Motion compensation based on the parameter estimation of a moving target has a strong influence on the inverse synthetic aperture radar(ISAR)imaging quality.For the target with built-in disturbance components or under...Motion compensation based on the parameter estimation of a moving target has a strong influence on the inverse synthetic aperture radar(ISAR)imaging quality.For the target with built-in disturbance components or under an extremely low signal-to-noise ratio(SNR),conventional parameter estimation methods based on cross-correlation processing of adjacent profiles,such as the cross-correlation method and the accumulated cross-correlation method,give sizable aligned errors and subsequently produce low-quality ISAR images.The fractional Fourier transform is capable of concentrating the signal power;however,a large computational complexity is induced by searching the matched order.In view of the problems above,a time-weighting symmetric accumulated cross-correlation method is proposed herein.This method maps the spectrum of the range profile into a single-peak envelope to reduce range alignment errors,and presents a symmetric accumulated manner to offset the accumulated error.The simulation results demonstrate that the proposed method yields much better estimation precision than other methods,and yields extremely low computational complexity.展开更多
Based on data of cloud-to-ground lightning detected by a lightning location system in Jiangsu Province from 2007 to 2012and data of thunderstorm days from seven meteorological observation stations in Huai'an durin...Based on data of cloud-to-ground lightning detected by a lightning location system in Jiangsu Province from 2007 to 2012and data of thunderstorm days from seven meteorological observation stations in Huai'an during 1961-2012,the spatial and temporal distribution characteristics of cloud-to-ground lightning in Huai'an were analyzed.The results show that the total frequency of cloud-to-ground lightning in one day was closely related to the intensity and frequency of thunder and lightning.The seasonal variations in the total frequency of cloud-to-ground lightning in Huai'an.The total frequency was shown in unimodal distribution,and the extreme values always appeared in July or August.Most cloud-to-ground lightning was negative,and its frequency accounted for about95.3% of the total frequency.Cloud-to-ground lightning density was high in the south of Huai'an and low in the north,and the serious and very serious ground flash zones concentrated in the south of Hongze County,and most parts of Xuyi and Jinhu County,so lightning protection should be an important task particularly in these regions.展开更多
基金This work is supported in part by the National Science Foundation for the Distinguished Young Scholars of China(No.61525103)the Shenzhen Fundamental Research Project(No.JCYJ20150930150304185).
文摘Motion compensation based on the parameter estimation of a moving target has a strong influence on the inverse synthetic aperture radar(ISAR)imaging quality.For the target with built-in disturbance components or under an extremely low signal-to-noise ratio(SNR),conventional parameter estimation methods based on cross-correlation processing of adjacent profiles,such as the cross-correlation method and the accumulated cross-correlation method,give sizable aligned errors and subsequently produce low-quality ISAR images.The fractional Fourier transform is capable of concentrating the signal power;however,a large computational complexity is induced by searching the matched order.In view of the problems above,a time-weighting symmetric accumulated cross-correlation method is proposed herein.This method maps the spectrum of the range profile into a single-peak envelope to reduce range alignment errors,and presents a symmetric accumulated manner to offset the accumulated error.The simulation results demonstrate that the proposed method yields much better estimation precision than other methods,and yields extremely low computational complexity.
文摘Based on data of cloud-to-ground lightning detected by a lightning location system in Jiangsu Province from 2007 to 2012and data of thunderstorm days from seven meteorological observation stations in Huai'an during 1961-2012,the spatial and temporal distribution characteristics of cloud-to-ground lightning in Huai'an were analyzed.The results show that the total frequency of cloud-to-ground lightning in one day was closely related to the intensity and frequency of thunder and lightning.The seasonal variations in the total frequency of cloud-to-ground lightning in Huai'an.The total frequency was shown in unimodal distribution,and the extreme values always appeared in July or August.Most cloud-to-ground lightning was negative,and its frequency accounted for about95.3% of the total frequency.Cloud-to-ground lightning density was high in the south of Huai'an and low in the north,and the serious and very serious ground flash zones concentrated in the south of Hongze County,and most parts of Xuyi and Jinhu County,so lightning protection should be an important task particularly in these regions.
