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Zhang, Yongqiang, Jianxiong Zhou, Zhiyong Song i Kaixin Zhou. "High-Precision GPU-Accelerated Simulation Algorithm for Targets under Non-Uniform Cluttered Backgrounds". Remote Sensing 15, nr 19 (22.09.2023): 4664. http://dx.doi.org/10.3390/rs15194664.
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This article presents a high-precision airborne video synthetic aperture radar (SAR) raw echo simulation method aimed at addressing the issue of simulation accuracy in video SAR image generation. The proposed method employs separate techniques for simulating targets and ground clutter, utilizing pre-existing SAR images for clutter simulation and employing the shooting and bouncing rays (SBR) approach to generate target echoes. Additionally, the method accounts for target-generated shadows to enhance the realism of the simulation results. The fast simulation algorithm is implemented using the C++ programming language and the Accelerated Massive Parallelism (AMP) framework, providing a fusion technique for integrating clutter and target simulations. By combining the two types of simulated data to form the final SAR image, the method achieves efficient and accurate simulation technology. Experimental results demonstrate that this method not only improves computational speed but also ensures the accuracy and stability of the simulation outcomes. This research holds significant implications for the development of algorithms pertaining to video SAR target detection and tracking, providing robust support for practical applications.
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Kumar, B. P., i C. S. Paidimarry. "Improved Real Time GPS RF Data Capturing for GNSS SDR Applications". Giroskopiya i Navigatsiya 28, nr 1 (2020): 42–53. http://dx.doi.org/10.17285/0869-7035.0023.
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Kumar, B. P., i C. S. Paidimarry. "Improved Real Time GPS RF Data Capturing for GNSS SDR Applications". Gyroscopy and Navigation 11, nr 1 (styczeń 2020): 59–67. http://dx.doi.org/10.1134/s2075108720010083.
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Tabibi, Sajad, Felipe G. Nievinski, Tonie van Dam i João F. G. Monico. "Assessment of modernized GPS L5 SNR for ground-based multipath reflectometry applications". Advances in Space Research 55, nr 4 (luty 2015): 1104–16. http://dx.doi.org/10.1016/j.asr.2014.11.019.
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Sajous, Patricia. "En route avec l’IA ! Incidence de l’IA et de l’informatique ubiquitaire dans l’établissement de la mobilité quotidienne : le cas des applications GPS". Flux Pub. anticipées, nr 4 (15.12.2022): I3—XV. http://dx.doi.org/10.3917/flux1.pr1.0003.
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L’IA (intelligence artificielle) colonise de plus en plus de secteurs du quotidien. Comment prendre cela en compte dans les recherches en sciences humaines portant sur la mobilité quotidienne ? Cet article est l’occasion de s’interroger sur les cadres théorique et méthodologique à mettre en place. Nous développons la notion de « corps augmenté » et considérons les objets techniques permettant l’augmentation comme des « non humains actants » (Callon, 2006). Nous débutons par une définition, précisons les modalités d’analyse de l’augmentation du corps en matière de mobilité quotidienne et mettons en perspective l’ancienneté de cette recherche. Le cadre théorique posé, nous nous penchons sur le cadre méthodologique permettant de cerner les ressorts de l’augmentation. Nous nous intéresserons alors aux applications GPS ( Global Positioning System ) intégrant l’IA, consultables sur smartphone. Objet d’un nombre croissant de téléchargements, nous montrons par une enquête exploratoire sur quatre applications, en France, comment l’IA fait évoluer la donne. Nous revenons dans la discussion sur le cadre réflexif mis en place et sur les tendances identifiées dans les résultats.
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Savelonas, Michalis A., Christos N. Veinidis i Theodoros K. Bartsokas. "Computer Vision and Pattern Recognition for the Analysis of 2D/3D Remote Sensing Data in Geoscience: A Survey". Remote Sensing 14, nr 23 (27.11.2022): 6017. http://dx.doi.org/10.3390/rs14236017.
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Historically, geoscience has been a prominent domain for applications of computer vision and pattern recognition. The numerous challenges associated with geoscience-related imaging data, which include poor imaging quality, noise, missing values, lack of precise boundaries defining various geoscience objects and processes, as well as non-stationarity in space and/or time, provide an ideal test bed for advanced computer vision techniques. On the other hand, the developments in pattern recognition, especially with the rapid evolution of powerful graphical processing units (GPUs) and the subsequent deep learning breakthrough, enable valuable computational tools, which can aid geoscientists in important problems, such as land cover mapping, target detection, pattern mining in imaging data, boundary extraction and change detection. In this landscape, classical computer vision approaches, such as active contours, superpixels, or descriptor-guided classification, provide alternatives that remain relevant when domain expert labelling of large sample collections is often not feasible. This issue persists, despite efforts for the standardization of geoscience datasets, such as Microsoft’s effort for AI on Earth, or Google Earth. This work covers developments in applications of computer vision and pattern recognition on geoscience-related imaging data, following both pre-deep learning and post-deep learning paradigms. Various imaging modalities are addressed, including: multispectral images, hyperspectral images (HSIs), synthetic aperture radar (SAR) images, point clouds obtained from light detection and ranging (LiDAR) sensors or digital elevation models (DEMs).
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Duan, Huizhi, Yongsheng Li, Bingquan Li i Hao Li. "Fast InSAR Time-Series Analysis Method in a Full-Resolution SAR Coordinate System: A Case Study of the Yellow River Delta". Sustainability 14, nr 17 (25.08.2022): 10597. http://dx.doi.org/10.3390/su141710597.
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Ground deformation is a major determinant of delta sustainability. Sentinel-1 Terrain Observation by Progressive Scans (TOPS) data are widely used in interferometric synthetic aperture radar (InSAR) applications to monitor ground subsidence. Due to the unparalleled mapping coverage and considerable data volume requirements, high-performance computing resources including graphics processing units (GPUs) are employed in state-of-the-art methodologies. This paper presents a fast InSAR time-series processing approach targeting Sentinel-1 TOPS images to process massive data with higher efficiency and resolution. We employed a GPU-assisted InSAR processing method to accelerate data processing. Statistically homogeneous pixel selection (SHPS) filtering was used to reduce noise and detect features in scenes with minimal image resolution loss. Compared to the commonly used InSAR processing software, the proposed method significantly improved the Sentinel-1 TOPS data processing efficiency. The feasibility of the method was investigated by mapping the surface deformation over the Yellow River Delta using SAR datasets acquired between January 2021 and February 2022. The findings indicate that several events of significant subsidence have occurred in the study area. Combined with the geological environment, underground brine and hydrocarbon extraction as well as sediment consolidation and compaction contribute to land subsidence in the Yellow River Delta.
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Shi, Ming Xing, Bi Yu Tang i Ao Peng. "A Cascade Tracking Loop for Weak GPS Signals". Applied Mechanics and Materials 719-720 (styczeń 2015): 1116–23. http://dx.doi.org/10.4028/www.scientific.net/amm.719-720.1116.
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It’s important to get accurate carrier phase and frequency information when using a standalone GPS receiver. In weak signal applications, to keep a stable tracking is hard to achieve because measuring error will be huge when the SNR is low. Different methods are used to improve the SNR before the detector in a tracking process, such as coherence integration. And this paper keeps eyes on a different viewpoint, on how to refine estimation results. A cascade structure is introduced for weak signal tracking. This structure is divided into two levels. In the first level, raw phase estimation and accurate frequency estimation is provided to achieve stable work in low CNR environment. In the second level, the raw phase estimation is refined to achieve accurate tracking requirement. This cascade structure can also work jointly with any other SNR-improving technology to get a better performance.
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Yao, Yan Xin, Yun Zhao i Jun Ye Zeng. "GPS Multipath Estimation with Improved SNR Adaptation Performance Utilizing Adaptive Filters". Advanced Materials Research 774-776 (wrzesień 2013): 1664–70. http://dx.doi.org/10.4028/www.scientific.net/amr.774-776.1664.
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Global positioning system multipath estimation is important for both high precision positioning and reflection applications. The paper aims at proposing a method for estimating multipath parameters including carrier phases with good SNR adaptation performance utilizing adaptive filters. The method takes the signal after demodulation and spectrum dispreading for the desired signal. It is found to have a desired signal with relatively higher SNR so that the filtering performance is relatively better than previously proposed method; whats more, the method could estimate multipath code delay preferable to carrier phase ambiguity problem. Simulations validate the method can estimate multipath profile including amplitudes, code delay and carrier phases of direct path and multipath signals with small errors of 2% correct amplitude, smaller than one sampling interval code delay and 0.01 cycles carrier phase at 11dB SNR. The multipath mitigation performance of the method is better than that of narrow correlator.
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Alwhibi, Mona S., Dina A. Soliman, Manal A. Awad, Asma B. Alangery, Horiah Al Dehaish i Yasmeen A. Alwasel. "Green synthesis of silver nanoparticles: Characterization and its potential biomedical applications". Green Processing and Synthesis 10, nr 1 (1.01.2021): 412–20. http://dx.doi.org/10.1515/gps-2021-0039.
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Abstract In recent times, research on the synthesis of noble metal nanoparticles (NPs) has developed rapidly and attracted considerable attention. The use of plant extracts is the preferred mode for the biological synthesis of NPs due to the presence of biologically active constituents. Aloe vera is a plant endowed with therapeutic benefits especially in skincare due to its unique curative properties. The present study focused on an environmental friendly and rapid method of phytosynthesis of silver nanoparticles (Ag-NPs) using A. vera gel extract as a reductant. The synthesized Ag-NPs were characterized by transmission electron microscopy (TEM), UV-Vis spectroscopy, Fourier transform infrared (FTIR), and dynamic light scattering (DLS). TEM micrographs showed spherical-shaped synthesized Ag-NPs with a diameter of 50–100 nm. The UV-Vis spectrum displayed a broad absorption peak of surface plasmon resonance (SPR) at 450 nm. The mean size and size distribution of the formed Ag-NPs were investigated using the DLS technique. Antibacterial studies revealed zones of inhibition by Ag-NPs of A. vera (9 and 7 mm) against Pseudomonas aeruginosa and Escherichia coli, respectively. Furthermore, the antifungal activity was screened, based on the diameter of the growth inhibition zone using the synthesized Ag-NPs for different fungal strains. Anticancer activity of the synthesized Ag-NPs against the mouse melanoma F10B16 cell line revealed 100% inhibition with Ag-NPs at a concentration of 100 µg mL−1. The phytosynthesized Ag-NPs demonstrated a marked antimicrobial activity and also exhibited a potent cytotoxic effect against mouse melanoma F10B16 cells. The key findings of this study indicate that synthesized Ag-NPs exhibit profound therapeutic activity and could be potentially ideal alternatives in medicinal applications.
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Mao, Wei-Lung, Chorng-Sii Hwang, Chung-Wen Hung i Jyh Sheen. "Narrowband Interference Cancellation using Set-membership Adaptive Predictor for GPS Receiver". International Journal of Applied Mathematics and Informatics 15 (16.11.2021): 59–64. http://dx.doi.org/10.46300/91014.2021.15.10.
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The global positioning system (GPS) provides accurate positioning and timing information that is useful in various civil and military applications. The adaptive filtering predictor for GPS jamming suppression applications is proposed. This research uses the gLab-G software to substitute for the hardware receiver to record the GPS signal waveform. The normalized least-mean-square (NLMS) and set-membership NLMS (SM-NLMS) filtering methods are employed for continuous wave interference suppression. Simulation results reveal that our proposed methods can provide the better performances when the interference-to-noise ratios (INR) are varied from 20 to 50 dB. The anti-jamming performances are evaluated via extensive simulation by computing mean squared prediction error (MSPE) and signal-to-noise ratio (SNR) improvements.
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Gao, Jay, i Yansui Liu. "Applications of remote sensing, GIS and GPS in glaciology: a review". Progress in Physical Geography: Earth and Environment 25, nr 4 (grudzień 2001): 520–40. http://dx.doi.org/10.1177/030913330102500404.
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Remote sensing has served as an efficient method of gathering data about glaciers since its emergence. The recent advent of Geographic Information Systems (GIS) and Global Positioning Systems (GPS) has created an effective means by which the acquired data are analysed for the effective monitoring and mapping of temporal dynamics of glaciers. A large number of researchers have taken advantage of remote sensing, GIS and GPS in their studies of glaciers. These applications are comprehensively reviewed in this paper. This review shows that glacial features identifiable from aerial photographs and satellite imagery include spatial extent, transient snowline, equilibrium line elevation, accumulation and ablation zones, and differentiation of ice/snow. Digital image processing (e.g., image enhancement, spectral ratioing and automatic classification) improves the ease and accuracy of mapping these parameters. The traditional visible light/infrared remote sensing of two-dimensional glacier distribution has been extended to three-dimensional volume estimation and dynamic monitoring using radar imagery and GPS. Longitudinal variations in glacial extent have been detected from multi-temporal images in GIS. However, the detected variations have neither been explored nor modelled from environmental and topographic variables. GPS has been utilized independent of remote sensing and GIS to determine glacier ice velocity and to obtain information about glacier surfaces. Therefore, the potential afforded by the integration of nonconventional remote sensing (e.g., SAR interferometry) with GIS and GPS still remains to be realized in glaciology. The emergence of new satellite images will make remote sensing of glaciology more predictive, more global and towards longer terms.
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Tan, Soon Heng Mavric, i Chai Kiat Yeo. "GPS Location Spoofing and FM Broadcast Intrusion Using Software-Defined Radio". International Journal of Interdisciplinary Telecommunications and Networking 12, nr 4 (październik 2020): 104–17. http://dx.doi.org/10.4018/ijitn.2020100108.
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This paper makes use of a simple and inexpensive software-defined radio (SDR) to demonstrate the potential threats posed to wireless communication. SDR is a radio communication system where components that are traditionally implemented in hardware are being replaced via software running on computing devices. The authors make use of a simple SDR to demonstrate how local disruption to wireless communication can be easily carried out. In particular, the authors show how FM radio broadcast can be hijacked and the spoofing of GPS location signals using a single SDR on a local basis as well as how Google Maps apps on an Android phone can be fooled by the spoofed GPS data. The authors also show how an ‘autonomous' car can be re-routed via emulation with a rigged up remote control toy car. The spoofing of GPS signals is a potential threat to all GPS-based applications, especially when powerful radios are used. The security threats on GPS-based navigation especially for drones and autonomous vehicles are real.
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Dong, Lei, Niangang Jiao, Tingtao Zhang, Fangjian Liu i Hongjian You. "GPU Accelerated Processing Method for Feature Point Extraction and Matching in Satellite SAR Images". Applied Sciences 14, nr 4 (14.02.2024): 1528. http://dx.doi.org/10.3390/app14041528.
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This paper addresses the challenge of extracting feature points and image matching in Synthetic Aperture Radar (SAR) satellite images, particularly focusing on large-scale embedding. The widely used Scale Invariant Transform (SIFT) algorithm, successful in computer vision and optical satellite image matching, faces challenges when applied to satellite SAR images due to the presence of speckle noise, leading to increased matching errors. The SAR–SIFT method is explored and analyzed in-depth, considering the unique characteristics of satellite SAR images. To enhance the efficiency of matching identical feature points in two satellite SAR images, the paper proposes a Graphics Processing Unit (GPU) mapping implementation based on the SAR–SIFT algorithm. The paper introduces a multi-GPU collaborative acceleration strategy for SAR image matching. This strategy addresses the challenge of matching feature points in the region and embedding multiple SAR images in large areas. The goal is to achieve efficient matching processing of multiple SAR images in extensive geographical regions. The proposed multi-GPU collaborative acceleration algorithm is validated through experiments involving feature point extraction and matching using 21 GF-3 SAR images. The results demonstrate the feasibility and efficiency of the algorithm in enhancing the processing speed of matching feature points in large-scale satellite SAR images. Overall, the paper contributes to the advancement of SAR image processing techniques, specifically in feature point extraction and matching in large-scale applications.
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Gaspar, João, Renato Ferreira, Pedro Sebastião i Nuno Souto. "Capture of UAVs Through GPS Spoofing Using Low-Cost SDR Platforms". Wireless Personal Communications 115, nr 4 (12.03.2020): 2729–54. http://dx.doi.org/10.1007/s11277-020-07211-7.
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Ferreira, Renato, João Gaspar, Pedro Sebastião i Nuno Souto. "Effective GPS Jamming Techniques for UAVs Using Low-Cost SDR Platforms". Wireless Personal Communications 115, nr 4 (6.03.2020): 2705–27. http://dx.doi.org/10.1007/s11277-020-07212-6.
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Nayak, B. Sathish, K. Krishna Naik, Odelu Ojjela i Surendra Pal. "GPS Receiver Simplification for Low cost Applications and Multipath Mitigation Analysis on SDR based Re configurable Software Receiver". Defence Science Journal 73, nr 06 (1.11.2023): 699–711. http://dx.doi.org/10.14429/dsj.73.19033.
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Many modern position-based applications rely heavily on the Global Navigation Satellite System (GNSS). Most applications require precise position data obtained through sophisticated hardware with a high computational capacity in the receiver. Some cost-effective applications may not require precise position data and require less complex signal processing. The use of efficient hardware and signal processing techniques to reduce the overall cost of a GNSS receiver is an active research topic. This paper considers Global Positioning System (GPS) constellation and proposes two factors to reduce the receiver complexity: sampling frequency and the number of tracking channels. A Keysight GNSS signal generator to record GPS signals, a Software Defined Radio board and a software-based GPS receiver are used in the experimentation. The sampling frequencies are 40, 20, 10 and 5 MHz considered, and tracking channels are reduced from 12 to 6 and then 4. The increase of error in the receiver position with 6 and 4 satellites is considerably small, but the number of tracking channels and signal processing requirements are reduced considerably. The GPS signals are affected by many errors; one of the significant sources of error is multipath propagation. Three distinct GPS multipath scenarios are generated for four satellite signal combinations with the GNSS simulator for the receiver performance analysis. Three multipath mitigation techniques, namely Early Minus Late (EML), Narrow correlator (NC) and strobe correlator (SC) methods, are considered because of their simple structure and fewer signal processing requirements. The error reductions of three multipath scenarios are compared, and the SC method performs better in all three multipath scenarios.
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Zimmermann, Florian, Berit Schmitz, Lasse Klingbeil i Heiner Kuhlmann. "GPS Multipath Analysis Using Fresnel Zones". Sensors 19, nr 1 (21.12.2018): 25. http://dx.doi.org/10.3390/s19010025.
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GNSS (Global Navigation Satellite Systems) multipath has been subject to scientific research for decades and although numerous methods and techniques have already been developed to mitigate this effect, it is still one of the accuracy-limiting factors in many GNSS applications. Since multipath is highly dependent on the individual antenna environment, there is still a need for new methods and further investigations to increase the understanding of this systematic effect. In this paper, the concept of Fresnel zones is applied to two different aspects of multipath. First, Fresnel zones are determined for the line-of-sight transmission between satellite and receiver. By comparing the boundary of the Fresnel zones to an obstruction adaptive elevation mask, potentially diffracted signals can be identified and excluded from the position estimation process. Both the percentage of epochs with fixed ambiguities and the positioning accuracy can be increased by the proposed method. Second, Fresnel zones are used to analyze the multipath induced by a horizontal and spatially-limited reflector. The comparison of simulated and real signal-to-noise (SNR) observations reveals a relationship between the percentage of the overlap of the Fresnel zone and reflector and the occurrence of multipath. It is found that an overlap of 50% is sufficient to induce multipath effects. This is of special interest, since this does not confirm theoretical assumptions of the multipath theory.
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Bruhn, Fredrik C., Nandinbaatar Tsog, Fabian Kunkel, Oskar Flordal i Ian Troxel. "Enabling radiation tolerant heterogeneous GPU-based onboard data processing in space". CEAS Space Journal 12, nr 4 (15.06.2020): 551–64. http://dx.doi.org/10.1007/s12567-020-00321-9.
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Abstract The last decade has seen a dramatic increase in small satellite missions for commercial, public, and government intelligence applications. Given the rapid commercialization of constellation-driven services in Earth Observation, situational domain awareness, communications including machine-to-machine interface, exploration etc., small satellites represent an enabling technology for a large growth market generating truly Big Data. Examples of modern sensors that can generate very large amounts of data are optical sensing, hyperspectral, Synthetic Aperture Radar (SAR), and Infrared imaging. Traditional handling and downloading of Big Data from space requires a large onboard mass storage and high bandwidth downlink with a trend towards optical links. Many missions and applications can benefit significantly from onboard cloud computing similarly to Earth-based cloud services. Hence, enabling space systems to provide near real-time data and enable low latency distribution of critical and time sensitive information to users. In addition, the downlink capability can be more effectively utilized by applying more onboard processing to reduce the data and create high value information products. This paper discusses current implementations and roadmap for leveraging high performance computing tools and methods on small satellites with radiation tolerant hardware. This includes runtime analysis with benchmarks of convolutional neural networks and matrix multiplications using industry standard tools (e.g., TensorFlow and PlaidML). In addition, a ½ CubeSat volume unit (0.5U) (10 × 10 × 5 cm3) cloud computing solution, called SpaceCloud™ iX5100 based on AMD 28 nm APU technology is presented as an example of heterogeneous computer solution. An evaluation of the AMD 14 nm Ryzen APU is presented as a candidate for future advanced onboard processing for space vehicles.
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Peng, Hailong, Chongchong Zhou, Shiming Zhong, Bibo Peng, Xuhua Zhou, Haoming Yan, Jie Zhang, Jinyang Han, Fengcheng Guo i Runjing Chen. "Analysis of Precise Orbit Determination for the HY2D Satellite Using Onboard GPS/BDS Observations". Remote Sensing 14, nr 6 (13.03.2022): 1390. http://dx.doi.org/10.3390/rs14061390.
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High-precision orbits of Low Earth Orbit (LEO) satellites are essential for many scientific applications, such as assessing the change in current global mean sea level, estimating the coefficients of gravity field, and so on. How to determinate the high-precision orbits for LEO satellites has gradually become an important research focus. HY2D is a new altimetry satellite of China, which is equipped with a Global Positioning System (GPS) and the third generations of the BeiDou Global Navigation Satellite System (BDS-3) in order to guarantee the reliability of orbital precision in radar altimetry mission. Therefore, this study adopts one month of spaceborne data to conduct the research of precise orbit determination (POD) for the HY2D satellite. Our analysis results are: (1) The standard deviation of residuals for the HY2D satellite based on spaceborne BDS and GPS data are 9.12 mm and 8.53 mm, respectively, and there are no significant systematic errors in these residuals. (2) The comparison results with Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS)-derived orbits indicate that the HY2D satellite, using spaceborne BDS and GPS data, can achieve the radial accuracy of 1.4~1.5 cm, and the mean three-dimensional (3D) accuracy are 5.3 cm and 4.3 cm, respectively, which can satisfy high-precision altimetry applications. (3) By means of satellite laser ranging (SLR), the accuracy of Global Navigation Satellite System (GNSS)-derived orbits of HY2D is approximately 3.3 cm, which reflects that the model strategies are reliable.
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Tamazin, Mohamed, Michael J. Korenberg, Haidy Elghamrawy i Aboelmagd Noureldin. "GPS Swept Anti-Jamming Technique Based on Fast Orthogonal Search (FOS)". Sensors 21, nr 11 (26.05.2021): 3706. http://dx.doi.org/10.3390/s21113706.
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Recently, there has been growing demand for GPS-based reliable positioning, with the broadening of a range of new applications that mainly rely on GPS. GPS receivers have, recently, been attractive targets for jamming. GPS signals are received below the noise floor. Thus, they are vulnerable to interference and jamming. A jamming signal can potentially decrease the SNR, which results in disruption of GPS-based services. This paper aims to propose a reliable and accurate, swept anti-jamming technique based on high-resolution spectral analysis, utilizing the FOS method to provide an accurate spectral estimation of the GPS swept jamming signal. resulting in suppressing the jamming signal efficiently at the signal processing stages in the GPS receiver. Experiments in this research are conducted using the SpirentTM GSS6700 simulation system to create a fully controlled environment to test and validate the developed method’s performance. The results demonstrated the proposed method’s capabilities to detect, estimate, and adequately suppress the GPS swept jamming signals. After the proposed anti-jamming module was employed, the software receiver was able to provide a continuous positioning solution during the presence of jamming within a 10 m positioning accuracy.
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Sana, Sahr, Kamelia Boodhoo i Vladimir Zivkovic. "Production of starch nanoparticles through solvent-antisolvent precipitation in a spinning disc reactor". Green Processing and Synthesis 8, nr 1 (28.01.2019): 507–15. http://dx.doi.org/10.1515/gps-2019-0019.
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Abstract The spinning disc reactor (SDR) uses surface rotation to produce thin film flow with improved mixing and reduced residence times in chemical processing applications. Solvent-antisolvent precipitation is one such process that can benefit from these properties. This study investigates the film hydrodynamics and precipitation of starch nanoparticles by contacting starch dissolved in sodium hydroxide with ethanol as the antisolvent. One objective of this study is to understand how interactions of the disc surface topography (grooved and smooth) with other parameters such as liquid flowrate, antisolvent to solvent flow ratio and disc speed impact the mixing and precipitation processes. Results indicate that an increase in flow rate and rotational speed leads to smaller nano-particles and narrower size distributions, which is attributed to increased shear and instabilities within the liquid film. It was also observed that an increased antisolvent to solvent ratio caused a reduction in particle size, as increased antisolvent generated higher supersaturation. Results showed that although particle size was not significantly influenced by the disc texture, the size distribution was narrower and higher yields were obtained with the grooved disc surface. The grooved disc therefore offers the opportunity for higher throughput in the solvent-antisolvent precipitation of starch particles with better product quality.
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Yin, Qiang, You Wu, Fan Zhang i Yongsheng Zhou. "GPU-Based Soil Parameter Parallel Inversion for PolSAR Data". Remote Sensing 12, nr 3 (28.01.2020): 415. http://dx.doi.org/10.3390/rs12030415.
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With the development of polarimetric synthetic aperture radar (PolSAR), quantitative parameter inversion has been seen great progress, especially in the field of soil parameter inversion, which has achieved good results for applications. However, PolSAR data is also often many terabytes large. This huge amount of data also directly affects the efficiency of the inversion. Therefore, the efficiency of soil moisture and roughness inversion has become a problem in the application of this PolSAR technique. A parallel realization based on a graphics processing unit (GPU) for multiple inversion models of PolSAR data is proposed in this paper. This method utilizes the high-performance parallel computing capability of a GPU to optimize the realization of the surface inversion models for polarimetric SAR data. Three classical forward scattering models and their corresponding inversion algorithms are analyzed. They are different in terms of polarimetric data requirements, application situation, as well as inversion performance. Specifically, the inversion process of PolSAR data is mainly improved by the use of the high concurrent threads of GPU. According to the inversion process, various optimization strategies are applied, such as the parallel task allocation, and optimizations of instruction level, data storage, data transmission between CPU and GPU. The advantages of a GPU in processing computationally-intensive data are shown in the data experiments, where the efficiency of soil roughness and moisture inversion is increased by one or two orders of magnitude.
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Xu, Jia, Luo i Hsu. "Intelligent GPS L1 LOS/Multipath/NLOS Classifiers Based on Correlator-, RINEX- and NMEA-Level Measurements". Remote Sensing 11, nr 16 (8.08.2019): 1851. http://dx.doi.org/10.3390/rs11161851.
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This paper proposes to use a correlator-level global positioning system (GPS) line-of-sight/multipath/non-line-of-sight (LOS/MP/NLOS) signal reception classifier to improve positioning performance in an urban environment. Conventional LOS/MP/NLOS classifiers, referred to as national marine electronics association (NMEA)-level and receiver independent exchange format (RINEX)-level classifiers, are usually performed using attributes extracted from basic observables or measurements such as received signal strength, satellite elevation angle, code pseudorange, etc. The NMEA/RINEX-level classification rate is limited because the complex signal propagation in urban environment is not fully manifested in these end attributes. In this paper, LOS/MP/NLOS features were extracted at the baseband signal processing stage. Multicorrelator is implemented in a GPS software-defined receiver (SDR) and exploited to generate features from the autocorrelation function (ACF). A robust LOS/MP/NLOS classifier using a supervised machine learning algorithm, support vector machine (SVM), is then trained. It is also proposed that the Skymask and code pseudorange double difference observable are used to label the real signal type. Raw GPS intermediate frequency data were collected in urban areas in Hong Kong and were postprocessed using a self-developed SDR, which can easily output correlator-level LOS/MP/NLOS features. The SDR measurements were saved in the file with the format of NMEA and RINEX. A fair comparison among NMEA-, RINEX-, and correlator-level classifiers was then carried out on a common ground. Results show that the correlator-level classifier improves the metric of F1 score by about 25% over the conventional NMEA- and RINEX-level classifiers for testing data collected at different places to that of training data. In addition to this finding, correlator-level classifier is found to be more feasible in practical applications due to its less dependency on surrounding scenarios compared with the NMEA/RINEX-level classifiers.
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Stiros, Stathis C., F. Moschas i P. Triantafyllidis. "Modal frequencies of bridges from GNSS (GPS) monitoring data: Experimental, statistical evidence". Bridge Structures 17, nr 1-2 (11.06.2021): 3–14. http://dx.doi.org/10.3233/brs-210184.
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GNSS technology (known especially for GPS satellites) for measurement of deflections has proved very efficient and useful in bridge structural monitoring, even for short stiff bridges, especially after the advent of 100 Hz GNSS sensors. Mode computation from dynamic deflections has been proposed as one of the applications of this technology. Apart from formal modal analyses with GNSS input, and from spectral analysis of controlled free attenuating oscillations, it has been argued that simple spectra of deflections can define more than one modal frequencies. To test this scenario, we analyzed 21 controlled excitation events from a certain bridge monitoring survey, focusing on lateral and vertical deflections, recorded both by GNSS and an accelerometer. These events contain a transient and a following oscillation, and they are preceded and followed by intervals of quiescence and ambient vibrations. Spectra for each event, for the lateral and the vertical axis of the bridge, and for and each instrument (GNSS, accelerometer) were computed, normalized to their maximum value, and printed one over the other, in order to produce a single composite spectrum for each of the four sets. In these four sets, there was also marked the true value of modal frequency, derived from free attenuating oscillations. It was found that for high SNR (signal-to-noise ratio) deflections, spectral peaks in both acceleration and displacement spectra differ by up to 0.3 Hz from the true value. For low SNR, defections spectra do not match the true frequency, but acceleration spectra provide a low-precision estimate of the true frequency. This is because various excitation effects (traffic, wind etc.) contribute with numerous peaks in a wide range of frequencies. Reliable estimates of modal frequencies can hence be derived from deflections spectra only if excitation frequencies (mostly traffic and wind) can be filtered along with most measurement noise, on the basis of additional data.
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Mikhailov, V. O., E. A. Kiseleva, E. P. Timoshkina, V. B. Smirnov, A. V. Ponomarev, P. N. Dmitriev, I. M. Kartashov i in. "Joint inversion of the GPS and SAR data for the Gorkha, Nepal earthquake of 25.04.2015". Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa 15, nr 4 (2018): 119–27. http://dx.doi.org/10.21046/2070-7401-2018-15-4-119-127.
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Basit, Abdul, Amil Daraz, Muhammad Irshad Khan, Farid Zubir, Salman A. AlQahtan i Guoqiang Zhang. "Design and Modelling of a Compact Triband Passband Filter for GPS, WiMAX, and Satellite Applications with Multiple Transmission Zero’s". Fractal and Fractional 7, nr 7 (28.06.2023): 511. http://dx.doi.org/10.3390/fractalfract7070511.
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Designing microwave filters with high selectivity and sharp roll-off between the stop and pass bands can be challenging due to the complex nature of the R.F. signals and the requirements for achieving high performance in a limited physical space. To achieve a high selectivity and sharp roll-off rate, this paper presents a compact filter with a triple passband response. The two different passbands at 1.57 GHz and 3.5 GHz are achieved using a step impedance resonator (SIR) with metallic slots perturbation added to the lower corner of the high impedance section of the SIRs, which helps to enhance the filter’s selectivity and size reduction greatly. The embedded L-shaped structure originates a third passband at 4.23 GHz, resulting in a triband response with eight transmission zeros below and above the passbands at 1.22/1.42/1.98/3.18/3.82/3.98/4.38/4.53 GHz, respectively. The prototype has low signal attenuation of <1.2 dB and high signal reflection of >25 dB for the three passbands. The fractional bandwidths achieved are 2.54%, 4.2%, and 1.65% at 1.57/3.57/4.23 GHz, respectively, with rejection levels in the stopband greater than 15 dB. Lastly, the structure is fabricated on RO-4350B PCB and observed good matching between experimental and measured results. This demonstrates that the prototype can be successfully implemented in real-world applications such as GPS, WiMAX, and Satellite systems. The area occupied by the filter on a substrate or in a circuit is 0.31 λg × 0.24 λg, where λg is the guided wavelength of the material calculated at the lowest frequency.
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Liu, Mingqian, Zhiyang Gao, Yunfei Chen, Hao Song, Yuting Li i Fengkui Gong. "Passive Detection of Moving Aerial Target Based on Multiple Collaborative GPS Satellites". Remote Sensing 12, nr 2 (12.01.2020): 263. http://dx.doi.org/10.3390/rs12020263.
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Passive localization is an important part of intelligent surveillance in security and emergency applications. Nowadays, Global Navigation Satellite Systems (GNSSs) have been widely deployed. As a result, the satellite signal receiver may receive multiple GPS signals simultaneously, incurring echo signal detection failure. Therefore, in this paper, a passive method leveraging signals from multiple GPS satellites is proposed for moving aerial target detection. In passive detection, the first challenge is the interference caused by multiple GPS signals transmitted upon the same spectrum resources. To address this issue, successive interference cancellation (SIC) is utilized to separate and reconstruct multiple GPS signals on the reference channel. Moreover, on the monitoring channel, direct wave and multi-path interference are eliminated by extensive cancellation algorithm (ECA). After interference from multiple GPS signals is suppressed, the cycle cross ambiguity function (CCAF) of the signal on the monitoring channel is calculated and coordinate transformation method is adopted to map multiple groups of different time delay-Doppler spectrum into the distance–velocity spectrum. The detection statistics are calculated by the superposition of multiple groups of distance-velocity spectrum. Finally, the echo signal is detected based on a properly defined adaptive detection threshold. Simulation results demonstrate the effectiveness of our proposed method. They show that the detection probability of our proposed method can reach 99%, when the echo signal signal-to-noise ratio (SNR) is only −64 dB. Moreover, our proposed method can achieve 5 dB improvement over the detection method using a single GPS satellite.
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Chen, Jiongming, Pengju Yang, Rong Zhang i Rui Wu. "A Fast Inverse Synthetic Aperture Radar Imaging Scheme Combining GPU-Accelerated Shooting and Bouncing Ray and Back Projection Algorithm under Wide Bandwidths and Angles". Electronics 13, nr 15 (2.08.2024): 3062. http://dx.doi.org/10.3390/electronics13153062.
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Inverse synthetic aperture radar (ISAR) imaging techniques are frequently used in target classification and recognition applications, due to its capability to produce high-resolution images for moving targets. In order to meet the demand of ISAR imaging for electromagnetic calculation with high efficiency and accuracy, a novel accelerated shooting and bouncing ray (SBR) method is presented by combining a Graphics Processing Unit (GPU) and Bounding Volume Hierarchies (BVH) tree structure. To overcome the problem of unfocused images by a Fourier-based ISAR procedure under wide-angle and wide-bandwidth conditions, an efficient parallel back projection (BP) imaging algorithm is developed by utilizing the GPU acceleration technique. The presented GPU-accelerated SBR is validated by comparison with the RL-GO method in commercial software FEKO v2020. For ISAR images, it is clearly indicated that strong scattering centers as well as target profiles can be observed under large observation azimuth angles, Δφ=90°, and wide bandwidths, 3 GHz. It is also indicated that ISAR imaging is heavily sensitive to observation angles. In addition, obvious sidelobes can be observed, due to the phase history of the electromagnetic wave being distorted resulting from multipole scattering. Simulation results confirm the feasibility and efficiency of our scheme by combining GPU-accelerated SBR with the BP algorithm for fast ISAR imaging simulation under wide-angle and wide-bandwidth conditions.
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Paun, Mirel. "Through-Wall Imaging Using Low-Cost Frequency-Modulated Continuous Wave Radar Sensors". Remote Sensing 16, nr 8 (17.04.2024): 1426. http://dx.doi.org/10.3390/rs16081426.
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Many fields of human activity benefit from the ability to create images of obscured objects placed behind walls and to map their displacement in a noninvasive way. Usually, imaging devices like Synthetic Aperture Radars (SARs) and Ground-Penetrating Radars (GPRs) use expensive dedicated electronics which results in prohibitive prices. This paper presents the experimental implementation and the results obtained from an imaging system capable of performing SAR imaging and interferometric displacement mapping of targets located behind walls, as well as 3D GPR imaging using a low-cost general-purpose radar sensor. The proposed solution uses for the RF section of the system a K-band microwave radar sensor module implementing Frequency-Modulated Continuous Wave (FMCW) operation. The low-cost sensor was originally intended for simple presence detection and ranging for domestic applications. The proposed system was tested in several scenarios and proved to operate as intended for a fraction of the cost of a commercial imaging device. In one scenario, it was able to detect and locate a 15 cm-diameter fire-extinguisher located at a distance of 3.5 m from the scanning system and 1.6 m behind a 3 cm-thick MDF (medium-density fiberboard) wall with cm-level accuracy. In a second test, the proposed system was used to perform interferometric displacement measurements, and it was capable of determining the displacement of a metal case with sub-millimeter accuracy. In a third experiment, the system was used to construct a 3D image of the inside of a wood table with cm-level resolution.
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Tabata, Kenichi, Madoka Nakajima i Naohiko Kohtake. "Design of Entry Detection Method for Top-Bounded Spaces Using GPS SNR and Spatial Characteristics for Seamless Positioning in Logistics Facilities". Sensors 20, nr 23 (30.11.2020): 6864. http://dx.doi.org/10.3390/s20236864.
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With the widespread use of indoor positioning technology, various services based on this technology are beginning to be offered to consumers and industrial applications. In the case of logistics facilities, in addition to indoor and outdoor spaces, there are top-bounded spaces (TBSs): elongated areas that are covered with roofs or eaves on the upper parts of buildings. The sides of such spaces are open, and workers and forklifts work in these areas. Only a few studies have been conducted on positioning methods for this unusual environment, and the way by which Signal-to-Noise Ratio (SNR) of Global Positioning System (GPS) changes with the stay in TBSs is unclear. Therefore, we conducted preliminary experiments and confirmed that TBS dwellings are difficult to stably detect with existing methods due to the combination of satellites with variable and unchanged SNRs. In this study, we designed a simple processing flow for selecting satellites with high probabilities of changing SNRs by using the spatial characteristics of TBSs as parameters (height, depth, and side opening orientation). We propose a method to detect the stay in TBSs using the SNR change rates of the selected satellites. As a result of evaluation experiments with three TBSs, we successfully detected the stay in TBSs with about 30% higher probability than those of an existing method.
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Stiros, Stathis C. "GNSS (GPS) Monitoring of Dynamic Deflections of Bridges: Structural Constraints and Metrological Limitations". Infrastructures 6, nr 2 (3.02.2021): 23. http://dx.doi.org/10.3390/infrastructures6020023.
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The advent of modern geodetic satellite techniques (GNSS, including GPS) permitted to observe dynamic deflections of bridges, initially of long flexible ones, and more recently of short, essentially stiff bridges with modal frequencies > 1 Hz, and with small SNR (signal-to-noise ratio), even SNR < 1. This was an enormous progress, but not without problems. Apart from monitoring results consistent with structural models, experimental data and serviceability criteria, there exist some apparently unexplained cases of stiff bridges for which there have been claimed apparent dynamic deflections too large for common healthy structures. Summarizing previous experience, this article: (i) discusses structural constraints, experimental evidence, and serviceability limits of bridges as constraints to GNSS monitoring; (ii) examines a representative case of careful monitoring of a reinforced concrete road bridge with reported excessive dynamic deflections; and (iii) explains such deflections as a result of a double process generated by large reflective surfaces of passing vehicles near the antenna; first corruption/distortion of the satellite signal because of high-frequency dynamic multipath, and second, shadowing of some satellites; this last effect leads to a modified observations system and to instantaneously changed coordinates and deflections. In order to recognize and avoid such bias in GNSS monitoring, a strategy based on practical rules and structural constraints is presented.
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Nayak, B. Sathish, Sidharth Bhonge, K. Krishna Naik, Odelu Ojjela i Surendra Pal. "Multi GNSS IRNSS L5 IRNSS S1 and GPS L1 Hybrid Simulator A Reconfigurable Low cost Solution for Research and Defence Applications". Defence Science Journal 72, nr 4 (26.08.2022): 581–91. http://dx.doi.org/10.14429/dsj.72.17873.
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Satellite-based positioning field of research is growing rapidly as there is an increase in demand for precise position requirements in various civil and commercial applications. There are many errors that affect the GNSS signals while propagation from satellite to receiver, which eventually induces errors in pseudo-range measurements. In order to assess the receiver characteristics for a specific error condition, the real-time signals may not be appropriate, and it is challenging to perform repeated experiments with the same error condition. The advantage of the GNSS simulator is that users can model the different scenarios for any given location on the globe, which are repeatable at any point of time. The conventional hardware simulators are expensive and have few limitations. In this paper, a reconfigurable hybrid simulator is proposed with some advantages over traditional hardware simulators, such as low cost, reconfigurability, and controllability over fundamental parameters. It can be able to record intermediate stage data, which makes it more suitable for the GNSS research field. The proposed multi-GNSS simulator considered implementing IRNSS-L5, IRNSS-S1, and GPS-L1 band signals. A general-purpose computer can perform the necessary calculations for signal generation. The hybrid simulator can be able to generate the digital I/Q data, which can be stored as I/Q data or can be connected to a general-purpose SDR (Software Defined Radio) for RF signal generation (bladeRF in this case). The I/Q data can be used with the software receiver to analyse the receiver performance concerning the specific error. The generated GNSS signals are validated with software and hardware receivers, and the obtained position is observed as expected.
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Gong, Xiaolin, i Tingting Qin. "Airborne Earth Observation Positioning and Orientation by SINS/GPS Integration Using CD R-T-S Smoothing". Journal of Navigation 67, nr 2 (20.09.2013): 211–25. http://dx.doi.org/10.1017/s0373463313000623.
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This paper addresses the issue of state estimation in the integration of a Strapdown Inertial Navigation System (SINS) and Global Positioning System (GPS), which is used for airborne earth observation positioning and orientation. For a nonlinear system, especially with large initial attitude errors, the performance of linear estimation approaches will degrade. In this paper a nonlinear error model based on angle errors is built, and a nonlinear estimation algorithm called the Central Difference Rauch-Tung-Striebel (R-T-S) Smoother (CDRTSS) is utilized in SINS/GPS integration post-processing. In this algorithm, the measurements are first processed by the forward Central Difference Kalman filter (CDKF) and then a separate backward smoothing pass is used to obtain the improved solution. The performance of this algorithm is compared with a similar smoother based on an extended Kalman filter known as ERTSS through Monte Carlo simulations and flight tests with a loaded SINS/GPS integrated system. Furthermore, a digital camera was used to verify the precision of practical applications in a check field with numerous reference points. All these validity checks demonstrate that CDRTSS is a better method and the work of this paper will offer a new approach for SINS/GPS integration for Synthetic Aperture Radar (SAR) and other airborne earth observation tasks.
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Williams, Simon D. P., Paul S. Bell, David L. McCann, Richard Cooke i Christine Sams. "Demonstrating the Potential of Low-Cost GPS Units for the Remote Measurement of Tides and Water Levels Using Interferometric Reflectometry". Journal of Atmospheric and Oceanic Technology 37, nr 10 (1.10.2020): 1925–35. http://dx.doi.org/10.1175/jtech-d-20-0063.1.
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AbstractA low-cost [$30 (U.S. dollars)] consumer grade GPS receiver with a sideways-mounted antenna has been applied to measure tidal water levels at a mesotidal coastal site using an interferometric reflectometry approach. The proof-of-concept system was installed approximately 16 m above mean sea level in close proximity to a conventional bubbler tide gauge that provided validation data. The received signal-to-noise ratios (SNR) for the satellites in view were recorded for several months during two successive years and the observed frequencies of the interferometric oscillations used to calculate the difference in elevation between the receiver and the water surface. Comparisons with concurrent and historic in situ tide gauge data at the site initially helped to identify a calibration issue with the in situ gauge. The GPS-based measurements were shown to be in excellent agreement with the corrected in situ gauge, exhibiting a root-mean-square difference of 5.7 cm over a tidal range exceeding 3 m at spring tides and a daily averaged RMS of 1.7 cm. The SNR data from the low-cost GPS receivers are shown to provide significantly higher-quality data for this purpose compared with high-end geodetic grade receivers at similar sites. This low-cost, widely available technology has the potential to be applied globally for monitoring water levels in a wide variety of circumstances and applications that would otherwise be cost or situation prohibitive. It could also be applied as an independent cross check and quality control measure for conventional water-level gauges.
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Wang, Mengyuan, Yuye Ling, Zhenxing Dong, Xinwen Yao, Yu Gan, Chuanqing Zhou i Yikai Su. "GPU-accelerated iterative method for FD-OCT image reconstruction with an image-level cross-domain regularizer". Optics Express 31, nr 2 (5.01.2023): 1813. http://dx.doi.org/10.1364/oe.478970.
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The image reconstruction for Fourier-domain optical coherence tomography (FD-OCT) could be achieved by iterative methods, which offer a more accurate estimation than the traditional inverse discrete Fourier transform (IDFT) reconstruction. However, the existing iterative methods are mostly A-line-based and are developed on CPU, which causes slow reconstruction. Besides, A-line-based reconstruction makes the iterative methods incompatible with most existing image-level image processing techniques. In this paper, we proposed an iterative method that enables B-scan-based OCT image reconstruction, which has three major advantages: (1) Large-scale parallelism of the OCT dataset is achieved by using GPU acceleration. (2) A novel image-level cross-domain regularizer was developed, such that the image processing could be performed simultaneously during the image reconstruction; an enhanced image could be directly generated from the OCT interferogram. (3) The scalability of the proposed method was demonstrated for 3D OCT image reconstruction. Compared with the state-of-the-art (SOTA) iterative approaches, the proposed method achieves higher image quality with reduced computational time by orders of magnitude. To further show the image enhancement ability, a comparison was conducted between the proposed method and the conventional workflow, in which an IDFT reconstructed OCT image is later processed by a total variation-regularized denoising algorithm. The proposed method can achieve a better performance evaluated by metrics such as signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), while the speed is improved by more than 30 times. Real-time image reconstruction at more than 20 B-scans per second was realized with a frame size of 4096 (axial) × 1000 (lateral), which showcases the great potential of the proposed method in real-world applications.
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Yang, Yinghui, Qiang Chen, Qian Xu, Yijun Zhang, Qi Yong i Guoxiang Liu. "Coseismic surface deformation of the 2014 Napa earthquake mapped by Sentinel-1A SAR and accuracy assessment with COSMO-SkyMed and GPS data as cross validation". International Journal of Digital Earth 10, nr 12 (8.03.2017): 1197–213. http://dx.doi.org/10.1080/17538947.2017.1299806.
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Guo, Hengyang, Jinyun Guo, Zhouming Yang, Guangzhe Wang, Linhu Qi, Mingsen Lin, Hailong Peng i Bing Ji. "On Satellite-Borne GPS Data Quality and Reduced-Dynamic Precise Orbit Determination of HY-2C: A Case of Orbit Validation with Onboard DORIS Data". Remote Sensing 13, nr 21 (28.10.2021): 4329. http://dx.doi.org/10.3390/rs13214329.
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Haiyang-2C (HY-2C) is a dynamic, marine-monitoring satellite that was launched by China and is equipped with an onboard dual-frequency GPS receiver named HY2_Receiver, which was independently developed in China. HY-2C was successfully launched on 21 September 2020. Its precise orbit is an important factor for scientific research applications, especially for marine altimetry missions. The performance of the HY2_Receiver is assessed based on indicators such as the multipath effect, ionospheric delay, cycle slip and data utilization, and assessments have suggested that the receiver can be used in precise orbit determination (POD) missions involving low-Earth-orbit (LEO) satellites. In this study, satellite-borne GPS data are used for POD with a reduced-dynamic (RD) method. Phase centre offset (PCO) and phase centre variation (PCV) models of the GPS antenna are established during POD, and their influence on the accuracy of orbit determination is analysed. After using the PCO and PCV models in POD, the root mean square (RMS) of the carrier-phase residuals is around 0.008 m and the orbit overlap validation accuracy in each direction reaches approximately 0.01 m. Compared with the precise science orbit (PSO) provided by the Centre National d’Etudes Spatiales (CNES), the RD orbit accuracy of HY-2C in the radial (R) direction reaches 0.01 m. The accuracy of satellite laser ranging (SLR) range validation is better than 0.03 m. Additionally, a new method is proposed to verify the accuracy of the RD orbit of HY-2C by using space-borne Doppler orbitography and radiopositioning integrated by satellite (DORIS) data directly. DORIS data are directly compared to the result calculated using the accurate coordinates of beacons and the RD orbit, and the results indicate that the external validation of HY-2C RD orbit has a range rate accuracy of within 0.0063 m/s.
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Massimo Aranzulla i Giuseppe Puglisi. "GPS tomography tests for DInSAR applications on Mt. Etna". Annals of Geophysics 58, nr 3 (27.07.2015). http://dx.doi.org/10.4401/ag-6750.
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<p>Tropospheric artifacts of SAR images in a volcanic area like Mt. Etna cause ambiguity in the interpretation of deformations with such technique. It would be useful to measure the delay caused by tropospheric anomalies in synthetic aperture radar (SAR) satellite signals (phase of the back-scattered radar wave) that could be interpreted as deformation. From the delay estimated through the GPS data processing, the tropospheric tomography of electromagnetic waves refractivity, has been performed using the SIMULps12 software. The aim of this study was to perform software synthetic tests by using SIMULps12 applied to atmospheric tomography and to verify the influence of the different GPS geodetic network configurations on obtaining a reliable tomography. Three different anomalies of increasing complexity have been investigated in order to understand the representative parameters of a correct tomography, the best spatial resolution and the portions of space in which the tomography is reliable. The tests also focused on fixing/establishing the a-priori atmospheric model and the critical values of the main parameters involved in the tomographic inversion. To this end, we made a random choice of two days, necessary to define the tomographic problem. Three different network configurations with 15, 30 and 90 GPS receivers were studied. The results indicate that the well-resolved area of tomographic images increases with the number of GPS receivers not linearly, and that the actual GPS network of 42 receivers is capable of revealing/detecting the atmospheric anomalies.</p>
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Martín, Angel, Ana Belén Anquela, Sara Ibáñez, Carlos Baixauli i Sara Blanc. "Python software to transform GPS SNR wave phases to volumetric water content". GPS Solutions 26, nr 1 (27.10.2021). http://dx.doi.org/10.1007/s10291-021-01190-3.
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AbstractThe global navigation satellite system interferometric reflectometry is often used to extract information about the environment surrounding the antenna. One of the most important applications is soil moisture monitoring. This manuscript presents the main ideas and implementation decisions needed to write the Python code to transform the derived phase of the interferometric GPS waves, obtained from signal-to-noise ratio data continuously observed during a period of several weeks (or months), to volumetric water content. The main goal of the manuscript is to share the software with the scientific community to help users in the GPS-IR computation.
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Alser, Mohammed, Taha Shahroodi, Juan Gómez-Luna, Can Alkan i Onur Mutlu. "SneakySnake: a fast and accurate universal genome pre-alignment filter for CPUs, GPUs and FPGAs". Bioinformatics, 26.12.2020. http://dx.doi.org/10.1093/bioinformatics/btaa1015.
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Abstract Motivation We introduce SneakySnake, a highly parallel and highly accurate pre-alignment filter that remarkably reduces the need for computationally costly sequence alignment. The key idea of SneakySnake is to reduce the approximate string matching (ASM) problem to the single net routing (SNR) problem in VLSI chip layout. In the SNR problem, we are interested in finding the optimal path that connects two terminals with the least routing cost on a special grid layout that contains obstacles. The SneakySnake algorithm quickly solves the SNR problem and uses the found optimal path to decide whether or not performing sequence alignment is necessary. Reducing the ASM problem into SNR also makes SneakySnake efficient to implement on CPUs, GPUs and FPGAs. Results SneakySnake significantly improves the accuracy of pre-alignment filtering by up to four orders of magnitude compared to the state-of-the-art pre-alignment filters, Shouji, GateKeeper and SHD. For short sequences, SneakySnake accelerates Edlib (state-of-the-art implementation of Myers’s bit-vector algorithm) and Parasail (state-of-the-art sequence aligner with a configurable scoring function), by up to 37.7× and 43.9× (>12× on average), respectively, with its CPU implementation, and by up to 413× and 689× (>400× on average), respectively, with FPGA and GPU acceleration. For long sequences, the CPU implementation of SneakySnake accelerates Parasail and KSW2 (sequence aligner of minimap2) by up to 979× (276.9× on average) and 91.7× (31.7× on average), respectively. As SneakySnake does not replace sequence alignment, users can still obtain all capabilities (e.g. configurable scoring functions) of the aligner of their choice, unlike existing acceleration efforts that sacrifice some aligner capabilities. Availabilityand implementation https://github.com/CMU-SAFARI/SneakySnake. Supplementary information Supplementary data are available at Bioinformatics online.
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Pal, Arghyadeep, Dilshad Ahmad, Srikanta Pal i Abu Nasar Ghazali. "Efficient and low SAR dual functional wearable antenna in RFID ISM and GPS L1 bands for positioning applications". Wireless Networks, 4.02.2023. http://dx.doi.org/10.1007/s11276-023-03238-3.
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Tseng, Tzu-Pang, Wen-Hao Yeh, Yung-Fu Tsai, Tung-Yuan Hsiao, Yi-Hsuan Tsai, Pei-Jung Kuo, Kun-Lin Chen i Yu-Shen Hsiao. "Satellite orbit determination and time synchronization using GPS single-frequency observables in low and high solar activities". Earth, Planets and Space 76, nr 1 (28.06.2024). http://dx.doi.org/10.1186/s40623-024-02033-4.
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AbstractWe assess the orbit accuracy and time synchronization error using the L1 and C1 observables during the different solar activities. In general, GPS single-frequency (SF) observable can be used for commercial applications in satellite industry. The accuracy of satellite orbit determination using the SF observations is dominated by solar activities. The solar activities are indexed by the F10.7 value. The different solar activities lead to the ionosphere perturbation, triggering off the occurrence probability of ionospheric irregularities. The ionospheric irregularity affects the amplitude and phase of GPS signal. The affected amplitude and phase are indexed by the S4 value. We determine the GRACE satellite orbit using the SF GPS observations and compare the resulting orbit to that derived by dual-frequency observations for the effectiveness. The SF phase data are very sensitive to the variation in electron density and indirectly affects both the orbit accuracy and the time synchronization error. This is most likely caused by the phase ambiguity disturbed by the ionosphere. However, the C1 is relatively free from such a disturbance due to the strong signal-to-noise ratio (SNR) and the phase shift keying technique. The C1 performs the consistent solution over the low and high solar activities. However, this is not the case for the L1. The L1-derived orbit solution during the high solar activities is worse than that during the low solar activities. On the other hand, the time synchronization errors derived by the L1 and C1 are also different. The L1-derived time synchronization error has a relatively large perturbation as compared to the C1-derived one, which shows a consistent solution for a long-term period. This work suggests that the C1 observable is able to produce a consistent the orbit solution and time synchronization for the commercial applications of the satellite industry. Graphical Abstract
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Kang, Zhigui, Srinivas Bettadpur, Himanshu Save i Peter Nagel. "GPS-Based Precise Orbit Determination of LEO Satellites Using Space-Based Double-Differenced Observations". Journal of the Astronautical Sciences 71, nr 3 (29.04.2024). http://dx.doi.org/10.1007/s40295-024-00444-9.
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AbstractOne of the important GPS applications in space is precise orbit determination (POD) of Low-Earth Orbit (LEO) satellites. Thousands of LEO satellites are currently in orbit. One of the challenges is how to efficiently and precisely determine the orbits to satisfy the relative and absolute accuracy needs of missions. Currently, GPS-based POD of LEO satellites can be performed using either un-differenced (UD) or ground-based double-differenced (DD) observations. The UD POD needs both precise GPS satellite orbits and clocks; the DD POD needs not only the precise orbits, but also global ground reference receivers. Therefore, the GPS-based LEO POD is based on either global ground stations or precise GNSS clocks, which are not convenient for near real-time or real-time data processing. The GPS orbits can be precisely predicted in certain time; the clocks are not. For some formation flying satellite missions (two or more LEO satellites), the absolute orbit accuracy requirements are not as stringent as the relative requirements. The problem is how to perform LEO POD without global station data and precise GPS clocks in near real-time or real-time to achieve the mission orbit accuracy requirement. Based on this motivation, we investigated the GPS-based LEO POD using space-based DD observations without using global ground station GPS data and precise GPS clock products. For this study, we processed the real GPS observations from two LEO satellites. The absolute and relative orbit accuracy is assessed using several tests, including analysis of the orbit fits, external orbit comparisons, Satellite Laser Ranging (SLR) and K-band Ranging (KBR) residuals.
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Robson, Stephen, i Manu Abderrahmane Haddad. "A sub-μs accuracy GPS alternative using electrical transmission grids as precision timing networks". Scientific Reports 14, nr 1 (15.04.2024). http://dx.doi.org/10.1038/s41598-024-56296-8.
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AbstractIt is widely recognised that over-reliance on GNSS (e.g GPS) for time synchronisation represents an acute threat to modern society, and a diversity of alternatives are required to mitigate the threat of an outage. This paper proposes a GNSS alternative using time dissemination over national scale transmission or distribution networks. The method utilises the same frequency bandwidth and coupling technology as established power line carrier technology in conjunction with modern chirp Spread Spectrum modulation. The basis of the method is the transmission of a time synchronised chirp from a central substation, coupled into the aerial modes of the transmission line. During GNSS operation, all substations can estimate the time of flight by correlating the received chirp with a time-synchronised local copy. During GNSS outage, time sychronisation to the central substation is maintained by correcting for the precalculated time of flight. It is shown that recent advances in chirp spread spectrum allow for a computationally efficient algorithm with the capacity to compute hundreds of thousand of chirp correlations every second, facilitating timing accuracy which satisfies the majority of smart grid applications. ATP-EMTP simulations of the method on large transmission networks demonstrate sub-μs timing accuracy even in the presence of low SNR and impulsive noise. An FPGA prototype demonstrates experimentally sub-μs accuracy for time dissemination over a distance of 700 m. Averaging over time is shown to facilitate satisfactory performance down to $$-20\,\hbox {dB}$$ - 20 dB , which could extend the range of the system to a national scale and a time dissemination network invulnerable to wireless spoofing and jamming attack vectors.
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Duan, Bingbing, Urs Hugentobler, Inga Selmke i Ningbo Wang. "Estimating ambiguity fixed satellite orbit, integer clock and daily bias products for GPS L1/L2, L1/L5 and Galileo E1/E5a, E1/E5b signals". Journal of Geodesy 95, nr 4 (31.03.2021). http://dx.doi.org/10.1007/s00190-021-01500-0.
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AbstractAmbiguity resolution of a single receiver is becoming more and more popular for precise GNSS (Global Navigation Satellite System) applications. To serve such an approach, dedicated satellite orbit, clock and bias products are needed. However, we need to be sure whether products based on specific frequencies and signals can be used when processing measurements of other frequencies and signals. For instance, for Galileo E5a frequency, some receivers track only the pilot signal (C5Q) while some track only the pilot-data signal (C5X). We cannot compute the differences between C5Q and C5X directly since these two signals are not tracked concurrently by any common receiver. As code measurements contribute equally as phase in the Melbourne-Wuebbena (MelWub) linear combination it is important to investigate whether C5Q and C5X can be mixed in a network to compute a common satellite MelWub bias product. By forming two network clusters tracking Q and X signals, respectively, we confirm that GPS C5Q and C5X signals cannot be mixed together. Because the bias differences between GPS C5Q and C5X can be more than half of one wide-lane cycle. Whereas, mixing of C5Q and C5X signals for Galileo satellites is possible. The RMS of satellite MelWub bias differences between Q and X cluster is about 0.01 wide-lane cycles for both E1/E5a and E1/E5b frequencies. Furthermore, we develop procedures to compute satellite integer clock and narrow-lane bias products using individual dual-frequency types. Same as the finding from previous studies, GPS satellite clock differences between L1/L2 and L1/L5 estimates exist and show a periodical behavior, with a peak-to-peak amplitude of 0.7 ns after removing the daily mean difference of each satellite. For Galileo satellites, the maximum clock difference between E1/E5a and E1/E5b estimates after removing the mean value is 0.04 ns and the mean RMS of differences is 0.015 ns. This is at the same level as the noise of the carrier phase measurement in the ionosphere-free linear combination. Finally, we introduce all the estimated GPS and Galileo satellite products into PPP-AR (precise point positioning, ambiguity resolution) and Sentinel-3A satellite orbit determination. Ambiguity fixed solutions show clear improvement over float solutions. The repeatability of five ground-station coordinates show an improvement of more than 30% in the east direction when using both GPS and Galileo products. The Sentinel-3A satellite tracks only GPS L1/L2 measurements. The standard deviation (STD) of satellite laser ranging (SLR) residuals is reduced by about 10% when fixing ambiguity parameters to integer values.