Backscattered fields from one-dimensional time-varying Gerstners sea surface are calculated utilising the secondorder small slope approximation.It is well known that spectral properties of the backscattered echoes rel...Backscattered fields from one-dimensional time-varying Gerstners sea surface are calculated utilising the secondorder small slope approximation.It is well known that spectral properties of the backscattered echoes relate to the velocity of the small elementary scatterers on sea surface profiles.Therefore,modeling Doppler spectra from the ocean requires an accurate description of the sea surface motion.The profile of nonlinear Gerstners sea surface shows verticalskewness of sea waves,it is sharper at the crest and flatter at the trough than linear waves,and its maximum slope position is closer to the crest than to the trough.Furthermore,the horizontal component of the small elementary scatterers orbit velocity on the sea surface,which yields noticeable influence on Doppler spectra,can be obtained conveniently by Gerstners sea surface model.In this study,the characteristics of Doppler spectra of backscattered fields from time-varying Gerstners sea surface are investigated and the dependences of the Doppler frequency and the Doppler bandwidth on the parameters,such as the wind speed,the radar frequency,the incident angle,etc.are discussed.It is shown that the Doppler bandwidth of microwave scattered fields from Gerstners sea surface is considerably broadened.For the case of high frequency backscattered fields,the values of the higher-order spectrum peaks are larger than those obtained by linear sea surface.展开更多
The azimuth resolution improvement problem is solved via a coherent combination of synthetic aperture radar(SAR) images with the quasi-non-overlapped Doppler bandwidth. Prior to the spectra combination, SAR images sho...The azimuth resolution improvement problem is solved via a coherent combination of synthetic aperture radar(SAR) images with the quasi-non-overlapped Doppler bandwidth. Prior to the spectra combination, SAR images should be co-registered, while phase biases induced by topography, atmospheric propagation delays and baseline measurement errors should be calibrated. However, the coregistration accuracy suffers from large Doppler decorrelation caused by the quasi-non-overlapped Doppler bandwidth. Furthermore, the method used to estimate phase biases from interferogram of azimuth pre-filtered SAR image pairs will fail when there is no overlapped spectrum. The fringe simulation and maximum sharpness optimization are adopted to deal with the problems. Accordingly, a novel algorithm to coherently synthesize SAR images is presented. The experiment with the Terra SAR X-band(TerraSAR-X) satellite data validates the performance of the presented method.展开更多
In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer,the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate t...In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer,the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening,and the spectrum standard deviation is calculated by an auto-correlation method.A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal.The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz.The suspension of carbon particles is driven by a syringe pump.The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation.The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans.The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to8.4 mm/s.The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.展开更多
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 40906088)the National Natural Science Foundation of China (Grant No. 60971067)Specialised Research Fund for the Doctoral Program of Higher Education (Grant No. 200804231021)
文摘Backscattered fields from one-dimensional time-varying Gerstners sea surface are calculated utilising the secondorder small slope approximation.It is well known that spectral properties of the backscattered echoes relate to the velocity of the small elementary scatterers on sea surface profiles.Therefore,modeling Doppler spectra from the ocean requires an accurate description of the sea surface motion.The profile of nonlinear Gerstners sea surface shows verticalskewness of sea waves,it is sharper at the crest and flatter at the trough than linear waves,and its maximum slope position is closer to the crest than to the trough.Furthermore,the horizontal component of the small elementary scatterers orbit velocity on the sea surface,which yields noticeable influence on Doppler spectra,can be obtained conveniently by Gerstners sea surface model.In this study,the characteristics of Doppler spectra of backscattered fields from time-varying Gerstners sea surface are investigated and the dependences of the Doppler frequency and the Doppler bandwidth on the parameters,such as the wind speed,the radar frequency,the incident angle,etc.are discussed.It is shown that the Doppler bandwidth of microwave scattered fields from Gerstners sea surface is considerably broadened.For the case of high frequency backscattered fields,the values of the higher-order spectrum peaks are larger than those obtained by linear sea surface.
基金supported by the National Natural Science Foundationof China(41001282)
文摘The azimuth resolution improvement problem is solved via a coherent combination of synthetic aperture radar(SAR) images with the quasi-non-overlapped Doppler bandwidth. Prior to the spectra combination, SAR images should be co-registered, while phase biases induced by topography, atmospheric propagation delays and baseline measurement errors should be calibrated. However, the coregistration accuracy suffers from large Doppler decorrelation caused by the quasi-non-overlapped Doppler bandwidth. Furthermore, the method used to estimate phase biases from interferogram of azimuth pre-filtered SAR image pairs will fail when there is no overlapped spectrum. The fringe simulation and maximum sharpness optimization are adopted to deal with the problems. Accordingly, a novel algorithm to coherently synthesize SAR images is presented. The experiment with the Terra SAR X-band(TerraSAR-X) satellite data validates the performance of the presented method.
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.U1204612)the Natural Science Foundation of He’nan Educational Committee(No.13A416180)
文摘In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer,the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening,and the spectrum standard deviation is calculated by an auto-correlation method.A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal.The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz.The suspension of carbon particles is driven by a syringe pump.The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation.The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans.The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to8.4 mm/s.The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.
