The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Robert Wang - One of the best experts on this subject based on the ideXlab platform.
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spaceborne airborne bistatic synthetic aperture radar focusing on an analytical bistatic point target Reference Spectrum
Iet Radar Sonar and Navigation, 2013Co-Authors: Hongjun Song, Yunkai Deng, Robert Wang, Xiuming Shan, Jian Yuan, Chunle WangAbstract:An analytical bistatic point target Reference Spectrum (BPTRS) is proposed. The BPTRS is derived from the one-to-one relationship between slow time and Doppler frequency with no Taylor series expansions. Based on the BPTRS, a two-dimensional frequency-domain focusing algorithm for spaceborne/airborne bistatic synthetic aperture radar is developed. The algorithm exploits a range-dependent sub-blocks processing method to perform range cell migration correction and quadratic Doppler term compensation, and then a scaled inverse Fourier transformation and a sinc interpolation are used to correct the geometric distortions in azimuth and range, respectively. Some simulation experiments are also presented to verify their performance.
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Spaceborne/airborne bistatic synthetic aperture radar focusing on an analytical bistatic point target Reference Spectrum
IET Radar Sonar & Navigation, 2013Co-Authors: Hongjun Song, Yunkai Deng, Robert Wang, Xiuming Shan, Jian Yuan, Chunle WangAbstract:An analytical bistatic point target Reference Spectrum (BPTRS) is proposed. The BPTRS is derived from the one-to-one relationship between slow time and Doppler frequency with no Taylor series expansions. Based on the BPTRS, a two-dimensional frequency-domain focusing algorithm for spaceborne/airborne bistatic synthetic aperture radar is developed. The algorithm exploits a range-dependent sub-blocks processing method to perform range cell migration correction and quadratic Doppler term compensation, and then a scaled inverse Fourier transformation and a sinc interpolation are used to correct the geometric distortions in azimuth and range, respectively. Some simulation experiments are also presented to verify their performance.
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Comparison and analysis of point target Reference Spectrum of FMCW synthetic aperture imaging sensor
EURASIP Journal on Advances in Signal Processing, 2012Co-Authors: Yue Liu, Yunkai Deng, Robert Wang, Xiaoxue Jia, Xiao-dong HanAbstract:Frequency-modulated continuous-wave (FMCW) synthetic aperture imaging sensor (SAIS) combines FMCW technology and SAIS techniques which makes a lightweight, high-resolution, and cost-effective imaging sensor. FMCW SAIS systems are going to play an important role in airborne and spaceborne earth observation fields. However, the stop-and-go approximation used in conventional pulsed SAIR (e.g., synthetic aperture radar—SAR) is no longer valid due to the long signal duration time or low wave propagation speed. To exploit the potentialities of an accurate signal model under FMCW SAIS circumstances, this article presents the relationship and remarkable differences between the analytical FMCW SAIS point target Reference Spectrum model and the traditional ones in pulsed SAR and Synthetic Aperture Acoustic imaging system, and validates the significance of the additional range–azimuth coupling term and range walk term in FMCW SAIS Spectrum introduced by the variation of slant range during the long pulse durations, and highlight the limitations of other two spectra. Finally, the simulation experiments are carried out to compare the performance of the aforementioned Spectrum formulations.
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Focus Squint FMCW SAR Data Using Inverse Chirp-Z Transform Based on an Analytical Point Target Reference Spectrum
IEEE Geoscience and Remote Sensing Letters, 2012Co-Authors: Yue Liu, Yunkai Deng, Robert WangAbstract:Frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) systems offer smaller size and lower cost compared with pulsed-mode systems. They are therefore widely used for Earth observation where frequent revisits at low costs or small sizes are desirable. By accurately formulating the instantaneous slant range during the transmitting and receiving operations, an analytical point target Reference Spectrum has been developed for the FMCW SAR system, where an additional range-azimuth coupling term is found. Based on previous work, this letter presents a modified inverse chirp-Z transform (ICZT) algorithm to deal with the range-azimuth coupling term, which appears to be a scaling factor in range. The new scaling factor is formulated in this letter for the first time. An ICZT is well suited for FMCW SAR since it can handle a dechirped signal without interpolations, thus reducing the computing load. Simulation experiment and real data processing result validate the proposed focusing algorithm.
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Bistatic point target Reference Spectrum in the presence of trajectory deviations
IET Radar Sonar & Navigation, 2009Co-Authors: Robert Wang, Otmar Loffeld, Holger Nies, A. Medrano-ortiz, Stefan KnedlikAbstract:The point target Reference Spectrum (BPTRS) of bistatic SAR in the presence of trajectory deviations based on Loffeld's bistatic formula (LBF) is developed. The presented BPTRS is suitable for the general air-borne bistatic configuration. For the air-borne bistatic SAR, both the transmitter and the receiver will contribute to the trajectory deviation. The compensation of trajectory deviations becomes more complex because of the separate locations of the transmitter and receiver. The authors focus on the effects of trajectory deviations on the point target Spectrum of bistatic SAR. The proposed BPTRS is verified by simulation experiments performed in the azimuth-invariant configuration.
Laetitia Gros - One of the best experts on this subject based on the ideXlab platform.
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Correction of the voice timbre distortions in telephone networks: method and evaluation
Speech Communication, 2004Co-Authors: Gaël Mahé, André Gilloire, Laetitia GrosAbstract:In a telephone link, the voice timbre is impaired by spectral distortions generated by the analog parts of the link. Our purpose is to restore a timbre as close as possible to that of the original voice of the speaker, using a blind equalizer centralized in the network, which compensates for the spectral distortions. We propose a spectral equalization algorithm, which consists in matching the long-term Spectrum of the processed signal to a Reference Spectrum within a limited frequency bandwidth (200-3150 Hz). Subjective evaluations show a satisfactory restoration of the timbre of the speakers, within the limits of the chosen equalization band. The A-law quantization of the output samples of the equalizer induces however a disturbing noise at the reception end. A subjective evaluation shows that speakers' voices with corrected timbre, even with quantization noise, are preferred to the same voices at the output of a link without timbre correction (and without noise). In order to make the Reference Spectrum more appropriate to the various speakers' voices, we classify them according to their long-term spectra and use a specific Reference Spectrum for each class. This leads to a decrease of the spectral distortion induced by the equalizer, significantly perceived as an improvement of the timbre correction, as a subjective test shows.
Gaël Mahé - One of the best experts on this subject based on the ideXlab platform.
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Correction of the voice timbre distortions in telephone networks: method and evaluation
Speech Communication, 2004Co-Authors: Gaël Mahé, André Gilloire, Laetitia GrosAbstract:In a telephone link, the voice timbre is impaired by spectral distortions generated by the analog parts of the link. Our purpose is to restore a timbre as close as possible to that of the original voice of the speaker, using a blind equalizer centralized in the network, which compensates for the spectral distortions. We propose a spectral equalization algorithm, which consists in matching the long-term Spectrum of the processed signal to a Reference Spectrum within a limited frequency bandwidth (200-3150 Hz). Subjective evaluations show a satisfactory restoration of the timbre of the speakers, within the limits of the chosen equalization band. The A-law quantization of the output samples of the equalizer induces however a disturbing noise at the reception end. A subjective evaluation shows that speakers' voices with corrected timbre, even with quantization noise, are preferred to the same voices at the output of a link without timbre correction (and without noise). In order to make the Reference Spectrum more appropriate to the various speakers' voices, we classify them according to their long-term spectra and use a specific Reference Spectrum for each class. This leads to a decrease of the spectral distortion induced by the equalizer, significantly perceived as an improvement of the timbre correction, as a subjective test shows.
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Multi-Referenced correction of the voice timbre distortions on telephone network
2003Co-Authors: Gaël Mahé, André GilloireAbstract:In a telephone link, the voice timbre is impaired by spectral distortions generated by the analog parts of the link. We first evaluate from a perceptual point of view an equalization method consisting in matching the long term Spectrum of the processed signal to a Reference Spectrum. This evaluation shows a satisfying restoration of the timbre for most speakers. For some speakers however, a noticeable spectral distortion remains. That is why we propose a multi-Referenced equalizer, based on a classification of speakers and using a different Reference Spectrum for each class. This leads to a decrease of the spectral distortion and, as a consequence, to a significant improvement of the timbre correction.
Yunkai Deng - One of the best experts on this subject based on the ideXlab platform.
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spaceborne airborne bistatic synthetic aperture radar focusing on an analytical bistatic point target Reference Spectrum
Iet Radar Sonar and Navigation, 2013Co-Authors: Hongjun Song, Yunkai Deng, Robert Wang, Xiuming Shan, Jian Yuan, Chunle WangAbstract:An analytical bistatic point target Reference Spectrum (BPTRS) is proposed. The BPTRS is derived from the one-to-one relationship between slow time and Doppler frequency with no Taylor series expansions. Based on the BPTRS, a two-dimensional frequency-domain focusing algorithm for spaceborne/airborne bistatic synthetic aperture radar is developed. The algorithm exploits a range-dependent sub-blocks processing method to perform range cell migration correction and quadratic Doppler term compensation, and then a scaled inverse Fourier transformation and a sinc interpolation are used to correct the geometric distortions in azimuth and range, respectively. Some simulation experiments are also presented to verify their performance.
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Spaceborne/airborne bistatic synthetic aperture radar focusing on an analytical bistatic point target Reference Spectrum
IET Radar Sonar & Navigation, 2013Co-Authors: Hongjun Song, Yunkai Deng, Robert Wang, Xiuming Shan, Jian Yuan, Chunle WangAbstract:An analytical bistatic point target Reference Spectrum (BPTRS) is proposed. The BPTRS is derived from the one-to-one relationship between slow time and Doppler frequency with no Taylor series expansions. Based on the BPTRS, a two-dimensional frequency-domain focusing algorithm for spaceborne/airborne bistatic synthetic aperture radar is developed. The algorithm exploits a range-dependent sub-blocks processing method to perform range cell migration correction and quadratic Doppler term compensation, and then a scaled inverse Fourier transformation and a sinc interpolation are used to correct the geometric distortions in azimuth and range, respectively. Some simulation experiments are also presented to verify their performance.
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Comparison and analysis of point target Reference Spectrum of FMCW synthetic aperture imaging sensor
EURASIP Journal on Advances in Signal Processing, 2012Co-Authors: Yue Liu, Yunkai Deng, Robert Wang, Xiaoxue Jia, Xiao-dong HanAbstract:Frequency-modulated continuous-wave (FMCW) synthetic aperture imaging sensor (SAIS) combines FMCW technology and SAIS techniques which makes a lightweight, high-resolution, and cost-effective imaging sensor. FMCW SAIS systems are going to play an important role in airborne and spaceborne earth observation fields. However, the stop-and-go approximation used in conventional pulsed SAIR (e.g., synthetic aperture radar—SAR) is no longer valid due to the long signal duration time or low wave propagation speed. To exploit the potentialities of an accurate signal model under FMCW SAIS circumstances, this article presents the relationship and remarkable differences between the analytical FMCW SAIS point target Reference Spectrum model and the traditional ones in pulsed SAR and Synthetic Aperture Acoustic imaging system, and validates the significance of the additional range–azimuth coupling term and range walk term in FMCW SAIS Spectrum introduced by the variation of slant range during the long pulse durations, and highlight the limitations of other two spectra. Finally, the simulation experiments are carried out to compare the performance of the aforementioned Spectrum formulations.
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Focus Squint FMCW SAR Data Using Inverse Chirp-Z Transform Based on an Analytical Point Target Reference Spectrum
IEEE Geoscience and Remote Sensing Letters, 2012Co-Authors: Yue Liu, Yunkai Deng, Robert WangAbstract:Frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) systems offer smaller size and lower cost compared with pulsed-mode systems. They are therefore widely used for Earth observation where frequent revisits at low costs or small sizes are desirable. By accurately formulating the instantaneous slant range during the transmitting and receiving operations, an analytical point target Reference Spectrum has been developed for the FMCW SAR system, where an additional range-azimuth coupling term is found. Based on previous work, this letter presents a modified inverse chirp-Z transform (ICZT) algorithm to deal with the range-azimuth coupling term, which appears to be a scaling factor in range. The new scaling factor is formulated in this letter for the first time. An ICZT is well suited for FMCW SAR since it can handle a dechirped signal without interpolations, thus reducing the computing load. Simulation experiment and real data processing result validate the proposed focusing algorithm.
Paul Dekker - One of the best experts on this subject based on the ideXlab platform.
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Development of white LED illuminants for colorimetry and recommendation of white LED Reference Spectrum for photometry
Metrologia, 2018Co-Authors: Alexander Kokka, Tuomas Poikonen, Peter Blattner, Sophie Jost, Alejandro Ferrero, Tomi Pulli, Mathias Ngo, Anders Thorseth, Thorsten Gerloff, Paul DekkerAbstract:General lighting is undergoing a revolutionary change towards LED-based technologies. To provide firm scientific basis for the related colorimetric and photometric measurements, this paper presents the development of new white-LED-based illuminants for colorimetry, and their evaluation to recommend a new Reference Spectrum for calibration of photometers. Spectra of 1516 LED products were measured and used to calculate eight representative spectral power distributions for LED sources of different correlated colour temperature categories. The suitability of the calculated representative spectra for photometer calibration was studied by comparing average spectral mismatch errors with CIE Standard Illuminant A, which has been used for decades as the Reference Spectrum for incandescent standard lamps in calibration of photometers. It was found that in general, when compared with Standard Illuminant A, all the potential LED calibration spectra reduced spectral mismatch errors when measuring LED products. Out of the potential LED calibration spectra tested, the white LED Spectrum with correlated colour temperature of 4103 K was found to be the most suitable candidate to complement Standard Illuminant A in luminous responsivity calibrations of photometers. When compared with Standard Illuminant A, employing the 4103 K Reference Spectrum reduced the spectral mismatch errors, on average, by approximately a factor of two in measurements of LED products and lighting. Furthermore, the new LED Reference Spectrum was found to reduce the spectral mismatch errors in measurements of daylight, and many types of fluorescent and discharge lamps, indicating that the proposed Reference Spectrum is a viable alternative to Standard Illuminant A for calibration of photometers.
