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

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 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 SOMARE-99: Observations of tropospheric scattering layers using multiple-frequency range imaging

Radio Science ◽  
2001 ◽  
Vol 36 (4) ◽  
pp. 681-693 ◽  
Author(s):  
Robert D. Palmer ◽  
Phillip B. Chilson ◽  
Andreas Muschinski ◽  
Gerhard Schmidt ◽  
Tian-You Yu ◽  
...  
Keyword(s):  
Multiple Frequency ◽  
Frequency Range ◽  
Range Imaging

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.

scholarly journals Effects of radar beam width and scatterer anisotropy on multiple-frequency range imaging using VHF atmospheric radar

Radio Science ◽  
2010 ◽  
Vol 45 (5) ◽  
pp. n/a-n/a ◽  
Author(s):  
Jenn-Shyong Chen ◽  
Jun-ichi Furumoto ◽  
Takuji Nakamura
Keyword(s):  
Beam Width ◽  
Multiple Frequency ◽  
Frequency Range ◽  
Range Imaging ◽  
Radar Beam

scholarly journals Range imaging observations of PMSE using the EISCAT VHF radar: Phase calibration and first results

2005 ◽  
Vol 23 (1) ◽  
pp. 207-220 ◽  
Author(s):  
J. R. Fernandez ◽  
R. D. Palmer ◽  
P. B. Chilson ◽  
I. Häggström ◽  
M. T. Rietveld
Keyword(s):  
Lower Layer ◽  
Layer Structure ◽  
Calibration Method ◽  
Clear Correlation ◽  
Range Imaging ◽  
Vhf Radar ◽  
First Results ◽  
Phase Calibration ◽  
Radar Simulator ◽  
Eiscat Radar

Abstract. A novel phase calibration technique for use with the multiple-frequency Range IMaging (RIM) technique is introduced based on genetic algorithms. The method is used on data collected with the European Incoherent SCATter (EISCAT) VHF radar during a 2002 experiment with the goal of characterizing the vertical structure of Polar Mesosphere Summer Echoes (PMSE) over northern Norway. For typical Doppler measurements, the initial phases of the transmitter and receiver are not required to be the same. The EISCAT receiver systems exploit this fact, allowing a multi-static configuration. However, the RIM method relies on the small phase differences between closely spaced frequencies. As a result, the high-resolution images produced by the RIM method can be significantly degraded if not properly calibrated. Using an enhanced numerical radar simulator, in which data from multiple sampling volumes are simultaneously generated, the proposed calibration method is validated. Subsequently, the method is applied to preliminary data from the EISCAT radar, providing first results of RIM images of PMSE. Data using conventional analysis techniques, and confirmed by RIM, reveal an often-observed double-layer structure with higher stability in the lower layer. Moreover, vertical velocity oscillations exhibit a clear correlation with the apparent motion of the layers shown in the echo power plots.

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.

Stabilizing Gain Regions of PID Controller for Time Delay Systems

2013 ◽  
Vol 313-314 ◽  
pp. 432-437
Author(s):  
Fu Min Peng ◽  
Bin Fang
Keyword(s):  
Stability Analysis ◽  
Time Delay ◽  
Pid Controller ◽  
Delay System ◽  
Nyquist Plot ◽  
Delay Systems ◽  
Time Delay Systems ◽  
Frequency Range ◽  
Time Delay System ◽  
Key Points

Based on the inverse Nyquist plot, this paper proposes a method to determine stabilizing gain regions of PID controller for time delay systems. According to the frequency characteristic of the inverse Nyquist plot, it is confirmed that the frequency range is used for stability analysis, and the abscissas of two kind key points are obtained in this range. PID gain is divided into several regions by abscissas of key points. Using an inference and two theorems presented in the paper, the stabilizing PID gain regions are determined by the number of intersections of the inverse Nyquist plot and the vertical line in the frequency range. This method is simple and convenient. It can solve the problem of getting the stabilizing gain regions of PID controller for time delay system.

scholarly journals Radiation in the neighbourhood of a double layer

2014 ◽  
Vol 32 (6) ◽  
pp. 677-687 ◽  
Author(s):  
R. Pottelette ◽  
M. Berthomier ◽  
J. Pickett
Keyword(s):  
Phase Space ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
Source Region ◽  
Double Layers ◽  
Small Scale ◽  
High Time Resolution ◽  
Local Electron ◽  
Nonlinear Phase ◽  
Electron Holes

Abstract. In the auroral kilometric radiation (AKR) source region, acceleration layers narrow in altitude and associated with parallel field-aligned potential drops of several kV can be identified by using both particles and wave-field high time-resolution measurements from the Fast Auroral SnapshoT explorer spacecraft (FAST). These so-called double layers (DLs) are recorded around density enhancements in the auroral cavity, where the enhancement can be at the edge of the cavity or even within the cavity at a small scale. Once immersed in the plasma, DLs necessarily accelerate particles along the magnetic field lines, thereby generating locally strong turbulent processes leading to the formation of nonlinear phase space holes. The FAST data reveal the asymmetric character of the turbulence: the regions located on the high-potential side of the DLs are characterized by the presence of electron holes, while on the low-potential side, ion holes are recorded. The existence of these nonlinear phase space holes may affect the AKR radiation pattern in the neighbourhood of a DL where the electron distribution function is drastically different from a horseshoe shape. We present some observations which illustrate the systematic generation of elementary radiation events occurring significantly above the local electron gyrofrequency in the presence of electron holes. These fine-scale AKR radiators are associated with a local electron distribution which presents a pronounced beam-like shape.

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