scholarly journals Measurement of Range-Weighting Function for Range Imaging of VHF Atmospheric Radars Using Range Oversampling

2014 ◽  
Vol 31 (1) ◽  
pp. 47-61 ◽  
Author(s):  
Jenn-Shyong Chen ◽  
Ching-Lun Su ◽  
Yen-Hsyang Chu ◽  
Ruey-Ming Kuong ◽  
Jun-ichi Furumoto
Keyword(s):  
Power Distribution ◽  
High Frequency ◽  
Weighting Function ◽  
Signal To Noise Ratio ◽  
Pulse Length ◽  
Range Imaging ◽  
Very High Frequency ◽  
Gaussian Form ◽  
Radar Echoes ◽  
Very High

Abstract Multifrequency range imaging (RIM) used with the atmospheric radars at ultra- and very high-frequency (VHF) bands is capable of retrieving the power distribution of the backscattered radar echoes in the range direction, with some inversion algorithms such as the Capon method. The retrieved power distribution, however, is weighted by the range-weighting function (RWF). Modification of the retrieved power distribution with a theoretical RWF may cause overcorrection around the edge of the sampling gate. In view of this, an effective RWF that is in a Gaussian form and varies with the signal-to-noise ratio (SNR) of radar echoes has been proposed to mitigate the range-weighting effect and thereby enhance the continuity of the power distribution at gate boundaries. Based on the previously proposed concept, an improved approach utilizing the range-oversampled signals is addressed in this article to inspect the range-weighting effects at different range locations. The shape of the Gaussian RWF for describing the range-weighting effect was found to vary with the off-center range location in addition to the SNR of radar echoes—that is, the effective RWF for the RIM was SNR and range dependent. The use of SNR- and range-dependent RWF can be of help to improve the range imaging to some degree at the range location outside the range extent of a sampling gate defined by the pulse length. To verify the proposed approach, several radar experiments were carried out with the Chung-Li (24.9°N, 121.1°E) and middle and upper atmosphere (MU; 34.85°N, 136.11°E) VHF radars.

scholarly journals Evaluation of multifrequency range-imaging technique implemented on the Chung–Li VHF atmospheric radar

2015 ◽  
Vol 8 (9) ◽  
pp. 10097-10120 ◽  
Author(s):  
J.-S. Chen ◽  
S.-C. Tsai ◽  
C.-L. Su ◽  
Y.-H. Chu
Keyword(s):  
Time Delay ◽  
Power Distribution ◽  
Weighting Function ◽  
Imaging Technique ◽  
Pulse Length ◽  
Radar Data ◽  
Range Imaging ◽  
Vhf Radar ◽  
Two Factors ◽  
Cable Lines

Abstract. Multifrequency range imaging technique (RIM) has been implemented on the Chung–Li VHF-array radar since 2008 after its renovation. This study made a more complete examination and evaluation of the RIM technique to facilitate the performance of the radar for atmospheric studies. Various experiments of RIM with different radar parameters such as pulse length, pulse shape, receiver bandwidth, transmitter frequency set, and so on, were conducted. The radar data employed for the study were collected from 2008 to 2013. It has been shown that two factors, the range/time delay of the signal traveling in the media and the standard deviation of Gaussian-shaped range-weighting function, play crucial roles in ameliorating the RIM-produced brightness (or power distribution); the two factors are associated with some radar parameters. In addition to radar parameters, long-term RIM data show that the aging of cable lines or key components of the radar system may result in an increase of the range/time delay of signal. It is also found that the range/time delay was visibly different for the echoes from the atmosphere with and without the presence of significant precipitation. A procedure of point-by-point correction of range/time delay was thus conducted to minimize the bogus brightness discontinuity at range gate boundaries. With the RIM technique, the Chung–Li VHF radar demonstrates its first successful observation of double-layer structures as well as their temporal and spatial variations with time.

MAGNETIC DISTURBANCES, SPORADIC E, AND RADIO ECHOES ASSOCIATED WITH THE AURORA

1954 ◽  
Vol 32 (5) ◽  
pp. 326-329 ◽  
Author(s):  
J. H. Meek ◽  
A. G. McNamara
Keyword(s):  
High Frequency ◽  
Field Variation ◽  
Magnetic Field Variation ◽  
Very High Frequency ◽  
High Frequency Radar ◽  
Radar Echoes ◽  
Sporadic E ◽  
Auroral Arcs ◽  
Very High ◽  
Magnetic Disturbances

A comparison of simultaneous data on the visible aurora, the earth's magnetic field variation, vertical and oblique ionosonde echoes, and very-high-frequency radar echoes has been made. Long-range high-frequency and very-high-frequency radio echoes do not appear to correlate individually. Reflections are observed, however, on both frequency ranges coincident with the appearance of low elevation auroral arcs, which are associated with magnetic bays.

POLARIZATION OF RADAR ECHOES FROM AURORA

1959 ◽  
Vol 37 (6) ◽  
pp. 690-697 ◽  
Author(s):  
A. Kavadas ◽  
D. G. Glass
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Ground Plane ◽  
Linear Component ◽  
Very High Frequency ◽  
General Direction ◽  
Radar Echoes ◽  
Linearly Polarized ◽  
Field Lines ◽  
Very High

Auroral radar echoes at very high frequency received at antennas sensitive to linearly polarized components in directions symmetrical to the plane of polarization of the vertically polarized transmitted wave and the ground plane indicate that the received wave, in addition to an unpolarized component, contains a linear component of polarization tilted in the general direction of the earth's magnetic field lines.

scholarly journals Evaluation of multifrequency range imaging technique implemented on the Chung–Li VHF atmospheric radar

2016 ◽  
Vol 9 (5) ◽  
pp. 2345-2355 ◽  
Author(s):  
Jenn-Shyong Chen ◽  
Shih-Chiao Tsai ◽  
Ching-Lun Su ◽  
Yen-Hsyang Chu
Keyword(s):  
Time Delay ◽  
Power Distribution ◽  
Weighting Function ◽  
Imaging Technique ◽  
Pulse Length ◽  
Radar Data ◽  
Range Imaging ◽  
Vhf Radar ◽  
Two Factors ◽  
The Media

Abstract. The multifrequency range imaging technique (RIM) has been implemented on the Chung–Li VHF array radar since 2008 after its renovation. This study made a more complete examination and evaluation of the RIM technique to facilitate the performance of the radar for atmospheric studies. RIM experiments with various radar parameters such as pulse length, pulse shape, receiver bandwidth, transmitter frequency set, and so on were conducted. The radar data employed for the study were collected from 2008 to 2013. It has been shown that two factors, the range/time delay of the signal traveling in the media and the standard deviation of Gaussian-shaped range-weighting function, play crucial roles in ameliorating the RIM-produced brightness (or power distribution); the two factors are associated with some radar parameters and system characteristics. The range/time delay of the signal was found to increase with time; moreover, it was slightly different for the echoes from the atmosphere with and without the presence of significant precipitation. A procedure of point-by-point correction of range/time delay was thus executed for the presence of precipitation to minimize the bogus brightness discontinuity at range gate boundaries. With the RIM technique, the Chung–Li VHF radar demonstrates its first successful observation of double-layer structures as well as their temporal and spatial variations with time.

scholarly journals Simultaneous Observations of Thin Humidity Gradients in the Lower Troposphere with a Raman Lidar and the Very High-Frequency Middle- and Upper-Atmosphere Radar

2010 ◽  
Vol 27 (5) ◽  
pp. 950-956 ◽  
Author(s):  
H. Luce ◽  
T. Takai ◽  
T. Nakamura ◽  
M. Yamamoto ◽  
S. Fukao
Keyword(s):  
High Frequency ◽  
Lower Troposphere ◽  
Upper Atmosphere ◽  
Raman Lidar ◽  
Range Imaging ◽  
Very High Frequency ◽  
Additional Information ◽  
Radar Measurements ◽  
Very High ◽  
Balloon Measurements

Abstract Humidity is, among other things, a key parameter in the evolution of atmospheric dynamics and in the formation of clouds and precipitation through latent heat release. The continuous observation of its vertical distribution is thus important in meteorology. In the absence of convection, humidity in the lower troposphere is distributed into nearly horizontally stratified layers. The thin humidity gradients at the edges of these layers are known to be the main cause of very high-frequency (VHF) stratosphere–troposphere (ST) radar backscatter in the lower troposphere. This property has been experimentally demonstrated many times in the literature from comparisons between balloon measurements and low-resolution radar observations. In the present work, original results of comparisons between Raman lidar measurements of water vapor and middle- and upper-atmosphere (MU) radar measurements of echo power using a range-imaging technique are shown at high spatial and temporal resolutions (∼50 m, ∼20 s). Other tremendous advantages of such comparisons are the simultaneity, time continuity, and colocalization of the lidar and radar measurements. The results show that the radar can be used for continuously monitoring the thin positive and negative gradients of humidity when operated in range-imaging mode. With additional information from balloon measurements, it would be possible to retrieve humidity profiles in the lower troposphere at an unprecedented vertical and time resolution.

Experimental Investigation of very High Frequency Slot Antenna on M-60A-1 Tank

1977 ◽  
Author(s):  
D. V. Campbell ◽  
William Kennebeck ◽  
A. Zanella ◽  
Paul Sexton
Keyword(s):  
Experimental Investigation ◽  
High Frequency ◽  
Slot Antenna ◽  
Very High Frequency ◽  
Very High

A collision feedback based multiple access control protocol for very high frequency data exchange system in E-navigation

2021 ◽  
pp. 1-16
Author(s):  
Xu Hu ◽  
Bin Lin ◽  
Ping Wang ◽  
Hongguang Lyu ◽  
Tie-Shan Li
Keyword(s):  
Access Control ◽  
High Frequency ◽  
Multiple Access ◽  
Data Exchange ◽  
High Frequency Data ◽  
Frequency Data ◽  
Exchange System ◽  
Very High Frequency ◽  
Time Division ◽  
Very High

Abstract The very high frequency data exchange system (VDES) is promising in promoting electronic navigation (E-navigation) and improving navigation safety. The multiple access control (MAC) protocol is crucial to the transmission performance of VDES. The self-organising time division multiple access (SOTDMA) protocol, as the only access mode given by current recommendations, leads to a high rate of transmission collisions in the traditional automatic identification system (AIS), especially with heavy traffic loads. This paper proposes a novel feedback based time division multiple access (FBTDMA) protocol to address the problems caused by SOTDMA, such that collision of transmissions can be avoided in information transmission among vessels. Simulation results demonstrate that the proposed FBTDMA outperforms the traditional SOTDMA in terms of channel utilisation and throughput, and significantly reduces the transmission collision rate. The study is expected to provide insights into VDES standardisation and E-navigation modernisation.

scholarly journals Measurement of Electrical Properties of Superconducting YBCO Thin Films in the VHF Range

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3360
Author(s):  
Yakir Dahan ◽  
Eldad Holdengreber ◽  
Elichai Glassner ◽  
Oz Sorkin ◽  
Shmuel E. Schacham ◽  
...  
Keyword(s):  
Thin Films ◽  
Theoretical Model ◽  
Quality Factor ◽  
High Frequency ◽  
Unit Length ◽  
Superconducting Thin Films ◽  
Electrical Parameters ◽  
Very High Frequency ◽  
Production Constraints ◽  
Very High

A new measurement technique of electrical parameters of superconducting thin films at the Very High Frequency (VHF) range is described, based on resonators with microstrip (MS) structures. The design of an optimal resonator was achieved, based on a thorough theoretical analysis, which is required for derivation of the exact configuration of the MS. A theoretical model is presented, from which an expression for the attenuation of a MS line can be derived. Accordingly, simulations were performed, and an optimal resonator for the VHF range was designed and implemented. Production constraints of YBa2Cu3O7 (YBCO) limited the diameter of the sapphire substrate to 3″. Therefore, a meander configuration was formed to fit the long λ/4 MS line on the wafer. By measuring the complex input reflection coefficients of a λ/4 resonator, we extracted the quality factor, which is mainly affected by the dielectric and conductor attenuations. The experimental results are well fitted by the theoretical model. The dielectric attenuation was calculated using the quasi-static analysis of the MS line. An identical copper resonator was produced and measured to compare the properties of the YBCO resonator in reference to the copper one. A quality factor of ~6·105 was calculated for the YBCO resonator, three orders of magnitude larger than that of the copper resonator. The attenuation per unit length of the YBCO layer was smaller by more than five orders of magnitude than that of the copper.

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