基于投影变换的线阵旋转扫描相机标定方法

针对线阵旋转扫描相机标定数据难以获取及模型解算不稳定的问题,提出了一种基于投影变换的线阵旋转扫描相机标定方法。首先构建了一种新的线阵旋转扫描相机成像模型,该模型可以根据相机旋转平台参数、线阵旋转扫描相机成像平面与其切平面的位置关系将旋转扫描图像投影为框幅式图像;然后根据构建出的成像模型,采用直接线性变换法和非线性优化方法进行相机标定和参数优化。试验结果表明,此方法简单易行,具有较高的精度。     

模糊聚类定权法对SLR定轨精度的影响

针对卫星激光测距(satellite laser ranging,SLR)精密定轨过程中存在的测站观测数据合理定权问题,将一种改进的模糊聚类算法引入到SLR观测数据定权中。基于国际激光测距服务(International Laser Ranging Service,ILRS)提供的全球SLR测站性能报告,对测站进行近实时滑动分类定权,改变SLR数据处理中权重的经验或者随意性选取模式。经过LAGEOS1卫星2014年1月至2016年12月3年全球SLR实测数据处理的测试。结果表明,当考虑LAGEOS标准点总数、LAGEOS标准点RMS值以及LAGEOS标准点合格率这3项测站质量控制因素确定的测站权值能最大限度地提高卫星定轨精度和观测数据的使用效率,对参与计算的365个3d弧段数据,91.46%弧段精度得到提高,平均提高约3.7mm,且每个测站的定轨残差RMS也得到了降低。这对于正在迈向毫米级测量精度的SLR技术至关重要。     

天文定位中几何精度衰减因子最小值分析

天文定位是一种重要的导航定位方法,被广泛应用于大地天文测量、天文航海等领域。该方法中观测恒星的选择会影响最终的定位精度,目前缺少针对同时测定经纬度天文定位算法中最优选星问题的研究。随着观测仪器自动化水平的提高,观测数据的获取变得更加高效,这就要求研究最优的选星方案以达到最高的定位精度。本文借鉴卫星导航中几何精度衰减因子GDOP的概念,研究了天顶距法中恒星的数量以及分布对定位精度的影响,最后通过仿真试验和实测数据验证得到结论:在天顶距观测误差的统计特性一定时,GDOP能够用来描述恒星的分布对定位结果影响的优劣,且观测的恒星方位角均匀分布时定位误差最小。考虑到不同高度的恒星天顶距大气折射改正残差不同,在实际测量中应尽量采用等天顶距且方位角均匀分布的恒星。     

基于POI数据的长沙市生活性服务业空间格局研究

生活性服务业是服务经济的重要组成部分,其合理布局对发展城市经济、满足居民消费需求具有重要作用。基于长沙市六区POI数据,运用核密度分析、熵指数、频数密度分析及空间聚类等方法研究长沙市生活性服务业的空间格局特征,发现长沙市生活性服务业的分布具有以下特点：1）主要受交通及城市规划指向性影响,沿交通主干道集聚分布,整体布局呈“一核四轴多极”且空间分布与人口集中度联系紧密,东西差异明显,东部多而密集、西部少而分散;2）不同类型的生活性服务业分布特征各异,在空间形态上主要表现为“单核心”、“双核心”和“多核心”等;3）其功能多样性布局呈现以五一广场为核心的“中心-外围”结构特征,功能多样且混合程度高的区域位于城市中心,城市边缘区生活性服务业集聚性较弱且多为单一功能或者双功能混合区。     

The effect of terrain factors on rice production: A case study in Hunan Province

Journal of Geographical Sciences - Rice (Oryza sativa L.) is the most important staple crop of China, and its production is related to both natural condition and human activities. It is fundamental...     

Trends and risk evolution of drought disasters in Tibet Region,China

Journal of Geographical Sciences - The risk posed by natural disasters can be largely reflected by hazard and vulnerability. The analysis of long-term hazard series can reveal the mechanisms by...     

Numerical Study on Tidal Mixing in the Bohai Sea

The spatial and temporal variability of tidal mixing in Bohai Sea is studied using a numerical approach. In calculating tidal mixing, accurate barotropic tidal current is obtained via a harmonic analysis package utilizing the simulated current output from a high-resolution regional ocean model. And a “small-scale” roughness map is adopted to describe the detailed topographic features of Bohai Sea. It is shown that the tidal mixing estimated in Bohai Sea is much higher than the level of global background, and fluctuates considerably at some regions within a single day. In Liaodong Bay, Bohai Bay and Bohai Strait, the mixing varies greatly, with the peak value of O (10^?2) m² s^?1. The order of magnitude of mixing in Laizhou Bay is about O (10^?5～10^?3) m² s^?1. Mixing with background level of O (10^?5) m² s^?1 only appears in central area. Result also shows that rough topography plays relatively a more important role than tidal current in enhancing diapycnal mixing in Bohai Sea. The distributions of tidal mixing in selected sections reveal that the vertical stratification in Bohai Sea is not obvious, generally renders a barotropic structure.     

Sea Level Prediction in the Yellow Sea From Satellite Altimetry With a Combined Least Squares-Neural Network Approach

Accessible high-quality observation datasets and proper modeling process are critically required to accurately predict sea level rise in coastal areas. This study focuses on developing and validating a combined least squares-neural network approach applicable to the short-term prediction of sea level variations in the Yellow Sea, where the periodic terms and linear trend of sea level change are fitted and extrapolated using the least squares model, while the prediction of the residual terms is performed by several different types of artificial neural networks. The input and output data used are the sea level anomalies (SLA) time series in the Yellow Sea from 1993 to 2016 derived from ERS-1/2, Topex/Poseidon, Jason-1/2, and Envisat satellite altimetry missions. Tests of different neural network architectures and learning algorithms are performed to assess their applicability for predicting the residuals of SLA time series. Different neural networks satisfactorily provide reliable results and the root mean square errors of the predictions from the proposed combined approach are less than 2?cm and correlation coefficients between the observed and predicted SLA are up to 0.87. Results prove the reliability of the combined least squares-neural network approach on the short-term prediction of sea level variability close to the coast.     

基于线粒体COI和16S rRNA基因的中国沿海相手蟹系统发育研究

相手蟹科的诸多种类因其形态极其相似成为方蟹总科分类中疑问较多的一个类群。通过对中国沿海相手蟹线粒体COI和16S rRNA基因序列进行分子系统发育分析,结果表明14种相手蟹COI和16S rRNA基因序列之间差异分别为5.7%～14.5%和1.5%～12.1%,均达到了种间差异水平。构建的系统发育树显示,14种相手蟹分别为独立有效物种,但分属于拟相手蟹属和近相手蟹属的4种拟相手蟹和3种近相手蟹,没有分别形成2个独立的支系,而是混合聚成一大支系。而属于螳臂相手蟹属的无齿螳臂相手蟹则首先与属于中相手蟹属的中华中相手蟹聚成一支,再与红螯螳臂相手蟹聚为一大支,表现出与形态分类的不一致。错综复杂的分子系统关系预示着相手蟹类为多系起源,也表明它们之间的种间关系乃至于属间关系尚有诸多问题有待进一步厘定。     

苯并（a）芘诱导下岩虫CYP基因的表达特征

Rapid amplification of cDNA ends(RACE) and real-time polymerase chain reaction(RT-PCR) were carried out to analyze the CYP4 gene expression in polychaete Marphysa sanguinea exposed to benzo[a]pyrene(BaP) in this study. The full length of MsCYP4 cDNA was 2 470 bp, and it encoded 512 amino acids. The deduced amino acid sequence showed 47% identity with CYP4 F from frog Xenopus tropicalis and shared high homology with other known CYP4 sequences. To analyse the role of CYP4 in protecting M. sanguinea from BaP exposure, three BaP groups were established: 0.5, 5 and 50 μg/L. Polychaetes were sampled after 3, 7 and 12 d. At 0.5 μg/L, the effect of BaP on MsCYP4 gene expression increased with time prolonged. MsCYP4 gene expression curve showed Ushaped trend with time in 5 and 50 μg/L BaP groups. Therefore, MsCYP4 gene may play an important role in maintaining the balance of cellular metabolism and protecting M. sanguinea from BaP toxicity.