The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform

Yi Liang - One of the best experts on this subject based on the ideXlab platform.

  • spectrum Compression Space time adaptive processing for tops sar system
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capa- ble of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space-time adaptive processing (SC-STAP) is pro- posed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully over- lapped clutter Space-time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm. Index Terms—Moving target, multichannel, Space-time adap- tive processing (STAP), spectrum Compression (SC), terrain ob- servation by progressive scans (TOPS) synthetic aperture radar (SAR).

  • Spectrum Compression Space–Time Adaptive Processing for TOPS SAR System
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capable of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space–time adaptive processing (SC-STAP) is proposed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully overlapped clutter Space–time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm.

Xueshi Li - One of the best experts on this subject based on the ideXlab platform.

  • spectrum Compression Space time adaptive processing for tops sar system
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capa- ble of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space-time adaptive processing (SC-STAP) is pro- posed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully over- lapped clutter Space-time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm. Index Terms—Moving target, multichannel, Space-time adap- tive processing (STAP), spectrum Compression (SC), terrain ob- servation by progressive scans (TOPS) synthetic aperture radar (SAR).

  • Spectrum Compression Space–Time Adaptive Processing for TOPS SAR System
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capable of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space–time adaptive processing (SC-STAP) is proposed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully overlapped clutter Space–time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm.

  • An Efficient Clutter Suppression Approach for TOPS SAR System
    EUSAR 2014; 10th European Conference on Synthetic Aperture Radar, 2014
    Co-Authors: Xueshi Li, Mengdao Xing, Min Wu, Yi Zhang, Yufeng Wu
    Abstract:

    Compared with single-channel TOPS SAR, a multichannel TOPS SAR system is capable of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. Therefore, the background clutter is highly aliased if the PRF is designed to be equal to or less than the instantaneous signal bandwidth, yielding degraded clutter suppression performance. To overcome this problem, a new method, referred to as spectrum Compression Space-time adaptive processing (SC-STAP), is proposed in this paper.

Mengdao Xing - One of the best experts on this subject based on the ideXlab platform.

  • spectrum Compression Space time adaptive processing for tops sar system
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capa- ble of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space-time adaptive processing (SC-STAP) is pro- posed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully over- lapped clutter Space-time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm. Index Terms—Moving target, multichannel, Space-time adap- tive processing (STAP), spectrum Compression (SC), terrain ob- servation by progressive scans (TOPS) synthetic aperture radar (SAR).

  • Spectrum Compression Space–Time Adaptive Processing for TOPS SAR System
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capable of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space–time adaptive processing (SC-STAP) is proposed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully overlapped clutter Space–time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm.

  • An Efficient Clutter Suppression Approach for TOPS SAR System
    EUSAR 2014; 10th European Conference on Synthetic Aperture Radar, 2014
    Co-Authors: Xueshi Li, Mengdao Xing, Min Wu, Yi Zhang, Yufeng Wu
    Abstract:

    Compared with single-channel TOPS SAR, a multichannel TOPS SAR system is capable of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. Therefore, the background clutter is highly aliased if the PRF is designed to be equal to or less than the instantaneous signal bandwidth, yielding degraded clutter suppression performance. To overcome this problem, a new method, referred to as spectrum Compression Space-time adaptive processing (SC-STAP), is proposed in this paper.

Yimin D. Zhang - One of the best experts on this subject based on the ideXlab platform.

  • spectrum Compression Space time adaptive processing for tops sar system
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capa- ble of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space-time adaptive processing (SC-STAP) is pro- posed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully over- lapped clutter Space-time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm. Index Terms—Moving target, multichannel, Space-time adap- tive processing (STAP), spectrum Compression (SC), terrain ob- servation by progressive scans (TOPS) synthetic aperture radar (SAR).

  • Spectrum Compression Space–Time Adaptive Processing for TOPS SAR System
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Xueshi Li, Mengdao Xing, Yimin D. Zhang, Yi Liang
    Abstract:

    A multichannel terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) system is capable of imaging a wider swath with a higher azimuth resolution for improved moving target detection. For TOPS SAR, due to antenna beam steering, the azimuth bandwidth of background clutter is much larger than the instantaneous signal bandwidth. To overcome this problem, a method referred to as spectrum Compression Space–time adaptive processing (SC-STAP) is proposed in this letter. Through the SC process, both the Doppler spectrum and the spatial spectrum of the background clutter are simultaneously compressed. This key step achieves fully overlapped clutter Space–time spectrum lines and, as such, enables effective clutter suppression and target signal alias compensation by applying linearly constrained STAP. Furthermore, in order to avoid the target ambiguities arising from the spectral wrapping, an approach based on deramp processing is proposed to focus the moving targets for TOPS SAR mode. Simulation results validate the effectiveness of the proposed algorithm.

Terrence W Simon - One of the best experts on this subject based on the ideXlab platform.

  • Thermal analysis of a compressor for application to Compressed Air Energy Storage
    Applied Thermal Engineering, 2014
    Co-Authors: Chao Zhang, Jacob Wieberdink, Eric Loth, Perry Y. Li, Terrence W Simon
    Abstract:

    Abstract In this paper, the topic of Compressed Air Energy Storage (CAES) is discussed and a program in which it is being applied to a wind turbine system for leveling power supplied to the grid is described. Noted is the importance of heat transfer in the design of the compressor and its effect on performance. Presented is a design for minimizing the temperature rise in the compressor during Compression. The design requires modeling regenerative heat transfer from the compressed air to solid material inserted in the Compression Space. Modeling requires characterizing pressure drop through the porous insert, interfacial heat transfer between solid and fluid in the matrix, and thermal dispersion within the porous regions. Computation and experimentation are applied for developing correlations for such terms. Two types of porous media are applied: interrupted plates and open-cell metal foams. Cases with foam inserts are computed and the results are discussed. Discovered in the results are some complex secondary flow features in Spaces above the porous inserts.

  • Numerical Analysis of Heat Exchangers Used in a Liquid Piston Compressor Using a One-Dimensional Model With an Embedded Two-Dimensional Submodel
    Volume 8A: Heat Transfer and Thermal Engineering, 2014
    Co-Authors: Chao Zhang, James Van De Ven, Jacob Wieberdink, Terrence W Simon, Perry Y. Li, Eric Loth
    Abstract:

    Copyright © 2014 by ASME.The present study presents a one-dimensional liquid-piston compressor model with an embedded two-dimensional submodel. The submodel is for calculating heat conduction across a representative internal plate of a porous heat exchanger matrix within the Compression Space. The liquid-piston compressor is used for Compressed Air Energy Storage (CAES). Porous-media-type heat exchangers are inserted in the compressor to absorb heat from air as it is compressed. Compression without heat transfer typically results in a temperature rise of a gas and a drop in efficiency, for the elevated temperature leads to wasted thermal energy, due to cooling during subsequent cooling back to ambient temperature. The use of heat exchangers can reduce the air temperature rise during the Compression period. A typical numerical model of a heat exchanger is a one-dimensional simplification of the two-energy-equation porous media model. The present authors proposed a one-dimensional model that incorporates the Volume of Fluid (VOF) method for application to the two-phase flow, liquid piston compressor with exchanger inserts. Important to calculating temperature distributions in both the solid and fluid components of the mixture is heat transfer between the two, which depends on the local temperature values, geometry, and the velocity of fluid through the matrix. In the one-dimensional model, although the axial temperatures vary, the solid is treated as having a uniform temperature distribution across the plate at any axial location. This may be in line with the physics of flow in most heat exchangers, especially when the exchangers are made of metal with high thermal conductivity. However, it must be noted that for application to CAES, the gas temperature in the Compression chamber rises rapidly during Compression and the core of the solid wall may heat up to a different temperature than that of the surface, depending on the geometry, solid material of the exchanger and fluid flow situation. Therefore, a new, one-dimensional model with embedded two-dimensional submodel is developed to consider two-dimensional heat conduction in a representative solid plate. The VOF concept is used in the model to handle the moving liquid-gas interface (liquid piston). The model gives accurate solutions of temperature distributions in the liquid piston Compression chamber. Six different heat exchangers with different length scales and different materials are simulated and compared.

  • Storage Power and Efficiency Analysis Based on CFD for Air Compressors used for Compressed Air Energy Storage
    Volume 7: Fluids and Heat Transfer Parts A B C and D, 2012
    Co-Authors: Chao Zhang, Terrence W Simon, Perry Y. Li
    Abstract:

    The Compression process in a piston cylinder devic e in a Compressed Air Energy Storage (CAES) system is studied computationally. Twelve different cases featuring f our different Compression Space length-to-radius aspect ratios an d three different Reynolds numbers are studied computationally using the commercial CFD code ANSYS FLUENT. The solutions show that for Compression with a constant velocity, the Compression can be approximated by a polytropic pressure vs. volume relation. The polytropic exponent, �, characterizes the heat transfer and temperature rise of the air being compressed. For the cases computed, it varies from 1.124 to 1.3 05 and is found to be more affected by Reynolds number and less by the length-to-radius ratio. Since the efficiency and st orage power of the compressor depend on pressure vs. volume trajec tory during Compression, they are written as functions of the p ressure rise ratio and the polytropic exponent, �. The efficiency is high at the beginning of the Compression process, and decre ases as the Compression proceeds. The effect of temperature ris e, or heat transfer, on efficiency and storage power is shown by comparing the efficiency and storage power vs. volume curves having

  • A 2-D CFD Model of a Free Piston Stirling Engine for Space Applications with Annular Heat Exchangers
    2nd International Energy Conversion Engineering Conference, 2004
    Co-Authors: Mounir B. Ibrahim, Terrence W Simon, Mayank Mittal, David Gedeon
    Abstract:

    The CFD-ACE commercial code has been utilized for a 2 -D model of a Free Piston Stirling Engine (FPSE). Several code validations were conducted including laminar flow in oscillatory pipe and parallel plate flows. The CFD results showed good agreement with available experimental data as well as analytical solutions. The 2-D model consisted of an Expansion Space (ES), Heater (HR), Regenerator (RG), Cooler (CR) and Compression Space (CS). The HR and CR were modeled as concentric fins, while the RG utilizes the CFD-ACE porous media model. CFD data were obtained for the PV power from the ES and CS as well as heat in and out of the heat exchangers. The model for the FPSE was conducted for two grids, coarse (64,823 cells) and fine (133,078 cells) and includes the CS, CR, RG, HR and ES. Both the power piston and displacer were also modeled. Results were obtained for energy in and out from each component including enthalpy flux at both sides of the regenerator. The CFD-ACE porous media model was utilized (which is known not to accurately represent the unsteady heat transfer process in the regenerator due to the assumption of gas-solid temperature equilibrium). The results obtained for 110 cycles (coarse grids) and 100 cycles (fine grids) were compared with Sage results. The codes for both cases seem to head towards the right direction of energy balance. The similarities and differences among the different cases were examined and discussed in the paper. Two approaches have been proposed to accelerate the convergence process: 1) Replace the solid walls (as much as possible, e.g. in the heater and cooler) by a uniform temperature surface. This might accelerate the convergence of the CFD process but will alter the B.C., which would result in different heat transfer rates, 2) Model computationally each component separately and merge them one at a time using user subroutine in CFD-ACE. Both approaches have been attempted and the results are encouraging.