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Chaudhry, Aizaz U., i Halim Yanikomeroglu. "Temporary Laser Inter-Satellite Links in Free-Space Optical Satellite Networks". IEEE Open Journal of the Communications Society 3 (2022): 1413–27. http://dx.doi.org/10.1109/ojcoms.2022.3198391.
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Lim, Hyung-Chul, Jong Uk Park, Mansoo Choi, Chul-Sung Choi, Jae-Dong Choi i Jongah Kim. "Performance Analysis of DPSK Optical Communication for LEO-to-Ground Relay Link Via a GEO Satellite". Journal of Astronomy and Space Sciences 37, nr 1 (marzec 2020): 11–18. http://dx.doi.org/10.5140/jass.2020.37.1.11.
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Satellite optical communication has gained significant attention owing to its many quality features (e.g., a larger bandwidth, license free spectrum, higher data rate, and better security) compared to satellite microwave communication. Various experiments have been performed during many space missions to demonstrate and characterize inter-satellite links, downlinks, and uplinks. Korea has also planned to establish an experimental communication system using a geostationary earth orbit (GEO) satellite and the Geochang station as an optical ground station for low Earth orbit (LEO)-to-ground optical relay links. In this study, the performance of inter-satellite communication links and downlinks was investigated for the new Korean experimental communication system in terms of link margin, bit error rate (BER), and channel capacity. In particular, the performance of the inter-satellite links was analyzed based on the receiving apertures and the transmitting power, while that of the downlink was analyzed in terms of atmospheric turbulence conditions and transmitting power. Finally, we discussed two system parameters of receiving aperture and transmitting power to meet the three criteria of link margin, BER, and channel capacity.
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Tiwari, Gayatri. "A Review on Inter-Satellite Links Free Space Optical Communication". Indian Journal of Science and Technology 13, nr 06 (14.02.2020): 712–24. http://dx.doi.org/10.17485/ijst/2020/v13i06/147998.
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Falodun, S. E., J. S. Ojo i O. L. Ojo. "Analysis of visibility effects on free space earth-to-satellite optical link based on measurement data in Nigeria". Nigeria Journal of Pure and Applied Physics 9, nr 1 (21.04.2020): 41–45. http://dx.doi.org/10.4314/njpap.v9i1.8.
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The effect of atmospheric variables on signals propagating from earth to space are of concern in the design and performance of wireless communications systems. Since atmospheric effects which led to atmospheric losses (attenuations, fading and scintillation) are location-dependent, climatological phenomena such as fog, snow, rain, and haze has much effect on Free Space Optical (FSO) and can cause reduction in the link availability. This paper analysed the effect of fog on FSO communication links from earth to satellite links over five selected locations (Ikeja, Akure, Enugu, Jos and Port-Harcourt) in Nigeria. One year (2012) visibility data obtained at Nigeria Meteorological Agency (NIMET) have been used to estimate the specific attenuation caused by fog on FSO communication links in the selected locations. Link margin was deduced in all the five locations. The estimated specific attenuation caused by fog was based on operating frequencies associated with a typical commercial FSO. The result shows that at 352 THz frequency, Ikeja recorded the highest value of about 38.60 dB/km for the specific attenuation due to fog on FSO link followed by Akure with value of about 30.33 dB/km. Enugu recorded the least estimated attenuation of about 14.19 dB/km . The implication of the result is that Ikeja and Akure will suffer more signal loss, while Enugu will suffer less signal loss. Result on link margin performed on FSO link also showed that Ikeja has the highest link margin of -109.79 dB, Port-Harcourt with link margin value of -91.99 dB while Jos experienced lowest link margin of about -37.48 dB.
Keywords: Free space optical systems; Fog induced specific attenuation; Earth-space links; Link margin
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Goncalves Teixeira, Mafalda, Julio Ramirez Molina i Vasco N. G. J. Soares. "Review on Free-Space Optical Communications for Delay and Disruption Tolerant Networks". Electronics 10, nr 13 (5.07.2021): 1607. http://dx.doi.org/10.3390/electronics10131607.
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The increase of data-rates that are provided by free-space optical (FSO) communications is essential in our data-driven society. When used in satellite and interplanetary networks, these optical links can ensure fast connections, yet they are susceptible to atmospheric disruptions and long orbital delays. The Delay and Disruption Tolerant Networking (DTN) architecture ensures a reliable connection between two end nodes, without the need for a direct connection. This can be an asset when used with FSO links, providing protocols that can handle the intermittent nature of the connection. This paper provides a review on the theoretical and state-of-the-art studies on FSO and DTN. The aim of this review is to provide motivation for the research of an optical wireless satellite network, with focus on the use of the Licklider Transmission Protocol. The assessment presented establishes the viability of these networks, providing many examples to rely on, and summarizing the most recent stage of the development of the technologies addressed.
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Viswanath, Anjitha, Pooja Gopal, Virander Kumar Jain i Subrat Kar. "Performance enhancement by aperture averaging in terrestrial and satellite free space optical links". IET Optoelectronics 10, nr 3 (1.06.2016): 111–17. http://dx.doi.org/10.1049/iet-opt.2015.0042.
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He, Wang, Liu, Song, Zhou, Wang, Gao i in. "Shipborne Acquisition, Tracking, and Pointing Experimental Verifications Towards Satellite-to-Sea Laser Communication". Applied Sciences 9, nr 18 (19.09.2019): 3940. http://dx.doi.org/10.3390/app9183940.
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Acquisition, tracking, and pointing (ATP) is a key technology in free space laser communication that has a characteristically high precision. In this paper, we report the acquisition and tracking of low-Earth-orbit satellites using shipborne ATP and verify the feasibility of establishing optical links between laser communication satellites and ships in the future. In particular, we developed a shipborne ATP system for satellite-to-sea applications in laser communications. We also designed an acquisition strategy for satellite-to-sea laser communication. In addition, a method was proposed for improving shipborne ATP pointing error. We tracked some stars at sea, achieving a pointing accuracy of less than 180μrad.We then acquired and tracked some low-Earth-orbit satellites at sea, achieving a tracking accuracy of about 20μrad. The results achieved in this work experimentally demonstrate the feasibility of ATP in satellite-to-sea laser communications.
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Gutiérrez-Montor, M., G. A. Yañez-Casas, C. E. Enríquez-Ortiz i J. J. Hernández-Gómez. "Teletraffic analysis and simulation on FSO systems: the traffic generators approach". Journal of Physics: Conference Series 2475, nr 1 (1.04.2023): 012003. http://dx.doi.org/10.1088/1742-6596/2475/1/012003.
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Abstract Free Space Optical Communications (FSO) has become an interesting topic to researchers in recent years since the amount of data generated by devices is growing, and it is necessary to use data links that support high bandwidth to transmit them from one device to another. This technology is used to establish not only terrestrial links but also space links. A CubeSat satellite is generally deployed in the Low Earth Orbit (LEO) region. To maintain the altitude, the satellite must have a high orbital speed. For that reason, the time to transmit data between a particular ground station and the CubeSat satellite is limited. On the other hand, the volume, mass, and energy storage capacity are restricted in a CubeSat. The greater the bandwidth capacity of radio frequency links, the greater the demand for volume, mass, and energy they require. For that reason, to transmit a significant amount of data, traditional radio frequency links are not suitable and are becoming replaced by FSO as technology improves. Despite research in physical layer technologies on FSO (modulation schemes, error mitigation techniques, pointing and tracking systems), there is very little research in the literature about data link layer protocols for FSO. Secondly, there is little research to measure the data traffic demand on CubeSat satellites so that a certain data link layer protocol can be selected or adapted to be implemented in an FSO system. This paper presents research to address the issue of teletraffic through the use of traffic generators. The result is the design and development of a traffic generator for a discrete event simulator that will later be used to observe the behavior and to measure the performance of the Selective Repeat ARQ protocol in a simulated satellite FSO link, in order to propose improvements to adapt the protocol to this scenario.
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Wang, Jing, i Bernardo A. Huberman. "An Overview on Deployment Strategies for Global Quantum Key Distribution Networks". Wireless Communications and Mobile Computing 2022 (25.04.2022): 1–15. http://dx.doi.org/10.1155/2022/9927255.
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We present a comprehensive literature review and comparative study on the deployment strategies of quantum key distribution (QKD) networks for global coverage. The state-of-the-art deployment strategies, including terrestrial QKD via optical fibers, free-space QKD via ground-based fixed links and ground-to-air dynamic links, and satellite QKD, are reviewed and compared in terms of channel loss, interference, distance limit, connection topology, and deployment cost. Selection criteria and deployment strategies are developed to enable a global coverage of QKD networks from intercontinental, long-haul, metro, to access networks.
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Wang, Jing, i Bernardo A. Huberman. "An Overview on Deployment Strategies for Global Quantum Key Distribution Networks". Wireless Communications and Mobile Computing 2022 (25.04.2022): 1–15. http://dx.doi.org/10.1155/2022/9927255.
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We present a comprehensive literature review and comparative study on the deployment strategies of quantum key distribution (QKD) networks for global coverage. The state-of-the-art deployment strategies, including terrestrial QKD via optical fibers, free-space QKD via ground-based fixed links and ground-to-air dynamic links, and satellite QKD, are reviewed and compared in terms of channel loss, interference, distance limit, connection topology, and deployment cost. Selection criteria and deployment strategies are developed to enable a global coverage of QKD networks from intercontinental, long-haul, metro, to access networks.
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Mihály, András, i László Bacsárdi. "Optical transmittance based store and forward routing in satellite networks". Infocommunications journal 15, nr 2 (2023): 8–13. http://dx.doi.org/10.36244/icj.2023.2.2.
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Quantum computing will play a crucial part in our security infrastructure for the coming years. Quantum networks can consist of direct optical fiber or free-space links. With the use of satellite channels, we can create a quantum network with higher coverage than using optical fibers where the distances are limited due to the properties of the fiber. One of the highest drivers of cost for satellite networks, apart from the cost of the technology needed for such systems, are the costs of launching and maintaining said satellites. By minimizing the satellites needed for a well-functioning quantum network, we can decrease said network’s cost, thus enabling a cheaper quantum internet. In this paper, we present an optical transmittance-based routing algorithm with which it is possible to conduct successful quantum entanglement transfer between terrestrial nodes.
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Zhai, Chao. "Performance of rectangular QAM/FSO communication systems in the anisotropic non-Kolmogorov ground-to-satellite uplink". Journal of Optical Communications and Networking 14, nr 9 (12.08.2022): 713. http://dx.doi.org/10.1364/jocn.456657.
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Quadrature amplitude modulation (QAM) is an exciting technology to accomplish a high communication data rate without increasing the system bandwidth, which can undoubtedly greatly improve the performance of free-space optical (FSO) communication systems. With the increase of experimental and theoretical results about atmospheric turbulence, scientists have confirmed that the anisotropy and non-Kolmogorov property cannot be ignored for atmospheric turbulence. In this paper, utilizing the new anisotropic non-Kolmogorov (ANK) turbulence spectrum models for the satellite links that are applicable to both vertical and slant links, we derive the average bit error rate (BER) expression of rectangular QAM for a Gaussian-beam transmission through the weak ANK ground-to-satellite uplink under the influences of both scintillation and beam wander. Numerical results display that, when the zenith angle is less than a certain angle, the average BER of the ground-to-satellite uplink decays with the enhancement of the anisotropic factor, but while the zenith angle is greater than the certain angle, the contrary trend will occur. Our work will benefit the design optimization of QAM/FSO communication systems in ANK satellite links.
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Velusamy, Gandhimathi, i Ricardo Lent. "Delay-Packet-Loss-Optimized Distributed Routing Using Spiking Neural Network in Delay-Tolerant Networking". Sensors 23, nr 1 (28.12.2022): 310. http://dx.doi.org/10.3390/s23010310.
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Satellite communication is inevitable due to the Internet of Everything and the exponential increase in the usage of smart devices. Satellites have been used in many applications to make human life safe, secure, sophisticated, and more productive. The applications that benefit from satellite communication are Earth observation (EO), military missions, disaster management, and 5G/6G integration, to name a few. These applications rely on the timely and accurate delivery of space data to ground stations. However, the channels between satellites and ground stations suffer attenuation caused by uncertain weather conditions and long delays due to line-of-sight constraints, congestion, and physical distance. Though inter-satellite links (ISLs) and inter-orbital links (IOLs) create multiple paths between satellite nodes, both ISLs and IOLs have the same issues. Some essential applications, such as EO, depend on time-sensitive and error-free data delivery, which needs better throughput connections. It is challenging to route space data to ground stations with better QoS by leveraging the ISLs and IOLs. Routing approaches that use the shortest path to optimize latency may cause packet losses and reduced throughput based on the channel conditions, while routing methods that try to avoid packet losses may end up delivering data with long delays. Existing routing algorithms that use multi-optimization goals tend to use priority-based optimization to optimize either of the metrics. However, critical satellite missions that depend on high-throughput and low-latency data delivery need routing approaches that optimize both metrics concurrently. We used a modified version of Kleinrock’s power metric to reduce delay and packet losses and verified it with experimental evaluations. We used a cognitive space routing approach, which uses a reinforcement-learning-based spiking neural network to implement routing strategies in NASA’s High Rate Delay Tolerant Networking (HDTN) project.
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Velusamy, Gandhimathi, i Ricardo Lent. "Smart Site Diversity for a High Throughput Satellite System with Software-Defined Networking and a Virtual Network Function". Future Internet 12, nr 12 (7.12.2020): 225. http://dx.doi.org/10.3390/fi12120225.
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High Throughput Satellite (HTS) systems aim to push data rates to the order of Terabit/s, making use of Extremely High Frequencies (EHF) or free-space optical (FSO) in the feeder links. However, one challenge that needs to be addressed is that the use of such high frequencies makes the feeder links vulnerable to atmospheric conditions, which can effectively disable channels at times or temporarily increases the bit error rates. One way to cope with the problem is to introduce site diversity and to forward the data through the gateways not affected, or at least less constrained, by adverse conditions. In this paper, a virtual network function (VNF) introduced through reinforcement learning defines a smart routing service for an HTS system. Experiments were conducted on an emulated ground-satellite system in CloudLab, testing a VNF implementation of the approach with software-defined networking virtual switches, which indicate the expected performance of the proposed method.
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Ivanov, Hristo, Frank Marzano, Erich Leitgeb i Pasha Bekhrad. "Testbed Emulator of Satellite-to-Ground FSO Downlink Affected by Atmospheric Seeing Including Scintillations and Clouds". Electronics 11, nr 7 (31.03.2022): 1102. http://dx.doi.org/10.3390/electronics11071102.
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Free Space Optics (FSO) technology enabling next-generation near-Earth communication is prone to severe propagation losses due to atmospheric-turbulence-induced fading and Mie scattering (clouds). As an alternative to the real-time evaluation of the weather effects over optical signal, a state-of-the-art laboratory testbed for verification of slant APD-based (Avalanche Photodiode) FSO links in laboratory conditions is proposed. In particular, a hardware channel emulator representing an FSO channel by means of fiber-coupled Variable Optical Attenuator (VOA) controlled by driver board and software is utilized. While atmospheric scintillation data are generated based on Radiosonde Observation (RAOB) databases combined with a statistical design approach, cloud attenuation is introduced using Mie theory together with empirical Log-Normal modeling. The estimation of atmospheric-turbulence-induced losses within the emulated optical downlink is done with an FSO IM/DD prototype (Intensity Modulation/Direct Detection) relying on two different data throughputs using a transmitter with external and internal modulation. Moreover, the receiver under-test is a high-speed 10 Gbps APD photodetector with integrated Transimpedance Amplifier (TIA) typically installed in OGSs (Optical Ground Stations) for LEO/GEO satellite communication. The overall testbed performance is addressed by a BER tester and a digital oscilloscope, providing BER graphs and eye diagrams that prove the applied approach for testing APD-TIA in the presence of weather-based disruptions. Furthermore, the testbed benefits from the used beam camera that measures the quality of the generated FSO beam.
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Sharma, Priyanka, i Himali Sarangal. "Simulation and Analysis of Filters Using Different Photodiode and Wavelength in Free Space Optics". Asian Journal of Computer Science and Technology 5, nr 1 (5.05.2016): 25–29. http://dx.doi.org/10.51983/ajcst-2016.5.1.1760.
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Free space optics is a technology which uses beam of light to provide optical connection for transmitting and receiving purposes. For the increasing demand for high bandwidth in different network topology, FSO links has been a solution to the connectivity bottleneck problem. Transmitter consists of NRZ modulating CW laser with the link range 1 km in the wavelength 1310 nm or 1550 nm. When the signal is transmitted in the channel, the performance could be severely degrated due to atmospheric attenuation and earth inequalities. The purpose of this paper is to find a suitable filter for any of the two receivers i.e APD and PIN for the reduction of noise. Filters used are low pass Bessel filter, low pass butterworth filter, low pass Chebyshev filter.
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Bas, Joan, i Alexis A. Dowhuszko. "On the Use of NB-IoT over GEO Satellite Systems with Time-Packed Optical Feeder Links for Over-the-Air Firmware/Software Updates of Machine-Type Terminals". Sensors 21, nr 12 (8.06.2021): 3952. http://dx.doi.org/10.3390/s21123952.
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The verticals of 5G, such as the automotive, smart grid, and smart cities sectors, will bring new sensors and IoT devices requiring Internet connectivity. Most of these machine-type terminals will be sparsely distributed, covering a very large geographical area and, from time to time, will have to update their software, firmware, and/or other relevant data. Given this situation, one viable solution to implement the “Over-the-Air” update of these IoT terminals can be done with the aid of GEO satellite systems. However, due to the ultra-dense radio frequency reuse factor that contemporary High-Throughput Satellite (HTS) systems implement in the access link to serve the IoT terminals, the use of a time-packed Free Space Optical (FSO) link represents a practical solution to avoid the bottleneck that the satellite gateway experiences in the feeder link. The performance of both Detect-and-Forward and Decode-and-Forward relaying strategies are studied, assuming that the single-carrier M-PAM symbols that are transmitted on the optical feeder link are mapped into M-QAM symbols that modulate the multiple sub-carriers of the OFDM-based radio access link. In addition, the benefits of encapsulating the NB-IoT frames into DVB-S2(X) satellite frames is also analyzed in detail. The effects of the impairments introduced in both the optical feeder and radio access links are characterized in detail, and the end-to-end error correction capabilities of the Modulation and Coding Schemes (MCS) defined in the contemporary releases of the NB-IoT and DVB-S2(X) standards are studied for different working regimes.
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Raj, A. Arockia Bazil, Prabu Krishnan, Ucuk Darusalam, Georges Kaddoum, Zabih Ghassemlooy, Mojtaba Mansour Abadi, Arun K. Majumdar i Muhammad Ijaz. "A Review–Unguided Optical Communications: Developments, Technology Evolution, and Challenges". Electronics 12, nr 8 (19.04.2023): 1922. http://dx.doi.org/10.3390/electronics12081922.
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This review paper discusses the complete evolution of free-space optical (FSO) communication, also known as unguided optical communication (UOC) technologies, all the way back to ancient man’s fire to today’s machine-learning-supported UOC systems. The principles, significance, and developments that have happened over the past several decades, as well as installation methodologies, technological limitations, and today’s challenges of UOCs are presented. All the subsets of UOC: FSO communication, underwater optical wireless communication (UOWC), and visible light communication (VLC), with their technology/system developments, potential applications, and limitations are reviewed. The state-of-the-art developments/achievements in (i) FSO channel effects and their mitigation techniques; (ii) radio-over-FSO techniques; (iii) wavelength division multiplexing and sub-carrier multiplexing techniques; (iv) FSO for worldwide interoperability for microwave access applications; (v) space optical satellite communication (SOSC); (vi) UWOC; (vii) photoacoustic communication (PAC); (viii) light-fidelity; (ix) VLC; (x) vehicular VLC (V2LC); and (xi) optical camera communication are reviewed. In addition, the current developments on emerging technologies such as artificial intelligence (to improve the performance of UOC systems), energy harvesting (for the effective utilization of UOC channels), and near-future communication network scenarios (mandatory for secured broadband digital links) are covered. Finally, in brief, to achieve the full potential of UOC systems, challenges that require immediate research attention are summarized.
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Kapsis, Theodore T., i Athanasios D. Panagopoulos. "Power Allocation for Reliable and Energy-Efficient Optical LEO-to-Ground Downlinks with Hybrid ARQ Schemes". Photonics 9, nr 2 (4.02.2022): 92. http://dx.doi.org/10.3390/photonics9020092.
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Satellites in low earth orbit (LEO) are currently being deployed for numerous communication, positioning, space and Earth-imaging missions. To provide higher data rates in direct-to-user links and earth observation downlinks, the free-space optics technology can be employed for LEO-to-ground downlinks. Moreover, the hybrid automatic repeat request (HARQ) can be adopted since the propagation latency is low for LEO satellites. In this work, a power allocation methodology is proposed for optical LEO-to-ground downlinks under weak turbulence employing HARQ retransmission schemes. Specifically, the average power consumption is minimized given a maximum transmitted power constraint and a target outage probability threshold to ensure energy efficiency and reliability, respectively. The optimization problem is formulated as a constrained nonlinear programming problem and solved for Type I HARQ, chase combining (CC) and incremental redundancy (IR) schemes. The solutions are derived numerically via iterative algorithms, namely interior-point (IP) and sequential quadratic programming (SQP), and validated through an exhaustive (brute-force) search. The numerical simulations provide insight into the performance of the retransmission schemes regarding average power. More specifically, Type I HARQ has the worst output, CC has a moderate one, and IR exhibits the best performance. Finally, the IP algorithm is a slower but more accurate solver, and SQP is faster but slightly less accurate.
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Tan, Zhenkun, Jiao Wang, Yingxiu Kong, Sichen Lei i Pengfei Wu. "An Effective Method for Enhancing Heterodyne Efficiency by Comparing the Effect of Degree of Polarization on an Uplink Path and a Downlink Path". Photonics 9, nr 11 (25.10.2022): 798. http://dx.doi.org/10.3390/photonics9110798.
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By analyzing the effect of the degree of polarization (DoP) of the partially coherent Gaussian Schell-model (GSM) beam on a heterodyne system of an uplink path and a downlink path, we developed an innovative and noteworthy theory according to which σsy (signal beam waist radius in the y direction component) and δSyy (coherence length of the signal beam in the yy direction component) had a more significant impact on heterodyne efficiency and DoP than the turbulence term on uplink and downlink paths. Namely, the DoP and heterodyne efficiency of an uplink path are higher than that of a downlink path when σsy > 0.02 m or δSyy ≥ 0.03 m. This innovative rule provides an efficient way for increasing the heterodyne efficiency of a signal beam propagating along an uplink or a downlink path channel in satellite-ground communication links in free-space optical heterodyne detection communication.
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Pandžic, M., D. Mihajlovic, J. Pandžic i N. Pfeifer. "ASSESSMENT OF THE GEOMETRIC QUALITY OF SENTINEL-2 DATA". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B1 (3.06.2016): 489–94. http://dx.doi.org/10.5194/isprsarchives-xli-b1-489-2016.
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High resolution (10 m and 20 m) optical imagery satellite Sentinel-2 brings a new perspective to Earth observation. Its frequent revisit time enables monitoring the Earth surface with high reliability. Since Sentinel-2 data is provided free of charge by the European Space Agency, its mass use for variety of purposes is expected. Quality evaluation of Sentinel-2 data is thus necessary. Quality analysis in this experiment is based on comparison of Sentinel-2 imagery with reference data (orthophoto). From the possible set of features to compare (point features, texture lines, objects, etc.) line segments were chosen because visual analysis suggested that scale differences matter least for these features. The experiment was thus designed to compare long line segments (e.g. airstrips, roads, etc.) in both datasets as the most representative entities. Edge detection was applied to both images and corresponding edges were manually selected. The statistical parameter which describes the geometrical relation between different images (and between datasets in general) covering the same area is calculated as the distance between corresponding curves in two datasets. The experiment was conducted for two different test sites, Austria and Serbia. From 21 lines with a total length of ca. 120 km the average offset of 6.031 m (0.60 pixel of Sentinel-2) was obtained for Austria, whereas for Serbia the average offset of 12.720 m (1.27 pixel of Sentinel-2) was obtained out of 10 lines with a total length of ca. 38 km.
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Pandžic, M., D. Mihajlovic, J. Pandžic i N. Pfeifer. "ASSESSMENT OF THE GEOMETRIC QUALITY OF SENTINEL-2 DATA". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B1 (3.06.2016): 489–94. http://dx.doi.org/10.5194/isprs-archives-xli-b1-489-2016.
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High resolution (10 m and 20 m) optical imagery satellite Sentinel-2 brings a new perspective to Earth observation. Its frequent revisit time enables monitoring the Earth surface with high reliability. Since Sentinel-2 data is provided free of charge by the European Space Agency, its mass use for variety of purposes is expected. Quality evaluation of Sentinel-2 data is thus necessary. Quality analysis in this experiment is based on comparison of Sentinel-2 imagery with reference data (orthophoto). From the possible set of features to compare (point features, texture lines, objects, etc.) line segments were chosen because visual analysis suggested that scale differences matter least for these features. The experiment was thus designed to compare long line segments (e.g. airstrips, roads, etc.) in both datasets as the most representative entities. Edge detection was applied to both images and corresponding edges were manually selected. The statistical parameter which describes the geometrical relation between different images (and between datasets in general) covering the same area is calculated as the distance between corresponding curves in two datasets. The experiment was conducted for two different test sites, Austria and Serbia. From 21 lines with a total length of ca. 120 km the average offset of 6.031 m (0.60 pixel of Sentinel-2) was obtained for Austria, whereas for Serbia the average offset of 12.720 m (1.27 pixel of Sentinel-2) was obtained out of 10 lines with a total length of ca. 38 km.
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Khaleel, Ahmed Ismael, i Shelan Khasro Tawfeeq. "Key rate estimation of measurement-device-independent quantum key distribution protocol in satellite-earth and intersatellite links". International Journal of Quantum Information 16, nr 03 (kwiecień 2018): 1850027. http://dx.doi.org/10.1142/s0219749918500272.
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In this work, an estimation of the key rate of measurement-device-independent quantum key distribution (MDI-QKD) protocol in free space was performed. The examined free space links included satellite-earth downlink, uplink and intersatellite link. Various attenuation effects were considered such as diffraction, atmosphere, turbulence and the efficiency of the detection system. Two cases were tested: asymptotic case with infinite number of decoy states and one-decoy state case. The estimated key rate showed the possibility of applying MDI-QKD in earth-satellite and intersatellite links, offering longer single link distance to be covered.
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Shehata, Mohamed I., M. Asmaa Zaki, Heba A. Fayed, Ahmed Abd El Aziz i Moustafa H. Aly. "Optical Inter-Satellite Link over Low Earth Orbit: Enhanced Performance". Journal of Physics: Conference Series 2128, nr 1 (1.12.2021): 012001. http://dx.doi.org/10.1088/1742-6596/2128/1/012001.
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Abstract Space communication systems are traditionally operated with microwave in satellite-to-satellite links. Now, more efficient and reliable operation is required, which lead to use optical links for Inter Satellite Links (ISLs). This paper investigates the system performance of an optical ISL proposed between satellites over Low Earth Orbit (LEO). In this study, the proposed link is simulated to obtain a maximum bit rate and minimum bit error rate (BER) over different links distances. The system performance is improved by investigating its dependency on the photo detector type, operating wavelength, transmitted optical power, RZ and NRZ schemes. Our work results that best Q- factor are approximately 40 leading to a minimum BER for the LEO orbit, at 600 km when utilizing an APD. While at our investigation of the system performance at visible light bands, it is found that Q-factor will be approximately 60 achieving minimum BER with neglecting the eye-safety precautions in addition to the ability to transmit 2 Gbps at 10−9 BER within many bands.
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Farkasvölgyi, Andrea, i István Frigyes. "Optical transfer in space communication". Infocommunications journal, nr 3 (2018): 9–13. http://dx.doi.org/10.36244/icj.2018.3.2.
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This paper presents the possibilities of Free-space optical connection (FSO) in space communication in case of satellite-to-spacecraft or satellite-to-satellite link. It summerizes the advantages and disadvantages of optical transmissions in case of near-earth and deep space region. We present the most significant problems during FSO link application and introduce some techniques to eliminate the drawbacks. In this paper, we introduce the use of multi-channel FSO system, which is the most appropriate in order to maximize channel parameters with minimizing the transmission error. It compares available maximum channel parameters of near future space missions. Under special conditions in satellite-earth connection, the usage of the optical link may become very uncertain, because of the strong turbulent medium. We describe conditions under which the optical link can be applied in satellite communication and when it is necessary to effectively modify the optical connection, This article discusses the application of multichannel or more precise diversity systems, which we recommend for space communication.
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Marz, Stefan, Anja Schlicht i Urs Hugentobler. "Toward a Geodesy and Time Reference in Space (GETRIS): A Study of Apparent Satellite Clocks of a Future GNSS Satellite Constellation". Geosciences 13, nr 6 (8.06.2023): 173. http://dx.doi.org/10.3390/geosciences13060173.
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Today, concepts within the Global Geodetic Observing System (GGOS) aim a Terrestrial Reference System (TRS) with 1 mm accuracy and long-term stability of 0.1 mm/year. GETRIS (Geodesy and Time Reference In Space) is a concept that aims to realize a relativistic reference system based on satellites as an extension to the TRS. This helps with another goal of the GGOS, namely, the connection of different satellite layers with the TRS. For a valuable contribution to the GGOS’s goals, we would expect to achieve precise determined satellite orbits at the level of 1–3 mm and satellite clocks with a picosecond accuracy. The use of increasingly precise links helps to improve the satellite precise orbit determination (POD) and is necessary to synchronize the clocks in the satellite/station network. We analyze a complementary use of high-precision optical dual one-way links at the level of 1 mm precision together with the L-band. In previous studies, we analyzed the benefit for satellite POD, achieving Medium Earth Orbit (MEO) as well as geosynchronous orbit (GSO) accuracies at the low-millimeter level. In this work, we analyze the capabilities for clock synchronization. We compare two different clock types for estimation and prediction. We analyze different satellite constellations and different combinations of measurement links.
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Aida M.Nor, Norhanis, Md Rafiqul Islam, Wajdi Al-Khateeb i Suriza A.Z. "Atmospheric Effects on Free Space Earth-to-Satellite Optical Link in Tropical Climate". International Journal of Computer Science, Engineering and Applications 3, nr 1 (28.02.2013): 17–36. http://dx.doi.org/10.5121/ijcsea.2013.3102.
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Matricciani, Emilio. "Geocentric Spherical Surfaces Emulating the Geostationary Orbit at Any Latitude with Zenith Links". Future Internet 12, nr 1 (18.01.2020): 16. http://dx.doi.org/10.3390/fi12010016.
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According to altitude, the orbits of satellites constellations can be divided into geostationary Earth orbit (GEO), medium Earth orbit (MEO), and low Earth orbit (LEO) constellations. We propose to use a Walker star constellation with polar orbits, at any altitude, to emulate the geostationary orbit with zenith paths at any latitude. Any transmitter/receiver will be linked to a satellite as if the site were at the equator and the satellite at the local zenith. This constellation design can have most of the advantages of the current GEO, MEO, and LEO constellations, without having most of their drawbacks. Doppler phenomena are largely minimized because the connected satellite is always seen almost at the local zenith. The extra free-space loss, due to the fixed pointing of all antennas, is at most 6 dBs when the satellite enters or leaves the service area. The connections among satellites are easy because the positions in the orbital plane and in adjacent planes are constant, although with variable distances. No steering antennas are required. The tropospheric propagation fading and scintillations are minimized. Our aim is to put forth the theoretical ideas about this design, to which we refer to as the geostationary surface (GeoSurf) constellation.
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Palkin, M. V. "Satellite Formation Flying Control Using Image Processing". Mekhatronika, Avtomatizatsiya, Upravlenie 20, nr 1 (15.01.2019): 52–58. http://dx.doi.org/10.17587/mau.20.52-58.
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A problem of a formation flying control is observed. As an example a concept of a multysatellite configuration ("space commercial") is described. Space advertisement is realized by groups of specialized free flying and cable-connected satellites, and their combinations. Construction of a space commercial satellite and a set of a control system equipment is presented. Several methods for group configuration are presented: periodic impulse correction of each flying satellite position formation; method of a satellite positioning on nocoplanar orbits. Other methods include combinations of methods mentioned above. Configuration control using onboard video camera with a wide-angle image detector is presented. Characteristics of an optical system are shown. Navigation parameters of a using a received observed videoimage are estimated. A method of a relative position measurement is described. The method detects a video track of a moving ahead satellite on the matrix detector. According to the method lines of the matrix detector are positioned transversely and columns are positioned in parallel with vertical axis of the orbital coordinate system. Course of the slave satellite is proportional to the travel of the centre of the lider satellite mark on the matrix detector columns. Pitch of the slave satellite is proportional to the travel of the centre of the leader satellite mark on the matrix detector lines. A video-display processing algorithm is developed and researched. The algorithm contains procedures of a forming, localization of the leader satellite mark, deviation angle calculation. The algorithm uses structural method, detecting bright spots (image syntactic characteristics). Efficiency of the algorithm depends on the leader satellite mark brightness, size, light-striking, distance.
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Chaudhary, Sushank, Lunchakorn Wuttisittikulkij, Jamel Nebhen, Abhishek Sharma, Demostenes Zegarra Rodriguez i Santosh Kumar. "Terabyte capacity-enabled (10 x 400 Gbps) Is-OWC system for long-haul communication by incorporating dual polarization quadrature phase shift key and mode division multiplexing scheme". PLOS ONE 17, nr 3 (10.03.2022): e0265044. http://dx.doi.org/10.1371/journal.pone.0265044.
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Inter-satellite optical wireless communication (Is-OWC) links can become promising solutions to realize the next-generation high-speed communication services. The operation of Global Navigation Satellite Systems can be improved with the use of Is-OWC links through ranging and communication services. However, the key challenge in Inter-satellite link (ISL) is its effective range which is limited due to pointing errors. In this work, we propose to develop a high-capacity and long-reach Is-OWC link by incorporating hybrid mode division multiplexing (MDM) and wavelength division multiplexing (WDM) schemes to transmit ten independent channels over 40000kms Is-OWC link. Each channel is capable of carrying 400Gbps data which is encoded by the dual polarization quadrature phase shift key technique with required signal to noise ratio (SNR) and received power. The proposed Is-OWC link satisfies the enhanced communication within Geostationary Earth Orbit (GEO) and Low Earth Orbit (LEO) satellites. The proposed Is-OWC is further evaluated under the impact of space turbulences, particularly transmitter and receiver pointing errors. The result reported that the proposed Is-OWC link can transmit 4Tbps data over 16000kms with the transmitter pointing error of 2μrad and receiver pointing error of 1μrad.
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Marbel, Revital, Boaz Ben-Moshe i Tal Grinshpoun. "Pico-Sat to Ground Control: Optimizing Download Link via Laser Communication". Remote Sensing 14, nr 15 (22.07.2022): 3514. http://dx.doi.org/10.3390/rs14153514.
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Consider a constellation of over a hundred low Earth orbit satellites that aim to capture every point on Earth at least once a day. Clearly, there is a need to download from each satellite a large set of high-quality images on a daily basis. In this paper, we present a laser communication (lasercom) framework that stands as an alternative solution to existing radio-frequency means of satellite communication. By using lasercom, the suggested solution requires no frequency licensing and therefore allows such satellites to communicate with any optical ground station on Earth. Naturally, in order to allow laser communication from a low Earth orbit satellite to a ground station, accurate aiming and tracking are required. This paper presents a free-space optical communication system designed for a set of ground stations and nano-satellites. A related scheduling model is presented, for optimizing the communication between a ground station and a set of lasercom satellites. Finally, we report on SATLLA-2B, the first 300 g pico-satellite with basic free-space optics capabilities, that was launched on January 2022. We conjecture that the true potential of the presented network can be obtained by using a swarm of few hundreds of such lasercom pico-satellites, which can serve as a global communication infrastructure using existing telescope-based observatories as ground stations.
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Yan, Zhizhong, Evan Meyer-Scott, Jean-Philippe Bourgoin, Brendon L. Higgins, Nikolay Gigov, Allison MacDonald, Hannes Hubel i Thomas Jennewein. "Novel High-Speed Polarization Source for Decoy-State BB84 Quantum Key Distribution Over Free Space and Satellite Links". Journal of Lightwave Technology 31, nr 9 (maj 2013): 1399–408. http://dx.doi.org/10.1109/jlt.2013.2249040.
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Lim, Hyung-Chul, Chul-Sung Choi, Ki-Pyoung Sung, Jong-Uk Park i Mansoo Choi. "Centroid Error Analysis of Beacon Tracking under Atmospheric Turbulence for Optical Communication Links". Remote Sensing 13, nr 10 (15.05.2021): 1931. http://dx.doi.org/10.3390/rs13101931.
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Optical satellite communication has received considerable attention as a promising alternative to radio frequency communication because of its potential advantages including higher data rates and license free spectrum. Many studies have conducted performance analyses of optical communication channels, but few have investigated beacon tracking channels under atmospheric turbulence. The centroid accuracy of beacon tracking channels is limited by not only noise sources, but also a finite delay time, which also fluctuates due to atmospheric turbulence. Consequently, the centroid error is an important figure of merit when evaluating the performance of a beacon tracking system. In this study, the closed-form expressions were derived for average centroid error and fade probability, based on received photoelectron counts depending on exposure time, taking into account the log-normal tracking channels. We analyzed the angular positioning performance of beacon tracking detectors onboard small satellites in the presence of atmospheric turbulence, in terms of centroid error and fade probability. We found that an optimal exposure time exists, which minimizes the centroid error, and that fade probability is inversely proportional to the exposure time. These are significant properties to consider in the design of beacon tracking systems.
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Jacobsen, K. "SYSTEMATIC GEOMETRIC IMAGE ERRORS OF VERY HIGH RESOLUTION OPTICAL SATELLITES". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-1 (26.09.2018): 233–38. http://dx.doi.org/10.5194/isprs-archives-xlii-1-233-2018.
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<p><strong>Abstract.</strong> Very high resolution optical satellites are imaging the object space by a combination of CCD-lines in one direction and by time, speed and satellite rotation in the other direction. The combination of the CCD-lines usually is known by pre-calibration. Remaining errors of the pre-calibration, also slightly depending upon the satellite movement and rotation, with few exceptions are usually small up to negligible. This may not be the case for the image component in the scan direction and the alignment of the line combinations - they are controlled by giros and stellar cameras. Stellar cameras are compensating giro drifts, but their recording frequency is limited as well as in general the accuracy of the satellite view direction. In addition the satellites may show a jitter caused by the fast rotation from one pointed area to another. Not all giros are able to record the jitter frequency. A limited accuracy of the view direction is causing systematic image errors in relation to the used mathematical model of geometric reconstruction.</p><p> The systematic image errors can be determined theoretically by image orientation based on ground control points (GCPs), but usually not a satisfying number and distribution of GCPs is available. Another possibility is the analysis of the intersection of corresponding rays in a stereo model and an analysis of generated height models against reference height models. Here also free of charge available height models as the SRTM Digital Surface Model (DSM) or AW3D30 can be used. Several very high resolution satellite cameras have been analyzed; this includes images from WorldView-2, WorldView-4, Kompsat-3, Kompsat-1, Pleiades, Cartosat-1, ZY3, OrbView-3, QuickBird, IKONOS, ASTER, IRS-1C, SPOT, SPOT-5 HRS, EROS-B, IKONOS, QuickBird, OrbView and GeoEye but only results of the today more important satellites are shown in detail. For few satellites the systematic image errors can be ignored, but others require a correction which may be just a levelling of the DSM but also a higher degree of deformation up to a compensation of the satellite jitter effect.</p><p> The used method cannot be named as calibration due to variation from image to image, only the character and size of deformation is typical for the used special optical satellite, but it depends also upon the operating conditions as fast satellite rotation. Due to the very high number of reference points in a DSM the determination of systematic image errors is independent upon random errors and also high frequent jitter can be determined with a standard deviation down to 0.1 ground sampling distance (GSD) or even better.</p>
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Isabona, Joseph, Agbotiname Lucky Imoize, Stephen Ojo, Cheng-Chi Lee i Chun-Ta Li. "Atmospheric Propagation Modelling for Terrestrial Radio Frequency Communication Links in a Tropical Wet and Dry Savanna Climate". Information 13, nr 3 (7.03.2022): 141. http://dx.doi.org/10.3390/info13030141.
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Atmospheric impairment-induced attenuation is the prominent source of signal degradation in radio wave communication channels. The computation-based modeling of radio wave attenuation over the atmosphere is the stepwise application of relevant radio propagation models, data, and procedures to effectively and prognostically estimate the losses of the propagated radio signals that have been induced by atmospheric constituents. This contribution aims to perform a detailed prognostic evaluation of radio wave propagation attenuation due to rain, free space, gases, and cloud over the atmosphere at the ultra-high frequency band. This aim has been achieved by employing relevant empirical atmospheric data and suitable propagation models for robust prognostic modeling using experimental measurements. Additionally, the extrapolative attenuation estimation results and the performance analysis were accomplished by engaging different stepwise propagation models and computation parameters often utilized in Earth–satellite and terrestrial communications. Results indicate that steady attenuation loss levels rise with increasing signal carrier frequency where free space is more dominant. The attenuation levels attained due to rain, cloud, atmospheric gases, and free space are also dependent on droplet depths, sizes, composition, and statistical distribution. While moderate and heavy rain depths achieved 3 dB and 4 dB attenuations, the attenuation due to light rainfall attained a 2.5 dB level. The results also revealed that attenuation intensity levels induced by atmospheric gases and cloud effects are less than that of rain. The prognostic-based empirical attenuation modeling results can provide first-hand information to radio transmission engineers on link budgets concerning various atmospheric impairment effects during radio frequency network design, deployment, and management, essentially at the ultra-high frequency band.
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Tottrup, Christian, Daniel Druce, Rasmus Probst Meyer, Mads Christensen, Michael Riffler, Bjoern Dulleck, Philipp Rastner i in. "Surface Water Dynamics from Space: A Round Robin Intercomparison of Using Optical and SAR High-Resolution Satellite Observations for Regional Surface Water Detection". Remote Sensing 14, nr 10 (17.05.2022): 2410. http://dx.doi.org/10.3390/rs14102410.
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Climate change, increasing population and changes in land use are all rapidly driving the need to be able to better understand surface water dynamics. The targets set by the United Nations under Sustainable Development Goal 6 in relation to freshwater ecosystems also make accurate surface water monitoring increasingly vital. However, the last decades have seen a steady decline in in situ hydrological monitoring and the availability of the growing volume of environmental data from free and open satellite systems is increasingly being recognized as an essential tool for largescale monitoring of water resources. The scientific literature holds many promising studies on satellite-based surface-water mapping, but a systematic evaluation has been lacking. Therefore, a round robin exercise was organized to conduct an intercomparison of 14 different satellite-based approaches for monitoring inland surface dynamics with Sentinel-1, Sentinel-2, and Landsat 8 imagery. The objective was to achieve a better understanding of the pros and cons of different sensors and models for surface water detection and monitoring. Results indicate that, while using a single sensor approach (applying either optical or radar satellite data) can provide comprehensive results for very specific localities, a dual sensor approach (combining data from both optical and radar satellites) is the most effective way to undertake largescale national and regional surface water mapping across bioclimatic gradients.
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Lazzaro, Riccardo, i Carlo Bettanini. "Evaluation of Satellite’s Point-Ahead Angle Derived from TLE for Laser Communication". Aerotecnica Missili & Spazio 101, nr 1 (2.02.2022): 7–15. http://dx.doi.org/10.1007/s42496-022-00106-9.
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AbstractAdvances in lasers, optics and electronics for Satellite’s optical communication are opening the possibility of very high performance near Earth space links with data rate up to several Gbps. Being the divergence of the laser beam typically of tens of $$\mu$$ μ rad, an extremely high precision pointing is needed to correctly establish and maintain data optical link. In particular, the relative motion between the satellite and the ground station shall be accurately evaluated to estimate how to correct pointing angles for future orbital locations. This correction is made via a point-ahead mirror (PAM) mechanism, which deviates the laser beam by an angle called point-ahead angle (PAA). The purpose of this paper is evaluate the possibility of accurately estimate the point-ahead angle in advance using the two-line elements sets for the orbiting satellite, which are available before the ground station overpass. The study evaluated TLE-based orbital evolution of Sentinel-6 satellite, comparing the results with the high precision data obtained by laser ranging from the crustal dynamics data information system (CDDIS). The maximum error observed between the estimated and measured point-ahead angles was less than 1$$\mu$$ μ rad, demonstrating the possibility of this point-ahead correction technique for LEO orbiting satellites.
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Yamamoto, Norimasa, Takako Kato i Frank B. Rosmej. "Opacity free and space resolved X-ray diagnostics based on satellite lines near H-like Lyα of highly charged ions". Journal of Quantitative Spectroscopy and Radiative Transfer 96, nr 3-4 (grudzień 2005): 343–61. http://dx.doi.org/10.1016/j.jqsrt.2004.12.027.
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Trinh, Le Hung, i Van Phu Le. "Application of Sentinel 1 imagery data to detect and classify oil spills on the ocean". Petrovietnam Journal 2 (21.03.2022): 32–38. http://dx.doi.org/10.47800/pvj.2022.02-05.
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Sentinel is the name of a series of Earth observation missions (from Sentinel 1 to Sentinel 6) developed by the Copernicus initiative and operated by the European Space Agency (ESA). Sentinel satellite image data, which includes optical and radar images, provided completely free of charge, has been widely and effectively used in Earth research. The paper presents a technical solution using Sentinel 1 satellite image in detecting and monitoring oil spill pollution at sea, testing for Mauritius sea area. The Otsu automatic thresholding method was applied to extract oil spills at sea from Sentinel 1A radar images. The processing was done on the Google Earth Engine (GEE) cloud computing platform. The results of the study contribute to improving the efficiency of the application of radar remote sensing data in early detection and classification of oil spills, supporting the response to oil spill pollution at sea.
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Strozzi, T., A. Wiesmann, A. Kääb, S. Joshi i P. Mool. "Glacial lake mapping with very high resolution satellite SAR data". Natural Hazards and Earth System Sciences 12, nr 8 (7.08.2012): 2487–98. http://dx.doi.org/10.5194/nhess-12-2487-2012.
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Abstract. Floods resulting from the outbursts of glacial lakes are among the most far-reaching disasters in high mountain regions. Glacial lakes are typically located in remote areas and space-borne remote sensing data are an important source of information about the occurrence and development of such lakes. Here we show that very high resolution satellite Synthetic Aperture Radar (SAR) data can be employed for reliably mapping glacial lakes. Results in the Alps, Pamir and Himalaya using TerraSAR-X and Radarsat-2 data are discussed in comparison to in-situ information, and high-resolution satellite optical and radar imagery. The performance of the satellite SAR data is best during the snow- and ice-free season. In the broader perspective of hazard management, the detection of glacial lakes and the monitoring of their changes from very high-resolution satellite SAR intensity images contributes to the initial assessment of hazards related to glacial lakes, but a more integrated, multi-level approach needs also to include other relevant information such as glacier outlines and outline changes or the identification of unstable slopes above the lake and the surrounding area, information types to which SAR analysis techniques can also contribute.
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Ashrafi, M., M. J. Kosch i F. Honary. "Comparison of the characteristic energy of precipitating electrons derived from ground-based and DMSP satellite data". Annales Geophysicae 23, nr 1 (31.01.2005): 135–45. http://dx.doi.org/10.5194/angeo-23-135-2005.
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Abstract. Energy maps are important for ionosphere-magnetosphere coupling studies, because quantitative determination of field-aligned currents requires knowledge of the conductances and their spatial gradients. By combining imaging riometer absorption and all-sky auroral optical data it is possible to produce high temporal and spatial resolution maps of the Maxwellian characteristic energy of precipitating electrons within a 240240 common field of view. These data have been calibrated by inverting EISCAT electron density profiles into equivalent energy spectra. In this paper energy maps produced by ground-based instruments (optical and riometer) are compared with DMSP satellite data during geomagnetic conjunctions. For the period 1995-2002, twelve satellite passes over the ground-based instruments' field of view for the cloud-free conditions have been considered. Four of the satellite conjunctions occurred during moderate geomagnetic, steady-state conditions and without any ion precipitation. In these cases with Maxwellian satellite spectra, there is 71% agreement between the characteristic energies derived from the satellite and the ground-based energy map method.
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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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Kent, G. S., M. P. McCormick i S. K. Schaffner. "Global optical climatology of the free tropospheric aerosol from 1.0-μm satellite occultation measurements". Journal of Geophysical Research 96, nr D3 (1991): 5249. http://dx.doi.org/10.1029/89jd03458.
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Gamon, J. A. "Optical sampling of the flux tower footprint". Biogeosciences Discussions 12, nr 6 (30.03.2015): 4973–5014. http://dx.doi.org/10.5194/bgd-12-4973-2015.
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Abstract. The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over two decades of proximal remote sensing at flux tower sites are reviewed. An organizing framework is the light-use efficiency (LUE) model, both because it is widely used, and because it provides a useful theoretical construct for integrating optical remote sensing with flux measurements. Multiple ways of driving this model, ranging from meteorological measurements to remote sensing, have emerged in recent years, making it a convenient conceptual framework for comparative experimental studies. New interpretations of established optical sampling methods, including the Photochemical Reflectance Index (PRI) and Solar-Induced Fluorescence (SIF), are discussed within the context of the LUE model. Multi-scale analysis across temporal and spatial axes is a central theme, because such scaling can provide links between ecophysiological mechanisms detectable at the level of individual organisms and broad patterns emerging at larger scales, enabling evaluation of emergent properties and extrapolation to the flux footprint and beyond. Proper analysis of sampling scale requires an awareness of sampling context that is often essential to the proper interpretation of optical signals. Additionally, the concept of optical types, vegetation exhibiting contrasting optical behavior in time and space, is explored as a way to frame our understanding of the controls on surface–atmosphere fluxes. Complementary NDVI and PRI patterns across ecosystems are offered as an example of this hypothesis, with the LUE model and light-response curve providing an integrating framework. We conclude that experimental approaches allowing systematic exploration of plant optical behavior in the context of the flux tower network provides a unique way to improve our understanding of environmental constraints and ecophysiological function. In addition to an enhanced mechanistic understanding of ecosystem processes, this integration of remote sensing with flux measurements offers many rich opportunities for upscaling, satellite validation, and informing practical management objectives ranging form assessing ecosystem health and productivity to quantifying biospheric carbon sequestration.
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Ashby, Neil, Peter L. Bender, John L. Hall, Jun Ye, Scott A. Diddams, Steven R. Jefferts, Nathan Newbury i in. "Measurement of gravitational time delay using drag-free spacecraft and an optical clock". Proceedings of the International Astronomical Union 5, S261 (kwiecień 2009): 414–19. http://dx.doi.org/10.1017/s1743921309990718.
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AbstractImproved accuracy in measurement of the gravitational time delay of electromagnetic waves passing by the sun may be achieved with two drag-free spacecraft, one with a stable clock and laser transmitter and one with a high-stability transponder. We consider one spacecraft near the Earth-Sun L1 point with an advanced optical clock, and the transponder on a second satellite, which has a 2 year period orbit and eccentricity e = 0.37. Superior conjunctions will occur at aphelion 1, 3, and 5 years after launch of the second spacecraft. The measurements can be made using carrier phase comparisons on the laser beam that would be sent to the distant spacecraft and then transponded back. Recent development of clocks based on optical transitions in cooled and trapped ions or atoms indicate that a noise spectral amplitude of about 5 × 10−15/ at frequencies down to at least 1 microhertz can be achieved in space-borne clocks. An attractive candidate is a clock based on a single laser-cooled Yb+ trapped ion. Both spacecraft can be drag-free at a level of 1×10−13m/s2/ at frequencies down to at least 1 microhertz. The corresponding requirement for the LISA gravitational wave mission is 3 × 10−15m/s2/ at frequencies down to 10−4 Hz, and Gravitational Reference Sensors have been developed to meet this goal. They will be tested in the LISA Pathfinder mission, planned by ESA for flight in 2011. The requirements to extend the performance to longer times are mainly thermal. The achievable accuracy for determining the PPN parameter γ is about 1 × 10−8.
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Gamon, J. A. "Reviews and Syntheses: optical sampling of the flux tower footprint". Biogeosciences 12, nr 14 (30.07.2015): 4509–23. http://dx.doi.org/10.5194/bg-12-4509-2015.
Pełny tekst źródłaStreszczenie:
Abstract. The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over 2 decades of proximal remote sensing at flux tower sites are reviewed. The organizing framework used here is the light-use efficiency (LUE) model, both because it is widely used, and because it provides a useful theoretical construct for integrating optical remote sensing with flux measurements. Multiple ways of driving this model, ranging from meteorological measurements to remote sensing, have emerged in recent years, making it a convenient conceptual framework for comparative experimental studies. New interpretations of established optical sampling methods, including the photochemical reflectance index (PRI) and solar-induced chlorophyll fluorescence (SIF), are discussed within the context of the LUE model. Multi-scale analysis across temporal and spatial axes is a central theme because such scaling can provide links between ecophysiological mechanisms detectable at the level of individual organisms and broad patterns emerging at larger scales, enabling evaluation of emergent properties and extrapolation to the flux footprint and beyond. Proper analysis of the sampling scale requires an awareness of sampling context that is often essential to the proper interpretation of optical signals. Additionally, the concept of optical types, vegetation exhibiting contrasting optical behavior in time and space, is explored as a way to frame our understanding of the controls on surface–atmosphere fluxes. Complementary normalized difference vegetation index (NDVI) and PRI patterns across ecosystems are offered as an example of this hypothesis, with the LUE model and light-response curve providing an integrating framework. I conclude that experimental approaches allowing systematic exploration of plant optical behavior in the context of the flux tower network provides a unique way to improve our understanding of environmental constraints and ecophysiological function. In addition to an enhanced mechanistic understanding of ecosystem processes, this integration of remote sensing with flux measurements offers many rich opportunities for upscaling, satellite validation, and informing practical management objectives ranging from assessing ecosystem health and productivity to quantifying biospheric carbon sequestration.
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Pehani, Peter, Tatjana Veljanovski, Žiga Kokalj i Krištof Oštir. "Six years of Sentinel-2 archive of Slovenia". Geodetski vestnik 66, nr 02 (czerwiec 2022): 220–57. http://dx.doi.org/10.15292/geodetski-vestnik.2022.02.220-257.
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The Sentinel-2 is a high resolution optical satellite mission, developed by the European Space Agency (ESA) for the European Commission. Currently the mission has two satellites in orbit: Sentinel-2A from 23rd June 2015, and Sentinel-2B from 7th March 2017. Revisit time for this twin constellation is five days. The twin satellites represent a very stable data source, but for the first six operational months (i.e. the second half of the 2015). From the very start of the mission, the Research Centre of the Slovenian Academy of Sciences and Arts (ZRC SAZU) is collecting its own archive of Sentinel-2 data for the extent of the Republic of Slovenia. The data is saved in its original processing state (Level-1C) and in four levels of processing. The archive has now been operating for six full years, which is a good milestone for a statistical overview. We analyse the archive of Sentinel-2 data of Slovenia from several aspects at the country level. A special focus is placed on cloud cover, as only cloud-free data can give an impression of the actual spatial and temporal usability of optical data.
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Hüsler, F., T. Jonas, M. Riffler, J. P. Musial i S. Wunderle. "A satellite-based snow cover climatology (1985–2011) for the European Alps derived from AVHRR data". Cryosphere 8, nr 1 (10.01.2014): 73–90. http://dx.doi.org/10.5194/tc-8-73-2014.
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Abstract. Seasonal snow cover is of great environmental and socio-economic importance for the European Alps. Therefore a high priority has been assigned to quantifying its temporal and spatial variability. Complementary to land-based monitoring networks, optical satellite observations can be used to derive spatially comprehensive information on snow cover extent. For understanding long-term changes in alpine snow cover extent, the data acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensors mounted onboard the National Oceanic and Atmospheric Association (NOAA) and Meteorological Operational satellite (MetOp) platforms offer a unique source of information. In this paper, we present the first space-borne 1 km snow extent climatology for the Alpine region derived from AVHRR data over the period 1985–2011. The objective of this study is twofold: first, to generate a new set of cloud-free satellite snow products using a specific cloud gap-filling technique and second, to examine the spatiotemporal distribution of snow cover in the European Alps over the last 27 yr from the satellite perspective. For this purpose, snow parameters such as snow onset day, snow cover duration (SCD), melt-out date and the snow cover area percentage (SCA) were employed to analyze spatiotemporal variability of snow cover over the course of three decades. On the regional scale, significant trends were found toward a shorter SCD at lower elevations in the south-east and south-west. However, our results do not show any significant trends in the monthly mean SCA over the last 27 yr. This is in agreement with other research findings and may indicate a deceleration of the decreasing snow trend in the Alpine region. Furthermore, such data may provide spatially and temporally homogeneous snow information for comprehensive use in related research fields (i.e., hydrologic and economic applications) or can serve as a reference for climate models.
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Geddes, A., i H. Bösch. "Tropospheric aerosol profile information from high-resolution oxygen A-band measurements from space". Atmospheric Measurement Techniques 8, nr 2 (20.02.2015): 859–74. http://dx.doi.org/10.5194/amt-8-859-2015.
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Abstract. Aerosols are an important factor in the Earth climatic system and they play a key role in air quality and public health. Observations of the oxygen A-band at 760 nm can provide information on the vertical distribution of aerosols from passive satellite sensors that can be of great interest for operational monitoring applications with high spatial coverage if the aerosol information is obtained with sufficient precision, accuracy and vertical resolution. To address this issue, retrieval simulations of the aerosol vertical profile retrieval from O2 A-band observations by GOSAT, the upcoming Orbiting Carbon Observatory-2 (OCO-2) and Sentinel 5-P missions, and the proposed CarbonSat mission have been carried out. Precise retrievals of aerosol optical depth (AOD) within the boundary layer were found to favour low-resolution, high signal-to-noise instruments such as Sentinel-5 P, whereas higher-resolution instruments such as OCO-2 showed greater performance at higher altitudes and in information content above the boundary layer. Retrieval of the AOD in the 0–2 km range with precision appears difficult from all studied instruments and the retrieval errors typically exceed a value of 0.05 for AODs up to 0.3. Constraining the surface albedo is a promising and effective way of improving the retrieval of aerosol, but the accuracy of the required prior knowledge is very high. Due to the limited information content of the aerosol profile retrieval, the use of a parameterised aerosol distribution is assessed, and we show that the AOD and height of an aerosol layer can be retrieved well if the aerosol layer is uplifted to the free troposphere; however, errors are often large for aerosol layers in the boundary layer. Additional errors are introduced by incorrect assumptions on surface pressure and aerosol mixture, which can both bias retrieved AOD and height by up to 45%. In addition, assumptions of the boundary layer temperature are found to yield an additional error of up to 8%. We conclude that the aerosol profile retrievals from O2 A-band using existing or upcoming satellite sensors will only provide limited information on aerosols in the boundary layer but such observations can be of great value for observing and mapping aerosol plumes in the free troposphere.
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Thomason, Larry W., Nicholas Ernest, Luis Millán, Landon Rieger, Adam Bourassa, Jean-Paul Vernier, Gloria Manney, Beiping Luo, Florian Arfeuille i Thomas Peter. "A global space-based stratospheric aerosol climatology: 1979–2016". Earth System Science Data 10, nr 1 (12.03.2018): 469–92. http://dx.doi.org/10.5194/essd-10-469-2018.
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Abstract. We describe the construction of a continuous 38-year record of stratospheric aerosol optical properties. The Global Space-based Stratospheric Aerosol Climatology, or GloSSAC, provided the input data to the construction of the Climate Model Intercomparison Project stratospheric aerosol forcing data set (1979–2014) and we have extended it through 2016 following an identical process. GloSSAC focuses on the Stratospheric Aerosol and Gas Experiment (SAGE) series of instruments through mid-2005, and on the Optical Spectrograph and InfraRed Imager System (OSIRIS) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data thereafter. We also use data from other space instruments and from ground-based, air, and balloon borne instruments to fill in key gaps in the data set. The end result is a global and gap-free data set focused on aerosol extinction coefficient at 525 and 1020 nm and other parameters on an “as available” basis. For the primary data sets, we developed a new method for filling the post-Pinatubo eruption data gap for 1991–1993 based on data from the Cryogenic Limb Array Etalon Spectrometer. In addition, we developed a new method for populating wintertime high latitudes during the SAGE period employing a latitude-equivalent latitude conversion process that greatly improves the depiction of aerosol at high latitudes compared to earlier similar efforts. We report data in the troposphere only when and where it is available. This is primarily during the SAGE II period except for the most enhanced part of the Pinatubo period. It is likely that the upper troposphere during Pinatubo was greatly enhanced over non-volcanic periods and that domain remains substantially under-characterized. We note that aerosol levels during the OSIRIS/CALIPSO period in the lower stratosphere at mid- and high latitudes is routinely higher than what we observed during the SAGE II period. While this period had nearly continuous low-level volcanic activity, it is possible that the enhancement in part reflects deficiencies in the data set. We also expended substantial effort to quality assess the data set and the product is by far the best we have produced. GloSSAC version 1.0 is available in netCDF format at the NASA Atmospheric Data Center at https://eosweb.larc.nasa.gov/. GloSSAC users should cite this paper and the data set DOI (https://doi.org/10.5067/GloSSAC-L3-V1.0).