针对时差估计(TDE)易受噪声影响产生模糊的问题,推导了单频信号、线性调频(LFM)信号以及二进制相移键控(BPSK)信号的互相关(CC)函数表达式,以最小二乘(LS)曲线拟合细化CC函数的幅度谱,获取精确的时差估计。首先对CC函数的幅度谱进行谱...针对时差估计(TDE)易受噪声影响产生模糊的问题,推导了单频信号、线性调频(LFM)信号以及二进制相移键控(BPSK)信号的互相关(CC)函数表达式,以最小二乘(LS)曲线拟合细化CC函数的幅度谱,获取精确的时差估计。首先对CC函数的幅度谱进行谱峰搜索,得到时差的粗估计,然后对CC函数的幅度谱以时差的粗估计为界,根据脉内调制类型,选择相应的一次或二次曲线,进行LS曲线拟合,降低噪声项对信号项的影响,可有效排除伪峰和局部最大,获得时差的精确估计。仿真结果显示,在信噪比大于6 d B时,BPSK信号的时差估计均方根误差接近零。展开更多
为了实现对星空观测图像中高亮目标产生的拖尾现象进行自动消除,建立了目标拖尾自动消除系统,对该系统所采用的图像背景高斯噪声分布参数估计、目标拖尾检测以及图像灰度值校正等算法进行研究。利用直方图最小二乘曲线拟合估计星空观测...为了实现对星空观测图像中高亮目标产生的拖尾现象进行自动消除,建立了目标拖尾自动消除系统,对该系统所采用的图像背景高斯噪声分布参数估计、目标拖尾检测以及图像灰度值校正等算法进行研究。利用直方图最小二乘曲线拟合估计星空观测图像背景高斯噪声的分布参数;利用观测图像中目标拖尾现象的特征提出一种基于统计信息的拖尾检测算法;在确定目标拖尾位置的基础上对被污染的像素进行灰度值校正;利用Visual Studio 2005开发出一套星空观测图像目标拖尾自动消除系统。实验结果表明:针对16bit,1 024×1 024的星空观测图像,单帧图像处理时间约为300ms,拖尾现象得到消除,恒星和目标等有用信息未被破坏。本文算法基本满足后续观测图像中弱小目标检测稳定、可靠、精度高等要求。展开更多
Five multiparameter empirical criteria were exclusively evaluated by comparing them with the strength data covering various stress conditions to find out which failure criterion best fits the test data and describes t...Five multiparameter empirical criteria were exclusively evaluated by comparing them with the strength data covering various stress conditions to find out which failure criterion best fits the test data and describes the mechanical behavior of the salt rock sequence (halite,bedded composite specimens and anhydrite interlayers).Full-scale comparison of all criteria for the three rock types was conducted based on five standard statistics calculated from least squares curve-fitting,which measures both the goodness of fitting and the quality of future prediction.The results indicate that all five nonlinear criteria with a basic power form are efficient in predicting the strength trend in the low tension area as well as in the high compression area of the soft rocks.The parameters obtained for the bedded rock salt are somewhat in the ones for the "pure" rocks and are even closer to those obtained for the halite.The generalized Hoek-Brown criterion is proven to perform best to two rock strength data followed by one for the Bieniawski empirical criterion,thus is the best candidate for the analysis of the salt rock.The Sheorey empirical criterion consistently achieves an intermediate performance for all the three rocks.It seems that the superiority of the poly-axial criteria (the Mogi 1967 criterion and the N-type criterion) over the former three triaxial criteria no longer exists when applied to the conventional triaxial strength data.Besides,the method of tension cut-off was proposed to solve the ambiguity problem of the two poly-axial criteria in the tension field in the plane of the major (σ1) andminor principal stress (σ3).展开更多
文摘针对时差估计(TDE)易受噪声影响产生模糊的问题,推导了单频信号、线性调频(LFM)信号以及二进制相移键控(BPSK)信号的互相关(CC)函数表达式,以最小二乘(LS)曲线拟合细化CC函数的幅度谱,获取精确的时差估计。首先对CC函数的幅度谱进行谱峰搜索,得到时差的粗估计,然后对CC函数的幅度谱以时差的粗估计为界,根据脉内调制类型,选择相应的一次或二次曲线,进行LS曲线拟合,降低噪声项对信号项的影响,可有效排除伪峰和局部最大,获得时差的精确估计。仿真结果显示,在信噪比大于6 d B时,BPSK信号的时差估计均方根误差接近零。
文摘为了实现对星空观测图像中高亮目标产生的拖尾现象进行自动消除,建立了目标拖尾自动消除系统,对该系统所采用的图像背景高斯噪声分布参数估计、目标拖尾检测以及图像灰度值校正等算法进行研究。利用直方图最小二乘曲线拟合估计星空观测图像背景高斯噪声的分布参数;利用观测图像中目标拖尾现象的特征提出一种基于统计信息的拖尾检测算法;在确定目标拖尾位置的基础上对被污染的像素进行灰度值校正;利用Visual Studio 2005开发出一套星空观测图像目标拖尾自动消除系统。实验结果表明:针对16bit,1 024×1 024的星空观测图像,单帧图像处理时间约为300ms,拖尾现象得到消除,恒星和目标等有用信息未被破坏。本文算法基本满足后续观测图像中弱小目标检测稳定、可靠、精度高等要求。
基金Project(2009CB724608) supported by the National Basic Research Program of China
文摘Five multiparameter empirical criteria were exclusively evaluated by comparing them with the strength data covering various stress conditions to find out which failure criterion best fits the test data and describes the mechanical behavior of the salt rock sequence (halite,bedded composite specimens and anhydrite interlayers).Full-scale comparison of all criteria for the three rock types was conducted based on five standard statistics calculated from least squares curve-fitting,which measures both the goodness of fitting and the quality of future prediction.The results indicate that all five nonlinear criteria with a basic power form are efficient in predicting the strength trend in the low tension area as well as in the high compression area of the soft rocks.The parameters obtained for the bedded rock salt are somewhat in the ones for the "pure" rocks and are even closer to those obtained for the halite.The generalized Hoek-Brown criterion is proven to perform best to two rock strength data followed by one for the Bieniawski empirical criterion,thus is the best candidate for the analysis of the salt rock.The Sheorey empirical criterion consistently achieves an intermediate performance for all the three rocks.It seems that the superiority of the poly-axial criteria (the Mogi 1967 criterion and the N-type criterion) over the former three triaxial criteria no longer exists when applied to the conventional triaxial strength data.Besides,the method of tension cut-off was proposed to solve the ambiguity problem of the two poly-axial criteria in the tension field in the plane of the major (σ1) andminor principal stress (σ3).
