Accounting for topography in the calculation of quasigeoidal heights and plumb-line deflections from gravity anomalies

A calculation of quasigeoidal heights and plumb-line deflections according to Molodensky formulae was carried out under elimination of the effect of topography from gravity anomalies. After the masses of topography had been removed a smoothed-out surface passing through astronomical and gravity stations was considered as representing the physical surface of the Earth. Thus it has been practically rendered possible to use the first-approximation formulae of Molodensky, and, in many cases, also the “zero-approximation” formulae analogous to the formulae of Stokes and Vening-Meinesz. The effect of the restored masses of topography was then added to the quantities found; the said effect was expressed as the effect of topography condensed on the normal equipotential surface passing through the point under investigation, plus a correction for condensation. Following some transformations, the resulting formulae (13) and (18) were obtained which formulae differ in their “zero-approximation” (15) and (20) from traditional formulas in that they contain terrait reductions added to free-air anomalies. Moreover, in the calculation of plumb-line deflections directly in mountain regions a correction for differing effects of topography before and after its condensation is to be introduced. A tentative expansion of terrain reduction in terms of spherical harmonics up to the third order is given; it can be seen therefrom that the Stokes series in its usual form is subject to a mean arror about 15–20%. It is also shown that the expansion of free-air anomalies in terms of spherical functions contains a first-order harmonic with a mean values about ±0.3 mgl. The said harmonic practically disappears in the expansion of the sum of free-air anomalies and terrain reductions.     

Methods for computing deflections of the vertical by modifying Vening-Meinesz' function

Summary The application of combined data (satellite and terrestrial data) to the practical computation of height anomalies or the deflections of the vertical was originally suggested by (Molodensky et al. 1962). This idea usually leads to the modification of Stokes' or Vening-Meinesz' functions in the integration procedure. In the recent decade there were various suggestions in this regard especially for the computation of height anomalies. For example, a considerable mathematical insight into the modification of Stokes' function and the truncation of its integral has been provided by (Meissl 1971, Houtze et al. 1979, Rapp 1980, Jekeli 1980). Five different methods for computing deflections of the vertical by modifying Vening-Meinesz' function are studied and compared with each other. The corresponding formulae, the values of the coefficients in each method and the estimations of their corresponding potential coefficient error and truncation error are given in this article. This paper was written at the Institut f. Angewandte Geod?sie, Technische Universit?t Graz, Austria.     

Systematic errors in levelings of mountainous areas

Sources of errors in the precise leveling influencing the results of measurements especially strongly in mountains are considered in this study. Data are given on new error sources, including (1) the difference in temperatures of invar bands of rods and of the air; and (2) displacements of rock bench marks during diurnal variations in temperature of rocks. The ranges of possible total systematic error in leveding are estimated.     

PM2.5浓度插值中不同空间插值方法对比

针对不同插值方法对于重点大气颗粒物污染源PM_(2.5)大区域内整体分布情况的插值效果和精度存在差异性的问题,该文以石家庄市赵县100个点的PM_(2.5)的数据作为样本点,利用反距离权重法、普通克里格插值法和协同克里格插值法,分别进行PM_(2.5)浓度的空间插值。利用研究区内另外20个PM_(2.5)的数据点进行插值精度的检验。研究结果表明:协同克里格插值的精度最高,但可视化效果不如其他两种方法。     

不同卫星定位加权方法的比较与分析

测量值随机误差加权模型是卫星定位的重要组成部分,它能够更加合理地分配各卫星在解算中所起的作用大小,并获得更高的定位精度。该文对目前基于卫星仰角与载噪比或信噪比两大影响因素的多种主流定权方法进行了系统阐述与讨论。通过GPS实测定位实验,对9种不同定权模型的效果进行了综合比较与分析。实验结果表明,各加权模型基本均能够在不同程度上提高定位精度,其中综合考虑仰角与载噪比或信噪比的加权模型具有最优的性能表现。另外,当定位条件较差时,由于测量值误差构成更为复杂,因此期待更加有效的加权模型与方法。     

A numerical investigation on height anomaly prediction in mountainous areas

This paper provides numerical examples for the prediction of height anomalies by the solution of Molodensky's boundary value problem. Computations are done within two areas in the Canadian Rockies. The data used are on a grid with various grid spacings from 100 m to 5 arc-minutes. Numerical results indicate that the Bouguer or the topographicisostatic gravity anomalies should be used in gravity interpolation. It is feasible to predict height anomalies in mountainous areas with an accuracy of 10 cm (1) if sufficiently dense data grids are used. After removing the systematic bias, the differences between the geoid undulations converted from height anomalies and those derived from GPS/levelling on 50 benchmarks is 12 cm (1) when the grid spacing is 1km, and 50 cm (1) when the grid spacing is 5. It is not necessary, in most cases, to require a grid spacing finer than 1 km, because the height anomaly changes only by 3 cm (1) when the grid spacing is increased from 100 m to 1000 m. Numerical results also indicate that, only the first two terms of the Molodensky series have to be evaluated in all but the extreme cases, since the contributions of the higher order terms are negligible compared to the objective accuracy.     

Geo-environment-aware adversarial transfer learning method for landslide susceptibility evaluation of complex mountainous areas

Landslide susceptibility evaluation (LSE) is a critical issue for disaster prevention. Limited by labor cost and observation technology, landslide samples are extremely limited in dense vegetation-covered and remote areas, making the common supervised learning model underfit with limited samples. Therefore, the reliability of analysis results in mountainous areas is low. Transfer learning can achieve reliable assessment without the need for representative samples. However, transfer learning suffers from environmental heterogeneity in regional LSE and may transfer incorrect classification knowledge of landslide features from dissimilar environments. Aiming at these challenges, we proposed a geo-environment-aware LSE method based on unsupervised adversarial transfer learning. The key is to consider the difference in landslide features in different geo-environments. The study areas were first divided into multiple sub-environments, and the similarity between the sub-environments was calculated. Then an environment-aware adversarial transfer model was built for fine-grained aligning of the landslide feature with similar sub-environments and for reducing negative transfer between dissimilar environments. The fitted classification model was employed to predict the target regions and to generate the final LSE. The experimental results indicated that the proposed method achieves reliable LSE for sample-free regions. The accuracy of the proposed method is 7–12% better than commonly used methods such as support vector machines, random forests, and artificial neural networks. The performance of the proposed method is even close to the results of supervised learning with the presence of representative samples, and it also performs more globally and objectively in susceptibility mapping. These results reveal that the proposed method effectively transfers the knowledge of landslide susceptibility from other regions to the sample-free region.     

倾斜摄影技术在丘陵山区大比例尺测图中的应用

针对丘陵山区大比例尺测图应用的需求,本文探讨了如何通过倾斜摄影的技术方法获取高精度的影像模型.首先通过分析航线布设方法、控制点布设采集要点、空三数据处理关键点等,获取满足丘陵山区大比例尺测图应用的数据模型,基于数据模型获取大比例尺地形图数据;然后通过与实地测量数据进行精度对比分析获取试验结果,结果表明倾斜摄影技术不但能...     

驱动山区农业产业遥感监测的GMG协同系统建设与应用

由于喀斯特山区地貌的支离破碎、地形的高低起伏及气候的多云与雾,难以通过常规遥感手段实现大范围农作物的快速监测,针对该情况,本文研发了内外业一体化的GMG协同系统。该系统利用GPS的精准定位、多媒体的丰富语义及GIS的数据处理优势,多向驱动贵州山区农业产业遥感监测。实践表明,该系统快速实现了省域监测中解译样本的多样性,有效弥补了局部区域内遥感监测的局限性,同时检验了解译数据的准确性。     

全极化SAR图像的山地低矮植被区域土壤含水量估计

山区土壤含水量对山区植被生长监测、滑坡预测等工作具有重要意义,因此针对山地低矮植被区域,提出了全极化SAR图像的土壤含水量估计方法。为解决山地区域SAR图像几何形变和极化旋转问题,根据入射角、坡度、坡向信息定义了可测区域与不可测区域,并对可测区域后向散射系数进行校正。其次以密西根模型为基础,发展了低矮植被的散射模型。在假定植被和土壤特征不变的情况下,基于此散射模型并结合校正数据建立了山区土壤含水量反演方法。结果表明,模型反演的土壤含水量和实验点实测值基本一致,两个实验点反演值分别为14%和15%,实测值为11.45%和15.80%,能够满足一般应用的需求。     

机载激光雷达在密林山区测绘中的应用

机载激光雷达是近年来发展迅速的高新测绘技术,具有机动性高、数据覆盖量大、作业效率高和精度可靠等特点。针对当前山区沟壑且有大量植被覆盖区域进行传统测量作业较为困难,危险性大的问题,采用机载激光雷达技术获取研究区原始点云数据,在此基础上,对比分析四种滤波算法的点云分类效果,得到适用于密林沟壑区的点云滤波方法,进而通过人机交互和地面点内插实现了测区高精度数字高程模型（digital elevation model,DEM）的构建,最终获得的DEM高程中误差为0.09 m,满足实际测绘生产需求,生产效率大大提高。研究结果表明,机载激光雷达技术应用于复杂危险地形测绘具有极大优势。     

Analysis of different methods for monitoring the urbanization process

The monitoring of urban sprawl in agricultural and natural areas requires the frequent acquisition of information relative to land cover changes. The loss of high capability agricultural lands is a major problem. The sound management of resources requires the knowledge of the nature and orientation of the urban dynamics.

Remote sensing is a useful tool for highlighting areas where changes have occured,for determining the type of change and for quantifying these changes. A spatial‐temporal analysis of the urban processes is carried out for the urban area of Montreal, Canada. Different sources of information are used: three Landsat MSS satellite images acquired in 1972, 1979 and 1982, planimetric data from the Department of Municipal Affairs of Quebec and statistics compiled by Environment Canada.

The satellite data shows a sharp increase, in the order of 65%, in urban areas during the period under consideration. These results are compared with governmental data derived from classical photo‐interpretation techniques.

On one hand, we observe that the results obtained by automatic classification of the satellite data are superior in the order of between 5% to 30%, depending on the year and the different governmental sources. On the other hand, we discuss problems of homogeneity in the use of terms related to land cover between the various governmental organizations.     

Improving operational measurement of precipitation using radar in mountainous terrain-Part I: methods

Four major rainfall events that affected the Western Alps between autumn 1994 and autumn 2000 are analyzed to assess the bias between the radar rainfall estimates at rain gauge locations and the gauge amounts. The aim of this study is to demonstrate the importance of: 1) bias adjustment; 2) the training procedure used to train various adjustment methods by means of independent data; and 3) a quality check of the radar-gauge couples that were used for the training itself. A first adjustment method is simply based on a single "bias-correction" coefficient. A weighted multiple regression (WMR) is well worth the additional effort of determining three additional coefficients, which give a spatial distribution of the adjustment factor rather than a constant one for the whole domain as the output. The independent dataset that was used to train the gauge-adjustment techniques consists of daily radar/gauge amounts accumulated during the first day of each event. The following days are used for an independent verification that is dealt with in a companion letter, which will validate the methods and illustrate the improvements and the feasibility of a real-time application during intense events. The WMR technique tries to correct not only the overall bias but also the beam-broadening, visibility, and orography influences. The training procedure of both the bulk- and WMR-adjustment methods highlighted a considerable radar underestimation, which is certainly not surprising in mountainous terrain. The WMR-derived coefficients also clearly show that the radar underestimates precipitation for higher sampling volumes and longer distances. Since the WMR is fast and simple to use, it represents an alternative to more sophisticated methods and seems to be particularly useful for operational services.     

Iterative vector methods for computing geodetic latitude and height from rectangular coordinates

 Two iterative vector methods for computing geodetic coordinates (φ, h) from rectangular coordinates (x, y, z) are presented. The methods are conceptually simple, work without modification at any latitude and are easy to program. Geodetic latitude and height can be calculated to acceptable precision in one iteration over the height range from −10⁶ to +10⁹ m. Received: 13 December 2000 / Accepted: 13 July 2001     

单基站GPS差分系统在山区线路测量中的应用探讨

RTK技术的出现,使得野外实时测量精度达到厘米级,RTK测量具有实时性好、精度高、速度快等优点,是常规测量所无法比拟的,RTK已经作为快速采集数据与定位的有效工具。本文比较分析了常规RTK系统和网络RTK的优缺点,并详细介绍了单基站GPS差分系统的特点,并在实际工程应用中对其精度和有效距离进行了探讨。     

Modelling position dependent errors in gravimetric deflections of the vertical

Comparisons of gravimetric and astrogeodetic deflections of the vertical in the Australian region indicate that the former are affected by position dependent systematic errors, even after orientation onto the Australian Geodetic Datum. These are probably due to errors in the predicted mean anomalies for gravimetrically unsurveyed oceanic regions to the east, south and west of the continent. Deflection component residuals (astrogeodetic minus oriented gravimetric) at 83 control stations are made the observables in a set of observation equations, based on the Vening Meinesz equations, from which pseudocorrections to the mean anomalies for a set of arbitrarily selected surface elements are computed. These pseudocorrections compensate for prediction errors in much larger unsurveyed regions. Their effects on individual deflection components are calculated using the Vening Meinesz equations. Statistical tests indicate that pseudocorrections computed for four large offshore elements and six smaller elements in unsurveyed areas produce corrections to the gravimetric deflections which make the ξ and η components in seconds of arc consistent with normally distributed populations N (0.00, 0.70²).