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Journal articles on the topic 'Non-line-of-sight-imaging'

Author: Grafiati
Published: 4 June 2021
Last updated: 1 February 2022

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1

Faccio, Daniele, Andreas Velten, and Gordon Wetzstein. "Non-line-of-sight imaging." Nature Reviews Physics 2, no. 6 (May 13, 2020): 318–27. http://dx.doi.org/10.1038/s42254-020-0174-8.

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2

Faccio, Daniele. "Non-Line-of-Sight Imaging." Optics and Photonics News 30, no. 1 (January 1, 2019): 36. http://dx.doi.org/10.1364/opn.30.1.000036.

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3

Tingyi Yu, 于亭义, 乔木 Mu Qiao, 刘红林 Honglin Liu, and 韩申生 Shensheng Han. "Non-Line-of-Sight Imaging Through Deep Learning." Acta Optica Sinica 39, no. 7 (2019): 0711002. http://dx.doi.org/10.3788/aos201939.0711002.

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4

Beckus, Andre, Alexandru Tamasan, and George K. Atia. "Multi-Modal Non-Line-of-Sight Passive Imaging." IEEE Transactions on Image Processing 28, no. 7 (July 2019): 3372–82. http://dx.doi.org/10.1109/tip.2019.2896517.

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5

Wu, Cheng, Jianjiang Liu, Xin Huang, Zheng-Ping Li, Chao Yu, Jun-Tian Ye, Jun Zhang, et al. "Non–line-of-sight imaging over 1.43 km." Proceedings of the National Academy of Sciences 118, no. 10 (March 3, 2021): e2024468118. http://dx.doi.org/10.1073/pnas.2024468118.

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Non–line-of-sight (NLOS) imaging has the ability to reconstruct hidden objects from indirect light paths that scatter multiple times in the surrounding environment, which is of considerable interest in a wide range of applications. Whereas conventional imaging involves direct line-of-sight light transport to recover the visible objects, NLOS imaging aims to reconstruct the hidden objects from the indirect light paths that scatter multiple times, typically using the information encoded in the time-of-flight of scattered photons. Despite recent advances, NLOS imaging has remained at short-range realizations, limited by the heavy loss and the spatial mixing due to the multiple diffuse reflections. Here, both experimental and conceptual innovations yield hardware and software solutions to increase the standoff distance of NLOS imaging from meter to kilometer range, which is about three orders of magnitude longer than previous experiments. In hardware, we develop a high-efficiency, low-noise NLOS imaging system at near-infrared wavelength based on a dual-telescope confocal optical design. In software, we adopt a convex optimizer, equipped with a tailored spatial–temporal kernel expressed using three-dimensional matrix, to mitigate the effect of the spatial–temporal broadening over long standoffs. Together, these enable our demonstration of NLOS imaging and real-time tracking of hidden objects over a distance of 1.43 km. The results will open venues for the development of NLOS imaging techniques and relevant applications to real-world conditions.
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La Manna, Marco, Fiona Kine, Eric Breitbach, Jonathan Jackson, Talha Sultan, and Andreas Velten. "Error Backprojection Algorithms for Non-Line-of-Sight Imaging." IEEE Transactions on Pattern Analysis and Machine Intelligence 41, no. 7 (July 1, 2019): 1615–26. http://dx.doi.org/10.1109/tpami.2018.2843363.

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7

La Manna, Marco, Ji-Hyun Nam, Syed Azer Reza, and Andreas Velten. "Non-line-of-sight-imaging using dynamic relay surfaces." Optics Express 28, no. 4 (February 12, 2020): 5331. http://dx.doi.org/10.1364/oe.383586.

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8

Klein, Jonathan, Martin Laurenzis, Matthias B. Hullin, and Julian Iseringhausen. "Calibration scheme for non-line-of-sight imaging setups." Optics Express 28, no. 19 (September 9, 2020): 28324. http://dx.doi.org/10.1364/oe.398647.

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9

Lin, Di, Connor Hashemi, and James R. Leger. "Passive non-line-of-sight imaging using plenoptic information." Journal of the Optical Society of America A 37, no. 4 (March 11, 2020): 540. http://dx.doi.org/10.1364/josaa.377821.

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10

Thrampoulidis, Christos, Gal Shulkind, Feihu Xu, William T. Freeman, Jeffrey H. Shapiro, Antonio Torralba, Franco N. C. Wong, and Gregory W. Wornell. "Exploiting Occlusion in Non-Line-of-Sight Active Imaging." IEEE Transactions on Computational Imaging 4, no. 3 (September 2018): 419–31. http://dx.doi.org/10.1109/tci.2018.2829599.

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11

Shen, Siyuan, Zi Wang, Ping Liu, Zhengqing Pan, Ruiqian Li, Tian Gao, Shiying Li, and Jingyi Yu. "Non-line-of-Sight Imaging via Neural Transient Fields." IEEE Transactions on Pattern Analysis and Machine Intelligence 43, no. 7 (July 1, 2021): 2257–68. http://dx.doi.org/10.1109/tpami.2021.3076062.

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12

Liu, Xiaochun, Ibón Guillén, Marco La Manna, Ji Hyun Nam, Syed Azer Reza, Toan Huu Le, Adrian Jarabo, Diego Gutierrez, and Andreas Velten. "Non-line-of-sight imaging using phasor-field virtual wave optics." Nature 572, no. 7771 (August 2019): 620–23. http://dx.doi.org/10.1038/s41586-019-1461-3.

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13

Heide, Felix, Matthew O’Toole, Kai Zang, David B. Lindell, Steven Diamond, and Gordon Wetzstein. "Non-line-of-sight Imaging with Partial Occluders and Surface Normals." ACM Transactions on Graphics 38, no. 3 (June 15, 2019): 1–10. http://dx.doi.org/10.1145/3269977.

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14

Chen, Wenzheng, Fangyin Wei, Kiriakos N. Kutulakos, Szymon Rusinkiewicz, and Felix Heide. "Learned feature embeddings for non-line-of-sight imaging and recognition." ACM Transactions on Graphics 39, no. 6 (November 26, 2020): 1–18. http://dx.doi.org/10.1145/3414685.3417825.

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15

O’Toole, Matthew, David B. Lindell, and Gordon Wetzstein. "Confocal non-line-of-sight imaging based on the light-cone transform." Nature 555, no. 7696 (March 2018): 338–41. http://dx.doi.org/10.1038/nature25489.

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16

Lindell, David B., Gordon Wetzstein, and Matthew O'Toole. "Wave-based non-line-of-sight imaging using fast f-k migration." ACM Transactions on Graphics 38, no. 4 (July 12, 2019): 1–13. http://dx.doi.org/10.1145/3306346.3322937.

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17

Xu, Kaida, Weiqi Jin, Shenyou Zhao, Jing Liu, Hui Guo, Su Qiu, and Dongsheng Wu. "Image contrast model of non-line-of-sight imaging based on laser range-gated imaging." Optical Engineering 53, no. 6 (December 16, 2013): 061610. http://dx.doi.org/10.1117/1.oe.53.6.061610.

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18

Huang, Luzhe, Xiaobin Wang, Yifan Yuan, Songyun Gu, and Yonghang Shen. "Improved algorithm of non-line-of-sight imaging based on the Bayesian statistics." Journal of the Optical Society of America A 36, no. 5 (April 23, 2019): 834. http://dx.doi.org/10.1364/josaa.36.000834.

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19

Buttafava, Mauro, Jessica Zeman, Alberto Tosi, Kevin Eliceiri, and Andreas Velten. "Non-line-of-sight imaging using a time-gated single photon avalanche diode." Optics Express 23, no. 16 (August 3, 2015): 20997. http://dx.doi.org/10.1364/oe.23.020997.

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20

Renna, Marco, Ji Hyun Nam, Mauro Buttafava, Federica Villa, Andreas Velten, and Alberto Tosi. "Fast-Gated 16 × 1 SPAD Array for Non-Line-of-Sight Imaging Applications." Instruments 4, no. 2 (May 25, 2020): 14. http://dx.doi.org/10.3390/instruments4020014.

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In this paper we present a novel single-photon detector specifically designed for Non-Line-Of-Sight (NLOS) imaging applications within the framework of the DARPA REVEAL program. The instrument is based on a linear 16 × 1 Complementary Metal-Oxide-Semiconductor (CMOS) Single-Photon Avalanche Diode (SPAD) array operated in fast-gated mode by a novel fast-gating Active Quenching Circuit (AQC) array, which enables the detectors with sub-ns transitions thanks to a SPAD-dummy approach. The detector exhibits a timing resolution better than 50 ps (Full Width at Half Maximum - FWHM) at a measurement repetition rate up to 40 MHz, and provides 16 independent outputs compatible with commercial Time-Correlated Single-Photon Counting (TCSPC) instrumentation. The instrument has been experimentally characterized and operated in preliminary NLOS imaging acquisitions where a 40 × 60 cm hidden object is successfully reconstructed by scanning over a grid of 150 × 150 positions.
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21

El-Shimy, Mohamed A., and Steve Hranilovic. "Spatial-Diversity Imaging Receivers for Non-Line-of-Sight Solar-Blind UV Communications." Journal of Lightwave Technology 33, no. 11 (June 1, 2015): 2246–55. http://dx.doi.org/10.1109/jlt.2015.2406672.

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22

Metzler, Christopher A., Felix Heide, Prasana Rangarajan, Muralidhar Madabhushi Balaji, Aparna Viswanath, Ashok Veeraraghavan, and Richard G. Baraniuk. "Deep-inverse correlography: towards real-time high-resolution non-line-of-sight imaging." Optica 7, no. 1 (January 16, 2020): 63. http://dx.doi.org/10.1364/optica.374026.

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23

Xu, Kaida, Weiqi Jin, Shenyou Zhao, Jing Liu, Hui Guo, Su Qiu, and Dongsheng Wu. "Errata: Image contrast model of non-line-of-sight imaging based on laser range-gated imaging." Optical Engineering 52, no. 12 (December 20, 2013): 129801. http://dx.doi.org/10.1117/1.oe.52.12.129801.

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24

Metzler, Christopher A., Felix Heide, Prasana Rangarajan, Muralidhar Madabhushi Balaji, Aparna Viswanath, Ashok Veeraraghavan, and Richard G. Baraniuk. "Deep-inverse correlography: towards real-time high-resolution non-line-of-sight imaging: erratum." Optica 7, no. 3 (March 19, 2020): 249. http://dx.doi.org/10.1364/optica.391291.

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25

Wei-hao XU, 徐伟豪, 苏秀琴 Xiu-qin SU, 汪书潮 Shu-chao WANG, 朱文华 Wen-hua ZHU, 陈松懋 Song-mao CHEN, 王定杰 Ding-jie WANG, and 邬京耀 Jing-yao WU. "Simulation Research of Non-line-of-sight Imaging System Based on Bidirectional Reflectance Distribution Function." ACTA PHOTONICA SINICA 49, no. 12 (2020): 157–69. http://dx.doi.org/10.3788/gzxb20204912.157.

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26

Wei-hao XU, 徐伟豪, 苏秀琴 Xiu-qin SU, 汪书潮 Shu-chao WANG, 朱文华 Wen-hua ZHU, 陈松懋 Song-mao CHEN, 王定杰 Ding-jie WANG, and 邬京耀 Jing-yao WU. "Simulation Research of Non-line-of-sight Imaging System Based on Bidirectional Reflectance Distribution Function." ACTA PHOTONICA SINICA 49, no. 12 (2020): 157–69. http://dx.doi.org/10.3788/gzxb20204912.1211002.

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27

Shi, Zhengyang, Xia Wang, Yang Li, Zhibin Sun, and Wenxi Zhang. "Edge re-projection method for high-quality edge reconstruction in non-line-of-sight imaging." Applied Optics 59, no. 6 (February 19, 2020): 1793. http://dx.doi.org/10.1364/ao.376403.

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28

Li, Mengdi, Anumol Mathai, Xiping Xu, Xin Wang, Yue Pan, and Xuefeng Gao. "Non-line-of-sight transparent object detection and reconstruction based on passive single-pixel imaging." Laser Physics Letters 18, no. 2 (January 23, 2021): 025204. http://dx.doi.org/10.1088/1612-202x/abd8d9.

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29

Callenberg, Clara, Zheng Shi, Felix Heide, and Matthias B. Hullin. "Low-cost SPAD sensing for non-line-of-sight tracking, material classification and depth imaging." ACM Transactions on Graphics 40, no. 4 (August 2021): 1–12. http://dx.doi.org/10.1145/3476576.3476611.

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30

Callenberg, Clara, Zheng Shi, Felix Heide, and Matthias B. Hullin. "Low-cost SPAD sensing for non-line-of-sight tracking, material classification and depth imaging." ACM Transactions on Graphics 40, no. 4 (August 2021): 1–12. http://dx.doi.org/10.1145/3450626.3459824.

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31

Reza, Syed Azer, Marco La Manna, Sebastian Bauer, and Andreas Velten. "Phasor field waves: A Huygens-like light transport model for non-line-of-sight imaging applications." Optics Express 27, no. 20 (September 27, 2019): 29380. http://dx.doi.org/10.1364/oe.27.029380.

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32

Lin, Di, and James R. Leger. "Locating non-line-of-sight features and recovering imagery conveyed through parallax in passive plenoptic imaging." Journal of the Optical Society of America A 38, no. 8 (July 8, 2021): 1104. http://dx.doi.org/10.1364/josaa.421295.

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33

Zhao, Shen You, Kai Da Xu, Su Qiu, Wei Qi Jin, Hui Guo, Xia Wang, and Kai Jia Jin. "Forward Reflection Characteristics of Typical Smooth Building Walls and the Simulation Analysis." Applied Mechanics and Materials 513-517 (February 2014): 3601–6. http://dx.doi.org/10.4028/www.scientific.net/amm.513-517.3601.

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Non-line-of-sight optical imaging technology is a novel application of imaging technology developed recently, achieving the effective imaging of the corner, basements and other scenes which are difficult to be directly observed by traditional vision with intermediate reflective surface. Smooth building walls, such as tiles and marbles, are typical intermediate reflective surfaces. Because reflecting surface is neither ideal specular reflective nor Lambertian reflective, the reflection characteristics of the intermediate reflective surface have a significant impact on the non-line-of-sight imaging. Based on the test data of the spectral bidirectional reflectance distribution function (BRDF) of common smooth tiles, the surface transfer function and angle spread function of smooth tiles are established according to the Harvey-Shack surface scatter theory in the paper. And the descriptions of the characteristics of specular reflection and forward scattering are implemented. Furthermore, according to the measured BRDF data at a certain wavelength for a certain angle of incidence, we can predict the reflection and scattering distribution at any other wavelengths or for other incident angles. The simulation results indicate that the curves fitted by the model basically are in agreement with the measured data, so that the simulation of the specular reflection and the forward scattering in the model is valid.
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34

Wang, Pei, Ke Zhang, and Cong Nie. "Research on Line-of-Sight Rate Estimation of Strapdown Seeker." Applied Mechanics and Materials 556-562 (May 2014): 3739–44. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.3739.

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As a new type of guidance technology, the strapdown imaging guidance technology, which helps improve the system reliability and reduce costs efficiently, has been paid great attention and developed quickly. However, the detecting information of strapdown seeker can’t be used to proportional navigation directly because it is coupled with missile attitude. A method to estimate the inertial Line-of-Sight (LOS) rate of strapdown imaging seeker based on Cubature Kalman filter (CKF) and Tracking-Differentiator (TD) was presented. As there were high nonlinearity in both state and measurement equations and more serious non-Gaussian noise in the measurements, the Extended Kalman filter (EKF) could not completely meet the requirements of filtering. Compared with EKF and Unscented Particle filter (UKF), CKF was a congruent method for states estimating in the conditions of nonlinearity and non-Gaussian noise. CKF was applied to estimate the LOS rate of strapdown imaging seeker. Because measurement noise of missile attitude will be reflected in estimation result, TD was used to decrease noise of the missile attitude measurements for improving the estimation precision. Monte Carlo simulation results show that the proposed method can improve the precision of guidance.
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35

Jin, Chenfei, Jiaheng Xie, Siqi Zhang, ZiJing Zhang, and Yuan Zhao. "Richardson–Lucy deconvolution of time histograms for high-resolution non-line-of-sight imaging based on a back-projection method." Optics Letters 43, no. 23 (November 30, 2018): 5885. http://dx.doi.org/10.1364/ol.43.005885.

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36

Yong, P., M. Paterson-Beedle, W. Liu, Z. Zhang, D. A. Beauregard, M. L. Johns, and Lynne E. Macaskie. "A Study of Biofilm and Non-Line-of-Sight Bio-Hydroxyapatite Coatings Using a Serratia sp." Advanced Materials Research 71-73 (May 2009): 741–44. http://dx.doi.org/10.4028/www.scientific.net/amr.71-73.741.

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This study describes biofilm formation as a non line-of-sight coating method on support materials such as polyurethane foam, porous glass, polypropylene (PP) and titanium alloy, using a Serratia sp., which can manufacture extracellular nanoscale scaffolded hydroxyapatite (HA) crystals via enzymatic cleavage of glycerol 2-phosphate (G2P) in the presence of CaCl2. Various microscopies and non-invasive magnetic resonance imaging were used to visualize the biofilm coating on the support surface. A novel micromanipulation technique was used to estimate the adhesive strength of native and HA-mineralized biofilms. The biofilm with HA was up to forty times stronger than that without HA. A coating of nano-HA (> 80 m) onto a biofilm-Ti disc was achieved.
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37

Chisham, G., and M. Pinnock. "Assessing the contamination of SuperDARN global convection maps by non-F-region backscatter." Annales Geophysicae 20, no. 1 (January 31, 2002): 13–28. http://dx.doi.org/10.5194/angeo-20-13-2002.

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Abstract. Global convection mapping using line-of-sight Doppler velocity data from the Super Dual Auroral Radar Network (SuperDARN) is now an accepted method of imaging high-latitude ionospheric convection. This mapping process requires that the flow measured by the radars is defined solely by the convection electric field. This is generally only true of radar backscatter from the ionospheric F-region. We investigate the extent to which the E-region and ground backscatter in the SuperDARN data set may be misidentified as F-region backscatter, and assess the contamination of global convection maps which results from the addition of this non-F-region backscatter. We present examples which highlight the importance of identifying this contamination, especially with regard to the mesoscale structure in the convection maps.Key words. Ionosphere (plasma convection) – Radio science (radio wave propagation; instruments and techniques)
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38

Islam, Shekh Md Mahmudul, Olga Borić-Lubecke, Yao Zheng, and Victor M. Lubecke. "Radar-Based Non-Contact Continuous Identity Authentication." Remote Sensing 12, no. 14 (July 15, 2020): 2279. http://dx.doi.org/10.3390/rs12142279.

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Non-contact vital signs monitoring using microwave Doppler radar has shown great promise in healthcare applications. Recently, this unobtrusive form of physiological sensing has also been gaining attention for its potential for continuous identity authentication, which can reduce the vulnerability of traditional one-pass validation authentication systems. Physiological Doppler radar is an attractive approach for continuous identity authentication as it requires neither contact nor line-of-sight and does not give rise to privacy concerns associated with video imaging. This paper presents a review of recent advances in radar-based identity authentication systems. It includes an evaluation of the applicability of different research efforts in authentication using respiratory patterns and heart-based dynamics. It also identifies aspects of future research required to address remaining challenges in applying unobtrusive respiration-based or heart-based identity authentication to practical systems. With the advancement of machine learning and artificial intelligence, radar-based continuous authentication can grow to serve a wide range of valuable functions in society.
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39

Pelouze, Gabriel, Frédéric Auchère, Karine Bocchialini, Clara Froment, Susanna Parenti, and Elie Soubrié. "Spectroscopic detection of coronal plasma flows in loops undergoing thermal non-equilibrium cycles." Astronomy & Astrophysics 634 (February 2020): A54. http://dx.doi.org/10.1051/0004-6361/201935872.

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Context. Long-period intensity pulsations were recently detected in the EUV emission of coronal loops and attributed to cycles of plasma evaporation and condensation driven by thermal non-equilibrium (TNE). Numerical simulations that reproduce this phenomenon also predict the formation of periodic flows of plasma at coronal temperatures along some of the pulsating loops. Aims. We aim to detect these predicted flows of coronal-temperature plasma in pulsating loops. Methods. We used time series of spatially resolved spectra from the EUV imaging spectrometer (EIS) onboard Hinode and tracked the evolution of the Doppler velocity in loops in which intensity pulsations have previously been detected in images of SDO/AIA. Results. We measured signatures of flows that are compatible with the simulations but only for a fraction of the observed events. We demonstrate that this low detection rate can be explained by line of sight ambiguities combined with instrumental limitations, such as low signal-to-noise ratio or insufficient cadence.
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40

Barczynski, Krzysztof, Brigitte Schmieder, Aaron W. Peat, Nicolas Labrosse, Pierre Mein, and Nicole Mein. "Spectro-imagery of an active tornado-like prominence: Formation and evolution." Astronomy & Astrophysics 653 (September 2021): A94. http://dx.doi.org/10.1051/0004-6361/202140976.

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Context. The dynamical nature of fine structures in prominences remains an open issue, including rotating flows in tornado prominences. While the Atmospheric Imaging Assembly imager aboard the Solar Dynamics Observatory allowed us to follow the global structure of a tornado-like prominence for five hours, the Interface Region Imaging Spectrograph, and the Multichannel Subtractive Double Pass spectrograph permitted to obtain plasma diagnostics of its fine structures. Aims. We aim to address two questions. Firstly, is the observed plasma rotation conceptually acceptable in a flux rope magnetic support configuration with dips? Secondly, how is the plasma density distributed in the tornado-like prominence? Methods. We calculated line-of-sight velocities and non-thermal line widths using Gaussian fitting for Mg II lines and the bisector method for Hα line. We determined the electron density from Mg II line integrated intensities and profile fitting methods using 1D non-LTE radiative transfer theory models. Results. The global structure of the prominence observed in Hα, and Mg II h, and k line fits with a magnetic field structure configuration with dips. Coherent Doppler shifts in redshifted and blueshifted areas observed in both lines were detected along rapidly-changing vertical and horizontal structures. However, the tornado at the top of the prominence consists of multiple fine threads with opposite flows, suggesting counter-streaming flows rather than rotation. Surprisingly we found that the electron density at the top of the prominence could be larger (1011 cm−3) than in the inner part of the prominence. Conclusions. We suggest that the tornado is in a formation state with cooling of hot plasma in a first phase, and following that, a phase of leakage of the formed blobs with large transverse flows of material along long loops extended away from the UV prominence top. The existence of such long magnetic field lines on both sides of the prominence would stop the tornado-like prominence from really turning around its axis.
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41

Lan 藍鼎文, Ting-Wen, and J. Xavier Prochaska. "Constraining magnetic fields in the circumgalactic medium." Monthly Notices of the Royal Astronomical Society 496, no. 3 (June 19, 2020): 3142–51. http://dx.doi.org/10.1093/mnras/staa1750.

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ABSTRACT We study the properties of magnetic fields in the circumgalactic medium (CGM) of z < 1 galaxies by correlating Faraday rotation measures (RMs) of ∼1000 high-redshift radio sources with the foreground galaxy number density estimated from the DESI Legacy Imaging Surveys. This method enables us to extract signals of RMs contributed by intervening gas around multiple galaxies. Our results show that there is no detectable correlation between the distribution of RMs and the number of foreground galaxies, contrary to several previous results. Utilizing the non-detection signals, we estimate 3σ upper limits to the RMs from the CGM of $\sim \!20 \rm \ rad\, m^{-2}$ within 50 kpc and $\sim \!10 \rm \ rad \, m^{-2}$ at separations of 100 kpc. By adopting a column density distribution of ionized gas obtained from absorption-line measurements, we further estimate the strengths of coherent magnetic fields parallel to the line of sight of $\lt \rm 2 \ \mu G$ in the CGM. We show that the estimated upper limits of RMs and magnetic field strengths are sufficient to constrain outputs of recent galaxy magnetohydrodynamic simulations. Finally, we discuss possible causes for the inconsistency between our results and previous works.
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42

Vasilyev, Gleb Sergeevich, Oleg R. Kuzichkin, and Dmitry I. Surzhik. "Performance analysis of MIMO communication system with NLOS UV channel." Photonics Letters of Poland 12, no. 4 (December 17, 2020): 91. http://dx.doi.org/10.4302/plp.v12i4.985.

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Performance analysis is carried out, of a multiple input, multiple output (MIMO) ultraviolet (UV) communication system with a non-line-of-sight (NLOS) UV channel. The achievable bit error coefficient is calculated using three spatial multiplexing methods for different bitrate values, azimuthal deviation between the directional diagrams of an optical transmitter and an optical receiver, and different noise levels. Full Text: PDF ReferencesZ. Xu, B. Sadler, "Ultraviolet communications: potential and state-of-the-art", IEEE Commun. Mag. 4667-73 (2009). CrossRef D. Han, Y. Liu, K. Zhang et al., "Theoretical and experimental research on diversity reception technology in NLOS UV communication system", Opt. Expr. 20(14), 15833 (2012). CrossRef Q. Guo, N. He, Z. He, "Research on the channel performances and transmission in UV-LED scatter communications", Study Opt. Comm. 3, 64 (2013). DirectLink G. Chen, L. Liao, Z. Li et al., "Experimental and simulated evaluation of long distance NLOS UV communication", Communication Systems, Networks and Digital Signal Processing (CSND-SP), 9th Int. Symp. on IEEE, 904-909 (2014). CrossRef M.A. El-Shimy, S. Hranilovic, "Spatial-Diversity Imaging Receivers for Non-Line-of-Sight Solar-Blind UV Communications", J. Lightwave Techn. 33(11), 2246 (2015). CrossRef G. Shaw, M. Nischan, M. Iyengar, S. Kaushik, M. Griffin, NLOS UV communication for distributed sensor systems, Proc. SPIE 412683, 96 (2000). CrossRef I.S. Konstantinov, G.S. Vasyliev, O.R. Kuzichkin, D.I. Surzhik, I.A. Kurilov, S.A. Lazarev, "AUV Link Mobile Ad-Hoc Network Examination", J. Eng. Adv. Techn. 8(5S) July 2019 CrossRef I.S. Konstantinov, G.S. Vasilyev, O.R. Kuzichkin, I.A. Kurilov, S.A. Lazarev, "Modeling and Analysis of the Characteristics of Ultraviolet Channels under Different Conditions of Radiation Propagation for the Organization of Wireless AD-HOC Network", J. Adv. Res. Dynam. Contr. Syst. 07, 1853 (2018) DirectLink I.S. Konstantinov, G.S. Vasyliev, O.R. Kuzichkin, D.I. Surzhik, I.A. Kurilov, S.A. Lazarev, "Development Of Uv Communication Channels Characteristics Modeling Algorithm In A Mobile Ad-Hoc Network", J. Adv. Res. Dynam. Contr. Syst. 11(08), 1920 (2019). CrossRef G. Chen, F. Abou-Galala, Z. Xu, B.M. Sadler, "Experimental evaluation of LED-based solar blind NLOS communication links", Opt. Expr. 16(19), 15059 (2008). CrossRef
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43

Zhang, P., É. Buchlin, and J. C. Vial. "Launch of a CME-associated eruptive prominence as observed with IRIS and ancillary instruments." Astronomy & Astrophysics 624 (April 2019): A72. http://dx.doi.org/10.1051/0004-6361/201834259.

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Aims. In this paper we focus on the possible observational signatures of the processes which have been put forward for explaining eruptive prominences. We also try to understand the variations in the physical conditions of eruptive prominences and estimate the masses leaving the Sun versus the masses returning to the Sun during eruptive prominences. Methods. As far as velocities are concerned, we combined an optical flow method on the Atmospheric Imaging Assembly (AIA) 304 Å and Interface Region Imaging Spectrograph (IRIS). Mg II h&k observations in order to derive the plane-of-sky velocities in the prominence, and a Doppler technique on the IRIS Mg II h&k profiles to compute the line-of-sight velocities. As far as densities are concerned, we compared the absolute observed intensities with values derived from non-local thermodynamic equilibrium radiative transfer computations to derive the total (hydrogen) density and consequently compute the mass flows. Results. The derived electron densities range from 1.3 × 109 to 6.0 × 1010 cm−3 and the derived total hydrogen densities range from 1.5 × 109 to 2.4 × 1011 cm−3 in different regions of the prominence. The mean temperature is around 1.1 × 104 K, which is higher than in quiescent prominences. The ionization degree is in the range of 0.1–10. The total (hydrogen) mass is in the range of 1.3 × 1014–3.2 × 1014 g. The total mass drainage from the prominence to the solar surface during the whole observation time of IRIS is about one order of magnitude smaller than the total mass of the prominence.
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44

Kasparova, Anastasia V., Ivan Yu Katkov, and Igor V. Chilingarian. "An excessively massive thick disc of the enormous edge-on lenticular galaxy NGC 7572." Monthly Notices of the Royal Astronomical Society 493, no. 4 (March 2, 2020): 5464–78. http://dx.doi.org/10.1093/mnras/staa611.

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ABSTRACT Galactic discs are known to have a complex multilayer structure. An in-depth study of the stellar population properties of the thin and thick components can elucidate the formation and evolution of disc galaxies. Even though thick discs are ubiquitous, their origin is still debated. Here we probe the thick disc formation scenarios by investigating NGC 7572, an enormous edge-on galaxy having R25 ≈ 25 kpc and Vrot ≈ 370 km s−1, which substantially exceeds the Milky Way size and mass. We analysed DECaLS archival imaging and found that the disc of NGC 7572 contains two flaring stellar discs (a thin and a thick disc) with similar radial scales. We collected deep long-slit spectroscopic data using the 6 m Russian BTA telescope and analysed them with a novel technique. We first reconstructed a non-parametric stellar line-of-sight velocity distribution along the radius of the galaxy and then fitted it with two kinematic components accounting for the orbital distribution of stars in thin and thick discs. The old thick disc turned out to be 2.7 times as massive as the intermediate-age thin component, 1.6 × 1011 M⊙ versus 5.9 × 1010 M⊙, which is very unusual. The different duration of the formation epochs evidenced by the [Mg/Fe] values of +0.3 and +0.15 dex for the thick and thin discs respectively, their kinematics, and the mass ratio suggest that in NGC 7572 we observe a rapidly formed very massive thick disc and an underdeveloped thin disc, whose growth ended prematurely due to the exhaustion of the cold gas likely because of environmental effects.
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45

Madjarska, Maria S., Klaus Galsgaard, Duncan H. Mackay, Kostadinka Koleva, and Momchil Dechev. "Eruptions from coronal hole bright points: Observations and non-potential modelling." Astronomy & Astrophysics 643 (October 27, 2020): A19. http://dx.doi.org/10.1051/0004-6361/202038287.

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Context. We report on the third part of a series of studies on eruptions associated with small-scale loop complexes named coronal bright points (CBPs). Aims. A single case study of a CBP in an equatorial coronal hole with an exceptionally large size is investigated to expand on our understanding of the formation of mini-filaments, their destabilisation, and the origin of the eruption triggering the formation of jet-like features recorded in extreme ultraviolet (EUV) and X-ray emission. We aim to explore the nature of the so-called micro-flares in CBPs associated with jets in coronal holes and mini coronal mass ejections in the quiet Sun. Methods. Co-observations from the Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory as well as GONG Hα images are used together with a non-linear force free field (NLFFF) relaxation approach, where the latter is based on a time series of HMI line-of-sight magnetograms. Results. A mini-filament (MF) that formed beneath the CBP arcade about 3−4 h before the eruption is seen in the Hα and EUV AIA images to lift up and erupt triggering the formation of an X-ray jet. No significant photospheric magnetic flux concentration displacement (convergence) is observed and neither is magnetic flux cancellation between the two main magnetic polarities forming the CBP in the time period leading to MF lift-off. The CBP micro-flare is associated with three flare kernels that formed shortly after the MF lift-off. No observational signature is found for magnetic reconnection beneath the erupting MF. The applied NLFFF modelling successfully reproduces both the CBP loop complex as well as the magnetic flux rope that hosts the MF during the build-up to the eruption. Conclusions. The applied NLFFF modelling is able to clearly show that an initial potential field can be evolved into a non-potential magnetic field configuration that contains free magnetic energy in the region that observationally hosts the eruption. The comparison of the magnetic field structure shows that the magnetic NLFFF model contains many of the features that can explain the different observational signatures found in the evolution and eruption of the CBP. In the future, it may eventually indicate the location of destabilisation that results in the eruptions of flux ropes.
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46

Schwaerzel, Marc, Claudia Emde, Dominik Brunner, Randulph Morales, Thomas Wagner, Alexis Berne, Brigitte Buchmann, and Gerrit Kuhlmann. "Three-dimensional radiative transfer effects on airborne and ground-based trace gas remote sensing." Atmospheric Measurement Techniques 13, no. 8 (August 14, 2020): 4277–93. http://dx.doi.org/10.5194/amt-13-4277-2020.

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Abstract. Air mass factors (AMFs) are used in passive trace gas remote sensing for converting slant column densities (SCDs) to vertical column densities (VCDs). AMFs are traditionally computed with 1D radiative transfer models assuming horizontally homogeneous conditions. However, when observations are made with high spatial resolution in a heterogeneous atmosphere or above a heterogeneous surface, 3D effects may not be negligible. To study the importance of 3D effects on AMFs for different types of trace gas remote sensing, we implemented 1D-layer and 3D-box AMFs into the Monte carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres (MYSTIC), a solver of the libRadtran radiative transfer model (RTM). The 3D-box AMF implementation is fully consistent with 1D-layer AMFs under horizontally homogeneous conditions and agrees very well (<5 % relative error) with 1D-layer AMFs computed by other RTMs for a wide range of scenarios. The 3D-box AMFs make it possible to visualize the 3D spatial distribution of the sensitivity of a trace gas observation, which we demonstrate with two examples. First, we computed 3D-box AMFs for ground-based multi-axis spectrometer (MAX-DOAS) observations for different viewing geometry and aerosol scenarios. The results illustrate how the sensitivity reduces with distance from the instrument and that a non-negligible part of the signal originates from outside the line of sight. Such information is invaluable for interpreting MAX-DOAS observations in heterogeneous environments such as urban areas. Second, 3D-box AMFs were used to generate synthetic nitrogen dioxide (NO2) SCDs for an airborne imaging spectrometer observing the NO2 plume emitted from a tall stack. The plume was imaged under different solar zenith angles and solar azimuth angles. To demonstrate the limitations of classical 1D-layer AMFs, VCDs were then computed assuming horizontal homogeneity. As a result, the imaged NO2 plume was shifted in space, which led to a strong underestimation of the total VCDs in the plume maximum and an underestimation of the integrated line densities that can be used for estimating emissions from NO2 images. The two examples demonstrate the importance of 3D effects for several types of ground-based and airborne remote sensing when the atmosphere cannot be assumed to be horizontally homogeneous, which is typically the case in the vicinity of emission sources or in cities.
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47

Morosin, Roberta, Jaime de la Cruz Rodríguez, Gregal J. M. Vissers, and Rahul Yadav. "Stratification of canopy magnetic fields in a plage region." Astronomy & Astrophysics 642 (October 2020): A210. http://dx.doi.org/10.1051/0004-6361/202038754.

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Context. The role of magnetic fields in the chromospheric heating problem remains greatly unconstrained. Most theoretical predictions from numerical models rely on a magnetic configuration, field strength, and connectivity; the details of which have not been well established with observational studies for many chromospheric scenarios. High-resolution studies of chromospheric magnetic fields in plage are very scarce or non existent in general. Aims. Our aim is to study the stratification of the magnetic field vector in plage regions. Previous studies predict the presence of a magnetic canopy in the chromosphere that has not yet been studied with full-Stokes observations. We use high-spatial resolution full-Stokes observations acquired with the CRisp Imaging Spectro-Polarimeter (CRISP) at the Swedish 1-m Solar Telescope in the Mg I 5173 Å, Na I 5896 Å and Ca II 8542 Å lines. Methods. We have developed a spatially-regularized weak-field approximation (WFA) method, based on the idea of spatial regularization. This method allows for a fast computation of magnetic field maps for an extended field of view. The fidelity of this new technique has been assessed using a snapshot from a realistic 3D magnetohydrodynamics simulation. Results. We have derived the depth-stratification of the line-of-sight component of the magnetic field from the photosphere to the chromosphere in a plage region. The magnetic fields are concentrated in the intergranular lanes in the photosphere and expand horizontally toward the chromosphere, filling all the space and forming a canopy. Our results suggest that the lower boundary of this canopy must be located around 400 − 600 km from the photosphere. The mean canopy total magnetic field strength in the lower chromosphere (z ≈ 760 km) is 658 G. At z = 1160 km, we estimate ⟨B∥⟩ ≈ 417 G. Conclusions. In this study we propose a modification to the WFA that improves its applicability to data with a worse signal-to-noise ratio. We have used this technique to study the magnetic properties of the hot chromospheric canopy that is observed in plage regions. The methods described in this paper provide a quick and reliable way of studying multi layer magnetic field observations without the many difficulties inherent to other inversion methods.
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48

Cao, Fang, Cheng Li, and Zhiyong Xu. "Research on the Coverage of Ultraviolet Communication Network in the Arbitrary Polygon Area." Photonics 8, no. 7 (June 28, 2021): 240. http://dx.doi.org/10.3390/photonics8070240.

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Given that the current ultraviolet (UV) networking model is established in a regular circular area, this article studies the coverage of a UV non-line-of-sight (NLOS) communication network creatively in the arbitrary polygon area. In this paper, the UV communication model and the basic concepts of network coverage are introduced first. Then the influence parameters of the UV node communication radius are studied, and the changes of the communication radius under different work patterns are analyzed. Finally, the coverage of the square target area is simulated under different communication parameters (transmitted power, data rate and node density). The results illustrate that the smaller the transceiver elevation angles are, the better the network coverage performance is. Additionally, we numerically compare the UV network models of polygonal and circular regions, which can be used as a reference for actual networking.
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49

Ronchin, Erika, Timothy Masterlark, John Dawson, Steve Saunders, and Joan Martì Molist. "Imaging the complex geometry of a magma reservoir using FEM-based linear inverse modeling of InSAR data: application to Rabaul Caldera, Papua New Guinea." Geophysical Journal International 209, no. 3 (March 24, 2017): 1746–60. http://dx.doi.org/10.1093/gji/ggx119.

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Summary We test an innovative inversion scheme using Green's functions from an array of pressure sources embedded in finite-element method (FEM) models to image, without assuming an a-priori geometry, the composite and complex shape of a volcano deformation source. We invert interferometric synthetic aperture radar (InSAR) data to estimate the pressurization and shape of the magma reservoir of Rabaul caldera, Papua New Guinea. The results image the extended shallow magmatic system responsible for a broad and long-term subsidence of the caldera between 2007 February and 2010 December. Elastic FEM solutions are integrated into the regularized linear inversion of InSAR data of volcano surface displacements in order to obtain a 3-D image of the source of deformation. The Green's function matrix is constructed from a library of forward line-of-sight displacement solutions for a grid of cubic elementary deformation sources. Each source is sequentially generated by removing the corresponding cubic elements from a common meshed domain and simulating the injection of a fluid mass flux into the cavity, which results in a pressurization and volumetric change of the fluid-filled cavity. The use of a single mesh for the generation of all FEM models avoids the computationally expensive process of non-linear inversion and remeshing a variable geometry domain. Without assuming an a-priori source geometry other than the configuration of the 3-D grid that generates the library of Green's functions, the geodetic data dictate the geometry of the magma reservoir as a 3-D distribution of pressure (or flux of magma) within the source array. The inversion of InSAR data of Rabaul caldera shows a distribution of interconnected sources forming an amorphous, shallow magmatic system elongated under two opposite sides of the caldera. The marginal areas at the sides of the imaged magmatic system are the possible feeding reservoirs of the ongoing Tavurvur volcano eruption of andesitic products on the east side and of the past Vulcan volcano eruptions of more evolved materials on the west side. The interconnection and spatial distributions of sources correspond to the petrography of the volcanic products described in the literature and to the dynamics of the single and twin eruptions that characterize the caldera. The ability to image the complex geometry of deformation sources in both space and time can improve our ability to monitor active volcanoes, widen our understanding of the dynamics of active volcanic systems and improve the predictions of eruptions.
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50

Xu, Feihu, Juntian Ye, Xin Huang, and Zheng-Ping Li. "Compressed sensing for non-line-of-sight imaging." Optics Express, December 21, 2020. http://dx.doi.org/10.1364/oe.413774.

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