The deviation of mean sea level from the mean geoid in the baltic sea

The mean sea level along the Swedish coast has been recomputed, taking into account the effect of the permanent tide on the height system. The recomputed data show the deviation of mean sea level (1960) from the mean geoid, i.e. the oceanographic deviation of mean sea level, with NAP as zero. On the basis of a conversion between the Finnish and Swedish height systems, mean sea level data from the Finnish coast are reduced to the same system as on the Swedish coast.The geodetically determined mean sea level values are compared with oceanographic model calculations. On the whole, the agreement between geodesy and oceanography is found to be good. Nevertheless, oceanography tends to yield somewhat larger deviations of the mean sea level than geodesy, especially in the extreme parts of both the Gulf of Bothnia and the Gulf of Finland. This might indicate that the oceanographic model has overestimated some effect. However, across the Gulf of Bothnia the oceanographic model predicts slightly smaller mean sea level differences than the geodetic data suggest.     

Geodetic positioning at sea

Recent accuracy requirements for navigational positioning at sea are such as to require the refinements of recent and past geodetic methods. The computational adjustment method, of this paper, is the technique of variation of parameters. All computations are performed directly on the surface of a reference ellipsoid, so as to preclude any distance restrictions. The methods presented are primarily for use with observations from electronic positioning systems of ranging (circular), and time or phase difference (hyperbolic) type. A new type of observation equation is presented which, when used with a hyperbolic system, results in the first non-iterative solution to the positioning problem. When redundant observational data is obtained, as is frequently the case, full use should be made of the data by using weighted observation equations. Through the use of the new equations, all electronic surveying observations can be processed simultaneously, in real time, with an electronic computer. A continuing error analysis, in the form of a variance-covariance matrix for both the observed and adjusted values, provides system error analysis and diagnoisis.     

Cartographic Activity in Great Britain 1961-64

Abstract

The following extract from “Report No. 2 on Cartographic Activity in Great Britain” is published with the kind permission of the Royal Society. The report has been prepared by the Cartography Sub-Committee of the British National Committee for Geography, and is to be presented to the delegates attending the Second General Assembly of the International Cartographic Association, July, 1964. It covers the period 1961 to 1964. Part I only is reproduced here: Part II covers some recent technical developments; and Part III gives details of the map production of the principal mapping organisations and firms in the country. Any enquiries about the Report should be addressed to the Executive Secretary, The Royal Society, Burlington House, London, W.1.     

The role of the Ordnance Survey of Great Britain

Abstract

This paper is concerned with the future of the British national mapping agency in a society which is markedly different from that in which the Ordnance Survey Review Committee of 1979 worked. The objective is to ascertain which topographic information is needed, who should provide it, on what terms and through which mechanisms. Prior to making an attempt to answer these questions, the essential characteristics of Ordnance Survey (OS) are summarised as deduced from available documentary evidence; the changing attitudes to information as a commodity, the growing competition in British mapping and the government's stringent requirements from the Survey are also outlined as just three of the many complexities which affect OS. Building upon Smith's classic 1979 paper and subsequent experience, the rationale for government involvement in mapping is examined. It is concluded that the Survey has a continuing vital role though there are a number of steps which the OS should take in order to adapt to changing circumstances.     

Effect of the processing methodology on satellite altimetry-based global mean sea level rise over the Jason-1 operating period

Determining how the global mean sea level (GMSL) evolves with time is of primary importance to understand one of the main consequences of global warming and its potential impact on populations living near coasts or in low-lying islands. Five groups are routinely providing satellite altimetry-based estimates of the GMSL over the altimetry era (since late 1992). Because each group developed its own approach to compute the GMSL time series, this leads to some differences in the GMSL interannual variability and linear trend. While over the whole high-precision altimetry time span (1993–2012), good agreement is noticed for the computed GMSL linear trend (of $3.1\pm 0.4$  mm/year), on shorter time spans (e.g., ${<}10~\hbox {years}$ ), trend differences are significantly larger than the 0.4 mm/year uncertainty. Here we investigate the sources of the trend differences, focusing on the averaging methods used to generate the GMSL. For that purpose, we consider outputs from two different groups: the Colorado University (CU) and Archiving, Validation and Interpretation of Satellite Oceanographic Data (AVISO) because associated processing of each group is largely representative of all other groups. For this investigation, we use the high-resolution MERCATOR ocean circulation model with data assimilation (version Glorys2-v1) and compute synthetic sea surface height (SSH) data by interpolating the model grids at the time and location of “true” along-track satellite altimetry measurements, focusing on the Jason-1 operating period (i.e., 2002–2009). These synthetic SSH data are then treated as “real” altimetry measurements, allowing us to test the different averaging methods used by the two processing groups for computing the GMSL: (1) averaging along-track altimetry data (as done by CU) or (2) gridding the along-track data into $2^{\circ }\times 2^{\circ }$ meshes and then geographical averaging of the gridded data (as done by AVISO). We also investigate the effect of considering or not SSH data at shallow depths $({<}120~\hbox {m})$ as well as the editing procedure. We find that the main difference comes from the averaging method with significant differences depending on latitude. In the tropics, the $2^{\circ }\times 2^{\circ }$ gridding method used by AVISO overestimates by 11 % the GMSL trend. At high latitudes (above $60^{\circ }\hbox {N}/\hbox {S}$ ), both methods underestimate the GMSL trend. Our calculation shows that the CU method (along-track averaging) and AVISO gridding process underestimate the trend in high latitudes of the northern hemisphere by 0.9 and 1.2 mm/year, respectively. While we were able to attribute the AVISO trend overestimation in the tropics to grid cells with too few data, the cause of underestimation at high latitudes remains unclear and needs further investigation.     

Inset town plans on large-scale maps of Great Britain

Abstract

Although widely known, the inset town plans which appeared on large-scale maps of Great Britain have never been systematically listed and analysed. Inset town plans are discussed in terms of their design and content, and the rare process of revision is illuminated. Particular attention is focussed on the sources of plans and patterns of occurrence and authorship are identified. From this detailed analysis, a picture of their strengths and weaknesses for the urban historian is developed.     

Effects of mass transfers between land-supported ice caps and oceans on the shape of the earth and on the observed mean sea level

In the first part of the paper, it is shown that if the present antarctic ice masses would melt, a large part in the present pearshapeness in the shape of the Earth would dissappear. In the second part of the paper, it is shown that should the present Antarctic ice masses melt, world oceans would not climb up to the present +65 meters elevation contour line as has appeared in the literature. The rise in the observed mean sea level at the shore lines of world oceans would only be 10 to 15 meters.     

A spectral optimally interpolated mean sea surface from satellite radar altimetry

 A technique is presented for the development of a high-precision and high-resolution mean sea surface model utilising radar altimetric sea surface heights extracted from the geodetic phase of the European Space Agency (ESA) ERS-1 mission. The methodology uses a cubic-spline fit of dual ERS-1 and TOPEX crossovers for the minimisation of radial orbit error. Fourier domain processing techniques are used for spectral optimal interpolation of the mean sea surface in order to reduce residual errors within the initial model. The EGM96 gravity field and sea surface topography models are used as reference fields as part of the determination of spectral components required for the optimal interpolation algorithm. A comparison between the final model and 10 cycles of TOPEX sea surface heights shows differences of between 12.3 and 13.8 cm root mean square (RMS). An un-optimally interpolated surface comparison with TOPEX data gave differences of between 15.7 and 16.2 cm RMS. The methodology results in an approximately 10-cm improvement in accuracy. Further improvement will be attained with the inclusion of stacked altimetry from both current and future missions. Received: 22 December 1999 / Accepted: 6 November 2000     

空间大地直角坐标与大地坐标反算的非迭代法

介绍一种国外提出的由空间直角坐标 X ,Y,Z不需迭代 ,直接求解大地坐标 B,L,H的算法 ,给出了具体计算公式     

Statistical analysis of discrepancies in levelling with applications to the first-order levelling of the nile delta

The methods of the analysis of variance and co-variance are used to investigate the variation of the quantity Survey of Egypt Paper No. 53. This paper was read September 18, 1954.     

文莱大地基准与坐标格网

介绍了文莱大地基准及其对应的坐标格网发展的过程与现状,给出了文莱各个基准间的关系与转换参数。可为我国南海护渔、人道主义救援提供地理空间信息,同时为了解文莱大地测量发展历程、促进我国与文莱的测绘技术交流提供参考。     

永久性潮汐与大地测量基准

社会、经济和科技的发展,对大地测量基准的精度、历元、框架等方面的要求愈来愈高,因此必须顾及具有同等精度量级的地球动力现象如潮汐、极移、地壳运动、冰后期反弹等对大地测量基准的影响。本文仅讨论永久性潮汐对重力基准、高程基准、大地水准面、垂线偏差等方面的影响。对大地测量基准中使用的无潮汐、平均湖汐和零潮汐等概念和相关计算进行了推导和讨论。