土地系统研究的几个问题

对土地系统研究的形成背景、研究现状及发展趋势进行了综述,并在此基础上,就土地系统研究的对象、理论基础和体系等进行了探讨。     

富钾海绿石的新发现:钾肥资源的评价研究的新方向

我国是一个人口众多的发展中国家,农业是国民经济的基础,农用钾肥主要都来自天然矿物资源,特别是我国东中部人口密集的主要农业基地的大部分省份,富钾的矿产资源十分贫乏。过去几十年来把蒸发盐建造的钾盐作为钾资源研究主要目标,到目前为止进展不大。根据最新矿产资...     

GC星表的系统差研究

本文介绍GC星表相对于FKS星表的系统差及其计算方法,对星表系统差中存在的差异进行了分析研究．主要内容包括以下几个方面．（1）在FK5系统内建立一个新的暗星系统（RFK5ex）．（2）GC星表中的暗星相对于RFK5ex的系统差．（3）GC星表中的亮星相对于FK5bas的系统差．（4）GC星表中的暗星系统与亮星系统的差别,以及GC星表系统差改正中的一些有关问题．     

一般气候站用P-T法分析大气稳定度系统误差方法的改进

使用一般气候站资料，用P－T法分析大气稳定度，其系统误差的大小主要在于缺少夜间的观测记录。本文针对这一资料特点，提出4种逼近夜间02:00实际情况的方法。经验证，4种方法都能保证基本结论不发生变化，达到与4时次记录相当的水平，系统性误差得到缓解，对实际工作有一定的参考作用。     

中国湖北钉螺(腹足纲:圆口螺科)分类现状

本文对采自中国境内不同水域、不同螺壳类型的14个螺群的同工酶数据进行了遗传分化研究,探讨中国湖北钉螺的分类现状。结果表明,中国钉螺存在重要的遗传分化及与遗传分化相关的可分辨的类型。对此进行研究后还发现了县城交叉传播和亚种间可能存在3个例外杂合螺群的依据;此外,螺群遗传分化类型与地理分布、螺壳刻纹和形态特征相一致。以此为基础,湖北钉螺(Oncomelania hupensis)再分成3个独立的亚种:滇川亚种(O.h. robertsoni )、福建亚种(O.h. tangi )和湖北亚种(O,h. hupensis).     

Broad scale forest cover reconstruction from historical topographic maps

Land cover change is one of the major contributors to global change, but long-term, broad-scale, detailed and spatially explicit assessments of land cover change are largely missing, although the availability of historical maps in digital formats is increasing. The problem often lies in efficiency of analyses of historical maps for large areas. Our goal was to assess different methods to reconstruct land cover and land use from historical maps to identify a time-efficient and reliable method for broad-scale land cover change analysis. We compared two independent forest cover reconstruction methods: first, regular point sampling, and second, wall-to-wall mapping, and tested both methods for the Polish Carpathians (20,000 km²) for the 1860s, 1930s and 1970s. We compared the two methods in terms of their reliability for forest change analysis, relative to sampling error, point location and landscape context including local forest cover, area of the spatial reference unit and forest edge-to-core ratio. Our results showed that the point-based analysis overestimated forest cover in comparison to wall-to-wall mapping by 1–3%, depending on the mapping period. The reasons for the differences were mainly the backdating approach and map generalisation rather than the point grid position or sampling error. When we compared forest cover trajectories over time, we found that the point-based reconstruction captured forest cover dynamics with a comparable accuracy to the wall-to-wall mapping. More broadly, our assessment showed that historical maps can provide valuable data on long-term land cover trends, and that point-based sampling can be an efficient and accurate way to assess forest area and change trends. We suggest that our point-based approach could allow land cover mapping across much of Europe starting in the 1800s. Our findings are important because they suggest that land cover change, a key component of global change, can be assessed over large areas much further back in time than it is commonly done. This would allow to truly understand path dependencies, land use legacies, and historical drivers of land cover change.     

USB-VLBI综合确定SMART-1环月探测器轨道

我国绕月探测工程中"嫦娥一号"(CE-1)卫星将综合使用统一S波段系统(USB)和甚长基线干涉仪(VLBI)完成测定轨任务。为了检验USB-VLBI综合测定轨精度,测控系统于2006年5月利用欧空局(ESA)的SMART-1环月探测器进行了USB-VLBI综合测定轨试验。本文对这次试验的测轨数据进行了分析,研究了不同观测弧长和不同类型观测数据组合情况下的定轨和预报精度,得出了一些结论。     

海洋测深网系统误差的平差计算

利用一般多项式模型、线性多项式与三角函数多项式结合的模型,将系统误差表示为与时间相关的量,对海洋测深网的系统误差值进行分离。引入半参数模型,将参数值与模型误差进行分离;结合实测的交叉点不符值进行平差计算,使平差后精度进一步提高。