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The incoherent scatter radar (ISR) technique provides an efficient tool for measuring ionosphere parameters. These parameters are of important significance for radio communication and satellite navigation. Modern incoherent scatte...
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The incoherent scatter radar (ISR) technique provides an efficient tool for measuring ionosphere parameters. These parameters are of important significance for radio communication and satellite navigation. Modern incoherent scatter radars rely on most complicated coding schemes to bring statistical accuracy to the measurements. In this paper, first we introduce a new hardware system for high-speed signal acquisition of ISR. Then two combination codes of alternating code and Barker code are presented which can facilitate full use of radar duty cycle and thus make the results accurate enough for analysis. The Barker-coded alternating code and the alternating-coded Barker code are suitable for E region and F region, respectively. Simulation experiment results demonstrate the validity of the presented methods.
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Orbital radar sounding systems could significantly improve our understanding of dynamic processes at ice sheet margins by enhancing the spatial and temporal coverage of subglacial observations. However, surface crevasses in these ...
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Orbital radar sounding systems could significantly improve our understanding of dynamic processes at ice sheet margins by enhancing the spatial and temporal coverage of subglacial observations. However, surface crevasses in these fast-flowing regions may contribute significant radar clutter that can impede detection of the ice sheet bed. It is currently unclear if particular radar center frequency choices might enhance or mitigate this clutter. To investigate this question, we analyze crevasse clutter returns in airborne radar sounding data collected at 195 MHz, 300 MHz, and 750 MHz. Additionally, we rescale the derived empirical angular scattering functions to simulate crevasse clutter in orbital geometries. In this data set, we find that, unlike rough surface clutter, crevasse clutter is reduced at higher frequencies. However, the small angles of incidence at orbital altitudes lead to sufficient clutter at all frequencies to dominate over the theoretical bed echo power. Our results suggest that surface crevassing may not necessarily limit the viability of UHF frequencies for orbital sounding. However, synthetic aperture focusing and narrow cross-track antenna beam patterns will be crucial regardless of system center frequency.
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Based on the wavefront modulation technique, we introduced the principle and imaging model of forward-looking imaging. Considering the scattering coefficient distribution of the complex target is no longer sparse, L1-regularized l...
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Based on the wavefront modulation technique, we introduced the principle and imaging model of forward-looking imaging. Considering the scattering coefficient distribution of the complex target is no longer sparse, L1-regularized least squares method based on sparse representation is proposed for reconstructing radar images of complex targets. The transformation matrix is generated by the dictionary learning method which provides a sparser representation of the scattering coefficient distribution of the complex target. By inversing the solved sparse vector under the transformation matrix, the reconstruction of complex targets can be realized. Simulation results show the effectiveness of the proposed method.
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In this paper, digital video broadcasting (DVB-T) transmitters are considered for passive SAR imaging of ground scenarios. A multilook processing scheme is proposed to reduce image noise, to improve the interpretation of the radar...
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In this paper, digital video broadcasting (DVB-T) transmitters are considered for passive SAR imaging of ground scenarios. A multilook processing scheme is proposed to reduce image noise, to improve the interpretation of the radar image and to make possible the correct detection and area delimitation of scattering targets in the radar scene. A measurement campaign was carried out to analyse and validate the proposed processing scheme. A DVB-T based passive radar was mounted in an EADS CASA C-295M aircraft to generate the synthetic aperture of the receiver. The acquired data was processed under different passive imaging configurations to analyse the radar image quality improvement of multilook processing scheme. Results show the reduction of image noise and the high increase of targets boundaries identification that can be used as a starting point for carrying on further passive SAR scattering characteristics analysis.
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Fast and accurate characterization of concealed threats and benign objects is of great importance for increasing the efficiency of mm-wave imaging radar personnel screening systems in airports. Correctly classifying low-loss and l...
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Fast and accurate characterization of concealed threats and benign objects is of great importance for increasing the efficiency of mm-wave imaging radar personnel screening systems in airports. Correctly classifying low-loss and lossless materials is essential in detecting threats. Previous work developed a real-time, fully automatic algorithm for characterizing lossy vs. lossless materials. This paper extends the mm-wave image-processing-based method to distinguish low-loss media, such as paper vs. lossless materials, that include explosives. The developed method is verified experimentally by applying it to experimentally measured radar data generated by a 10–40 GHz wideband laboratory airport screening prototype.
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In high frequency region, the scattering response of an extended target can be well approximated as a sum of responses from individual scattering centers. The spatially variant point spread function (PSF) of MIMO radar near-field ...
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In high frequency region, the scattering response of an extended target can be well approximated as a sum of responses from individual scattering centers. The spatially variant point spread function (PSF) of MIMO radar near-field imaging system makes it difficult to extract scattering centers. Based on the spatial wavenumber support domain of the MIMO radar, this paper proposes a spatially variant Relax (SV-Relax) algorithm for its scattering center extraction. The spatial wavenumber support domain of the MIMO radar is firstly analyzed. Then the process of the SV-Relax algorithm is discussed in detail. Finally, both numerical and measured data are processed to demonstrate the validity of proposed algorithm.
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In this paper, the full calibration chain of FMCW radar with simultaneous transmission of two orthogonally polarized orthogonal waveforms is considered. Specifically for this type of polarimetric radar, compensation of signals' bi...
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In this paper, the full calibration chain of FMCW radar with simultaneous transmission of two orthogonally polarized orthogonal waveforms is considered. Specifically for this type of polarimetric radar, compensation of signals' biases and equalization of the amplification gains of the parallel polarimetric channels in the receiver are jointly performed using the noise measurements. The calibrations of the absolute complex gains of the transmitter's polarimetric channels together with complex antenna gains are done using the model-based fit of the measurements of the rotating dihedral reflector. Phase relations between polarimetric channels are treated in the Doppler domain using the unfolded velocity of the target. The performed calibration results in high-accurate measurements of the radar targets' polarimetric scattering matrix (PSM) in the Doppler domain. All the proposed calibration steps are illustrated using real radar data.
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This paper investigates rough surface scattering characteristics at 94 GHz band by means of an electromagnetic field integral equation. The 94 GHz band which has the least atmospheric attenuation between 75 GHz and 110 GHz and is ...
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This paper investigates rough surface scattering characteristics at 94 GHz band by means of an electromagnetic field integral equation. The 94 GHz band which has the least atmospheric attenuation between 75 GHz and 110 GHz and is considered to have narrower beamwidth and wider bandwidth in general, is vigorously studied for various applications, such as, collision avoidance vehicle radar, weather radar and remote sensing with ultra wide band radar. In these applications, the scatterer such as asphalt pavement, pebbles and rain drops should be of almost the same order as the 94 GHz band wavelength. The 94 GHz band scattering characteristics are thus considered to belong in the Mie region, not in the Rayleigh region, and thereby should be unique as compared with microwave bands. From this point of view, we have initiated the study of scattering characteristics for various scattering objects (land vehicle, rough ground, grass, etc.) in order to evaluate signal-to-clutter (land clutter) ratio at 94 GHz band. In this work we carried out the prediction of 94 GHz band scattering electromagnetic wave field from rough surface with perfect conductivity for the purpose of understanding the following two points: (1) 94 GHz band radar cross section (RCS) as a function of scatterer's roughness and (2) its polarization dependence.
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Radar response saturation sets limits in the use of active systems for monitoring forest biomass on a global scale. The possibility of widening the range of observable biomass is analyzed by considering a bistatic radar configuration.
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This paper discusses the modification of a single-frequency Doppler radar (9.6 GHz) to accommodate dual-frequency operation for the study of the microphysical character of precipitation. The modification involves the ER-2 Doppler ...
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This paper discusses the modification of a single-frequency Doppler radar (9.6 GHz) to accommodate dual-frequency operation for the study of the microphysical character of precipitation. The modification involves the ER-2 Doppler radar (EDOP), an airborne, meteorological research radar of the NASA/Goddard Space Flight Center. Radar operation is modified to provide reflectivity signals at two distinct frequencies at 9% separation. Differential reflectivity results are shown from ground-based measurement. Future work will derive drop size distribution estimates from these measurements.
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