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排序方式: 共有103条查询结果,搜索用时 15 毫秒
1.
1∶500基础地理信息数据库更新方法探讨   总被引:2,自引:0,他引:2  
城市的快速发展给城市面貌带来了日新月异的变化,已建成的基础地理信息数据库需要及时更新,确保数据的现势性,才能满足政府部门及社会公众服务的需求。本文在介绍1∶500基础地理信息数据库快速更新数据源的基础上,重点阐述了1∶500基础地理信息数据的更新方法,提出通过1∶500地形图更新1∶500基础地理信息数据库的方法,并通过实例对更新方法进行了验证。最后论述了建立1∶500基础地理信息数据库更新机制的意义,对反映城市变化及推进共建共享机制具有重要作用。  相似文献   
2.
GPS接收机仪器偏差的长期变化特性分析   总被引:3,自引:1,他引:2  
基于欧洲定轨中心2001-2009年发布的部分IGS测站接收机仪器偏差估值,分析了不同类型接收机DCB的长期变化特性.结果表明:各类接收机DCB的长期时变特征均具备一定的周期性,其中以月和年周期最为明显;接收机DCB的长期变化中还存在一定的波动,部分接收机DCB的稳定性随时间积累逐渐变差,甚至存在偏移.  相似文献   
3.
We investigate a new proxy for ENSO climate variability based on particle‐size data from long‐term, coastal sediment records preserved in a barrier estuary setting. Corresponding ~4–8 year periodicities identified from Wavelet analysis of particle‐size data from Pescadero Marsh in Central Coast California and rainfall data from San Francisco reflect established ENSO periodicity, as further evidenced in the Multivariate ENSO Index (MEI), and thus confirms an important ENSO control on both precipitation and barrier regime variability. Despite the fact that barrier estuary mean particle size is influenced by coastal erosion, precipitation and streamflow, balanced against barrier morphology and volume, it is encouraging that considerable correspondence can also be observed in the time series of MEI, regional rainfall and site‐based mean particle size over the period 1871–2008. This correspondence is, however, weakened after c.1970 by temporal variation in sedimentation rate and event‐based deposition. These confounding effects are more likely when: (i) accommodation space may be a limiting factor; and (ii) particularly strong El Niños, e.g. 1982/1983 and 1997/1998, deposit discrete >cm‐thick units during winter storms. The efficacy of the sediment record of climate variability appears not to be compromised by location within the back‐barrier setting, but it is limited to those El Niños that lead to barrier breakdown. For wider application of this particle size index of ENSO variability, it is important to establish a well‐resolved chronology and to sample the record at the appropriate interval to characterize deposition at a sub‐annual scale. Further, the sample site must be selected to limit the influence of decreasing accommodation space through time (infilling) and event‐based deposition. It is concluded that particle‐size data from back‐barrier sediment records have proven potential for preserving evidence of sub‐decadal climate variability, allowing researchers to explore temporal and spatial patterns in phenomena such as ENSO. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   
4.
Trend identification is a substantial issue in hydrologic series analysis, but it is also a difficult task in practice due to the confusing concept of trend and disadvantages of methods. In this article, an improved definition of trend was given as follows: ‘a trend is the deterministic component in the analysed data and corresponds to the biggest temporal scale on the condition of giving the concerned temporal scale’. It emphasizes the intrinsic and deterministic properties of trend, can clearly distinguish trend from periodicities and points out the prerequisite of the concerned temporal scale only by giving which the trend has its specific meaning. Correspondingly, the discrete wavelet‐based method for trend identification was improved. Differing from those methods used presently, the improved method is to identify trend by comparing the energy difference between hydrologic data and noise, and it can simultaneously separate periodicities and noise. Furthermore, the improved method can quantitatively estimate the statistical significance of the identified trend by using proper confidence interval. Analyses of both synthetic and observed series indicated the identical power of the improved method as the Mann–Kendall test in assessing the statistical significance of the trend in hydrologic data, and by using the former, the identified trend can adaptively reflect the nonlinear and nonstationary variability of hydrologic data. Besides, the results also showed the influences of three key factors (wavelet choice, decomposition level choice and noise content) on discrete wavelet‐based trend identification; hence, they should be carefully considered in practice. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
5.
通过分析多路径误差的产生机理,提出了一些测量中常用的消弱多路径误差的措施,并探讨了多路径误差与温度和气压之间的关系。重点研究固定台站多路径误差的性质,推断出此误差具有时间相关性,多路径误差这种相关性每天会延迟4 min。探讨这些性质有利于消弱多路径误差对GPS地震观测的影响。  相似文献   
6.
漳河流域近60年径流变化分析   总被引:1,自引:0,他引:1       下载免费PDF全文
近年来,漳河流域径流量显著减少,严重影响流域内水资源的开发与利用。采用多种数理统计方法,分析了径流量的演变特征。结果表明:漳河流域年径流量呈显著性减少趋势,其中下游减少的趋势更加显著;20世纪80年代以前年径流量高于多年平均值,80年代以后低于多年平均值,且不同年代变幅较大;漳河流域实测径流量在20世纪70年代中后期出现变异点,变异点之后年径流量比变异点之前明显偏小。径流量系列存在6~7a的准周期。  相似文献   
7.
极端气候事件是在一定时间尺度上发生的不同于气候系统平均状态的气候突变.早第三纪的最热事件(PETM),第四纪中国黄土高原古土壤S4、S5记录的暖湿事件,砂黄土L9、L15记录的干冷事件等都是在轨道时间尺度上发生的极端气候事件.末次冰消期的YD冷事件、全新世9次冷事件是在千—百年尺度上发生的极端气候事件.这些极端气候事件出现于地球气候系统不同的冷暖背景下,它们的成因机制和表现形式有很多不确定性.20世纪以来发生的干旱、洪水、飓风、雪灾、沙尘暴等极端气候事件,无法用持续增加的温室气体的变化来解释.关于极端气候事件发生频率和强度随"全球变暖"而增加的结论也存在一定程度的不确定性.因此,简单地将现代极端气候事件统统归因于"气候变暖"既不科学也不合理.深入研究各个时间尺度上发生的极端气候事件的波动性、周期性和不确定性特征,有助于科学预测未来气候变化背景下极端气候事件的发展趋势.  相似文献   
8.
AR5395及AR6659的贮能释能周期性   总被引:1,自引:0,他引:1  
本文分析了了AR5395和AR6659的X射线耀斑活动周期性,耀斑强度周期的存在表明活动区的能量积累和释放过程具有可重复性,包括贮存的能量大小也具可重复性,计算得出AR5395的耀风强度周期为24.49小时,而AR6659的周期为57.39小时,耀斑指数按周期的分布证明在一个贮能周期中活动区贮存的能量大致相同,周期内的平均耀斑指数代表能量积累效率,AR6659较之AR5395有较长的能量积累周期和较高的能量积累效率.此外,本文还讨论了耀斑事件出现的周期.这种周期的长短代表活动区磁结构对于耀斑出现的稳定程度,并且,当活动区处于较高能量状态(即相对势场状态的偏离较大)时,出现耀斑不稳定性的可能性增加。  相似文献   
9.
INTRODUCTIONThemainpurposeofthisstudywastodeterminethemagnitudeandfrequencyofharmfuldiatomanddinoflagellateoutbreaksinHongKong’swesternandeasternwaters (e .g.LammaStraitsandPortShelterrespectively)fortheperiodJanuary 1 997toDecember1 999.Thiswasdoneinordertod…  相似文献   
10.
Gordon  Hendler 《Marine Ecology》1984,5(4):379-401
Abstract. In the first decisive study of color-change in brittlestars, four Caribbean species, Ophiocoma echinata, 0. paucigranulata, O. pumila, and O. wendti are reported to change color from day to night. Color-change is most striking in O. wendti, which is dark brown during the day, and is banded gray and black from dusk to dawn. The transformation occurs over a 3 to 4 hour period and is effected by chromatorphores which appear to respond to illumination, independently of the central nervous system. Color-change may also be mediated by an endogenous rhythm. Ophiocoma wendti is more responsive to light than the other 3 species tested. It reacts to lower levels of illumination at night than during the day, exhibiting negative phototaxis in moonlight as well as in sunlight. I suggest that color-change may expose (or shield) photosensitive tissues that control the brittlestar's detection of shaded fissures in the reef. Thereby, chromatophore activity may be connected with the brittlestar's chief defense from predators, the ability to detect shadow and escape into darkened crevices. Although experiments to date with predacious fish are equivocal. the color patterns of Ophiocoma species mav provide protective camouflage.  相似文献   
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