MODIS数据具有高时相分辨率、高光谱分辨率和中等地面分辨率的特征,利用MODIS数据来监测和提取旱情严重地区的水体信息已经成为一个重要的研究方向.本文利用各类地物在MODIS各个波段上的波谱特征差异性进行水体提取,但与以往水体信息提...MODIS数据具有高时相分辨率、高光谱分辨率和中等地面分辨率的特征,利用MODIS数据来监测和提取旱情严重地区的水体信息已经成为一个重要的研究方向.本文利用各类地物在MODIS各个波段上的波谱特征差异性进行水体提取,但与以往水体信息提取方法有创新之处在于:本文借助于非线性的指数函数对低反射的水体的反射率进行了拉伸而对高反射的非水体地物的反射率进行了压缩,从而提高了水体在短波红外上的反射率而抑制了非水体在红波段上的反射率,通过波段间的归一化处理进而构建出EXPWI(EXP Water Index)方法 .为了更进一步地提高水体信息提取的自动化程度,本文用ENVI/IDL编写了EXPWI模型.研究表明利用IDL编写的EXPWI法快速实现了中等分辨率遥感影像中水体信息的自动提取,能有效的抑制背景地物的干扰而清晰的识别出湖泊、河道和地表的微弱水体信息,而且能有效降低云对水体信息提取的干扰,更重要的是在抑制大气噪音对提取结果的干扰方面,EXPWI法的效果很好.展开更多
Various calibration methods have been propounded to determine profiles of apparent bulk soil electrical conductivity (ECa) and soil electrical conductivity of a saturated soil paste extract (ECe) or a 1:5 soil water e...Various calibration methods have been propounded to determine profiles of apparent bulk soil electrical conductivity (ECa) and soil electrical conductivity of a saturated soil paste extract (ECe) or a 1:5 soil water extract (EC1:5) using an electromagnetic induction instrument (EM38). The modeled coefficients, one of the successful and classical methods hitherto, were chosen to calibrate the EM38 measurements of the inverted salinity profiles of characteristic coastal saline soils at selected sites of Xincao Farm, Jiangsu Province, China. However, this method required three parameters for each depth layer. An integration approach, based on an exponential decay profile model, was proposed and the model was fitted to all the calibration sites. The obtained model can then be used to predict EC1:5 at a certain depth from electromagnetic measurements made using the EM38 device positioned in horizontal and vertical positions at the soil surface. This exponential decay model predicted the EC1:5 well according to the results of a one-way analysis of variance, and the further comparison indicated that the modeled coefficients appeared to be slightly superior to, but not statistically different from, this exponential decay model. Nevertheless, this exponential decay model was more significant and practical because it depended on less empirical parameters and could be used to perform point predictions of EC1:5 continuously with depth.展开更多
The reliability assessment of unit-system near two levels is the mostimportant content in the reliability multi-level synthesis of complex systems. Introducing theinformation theory into system reliability assessment,...The reliability assessment of unit-system near two levels is the mostimportant content in the reliability multi-level synthesis of complex systems. Introducing theinformation theory into system reliability assessment, using the addible characteristic ofinformation quantity and the principle of equivalence of information quantity, an entropy method ofdata information conversion is presented for the system consisted of identical exponential units.The basic conversion formulae of entropy method of unit test data are derived based on the principleof information quantity equivalence. The general models of entropy method synthesis assessment forsystem reliability approximate lower limits are established according to the fundamental principleof the unit reliability assessment. The applications of the entropy method are discussed by way ofpractical examples. Compared with the traditional methods, the entropy method is found to be validand practicable and the assessment results are very satisfactory.展开更多
文摘MODIS数据具有高时相分辨率、高光谱分辨率和中等地面分辨率的特征,利用MODIS数据来监测和提取旱情严重地区的水体信息已经成为一个重要的研究方向.本文利用各类地物在MODIS各个波段上的波谱特征差异性进行水体提取,但与以往水体信息提取方法有创新之处在于:本文借助于非线性的指数函数对低反射的水体的反射率进行了拉伸而对高反射的非水体地物的反射率进行了压缩,从而提高了水体在短波红外上的反射率而抑制了非水体在红波段上的反射率,通过波段间的归一化处理进而构建出EXPWI(EXP Water Index)方法 .为了更进一步地提高水体信息提取的自动化程度,本文用ENVI/IDL编写了EXPWI模型.研究表明利用IDL编写的EXPWI法快速实现了中等分辨率遥感影像中水体信息的自动提取,能有效的抑制背景地物的干扰而清晰的识别出湖泊、河道和地表的微弱水体信息,而且能有效降低云对水体信息提取的干扰,更重要的是在抑制大气噪音对提取结果的干扰方面,EXPWI法的效果很好.
基金Project supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (No. KZCX2-YW-406-3)the National Key Basic Research Support Foundation (NKBRSF) of China (No. 2005CB121108).
文摘Various calibration methods have been propounded to determine profiles of apparent bulk soil electrical conductivity (ECa) and soil electrical conductivity of a saturated soil paste extract (ECe) or a 1:5 soil water extract (EC1:5) using an electromagnetic induction instrument (EM38). The modeled coefficients, one of the successful and classical methods hitherto, were chosen to calibrate the EM38 measurements of the inverted salinity profiles of characteristic coastal saline soils at selected sites of Xincao Farm, Jiangsu Province, China. However, this method required three parameters for each depth layer. An integration approach, based on an exponential decay profile model, was proposed and the model was fitted to all the calibration sites. The obtained model can then be used to predict EC1:5 at a certain depth from electromagnetic measurements made using the EM38 device positioned in horizontal and vertical positions at the soil surface. This exponential decay model predicted the EC1:5 well according to the results of a one-way analysis of variance, and the further comparison indicated that the modeled coefficients appeared to be slightly superior to, but not statistically different from, this exponential decay model. Nevertheless, this exponential decay model was more significant and practical because it depended on less empirical parameters and could be used to perform point predictions of EC1:5 continuously with depth.
文摘The reliability assessment of unit-system near two levels is the mostimportant content in the reliability multi-level synthesis of complex systems. Introducing theinformation theory into system reliability assessment, using the addible characteristic ofinformation quantity and the principle of equivalence of information quantity, an entropy method ofdata information conversion is presented for the system consisted of identical exponential units.The basic conversion formulae of entropy method of unit test data are derived based on the principleof information quantity equivalence. The general models of entropy method synthesis assessment forsystem reliability approximate lower limits are established according to the fundamental principleof the unit reliability assessment. The applications of the entropy method are discussed by way ofpractical examples. Compared with the traditional methods, the entropy method is found to be validand practicable and the assessment results are very satisfactory.
