Global height datum unification: a new approach in gravity potential space

The problem of “global height datum unification” is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid’s potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth’s gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid’s potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the “potential space”, which is transferred into “geometry space” using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid’s potential value W ₀=62636855.8 m²/s². According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid.     

太平洋板块俯冲对中国大陆的影响

在中国大陆及周边地区ITRF2000速度场的基础上,建立欧亚板块整体旋转与线性应变运动模型,得到中国大陆及邻区的局部形变场,分析此形变场发现东北块体和华北块体东部地壳存在一致的向西或北西西向运动,平均运动速率东北为2.9 mm/a,华北东部为1.4 mm/a,推测这是太平洋板块向欧亚板块俯冲的影响。其影响范围仅限于东北和华北块体,影响较大的是120°E以东和40°N以北地区。并分析太平洋板块俯冲对中国大陆影响的表现形式和形成机制。     

Surfer在地球重力场数据可视化中的应用

介绍了应用Surfer实现地球重力场数据可视化的方法和步骤,结合重力场数据格式特点,编制了简单的格式转换程序,直接操作Surfer绘制重力场数据二维、三维信息图,实现了地球重力场数据的快速可视化。     

RTK在大比例尺地形图航测数字化测图中的应用

结合某开发区1：2000地形图航测数字化测图工程，探讨了采用GPSRTK的自由基站二步法拟合方式测量航外像控点（平高点），实施大比例尺地形图野外检测的可行性。对比测量实验表明，该方式在像控点要求的特定位置不仅能保证平面精度，也可以保证高程精度；与常规的RTK相比，该方式具有基站设置位置灵活、不需单独提前解算基准转换参数，以及显著提高工效等优点。     

A technique for modeling the Earth’s gravity field on the basis of satellite accelerations

A technique is proposed for Earths gravity field modeling on the basis of satellite accelerations that are derived from precise orbit data. The functional model rests on Newtons second law. The computational procedure is based on the pre-conditioned conjugate-gradient (PCCG) method. The data are treated as weighted average accelerations rather than as point-wise ones. As a result, a simple three-point numerical differentiation scheme can be used to derive them. Noise in the orbit-derived accelerations is strongly dependent on frequency. Therefore, the key element of the proposed technique is frequency-dependent data weighting. Fast convergence of the PCCG procedure is ensured by a block-diagonal pre-conditioner (approximation of the normal matrix), which is derived under the so-called Colombo assumptions. Both uninterrupted data sets and data with gaps can be handled. The developed technique is compared with other approaches: (1) the energy balance approach (based on the energy conservation law) and (2) the traditional approach (based on the integration of variational equations). Theoretical considerations, supported by a numerical study, show that the proposed technique is more accurate than the energy balance approach and leads to approximately the same results as the traditional one. The former finding is explained by the fact that the energy balance approach is only sensitive to the along-track force component. Information about the cross-track and the radial component of the gravitational potential gradient is lost because the corresponding force components do no work and do not contribute to the energy balance. Furthermore, it is shown that the proposed technique is much (possibly, orders of magnitude) faster than the traditional one because it does not require the computation of the normal matrix. Hints are given on how the proposed technique can be adapted to the explicit assembling of the normal matrix if the latter is needed for the computation of the model covariance matrix.Acknowledgments. Professor R. Klees is thanked for support of the project and for numerous fruitful discussions. The authors are also thankful to Dr. J. Kusche for useful remarks and to Dr. E. Schrama, his solid background in satellite geodesy proved to be very helpful. A large number of valuable comments were made by Dr. S.-C. Han, Dr. P. Schwintzer, and an anonymous reviewer; their contribution is greatly acknowledged. The satellite orbits used in the numerical study were kindly provided by Dr. P. Visser (Aerospace Department, Delft University of Technology). Access to the SGI Origin 3800 computer was provided by Stichting Nationale Computerfaciliteiten (NCF), grant SG-027.     

多时相Radarsat数据在广东肇庆地区稻田分类中的应用

将1996年获取的4个时相的Radarsat图像用于广东肇庆地区的稻田分类试验,结果表明,多时相Radarsat数据对水稻类型的识别精度较高,而且稻田的轮作规律容易推测出来。本文系统地介绍了这一试验研究的最新进展,探讨了神经网络分类方法在SAR图像处理中的应用潜力和Radarsat数据在中国南方水稻监测中的最佳时相选择和有效分辨率问题。     

天地图野外数据采集系统设计与实现

针对传统的地质灾害危险性评估野外调查效率不高和采集数据的正确性较低的问题,提出采用天地图API(Android版)提供的地理信息服务接口、结合Android开发和SQLite数据库技术构建地质灾害危险性评估野外数据采集系统。采用天地图提供的数据服务,解决纸质地图比例尺固定和幅面大小限制的问题,实现野外底图不同级别缩放和无限制的底图范围;基于天地图的功能服务,实现实时定位、经济合理的线路规划以及调查点的分布;采用规范化的电子记录模式,解决室外纸质记录的随意性、室内入库的效率和准确性问题,实现数据的采集与编辑。应用测试表明,有效提高了评估工作效率和质量。     

地面检校场的非量测型数码相机检校

由于相机检校作为非量测型数码相机应用于摄影测量前的必经步骤,其精度直接决定着后续测图的精度,因此针对传统的相机检校方法不能较真实地反映相机的物理状态、检校精度不高的问题,该文给出了基于地面检校场进行检校的流程,并以和静县数据为例,将该方法的检校精度与基于室内三维检校场以及基于纯平液晶显示器的检校精度进行了对比。实验表明:经该方法检校出来的相机参数精度更高,能够满足大比例尺测图要求。     

CORS网区域重力场变化与地面稳定性跟踪监测方法

为了实现地面稳定性降低时间与地点、持续作用时间与空间影响分布的全面跟踪监测,该文基于卫星定位连续运行站(CORS)站网观测数据,结合地表水、大气及海平面变化资料,提出了CORS站网时变重力场及负荷形变场精化的已知负荷移去恢复法,建立了基于时变重力场的确定性地面稳定性变化定量辨识准则。以丽水温州地区为例,利用2015-2017年CORS网及有关水文观测数据进行计算分析,根据40起已发生的历史地质灾害(险情)事件对结果进行验证:丽水温州地区的CORS网具备区域重力场变化与地面稳定性跟踪监测能力,具备地质灾害灾变过程追踪与前兆捕获能力,CORS站网的地质灾害前兆提前捕获率可达92.5%。