CALCULATION OF POLARIZATION LOSSES FOR HF COMMUNICATION CHANNEL (PART 2)

2021 ◽  
pp. 17-28
Author(s):  
M. M. Anishin ◽  
G. A. Zhbankov
Keyword(s):  
Computational Experiment ◽  
Communication Channel ◽  
Elevation Angle ◽  
Operating Frequency ◽  
Geographic Position ◽  
Receiving Antenna ◽  
Practical Recommendations

The article is devoted to the description of the procedure for calculating the loss for polarization mismatch in the receiving antenna. The results of a computational experiment of these losses are presented as a function of the operating frequency, azimuth of the receiving antenna, its geographic position and the elevation angle of the rays at the reception center. Based on the results of the calculation, conclusions are drawn about the dependence of losses on various parameters, and practical recommendations are given on the location and polarization of receiving antennas.

scholarly journals Development and validation of comprehensive closed formulas for atmospheric delay and altimetry correction in ground-based GNSS-R

2021 ◽  
Author(s):  
Thalia Nikolaidou ◽  
Marcelo Santos ◽  
Simon Williams ◽  
Felipe Geremia-Nievinski
Keyword(s):  
Elevation Angle ◽  
Satellite System ◽  
Radio Waves ◽  
Atmospheric Refraction ◽  
Refraction Effect ◽  
Receiving Antenna ◽  
Coastal Sea ◽  
Global Navigation Satellite ◽  
Development And Validation ◽  
Atmospheric Delays

Radio waves used in Global Navigation Satellite System Reflectometry (GNSS-R) are subject to atmospheric refraction, even for ground-based tracking stations in applications such as coastal sea-level altimetry. Although atmospheric delays are best investigated via ray-tracing, its modification for reflections is not trivial. We have developed closed-form expressions for atmospheric refraction in ground-based GNSS-R and validated them against raytracing. We provide specific expressions for the linear and angular components of the atmospheric interferometric delay and corresponding altimetry correction, parameterized in terms of refractivity and bending angle. Assessment results showed excellent agreement for the angular component and good for the linear one. About half of the delay was found to originate above the receiving antenna at low satellite elevation angles. We define the interferometric slant factor used to map interferometric zenithal delays to individual satellites. We also provide an equivalent correction for the effective satellite elevation angle such that the refraction effect is nullified. Lastly, we present the limiting conditions for negligible atmospheric altimetry correction (sub-cm), over domain of satellite elevation angle and reflector height. For example, for 5-meter reflector height, observations below 20° elevation angle have more than 1-centimeter atmospheric altimetry error.

Impact of Earth's curvature on coastal sea level altimetry with ground-based GNSS Reflectometry

2021 ◽  
Author(s):  
Vitor Hugo Almeida Junior ◽  
Marcelo Tomio Matsuoka ◽  
Felipe Geremia-Nievinski
Keyword(s):  
Sea Level ◽  
Elevation Angle ◽  
Rate Of Change ◽  
Tide Gauges ◽  
Reflection Point ◽  
Promising Alternative ◽  
The Earth ◽  
Receiving Antenna ◽  
Coastal Sea ◽  
Gnss Reflectometry

<p>Global mean sea level is rising at an increasing rate. It is expected to cause more frequent extreme events on coastal sites. The main sea level monitoring systems are conventional tide gauges and satellite altimeters. However, tide gauges are few and satellite altimeters do not work well near the coasts. Ground-based GNSS Reflectometry (GNSS-R) is a promising alternative for coastal sea level measurements. GNSS-R works as a bistatic radar, based on the use of radio waves continuously emitted by GNSS satellites, such as GPS and Galileo, that are reflected on the Earth’s surface. The delay between reflected and direct signals, known as interferometric delay, can be used to retrieve geophysical parameters, such as sea level. One advantage of ground-based GNSS-R is the slant sensing direction, which implies the reflection points can occur at long distances from the receiving antenna. The higher is the receiving antenna and the lower is the satellite elevation angle, the longer will be the distance to the reflection point. The geometrical modeling of interferometric delay, in general, adopts a planar and horizontal model to represent the reflector surface. This assumption may be not valid for far away reflection points due to Earth’s curvature. It must be emphasized that ground-based GNSS-R sensors can be located at high altitudes, such in lighthouses and cliffs, and GNSS satellites are often tracked near grazing incidence and even at negative elevation angles. Eventually, Earth’s curvature would have a significant impact on altimetry retrievals. The osculating spherical model is more adequate to represent the Earth’s surface since its mathematical complexity is in between a plane and an ellipsoid. The present work aims to quantify the effect of Earth’s curvature on ground-based GNSS-R altimetry. Firstly, we modeled the interferometric delay for each plane and sphere and we calculated the differences across the two surface models, for varying satellite elevation and antenna altitude. Then, we developed an altimetry correction in terms of half of the rate of change of the delay correction with respect to the sine of elevation. We simulated observation scenarios with satellite elevation angles from zenith down to the minimum observable elevation on the spherical horizon (negative) and antenna altitudes from 10 m to 500 m. We noted that due to Earth’s curvature, the reflection point is displaced, brought closer in the x-axis and bent downward in the y-axis. The displacement of the reflection point increases the interferometric delay. Near the planar horizon, at zero elevation, the difference increases quickly and so does the altimetry correction. Finally, considering a 1-cm altimetry precision threshold to sea-level measurements, we observed that the altimetry correction for Earth’s curvature is needed at 10°, 20°, and 30° satellite elevation, for an antenna altitude of 60 m, 120 m, and 160 m, respectively.</p>

scholarly journals Communication based on scattered laser radiation in a medium with high turbidity or in the presence of a noise source

2021 ◽  
Vol 2140 (1) ◽  
pp. 012009
Author(s):  
E S Poznakharev ◽  
V V Belov ◽  
M V Tarasenkov ◽  
A V Fedosov ◽  
V N Abramochkin
Keyword(s):  
Laser Radiation ◽  
Error Probability ◽  
Communication Channel ◽  
Azimuthal Angle ◽  
Elevation Angle ◽  
Atmospheric Environment ◽  
Laser Source ◽  
Aerosol Chamber ◽  
High Turbidity ◽  
Optical Communication Channel

Abstract The results of laboratory studies of an optical communication channel based on scattered radiation in the Big Aerosol Chamber of IAO SB RAS in a clean atmospheric environment, in the case of the chamber filled with vapor of the water-glycerin mixture, and in the presence of an noise laser source are analyzed. It is found that with the non-coplanar communication geometry in the chamber filled with the water-glycerin mixture, stable data transmission is possible with the azimuthal angle of orientation of the detector optical axis up to 5°. The error probability in the communication channel increases more slowly with an increase of the detector elevation angle in the chamber filled with the water-glycerin mixture than that in the chamber without this mixture does. The presence of an interfering laser radiation at a wavelength λ = 510 nm in the communication channel affects the communication quality. When the power of the noise laser source achieves 70 mW, the maximal error probability corresponds to 0.02.

scholarly journals Development and validation of comprehensive closed formulas for atmospheric delay and altimetry correction in ground-based GNSS-R

2021 ◽  
Author(s):  
Thalia Nikolaidou ◽  
Marcelo Santos ◽  
Simon Williams ◽  
Felipe Geremia-Nievinski
Keyword(s):  
Elevation Angle ◽  
Satellite System ◽  
Radio Waves ◽  
Atmospheric Refraction ◽  
Refraction Effect ◽  
Receiving Antenna ◽  
Coastal Sea ◽  
Global Navigation Satellite ◽  
Development And Validation ◽  
Atmospheric Delays

Radio waves used in Global Navigation Satellite System Reflectometry (GNSS-R) are subject to atmospheric refraction, even for ground-based tracking stations in applications such as coastal sea-level altimetry. Although atmospheric delays are best investigated via ray-tracing, its modification for reflections is not trivial. We have developed closed-form expressions for atmospheric refraction in ground-based GNSS-R and validated them against raytracing. We provide specific expressions for the linear and angular components of the atmospheric interferometric delay and corresponding altimetry correction, parameterized in terms of refractivity and bending angle. Assessment results showed excellent agreement for the angular component and good for the linear one. About half of the delay was found to originate above the receiving antenna at low satellite elevation angles. We define the interferometric slant factor used to map interferometric zenithal delays to individual satellites. We also provide an equivalent correction for the effective satellite elevation angle such that the refraction effect is nullified. Lastly, we present the limiting conditions for negligible atmospheric altimetry correction (sub-cm), over domain of satellite elevation angle and reflector height. For example, for 5-meter reflector height, observations below 20° elevation angle have more than 1-centimeter atmospheric altimetry error.

Ultimate resolution and information in electron microscopy

1991 ◽  
Vol 49 ◽  
pp. 496-497
Author(s):  
D. Van Dyck
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Transfer Function ◽  
Information Transfer ◽  
Communication Channel ◽  
Structural Information ◽  
Information Rate ◽  
Noise Power ◽  
Signal Power ◽  
Imaging Device

An (electron) microscope can be considered as a communication channel that transfers structural information between an object and an observer. In electron microscopy this information is carried by electrons. According to the theory of Shannon the maximal information rate (or capacity) of a communication channel is given by C = B log2 (1 + S/N) bits/sec., where B is the band width, and S and N the average signal power, respectively noise power at the output. We will now apply to study the information transfer in an electron microscope. For simplicity we will assume the object and the image to be onedimensional (the results can straightforwardly be generalized). An imaging device can be characterized by its transfer function, which describes the magnitude with which a spatial frequency g is transferred through the device, n is the noise. Usually, the resolution of the instrument ᑭ is defined from the cut-off 1/ᑭ beyond which no spadal information is transferred.

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