共查询到19条相似文献，搜索用时 234 毫秒
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精确测定时间对于天文测量至关重要。针对图像全站仪拍摄恒星存在时延的问题,利用计算机内部时钟与全站仪拍照之间的时间关系,设计了一种简便高效准实时的时延标定方法。推导了拍照时延对天文方位角测量的影响公式,并以北极星定向为例进行了数值分析。大量野外实测数据表明,拍照时延的大小约为4.2 s,且半年内较稳定。经过拍照时延改正之后,能够满足利用北极星时角法进行一等天文方位角测量的精度要求。 相似文献
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惯性制导设备初始方位角标定通常采用一等天文方位角作为基准。在实际作业中,标定位置常因场地受限而无法直接进行天文观测,需要通过边角测量将实测天文方位角精确传递至标定位置。因此,标定基准方位角的精度受天文方位角测量精度和方位角传递精度的共同影响。对近年实测的多组一等天文方位角成果进行统计分析,通过中误差和正反方位角不符值两个精度指标,估计一等天文方位角测量精度在±0.5″左右。角度传递测量后,按照导线网平差中最弱边方位角精度估计公式,在传递4次的情况下,方位角闭合传递得到的基准方位角精度在±1.2″左右;经纬仪互瞄传递得到的基准方位角精度在±0.8″左右。 相似文献
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由于地球自转参数(ERP)的滞后性,目前主要使用国际地球自转和参考服务IERS发布的Bulletin A(简称A公报)预报值进行解算,ERP预报误差对于天文测量的影响目前缺少系统的研究。为此,本文选取IERS 2015—2021近7年A公报的ERP参数对其长期预报及不同时间跨度预报误差分析,并以某站数字天顶望远镜观测结果为例,分析了ERP预报误差对于天文测量的影响。结果表明,随着时间的增加,预报精度越来越差,对于极移参数,1年跨度的预报误差值达到了0.021 as,预报误差对天文经、纬度及方位角的影响分别为0.045 as、0.041 as和0.042 as,完全满足一等天文测量的精度要求;而UT1-UTC预报精度是限制A公报精度的主要因素,60天UT1-UTC的预报误差值已达到了0.007 s,对天文经度的影响达到了0.379 as,已超出一等天文测量的精度要求。为了满足一等天文测量的要求,选取UT1-UTC预报值时,其时间跨度最大为40 d。 相似文献
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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。 相似文献
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介绍北极星时角法测定天文方位角的基本方法，进而说明解析法测定天文方位角的基本原理，阐述计算软件的功能、菜单设计特点和操作方法，以实例说明软件的实用性。 相似文献
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在精度要求±1′内的方位角测量中,总是力求定向方法简便易行。本文推导出一种既不要对表,也不要精确读取表面时,还不需查天文年历的一种观测太阳天顶距测定地面目标方位角的简便方法,介绍了有关原理,并进行了观测试验,表明可以满足±1′的精度要求。 相似文献
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本法在不同时间预测两颗相对于北方向足够对称的未知恒星，可精确测定目标的天文方位角和测站的天文纬度，与只用一颗未知星的类似方法相比，这种方法具有减少预测所需时间，可提供足够数量的解算方程及可提高结果精度等优点。此外，所提出了方法不需要测站的推算位置，与时间观测无关，并且不需要知道星历。一般说来，除了能观测恒星外，不需要天文知识。 相似文献
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苏联克拉索夫斯基教授于1924年提出了以观测北极星与一辅助星之间的水平夹角为基础来测定地面目标方位角的方法。此法仅需用普通的经纬仪,不需要天文钟即可进行,而且对测站的经纬度及恒星座标数值精度的要求亦不 相似文献
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A novel method of calibration of non-topographic cameras is described, involving a simple three dimensional test object for photography at short object distances. The position of the camera with respect to the test object is resected at the same time as the computation of values of the interior orientation elements. 相似文献
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Ye. B. Pospelova 《地理信息系统科学与遥感》2013,50(2):108-115
The author outlines a method for extrapolating reference spectral data describing the condition of certain crops obtained for a particular point in time to periods for which reliable remote sensing data are not available. Examination of the correspondence between crop “condition classes,” identified through visual interpretation of aerial imagery, and actual yields/biomass for a number of phases of crop development of winter wheat for several crop years provides basic information for a probability matrix of the condition of a crop at times B, C, and D based on previous conditions at times A, B, and C. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1988, No. 4, pp. 73-79. 相似文献
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《地理信息系统科学与遥感》2013,50(3):183-190
Many remote sensing applications are predicated on the fact that there is a known relationship between climate and vegetation dynamics as monitored from space. However, few studies investigate vegetation index variation on individual homogeneous land cover units as they relate to specific climate and environmental influences at the local scale. This study focuses on the relationship between the Palmer Drought Severity Index (PDSI) and different vegetation types through the derivation of vegetation indices from Landsat 7 ETM+ data (NDVI, Tasseled Cap, and SAVI). A series of closely spaced through time images from 1999 to 2002 were selected, classified, and analyzed for an area in northeastern Ohio. Supervised classification of the images allowed us to monitor the response in individual land cover classes to changing climate conditions, and compare these individual changes to those over the entire larger areas. Specifically, the images were compared using linear regression techniques at various time lags to PDSI values for these areas collected by NOAA. Although NDVI is a robust indicator of vegetation greenness and vigor, it may not be the best index to use, depending on the type of vegetation studied and the scale of analysis used. A combination of NDVI and other prominent vegetation indices can be used to detect subtle drought conditions by specifically identifying various time lags between climate condition and vegetation response. 相似文献
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本文主要介绍了地面辐射温度测量和地下不同深度的温度测量方法及结果,同时对地下输油管道产生的热异常成因机理进行了初步探讨。根据测试结果分析了热红外扫描成像有利的时间和季节;讨论了异常强度及地温的垂直衰减幅度;进行了温度梯度与热流值计算;总结了地下输油管道上覆土壤的热传导作用在夜间的变化规律。 相似文献
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Spectral reflectances of artificial pastures are examined at various wavelengths and stages in the grazing/field work cycle to identify inadequately drained, marginally productive sites. Mesophytic pasture grasses and crops on well-drained sites are replaced by more hygrophytic species on poorly drained sites (each group with distinctive brightness values). This relationship, plus less significant spectral differences reflecting grazing intensity and soil moisture content at particular points in time, provided a methodological basis for the study. Poorly drained pastures are most reliably identified in the infrared and visible green portions of the spectrum during the middle of the grazing season. Translated from: Geografiya I prirodnyye resursy, 1988, No. 1, pp. 134-139. 相似文献
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根据中国地壳运动观测网络基准网1999年3月至2003年8月的GPS观测时间序列,采用滤波法、差分法和残差估计法对时间序列的各个分量(东西、南北、垂直)分别进行了精度评定,并进行了比较,得出了一些结论,可根据实际需要,应用不同的精度分析方法。 相似文献
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频谱分析在周期拟合中的应用 总被引：5，自引：0，他引：5
在时间序列数据处理中常碰到确定性信息的提取。确定性信息包含趋势项和周期项。拟合周期项需要知道频率，利用频谱分析则可准确地捕捉频率，从而获得良好的计算结果。 相似文献
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《测量评论》2013,45(90):146-152
AbstractIn previous contributions to the Review the author outlined the development of hydrographic surveying in this country during the latter half of the 18th century. The surveys which Mackenzie, Spence and Bligh carried out at this time were largely inshore, covering areas within sight of land where prominent marks could be used for fixing by sextant resection. This was natural enough, for the accurate delineation of the hydrography of coastal waters and channels was an obvious starting point once the navigator had become convinced of the value of a precise hydrographic survey in his quest for safe navigation. It was soon apparent, however, that some of the offshore banks were equally dangerous from a navigation standpoint, particularly in the North Sea where many shoals and banks lay close to established and well-used shipping lanes. Time and time again vessels had foundered on these banks simply through a lack of accurate information about their true position and extent; on the existing charts they were either badly misplaced or oftimes not shown at all. 相似文献