在天气图传真信号数字化中的几个问题

本文讨论在天气图传真信号数字化中,通过适当限制取样点密度和线条粗细以控制图像复制质量,并简单介绍解决上述问题的实验装置。     

关于正确建立渗流数学模型的若干问题

在某些文献中,有原则性问题的渗流数学模型不乏其见。本文什对问题发生的原因,论述了关于正确建立渗流数学模型的若干要点,给出了体现要点的若干实例分析。     

Comparing historical and contemporary maps - a methodological framework for a cartographic map comparison applied to Swiss maps

Topographic maps are powerful tools for the purpose of identifying land use and cover change (LUCC) as they are among the most reliable representations of past landscapes for the time prior to the existence of aerial photography. In light of the increased availability of historical maps, we argue that there is a need for a standardized process to assess map comparability in a systematic way in order to avoid, or at least minimize, the detection of spurious landscape changes due to incompatible map series. A full understanding of map quality, background and error distributions is fundamental to attain reliable LUCC results. The conceptual framework presented in this study considers the context, distortion and cartographic generalization of topographic maps. Furthermore, it includes an approach to homogenize the level of generalization of landscape elements (e.g. forests) from maps with different scales. To demonstrate its application, we assessed the comparability of seven topographic maps from Canton Zurich covering a time span of 336 years (1664–2000). Overall, for the maps of Canton Zurich, a wall-to-wall comparison of forest cover based on the topographic maps presented here can be problematic for the oldest map from 1664. Based on the results, a wall-to-wall comparison with the later maps is not recommended, due to its substantial distortion. Yet, after re-generalization of natural landscape elements, such as forests, a comparison based on landscape indices is possible, even for the oldest map. Furthermore, our results demonstrate that maps from the mid-19^th century onward possess an acceptable level of accuracy. This framework can be applied to a wide range of maps at regional, national, or global levels, providing the opportunity to look at land cover history over multiple centuries.     

Spherical harmonic analysis of earth’s conductive heat flow

A reappraisal of the international heat flow database has been carried out and the corrected data set was employed in spherical harmonic analysis of the conductive component of global heat flow. Procedures used prior to harmonic analysis include analysis of the heat flow data and determination of representative mean values for a set of discretized area elements of the surface of the earth. Estimated heat flow values were assigned to area elements for which experimental data are not available. However, no corrections were made to account for the hypothetical effects of regional-scale convection heat transfer in areas of oceanic crust. New sets of coefficients for 12° spherical harmonic expansion were calculated on the basis of the revised and homogenized data set. Maps derived on the basis of these coefficients reveal several new features in the global heat flow distribution. The magnitudes of heat flow anomalies of the ocean ridge segments are found to have mean values of less than 150 mW/m². Also, the mean global heat flow values for the raw and binned data are found to fall in the range of 56–67 mW/m², down by nearly 25% compared to the previous estimate of 1993, but similar to earlier assessments based on raw data alone. To improve the spatial resolution of the heat flow anomalies, the spherical harmonic expansions have been extended to higher degrees. Maps derived using coefficients for 36° harmonic expansion have allowed identification of new features in regional heat flow fields of several oceanic and continental segments. For example, lateral extensions of heat flow anomalies of active spreading centers have been outlined with better resolution than was possible in earlier studies. Also, the characteristics of heat flow variations in oceanic crust away from ridge systems are found to be typical of conductive cooling of the lithosphere, there being little need to invoke the hypothesis of unconfined hydrothermal circulation on regional scales. Calculations of global conductive heat loss, compatible with the observational data set, are found to fall in the range of 29–34 TW, nearly 25% less than the 1993 estimate, which rely on one-dimensional conductive cooling models.     

数字摄影测量相机的畸变测量与纠正

在研究数字相机畸变误差来源和测量原理的基础上,设计出基于光学测角法原理的数字相机畸变测量装置。对目前常用10参数畸变纠正模型进行理论分析,并提出畸变纠正精度评价方法。最后进行了畸变测量和纠正实验。结果表明,畸变纠正精度优于0.002mm,满足相关标准的要求。     

基于华浩超算平台几何精校正模块的波段配准研究

KOMPSAT3(阿里郎三号)卫星携带高分辨率0.7 m全色和2.8 m多光谱有效载荷,回访周期短,覆盖范围广,得到了广泛的应用。但由于受太阳辐射、大气干扰、云折射等物理因素的影响,造成波段之间在局部区域图像上发生非线性几何畸变,导致多光谱假彩色合成数据产生重叠现象,严重影响多光谱数据质量。本文针对在极端条件下产生的图像局部非线性几何畸变现象,探索国内外各种波段间配准方法,研究发现基于华浩超算平台的几何精校正算法能很好地达到波段间配准效果,消除了多光谱假彩色合成数据的影像重叠现象。     

利用验潮站资料的中国近岸海潮模型精度评估

针对全球海潮模型在我国近海海域精度较差的问题,该文采用中国沿岸30个长期验潮站的调和常数,对比了3种全球海潮模型DTU10、TPXO7.2、NAO.99b和1个区域海潮模型NAO.99Jb在中国沿岸的准确度。通过海潮模型与验潮站分潮的振幅中误差、迟角中误差以及8个主要分潮的预报误差,对渤海、黄海、东海和南海北部进行了详细的分析。结果表明,NAO.99Jb在中国海域精度最高,NAO.99b次之。在渤海海域,DTU10在Q_1分潮精度最高,NAO.99b在K2分潮精度最高,其余分潮均是NAO.99Jb精度最高;在黄海海域,NAO.99b在Q_1分潮精度最高,其余分潮均是NAO.99Jb精度最高;在东海海域,DTU10在Q_1分潮精度最高,TPXO7.2在P1精度最高,NAO.99Jb在O1、M2分潮精度最高,其余分潮均是NAO.99b精度最高;在南海北部海域,DTU10在N2、S2分潮精度最高,其余分潮均是NAO.99Jb精度最高。     

Computation of spherical harmonic coefficients and their error estimates using least-squares collocation

 Equations expressing the covariances between spherical harmonic coefficients and linear functionals applied on the anomalous gravity potential, T, are derived. The functionals are the evaluation functionals, and those associated with first- and second-order derivatives of T. These equations form the basis for the prediction of spherical harmonic coefficients using least-squares collocation (LSC). The equations were implemented in the GRAVSOFT program GEOCOL. Initially, tests using EGM96 were performed using global and regional sets of geoid heights, gravity anomalies and second-order vertical gravity gradients at ground level and at altitude. The global tests confirm that coefficients may be estimated consistently using LSC while the error estimates are much too large for the lower-order coefficients. The validity of an error estimate calculated using LSC with an isotropic covariance function is based on a hypothesis that the coefficients of a specific degree all belong to the same normal distribution. However, the coefficients of lower degree do not fulfil this, and this seems to be the reason for the too-pessimistic error estimates. In order to test this the coefficients of EGM96 were perturbed, so that the pertubations for a specific degree all belonged to a normal distribution with the variance equal to the mean error variance of the coefficients. The pertubations were used to generate residual geoid heights, gravity anomalies and second-order vertical gravity gradients. These data were then used to calculate estimates of the perturbed coefficients as well as error estimates of the quantities, which now have a very good agreement with the errors computed from the simulated observed minus calculated coefficients. Tests with regionally distributed data showed that long-wavelength information is lost, but also that it seems to be recovered for specific coefficients depending on where the data are located. Received: 3 February 2000 / Accepted: 23 October 2000     

在推求地球外部扰动重力场中数据的采用

地球外部点的重力矢量值是由已知的全球重力位模型和各种不同方块的平均重力异常数据推求得到的。过去对选择和使用这些数据的依据不够充分,这就造成了某些随意性。本文对扰动重力在各种高度上的谱信息特征进行了分析,讨论了在一定的精度指标下各类平均异常数据区的大小范围以便为今后的实际工作提供必要的依据。     

海潮负荷潮的研究

本文讨论海水质量守恒改正和等潮图的差异对计算负荷效应的影响,并研制海潮主要分波的球谐模型。数值计算结果表明:在按Schwiderski全球1°×1°等潮数据计算中国大陆的海潮负荷效应时,须用我国更精细的近海潮汐资料对其进行修正,同时还应该进行海水质量守恒改正。用褶积和级数相结合的方法计算倾斜海潮负荷潮的精度为0.04ms。