scholarly journals High?Frequency Backscatter Observations at Salisbury, South Australia

1956 ◽  
Vol 9 (4) ◽  
pp. 454 ◽  
Author(s):  
CG McCue
Keyword(s):  
Time Delay ◽  
High Frequency ◽  
Elevation Angle ◽  
South Australia ◽  
Angle Of Arrival ◽  
Simultaneous Observation ◽  
Pulse Technique ◽  
Directional Characteristics ◽  
Resultant Increase

An improved pulse technique which permits simultaneous observation of time delay and elevation angle of arrival of ionospheric echoes has enabled recognition of seven different modes of backscatter propagation involving both ionospheric and ground origins. By the use of four transmitting aerials with differing directional characteristics, it is shown that land is a more prominent source of backscatter than sea at low angles of elevation and that extremely large changes in land roughness can be identified by the resultant increase of backscatter echo amplitude.

Effects of Time Delay Between Unipolar Pulses in High Frequency Nano-Electrochemotherapy

2021 ◽  
pp. 1-1
Author(s):  
Vitalij Novickij ◽  
Austeja Baleviciute ◽  
Veronika Malysko ◽  
Augustinas Zelvys ◽  
Eivina Radzeviciute ◽  
...  
Keyword(s):  
Time Delay ◽  
High Frequency

scholarly journals Mapping ionospheric backscatter measured by the SuperDARN HF radars – Part 2: Assessing SuperDARN virtual height models

2008 ◽  
Vol 26 (4) ◽  
pp. 843-852 ◽  
Author(s):  
T. K. Yeoman ◽  
G. Chisham ◽  
L. J. Baddeley ◽  
R. S. Dhillon ◽  
T. J. T. Karhunen ◽  
...  
Keyword(s):  
Large Scale ◽  
Elevation Angle ◽  
Field Measurements ◽  
Companion Paper ◽  
Hf Radar ◽  
Propagation Path ◽  
Angle Of Arrival ◽  
Virtual Height ◽  
F Region ◽  
Propagation Paths

Abstract. The Super Dual Auroral Radar Network (SuperDARN) network of HF coherent backscatter radars form a unique global diagnostic of large-scale ionospheric and magnetospheric dynamics in the Northern and Southern Hemispheres. Currently the ground projections of the HF radar returns are routinely determined by a simple rangefinding algorithm, which takes no account of the prevailing, or indeed the average, HF propagation conditions. This is in spite of the fact that both direct E- and F-region backscatter and 1½-hop E- and F-region backscatter are commonly used in geophysical interpretation of the data. In a companion paper, Chisham et al. (2008) have suggested a new virtual height model for SuperDARN, based on average measured propagation paths. Over shorter propagation paths the existing rangefinding algorithm is adequate, but mapping errors become significant for longer paths where the roundness of the Earth becomes important, and a correct assumption of virtual height becomes more difficult. The SuperDARN radar at Hankasalmi has a propagation path to high power HF ionospheric modification facilities at both Tromsø on a ½-hop path and SPEAR on a 1½-hop path. The SuperDARN radar at Þykkvibǽr has propagation paths to both facilities over 1½-hop paths. These paths provide an opportunity to quantitatively test the available SuperDARN virtual height models. It is also possible to use HF radar backscatter which has been artificially induced by the ionospheric heaters as an accurate calibration point for the Hankasalmi elevation angle of arrival data, providing a range correction algorithm for the SuperDARN radars which directly uses elevation angle. These developments enable the accurate mappings of the SuperDARN electric field measurements which are required for the growing number of multi-instrument studies of the Earth's ionosphere and magnetosphere.

scholarly journals Mapping ionospheric backscatter measured by the SuperDARN HF radars – Part 1: A new empirical virtual height model

2008 ◽  
Vol 26 (4) ◽  
pp. 823-841 ◽  
Author(s):  
G. Chisham ◽  
T. K. Yeoman ◽  
G. J. Sofko
Keyword(s):  
Elevation Angle ◽  
Propagation Path ◽  
Angle Of Arrival ◽  
Velocity Measurements ◽  
Actual Distribution ◽  
Virtual Height ◽  
Radar Network ◽  
Straight Line ◽  
Target Locations ◽  
Height Model

Abstract. Accurately mapping the location of ionospheric backscatter targets (density irregularities) identified by the Super Dual Auroral Radar Network (SuperDARN) HF radars can be a major problem, particularly at far ranges for which the radio propagation paths are longer and more uncertain. Assessing and increasing the accuracy of the mapping of scattering locations is crucial for the measurement of two-dimensional velocity structures on the small and meso-scale, for which overlapping velocity measurements from two radars need to be combined, and for studies in which SuperDARN data are used in conjunction with measurements from other instruments. The co-ordinates of scattering locations are presently estimated using a combination of the measured range and a model virtual height, assuming a straight line virtual propagation path. By studying elevation angle of arrival information of backscatterred signals from 5 years of data (1997–2001) from the Saskatoon SuperDARN radar we have determined the actual distribution of the backscatter target locations in range-virtual height space. This has allowed the derivation of a new empirical virtual height model that allows for a more accurate mapping of the locations of backscatter targets.

scholarly journals Effect of self focusing on the prolongation of laser produced plasma channel

2009 ◽  
Vol 27 (1) ◽  
pp. 33-39 ◽  
Author(s):  
U. Verma ◽  
A.K. Sharma
Keyword(s):  
Theoretical Model ◽  
Time Delay ◽  
Laser Pulse ◽  
Density Profile ◽  
Plasma Channel ◽  
Ion Density ◽  
Pulse Technique ◽  
Recombination Time ◽  
Self Focusing ◽  
Gaseous Plasma

AbstractA theoretical model for the prolongation of lifetime of a gaseous plasma channel formed by two pulse technique at laser intensities below the tunnel ionization threshold is developed. The first laser pulse ionizes the gas completely on the axis and partially off the axis, causing self-defocusing of the pulse. After the passage of the pulse, the plasma expands radially, creating an atom/ion density profile with a minimum on the axis. Partial recombination also sets in. As the second pulse arrives, after a time delay of less than the recombination time (~ns), the electrons get heated, and the recombination rate is slowed down. The second pulse self focuses, enhancing the heating rate and lengthening the lifetime of the plasma channel.

Analysis for Electrical Performance of Antenna Considering Gravity Deformation Based on Different Band and Elevation Angle

2017 ◽  
Vol 863 ◽  
pp. 266-272
Author(s):  
Kai Yu Hu ◽  
Kai Wang ◽  
Pei Zhang Wu ◽  
Yi Jiang
Keyword(s):  
High Frequency ◽  
High Reliability ◽  
Elevation Angle ◽  
Electrical Performance ◽  
High Frequency Band ◽  
Deep Space Exploration ◽  
Elevation Changes ◽  
Gain Loss ◽  
Deformation Error ◽  
Meaningful Data

Abstract.In order to ensure higher accuracy and better electrical performance of large antennas in future,this paper does some research for deformation of antenna’s reflector:modeling for 25m antenna and reappearing deformation when elevation changes every 15° just considering gravity by using ANSYS.Using results of simulation obtains deformation error curves with elevation changes, creates the conditions for compensating distortion and has a certain value. By using Ruze formula, deeply studies the regular about antenna’s electrical performance influenced by deformation because of elevation changes,obtains meaningful data and tables of relationship between elevation and parameters of electrical performance in nine bands of 25m antenna.It finds out that when working in high-frequency band, efficiency and gain loss of antenna will be more affected by elevation angle changes.Finally creates conditions for optimizing antenna parameters and performing high reliability tasks such as deep space exploration and aerospace communication.

scholarly journals Sound Source Localization Fusion Algorithm and Performance Analysis of a Three-Plane Five-Element Microphone Array

2019 ◽  
Vol 9 (12) ◽  
pp. 2417
Author(s):  
Hongyan Xing ◽  
Xu Yang
Keyword(s):  
Time Delay ◽  
Source Localization ◽  
Sound Source ◽  
Microphone Array ◽  
Elevation Angle ◽  
Measurement Precision ◽  
Sound Source Localization ◽  
Fusion Algorithm ◽  
Single Plane ◽  
Horizontal Angle

To reduce the negative effect on sound source localization when the source is at an extreme angle and improve localization precision and stability, a theoretical model of a three-plane five-element microphone array is established, using time-delay values to judge the sound source’s quadrant position. Corresponding judgment criteria were proposed, solving the problem in which a single-plane array easily blurs the measured position. Based on sound source geometric localization, a formula for the sound source azimuth calculation of a single-plane five-element microphone array was derived. The sinusoids and cosines of two elevation angles based on two single-plane arrays were introduced into the sound source spherical coordinates as composite weighted coefficients, and a sound source localization fusion algorithm based on a three-plane five-element microphone array was proposed. The relationship between the time-delay estimation error, elevation angle, horizontal angle, and microphone array localization performance was discussed, and the precision and stability of ranging and direction finding were analyzed. The results show that the measurement precision of the distance from the sound source to the array center and the horizontal angle are improved one to threefold, and the measurement precision of the elevation angle is improved one to twofold. Although there is a small error, the overall performance of the sound source localization is stable, reflecting the advantages of the fusion algorithm.

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