关于现代城市影像地图集编制的探讨

城市影像地图集是一种基于航空影像和卫星遥感影像,以城市为空间表达对象的城市地图品种,本文以《乌海综合影像地图集》为例,探讨了现代影像地图集不同于以往影像地图集的特点和总体设计要点.     

运用SI-Harris算子提取遥感图像点特征

推导了SI-Harris算子(尺度不变Harris算子)的理论公式,并将其应用于遥感图像的点特征提取。重点对Harris算子与SI-Harris算子在不同空间分辨率遥感图像上的点特征提取进行实验比较,利用"重复率"指标对实验结果进行定量评价。实验表明:SI-Harris算子"重复率"较Harris算子有明显提升,可用于不同空间分辨率遥感图像的点特征提取,进而可服务于不同空间分辨率遥感图像的匹配。     

高轨空间碎片的观测模拟

对高轨空间碎片进行了观测模拟。在观测模拟中，分别选取南京和云南两个观测站；采用2种跟踪方式：跟踪恒星和跟踪卫星；对于同一地理经度上的同步卫星进行了观测；提供了发现新目标的方法；并给出了新目标的初轨。这为我国空间碎片的数据库的建立作了有益的尝试，对于卫星和航天器的飞行安全具有特别重要的意义。     

结合ASIFT和归一化的抗仿射变换遥感影像盲水印算法

针对遥感影像使用过程中,含水印影像经过仿射变换后水印与影像的同步性被破坏,导致水印无法正常检测的问题,本文提出了一种适用于遥感影像的抗仿射变换盲水印算法。首先通过ASIFT算法提取影像具有仿射不变性的特征点,根据特征尺度的大小与特征点间的欧式距离筛选适量特征点,构造对应的正方形特征区域;然后通过计算特征区域的仿射不变矩得出归一化变换函数的参数,对特征区域进行归一化处理,并以归一化特征区域的不变质心为中心提取子区域作为水印嵌入区域,对该区域进行二级离散小波变换,得到水印嵌入区域的低频信息;运用量化嵌入规则将水印嵌入到低频信息中,依次进行低频信息逆小波变换,水印嵌入前后特征区域差值图像反归一化,最后将反归一化差值图像叠加在原始影像特征区域上,完成水印的嵌入。实验选用了3000像素×3000像素的高分二号遥感影像作为载体影像,含版权信息的二值图像作为水印,实验表明：含水印的遥感影像经过旋转、平移、缩放在内的仿射变换后,仍能准确提取水印信息;算法可有效抵抗加噪、滤波、裁剪等常规水印攻击,攻击后影像提取的水印与原水印相关系数均高于0.9;水印具有良好不可感知性;在水印提取时无需原始遥感影像,属于盲水印算法。     

基于全球MGEX数据的北斗导航星座精密轨道确定

利用全球分布的MGEX站观测数据,使用"两步法"以双差方式对北斗卫星进行精密定轨。主要研究北斗卫星轨道确定的处理策略,重点分析轨道确定的流程,并通过实验评价了3种不同类型轨道的精度。结果显示,MEO和IGSO卫星的定轨内符合精度优于0.2m,其中径向优于10cm,外符合精度优于30cm;GEO(以C05号为例)卫星外符合精度优于0.7m,且径向优于10cm。     

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

A thorough understanding of rainfall recharge processes and their controlling factors is essential for management of groundwater systems. This study investigates the effects of various meteorological and hydrogeological factors on the gross recharge percentages, the rainfall–recharge relationships and the recharge threshold values for unconfined sandy aquifers under an equatorial climate. Among the meteorological factors investigated, rainfall intensity was found to have the most significant impact on the gross recharge rate. The effects of potential evaporation rate, relative humidity and air temperature on the gross recharge percentage were significant when the vadose zone thickness is larger than 2·5 m. The recharge threshold values were found to depend strongly on the vadose zone thickness. The rainfall–recharge relationships could generally be well defined by a normal–log relationship. The rainfall–recharge relationships derived here are applicable to yield estimates of gross recharge percentages for unconfined sandy aquifers under an equatorial climate, using rainfall intensity and vadose zone thickness as input variables. In this study, a theory was developed and validated to provide physical explanations for the observations, based on the residence time of the percolated rainwater within the vadose zone. Among the soil hydraulic parameters tested, porosity and saturated hydraulic conductivity were found to have the most pronounced effects on the gross recharge percentage. Utilizing the sensitivity results and the theory derived, an approach was developed for extending the application of the derived rainfall–recharge relationships to other sand textures. The approach was found to be capable of producing rough and fast estimations of gross recharge percentage for other sand textures. Copyright © 2007 John Wiley & Sons, Ltd.     

IAG2001年科学大会与大地测量学的最新进展

扼要报导了国际大地测量学术界的一次重要会议－IAG2001年科学大会。根据会议的学术报告，对坐标系统的统一与协调，全球重力场研究，导航卫星的应用，地壳形变与地球动力学等方面的研究进展作了详细介绍。     

基于CPLD的高精度门控电路的设计

距离门控制电路是卫星激光测距(SLR)系统的一个重要组成部分,高精度距离门控制可有效提高卫星测距探测成功概率。介绍了一种基于CPLD(复杂可编程逻辑器件)的高精度门控电路的设计。在该设计中,采用硬件描述语言VHDL对CPLD进行编程,使其与单片机、PC机协调工作,从而实现高精度的距离门控制电路。     

Meteorological assessment of the surface temperatures on Titan: constraints on the surface type

The latitudinal profile of near-surface air temperature on Titan retrieved by Voyager 1 has been difficult to understand and raised several speculations about possible exotic processes that might be occurring near Titan's surface, while the thermal properties of the surface itself are unknown. This study systematically investigates the seasonal and spatial variation of the surface temperature and air temperature in the lower troposphere by a 3-dimensional general circulation model for different putative surface types (porous icy regolith, rock-ice mixture, hydrocarbon lakes). For any viable surface type the surface temperature is unlikely to be constant through the year and should more or less vary seasonally and even diurnally, most likely by a few K. Recent observations of tropospheric clouds may be evidence of seasonal variation of the surface temperature and the model predicts in the case of solid surface the development of a convective layer with superadiabatic lapse rates near the surface exactly at those latitudes and seasons where clouds have been identified. The latitudinal profile of the surface temperature retrieved from Voyager 1 infrared spectra can be explained without invoking exotic effects, provided the thermal inertia of the surface is relatively small and/or the surface albedo is low. A dominance of water ice (high thermal inertia and high albedo) at the surface is unfavorable to reproduce the observation. The latitudinal gradient of the surface temperature is particularly large at the hydrocarbon lake surface due to low albedo and small surface drag. Local anomalies of the surface albedo or surface thermal inertia are likely to cause substantial inhomogeneities of the surface temperature. Quasi-permanent accumulation of stratospheric haze at both poles would create a perennial equator-to-pole contrast of the surface temperature, but also a substantially lower global-mean surface temperature due to an enhanced anti-greenhouse effect in summer. The air temperature in the lower troposphere exhibits a tiny latitudinal gradient and a pole-to-pole gradient due to the presence of a pole-to-pole Hadley circulation, indicating that the temperature within the planetary boundary layer may exhibit a vertical profile characteristic of season, location and scenario. There may be a shallow near-surface inversion layer in cold seasons and a shallow convective layer in warm seasons.