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Microwave Doppler Spectra of Sea Echoes at High Incidence Angles: Influences of Large-Scale Waves
Yunhua Wang;Yan-Min Zhang;Li-Xin Guo
PIER B , 2013, DOI: 10.2528/PIERB12123004
Abstract: Within the framework of the composite surface scattering model, analytical formulas for Doppler shift and bandwidth of radar echoes backscattered from time-varying sea surface are derived in the forms of three-dimensional integrals. In our derivations, the influences of the tilt modulation (TM), the hydrodynamic modulation (HM), the shadow and the curvature of large-scale undulating waves are all taken into account for achieving more reasonable results. Comparisons between our theoretical curves and the results obtained directly by exact numerical method demonstrate that our formulas can improve the simulated results. On the other hand, the simulations by our formulas can also help to estimate the effects of the TM, the HM, and the shadow of large-scale waves on Doppler behaviors individually. We find that the predicted Doppler shifts are always larger in HH-polarization than in VV-polarization due to the TM. Meanwhile, the simulations also show that the predicted Doppler shifts for both HH- and VV-polarizations would become larger when the HM is considered. In addition, at low-grazing angles (LGA), the shadow effect results in a rapid increase in the predicted Doppler shift, and on the contrary makes the bandwidth narrower.
Stochastic Maximum Likelihood (SML) parametric estimation of overlapped Doppler echoes
V. K. Anandan, C. J. Pan, T. Rajalakshmi,G. Ramachandra Reddy
Annales Geophysicae (ANGEO) , 2004,
Abstract: Multitaper spectral analysis using sinusoidal taper has been carried out on the backscattered signals received from the troposphere and lower stratosphere by the Gadanki Mesosphere-Stratosphere-Troposphere (MST) radar under various conditions of the signal-to-noise ratio. Comparison of study is made with sinusoidal taper of the order of three and single tapers of Hanning and rectangular tapers, to understand the relative merits of processing under the scheme. Power spectra plots show that echoes are better identified in the case of multitaper estimation, especially in the region of a weak signal-to-noise ratio. Further analysis is carried out to obtain three lower order moments from three estimation techniques. The results show that multitaper analysis gives a better signal-to-noise ratio or higher detectability. The spectral analysis through multitaper and single tapers is subjected to study of consistency in measurements. Results show that the multitaper estimate is better consistent in Doppler measurements compared to single taper estimates. Doppler width measurements with different approaches were studied and the results show that the estimation was better in the multitaper technique in terms of temporal resolution and estimation accuracy.
Study on the electromagnetic scattering from a conducting plate above the time-dependant sea surface
时变海面与其上方导体平板的复合电磁散射研究

GUO Li-Xin,WANG Rui,WANG Yun-Hua,WU Zhen-Sen,
郭立新

地球物理学报 , 2008,
Abstract: Using current numerical techniques to evaluate the electromagnetic scattering between a time-dependant sea surface and a target,due to varying with the time,the elements of the impedance matrix and the surface electric current of the sea surface must be re-evaluated at different moment.Therefore,vast memory and computational requirements are required.In order to overcome this problem,in this paper,the surface electric current of the conducting sea surface and the first-order scattering from the conducting plate are obtained by employing Physic Optics(PO) method.The backscattering field of the time-dependant sea surface is calculated by using Kirchhoff Approximation.Meanwhile,taking the advantage of a newly developed technique that utilizes the reciprocity theorem,the difficulty in formulating the secondary scattered fields from the composite target is reduced.The dependences of the backscattered field on the parameters,such as the wind speed and the sizes of the plate are discussed.In addition,a model is formulated for Doppler spectral shift of the coupling field,and the characteristic of the Doppler spectrum of the composite backscattering field is analyzed in detail.
Experimental Research of UHF Radio Backscattered from Fresh and Seawater Surface
Wei Shen;Biyang Wen
PIER M , 2010, DOI: 10.2528/PIERM10010308
Abstract: The backscattering experiments of water surface by Ultra-High Frequency (UHF, 300 ~ 3000 MHz) Radar are presented in this paper. In order to study UHF radio propagation and backscatter mechanisms from fresh and salty water surfaces at a very low grazing angle, two experiments are carried out on Yangtze River bridge and cliff which face open sea with the same radar system. The physical parameters of different water surfaces are introduced as well as the signature of backscattered echoes.
On differentiating ground clutter and insect echoes from Doppler weather radars using archived data  [PDF]
S. J. Rennie,A. J. Illingworth,S. L. Dance
Atmospheric Measurement Techniques Discussions , 2010, DOI: 10.5194/amtd-3-1843-2010
Abstract: Normally wind measurements from Doppler radars rely on the presence of rain. During fine weather, insects become a potential radar target for wind measurement. However, it is difficult to separate ground clutter and insect echoes when spectral or polarimetric methods are not available. Archived reflectivity and velocity data from repeated scans provide alternative methods. The probability of detection (POD) method, which maps areas with a persistent signal as ground clutter, is ineffective when most scans also contain persistent insect echoes. We developed a clutter detection method which maps the standard deviation of velocity (SDV) over a large number of scans, and can differentiate insects and ground clutter close to the radar. Beyond the range of persistent insect echoes, the POD method more thoroughly removes ground clutter. A new, pseudo-probability clutter map was created by combining the POD and SDV maps. The new map optimised ground clutter detection without removing insect echoes.
Analytical Model of Doppler Spectra of Light Backscattered from Rotating Convex Bodies of Revolution in the Global Cartesian Coordinate System

GONG Yan-Jun,WU Zhen-Sen,WU Jia-Ji,

中国物理快报 , 2009,
Abstract: We present an analytical model of Doppler spectra in backscattering from arbitrary rough convex bodies of revolution rotating around their axes in the global Cartesian coordinate system. This analytical model is applied to analyse Doppler spectra in backscatter from two cones and two cylinders, aswell as two ellipsoids of revolution. We numerically analyse the influences of attitude and geometry size of objects on Doppler spectra. The analytical model can give contribution of the surface roughness, attitude and geometry size of convex bodies of revolution to Doppler spectra and may contribute to laser Doppler velocimetry as well as ladar applications.
An adjusted location model for SuperDARN backscatter echoes
E. X. Liu, H. Q. Hu, R. Y. Liu, Z. S. Wu,M. Lester
Annales Geophysicae (ANGEO) , 2012,
Abstract: The radars that form the Super Dual Auroral Radar Network (SuperDARN) receive scatter from ionospheric irregularities in both the E- and F-regions, as well as the Earth's surface, either ground or sea. For ionospheric scatter, the current SuperDARN standard software considers a straight-line propagation from the radar to the scattering zone with an altitude assigned by a standard height model. The knowledge of the group delay to a scatter volume is not sufficient for an exact determination of the location of the irregularities. In this study, the difference between the locations of the backscatter echoes determined by SuperDARN standard software and by ray tracing has been evaluated, using the ionosonde data collected at Sodankyl , which is in the field-of-view of Hankasalmi SuperDARN radar. By studying elevation angle information of backscattered echoes from the data sets of Hankasalmi radar in 2008, we have proposed an adjusted fitting location model determined by slant range and elevation angle. To test the reliability of the adjusted model, an independent data set is selected in 2009. The result shows that the difference between the adjusted model and the ray tracing is significantly reduced and the adjusted model could provide a more accurate location for backscatter targets.
An adjusted location model for SuperDARN backscatter echoes
E. X. Liu,H. Q. Hu,R. Y. Liu,Z. S. Wu
Annales Geophysicae (ANGEO) , 2003, DOI: 10.5194/angeo-30-1769-2012
Abstract: The radars that form the Super Dual Auroral Radar Network (SuperDARN) receive scatter from ionospheric irregularities in both the E- and F-regions, as well as the Earth's surface, either ground or sea. For ionospheric scatter, the current SuperDARN standard software considers a straight-line propagation from the radar to the scattering zone with an altitude assigned by a standard height model. The knowledge of the group delay to a scatter volume is not sufficient for an exact determination of the location of the irregularities. In this study, the difference between the locations of the backscatter echoes determined by SuperDARN standard software and by ray tracing has been evaluated, using the ionosonde data collected at Sodankyl , which is in the field-of-view of Hankasalmi SuperDARN radar. By studying elevation angle information of backscattered echoes from the data sets of Hankasalmi radar in 2008, we have proposed an adjusted fitting location model determined by slant range and elevation angle. To test the reliability of the adjusted model, an independent data set is selected in 2009. The result shows that the difference between the adjusted model and the ray tracing is significantly reduced and the adjusted model could provide a more accurate location for backscatter targets.
Embedded System for Real-Time Digital Processing of Medical Ultrasound Doppler Signals  [cached]
S. Ricci,A. Dallai,E. Boni,L. Bassi
EURASIP Journal on Advances in Signal Processing , 2008, DOI: 10.1155/2008/418235
Abstract: Ultrasound (US) Doppler systems are routinely used for the diagnosis of cardiovascular diseases. Depending on the application, either single tone bursts or more complex waveforms are periodically transmitted throughout a piezoelectric transducer towards the region of interest. Extraction of Doppler information from echoes backscattered from moving blood cells typically involves coherent demodulation and matched filtering of the received signal, followed by a suitable processing module. In this paper, we present an embedded Doppler US system which has been designed as open research platform, programmable according to a variety of strategies in both transmission and reception. By suitably sharing the processing tasks between a state-of-the-art FGPA and a DSP, the system can be used in several medical US applications. As reference examples, the detection of microemboli in cerebral circulation and the measurement of wall _distension_ in carotid arteries are finally presented.
The Effect of Sea Surface Slicks on the Doppler Spectrum Width of a Backscattered Microwave Signal  [PDF]
Vladimir Karaev,Mikhail Kanevsky,Eugeny Meshkov
Sensors , 2008, DOI: 10.3390/s8063780
Abstract: The influence of a surface-active substance (SAS) film on the Doppler spectrum width at small incidence angles is theoretically investigated for the first time for microwave radars with narrow-beam and knife-beam antenna patterns. It is shown that the requirements specified for the antenna system depend on the radar motion velocity. A narrow-beam antenna pattern should be used to detect slicks by an immobile radar, whereas radar with a knife-beam antenna pattern is needed for diagnostics from a moving platform. The study has revealed that the slick contrast in the Doppler spectrum width increases as the radar wavelength diminishes, thus it is preferable to utilize wavelengths not larger than 2 cm for solving diagnostic problems. The contrast in the Doppler spectrum width is generally weaker than that in the radar backscattering cross section; however, spatial and temporal fluctuations of the Doppler spectrum width are much weaker than those of the reflected signal power. This enables one to consider the Doppler spectrum as a promising indicator of slicks on water surface.
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