内插法布设无碴轨道铺轨控制测量网方法

针对勘测设计阶段测量精度要求较低,而无碴轨道施工测量精度要求很高的情况。提出在勘测设计控制网中内插高精度施工控制网的方法。导出保持线路控制网两端切线(直线)实地位置不变,布设高精度施工控制网的办法。     

法国国家测绘局（IGN）述评

法国是世界测绘强国之一。法国国家测绘局（IGN）是法国测绘的领导机构。本文介绍了IGN的概况，并对IGN大地测量、地图制图、对外服务、研究机构等情况作了较详细的描述。在此基础上对IGN的未来发展特点提出了几点看法。     

Non-tidal variations in the deflection of the vertical at Beijing Observatory

At Beijing Observatory both astrometric and gravimetric observations are available to study the non-tidal variations in the deflections of the vertical (or non-tidal plumbline variations, PLVs). From repeated gravimetric observations performed in a network around the observatory, the PLVs at Beijing Observatory during the period 1987.0–1996.0 have been calculated. After comparison with the observational residuals (which also contain the PLV components) of the photoelectric astrolabe located at the observatory, the accuracy of the obtained PLV results has been examined. It is shown that, due to the asymmetry of the gravimetric network, the qualities of the two different PLV components are not equal. The longitude component of the PLV at Beijing has been determined successfully, to be of the order of 0.05, with a contribution of about 0.02 in the inter-annual time scale. The result for the latitude PLV component is not good enough to draw a conclusion. Although both techniques are able to measure the PLV, the result of the determination depends very much on the availability of observational data.     

Single frequency processing of Ørsted GPS radio occultation measurements

The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation.     

World-wide synthetic tide parameters for gravity and vertical and horizontal displacements

The response of the Earth’s crust to the direct effect of lunisolar gravitational forcing is known as the body tide. The body tide is superimposed by surface-loading forces due to the pressure of the periodically varying ocean tide acting on the Earth, called ocean tide loading (OTL). Both body tide and OTL can be decomposed into components of the same frequency known as tidal parameters. However, OTL is more complicated than body tides because of the dynamic effects of the ocean. Estimating OTL requires a model of the ocean tides and knowledge of the elastic properties of the solid Earth. Thus, synthetic tide parameters (amplitude factors and phase leads) have been developed here on a world-wide grid for gravity and positional displacements. The body tide contributions were added to the oceanic contribution to provide the Earth tide response. The accuracy and reliability of the synthetic tidal parameters have been estimated by comparing observed gravity and vertical-displacement tide parameters with those interpolated from our synthetic model, which shows good agreement. Tests also indicate that the synthetic tide parameters provide realistic gravimetric and displacements for practical use in tidal prediction.     

Change in cloud-top temperatures over Europe

Long-term measurements from Advanced Very High Resolution Radiometer (AVHRR) onboard the National Oceanic and Atmospheric Administration satellites were evaluated to assess variability in cloud-top temperatures over central and eastern Europe that saw radical infrastructural changes after the fall of the East Bloc in 1989 that has affected the pollution levels and hence cloud albedo. Four years in the late 1980s (1985-1988) and in the late 1990s (1997-2000) were chosen, as these are distinctively marked as episodes of very high and lower air pollution (sulphates and particulate matter). During the late 1980s, low- and medium-level clouds were colder by more than 2 K and convective clouds even by 4 K. Cloud-tops over and around polluted regions are higher, and their temperatures showed stronger variability, suggesting an indirect aerosol effect in the thermal spectral range as well.     

Quality Assessment Of Digital Surface Models Generated From IKONOS Imagery

The growing applications of digital surface models (DSMs) for object detection, segmentation and representation of terrestrial landscapes have provided impetus for further automation of 3D spatial information extraction processes. While new technologies such as lidar are available for almost instant DSM generation, the use of stereoscopic high-resolution satellite imagery (HRSI), coupled with image matching, affords cost-effective measurement of surface topography over large coverage areas. This investigation explores the potential of IKONOS Geo stereo imagery for producing DSMs using an alternative sensor orientation model, namely bias-corrected rational polynomial coefficients (RPCs), and a hybrid image-matching algorithm. To serve both as a reference surface and a basis for comparison, a lidar DSM was employed in the Hobart testfield, a region of differing terrain types and slope. In order to take topographic variation within the modelled surface into account, the lidar strip was divided into separate sub-areas representing differing land cover types. It is shown that over topographically diverse areas, heighting accuracy to better than 3 pixels can be readily achieved. Results improve markedly in feature-rich open and relatively flat terrain, with sub-pixel accuracy being achieved at check points surveyed using the global positioning system (GPS). This assessment demonstrates that the outlook for DSM generation from HRSI is very promising.     

基于Servlet的WebGIS安全机制探讨

针对WebGIS服务中可能出现的安全问题,阐述利用Servlet的数据加密和安全机制,特别是访问控制列表,来实现WebGIS的安全服务的具体做法。     

测绘职业教育教学改革探讨

随着空间科学技术和计算机技术的发展，以“3S”技术为代表的测绘高新技术已普遍应用于测绘生产中。作为培养测绘实用型人才的测绘职业学校，测绘专业如何重新划分、测绘教育与教学内容如何改革，是测绘教育界普遍关注的问题，本文从教学的角度对有关问题进行了探讨。