北京地区地闪活动时空分布特征

基于国家雷电定位网2010—2014年雷电定位数据和2010—2013年地面气象资料,分析了北京地区各季地闪活动时空分布特征及其与降水量的关系。结果表明,北京地区雷电活动具有明显的日变化特征;雷电发生频次随季节变化明显,负闪和全地闪在秋季变化幅度最大;雷电发生频次最大值和最小值出现时间随季节变化,春季、夏季日循环峰值出现时间在22∶00—23∶00(北京时间),秋季日循环峰值出现时间在01∶00,冬季则为15∶00且不具有显著性;从空间分布上看,可以看出雷电活动分布具有局地性特征,北京地区雷电活动最频繁的地区集中在密云县和平谷区的迎风坡一带、通州区与市辖区交界处,高雷暴日区域位于延庆县、昌平区和平谷西部,延庆县和怀柔区的北部及房山区和门头沟交界处的西部,雷暴发生频次和雷暴日空间分布不完全吻合。通过各季雷电发生频次日变化序列的谐波分析可知,日循环为日变化的主要信号。春季、夏季、秋季雷电发生频次和降水量两者整体变化趋势一致,降水量较雷电发生频次变化缓慢。     

河口挡潮闸对三角洲潮汐不对称时空变化的影响

三角洲内部潮汐不对称性与三角洲地貌演变方向有重要关系。目前诸多研究关注海洋、陆地边界的改变对三角洲内的潮汐不对称性演变规律的影响。实际上, 大规模的河口工程也会对三角洲内的潮汐不对称性产生影响。在众多河口工程中, 河口挡潮闸由于直接削弱口门处海洋潮动力, 影响最为直接。荷兰三角洲是潮动力主导型三角洲, 受洪潮灾害影响较为严重, 为此在荷兰西南部修建了世界上著名的三角洲挡潮闸工程。文章以荷兰莱茵河-默兹河三角洲为研究对象, 分析以挡潮闸为主的河口工程对三角洲内河网潮汐不对称性演变特征的影响。选取莱茵河-默兹河三角洲13个潮位站点的50~60年的水文资料, 利用非平稳调和分析方法计算分析三角洲内部潮汐传播特性, 并进一步研究潮汐涨落潮历时不对称性演变特征, 揭示河口挡潮闸工程对潮汐河网中潮汐动力和潮汐不对称性的影响。研究表明, 莱茵河-默兹河三角洲为显著的涨潮占优型河口, 潮汐不对称现象总体向上游沿程增强。河口挡潮闸修建后受河网径流量和潮动力剧烈变化的影响, 封闭的南部通道内的潮波大幅度削弱, 潮汐不对称现象在下游增强在上游减弱。北部、中部通道其他站点则因为通道径流增大, 潮汐不对称现象增强, 中部站点变化更为显著。     

便携式消费级无人机相机标定有效性评估

本文针对近年来在各行业中广泛使用的便携式消费级无人机开展了相机标定有效性研究,分别通过室内标定场和后处理软件对相机进行标定和自标定,在对比无相机标定、飞前相机标定、飞后相机标定和自标定迭代校正等方法所得成图精度后,对不同相机标定方案的有效性进行了评估。结果表明：各种方案成图总体精度差别不大;飞前、飞后相机标定与无相机标定的成图精度相当;自标定迭代校正的成图精度略高于其他方案。可见采用航拍照片自标定参数迭代校正的方法更适合于飞行控制精度和成像系统稳定性都不高的便携式消费级无人机相机标定。     

温度对陀螺经纬仪稳定性影响的一种测试方法

本文提出了一种温度对陀螺经纬仪稳定性影响的测试方法,引入了单因素方差分析的数理统计方法,评价陀螺经纬仪在高低温环境下的稳定性;对高低温稳定性测试过程中观测窗变形的影响进行了分析和实验研究,认为本文中采用的高低温室观测窗的变形量,对中低精度的陀螺经纬仪高低温稳定性测试而言可以忽略;最后通过实际测试数据验证了该方法的可行性。     

Algorithm for Harmonic Tidal Analysis along T/P Tracks： Taking Differences of Observed Sea Surface Heights at Adjacent Points as Observations

An algorithm （differential mode） is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean （2°-50° N,105°-150° E） are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm.     

基于车载序列影像的建筑立面纹理的快速重建

提出了一种基于车载序列影像的建筑立面纹理快速重建的方法。首先进行影像预处理,包括畸变差改正、树木遮挡去除等,然后对影像进行自动纠正,在此基础上,自动选择拼接点对影像进行拼接。实验证明了本文方法的有效性。     

地磁场模型和冠谐分析

地磁场是由内源场(地核场和地壳场)和外源场(电离层场和磁层场)组成的,地磁场模型是表示地磁场时空分布的数学表达式.本文简述了地磁场全球模型和区域模型的计算方法和应用;评述了冠谐分析方法及其在地磁学中的应用;介绍了地磁场模型误差的主要来源.     

TRMM多卫星降水分析资料揭示的青藏高原及其周边地区夏季降水日变化

本文在对比了TRMM多卫星降水分析TMPA(TRMM Multi-satellite Precipitation Analysis)资料和中国643个气象站观测降水量时空分布的基础上,采用2002~2006年夏季TMPA每小时降水量资料,用合成分析和谐波分析的方法研究了青藏高原及其周边地区夏季降水量和降水频率的日变化特征.分析结果表明,平均降水量和降水频率日变化谐波分析的标准振幅显示出青藏高原地区夏季降水具有显著的日变化特征,高原中部地区对流活动日变化最强,其次是高原西南方向的印度半岛地区.谐波分析的位相表明降水量和降水频率最大值出现的时间具有选择性,高原中部降水量最大值多集中在傍晚前后,高原以东的四川盆地通常在夜晚,尤其是在后半夜达到最大值,而长江上游和中下游地区对流活动则分别在上午和下午最为活跃.青藏高原以东地区降水量日变化的位相明显不同于其他陆地地区,也不同于高原中部,具有自西向东传播的信号,四川盆地的夜雨现象可能是高原地区对流活动日变化自西向东传播的结果.     

Harmonic analysis of tides and tidal currents in South San Francisco Bay,California

Water level observations from tide stations and current observations from current-meter moorings in South San Francisco Bay (South Bay), California have been harmonically analysed. At each tide station, 13 harmonic constituents have been computed by a least-squares regression without inference. Tides in South Bay are typically mixed; there is a phase lag of approximately 1 h and an amplification of 1·5 from north to south for a mean semi-diurnal tide. Because most of the current-meter records are between 14 and 29 days, only the five most important harmonics have been solved for east-west and north-south velocity components. The eccentricity of tidal-current ellipse is generally very small, which indicates that the tidal current in South Bay is strongly bidirectional. The analyses further show that the principal direction and the magnitude of tidal current are well correlated with the basin bathymetry. Patterns of Eulerian residual circulation deduced from the current-meter data show an anticlockwise gyre to the west and a clockwise gyre to the east of the main channel in the summer months due to the prevailing westerly wind. Opposite trends have been observed during winter when the wind was variable.     

A study of non-linear tidal propagation in shallow inlet/estuarine systems Part I: Observations

The offshore tide becomes strongly distorted as it propagates into shallow estuarine systems. Observations of sea surface elevation and horizontal currents over periods ranging from three days to one year, at nine stations within Nauset inlet/estuary, document the non-linear interaction of the off-shore equilibrium tidal constituents. Despite strong frictional attenuation within the estuary, the overtides and compound tides of M₂, S₂ and N₂, in particular, reach significant amplitude, resulting in strong tidal distortion. High frequency forced constituents in sea surface are phase-locked, consistently leading the forcing tides by 60–70°, resulting in a persistent distortion where falling tide is longer than rising tide. Forced constituents in currents are more nearly in phase with equilibrium constituents, producing flood currents which are shorter but more intense than ebb currents. A compound fortnightly tide, MS_f, modulates the mean water level such that lowest tides occur during neap phase instead of spring phase. This fortnightly tide can be contaminated by storm surge, changing the phase characteristics of this constituent. Implications of the overtides, compound tides, and lower frequency tides on near-bed, suspended and dissolved material transport are profound.