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.

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 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 High-Range Resolution Spectral Analysis of Precipitation Through Range Imaging of the Chung-Li VHF Radar

2017 ◽  
Author(s):  
Shih-Chiao Tsai ◽  
Jenn-Shyong Chen ◽  
Yen-Hsyang Chu ◽  
Ching-Lun Su ◽  
Jui-Hsiang Chen
Keyword(s):  
Weighting Function ◽  
Power Doppler ◽  
Power Spectra ◽  
Doppler Frequency ◽  
Doppler Velocity ◽  
Small Scale ◽  
Range Imaging ◽  
Very High Frequency ◽  
Vhf Radar ◽  
Range Resolution

Abstract. Multi-frequency range imaging (RIM) has been implemented in the Chung-Li very-high-frequency (VHF) radar, located on the campus of National Central University, Taiwan, since 2008. RIM processes the echo signals with a group of closely spaced transmitting frequencies through appropriate inversion methods to obtain high-resolution distribution of echo power in the range direction. This is beneficial to the investigation of the small scale structure embedded in dynamic atmosphere. Five transmitting frequencies were employed in the radar experiment for observation of the precipitating atmosphere during the period between 21 and 23 Aug, 2013. Using the Capon and Fourier methods, the radar echoes were synthesized to retrieve the temporal signals at a smaller range step than the original range resolution defined by the pulse width, and such retrieved temporal signals were then processed in the Doppler frequency domain to identify the atmosphere and precipitation echoes. An analysis called conditional averaging was further executed for echo power, Doppler velocity, and spectral width to verify the potential capabilities of the retrieval processing in resolving small-scale precipitation and atmosphere structures. Point-by-point correction of range delay combined with compensation of range weighting function effect has been performed during the retrieval of temporal signals to improve the continuity of power spectra at gate boundaries, making the small-scale structures in the power spectra more natural and reasonable. We examined stratiform and convective precipitations and demonstrated their different structured characteristics by means of the Capon-processed results.

scholarly journals Extended Application of a Novel Phase Calibration Approach of Multiple-Frequency Range Imaging to the Chung-Li and MU VHF Radars

2009 ◽  
Vol 26 (11) ◽  
pp. 2488-2500 ◽  
Author(s):  
Jenn-Shyong Chen ◽  
Ching-Lun Su ◽  
Yen-Hsyang Chu ◽  
Gernot Hassenpflug ◽  
Marius Zecha
Keyword(s):  
Time Delay ◽  
Double Layers ◽  
Small Scale ◽  
Multiple Frequency ◽  
Frequency Range ◽  
Range Imaging ◽  
Vhf Radar ◽  
Phase Calibration ◽  
Phase Bias ◽  
Calibration Approach

Abstract Multiple-frequency range imaging (RIM), designed to improve the range resolution of radar echo distribution, is now available for the recently upgraded Chung-Li VHF radar (24.9°N, 121.1°E). To complete the RIM technique of this radar, a novel phase calibration approach, proposed initially for the Ostsee Wind (OSWIN) VHF radar, was employed to examine the effects of phase bias and the range-weighting function on the received radar echoes. The estimated phase bias indicated a time delay of ∼1.83 μs for the signal in the radar system. In contrast, such a time delay is more difficult to determine from the phase distribution of two-frequency cross-correlation functions. The same calibration approach was also applied successfully to the middle and upper atmosphere (MU) radar (34.85°N, 136.11°E) and revealed a time delay of ∼0.33 μs for the radar parameters employed. These calibration results for various radars demonstrate the general usability of the proposed calibration approach. With the high-resolution performance of RIM, some small-scale Kelvin–Helmholtz (KH) billows, double-layer structures, and plumelike structures in the troposphere that cannot be seen in height–time intensity plots have been recognized in present observations. The billows and double layers were found to be closely related to strong vertical wind shear and small Richardson number, supporting the hypothesis of a dynamic process of KH instability. On the other hand, the plumelike structures were observed to grow out of a wavy layer and could be attributed to saturation and breaking of gravity waves. These fine structures have shown some remarkable features resolved by the RIM method applied to VHF radars in the lower atmosphere.

scholarly journals High-range resolution spectral analysis of precipitation through range imaging of the Chung-Li VHF radar

2018 ◽  
Vol 11 (1) ◽  
pp. 581-592
Author(s):  
Shih-Chiao Tsai ◽  
Jenn-Shyong Chen ◽  
Yen-Hsyang Chu ◽  
Ching-Lun Su ◽  
Jui-Hsiang Chen
Keyword(s):  
Spectral Analysis ◽  
Weighting Function ◽  
Power Doppler ◽  
Power Spectra ◽  
Convective Precipitation ◽  
Doppler Velocity ◽  
Small Scale ◽  
Range Imaging ◽  
Vhf Radar ◽  
Range Resolution

Abstract. Multi-frequency range imaging (RIM) has been operated in the Chung-Li very high-frequency (VHF) radar, located on the campus of National Central University, Taiwan, since 2008. RIM processes the echo signals with a group of closely spaced transmitting frequencies through appropriate inversion methods to obtain high-resolution distribution of echo power in the range direction. This is beneficial to the investigation of the small-scale structure embedded in dynamic atmosphere. Five transmitting frequencies were employed in the radar experiment for observation of the precipitating atmosphere during the period between 21 and 23 August 2013. Using the Capon and Fourier methods, the radar echoes were synthesized to retrieve the temporal signals at a smaller range step than the original range resolution defined by the pulse width, and such retrieved temporal signals were then processed in the Doppler frequency domain to identify the atmosphere and precipitation echoes. An analysis called conditional averaging was further executed for echo power, Doppler velocity, and spectral width to verify the potential capabilities of the retrieval processing in resolving small-scale precipitation and atmosphere structures. Point-by-point correction of range delay combined with compensation of range-weighting function effect has been performed during the retrieval of temporal signals to improve the continuity of power spectra at gate boundaries, making the small-scale structures in the power spectra more natural and reasonable. We examined stratiform and convective precipitation and demonstrated their different structured characteristics by means of the Capon-processed results. The new element in this study is the implementation of RIM on spectral analysis, especially for precipitation echoes.

Protection Coordination of 33/11 kV Power Distribution Substation in Iraq

2021 ◽  
Vol 39 (5A) ◽  
pp. 723-737
Author(s):  
Yamur M. Obied ◽  
Thamir M. Abdul Wahhab
Keyword(s):  
Time Delay ◽  
Power System ◽  
Power Distribution ◽  
Software Package ◽  
Short Circuit ◽  
Distribution Network ◽  
Circuit Breaker ◽  
Short Circuit Current ◽  
Earth Fault ◽  
Current Characteristics

The coordination between protective devices is the process of determining the most appropriate timing of power interruption during abnormal conditions in the power system. The aim of this work is to coordinate the protection of the 33/11 kV power distribution substation in Iraq using the CYME 7.1 software package. In this paper overcurrent and earth fault relays are simulated in two cases, with time delay setting and instantaneous setting, to obtain the Time Current Characteristics (TCC) curves for each Circuit Breaker (CB) relay of Al-Karama substation (2×31.5 MVA, 33/11 kV) in Babil distribution network. The short circuit current at each CB is calculated and accordingly, the protection coordination for Al-Karama substation has been simulated. The TCC curves have been obtained in two cases for overcurrent and earth fault relays; in a case with time delay setting and in the case with the instantaneous setting. The setting takes into consideration the short circuit current at the furthest point of the longest outgoing feeder and the shortest outgoing feeder.

scholarly journals Multi-technique investigations of storm-time ionospheric irregularities over the São Luís equatorial station in Brazil

2004 ◽  
Vol 22 (10) ◽  
pp. 3513-3522 ◽  
Author(s):  
E. R. de Paula ◽  
K. N. Iyer ◽  
D. L. Hysell ◽  
F. S. Rodrigues ◽  
E. A. Kherani ◽  
...  
Keyword(s):  
Electric Fields ◽  
Power Spectra ◽  
Spectral Width ◽  
Radar Data ◽  
Ionospheric Irregularities ◽  
Quiet Time ◽  
Vhf Radar ◽  
Equatorial Station ◽  
Plasma Irregularities ◽  
Magnetospheric Convection

Abstract. On 11 April 2001, a large magnetic storm occurred with SSC at 13:43 UT, and Dst reached below -200nT after two southward Bz excursions. The Kp index during this storm reached 8 and remained high (>4) for about 21h, and the São Luís magnetometer H component presented simultaneous oscillations and decreased substantially relative to the previous magnetically quiet days. This storm triggered strong ionospheric irregularities, as observed by a recently installed 30MHz coherent scatter radar, a digisonde, and a GPS scintillation receiver, all operating at the São Luís equatorial station (2.33° S, 44° W, dip latitude 1.3° S). The ionospheric conditions and the characteristics of the ionospheric irregularities observed by these instruments are presented and discussed. The VHF radar RTI (Range Time Intensity) echoes and their power spectra and spectral width for the storm night 11-12 April 2001, were used to analyse the nature and dynamics of the plasma irregularities and revealed the coexistence of many structures in the altitudinal range of 400-1200km, some locally generated and others that drifted from other longitudinal sectors. The radar data also revealed that the plumes had periodic eastward and westward zonal velocities after 22:20 UT, when well-developed quiet-time plumes typically drift eastward. Another interesting new observation is that the F-layer remained anomalously high throughout the 11-12 April 2001 storm night (21:00 UT to 09:00 UT next day) (the LT at São Luís is UT -3h), as indicated by the digisonde parameters hmF2 and h'F, which is a condition favourable for spread F generation and maintenance. The AE auroral index showed enhancements (followed by decreases) that are indicative of magnetospheric convection enhancements at about 15:00 UT, 20:00 UT and 22:00 UT on 11 April 2001 and at 00:20 UT (small amplitude) on 12 April 2001, associated with many Bz fluctuations, including clear two southward incursions that gave rise to large and long lasting Kp values and large negative Dst values. This intense auroral activity generated disturbance dynamo and prompt penetration electric fields that were responsible for the maintenance of the F-layer at a high altitude along the night of 11-12 April 2001. The short-lived F-region height rise seen between 16:00 to 18:00 UT on 11 April 2001 is probably due to the prompt penetration eastward electric fields of magnetospheric origin during the first IMF Bz turning to south around 15:00 UT.

scholarly journals ESR and EISCAT observations of the response of the cusp and cleft to IMF orientation changes

2000 ◽  
Vol 18 (9) ◽  
pp. 1009-1026 ◽  
Author(s):  
I. W. McCrea ◽  
M. Lockwood ◽  
J. Moen ◽  
F. Pitout ◽  
P. Eglitis ◽  
...  
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Plasma Temperature ◽  
Radar Data ◽  
Auroral Oval ◽  
Hf Radar ◽  
High Electron ◽  
Vhf Radar ◽  
Ionosphere Plasma ◽  
Main Cusp

Abstract. We report observations of the cusp/cleft ionosphere made on December 16th 1998 by the EISCAT (European incoherent scatter) VHF radar at Tromsø and the EISCAT Svalbard radar (ESR). We compare them with observations of the dayside auroral luminosity, as seen by meridian scanning photometers at Ny Ålesund and of HF radar backscatter, as observed by the CUTLASS radar. We study the response to an interval of about one hour when the interplanetary magnetic field (IMF), monitored by the WIND and ACE spacecraft, was southward. The cusp/cleft aurora is shown to correspond to a spatially extended region of elevated electron temperatures in the VHF radar data. Initial conditions were characterised by a northward-directed IMF and cusp/cleft aurora poleward of the ESR. A strong southward turning then occurred, causing an equatorward motion of the cusp/cleft aurora. Within the equatorward expanding, southward-IMF cusp/cleft, the ESR observed structured and elevated plasma densities and ion and electron temperatures. Cleft ion fountain upflows were seen in association with elevated ion temperatures and rapid eastward convection, consistent with the magnetic curvature force on newly opened field lines for the observed negative IMF By. Subsequently, the ESR beam remained immediately poleward of the main cusp/cleft and a sequence of poleward-moving auroral transients passed over it. After the last of these, the ESR was in the polar cap and the radar observations were characterised by extremely low ionospheric densities and downward field-aligned flows. The IMF then turned northward again and the auroral oval contracted such that the ESR moved back into the cusp/cleft region. For the poleward-retreating, northward-IMF cusp/cleft, the convection flows were slower, upflows were weaker and the electron density and temperature enhancements were less structured. Following the northward turning, the bands of high electron temperature and cusp/cleft aurora bifurcated, consistent with both subsolar and lobe reconnection taking place simultaneously. The present paper describes the large-scale behaviour of the ionosphere during this interval, as observed by a powerful combination of instruments. Two companion papers, by Lockwood et al. (2000) and Thorolfsson et al. (2000), both in this issue, describe the detailed behaviour of the poleward-moving transients observed during the interval of southward Bz, and explain their morphology in the context of previous theoretical work.Key words: Ionosphere (ionosphere - magnetosphere interactions; auroral ionosphere; plasma temperature and density)

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