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ultra high frequency (UHF) | 超高频
| See FREQUENCY: RADIO. | 无线电通讯中，电磁波的有效辐射频率。无线电频率通常分为：甚低频（30千赫以内）、低频（30-300千赫）... more |
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ultrashort wave | 超短波
| See WAVE. | 波长小于10米的无线电波。 |
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ultrasonic | 超声波的
| (adj.). Having a FREQUENCY above the audible RANGE. | 具有超出可听范围的频率。 |
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ultrasonic depth finder | 回声测深仪
| See ECHO SOUNDER. | 通过测定声波或超声波信号从发射到海底反射回的时间间隔来确定水深的一种仪器。亦称声音测深仪。 |
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ultrasonics | 超声学
| The science and technology relating to SOUND WAVES of FREQUENCIES above the audible RANGE. | 研究有关超出可听范围频率声波的科学和技术。 |
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ultraviolet | 紫外线的
| (adj.). Having a FREQUENCY immediately beyond the violet end of the visible SPECTRUM. Said of RAYS of shorter WAVE LENGTH than visible light... more | 具有刚刚超出可见谱紫光一端的频率的。一般认为其波长射线比可见光短，但比X光射线长。 |
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uncontrolled mosaic | 无控制点镶嵌图
| A MOSAIC composed of uncorrected PRINTS, the detail of which has been matched from print to print without GROUND CONTROL or other ORIENT... more | 由未纠正像片组成的镶嵌图，在没有进行地面控制或其他定向的情况下，将像片一张张地拼接起来。 |
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uncovered | 露出的，干出的
| (adj.). Above water. The opposite is SUBMERGED. | 露出水面的。其反义词是submerged（淹没的）。 |
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uncovers | 露出，干出，干出物
| See COVERS AND UNCOVERS. | 指礁区或水体底部的其它突出部分周期地露出水面和没入水下。亦指干出或裸露。 |
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undercliff | 崩崖
| A TERRACE or lower CLIFF formed by a LANDSLIDE. Also written as two words. | 由山崩形成的台地或较低的悬崖。亦可分开写作两个单词。 |
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undercurrent | 潜流
| A CURRENT below the surface, particularly one flowing in a direction or at a SPEED differing from the SURFACE CURRENT. | 水下急流，尤指其流向或速度与表层流不同的水流。 |
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underground mark | 地下标志；下层标石
| A STATION MARK set and plumbed below the centre of a SURFACE MARK and separated therefrom so as to preserve the STATION in case of accident ... more | 一种测站标石；设置在地面标石的下面，为了防备地面标石遭到破坏，与地面标石隔开。 |
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underkeel clearance | 富余深度
| The distance (usually a required minimum distance) between the lowest point of a ship's hull and the SEABED. | 船体最下端（一般为龙骨上某一点）到海底之间的距离。 |
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underkeel allowance | 容许量
| The minimum UNDERKEEL CLEARANCE estimated, or specified by a relevant authority for a defined area or vessel type, to account for vessels' s... more | 顾及涌浪、不同潮高等情况下前进中船的尾部下坐量，由此估算某航道的最小龙骨下富余深度。 |
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undertow | 回卷；下层逆流
| A seaward FLOW near the BOTTOM of a sloping BEACH. The subsurface return by gravity flow of the water carried up on SHORE by WAVES or BREAKE... more | 斜坡海滩底部附近的向海水流。波或碎浪在海岸上卷起的重力水流所引起的下层逆流。 |
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underwater acoustics | 水声学
| A special field of technical acoustics dealing with the physics of sound propagation in the water. | 有关水下声传播物理性质的专门技术领域。 |
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underwater ice | 底冰
| See ANCHOR ICE. | 附在海底的冰（不考虑其形成的特征）。 |
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underwater navigation | 水下航行，潜航
| See NAVIGATION. | 某一水下船只的航行，有时亦称潜水艇航行。 |
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underwater photogrammetry | 水下摄影测量（学）
| See PHOTOGRAMMETRY. | 有关从像片获取可靠测量数据的科学或技术。 |
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underwater position fixing | 水下定位
| A method of position fixing for surface vessels, submersibles or towed devices in relation to a network of underwater acoustic beacons on th... more | 根据已知位置的海底水下声标网，确定水面船只、潜水艇或拖带装置位置的一种定位方法。 |