We predict the electromagnetic wave propagation in space environments using geometrical optics. The effective indices of the troposphere, stratosphere, and ionosphere are computed, and the reflection, refraction, and attenuation of electromagnetic waves in space environments are calculated based on the ray tracing technique and geometrical optics. The influence of the refractive index and loss of atmosphere and the incident angle of the antenna on electromagnetic wave propagation is discussed.Key Words: Electromagnetic Wave Propagation, Geometrical Optics, Ray Tracing Technique, Space Environment. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ
Food web dynamics outline the ecosystem processes that regulate community structure. Challenges in the approaches used to capture topological descriptions of food webs arise due to the difficulties in collecting extensive empirical data with temporal and spatial variations in community structure and predator–prey interactions. Here, we use a Kohonen self-organizing map algorithm (as a measure of community pattern) and stable isotope-mixing models (as a measure of trophic interaction) to identify food web patterns across a low-turbidity water channel of a temperate estuarine-coastal continuum. We find a spatial difference in the patterns of community compositions between the estuarine and deep-bay channels and a seasonal difference in the plankton pattern but less in the macrobenthos and nekton communities. Dietary mixing models of co-occurring dominant taxa reveal site-specific but unchanging food web topologies and the prominent role of phytoplankton in the trophic base of pelagic and prevalent-detrital benthic pathways. Our approach provides realistic frameworks for linking key nodes from producers to predators in trophic networks.
We propose a novel method to calculate the propagation from a geostationary orbit (GEO) satellite to a ground station considering dispersive and inhomogeneous atmospheric environments with an actual satellite parabolic reflector antenna. The proposed simulation method is based on the hybrid numerical techniques including physical optics (PO), the 3-dimensional (3-D) ray tracing technique, and geometrical optics (GO). The electromagnetic propagation from an actual GEO satellite parabolic reflector antenna to a ground station at Seoul, Korea is calculated using PO. Reflections and refractions at the boundaries of the stratified refractive index model for the atmosphere are then calculated by the ray tracing approach and GO to take into account inhomogeneous atmospheric environments. Our method is verified by comparing with the results with the prediction method of rain attenuation given in ITU-R P.618-13 and the unified model. The comparison generally shows a good agreement. Atmospheric attenuation and boresight errors from a GEO satellite to a ground station are calculated and discussed. As a result of the calculations, when the rainfall rate is 26.19 mm/h, the atmospheric attenuation from a GEO satellite (COMS-1) to a ground station at Seoul, Korea is 12.1621 dB and the boresight error is 0.0336 degrees. INDEX TERMS Atmospheric environments, 3-D ray tracing technique, geometrical optics, physical optics, dispersive and inhomogeneous media.
We propose a novel method to calculate the electromagnetic (EM) wave propagation from low-earth orbit satellite (LEO) to a ground station based on the physical optics (PO), ray tracing technique, and geometric optics (GO) considering interpolated atmospheric environments. Our method includes the reflector antenna analysis using PO, the interpolation of the meteorological data using PCHIP and Kriging interpolation, transmission analysis using ray tracing and geometrical optics. Tropospheric and stratospheric environments are modeled using meteorological data-air pressure and temperature, relative humidity, and rain rate-measured at 9 different radiosonde observatories in and around South Korea. Furthermore, we utilize Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) and Kriging-exponential methods for vertical and horizontal interpolations of the raw meteorological data, respectively. Hence, the interpolated atmospheric environments are amenable to the best use of ray tracing technique and GO. Subsequently, effective refractive indices of the stratified media can be extracted via millimeter-propagation-model93. The simplified Appleton-Hartree equation characterizes the ionospheric environment. Considering a sunsynchronous orbit satellite passing through South Korea, we calculate atmospheric attenuation, boresight error, received power, and compensation angle of satellite antenna for various conditions.INDEX TERMS electromagnetic wave propagation, low-earth orbit satellite, atmospheric environments, ray tracing technique, piecewise cubic Hermite interpolating polynomial.
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