Bio-optical model describing the distribution of irradiance at the sea surface resulting from a point source embedded in the ocean

Conventional direction-of-arrival (DOA) estimation methods are primarily used in point source scenarios and based on array signal processing. However, due to the local scattering caused by sea surface, signals observed from radar antenna cannot be regarded as a point source but rather as a spatially dispersed source. Besides, with the advantages of flexibility and comparably low cost, synthetic aperture radar (SAR) is the present and future trend of space-based systems. This paper proposes a novel DOA estimation approach for SAR systems using the simulated radar measurement of the sea surface at different operating frequencies and wind speeds. This article’s forward model is an advanced integral equation model (AIEM) to calculate the electromagnetic scattered from the sea surface. To solve the DOA estimation problem, we introduce a convolutional neural network (CNN) framework to estimate the transmitter’s incident angle and incident azimuth angle. Results demonstrate that the CNN can achieve a good performance in DOA estimation at a wide range of frequencies and sea wind speeds.

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Oil Droplet Clouds Suspended in the Sea. Can they be Remotely Detected?

10.20944/preprints201608.0201.v1 ◽

2016 ◽

Author(s):

Zbigniew Otremba

Keyword(s):

Monte Carlo ◽

Visible Light ◽

Ray Tracing ◽

Layer Thickness ◽

Optical Model ◽

Microwave Spectrum ◽

Sea Surface ◽

Oil Droplet ◽

Sea Area ◽

The Impact

Oil floating on the sea surface can be detected by both passive and active methods using the ultraviolet-to-microwave spectrum, whereas oil immersed below the sea surface can signal its presence only in visible light. This paper presents an optical model of a sea area deeply polluted by an oil suspension (10 ppm) located in a layer (thickness 5 m) separated from the sea surface by a clear layer (thickness 1 m). The impact of wavelength and state of the sea surface on reflectance changes is shown based on the results of Monte Carlo ray tracing. A two-wavelength index of reflectance is proposed to detect oil suspended in the water column (645-469 nm).

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Prediction of Sound Scattering from Deep-Sea Targets Based on Equivalence of Directional Point Sources

Applied Sciences ◽

10.3390/app11115160 ◽

2021 ◽

Vol 11 (11) ◽

pp. 5160

Author(s):

Jinpeng Liu ◽

Zheng Zhu ◽

Yongqiang Ji ◽

Ziyang Chen ◽

Chao Zhang ◽

...

Keyword(s):

Finite Element ◽

Point Source ◽

Deep Sea ◽

Free Field ◽

Acoustic Scattering ◽

Sea Surface ◽

Elastic Structure ◽

Theoretical Modelling ◽

Sound Scattering ◽

Scattering Field

A fast prediction method is proposed for calculating the sound scattering of targets in the deep-sea acoustic channel by equating the sound scattering field of a complex elastic target to the acoustic field excited by a directional point source. In deep-sea conditions, the effects of the sea surface on the impedance characteristics of the elastic target surface can be ignored. Through the finite element simulation of the acoustic scattering of the target in the free field, the sound scattering field is equated to the radiation field of a directional point source. Subsequently, the point source is placed in the channel, and the acoustic ray method is used to calculate the distribution of the scattering field. On the basis of theoretical modelling, the method of obtaining the directional point source and the influence of the sea surface on the impedance of the scattering field are analysed. Subsequently, the proposed method is compared with the finite element method in terms of computational efficiency. The result shows that the method considers the multiple complex coupling effects between the elastic structure and marine environment. The influence of the boundary is approximately negligible when the distance from the ocean boundary to the elastic structure is equal to the wavelength. The method only performs finite element coupling calculation in the free field; the amount of mesh size is greatly reduced and the calculation efficiency is significantly improved when compared with the finite element calculation in the entire channel, the. The calculation time in the example can be reduced by more than one order of magnitude. This method organically combines the near-field calculation with acoustic ray theory and it can realise the rapid calculation of the large-scale acoustic scattering field in complex marine environments.

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XRMF applications of a monolithic, polycapillary, focusing x-ray optic

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100163666 ◽

1996 ◽

Vol 54 ◽

pp. 240-241

Author(s):

D. A. Carpenter ◽

Ning Gao ◽

G. J. Havrilla

Keyword(s):

Trace Elements ◽

Point Source ◽

Focal Spot ◽

Fluorescence Analysis ◽

X Rays ◽

Focal Distance ◽

Spot Diameter ◽

X Ray ◽

Focal Spot Diameter

A monolithic, polycapillary, x-ray optic was adapted to a laboratory-based x-ray microprobe to evaluate the potential of the optic for x-ray micro fluorescence analysis. The polycapillary was capable of collecting x-rays over a 6 degree angle from a point source and focusing them to a spot approximately 40 µm diameter. The high intensities expected from this capillary should be useful for determining and mapping minor to trace elements in materials. Fig. 1 shows a sketch of the capillary with important dimensions.The microprobe had previously been used with straight and with tapered monocapillaries. Alignment of the monocapillaries with the focal spot was accomplished by electromagnetically scanning the focal spot over the beveled anode. With the polycapillary it was also necessary to manually adjust the distance between the focal spot and the polycapillary.The focal distance and focal spot diameter of the polycapillary were determined from a series of edge scans.

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