Unit 6 Methods of Elevation Determination

Unit6MethodsofElevationDeterminationIElevationIIMethodsformeasuringdifferenceinelevationIIISpiritlevelingIVTrigonometriclevelingElevationElevationAnelevationisaverticaldistanceaboveorbelowareferencedatum.（高程是高于或低于一个参考基准的一个垂直距离。）Meansealevel(MSL)Althoughverticaldistancecanbereferencedtoanydatum,insurveying,thereferencedatumthatisuniversallyemployedisthatofmeansealevel(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））MSLisassignedaverticalvalue(elevation)of0.000ftor0.000m.（MSL被赋予【assign】一个0.000英尺或0.000米的高程）Allotherpointsontheearthcanbedescribedbytheelevationsaboveorbelowzero.（地球上所有其它点可以用高于或低于0的高程来描述）Nationalverticaldatum国家高程基准Permanentpointswhoseelevationshavebeenpreciselydetermined(benchmarks)areavailableinmostareasforsurveyuse.（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）ThedevelopmentofNationalVerticalDatumInchina,7yearsofobservationsattidalstationsinQingdaofrom1950to1956werereducedandadjustedtoprovidetheHuanghaiverticaldatumof1956.（在中国，利用青岛验潮站【tidalstationsinQingdao】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）Inthe1987,thisdatumwasfurtherrefinedtoreflectlongperiodicaloceantidechangetoprovideanewnationalverticaldatumof1985,accordingtotheobservationsattidalstationsfrom1952to1979.（1987年，在依照了【accordingto】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,strictlyspeaking,thenationalverticaldatummaynotpreciselyagreewiththeMSLatspecificpointsontheearth’ssurface,thetermMSLisgenerallyusedtodescribethedatum.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】）Methodsformeasuringdifferenceinelevation高差测量方法(JamesM.AndersonandEdwardM.Mikhail.1998)Directorspiritleveling水准测量bymeasuringverticaldistancesdirectly.Directlevelingismostprecisemethodofdeterminingelevationsandtheonecommonlyused.直接测得垂直距离【高程】）（水准测量是高程测量方法中精度最高、使用最普遍的方法）Indirectortrigonometricleveling三角高程测量bymeasuringverticalanglesandhorizontalorslopedistances.利用测量竖直角和水平或斜距来测高程Stadialeveling视距高程测量inwhichverticaldistancesaredeterminedbytacheometryusingengineer’stransitandlevelrod;plane-tableandalidadeandlevelrod;orself-reducingtacheometerandlevelrod.（，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】）Barometricleveling气压水准测量bymeasuringthedifferencesinatmosphericpressureatvariousstationsbymeansofabarometer.（【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）Gravimetricleveling重力水准测量bymeasuringthedifferencesingravityatvariousstationsbymeansofagravimeterforgeodeticpurposes.（，通过使用【bymeansof】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）Inertialpositioningsystem惯性定位系统inwhichaninertialplatformhasthreemutuallyperpendicularaxes,oneofwhichis“up”,sothatthesystemyieldselevationasoneoftheoutputs.（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。）GPSsurveyelevationsGPS高程测量GPSsurveyelevationsarereferencedtotheellipsoidbutcanbecorrectedtothedatumifasufficientnumberofpointswithdatumelevationsarelocatedintheregionsurveyed.（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）SpiritlevelingThemostprecisemethodofdeterminingelevationsandmostcommonlyusedmethod,meansmeasuringtheverticaldistancedirectly.（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）Differentialleveling微差水准测量isusedtodeterminedifferencesinelevationbetweenpointsthatareremotefromeachotherbyusingasurveyor’sleveltogetherwithagraduatedmeasuringrod.是利用测量者的水准仪【level水准仪、水平仪】和【togetherwith】有刻度的【graduated】尺来测定远距离的【remote遥远的】相隔点的高差）Figure1Equation:HB＝HA+a–bNotice:1.aiscalledBacksight(BS)whichisarodreadingtakenonapointofknownelevationinordertoestablishtheelevationoftheinstrumentlineofsight.（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。）2.biscalledForesight(FS)whichisarodreadingtakenonaturningpoint,benchmark,ortemporarybenchmarkinordertodetermineitselevation.（b被称为Foresight【后尺读数】，是一个放在转点【turningpointTP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）3.HA+areferstotheHeightofInstrument(HI)whichistheelevationofthelineofsightthroughthelevel.（HA+a指的是仪器高度（HI），是过水准仪的视线的高程）4.Owingtorefraction,actuallythelineofsightisslightlycurved,theeffectsofcurvatureandrefractionforthehorizontaldistancecanbereducedtoanegligibleamountandnocorrectionforcurvatureandrefractionisnecessaryifbacksightandforesightdistancesarebalancedinpracticaloperation.（由于【Owingto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【bereducedto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】。）TrigonometriclevelingWheretousetrigonometriclevelingTrigonometriclevelingisusedwheredifficultterrain,suchasmountainousareas,precludestheuseofconventionaldifferentialleveling.（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。）Themodernapproachistomeasuretheslopedistanceandverticalangletothepointinquestion.（现代的三角高程测量方法是测量到未知点【thepointinquestion】的斜距和垂直角）HowtomeasureSlopedistanceismeasuredusingelectromagneticdistancemeasurersandthevertical(orzenith)angleusingatheodolite,orthetotalstationthatintegratethesetwoinstrumentsintoasingle