scholarly journals Meteorological information in GPS-RO reflected signals

2011 ◽  
Vol 4 (1) ◽  
pp. 1199-1231 ◽  
Author(s):  
K. Boniface ◽  
J. M. Aparicio ◽  
E. Cardellach
Keyword(s):  
Refractive Index ◽  
Ray Tracing ◽  
Electromagnetic Waves ◽  
Radio Occultation ◽  
Good Description ◽  
Weather Prediction ◽  
Three Dimensional ◽  
Perturbation Approach ◽  
Vertical Profiles ◽  
Reflected Signal

Abstract. Vertical profiles of the atmosphere can be obtained globally with the radio-occultation technique. However, the lowest layers of the atmosphere are less accurately extracted. A good description of these layers is important for the good performance of Numerical Weather Prediction (NWP) systems, and an improvement of the observational data available for the low troposphere would thus be of great interest for data assimilation. We outline here how supplemental meteorological information close to the surface can be extracted whenever reflected signals are available. We separate the reflected signal through a radioholographic filter, and we interpret it with a ray tracing procedure, analyzing the trajectories of the electromagnetic waves over a three-dimensional field of refractive index. A perturbation approach is then used to perform an inversion, identifying the relevant contribution of the lowest layers of the atmosphere to the properties of the reflected signal, and extracting some supplemental information to the solution of the inversion of the direct propagation signals. The methodology is applied to one reflection case.

scholarly journals Meteorological information in GPS-RO reflected signals

2011 ◽  
Vol 4 (7) ◽  
pp. 1397-1407 ◽  
Author(s):  
K. Boniface ◽  
J. M. Aparicio ◽  
E. Cardellach
Keyword(s):  
Refractive Index ◽  
Ray Tracing ◽  
Numerical Weather Prediction ◽  
Electromagnetic Waves ◽  
Radio Occultation ◽  
Good Description ◽  
Weather Prediction ◽  
Perturbation Approach ◽  
Vertical Profiles ◽  
Reflected Signal

Abstract. Vertical profiles of the atmosphere can be obtained globally with the radio-occultation technique. However, the lowest layers of the atmosphere are less accurately extracted. A good description of these layers is important for the good performance of Numerical Weather Prediction (NWP) systems, and an improvement of the observational data available for the low troposphere would thus be of great interest for data assimilation. We outline here how supplemental meteorological information close to the surface can be extracted whenever reflected signals are available. We separate the reflected signal through a radioholographic filter, and we interpret it with a ray tracing procedure, analyzing the trajectories of the electromagnetic waves over a 3-D field of refractive index. A perturbation approach is then used to perform an inversion, identifying the relevant contribution of the lowest layers of the atmosphere to the properties of the reflected signal, and extracting some supplemental information to the solution of the inversion of the direct propagation signals. It is found that there is a significant amount of useful information in the reflected signal, which is sufficient to extract a stand-alone profile of the low atmosphere, with a precision of approximately 0.1 %. The methodology is applied to one reflection case.

scholarly journals Validation of Three-Dimensional Ray-Tracing Algorithm for Indoor Wireless Propagations

2011 ◽  
Vol 2011 ◽  
pp. 1-5 ◽  
Author(s):  
Majdi Salem ◽  
Mahamod Ismail ◽  
Norbahiah Misran
Keyword(s):  
Ray Tracing ◽  
Electromagnetic Waves ◽  
Three Dimensional ◽  
Prediction Method ◽  
Access Point ◽  
Network Access ◽  
Multiple Reflections ◽  
Indoor Wireless ◽  
3D Ray Tracing ◽  
Tracing Algorithm

A 3D ray tracing simulator has been developed for indoor wireless networks. The simulator uses geometrical optics (GOs) to propagate the electromagnetic waves inside the buildings. The prediction technique takes into account multiple reflections and transmissions of the propagated waves. An interpolation prediction method (IPM) has been proposed to predict the propagated signal and to make the ray-tracing algorithm faster, accurate, and simple. The measurements have been achieved by using a single Wi-Fi network access point as a transmitter and a laptop as a receiver. Measured data had been collected at different positions in indoor environment and compared with predicted signals. The comparison of the predicted and measured received signals gave root mean square error of 2.96 dB and std. deviation of 2.98 dB.

scholarly journals Synthesis methods for realistic images of three-dimensional scenes containing media with a refractive index gradient

2020 ◽  
Author(s):  
Dmitriy Zhdanov ◽  
Igor' Potemin ◽  
Andrey Zhdanov ◽  
Vladimir Galaktionov ◽  
Alexey Garbul
Keyword(s):  
Refractive Index ◽  
Ray Tracing ◽  
Three Dimensional ◽  
Image Synthesis ◽  
Synthesis Methods ◽  
Refractive Index Gradient ◽  
Photorealistic Rendering ◽  
Runge Kutta Method ◽  
Index Gradient ◽  
Program Interface

The paper presents the results of a study of the possibility of implementing an effective and physically correct stochastic ray tracing in gradient media based on the Runge-Kutta method. For implementation in the photorealistic rendering system, the specifics of the ray tracing method in complex three-dimensional scenes were considered. One of the main features of ray tracing in geometrically complex scenes is the large volume of geometric primitives that need to be tested for the intersection of the ray segment with the primitives. A method of ray propagation in voxel space of the scene is proposed. The method allows significant speeding up the process of searching for ray intersections with geometry primitives. To implement these ray tracing features the special program interface for gradient media was proposed, which can become the basic interface for a media of all types. Methods for calculating the luminance of all lighting components in gradient media were considered. The results of modeling the propagation of rays and image synthesis in a fiber with a refractive index gradient are presented.

scholarly journals Photonic Crystal Stimuli-Responsive Chromatic Sensors: A Short Review

Micromachines ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 290 ◽  
Author(s):  
Andrea Chiappini ◽  
Lam Thi Ngoc Tran ◽  
Pablo Marco Trejo-García ◽  
Lidia Zur ◽  
Anna Lukowiak ◽  
...  
Keyword(s):  
Refractive Index ◽  
Photonic Crystal ◽  
Electromagnetic Waves ◽  
Low Cost ◽  
Physical Phenomenon ◽  
Spectral Characteristics ◽  
Three Dimensional ◽  
Short Review ◽  
Optical Measurements ◽  
Energy Harvest

Photonic crystals (PhC) are spatially ordered structures with lattice parameters comparable to the wavelength of propagating light. Their geometrical and refractive index features lead to an energy band structure for photons, which may allow or forbid the propagation of electromagnetic waves in a limited frequency range. These unique properties have attracted much attention for both theoretical and applied research. Devices such as high-reflection omnidirectional mirrors, low-loss waveguides, and high- and low-reflection coatings have been demonstrated, and several application areas have been explored, from optical communications and color displays to energy harvest and sensors. In this latter area, photonic crystal fibers (PCF) have proven to be very suitable for the development of highly performing sensors, but one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) PhCs have been successfully employed, too. The working principle of most PhC sensors is based on the fact that any physical phenomenon which affects the periodicity and the refractive index of the PhC structure induces changes in the intensity and spectral characteristics of the reflected, transmitted or diffracted light; thus, optical measurements allow one to sense, for instance, temperature, pressure, strain, chemical parameters, like pH and ionic strength, and the presence of chemical or biological elements. In the present article, after a brief general introduction, we present a review of the state of the art of PhC sensors, with particular reference to our own results in the field of mechanochromic sensors. We believe that PhC sensors based on changes of structural color and mechanochromic effect are able to provide a promising, technologically simple, low-cost platform for further developing devices and functionalities.

scholarly journals Studying tropospheric turbulence with GNSS

2021 ◽  
Author(s):  
Steffen Schön ◽  
Gaël Kermarrec
Keyword(s):  
Refractive Index ◽  
Power Spectrum ◽  
Carrier Phase ◽  
Prediction Models ◽  
Weather Prediction ◽  
Atomic Clock ◽  
Three Dimensional ◽  
Satellite System ◽  
Free Atmosphere ◽  
Phase Measurements

<p>Long-term variations of the tropospheric refractive index delay the carrier phase measurements from Global Navigation Satellite System (GNSS). This information is now operationally integrated in Weather prediction models. Random fluctuations of the refractive index correlate the phase measurements and induces non-stationary noise processes. The correlation structure and spectral properties of observation residuals from GNSS relative positioning provide a unique opportunity to study specific properties of the turbulent atmosphere. In this contribution, we will give a short overview on turbulent processes and their impact on GNSS carrier phase measurements. We will discuss our data analysis concepts to separate the tropospheric fluctuations from other temporally varying error sources such as GNSS receiver clock errors or multipath. The analysis is based on the power spectrum of single or double differences of carrier phase measurements. This approach enables a determination of the cut-off frequencies of the atmospheric noise and the associated power law processes with their typical slopes. The obtained values are compared with theoretical expectations. We will show results for GPS from the Seewinkel network (Austria), as well as from a small network at Physikalisch-Technische Bundesanstalt (PTB, Germany) where all receivers are connected to a common highly stable atomic clock. We show that (i) a two slopes power spectrum can be reliably determined and (ii) that the outer scale length can be taken to a constant value, close to the physically expected one and in relation with the size of the eddies at tropospheric height. The study of their dependencies with the satellite geometry, the Day of the Year (DOY) or the time of the day provides a new insight on the two- and three-dimensional atmospheric turbulence in the free atmosphere.</p>

scholarly journals Variational Assimilation of Radio Occultation Observations into Numerical Weather Prediction Models: Equations, Strategies, and Algorithms

2019 ◽  
Vol 11 (24) ◽  
pp. 2886 ◽  
Author(s):  
Michael Gorbunov ◽  
Razvan Stefanescu ◽  
Vladimir Irisov ◽  
Dusanka Zupanski
Keyword(s):  
Ray Tracing ◽  
Radio Occultation ◽  
Prediction Models ◽  
Weather Prediction ◽  
Standard Form ◽  
Plane Curve ◽  
Variational Assimilation ◽  
Observation Operator ◽  
Global Atmospheric Circulation ◽  
Bending Angles

We review different approaches to the variational assimilation of radio occultation (RO) observations into models of global atmospheric circulation. We derive the general equation for the bending angle that reduces to the Abel integral for a spherically layered atmosphere. We review the full 3-D observation operator for bending angles, which provides the strictest solution, but is also most computationally expensive. Commonly used is the 2-D approximation that allows treating rays as plane curve. We discuss a simple 1-D approach to the assimilation of bending angles. The observation operator based on the standard form of the Abel integral has a disadvantage, because it cannot account for waveguides. Alternative approaches use 1-D ray-tracing. The most straightforward way is to use the same framework as for the 3-D observation operator, with the refractivity field reduced to a single profile independent from the horizontal coordinates. An alternative 1-D ray-tracing approach uses the form of ray equation in a spherically layered medium that uses an invariant. The assimilation of refractivity has also 1-D and 3-D options. We derive a new simple form of the refractivity-mapping operator. We present the results of numerical tests of different 3-D and 1-D observation operators, based on Spire data.

Ray tracing in 3-D complex isotropic media: An analysis of the problem

Geophysics ◽  
1991 ◽  
Vol 56 (12) ◽  
pp. 2057-2069 ◽  
Author(s):  
Jean Virieux ◽  
Véronique Farra
Keyword(s):  
Ray Tracing ◽  
Spline Interpolation ◽  
Linear Equations ◽  
Three Dimensional ◽  
Sampling Strategy ◽  
Perturbation Approach ◽  
Implicit Representation ◽  
B Splines ◽  
Isotropic Media ◽  
Numerical Solver

Procedures for accurate ray tracing in complex three‐dimensional media with interfaces are proposed. The ray tracing equations and the associated paraxial linear equations are solved either by a numerical solver or by an analytical perturbation approach. Interfaces are described with an explicit representation or an implicit representation using B-spline interpolation. For the implicit representation, we exploit two important properties of B-splines, the convex hull and subdivision properties, in order to determine the intersection of the ray with the interface. At the free surface where the recording system is located, a sampling strategy is proposed: limits of branches at caustics, shadow zones, and medium boundaries are detected for a fixed azimuth while the take‐off angle is automatically adjusted in order to have a roughly homogeneous spacing between end points of the rays. The same strategy is also possible for a fixed take‐off angle. The assumed continuity of the traveltime surface between two adjacent azimuths enables one to obtain the initial condition of a ray arriving at any station located on the portion of surface delimited by these two azimuths. This procedure allows for the classification of rays arriving at a given station as we show on different synthetic examples.

Detection of delamination in composites by using electromagnetic penetrating radar

2014 ◽  
Vol 5 (2) ◽  
pp. 151-156
Author(s):  
Z. Mechbal ◽  
A. Khamlichi
Keyword(s):  
Electromagnetic Wave ◽  
Electromagnetic Waves ◽  
Electromagnetic Wave Propagation ◽  
Wave Reflection ◽  
Image Features ◽  
Partial Reflection ◽  
Straight Path ◽  
Reflected Signal ◽  
Short Time ◽  
Intervening Factors

Composites made from E-glass/epoxy or aramid/epoxy are frequently used in aircraft and aerospace industries. These materials are prone to suffer from the presence of delamination, which can reduce severely the performance of aircrafts and even threaten their safety. Since electric conductivity of these composites is rather small, they can propagate electromagnetic waves. Detection of delamination damage can then be monitored by using an electromagnetic penetrating radar scanner, which consists of emitting waves having the form of short time pulses that are centered on a given work frequency. While propagating, these waves undergo partial reflection when running into an obstacle or a material discontinuity. Habitually, the radar is moved at constant speed along a straight path and the reflected signal is processed as a radargram that gives the reflected energy as function of the two-way time and the antenna position.In this work, modeling of electromagnetic wave propagation in composites made from E-glass/epoxy was performed analytically. The electromagnetic wave reflection from a delamination defect was analyzed as function of key intervening factors which include the defect extent and depth, as well as the work frequency. Various simulations were performed and the obtained results have enabled to correlate the reflection pattern image features to the actual delamination defect characteristics which can provide quantification of delamination.

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