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【respectively】，据相关报告，在60和100km的距离上，其精度能达到15到50cm）

The equipment cost is extremely high and applications are restricted to very large projects where terrain, weather, time, and access impose special constraints on traditional methods.（这种装置成本极【extremely极端地】高，只限于【restricted受限的】非常大的项目，这些项目地质、气象、授时、以及？？施加【impose】特殊限制【constraints】在传统方法上【即，在这些项目上传统测量方法受限】）

7. GPS survey elevations are referenced to the ellipsoid but can be corrected to the datum if a sufficient number of points with datum elevations are located in the region surveyed.（GPS高程测量，它的参考面是地球椭球面，但是如果在测区有充分的高程点，可以修正至高程基准上来）

Standard deviations in elevation differences of 0.053 to 0.094 m are possible under these conditions.（在这种情况下【上句中的情况】，其高差的标准差【Standard deviation】能够达到0.053到0.094米。）

Spirit leveling （水准测量）

The most precise method of determining elevations and most commonly use method is direct leveling or spirit leveling which means measuring the vertical distance directly.（精度最高、使用最普遍的高程测量方法就是直接测垂直距离的水准测量方法）

Differential leveling is used to determine differences in elevation between points that are remote from each other by using a surveyor’s level together with a graduated measuring rod.（微差水准测量是利用测量者的水准仪【level水准仪、水平仪】和【together with】有刻度的【graduated】尺来测定远距离的【remote遥远的】相隔点的高差）

For example, to determine the elevations of desired point B with respect to a point of known elevation A (see Figure 1), the elevation of which (BM) is known to be above sea level, the level is set up at intermediate point between A and B, and rod readings are taken at both locations as a and b respectively.（例如，确定欲测【desired想得到的】关于点A的点B的高程，（如图1），A点的高程已知（BM点）【above sea level不用翻译】，在A和B点之间的中【intermediate居中的】点处安置水准尺，分别【respectively分别地】以a和b代表在这两处水准尺上的读数）

Then the elevation of the line of sight of the instrument (being horizontal) is known to be the line of sight of the instrument HA + a.（那么，仪器（整平后）的视线高程就是：HA + a）【怀疑这句话不对 the line of sight of the instrument多余了】

The elevation of point B can be determined by equation（B点的高程可以由方程【equation】来确定）

HB=HA + a － b

In addition to determining the elevation of point B, the elevations of any other points, lower than the line of sight and visible from the level, can be determined in a similar manner.（除确定B点的高程之外【In addition to除……之外】，其它点的高程，低于视线的【高于视线的点，水准仪无法测得读数】和水准仪可以看见的点，都可以以相似的方法得到。）

But some terms should be mentioned from above.（但是上面的一些术语需要提一下）

a is called Backsight (BS) which is a rod reading taken on a point of known elevation in order to establish the elevation of the instrument line of sight.（a 被称为Backsight【后尺读数】，是一个放在已知高程点上的尺的读数，用来求得【establish建立】仪器视线的高程。）

b is called Foresight (FS) which is a rod reading taken on a turning point, benchmark, or temporary benchmark in order to determine its elevation.（b 被称为Foresight【后尺读数】，是一个放在转点【turning point TP点】、水准点、或者是临时水准点之上的尺的读数，用来确定该点的高程）

HA + a refers to the Height of Instrument (HI) which is the elevation of the line of sight through the level.（HA + a 指的是仪器高度（HI），是过水准仪的视线的高程）

Owing to refraction, actually the line of sight is slightly curved, the effects of curvature and refraction for the horizontal distance can be reduced to a negligible amount and no correction for curvature and refraction is necessary if backsight and foresight distances are balanced in practical operation.（由于【Owing to因……的缘故】大气折光【refraction折光】的缘故，实际上视线是有些【slightly些微地】弯曲的，曲率【地球曲率】和折光的影响可以被当作【be reduced to被处理为】可忽略的【negligible可忽略的】值【amount数量】，不必【necessary必要的】加入球气改正，如果在实际【practical】工作【operation】中后视距和前视距是相等的【可提前到本句中间】。）

Trigonometric Leveling（三角高程测量）

Trigonometric leveling is used where difficult terrain, such as mountainous areas, precludes the use of conventional differential leveling.（三角高程测量适用于困难地形，例如在山区，不能【preclude排除v.】使用常规的【conventional】微差水准测量。）

The modern approach is to measure the slope distance and vertical angle to the point in question.（现代的三角高程测量方法是测量到未知点【the point in question】的斜距和垂直角）

Slope distance is measured using electromagnetic distance measurers and the vertical (or zenith) angle using a theodolite, or the total station that integrate these two instruments into a single instrument.（斜距由电磁波测距仪【measurer测量器】测得，垂直角（或天顶距）由经纬仪测得，或者利用整合【integrate整合v.】了这两种仪器为一体的全站仪来测）

Total stations contain built-in microprocessors that calculate and display the horizontal distance from the measured slope distance and vertical height.（全站仪包含了【contain】内置的【built-in内置的】微处理器，用来根据测得的斜距和垂直角计算和显示水平距离）

This latter facility has resulted in trigonometrical leveling being used for a wide variety of heighting procedures, including contouring.（这种后来的【latter】设备【facility工具、设备、熟练、容易、敏捷】导致了【result in导致】三角高程测量被广泛用于多种【a variety of多种的】高度测量工作【procedure程序、手续】，包括测绘等高线【contour等高线】

The basic concept of trigonometrical leveling can be seen from Figure 2.（三角高程测量的基本原理【concept概念】可以看图2）

When measuring the vertical angle α and the horizontal distance S is used, then the difference in elevation hAB between ground points A and B is therefore:（当我们用α和S分别表示垂直角和水平距离时，A点和B点之间的高差为：）

hAB=S×tanα+i – v

where i is the vertical height of the measuring center of the instrument above A and v is the vertical height of the center of the target above B.（i 是A点上仪器中心的高度，v是B点上目标中心的垂直高度）

The vertical angles are positive for angles of elevation and negative for angles of depression.（垂直角为仰角【elevation仰角】时为正，俯角【depression俯角】时为负）

The zenith angles are always positive, but naturally when greater than 90° they will produce a negative result. （天顶距总是正的，但是自然的当超过了90°时，它们将产生一个相反的结果【指的是相对于地平线来说】）

Trigonometrical leveling method of determining difference in elevation is limited to horizontal distance less than 300 m when moderate precision is sufficient, and to proportionately shorter distances as high precision is desired.（普通【moderate普通的】精度要求下【sufficient充足的】【precision精度】，三角高程测量方法测高差水平距离不能超过300m，如果要求高的精度，则要相应【proportionately相应地】缩短距离。）

For the distance beyond 300 m the effects of curvature and refraction must be considered and applied.（因为超过300m时，地球曲率和折光影响必需考虑【apply应用 可以不翻译】）

To eliminate the uncertainty in the curvature and refraction correction, vertical-angle observations are made at both ends of the line as close in point of time as possible.（为了消除【eliminate消除】地球曲率和折光改正【correction修正、改正】的不确定因素，垂直角观测时应采用在观测方向两端尽量同时【as close in point of time as possible】相向观测的方法。【就是对向观测嘛】）

This pair of observations is termed reciprocal vertical-angle observation.（这种观测称为【is termed】垂直角对向观测【reciprocal observation 对向观测】）

The correct difference in elevation between the two ends of the line is the mean of the two values computed both ways either with or without taking into account curvature and refraction（线两端正确的【correct】高程之差是计算得到的两高程值的平均值【mean】，不管计算有无考虑【take into account】球气差.）

The important notes should be mentioned here is that surveyors used to working with spirit levels have referenced orthometric heights (H) to the “average” surface of the earth, as depicted by MSL.（这里需要注意的是，测量者在水准测量工作中使用的是参考地球“平均”表面的正高，这个平均表面描述为【称为】MSL）

However, the elevation coordinate (h) given by GPS solutions refers to the height from the surface of the ellipsoid to the ground station.（然而，GPS方法【solution】给出的是地球椭球面到地面站【ground station】的大地高【其实大地高的英文名字应该是：geodetic height，或ellipsoidal height，但这里讲的就是大地高，直接译为大地高】）

6高程测量方法