Interference analysis involving HEO satellites and fixed service receivers: probabilistic modeling of the fixed service receiving antenna elevation angle

2014 ◽  
Author(s):  
Ana Gabriela Correa ◽  
Jose Mauro Fortes
Keyword(s):  
Elevation Angle ◽  
Probabilistic Modeling ◽  
Interference Analysis ◽  
Receiving Antenna

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>

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.

The elevation angle of the vagina (EAV) following different pelvic reconstructive procedures

2018 ◽  
Author(s):  
J Neymeyer ◽  
AY Weintraub ◽  
S Weinberger ◽  
DE Moldovan ◽  
K Kornienko ◽  
...  
Keyword(s):  
Elevation Angle ◽  
Reconstructive Procedures
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