suitable for Chinese image spam filtering. During which discriminating the potential image spam character features from ham ones is sufficient, instead of recognizing them. What's more, a novel Chinese key-point based character feature specific for pseudo-OCR is also devised and extracted using a carefully designed algorithm, which outperforms classic corner detection methods in finding such key-points. Experiment results show that our proposed system usually has a better performance than traditional OCR based method while maintaining a low false positive rate.

On the potential of data assimilation to generate SMOS-Level 4 maps of sea surface salinity

The Soil Moisture/Ocean Salinity (SMOS) satellite, launched in November 2009, measures visibilities at L-band, from which brightness temperatures are computed. This information is used to retrieve values of the sea surface salinity (SSS) and soil moisture; two variables whose observation is a key to better understand the oceanic component of the water cycle. A hierarchy of SSS products has been defined in the SMOS data processing chain. This work focuses on the so-called Level 3 (binned maps of SSS) and Level 4 (products combining SMOS data with any other source of information). The objective is to illustrate the feasibility of using data assimilation to produce Level 4 maps of sea surface salinity. The numerical model will increase the geophysical coherence of SMOS data as a dynamical interpolator. Here, the employment of data assimilation differs from its usual applications (improving model outputs for example). Indeed, the numerical model will interpolate the observations according to the general laws of fluid mechanics and, if possible, reduce the error contained in the original observations. The data assimilation method analyzed is a nudging algorithm. The domain of application for this feasibility study is the Northeast subtropical Atlantic gyre, a challenging region due to the presence of a large amount of noise that deteriorates the SMOS data. The main sources of errors are the vicinity of large landmasses that introduce a spurious bias, and the presence of a significant amount of artificial radio frequency interferences (RFI). While the Quality Controls already set up in the SMOS processing chain do filter the retrievals containing too large errors, wrong data are still present in Level 3 maps. Despite this difficulty, the results provide meaningful SMOS SSS Level 4 products in terms of their geophysical coherence (estimated using singularity analysis) and better agreement with in-situ data than Level 3 product.

A Experiment Study of De-Noising to Reduce the Effect of Artificial Light Interferences for Visible Light Communications Using White-LEDs

The optical power penalty (OPP) due to the artificial light interference (ALI) can influence the performance of the Visible Light Communications (VLC) system significantly. In this paper, a de-noising scheme based on band-pass filter is achieved in a voice-transmission VLC experiment system and it was proved a effective scheme to improve the quality of the transmission significantly

HGM을 이용한 질날늪 기능평가 연구

Wetlands occupy an important ecological position on the earth, carrying out very important functions and roles both ecologically and hydrologically. However, due to past industrialization, not only wetland areas but also the biodiversity of organisms has severely decreased due to several artificial interferences and damage as wetlands began to be perceived simply as targets for development and reclamation. However in recent times, with the importance of wetlands coming to the fore, the assessment of the function and value of wetlands is being made for their wise use and systematic maintenance. Accordingly, this study targeted the Jilnal Wetlands located in Haman, Gyeongnam, and conducted a functional appraisal of this wetland using the modified HGM Model which was modified & developed appropriately for the actual conditions of our country. The result of its appraisal by selecting the Upo Wetland as the reference wetland, which is a criterion of the index, showed a comparatively positive functional index with 0.89 of the Upo Wetland average. This means that the Jilnal Wetland carrys out more than 89% of the functioning of the Upo Wetland. In this regard, it is thought that the Jilnal Wetland could carry out the wetland functioning equivalent to that of the Upo Wetland through a little more systematic management.

Detection of microwave emission due to rock fracture as a new tool for geophysics: A field test at a volcano in Miyake Island, Japan

Abstract This paper describes a field test to verify a newly discovered phenomenon of microwave emission due to rock fracture in a volcano. The field test was carried out on Miyake Island, 150 km south of Tokyo. The main objective of the test was to investigate the applicability of the phenomenon to the study of geophysics, volcanology, and seismology by extending observations of this phenomenological occurrence from the laboratory to the natural field. We installed measuring systems for 300 MHz, 2 GHz, and 18 GHz-bands on the mountain top and mountain foot in order to discriminate local events from regional and global events. The systems include deliberate data subsystems that store slowly sampled data in the long term, and fast sampled data when triggered. We successfully obtained data from January to February 2008. During this period, characteristic microwave pulses were intermittently detected at 300 MHz. Two photographs taken before and after this period revealed that a considerably large-scale collapse occurred on the crater cliff. Moreover, seismograms obtained by nearby observatories strongly suggest that the crater subsidence occurred simultaneously with microwave signals on the same day during the observation period. For confirmation of the microwave emission caused by rock fracture, these microwave signals must be clearly discriminated from noise, interferences, and other disturbances. We carefully discriminated the microwave data taken at the mountaintop and foot, checked the lightning strike data around the island, and consequently concluded that these microwave signals could not be attributed to lightning. Artificial interferences were discriminated by the nature of their waveforms. Thus, we inferred that the signals detected at 300 MHz were due to rock fractures during cliff collapses. This result may provide a useful new tool for geoscientists and for the mitigation of natural hazards.

The difficult relationship between occlusal interferences and temporomandibular disorder – insights from animal and human experimental studies

The aetiology of temporomandibular disorder (TMD) is multifactorial, and numerous studies have addressed that occlusion may be of great importance. However, whether occlusion plays a crucial role in the pathogenesis of TMD remains controversial. Study designs utilising animal models have been used to study the effects of artificial occlusal alterations. Experimental traumatic occlusion affects blood flow in the temporomandibular joint and results in changes in the condylar cartilage, and artificial occlusal interference induces masticatory muscle nociceptive responses that are associated with peripheral sensitisation and lead to central sensitisation, which maintains masticatory muscle hyperalgesia. The possibility that occlusal interference results in TMD has been investigated in humans using a double-blind randomised design. Subjects without a history of TMD show fairly good adaptation to interferences. In contrast, subjects with a history of TMD develop a significant increase in clinical signs and self-report stronger symptoms (occlusal discomfort and chewing difficulties) in response to interferences. Meanwhile, psychological factors appear meaningful for symptomatic responses to artificial interferences in subjects with a history of TMD. Thus, individual differences in vulnerability to occlusal interferences do exist. Although there are advantages and disadvantages to using human and animal occlusal interference models, these approaches are indispensable for discovering the role of occlusion in TMD pathogenesis.