激光在天空对地观测中的应用

1960年7月世界上第一台激光器问世后，激光测距迅速兴起，不管是地面激光测距，还是激光测卫和激光测月，都为大地测量学的发展作出了重大贡献；特别是激光测卫测月成果，为我们深化对地球动态效应的认识，揭示地球的奥秘，提供了许多重要的科学数据，本文综析了值得注视的下列新近发展。.在IGEX-98国际大联测中，求定GLONASS卫星的激光轨道与微波轨道之差；.评定PRN05/06号GPS卫星星历的精度；.检核Topex/Poseidon海洋测高卫星用GPS定轨的测量误差，.用机载激光测深系统测量海水的浓度；.用EOS-ALT星载激光测距/测高系统测量地球动态参数。     

空地一体化测绘在城市更新中的应用

在大范围测图中,传统的单点测量模式效率低下,很难满足实际需要。随着近些年无人机倾斜摄影与三维激光扫描技术的快速发展与广泛应用,这个难题在一定程度上得到了解决,不过单项技术独立用于测图仍然存在一些不足。本文分析这两种技术的优缺点,用三维激光扫描辅助无人机倾斜摄影进行空地一体化测绘,可以全方位采集数据,提高测量精度和测图效率,并成功用于城市更新基础数据调查。     

消除CCD天光背景的一种组合式分割方法

基于迭代阈值法和统计模型提出了一种新的组合式分割方法,该方法精确地描述了天光背景的分布情况,既能够精确确定图像分割的最优阈值,有效地消除天光背景的影响,又可以精确地估计出天光的平均强度,有利于天体亮度的精确计算及暗星的探测.     

消除CCD天光背景的一种组合式分割方法

基于迭代阈值法和统计模型提出了一种新的组合式分割方法，该方法精确地描述了天光背景的分布情况，既能够精确确定图像分割的最优阈值，有效地消除天光背景的影响，又可以精确地估计出天光的平均强度，有利于天体亮度的精确计算及暗星的探测。     

长波天波授时可行性分析

为扩展现有长河二号系统的授时覆盖范围,提出利用天波实现远距离授时。结合实测数据以及长波天波场强和时延理论算法,分析了天波场强和时延随传播路径及昼夜变化的规律,并通过天地波场强的对比验证了利用天波授时的可行性。     

Eye on the Ionosphere: GPS after SA

Selective Availability (SA), the intentional degradation of the accuracy of the single-frequency GPS position by the DoD, was ended on May 2, 2000. This major policy decision, promised to occur some time in the next 5 years, had an instantaneous and dramatic impact on the users of single-frequency GPS. Figure 1 shows the “before and after” of the turn-off of SA, and illustrates how significant and error source SA was. SA was turned off at 0400 UTC, the point on the graph at which the horizontal and vertical errors were markedly reduced. The magnitudes of the Standard Positioning Service (SPS) circular error probable (CEP), and sperical error probable (SEP) – the uncertainty in a fix – were reduced to less than 5 meters. ? 2001 John Wiley & Sons, Inc.     

地图学眼动研究及实验参数解析

从疏理地图学眼动研究发展轨迹出发,阐述地图学眼动研究的相关概念,论述眼动实验原理、仪器和步骤,并在分析主要眼动参数及其在地图学理论、地图设计等领域应用的基础上,展望地图学眼动研究新的发展方向。     

TERRA/MODIS热红外通道陆地晴空大气可降水分裂窗反演

大气水汽在遥感反演地表温度中起到关键作用,精确的大气水含量对于提升反演精度有着重要意义,而热红外方法是夜晚获得区域大气水汽含量的唯一方法。本研究采用热红外方法中的改良分裂窗算法,首先,使用TIGR大气廓线与MODIS波谱响应函数通过MODTRAN辐射传输模式进行模拟,将大气廓线的水汽含量与大气透过率进行回归;然后,根据MODIS数据产品特点,使用2015年夏季MODIS数据观测角小于20°的范围进行反演;最后,将白天反演水汽分别与全球GPS地基大气水汽观测网络和MODIS近红外水汽产品进行比较,均方根误差分别为5.5 g/cm2和6.4 g/cm2,显示了高度的区域一致性。由于MODIS观测角度较大,本研究未对其他角度进行反演,若对其余角度的MODIS数据进行反演,可根据余弦角度变化,针对不同角度范围进行模拟与回归。     

低空遥感平台摄影测量技术的探索和应用

为了适应城市建设的快速发展和分散的小面积航空摄影测量的需求,本文简要介绍了低空遥感平台,并对小面积的低空遥感平台摄影测量进行了实验和试生产,探索出了一套完整的生产工艺,解决了部分实际问题,为低空遥感平台摄影测量的应用和发展奠定了一定的基础。     

Modeling the Global Solar Radiation Under Cloudy Sky Using Meteosat Second Generation High Resolution Visible Raw Data

This paper presents an improved model for mapping both hourly and daily values of the global radiation reaching the earth’s surface from satellite data over Algeria. An empirical model with a large spectral band using Linke atmospheric turbidity was chosen to modeling the clear-sky global radiation. The extinction of the solar radiation (absorption plus scattering) is described by an exponential decay function of the cloud albedo and cloud index. To compute these two parameter, we resolve the sun-pixel-satellite radiative model equation using the following hypothesizes. The first one supposes the total transmittance of the atmospheric in the pixel-satellite direction as the ratio of the direct radiation in real sky to the same quantity in case of a very clean sky. The second one estimates that the noise energy reflected back towards the radiometer by molecules of gases in the upper levels of the atmosphere represents about 5 % of the energy measured by the radiometer. The model performance was validated for five radiometric stations across the country for three selected months in 2013 and satisfactory results were obtained and discussed.     

A Uniform Sky Illumination Model to Enhance Shading of Terrain and Urban Areas

Users of geographic information systems (GIS) usually render terrain using a point light source defined by an illumination vector. A terrain shaded from a single point provides good perceptual cues to surface orientation. This type of hill shading, however, does not include any visual cues to the relative height of surface elements. We propose shading the terrain under uniform diffuse illumination, where light arrives equally from all directions of a theoretical sky surrounding the terrain. Surface elements at lower elevations tend to have more of the sky obscured from view and are thus shaded darker. This tinting approach has the advantage that it provides more detailed renderings than point source illumination. We describe two techniques of computing terrain shading under uniform diffuse illumination. One technique uses a GIS–based hill-shading and shadowing tool to combine many point source renderings into one approximating the terrain under uniform diffuse illumination. The second technique uses a C++ computer algorithm for computing the inclination to the horizon in all azimuth directions at all points of the terrain. These virtual horizons are used to map sky brightness to the rendering of the terrain. To evaluate our techniques, we use two Digital Elevation Models (DEMs)—of the Schell Creek Range of eastern Nevada and a portion of downtown Houston, Texas, developed from Light Detection and Ranging (lidar) data. Renderings based on the uniform diffuse illumination model show more detailed changes in shading than renderings based on a point source illumination model.