scholarly journals Performance Analysis of Ionospheric Scintillation Effect on P-Band Sliding Spotlight SAR System

Sensors ◽  
2019 ◽  
Vol 19 (9) ◽  
pp. 2161 ◽  
Author(s):  
Lei Yu ◽  
Yongsheng Zhang ◽  
Qilei Zhang ◽  
Yifei Ji ◽  
Zhen Dong
Keyword(s):  
Theoretical Analysis ◽  
Coherence Function ◽  
Active Regions ◽  
Integration Time ◽  
Ionospheric Scintillation ◽  
Imaging Geometry ◽  
Operational Solution ◽  
Imaging Resolution ◽  
Imaging Performance ◽  
Multi Mode

The space-borne P-band synthetic aperture radar (SAR) maintains excellent penetration capability. However, the low carrier frequency restricts its imaging resolution. The sliding spotlight mode provides an operational solution to meet the requirement of high imaging resolution in P-band SAR design. Unfortunately, the space-borne P-band SAR will be inevitably deteriorated by the ionospheric scintillation. Compared with the stripmap mode, the sliding spotlight SAR will suffer more degradation when operating in the scintillation active regions due to its long integration time and complex imaging geometry. In this paper, both the imaging performance and scintillation effect for P-band sliding spotlight mode are studied. The theoretical analysis of scintillation effect is performed based on a refined model of the two-frequency and two-position coherence function (TFTPCF). A novel scintillation simulator based on the reverse back-projection (ReBP) algorithm is proposed to generate the SAR raw data for sliding spotlight mode. The proposed scintillation simulator can also be applied to predict the scintillation effect for other multi-mode SAR systems such as terrain observation by progressive scans (TOPS) and ScanSAR. Finally, a group of simulations are carried out to validate the theoretical analysis.

Monitoring of Curing Temperature of Early-Age Cement Paste Using Biconical Tapered Fiber Sensor

2011 ◽  
Vol 250-253 ◽  
pp. 3549-3553 ◽  
Author(s):  
Dong Lou ◽  
Zainah Ibrahim ◽  
Zubaidah Ismail
Keyword(s):  
Theoretical Analysis ◽  
Cement Paste ◽  
Curing Temperature ◽  
Fiber Sensor ◽  
Early Age ◽  
Curing Process ◽  
Tapered Fiber ◽  
Numerical Result ◽  
Multi Mode ◽  
Step Index Fiber

In this paper, a biconical tapered fiber sensor is applied to monitor the temperature of cement paste during curing process. A simple sensing principle of the proposed sensor is presented by analyzing the V-number of leaky rays. An experimental is carried out by tapering the plastic multi-mode step-index fiber to measure the temperature of the cement paste. The numerical result shows that the V-number of leaky ray is increasing with the raised in temperature. The experimental results are in agreement with the results from the theoretical analysis.

Multi-Mode Narrow-Frame Antenna for 4G/5G Metal-Rimmed Mobile Phones

2020 ◽  
Vol 35 (8) ◽  
pp. 908-915
Author(s):  
Ming Yang ◽  
Yu-Fa Sun ◽  
Tong-Qing Liao
Keyword(s):  
Theoretical Analysis ◽  
Mobile Phones ◽  
Communication Systems ◽  
Return Loss ◽  
Band 3 ◽  
Monopole Antenna ◽  
Experimental Results ◽  
5G Communication ◽  
Multi Mode

A novel multi-mode narrow-frame antenna is presented for 4G/5G metal-rimmed mobile phones in this paper. The proposed antenna is constituted by a monopole antenna and a coupling strip, which is printed on FR4 substrate with thickness of 0.8 mm. The overall area occupied by the antenna is only 60 × 10.4 mm2, which can be used as a promising narrow-frame antenna. The simulated results shows that the return loss of the antenna can provide four operating bandwidths of 822– 961 (band 1), 1697–3075 (band 2), 3280–3835 (band 3) and 4475–5050 MHz (band 4), which respectively cover 824–960, 1710–2690, 3300–3600 and 4800–5000 MHz in 4G/5G communication systems. In order to verify the accuracy of theoretical analysis and simulated results, the proposed antenna is fabricated and measured. The experimental results are basically consistent with the simulated results, suggesting that the presented antenna has attractive performance for mobile phones.

scholarly journals Elevation Spatial Variation Analysis and Compensation in GEO SAR Imaging

2021 ◽  
Vol 13 (10) ◽  
pp. 1888
Author(s):  
Faguang Chang ◽  
Dexin Li ◽  
Zhen Dong ◽  
Yang Huang ◽  
Zhihua He ◽  
...  
Keyword(s):  
Spatial Variation ◽  
Three Dimensional ◽  
Integration Time ◽  
Imaging Method ◽  
Imaging Geometry ◽  
Sensing Applications ◽  
Sar Imaging ◽  
High Orbit ◽  
Long Term Observation ◽  
Space Variant

Due to geosynchronous synthetic aperture radar’s (GEO SAR) high orbit and low relative speed, the integration time reaches up to hundreds of seconds for a fine resolution. The short revisit cycle is essential for remote sensing applications such as disaster monitoring and vegetation measurements. Three-dimensional (3D) scene imaging mode is crucial for long-term observation using GEO SAR. However, this mode will bring a new kind of space-variant error in elevation. In this paper, we focus on the analysis of the elevation space-variant error. First, the decorrelation problems caused by the spatial variation are presented. Second, by combining with the SAR imaging geometry, the elevation spatial variation is decomposed into two-dimensional (2D) space variation of range and azimuth. Third, an imaging algorithm is proposed to solve the 3D space variation and improve the focusing depth. Finally, simulations with dot-matrix targets and distributed targets are performed to validate the imaging method.

Synoptic Charts of the Solar Eclipses of 1990 and 1991

1994 ◽  
Vol 144 ◽  
pp. 517-521
Author(s):  
Z. Mouradian ◽  
G. Buchholtz ◽  
G. Zlicaric
Keyword(s):  
Solar Limb ◽  
Active Regions ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractThe synoptic charts of solar rotations 1831 and 1844 have been drawn up, corresponding to the eclipses of 22 July 1990 and 11 July 1991. These charts contain the active regions and the filaments, and show the position of the solar limb, at the time of the eclipse. They are for use in studying the coronal structures observed during these eclipses. The variation of these structures is given in the table. The last section of the article contains a formula for identifying the structures out of the limb.

Solar Corona Investigation by the Coronal Line Photometer at Lomnický Peak

1994 ◽  
Vol 144 ◽  
pp. 431-434
Author(s):  
M. Minarovjech ◽  
M. Rybanský
Keyword(s):  
Solar Corona ◽  
Time Resolution ◽  
Active Regions ◽  
High Time ◽  
High Time Resolution ◽  
List Type ◽  
Type Number ◽  
Coronal Line ◽  
Global Cycle

AbstractThis paper deals with a possibility to use the ground-based method of observation in order to solve basic problems connected with the solar corona research. Namely:1.heating of the solar corona2.course of the global cycle in the corona3.rotation of the solar corona and development of active regions.There is stressed a possibility of high-time resolution of the coronal line photometer at Lomnický Peak coronal station, and use of the latter to obtain crucial observations.

Symmetric Multistep Methods Revisited: II. Numerical Experiments

1999 ◽  
Vol 173 ◽  
pp. 309-314 ◽  
Author(s):  
T. Fukushima
Keyword(s):  
Multistep Methods ◽  
Computational Time ◽  
Integration Time ◽  
Implicit Methods ◽  
Symmetric Methods ◽  
Celestial Bodies ◽  
The Stability ◽  
Predictor Corrector ◽  
Symmetric Multistep Methods ◽  
Integration Errors

AbstractBy using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

Interpretation of the Filament Depression at Millimetric and Centimetric Wavelengths

1979 ◽  
Vol 44 ◽  
pp. 131-134
Author(s):  
A. Raoult ◽  
P. Lantos ◽  
E. Fürst
Keyword(s):  
Radio Telescope ◽  
Active Regions ◽  
Simple Shape ◽  
Quiet Sun ◽  
Unstable Process

The depressions at centimetric and millimetric wavelengths associated with the filaments are studied using already published maps as well as unpublished observations from the Effelsberg 100 m radio telescope of the M.P.I., Bonn. The study has been restricted to large Ha quiescent prominences of relatively simple shape, situated far from the limb and from active regions. The data has been reduced employing one method whose main characteristics are choice of a local quiet sun definition and avoidance of the unstable process of deconvolution.

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