The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform

Joel T. Johnson - One of the best experts on this subject based on the ideXlab platform.

  • A comparison of models for predicting near-specular bistatic scattering from rough surfaces
    2017 International Conference on Electromagnetics in Advanced Applications (ICEAA), 2017
    Co-Authors: Jeonghwan Park, Matthew Buchanan, Andrew O'brien, Joel T. Johnson
    Abstract:

    This paper provides a comparison of scattering models for near-specular bistatic scattering from rough surfaces. While the Geometrical Optics (GO) approximation is widely accepted for surfaces having large roughness compared to the Electromagnetic Wavelength, small differences in the literature exist between GO formulations. The Physical Optics (PO) and Small Slope Approximation (SSA) methods are also available and may provide differing predictions for moderately non-specular geometries. Comparisons of these models are reported in this paper, with a particular emphasis on analysis of near-specular surface scattering returns obtained from the GNSS-R mode of the radar receiver in NASA's Soil Moisture Active/Passive (SMAP) mission.

  • A theoretical study of sea surface up/down wind brightness temperature differences
    IEEE Transactions on Geoscience and Remote Sensing, 2002
    Co-Authors: Joel T. Johnson, Yongyao Cai
    Abstract:

    The small slope approximation (SSA) for polarimetric thermal emission from a rough surface is applied to study the up/down wind difference of sea surface brightness temperatures. A complete third-order theory is used, with results expressed in terms of an integral over the sea surface bispectrum. An approximation is developed to obtain emission contributions for surface length scales much larger than the Electromagnetic Wavelength and in this limit, the up/down wind brightness temperature difference is determined entirely by a combination of third moments of surface slope. Polarization dependencies in this limit however do not match those obtained from the Jet Propulsion Laboratory (JPL) WindRAD empirical model. Another approximation is derived to capture up/down wind emission asymmetry due to short waves which are modulated by longer waves. In this case, an integral of emission "weighting functions" over a pair of "reduced" bispectra is obtained, and examination of the weighting functions shows the importance of surface length scales comparable to the Electromagnetic Wavelength. The polarization dependencies of these weighting functions illustrate the possibility of matching the WindRAD model, but the absence of an effective hydrodynamic model for short gravity-capillary wave modulation by longer waves limits detailed comparisons.

Yongyao Cai - One of the best experts on this subject based on the ideXlab platform.

  • A theoretical study of sea surface up/down wind brightness temperature differences
    IEEE Transactions on Geoscience and Remote Sensing, 2002
    Co-Authors: Joel T. Johnson, Yongyao Cai
    Abstract:

    The small slope approximation (SSA) for polarimetric thermal emission from a rough surface is applied to study the up/down wind difference of sea surface brightness temperatures. A complete third-order theory is used, with results expressed in terms of an integral over the sea surface bispectrum. An approximation is developed to obtain emission contributions for surface length scales much larger than the Electromagnetic Wavelength and in this limit, the up/down wind brightness temperature difference is determined entirely by a combination of third moments of surface slope. Polarization dependencies in this limit however do not match those obtained from the Jet Propulsion Laboratory (JPL) WindRAD empirical model. Another approximation is derived to capture up/down wind emission asymmetry due to short waves which are modulated by longer waves. In this case, an integral of emission "weighting functions" over a pair of "reduced" bispectra is obtained, and examination of the weighting functions shows the importance of surface length scales comparable to the Electromagnetic Wavelength. The polarization dependencies of these weighting functions illustrate the possibility of matching the WindRAD model, but the absence of an effective hydrodynamic model for short gravity-capillary wave modulation by longer waves limits detailed comparisons.

Min Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical study of the small slope approximation for ocean polarimetric thermal emission
    IEEE Transactions on Geoscience and Remote Sensing, 1999
    Co-Authors: J.t. Johnson, Min Zhang
    Abstract:

    Analytical models for ocean surface polarimetric thermal emission based on the small perturbation method (SPM) have shown success in matching brightness temperature azimuthal variations from aircraft based measurements. It has also been shown that use of the small perturbation method for calculation of surface emissivity results in a series in surface slope, not surface height, so that the method remains accurate for large height surface emission even when it fails for the corresponding scattering calculations. This paper presents a detailed analysis of the SPM/small slope approximation (SPM/SSA) for ocean surface polarimetric thermal emission, and investigates the extent to which varying ocean surface length scales contribute to brightness temperature zeroth and second azimuthal harmonics. It is found that ocean waves of lengths both comparable to and much greater than the Electromagnetic Wavelength can contribute to these harmonics, depending on the extent to which the ocean surface spectral model places asymmetry in these length scales. In addition, the SPM/SSA is approximated for the contributions of both very long and very short ocean length scales compared to the Electromagnetic Wavelength, and it is found that both long and short wave contributions can be expressed in simple equations involving either standard or modified ocean surface slope variances.

Daniele Riccio - One of the best experts on this subject based on the ideXlab platform.

  • Gaussian Rough Surfaces and
    1999
    Co-Authors: Antonio Collaro, Giorgio Franceschetti, Maurizio Migliaccio, Daniele Riccio
    Abstract:

    Electromagnetic scattering is often solved by ap- plying Kirchhoff approximation to the Stratton-Chu scattering integral. In the case of rough surfaces, it is usually assumed that this is possible if the incident Electromagnetic Wavelength is small compared to the mean radius of curvature of the surface. Accordingly, evaluation of the latter is an important issue. This paper generalizes the groundwork of Papa and Lennon (1) by computing the mean radius of curvature for Gaussian rough surfaces with no restriction on its correlation function. This is an interesting extension relevant to a variety of natural surfaces. Relations between the surface parameters and the mean radius of curvature are determined and particular attention is paid to the relevant small slope regime.

  • Gaussian rough surfaces and Kirchhoff approximation
    IEEE Transactions on Antennas and Propagation, 1999
    Co-Authors: Antonio Collaro, Giorgio Franceschetti, Maurizio Migliaccio, Daniele Riccio
    Abstract:

    Electromagnetic scattering is often solved by applying the Kirchhoff approximation to the Stratton-Chu scattering integral. In the case of rough surfaces, it is usually assumed that this is possible if the incident Electromagnetic Wavelength is small compared to the mean radius of curvature of the surface. Accordingly, evaluation of the latter is an important issue. This paper generalizes the groundwork of Papa and Lemon (see ibid., vol.36, p.647-50, May 1988) by computing the mean radius of curvature for Gaussian rough surfaces with no restriction on its correlation function. This is an interesting extension relevant to a variety of natural surfaces. Relations between the surface parameters and the mean radius of curvature are determined and particular attention is paid to the relevant small slope regime.

Hiroyuki Shinoda - One of the best experts on this subject based on the ideXlab platform.

  • Flexible Tactile Sensor Skin Using Wireless Sensor Elements Coupled with 2D Microwaves
    Journal of Robotics and Mechatronics, 2010
    Co-Authors: Hiroyuki Shinoda, Hiromasa Chigusa, Yasutoshi Makino
    Abstract:

    The stretchable sensor skin we propose uses microwaves propagating in a two-Dimensional Signal Transmission (2DST) sheet. A small tactile sensor chip with a pair of Resonant Proximity Connectors (RPCs) couples with 2D microwaves carrying signals. Chip operating power is also supplied by 2D microwaves. The RPC is a spiral electrode whose arc length is a quarter of the Electromagnetic Wavelength. Chip operating power is supplied by 2D microwaves. Sensor chips are connected to the 2DST sheet by RPCs without electrical contacts anywhere on the sheet. Resonance induced at the electrode reduces impedance between the connector and the conductive layer of the 2DST sheet, enabling sensor chips to be connected stably to the sheet. Experimental results on the RPC show the concept to be effective. We fabricated a 1-bit (touch detection) tactile sensor element consisting of a RFID-tag and RPCs, and confirmed in experiments that the sensor element operates in a stretchable 2DST sheet.

  • WHC - Large Area Sensor Skin based on Two-Dimensional Signal Transmission Technology
    Second Joint EuroHaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems (WHC'07), 2007
    Co-Authors: Hiromasa Chigusa, Yasutoshi Makino, Hiroyuki Shinoda
    Abstract:

    In this paper, we propose a stretchable large area sensor skin based on two-dimensional signal transmission (2DST) technology. A small tactile sensor chip with stable non-contact connectors (resonant proximity connector: RPC) to a 2DST sheet is developed. The sensor nodes communicate by microwave that propagates in a two-dimensional sheet. Sensor nodes connect to the 2DST sheet via RPCs without electrical contact anywhere on the sheet and also receive the power for operation from the microwave in the sheet. RPC is a spiral electrode whose total length is a quarter of the Electromagnetic Wavelength. The induced resonance around the electrode reduces the impedance between the connector and 2DST sheet, which allows sensor chips to connect to the 2DST sheet stably. Simulation results on spiral RPCs show that the concept is effective. We produce an on-off type tactile sensor element which consists of a RFID-tag and RPC, and experimentally confirm that the sensor element works in a stretchable 2DST sheet

  • Large Area Tactile Sensor based on Proximity Connection of Tactile Sensing Elements
    2006
    Co-Authors: Hiromasa Chigusa, Yasutoshi Makino, Hiroyuki Shinoda
    Abstract:

    In this paper, we propose a stable proximity connector RPC (Resonant Proximity Connector) to TDC (Two-Dimensional Communication) sheet for integration of tactile sensor chips in a large area robot skin. RPC is an electrode whose length is a quarter of the Electromagnetic Wavelength. The induced resonance around the electrode reduces the impedance between the connector and TDC sheet, which allows sensor chips to connect with TDC sheet stably. Simulation results on straight, ring, spiral RPCs show that the concept is effective. We also confirmed experimentally that power can be supplied to the sensor element in TDC sheet successfully.

  • Resonant Proximity Connector for Two-Dimensional Sensor Implantation
    2006 SICE-ICASE International Joint Conference, 2006
    Co-Authors: Hiromasa Chigusa, Yasutoshi Makino, Hiroyuki Shinoda
    Abstract:

    In this paper, we propose a stable proximity connector RPC (Resonant Proximity Connector) to TDC (Two-Dimensional Communication) sheet. RPC is an electrode whose length is a quarter of the Electromagnetic Wavelength. The induced resonance around the electrode reduces the impedance between the connector and TDC sheet, which allows sensor chips to communicate with TDC sheet stably. Since the resonance depends on only the length of the electrode, this connector realizes stable connection of the sensor chip to TDC sheet for the variable gap distance between them. Using this technology, we can construct high density sensor networks on surfaces of clothes, desks, vehicles, and rooms without complicated wiring. The communication sheet can be made of flexible materials like fabric or rubber. We demonstrate the principle of RPC and simulation and experimental results.