The gravity field and steady-state ocean circulation explorer (GOCE) satellite mission has provided numerous Global Geopotential Models (GGMs) with different processing methodologies and model accuracies. In the curre...The gravity field and steady-state ocean circulation explorer (GOCE) satellite mission has provided numerous Global Geopotential Models (GGMs) with different processing methodologies and model accuracies. In the current contribution, the latest releases of GOCE-based GGMs are evaluated on the regional scale using the available terrestrial GPS/Levelling and gravity data collected over Egypt. To overcome the spectral inconsistency between the GOCE-based GGMs and the ground-based data, the spectral enhancement method (SEM) is applied. Five of GOCE-based GGMs have been used, namely GOSG01S, IGGT_R1, IfE_GOCE05s_ GO_CONS_GCF_2_SPW_R5 (SPW_R5 in the following) and NULP-02. The evaluation process of GOCE-based GGMs with the available ground data over Egypt considering the SEM method shows remarkable improvements obtained from the SPW_R5 model. The model provides lower differences of the standard deviations with respect to the EGM2008 and the other applied geopotential gravity models as well as the applied ground-based gravity and GPS/Levelling data. The findings regarding the ground-based data show obvious reductions of about 15.16% and 32.22% achieved by the GOCE-based model in term of standard deviations differences of gravity anomalies and geoid heights, respectively. Therefore, the SPW_R5 model is recommended to be applied as a reference model for compensating the long-to-short wavelength (up to spherical harmonics degree/order 280) components when modelling the gravimetric geoid over Egypt.展开更多
函数加密是一种新型原语,通过函数密钥解密可以得到关于消息的函数值,而不会泄露消息的其他信息.通用群模型(generic group model,GGM)是一种可以用来分析方案构造安全性的理想化模型.由于目前还没有针对GGM的有效攻击,且能在GGM下证明...函数加密是一种新型原语,通过函数密钥解密可以得到关于消息的函数值,而不会泄露消息的其他信息.通用群模型(generic group model,GGM)是一种可以用来分析方案构造安全性的理想化模型.由于目前还没有针对GGM的有效攻击,且能在GGM下证明安全的方案都比较高效,越来越多的函数加密方案在GGM下证明安全性.2017年,Baltico等人提出了第一个公钥二次函数加密方案,并在GGM下证明了自适应的不可区分安全性.然而,目前无论是在标准假设还是GGM下,没有能达到自适应可模拟安全性的公钥二次函数加密方案.本文根据公钥二次函数加密可模拟安全的定义,证明了Baltico等人提出的方案在GGM下具有更强的自适应可模拟安全性.由于证明过程繁琐,本文借助计算机辅助,设计了在GGM下证明公钥二次函数加密方案具有可模拟安全性的自动证明工具.该工具是第一个针对函数加密方案设计的自动证明工具,且该工具不仅能快速测试在GGM下构造的函数方案是否具有可模拟安全性,还可以作为标准假设下构造安全函数加密方案的初步验证.展开更多
The Global Geopotential Models (GGMs) of GOCE (Gravity Recovery and steady- state Ocean Circulation Explorer) differ globally as well as regionally in their accuracy and resolution based on the maximum degree and orde...The Global Geopotential Models (GGMs) of GOCE (Gravity Recovery and steady- state Ocean Circulation Explorer) differ globally as well as regionally in their accuracy and resolution based on the maximum degree and order (d/o) of the fully normalized spherical harmonic (SH) coefficients, which express each GGM. The main idea of this study is to compare the free-air gravity anomalies and quasi geoid heights determined from several recent GOCE-based GGMs with the corresponding ones from the Earth Gravitational Model 2008 (EGM2008) over Egypt on the one hand and with ground-based measurements on the other hand. The results regarding to the comparison of GOCE-based GGMs with terrestrial gravity and GPS/levelling data provide better improvement with respect to EGM2008. The 4th release GOCE-based GGM developed with the use of space-wise solution strategy (SPW_R4) approximates the gravity field well over the Egyptian region. The SPW_R4 model is accordingly suggested as a reference model for recovering the long wavelength (up to SH d/o 200) components of quasi geoid heights when modelling the gravimetric quasi-geoid over the Egypt. Finally, three types of transformation models: Four-, Five- and Seven-parameter transformations have been applied to reduce the data biases and to provide a better fitting of quasi geoid heights obtained from the studied GOCE-based GGMs to those from GPS/levelling data. These models reveal that the standard deviation of vertical datum over Egypt is at the level of about 32 cm.展开更多
广义最小二乘估计(Generalized least squares estimation,GLSE)是最佳线性无偏估计,却有计算复杂高和依赖未知信息的局限性,使得普通最小二乘估计(Ordinary least squares estimation,OLSE)经常成为应用的无奈之选。本文探讨该现象背...广义最小二乘估计(Generalized least squares estimation,GLSE)是最佳线性无偏估计,却有计算复杂高和依赖未知信息的局限性,使得普通最小二乘估计(Ordinary least squares estimation,OLSE)经常成为应用的无奈之选。本文探讨该现象背后的三个循序渐进的理论问题:第一,GLSE的退化问题,给出GLSE完全退化为OLSE的充要条件;第二,退化的分类问题,依据设计矩阵和误差协方差阵的结构把退化现象分为三类,并给出典型的退化特例;第三,不完全退化问题,研讨导致效率退化的因素,刻画效率曲线和效率曲面,最后给出效率不低于95%的退化边界。效率退化和边界分析的潜在应用价值主要包括两方面:第一,为进一步优化试验方案提供效率视角和反馈信息;第二,为设计更简洁更可靠的算法提供理论依据。展开更多
文摘The gravity field and steady-state ocean circulation explorer (GOCE) satellite mission has provided numerous Global Geopotential Models (GGMs) with different processing methodologies and model accuracies. In the current contribution, the latest releases of GOCE-based GGMs are evaluated on the regional scale using the available terrestrial GPS/Levelling and gravity data collected over Egypt. To overcome the spectral inconsistency between the GOCE-based GGMs and the ground-based data, the spectral enhancement method (SEM) is applied. Five of GOCE-based GGMs have been used, namely GOSG01S, IGGT_R1, IfE_GOCE05s_ GO_CONS_GCF_2_SPW_R5 (SPW_R5 in the following) and NULP-02. The evaluation process of GOCE-based GGMs with the available ground data over Egypt considering the SEM method shows remarkable improvements obtained from the SPW_R5 model. The model provides lower differences of the standard deviations with respect to the EGM2008 and the other applied geopotential gravity models as well as the applied ground-based gravity and GPS/Levelling data. The findings regarding the ground-based data show obvious reductions of about 15.16% and 32.22% achieved by the GOCE-based model in term of standard deviations differences of gravity anomalies and geoid heights, respectively. Therefore, the SPW_R5 model is recommended to be applied as a reference model for compensating the long-to-short wavelength (up to spherical harmonics degree/order 280) components when modelling the gravimetric geoid over Egypt.
文摘函数加密是一种新型原语,通过函数密钥解密可以得到关于消息的函数值,而不会泄露消息的其他信息.通用群模型(generic group model,GGM)是一种可以用来分析方案构造安全性的理想化模型.由于目前还没有针对GGM的有效攻击,且能在GGM下证明安全的方案都比较高效,越来越多的函数加密方案在GGM下证明安全性.2017年,Baltico等人提出了第一个公钥二次函数加密方案,并在GGM下证明了自适应的不可区分安全性.然而,目前无论是在标准假设还是GGM下,没有能达到自适应可模拟安全性的公钥二次函数加密方案.本文根据公钥二次函数加密可模拟安全的定义,证明了Baltico等人提出的方案在GGM下具有更强的自适应可模拟安全性.由于证明过程繁琐,本文借助计算机辅助,设计了在GGM下证明公钥二次函数加密方案具有可模拟安全性的自动证明工具.该工具是第一个针对函数加密方案设计的自动证明工具,且该工具不仅能快速测试在GGM下构造的函数方案是否具有可模拟安全性,还可以作为标准假设下构造安全函数加密方案的初步验证.
文摘The Global Geopotential Models (GGMs) of GOCE (Gravity Recovery and steady- state Ocean Circulation Explorer) differ globally as well as regionally in their accuracy and resolution based on the maximum degree and order (d/o) of the fully normalized spherical harmonic (SH) coefficients, which express each GGM. The main idea of this study is to compare the free-air gravity anomalies and quasi geoid heights determined from several recent GOCE-based GGMs with the corresponding ones from the Earth Gravitational Model 2008 (EGM2008) over Egypt on the one hand and with ground-based measurements on the other hand. The results regarding to the comparison of GOCE-based GGMs with terrestrial gravity and GPS/levelling data provide better improvement with respect to EGM2008. The 4th release GOCE-based GGM developed with the use of space-wise solution strategy (SPW_R4) approximates the gravity field well over the Egyptian region. The SPW_R4 model is accordingly suggested as a reference model for recovering the long wavelength (up to SH d/o 200) components of quasi geoid heights when modelling the gravimetric quasi-geoid over the Egypt. Finally, three types of transformation models: Four-, Five- and Seven-parameter transformations have been applied to reduce the data biases and to provide a better fitting of quasi geoid heights obtained from the studied GOCE-based GGMs to those from GPS/levelling data. These models reveal that the standard deviation of vertical datum over Egypt is at the level of about 32 cm.
文摘广义最小二乘估计(Generalized least squares estimation,GLSE)是最佳线性无偏估计,却有计算复杂高和依赖未知信息的局限性,使得普通最小二乘估计(Ordinary least squares estimation,OLSE)经常成为应用的无奈之选。本文探讨该现象背后的三个循序渐进的理论问题:第一,GLSE的退化问题,给出GLSE完全退化为OLSE的充要条件;第二,退化的分类问题,依据设计矩阵和误差协方差阵的结构把退化现象分为三类,并给出典型的退化特例;第三,不完全退化问题,研讨导致效率退化的因素,刻画效率曲线和效率曲面,最后给出效率不低于95%的退化边界。效率退化和边界分析的潜在应用价值主要包括两方面:第一,为进一步优化试验方案提供效率视角和反馈信息;第二,为设计更简洁更可靠的算法提供理论依据。
