- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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[IEEE 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Zhenjiang, China (2019.8.4-2019.8.8)] 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Study on the Influence of Copper Powder Smoke on Laser Transmission Characteristics
摘要： Breaking ocean waves influence wave dynamics, momentum transfer, air–sea exchange, ocean albedo, and ambient noise generation, all of which are impacted by the transient, two-phase flow in a whitecap. Lasting O(1s) or so, actively breaking whitecaps contain air fractions up to 0.6, bubbles ranging in size O(10–1000) μm and turbulent dissipation rates O(1) W·kg?1. Strong fluid turbulence, high air fractions, large bubbles, and short duration make active whitecaps a challenging process to study. This paper presents a model for the performance of high-frequency Doppler sonar (0.5–2 MHz) when used to probe the interior of actively breaking whitecaps. The results suggest that the ability of high-frequency sonars to penetrate the interior of bubble plumes in whitecaps becomes limited for air fractions greater than 0.03–0.06 and plumes become completely impenetrable for air fractions greater than 0.08–0.17. This severely limits their usefulness as a tool to probe the interior of breaking waves. Moreover, the bias introduced by the terminal rise velocity of large bubbles interacting with fluid turbulence within the wave crest will need to be accounted for when interpreting any backscatter signals that are returned from the plume interior. At this time, in situ methods such as optical fiber probes, conductivity cells, and cameras remain the best option for field studies of the interior of breaking oceanic waves.
关键词： turbulence,Doppler sonar,Bubble plumes,wave breaking
更新于2025-09-23 15:21:01
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Assessment with Controlled In-Situ Data of the Dependence of L-Band Radiometry on Sea-Ice Thickness
摘要： The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) and the National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) missions are providing brightness temperature measurements at 1.4 GHz (L-band) for about 10 and 4 years respectively. One of the new areas of geophysical exploitation of L-band radiometry is on thin (i.e., less than 1 m) Sea Ice Thickness (SIT), for which theoretical and empirical retrieval methods have been proposed. However, a comprehensive validation of SIT products has been hindered by the lack of suitable ground truth. The in-situ SIT datasets most commonly used for validation are affected by one important limitation: They are available mainly during late winter and spring months, when sea ice is fully developed and the thickness probability density function is wider than for autumn ice and less representative at the satellite spatial resolution. Using Upward Looking Sonar (ULS) data from the Woods Hole Oceanographic Institution (WHOI), acquired all year round, permits overcoming the mentioned limitation, thus improving the characterization of the L-band brightness temperature response to changes in thin SIT. State-of-the-art satellite SIT products and the Cumulative Freezing Degree Days (CFDD) model are veri?ed against the ULS ground truth. The results show that the L-band SIT can be meaningfully retrieved up to 0.6 m, although the signal starts to saturate at 0.3 m. In contrast, despite the simplicity of the CFDD model, its predicted SIT values correlate very well with the ULS in-situ data during the sea ice growth season. The comparison between the CFDD SIT and the current L-band SIT products shows that both the sea ice concentration and the season are fundamental factors in?uencing the quality of the thickness retrieval from L-band satellites.
关键词： sea ice thickness,retrieval model validation,upward looking sonar,Arctic,Soil Moisture Active Passive (SMAP),Soil Moisture and Ocean Salinity (SMOS) mission,L-band radiometry
更新于2025-09-23 15:19:57
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[IEEE 2019 International Conference on Communication and Electronics Systems (ICCES) - Coimbatore, India (2019.7.17-2019.7.19)] 2019 International Conference on Communication and Electronics Systems (ICCES) - Saturable Absorbers for Mode-Locking of Lasers Operating at Ultraviolet Wavelengths
摘要： Breaking ocean waves influence wave dynamics, momentum transfer, air–sea exchange, ocean albedo, and ambient noise generation, all of which are impacted by the transient, two-phase flow in a whitecap. Lasting O(1s) or so, actively breaking whitecaps contain air fractions up to 0.6, bubbles ranging in size O(10–1000) μm and turbulent dissipation rates O(1) W·kg?1. Strong fluid turbulence, high air fractions, large bubbles, and short duration make active whitecaps a challenging process to study. This paper presents a model for the performance of high-frequency Doppler sonar (0.5–2 MHz) when used to probe the interior of actively breaking whitecaps. The results suggest that the ability of high-frequency sonars to penetrate the interior of bubble plumes in whitecaps becomes limited for air fractions greater than 0.03–0.06 and plumes become completely impenetrable for air fractions greater than 0.08–0.17. This severely limits their usefulness as a tool to probe the interior of breaking waves. Moreover, the bias introduced by the terminal rise velocity of large bubbles interacting with fluid turbulence within the wave crest will need to be accounted for when interpreting any backscatter signals that are returned from the plume interior. At this time, in situ methods such as optical fiber probes, conductivity cells, and cameras remain the best option for field studies of the interior of breaking oceanic waves.
关键词： turbulence,Doppler sonar,Bubble plumes,wave breaking
更新于2025-09-23 15:19:57
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[IEEE 2019 International Conference on Signal Processing and Communication (ICSC) - NOIDA, India (2019.3.7-2019.3.9)] 2019 International Conference on Signal Processing and Communication (ICSC) - Design and Analysis of HgCdTe Infrared Photodetector
摘要： Breaking ocean waves influence wave dynamics, momentum transfer, air–sea exchange, ocean albedo, and ambient noise generation, all of which are impacted by the transient, two-phase flow in a whitecap. Lasting O(1s) or so, actively breaking whitecaps contain air fractions up to 0.6, bubbles ranging in size O(10–1000) μm and turbulent dissipation rates O(1) W·kg?1. Strong fluid turbulence, high air fractions, large bubbles, and short duration make active whitecaps a challenging process to study. This paper presents a model for the performance of high-frequency Doppler sonar (0.5–2 MHz) when used to probe the interior of actively breaking whitecaps. The results suggest that the ability of high-frequency sonars to penetrate the interior of bubble plumes in whitecaps becomes limited for air fractions greater than 0.03–0.06 and plumes become completely impenetrable for air fractions greater than 0.08–0.17. This severely limits their usefulness as a tool to probe the interior of breaking waves. Moreover, the bias introduced by the terminal rise velocity of large bubbles interacting with fluid turbulence within the wave crest will need to be accounted for when interpreting any backscatter signals that are returned from the plume interior. At this time, in situ methods such as optical fiber probes, conductivity cells, and cameras remain the best option for field studies of the interior of breaking oceanic waves.
关键词： turbulence,Doppler sonar,Bubble plumes,wave breaking
更新于2025-09-19 17:13:59
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Coupled micro-Doppler signatures of closely located targets
摘要： The classical Doppler shift originates from the movement of a target’s center of mass, but it does not hold information about the internal dynamics of the scattering object. In contrast, micro-Doppler signatures contain data about the micromotions that arise from internal degrees of freedom within the target (such as rotation and vibration), which can be remotely detected by careful analysis of the scattered ?eld. Here we investigate, both theoretically and experimentally, how coupling between a pair of closely situated targets affects the resulting micro-Doppler signatures. The presented model considers a pair of near-?eld coupled resonators with dynamically recon?gurable scattering properties. Voltage controlled varactor diodes enable modulating the scattering cross section of each target independently, mimicking rotational degrees of freedom. As a result, coupled micro-Doppler combs are observed, containing frequency components that arise from the near ?eld interactions, making it possible to extract information about the internal geometry of the system from far-?eld measurements. From a practical point of view, micro-Doppler spectroscopy allows remote classi?cation of distant objects, while deep understanding of the coupling effects on such signatures in the low frequency regime can provide valuable insight for radar and sonar systems, as well as optical and stellar radio-interferometry, among many others.
关键词： sonar,coupled resonators,stellar radio-interferometry,micro-Doppler signatures,radar,optical interferometry
更新于2025-09-16 10:30:52
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Failure Analysis of Metallic Armoured Electro-Optic Mechanical Cables in Underwater Towed Sonar Systems
摘要： In towed sonar systems generally, the array is towed behind a ship using a combination of electro-optic mechanical (EOM) tow cables - negatively buoyant metallic armoured Heavy Cable and neutrally buoyant fibre armoured Light Cable- the former for depth control and latter for depth maintenance. Any failure in these cables can affect the performance of the sensor array and can even result in loss of the towed system to sea. During a series of towed array trials, it was observed that the metallic armoured cable had lost its circularity and became flattened during deployment and retrieval from ship. This may be due to the extreme radial forces acting on the cable while passing through a) rollers located at winch spooler and b) main fairlead comprising of 5 rollers located at aft end of ship, which causes permanent changes in cable’s internal configuration. To verify the cause and study the effects of such flattening on functionality and life of the cable, cyclic load testing studies were carried out after simulating the actual deployment-retrieval conditions as that in the ship. Both indigenously developed and imported cable samples were chosen as test samples for performance comparison. During the tests, it was observed that severe flattening of armour and core cable resulting in failure of electrical & optical lines had occurred in indigenous cable samples. The imported cable samples showed no flatness or failure of lines. Based on the results, steps were taken to improve the radial load bearing capacity of the indigenous cable. Modifications were made in a) core cable sheath material b) core cable sheath thickness & c) armour wire material and an improved indigenous cable was developed, which has withstood all the above tests and is now ready to be inducted to the system for sea trials.
关键词： Towed array sonar,Metallic armored cable,Electro-Optic Mechanical (EOM) tow cables,Cyclic load testing
更新于2025-09-12 10:27:22
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Ultra-Thin Fiber Laser Hydrophone With Static Pressure Equalization and Improved Response
摘要： In this paper, we propose a new scheme that combines a capillary tube with an elastic cavity to develop a thin fiber laser hydrophone (FLH) with static pressure equalization, enhanced dynamic pressure sensitivity and broadband flat response. We demonstrate the improvement on the hydrophone response characteristics by introducing the compensation structure into a diaphragm-based FLH. A hydrophone prototype with a diameter of 7.2 mm was packaged and the hydrophone has a flat pressure sensitivity of 9×10-3 pm/Pa (120 dB re Hz/Pa) over a bandwidth from 40 Hz to 4 kHz. The static pressure sensitivity is ?11×10-6 pm/Pa in the measurement range of 0 to 3 MPa.
关键词： Sonar arrays,optical fiber lasers,hydrophones,optical fiber sensors,pressure equalization
更新于2025-09-11 14:15:04
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Design of Low-Complexity 3-D Underwater Imaging System With Sparse Planar Arrays
摘要： The development of a real-time 3-D underwater imaging system with a planar array is restricted by the huge hardware cost and computational burden associated with the large number of elements required. In this paper, a new design of low-complexity 3-D underwater imaging system is proposed, involving two key parts: a special sparse array with low hardware cost and an ef?cient beamforming with low computational burden. Especially, the simulated annealing algorithm is optimized based on distributed and parallel subarray (DPS) beamforming and results in fewer active elements than existing methods. To improve the computational ef?ciency especially for sparse arrays, an optimized DPS beamforming is presented with the pruning fast Fourier transform technology. To test the validity of the design, a real system based on the proposed methods was devised and employed in the lake and sea trials. The experiment results demonstrate that the low-complexity 3-D underwater imaging system can provide a satisfactory imaging quality.
关键词： sparse planar arrays,underwater acoustic imaging,sonar signal processing,simulated annealing (SA) algorithm,3-D sonar systems
更新于2025-09-09 09:28:46
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Watermarking of linear frequency modulated pulses using chirplet graphs and stretch processing
摘要： In many underwater acoustics problems such as search and rescue, it is desirable to establish the source of the sonar pings. In this paper a methodology is proposed to watermark sonar pulses prior to transmission by embedding them with a chain of low power chirplets represented by a graph. Watermark detection is formulated using stretch processing where chirplet energies are focused on a single beat frequency only if the graph is traversed along the same path used at the source. The algorithm is tested by simulation in shallow water at varying ranges.
关键词： watermarking,stretch processing,linear frequency modulated pulses,sonar,chirplet graphs
更新于2025-09-09 09:28:46