6高程测量方法

Unit 6 Methods of Elevation Determination（高程测量方法）

An elevation is a vertical distance above or below a reference datum.（高程是高于或低于一个参考基准的一个垂直距离。）

Although vertical distance can be referenced to any datum, in surveying, the reference datum that is universally employed is that of mean sea level (MSL).（虽然垂直距离可以参考任何一个基准，但是在测量上，这个参考基准一般使用【employ使用、雇佣】的是平均海平面（MSL））

MSL is assigned a vertical value (elevation) of 0.000 ft or 0.000 m.（MSL被赋予【assign】一个0.000英尺或0.000米的高程）

All other points on the earth can be described by the elevations above or below zero.（地球上所有其它点可以用高于或低于0的高程来描述）

Permanent points whose elevations have been precisely determined (benchmarks) are available in most areas for survey use.（高程精确测出的永久点（水准点）被用于【available可利用、可用到的】大多数区域的测量工作）

In China, 7 years of observations at tidal stations in Qingdao from 1950 to 1956 were reduced and adjusted to provide the Huanghai vertical datum of 1956.（在中国，利用青岛验潮站【tidal stations in Qingdao】从1950年到1956年7年的观测数据处理【reduce处理、分析、减少】和平差，建立了56黄海高程系统）

In the 1987, this datum was further refined to reflect long periodical ocean tide change to provide a new national vertical datum of 1985, according to the observations at tidal stations from 1952 to 1979.（1987年，在依照了【according to】验潮站1952到1979年的观测资料后，这个基准【56基准】被进一步精确【refine精确、精制v.】——反映长时期海潮变化的85国家高程基准建立起来。）

Although, strictly speaking, the national vertical datum may not precisely agree with the MSL at specific points on the earth’s surface, the term MSL is generally used to describe the datum.（虽然，严格说来【strictly speaking】，国家高程基准在特殊的【specific特定的、特殊的】点上与MSL并不恰好【precisely】吻合，术语MSL一般【generally】还是用来描述它【国家高程基准】）

MSL is assigned a vertical value (elevation) of 0.000 ft or 0.000 m.（MSL高程的赋值为0.000英尺或米）Difference in elevation may be measured by the following methods:(James M. Anderson and Edward M. Mikhail. 1998)（高程的差异【高差】可以由下列方法测得（詹姆斯.安德森和爱德华.？？？））

1. Direct or spirit leveling, by measuring vertical distances directly.（水准测量【Direct leveling、spirit leveling都是水准测量的意思】，直接测得垂直距离【高程】）

Direct leveling is most precise method of determining elevations and the one commonly used.（水准测量是高程测量方法中精度最高、使用最普遍的方法）

2. Indirect or trigonometric leveling, by measuring vertical angles and horizontal or slope distances.（三角高程测量，利用测量竖直角和水平或斜距来测高程）

3. Stadia leveling, in which vertical distances are determined by tacheometry using engineer’s transit and level rod; plane-table and alidade and level rod; or self-reducing tacheometer and level rod.（视距高程测量，利用视距测量【tacheometry】，使用工程经纬仪和水准尺；平板仪和照准仪和水准尺；或者自处理视距仪【tacheometer视距仪、准距仪】和水准尺测得垂直距离【高程】）

4. Barometric leveling, by measuring the differences in atmospheric pressure at various stations by means of a barometer.（气压水准测量【Barometric大气压力】，通过使用气压计【barometer】测量不同站点大气压力的差值来测高程）

5. Gravimetric leveling, by measuring the differences in gravity at various stations by means of a gravimeter for geodetic purposes.（重力水准测量，通过使用【by means of】重力计测量不同站点的重力值差值来测高程，用于大地测量学的目的）

6. Inertial positioning system, in which an inertial platform has tree mutually perpendicular axes, one of which is “up”, so that the system yields elevation as one of the outputs.（惯性定位系统，含有一个惯性平台，具有三个互相【mutually 相互地】垂直【perpendicular垂直的】轴，其中一个是“向上”的，所以这个系统产生【yield产生v.】的输出【output 输出n.】其中一个就是高程。）

Vertical accuracies from 15 to 50 cm in distances of 60 and 100 km, respectively, have been reported.（各自地