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Remote Sensing Image Restoration Based on an improved Landweber Iterative Method for Forest Monitoring and Management
摘要： As an advanced space exploration technologies, remote sensing technology has been widely used in forest monitoring and management. Forest current conditions could be reflected in real-time remote sensing images, but due to various imaging system and its environmental constraints, the original remote sensing images is often blurred. In this paper, two common remote-sensing imaging blurs, named motion blur and atmospheric turbulence blur, were studied and discussed the mechanism of the image blurred, and proposed a remote sensing image restoration method based on an improved Landweber iteration method which expedites the convergence only in the signal domain. As a result, we can still improve the image restoration accuracy of results at the same time of speeding up convergences.
关键词： remote sensing,image restoration,forest monitoring,motion blur,atmospheric turbulence blur,Landweber iteration
更新于2025-09-10 09:29:36
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Vortex instability in turbulent free-space propagation
摘要： The spatial structuring of optical fields is integral within many next generation optical metrology and communication techniques. A verifiable physical model of the propagation of these optical fields in a turbulent environment is important for developing effective mitigation techniques for the modal degradation that occurs in a free-space link. We present a method to simulate this modal degradation that agrees with recently reported experimental findings. A 1.5 km free-space link is emulated by decomposing the optical turbulence that accumulates over a long distance link, into many, weakly perturbing steps of 10 m. This simulation shows that the high-order vortex at the centre of the helical phase profiles in modes that carry orbital angular momentum of ? are unstable and fracture into many vortices when they propagate over the link. This splitting presents issues for the application of turbulence mitigation techniques. The usefulness of pre-correction, post-correction, and complex field conjugation techniques are discussed.
关键词： optical propagation,orbital angular momentum,adaptive optics,optical vortices,atmospheric turbulence
更新于2025-09-09 09:28:46
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Turbulent Lidar: I?Design
摘要： Two designs of a laser radar system based on the backscatter amplification effect (BSA) are suggested. The system is a micropulse aerosol lidar with two receiving channels, one of which records an increase in the lidar returns at the laser beam axis as the atmospheric turbulence intensifies. The second channel does not respond to the BSA and is required for calibration. The BSA effect manifests itself in a narrow spatial region around the laser beam axis; so, the receiver aperture should be small enough and comparable with the Fresnel zone. The creation of the turbulent lidar became possible with the advent of compact diode-pumped micropulsed lasers with high pulse repetition rates. The lidar is intended for continuous long-term unattended operation. It is eye-safe. Two designs of the turbulent lidar based on an afocal Mersenne telescope (mirror collimator) are suggested. BSA-2 and BSA-3 turbulent lidars are described. An algorithm is suggested for retrieval of the structure parameter of optical turbulence from lidar data based on the Vorob’ev’s approximation for a statistically homogeneous turbulent medium.
关键词： lidar,backscatter amplification effect,atmospheric turbulence
更新于2025-09-09 09:28:46
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Impact of transmission techniques in asymmetric RF/FSO system over Nakagami- <i>m</i> and gamma-gamma fading channels with pointing errors
摘要： In this paper, the performance of transmission techniques on the fixed‐gain amplify‐and‐forward–based asymmetric radio frequency/free space optical (RF/FSO) communication system is studied. The RF link and FSO link are, respectively, modeled by the Nakagami‐m and Gamma‐Gamma fading channels under the effect of zero boresight and non‐zero boresight pointing errors subject to heterodyne detection. Maximum ratio transmission (MRT) and orthogonal space‐time block coding (OSTBC) techniques are the transmission scenarios considered at the system source while selection combining is used for reception at the relay and destination for the signal detection. Moreover, a unified cumulative density distribution (CDF) of end‐to‐end signal‐to‐noise ratio is derived for the system. By utilizing this channel statistical CDF, the closed‐form expressions for the outage probability and average bit error rate for the M‐ary phase shift keying modulation are then obtained for the system. The analysis presented illustrates that both the atmospheric turbulence and pointing error significantly degrade the system performance. Based on this, the MRT transmission technique offers a better performance compared with the OSTBC techniques under the same system conditions. The accuracy of the analytical results is verified by Monte‐Carlo simulations.
关键词： transmit diversity,free space optical,Nakagami‐m fading,pointing errors,atmospheric turbulence
更新于2025-09-09 09:28:46
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Propagation of Optical Coherence Vortex Lattices in Turbulent Atmosphere
摘要： Propagation properties in the turbulence atmosphere of the optical coherence vortex lattices (OCVLs) are explored by the recently developed convolution approach. The evolution of spectral density distribution, the normalized M2-factor, and the beam wander of the OCVLs propagating through the atmospheric turbulence with Tatarskii spectrum are illustrated numerically. Our results show that the OCVLs display interesting propagation properties, e.g., the initial Gaussian beam distribution will evolve into hollow array distribution on propagation and ?nally becomes a Gaussian beam spot again in the far ?eld in turbulent atmosphere. Furthermore, the OCVLs with large topological charge, large beam array order, large relative distance, and small coherence length are less affected by the negative effects of turbulence. Our results are expected to be used in the complex system optical communications.
关键词： optical coherence vortex lattices,evolution properties,atmospheric turbulence,free-space optical communications
更新于2025-09-04 15:30:14
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Real-time selection for free-space measurement device independent quantum key distribution
摘要： In consideration of the time-dependent transmittance caused by atmospheric turbulence, we combine real-time selection (RTS) method with measurement device independent quantum key distribution (MDI-QKD). The modi?ed scheme ?lters out the intervals with high channel transmittance and thus in turn increases the secure key rate. The optimal threshold of post-selection is determined by an iterative algorithm in advance, which balances the decrease in the total number of signals and the increase in average transmittance. Simulation results show that our modi?ed scheme has apparent advances in both maximum tolerant loss and secure key rate compared to the original MDI-QKD protocol. The MDI-QKD with RTS even performs better when the level of turbulence becomes larger. Furthermore, the modi?ed scheme is more stable against the statistical ?uctuation as well.
关键词： Quantum key distribution,Measurement device independent quantum key distribution,Atmospheric turbulence
更新于2025-09-04 15:30:14
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Performance Analysis of Hybrid RF/FSO System using BPSK-SIM and DPSK-SIM over Gamma-Gamma Turbulence Channel with Pointing errors for Smart City Applications
摘要： The in wireless communication -Free space optics (FSO) offers lots of merits over radio frequency (RF) links due to its license free bandwidth, ease of installation, high security features, and viable cost for short distance communication. It's high speed data rate and immunity against Electromagnetic Interference (EMI) makes FSO the emerging technology of today. But, FSO is not always reliable especially during Atmospheric conditions like fog, rain, mist and snow. Hence, in account a new technique of Hybrid FSO/RF, this includes advantages of both FSO and RF technologies. Through this paper intend to perform an extensive analysis of the error and misalignment effects encountered in Line Of Sight (LOS) communication. Pointing error and turbulence effects are the main drawback parameters for our analysis. For this purpose I have taken into consideration different modulation techniques-Binary Phase Shift keying-Subcarrier Intensity Modulation (BPSK-SIM), Differential Phase Shift Keying- Subcarrier Intensity Modulation (DPSK-SIM) communication system with reference to OOK Modulation. The novel expressions for outage probability and BER for both FSO and RF system are derived which uses Rician Channel and 16QAM Modulation scheme alongside Hybrid FSO/RF system for weak, moderate, strong turbulence regimes using Meijer-G Function.
关键词： Free space optics,Hybrid RF/FSO,Gamma-Gamma Channel,Atmospheric turbulence
更新于2025-09-04 15:30:14
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[IEEE 2018 11th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP) - Budapest (2018.7.18-2018.7.20)] 2018 11th International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP) - Modeling and Throughput Analysis of FSO Systems using GBN-ARQ and AR Transmission over Atmospheric Turbulence Channels
摘要： This paper addresses the error-control issue in free-space optical (FSO) communications. In particular, we model and analyze the throughput performance of FSO systems over atmospheric fading channel when the go-back-N (GBN) automatic repeat request (ARQ) and adaptive rate (AR) transmission schemes are employed. For this purpose, we first build the model to capture the time-varying behavior in atmospheric fading channels. We then use that channel model to develop the burst error model for GBN-ARQ with AR in order to analytically derive the system throughput. Numerical results quantitatively show the impacts of atmospheric turbulence on the throughput and confirm the effectiveness of the GBN/ARQ. Monte Carlo simulations are also performed to validate the analytical results.
关键词： throughput performance,go-back-N (GBN) automatic repeat request (ARQ),atmospheric turbulence,adaptive rate (AR) transmission,Free-space optical (FSO) communications
更新于2025-09-04 15:30:14
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Turbulence-induced optical loss and cross-talk in spatial-mode multiplexed or single-mode free-space communication channels
摘要： Single-mode or mode multiplexed free-space atmospheric optical channels have drawn increasingly more attention in the past decade. The scope of their possible applications spans from the compatibility with the telecom WDM technology, fiber amplifiers, and modal multiplexing for increasing the channel throughput to various quantum communication related primitives such as entanglement distribution, high-dimensional spatially encoded quantum key distribution, and relativistic quantum cryptography. Many research papers discuss application of specific mode sets, such as optical angular momentum modes, for communication in the presence of atmospheric turbulence. At the same time some basic properties and key relations for such channels exposed to the atmospheric turbulence have not been derived yet. In the current paper we present simple analytic expressions and a general framework for assessing probability density functions of channel transmittance as well as modal cross-talk coefficients. Under some basic assumptions the presented results can be directly used for estimation of the Fried parameter of the turbulent channel based on the measured statistics of the fundamental mode transmittance coefficient.
关键词： free-space optical communication,single-mode channels,spatial-mode multiplexing,atmospheric turbulence,quantum communication
更新于2025-09-04 15:30:14