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	Term	术语	Definition	定义
	north: magnetic	磁北	The direction indicated by the north seeking POLE of a freely suspended MAGNETIC NEEDLE influenced only by the EARTH's MAGNETIC FIELD.	自由悬式磁针在仅受地球磁场作用时指北端表示的方向。
	north: true	真北	The DIRECTION of the north GEOGRAPHIC POLE.	地理北极的方向。
	north celestial pole	北天极	See POLE: CELESTIAL.	参见celestial pole（天极）。
	north geographical pole	地理北极	See POLE: GEOGRAPHICAL.	参见geographical pole（地极）。
	northing	北航（进，距）	The distance a craft makes good to the north. The opposite is SOUTHING. In a cartesian reference system the value of one coordinate, usually... more The distance a craft makes good to the north. The opposite is SOUTHING. In a cartesian reference system the value of one coordinate, usually expressed in metres, measured from the origin in north-south direction; used e.g. in the UTM system.	船只保持向北航行的距离。相反为南距（Southing）。在笛卡尔坐标系中，某一坐标的值，通常以米为单位，从原点顺南北方向量取。应用实例：通用横轴墨卡托投影（UTM）系统。
	north magnetic pole	磁北极	See MAGNETIC POLE.	参见magnetic pole（磁极）。
	notch (or gap)	山峡	A narrow passage between two ELEVATIONS, as MOUNTAINS; a deep close PASS; a DEFILE.	（或gap<峡谷>）两块高地（如山脉）间的狭窄通道；隘路；峡谷。
	Notice to Mariners	航海通告	A periodical or casual notice issued by hydrographic offices, or other competent authorities, regarding changes in AIDS TO NAVIGATION, dang... more A periodical or casual notice issued by hydrographic offices, or other competent authorities, regarding changes in AIDS TO NAVIGATION, dangers to NAVIGATION, important new SOUNDINGS, and, in general, all such information as affects NAUTICAL CHARTS, SAILING DIRECTIONS, LIGHT LISTS and other nautical publications.	海道测量或其它主管机构发布的定期或临时通知，内容包括：航标变更、航行障碍物、重要新水深，以及影响海图、航行指南、航标表和其它航海出版物的所有信息。
	nuclear precession magnetometer	核子旋进磁力仪	See MAGNETOMETER.	利用氢原子核处于环境磁场中的旋进特性制成的磁力仪。亦称proton precession magnetometer（质子旋进磁力仪）。
	numerical scale	数字比例尺	See SCALE: NATURAL.	参见natural scale（自然比例尺）。
	nunatak	冰原岛峰	An isolated hill or mountain peak of rock projecting above an INLAND ICE SHEET.	突出于内陆冰盖的孤立石山峰。
	nun buoy	锤形浮标	A BUOY the above water part of which is in the shape of a cone or a truncated cone.	水上部分为圆锥形或截断圆锥形的浮标。
	nutation	章动	Irregularities in the precessional motion of the EQUINOXES because of varying positions of the MOON, and, to a lesser extent, of other CELES... more Irregularities in the precessional motion of the EQUINOXES because of varying positions of the MOON, and, to a lesser extent, of other CELESTIAL BODIES, with respect to the ECLIPTIC. Because of nutation the EARTH's AXIS nods like a top, describing an irregular circle about the mean pole in a period of about 19 years.	由月亮相对于黄道的位置变化引起的二分点不规则岁差运动，其他天体的位置变化也存在较小程度的影响。由于章动，地轴像陀螺般摇摆运行，约以19年为周期形成一个绕平极的不规则圆。
	Nyquist frequency	尼奎斯特频率	The highest frequency that may be uniquely resolved in a time series from a given sampling interval. The Nyquist frequency is equal to twic... more The highest frequency that may be uniquely resolved in a time series from a given sampling interval. The Nyquist frequency is equal to twice the sampling interval. Analyzing frequencies for which the Nyquist criterion is not met leads to ALIASING.	在一个给定采样间隔中按照某一时间序列可被单值分辨的最高频率。尼奎斯特频率等于采样间隔的两倍。根据奈奎斯特原理，只要离散系统的奈奎斯特频率高于采样信号的最高频率或带宽，就可以避免混叠现象。
	object-glass	物镜	See OBJECTIVE LENS.	参见objective lens（物镜）。
	objective	物镜	See OBJECTIVE LENS.	参见objective lens（物镜）。
	objective lens	物镜	In TELESCOPES and microscopes,the optical component which receives light from the object and forms the first or primary IMAGE. In a CAMERA, ... more In TELESCOPES and microscopes,the optical component which receives light from the object and forms the first or primary IMAGE. In a CAMERA, the IMAGE formed by the objective lens is the final IMAGE. In a TELESCOPE or microscope used visually, the IMAGE formed by the objective lens is magnified by the EYEPIECE. Also called objective or object-glass.	指在望远镜及显微镜中接收来自目标的光线并形成第一次像或原像的光学元件。在摄像机中，物镜所成的像为最终像。在目视望远镜或显微镜中，物镜成像由目镜放大。亦称objective或object-glass（物镜）。
	oblate spheroid	扁球体	See SPHEROID.	以短轴为旋转轴的旋转椭球体。地球近似于扁球体。
	oblique photograph	倾摄像片，倾斜摄影像片	See PHOTOGRAPH.	摄影轴位于水平线和垂直线之间时所拍摄的像片。
	oblique plotting instrument	倾斜测图仪	An instrument (usually monocular) for plotting from OBLIQUE PHOTOGRAPHS.	用于倾斜像片测图的仪器（常为单镜）。
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