Improved Method to Suppress Azimuth Ambiguity for Current Velocity Measurement in Coastal Waters Based on ATI-SAR Systems

Measurements of ocean surface currents in coastal waters are crucial for improving our understanding of tidal atlases, as well as for ecosystem and water pollution monitoring. This paper proposes an improved method for estimating the baseline-to-platform speed ratio (BPSR) for improving the current line-of-sight (LOS) velocity measurement accuracy in coastal waters with along-track interferometric synthetic aperture radar (ATI-SAR) based on eigenvalue spectrum entropy (EVSE) analysis. The estimation of BPSR utilizes the spaceborne along-track interferometry and considers the effects of a satellite orbit and an inaccurate baseline responsible for azimuth ambiguity in coastal waters. Unlike the existing methods, which often assume idealized rather than actual operating environments, the proposed approach considers the accuracy of BPSR, which is its key advantage applicable to many, even poorly designed, ATI-SAR systems. This is achieved through an alternate algorithm for the suppression of azimuth ambiguity and BPSR estimation based on an improved analysis of the eigenvalue spectrum entropy, which is an important parameter representing the mixability of unambiguous and ambiguous signals. The improvements include the consideration of a measurement of the heterogeneity of the scene, the corrections of coherence-inferred phase fluctuation (CPF), and the interferogram-derived phase variability (IPV); the last two variables are closely related to the determination of the EVSE threshold. Besides, the BPSR estimation also represents an improvement that has not been achieved in previous work of EVSE analysis. When the improved method is used on the simulated ocean-surface current LOS velocity data obtained from a coastal area, the root-mean-square error is less than 0.05 m/s. The other strengths of the proposed algorithm are adaptability, robustness, and a limited user input requirement. Most importantly, the method can be adopted for practical applications.

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Current Measurements in European Coastal Waters and Rivers by Along-Track InSAR

Remote Sensing of the European Seas ◽

10.1007/978-1-4020-6772-3_31 ◽

2008 ◽

pp. 411-422 ◽

Cited By ~ 2

Author(s):

R. Romeiser ◽

H. Runge

Keyword(s):

Coastal Waters ◽

Along Track

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Numerical Analysis of the Effect of Binary Typhoons on Ocean Surface Waves in Waters Surrounding Taiwan

Frontiers in Marine Science ◽

10.3389/fmars.2021.749185 ◽

2021 ◽

Vol 8 ◽

Author(s):

Tzu-Yin Chang ◽

Hongey Chen ◽

Shih-Chun Hsiao ◽

Han-Lun Wu ◽

Wei-Bo Chen

Keyword(s):

Surface Waves ◽

Ocean Surface ◽

Separation Distance ◽

Ocean Surface Waves ◽

Significant Wave ◽

Storm Wave ◽

Wave Heights ◽

Significant Wave Heights ◽

The One ◽

Along Track

The ocean surface waves during Super Typhoons Maria (2018), Lekima (2019), and Meranti (2016) were reproduced using hybrid typhoon winds and a fully coupled wave-tide-circulation modeling system (SCHISM-WWM-III). The hindcasted significant wave heights are in good agreement with the along-track significant wave heights measured by the altimeters aboard the SARAL (Satellite with ARgos and ALtiKa) and Jason-2 satellites. Two numerical experiments pairing Super Typhoons Maria (2018) and Meranti (2016) and Super Typhoons Lekima (2019) and Meranti (2016) were conducted to analyze the storm wave characteristics of binary and individual typhoons. Four points located near the tracks of the three super typhoons were selected to elucidate the effects of binary typhoons on ocean surface waves. The comparisons indicate that binary typhoons not only cause an increase in the significant wave height simulations at four selected pints but also result in increases in the one-dimensional wave energy and two-dimensional directional wave spectra. Our results also reveal that the effects of binary typhoons on ocean surface waves are more significant at the periphery of the typhoon than near the center of the typhoon. The interactions between waves generated by Super Typhoons Maria (2018) and Meranti (2016) or Super Typhoons Lekima (2019) and Meranti (2016) might be diminished by Taiwan Island even if the separation distance between two typhoons is <700 km.

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An Improved Method for the Processing of Signals Contaminated With Strong Common-Mode Periodic Noise in Correlation Velocity Measurement

IEEE Sensors Letters ◽

10.1109/lsens.2019.2925665 ◽

2019 ◽

Vol 3 (7) ◽

pp. 1-4 ◽

Cited By ~ 1

Author(s):

Kamel Reda ◽

Yong Yan

Keyword(s):

Velocity Measurement ◽

Improved Method ◽

Common Mode ◽

Periodic Noise

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Fast Meshless Solution With Lumped Friction for Water Hammer

BATH/ASME 2020 Symposium on Fluid Power and Motion Control ◽

10.1115/fpmc2020-2789 ◽

2020 ◽

Author(s):

Yuanzhi Xu ◽

Zongxia Jiao ◽

Longfei Zhao

Keyword(s):

Computational Grid ◽

Water Hammer ◽

Friction Model ◽

Time Cost ◽

Improved Method ◽

Fluid Friction ◽

Time Line ◽

Practical Applications ◽

Distributed Friction ◽

Mesh Grid

Abstract The water hammer in pipelines, with the absence of fluid friction, could be solved by a time-domain exact solution, using a simple recursive process. No computational grid was needed, but the calculation time cost was extremely high. Its improved method, named as the fast meshless solution (FMS), was developed to speed the computation by introducing the time-line interpolation. For the purpose of practical applications, the attempt to consider fluid friction in the FMS is presented here. As there is no mesh grid in the distance-time plane, the distributed friction model can not be employed upon the presented method directly. The fluid friction lumped at the pipe end is proposed, and both steady and unsteady friction are studied. A benchmark problem of the water hammer in a reservoir-pipe-valve (RPV) system is employed for the validation and comparison. The water hammer considering lumped friction can be calculated fast by the FMS, and the accuracy is acceptable. The method discussed here may be of interest in a quick assessment of the piping water hammer.

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Ocean Surface Topography Altimetry by Large Baseline Cross-Interferometry from Satellite Formation

Remote Sensing ◽

10.3390/rs12213519 ◽

2020 ◽

Vol 12 (21) ◽

pp. 3519

Author(s):

Weiya Kong ◽

Bo Liu ◽

Xiaohong Sui ◽

Running Zhang ◽

Jinping Sun

Keyword(s):

Surface Topography ◽

Ocean Surface ◽

Baseline Length ◽

Radar Altimeter ◽

Satellite Formation ◽

Satellite Platform ◽

Marine Gravity ◽

Development Tendency ◽

Cross Track ◽

Along Track

Imaging Radar Altimeter (IRA) is the current development tendency for ocean surface topography (OST) altimetry, which utilizes Synthetic Aperture Radar (SAR) and interferometry to improve the spatial resolution of OST to several kilometers or even better. Meanwhile, centimetric altimetry accuracy should be guaranteed for applications such as geostrophic currents or marine gravity anomaly inversion. However, the baseline length of IRA which determines the altimetric sensitivity is confined by the satellite platform, in consideration of baseline vibration and payload capability. Therefore, the baseline length from a single satellite can extend to only tens of meters, making it difficult to achieve centimetric accuracy. Referring to the successful experience from TerraSAR-X/TanDEM-X, satellite formation can easily extend the baseline length to hundreds or thousands of meters, depending on the helix orbit. Therefore, we propose the large baseline IRA (LB-IRA) from satellite formation for OST altimetry: the carrier frequency shift (CFS) is brought in to compensate for the severe baseline decorrelation, and the helix orbit is carefully selected to prevent severe time decorrelation from along-track baseline. The numerical results indicate that the LB-IRA, whose cross-track baseline ranges between 629~1000 m and along-tack baseline ranges between 0~40 m, can achieve ~1 cm relative accuracy at 1 km resolution.

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