测绘外文翻译_GPS

第一篇 中英文互译

外文原文

Recently, according to the requirements of some important GPS research subjects in the fields of Geodesy, Geophysics, Space-Physics and navigation in China, we studied systematically how to correcting the effects of the ionosphere on GPS, with high-precision and accuracy. As the parts of the main contributions, the research projects focus mainly on how to improve GPS surveying by reducing ionospheric delay for dual/single frequency kinematic/static users: high accuracy correction of ionospheric delay for single/dual frequency GPS users on the earth and in space, China WAAS ionospheric modeling and the theory and method of monitoring of ionosphere using GPS.

The main contents of this Ph.D paper consist of two parts:

Fisrt part---the outline of research background and the systematic introduction and summarization of the previous research results of this work.

Second part---the main contribution and research results of this paper are focused on as follows:

(1) How to use the measurements of a dual frequency GPS receiver to determine the ionospheric delay correction model for single frequency GPS of a local range; (2) How to separate the instrumental biases with the ionospheric delays in GPS observation;

(3) How to establish a large range grid ionosphere model and use the GPS data of Chinese crust movement observation network to investigate the change law of ionospheric TEC of China area;

(4) How to improve the effectiveness of correcting ionospheric delays for WAAS’s users under adverse conditions.

(5) How to establish the basic theory and the corresponding framework of monitoring the stochastic ionospheric disturbance using GPS

(6) How to improve the modelling ability of ionospheric delay according to its diurnal, seasonal, annual variations based on GPS;

(7) How to meet the demand of correcting the ionospheric delay of high-precision orbit determination for low-earth satellite using a single frequency GPS receiver 1 Extracting (local) ionospheric information from GPS data with high-precision The factors are systematically described and analyzed which limit the precision of using GPS data to extract ionospheric delays. The precision of determining ionospheric delay using GPS is improved based on the further research of the related models and methods. The main achievements of this work include the some aspects as follows:

(1) Based on a simple model with constant number of parameters, which consists of a set of trigonometric series functions, a generalized ionospheric model is constructed whose parameters can be adjusted. Due to the property of selecting the different parameters according to the change law of ionospheric delay, the new model has better availability in the field of the related theoretic research and engineering application. The experimental results show that the model can indicate the characteristic of ionospheric actions, improves further the modeling ability of local ionosphere and may be used to correct efficiently ionospheric delay of the single frequency GPS uses serviced by DGPS.

(2) Different calculating schemes are designed which are used to analyze in detail the characteristics of the effect from instrumental bias (IB) in GPS observations on determining ionospheric delays. IB is different from noise in GPS observations. The experimental results show that the effect of IB is much larger than that of the noise on estimating ionospheic delay, and IB can cause ionospheric delay measurements to include systematic errors of the order of several meters. Therefore, one must significantly take notice of IB and remove its negative effect, and should not casually consider IB as part of noise whenever GPS data are used to fit ionospheric model or to directly calculate ionospheric delay.

(3) Stability of IB is studied with a refined method for separating it from ionospheric delay using multi-day GPS phase-smoothed code data. The experimental results show

that, by using averaging of noise with phase-smoothed code observation，the effect of noise on separating IB from ION can be efficiently reduced, and satellite bias plus receiver bias are relatively stable and may be used to predict the IBs of the next session or even that of the next several days.

(4) A new algorithm about static real time determination of ionospheric delay is presented on the basis of the predicted values of IB and the technique of real time averaging of noise and weighted-adjustment of dual P-code and carrier phase measurements. The preliminary results show that the new method, which is by post-processing phase-smoothed code data to calculate the IB and then with them to predict and to correct the IB of data needed to remove its effects in real time in the next observation periods, has relatively better accuracy and effectiveness in estimating ionospheric delay. It is very obvious that the scheme can relatively decrease the number of unknown parameters, can efficiently reduce the main negative effect from instrumental bias, and can be easily used to directly and precisely determine ionospheric delay with dual-frequency GPS data. Hence, the method may be considered as an available scheme to determine ionospheric delays for WAAS and many other large range GPS application systems.

2 A method of constructing large range (regional and global) high-precision grid ionospheric model─—the Different Area for Different Stations (DADS) and its application in China

Based on the systematic and further research of the principle and methods of establishing grid ionospheric model (GIM), a new method of establishing a GIM ----- Different Areas for Different Stations (DADS) is investigated which is advantageous for considering the local characters of ionosphere, avoiding the effects of the geometrical construction of GPS reference network on estimating the external precision of the GIM, and improving the precision of calculating model parameters. The above results are used to make a preliminary estimation of the latent precision that can be obtained by establishing a large range high precision grid ionospheric model based on the Chinese crust movement observation network, and to investigate the possibility that the GIM provides high-precision ionospheric correction, and to

identify the relevant problems which need to be solved for the planned GPS Wide area Augmentation System (WAAS) of China.

3 A method of efficiently correcting ionospheric delays for WAAS’s users under typical adverse conditions ——the Absolute Plus Relative Scheme (APR-I)

The commonly used WAAS’s DIDC received by single frequency GPS receivers can usually provide the effective correction of the ionospheric delays for the users under normal conditions and in the fields of calm ionosphere. However, the ionospheric delays cannot be efficiently accounted for during those periods when the WAAS cannot broadcast the DIDC values to users, or when the receivers cannot receive the DIDCs for whatever reason. The ionospheric delay corrections will be less well known in cases when the variations of the ionospheric delays may be very large due to ionospheric disturbances. The above difficulties cannot be avoided to be encountered and must be solved for the WAAS.

For this, a new ionospheric delay correction scheme for single frequency GPS data—the APR-I scheme is proposed which can efficiently address the above problems.

1) The theoretic basis of constructing the APR-I Scheme

The WAAS can provide high-precision absolute ionospheric delay estimates when it operates properly. Meanwhile, a single frequency GPS receiver serviced by the WAAS can efficiently determine the relative variation of the ionospheric delays between two arbitrary epochs even under adverse conditions if without considering observation noises. 2) On the APR-I Scheme

Based on a robust recurrence procedure and an efficient combination approach between absolute ionospheric delays and ionospheric relative changes, the APR-I scheme is present which is an new method of correcting ionospheric delay for single frequency GPS user. The formula of estimating the precision of the APR-I scheme is given. An implementation approach of the APR-I scheme is analyzed as well. The experimental results discussed above show that the APR-I scheme not only retains the characteristic of high accuracy of the DIDC from the WAAS under normal

ionospheric and reception conditions, but also has relatively better correction effectiveness under different abnormal conditions. The implementation of this method need not change the present basic ionospheric delay correction algorithm of the WAAS. In addition, the APR-I method does not impose new demands on receiver hardware, and only requires a few improvements to receiver software. Hence it can be easily used by single frequency GPS users.

4 A new theory of monitoring the random signal —Auto-Covariance Estimation of Variable Samples(ACEVS) and its application in using GPS to monitor the random ionosphere

A new approach for monitoring ionospheric delays is found and developed, based on the characteristic of time series observation of GPS, an investigation of the statistical properties of the estimated auto-covariance of the random ionospheric delay when changing the number of samples in the time series, the development of the related basic theory and the corresponding framework scheme, and the further research of using GPS and the above research results to study ionosphere. The concrete work is as follows:

1) Studied the Auto-Covariance Estimation of Variable Samples (ACEVS)

From a general mathematical aspect, the basic model of ACEVS is established. The theoretic and approximate solution formulas for ACEVS are derived based on the improvement of theory of white noise and then a test raw of the state of a random signal is established based on ACEVS;

2) Verified and modeled the possibility of using ACEVS to test the change of state of stochastic delays

The possibility of using ACEVS to monitor ionosphere is verified in terms of theory. Also it is found that the statistical property of ACEVS is sensitive to the change of the random ionospheric delay, on the basis of modeling the characteristics of ACEVS using a dual frequency GPS receiver. The application conditions of using ACEVS to monitor the variation of TEC extracted by GPS data are preliminarily discussed and analyzed as well.

3) Established a preliminary framework scheme of using GPS to monitor the

disturbance of random ionospheric delay.

According to ACVES and all other results of the above and the characteristic of the time series observations of GPS, a preliminary framework scheme for monitoring the disturbance of random ionospheric delay using GPS is established. Although this method is proposed for real time monitoring, it can be easily applied to post-processing of GPS data. The framework scheme based on ACVES can be used to design many practical schemes for monitoring ionosphere variation using a (static or kinematic) dual frequency GPS receiver.

5 A new method of modelling ionospheric delay using GPS data ——Ionospheric Eclipse Factor Method (IEFM)

The Ionospheric Eclipse Factor (IEF) and its influence factor (IFF) of Ionospheric Pierce Point (IPP) is present and a simple method of calculating the IEF is also given. By combining the IEF and IFF with the local time t of IPP, a new method of modelling ionospheric delay using GPS data —Ionospheric Eclipse Factor Method (IEFM) is developed. The IEF and its IFF can efficiently combine the different ionospheric models for different seasons according to the diurnal, seasonal and annual variations of ionosphere. The preliminary experimental results show that the correction accuracy of the ionospheric delay modeled by IEFM is very close to that of using the ionosphere- free observation to correct directly the ionospheric delay, that is, the precision of using IEFM to model ionospheric delay for single GPS users seems to has a breakthrough improvement and be similar to that of using the corresponding dual frequency GPS data to correct directly the ionospheric delays. The IEFM also suits to model the ionospheric delays for a kinematic based–single GPS receiver embeded in low-earth satellite with high rapid due to its good ability in distinguishing the daytime and nighttime of the earth ionosphere for an IPP.

6 A new strategy of correcting ionospheric delay for high-precision orbit determination for low-earth satellite using a single frequency GPS receiver ---the APR-II scheme, i.e., Space-based APR scheme

Analyzed the shortcomings of using the previous methods to divide with high accuracy the earth ionosphere into different layers. Used GPS data to model global

ionospheric TEC. Established a high precision grid ionospheric model. Discussed the possibility of finding out some local areas whose ionospheric construction and action have relatively better obvious law with respect to the other areas on a global scale. Designed a scheme for combining GPS-grounded data with GPS-spaced data to divide efficiently the ionosphere into some layers. Given the corresponding formula of estimating the precision of the scheme. The preliminary precision estimation and the experimental results show the possibility and property of the above idea of dividing ionosphere into different layers according to application requirement and its implementation scheme. Based on the above research, the APR-II scheme is presented which is a new and combined method of correcting the ionospheric delays of high-precision orbit determination for low-earth satellite using a single frequency GPS receiver. The preliminary experimental results based on two different sets of GPS-grounded data show that the APR-II scheme can provide the effective ionospheric delay correction for high-precision orbit determination for low-earth satellite.

中文翻译

根据当前大地测量、地球物理、空间物理和导航等领域的科学研究和工程应用中的若干重要GPS科研项目的需要，近年来，我们系统研究了电离层延迟的高精度模拟和改正方法。本文报告的内容，是我们研究工作的部分贡献，主要涉及基于GPS的电离层监测及延迟的高精度改正的理论与方法的研究：如何通过修正静、动态单、双频用户的电离层延迟影响，进一步改善GPS 测量的精度和可靠性；增强型GPS广域差分系统的电离层模拟及利用GPS监测电离层的理论和方法等方面。

本文主要包括两方面的内容：

一、研究背景的一般性描述及相关基础研究的系统总结和介绍,主要涉及：地球电离层研究意义, 地球电离层探测技术与相关理论研究的内容,现代大地测量中电离层问题的由来、严重性与新课题, 地球电离层的基本特性及其对电波传播的影响，GPS定位的基本理论与方法，电离层延迟对GPS测量的影响，GPS的

电离层延迟改正的基本方法，基于GPS的电离层研究的基本原理与方法等。进而论述了解决GPS的电离层延迟影响的重要性和切入点。

二、具体研究工作的系统报告，主要集中在以下几方面:

①研究如何利用单台双频GPS接收机的观测信息确定电离层延迟改正模型，为小范围的单频用户服务；

②研究如何实时分离GPS观测中的仪器偏差与电离层延迟；

③研究如何建立较大区域的电离层格网模型，进而初步设想利用中国地壳运动观测网络深入研究我国领域的电离层的电子浓度变化规律；

④研究单频用户在不利条件下，如何更好地利用电离层延迟改正信息； ⑤研究利用GPS监测随机电离层扰动的基本理论和框架方案；

⑥研究如何综合顾及电离层的周日、季节和年变化，进一步提高利用GPS模拟电离层延迟的能力；

⑦研究如何实现星载单频GPS低轨卫星的精密测轨中的电离层延迟改正要求。

1. (局部)电离层延迟的高精度提取

系统论述和分析了影响利用GPS观测精确提取电离层延迟信息的各类因素。通过对有关模型和方法问题的深入研究，进一步提高了利用GPS提取电离层延迟信息的精度。主要包括：

（1）将参数固定的三角级数函数电离层模型，扩展为更适用于理论研究和实际应用的参数可调型广义形式，实现了根据电离层延迟时空变化特征，选择不同的特征参数模拟电离层延迟的影响。试算结果表明，它能较好地反映电离层活动特性，提高了局部电离层延迟模拟能力，适用于DGPS系统修正其服务区域内的单频GPS用户的电离层延迟。

（2）设计了几种不同的计算方案，用于分析仪器偏差对确定电离层延迟的影响的特点。研究表明，仪器偏差对求解电离层延迟的影响远大于观测噪声的影响，给电离层延迟观测值带来高达数米的系统误差。利用GPS观测数据求解电离层模型或直接计算斜距电离层延迟时，都须慎重处理仪器偏差，不应简单把其作为噪声处理;

（3）利用相位平滑测码数据进一步精化了仪器偏差分离方法，探讨了仪器偏差的稳定性。研究发现，新方法可有效克服噪声对分离仪器偏差的影响，而且

仪器偏差相对稳定并可有效进行测段间及数日间预报。

（4）基于实时平均去噪和码、相位观测数据的加权联合处理的思想，提出了一种实时分离仪器偏差和求解电离层延迟量的新方案。算例表明，新方法通过采用平均去噪分离方法后处理相位平滑测码数据，求出仪器偏差并对需要实时处理仪器偏差的观测数据进行预报改正，直接利用观测值确定电离层延迟量，待估参数少、能消除仪器偏差的大部分影响，具有较好的精度，可作为WAAS及其他GPS网络系统确定电离层延迟的可行的参考方案。

2. 一种构建大规模(区域性和全球性)高精度格网电离层模型的新方法

——站际分区法及其在中国的初步实现

在系统深入研究了格网电离层模型建立原理与方法的基础上，为避免基准站网的几何结构对模型精度估计的影响，充分顾及电离层延迟影响的局部特性，进一步提高格网电离层模型的构建精度，提出了一种新的格网电离层模型构建方法——站际分区格网法。在以上研究的的基础上，估计了利用地壳运动观测网络的基准网建立格网电离层模型的精度，初步探讨中国域内拟建立的广域差分GPS增强系统，采用格网电离层模型提供电离层改正信息的可行性及有待进一步研究的问题。

3. 不利条件下为WAAS的单频GPS用户提供电离层延迟改正

的新方法——APR-I方案

在正常条件和平静电离层区域，WAAS能够满足单频用户的电离层延迟改正要求，但当用户无法正常获取电离层延迟改正信息时，如在差分系统突然中断信息发送或用户步入无法正常接收差分改正信息的位置等不利条件下，单频GPS接收机不能有效进行实时电离层延迟改正，尤其在电离层活动异常区域如电离层扰动条件下，实时差分改正效果将受到严重影响。这些问题在WAAS的实际运行中是难以避免和必须解决的。而以往的研究结果，均为后处理方法，不能满足(准)实时处理电离层扰动的要求。

针对这种状况，我们通过设计能有效结合电离层延迟绝对量和相对变化量的抗差递推过程，提出了一种可在以上不利条件下有效实时改正单频GPS用户电离层延迟的方法—APR-I方案。

1）构建APR-I方案的理论依据

WAAS正常运转和正常条件下可提供高精度的电离层延迟改正信息(绝对量)，

而WAAS所服务区域内的单频GPS接收机在不利条件下也能有效提供电离层延迟变化量(相对量)，且在不考虑噪声影响，可直接计算任意两观测历元间的电离层变化量的近似值。

2）提出APR-I方案

通过设计能有效结合电离层延迟绝对量和相对变化量的抗差递推过程，研究了一种新的单频GPS电离层延迟改正方案(称为APR方案,即Absolute Plus Relative Scheme)；给出了APR-I方案的精度估计公式；分析实施APR-I方案的有效途径。

研究表明，新方案既保留正常条件下差分电离层延迟信息的精确改正效果，也确保了在不利条件下单频GPS用户的电离层延迟改正效果。APR-I方案的实施，不需改变WAAS原有的整体设计思想，对硬件无新的要求，只需对用户GPS软件稍加改进，实施简便，是WAAS和单频GPS用户均可接受和易于实现的。 4. 检测随机信号的新理论——变样本自协方差估计的提出

及其在GPS监测随机电离层扰动中的应用

根据GPS时序观测的特点，通过设计先研究样本时序变化时随机电离层折射的自协方差估计的统计特性，再探讨利用GPS实时监测电离层活动的新方法的思路，从基础理论的提出到框架方案的建立，系统深入研究了利用GPS监测随机电离层扰动的基本理论与方法。具体包括：

1）研究变样本自协方差估计(ACEVS)理论

从一般的数学意义上建立了ACEVS的基本模型，并在进一步扩展白噪声理论的基础上，得到了ACEVS估计的理论和简化解式，即变样本自协方差估计的统计模型参数估计解式，进而建立了随机信号扰动的诊断准则。

2）ACEVS估计应用于GPS电离层监测的可行性的理论证明与模拟分析 不仅从理论上证明了ACEVS应用于GPS电离层监测的可行性，而且利用双频GPS数据也成功地模拟了随机电离层折射的ACEVS估计的特性，并发现，变样本自协方差估计的统计特性对随机电离层延迟变化是敏感的；初步讨论和分析了GPS观测提供的TEC变化也适用于ACEVS方法应用条件.

3）建立利用GPS监测随机电离层扰动的框架方案

综合ACEVS理论及相关的结论和GPS时序采样的特点，初步给出一种基于GPS的电离层扰动监测的框架方案。

以上方法尽管是针对实时监测要求提出的，但它完全可用于后处理情况。电离层扰动的GPS探测方案，主要分后处理和实时两种情况，静、动态实时方案基本相同，差别主要取决于硬件要求。试验结果表明，利用ACEVS研究基于GPS的随机电离层活动的监测方法的设想是基本可行的；所给出的框架方案可作为设计各类利用单台(静、动态)双频GPS接收机监测电离层活动的方法的参考方案之一。

5. 利用GPS数据精确模拟电离层延迟的新构想

——电离层蚀因子法及初步实现

提出了IPP点的电离层蚀因子及其影响因子的概念，给出了简便的计算方法，进而提出了一种利用GPS数据确定电离层延迟改正模型的新方法——电离层蚀因子法。电离层蚀因子及其影响因子，能够根据电离层随周日、季节、半年和周年的变化，将适应于不同季节的电离层延迟模型有效结合起来。研究表明，利用蚀因子法模拟的电离层延迟的改正精度与利用电离层无关观测的消除电离层延迟的精度很接近，使得单频GPS观测的电离层延迟的改正精度有望实现突破性提高，从而接近双频GPS观测自校正电离层延迟的精度。同时，由于它具有很好的描述和区分电离层日间和夜间的能力，所以很适合模拟高动态低轨卫星的星载单频GPS观测数据的电离层延迟的变化特性。

6. 高精度修正星载单频GPS低轨卫星的电离层延迟的新对策

——APR-II方案，即空基APR方案

分析了现有方法无法保证高精度和高可靠性地进行电离层分层这一严重不足；利用实测数据模拟全球电离层模型和建立高精度区域格网电离层模型，初步分析了在全球范围内寻找若干个电离层结构和活动相对较有规律的局部区域的可行性；设计了在选定的局部电离层区域，联合处理地基和低轨空基用户的GPS观测数据有效进行电离层分层的具体方法，给出了相应的精度估计公式。初步的精度估算和试算结果表明，这种在局部区域进行有效电离层分层的设想及给出的实施方法是可行的。进而系统性地提出了一种用于星载单频GPS接收机精密测轨中电离层延迟改正的综合方法—APR-II方案。地面GPS数据进行的两个初步模拟计算结果显示，利用APR-II可满足低轨卫星等低轨航天器精密测轨时的电离层延迟的高精度改正要求。

Level Rods and Lenels

There are many kinds of lenel rods available.Some are in one piece and others (for ease of transporting) are either telescoping or hinged.Level rods are usually made of wood and are graduated from zero at the bottom.They may be either selfreading rods that are read directly through the telescope or targetrods where the rodman sets a sliding target on the rod and takes the reading directly. Most rods serve as either self-reading or as target rods.

Among the several types of level rods available are the Philadelphia rod,the Chicago rod, and the Florida rod. The Philadelphia rod, the most common one, is made in two sections. It has a rear section that slides on the front section. For readings between 0 and 7 ft, the rear section is not extended; for reading between 7 and 13 ft, it is necessary to extended the rod. When the rod is extended,it is called a high rod. The Philadelphia rod is distinctly divided into feet, tenths, and hundredths by means of alternating black and white spaces painted on the rod.

The Chicago rod is 12 ft long and is graduated in the same way as the Philadelphia rod, but it consists of three sliding section. The Florida rod is 10 ft long and is graduated in white an red stripes, each stripe being 0.10 ft wide. Also available for ease of transportation are tapes or ribbons of waterproofed fabric which are marked in the same way that a regular level rod is marked and which can be attached to ordinary wood strips. Once a job is completed, the ribbon can, be removed and rolled up. The wood strip can be thrown away. The instrumentman can clearly read these various level rods through his telescope for distances up to 200 or 300 ft, but for greater distances he must use a target. A target is a small red and white piece of metal attached to the rod. The target has a vemier that enables the rodman to take a reading to the nearest 0.001 ft.

If the rodman is taking the readings with a target and if the line of sight of the telescope is above the 7-ft mark, it is obvious that he cannot take the reading directly in the normal fashion. Therefore, the back face of the rod is numbered downward from 7 to 13 ft. The target is set at acertain mark on the front face of the rod and as the back section is pushed upward, it runs under an index scale and a vernier which

enables the rodman to take the reading on the front.

Before setting up the level the instrumentman should give some though to where he must stand in orde to make his sights. In other words, he will consider how to place the tripod legs so that he can stand comfortably between them for the lay-out of the work that he has in mind.

The tripod is desirably placed in solid ground where the instrument will not settle as it mose certainly will in muddy or swampy areas. It may be necessary to provide some special support for the instrument, such as stakes or a platform. The tripod legs should be well spread apart and adjustde so that the footplate under the leveling screws is approximately level. The insatrumentman walks around the instrument and pushes each leg frimly into the ground. On hillsides it is usually convenient to place ong leg uphill and two downhill.

After the instrument has been levelde as much as possible by adjusting the tripod legs, the telescope is turned over a pair of opposite leveling screws if a four-screw instrument is being used.Then the bubble is roughly centered by turning that pair of screw in opposite directions to each other. The bubble will move in the direction of the left thumb. Next, the telescope is turned over the other pair of leveling screws and the bubble is again roughly centered. The telescope is turned back iver the first pair and the bubble is again roughly centered, and so on. This process is repeated a few more times with increasing care untill the bubble is centered with the telescope turned over either pair of screws. If the level is properly sdjusted, the bubble should remain centered when the telescopeis turued in any direction. It is to be expected that there will be a slight maladjustment of the instrument that will result in a slight movement of the bubble; however, the precision of thework should not be adversely affected if the bubble is centered each time a rod reading is taken.

The first step in leveling a three-screw instrument is to turn the telescope untill the bubble tube is parallel to two of the screws. The bubble is centered by turning these two screws in opposite directions.

Next, the telescope is turned so that the bubble tube is perpendicular to a line through screws. The bubble is centered by turning screw .

These steps are repeated untill the bubble stays centered when the telescope is turned back and forth.

Electronic Distance Measurements

A major advance in surveying in recent years has been the development of electronic distance-measuring instruments (ED-MIs). These devices determine lengths based on phase changes that occur as eletromagnetic energy of known wavelength travels from one end of a line to the other and returns.

The first EDM instrument was intronduced in 1948 by Swedish physicist Erik Bergstrand. His device, called the geodimeter(an acronym for geodetic distance meter), resulted from attempts to improve methods for measuring the velocity of light. The instrument transmetted visible light and was capable of accurately measuring distances up to about 25 mi (40km) at night. In 1957 a second EDM apparatus. the tellurometer. Designed by Dr.D.L.Wadley and introduced in South Africa, transmitted invisible microwaves and was capable of measuring distances up to 50 mi (80km) or more.day or night.

The potential value of these early EDM models to the Surveying profession was immediately recognized: houever, they were expensive and not readily portable for field operations. Furthermore, measuring procedures were lengthy and mathematical reductions to obtain distances from observed values were difficult and time-consuming. In addition. The range of operation of the first geodimeter was limited in daytime use. Continued research and development have overcome all these deficiencies.

The chief advantages of electronic surveying are the speed and accuracy with which distances can be measured. If a line of sight is available, long or short lengths can be measured over bodies of water or terrain that is inaccessible for taping. With modern EDM equipment, distance are automatically displayed in digital form in feet or meters, and many have built-in microcomputers that give results internally reduced to horizontal and vertical components. Their many significant advantages have revolutionized surveying procedures and gained worldwide acceptance. The long-distance measurements possible with EDM equipment make use of radios for

communication, which is an absolute necessity in modern practice.

One syetem for classifying EDMIs is by wavelength of transmitted electromagnetic energy ; the following categories exist :

Electro-optical instruments Which transmit either modulatedlaser or infrared light having wavelengths within or slightly beyond the visible region of the spectrum.

Microwave equipments Which transmits microwaves with frequencies in the range of 3 to 35 GHz corresponding to wavelengths of about 1.0 to 8.6 mm.

Another classification system for EDMIs is by operational range . It is rather subjective , but in general two divisions fit into this system : short and medium range .The short-range group includes those devices whose macimum measuring capability does not exceed about 5km . Most equipment in this division is the electro –optical type and uses infrared light . These instruments are small, portable, easy to operate, suitable for a wide variety of field surveying work, and used by many practitioners.

Instruments in the medium-range group have measuring capabilities extending to about 100 km and are either the electro-optical (using laser light) or microwave type. Although frequently used in precise geodetic they are also suitable for land and engineering surveys. Longer-range device also available can measure lines longer than 100km,but they are nit generally used in ordinary surveying work. Most operate by trasmitting long radio waves, but some employ microwaves. They are used primarily in oceanogaraphic and hydrograpgic surving and navigation.

In general, EDM equiment measures distances by comparing aline of unkown length to the known wavelength of modulated electromagnetic energy. This is similar to relating a needed distance to the calibrated length of a steel tape.

Electromagnetic energy propagates through the atmosphere in accordances with the following equation:

V=fλ (1)

Where Vis the velocity of electromanetic energy, in meters per second;f the modulated frequency of the energy ,in hertz, and λthe wavelenth, in meteres.

With EDMIs frequency can be precisely controlled but velocity varies with

atmophere temperature, pressure,and humidity. Thus wavelength and frequency must vary in conformance with EQ.(1). For accurate electronic distance measuement, therefor., the atmosphere must be sampled and corrctios made accordingly.

The generalizedprocedure of measuring distance electronically is depicted in Fig.8-1. an edm device, centered by means of a plumb bob or optical plummit over staton A, trasmits a carrier signal of electromagnetic energy upon which a reference frequency has been superimposed or modulated. The signal is returned from staion B to the revevier, so its trvel path is double the slope distance AB. In Fig.8-1,the modulated electromagnetic energy is represented by a series of sine waves having wave-length λ. Any position along a givenj wave can be specified by its phase angle, which is 0°at its beginning, 180°at the midpoint, and 360°at its end.

EDM devices used in surveying operate by measuring phase shift. In this procedure, the returned energy undergoes a complete 360°phase change for each even multiple of exactly one-half the wavelength separating the line-s endpoints. If, therefore, the distance is precisely equal to a full multiple of the half-wave-length, the indicated phase change will be zero. In Fig.8-1.for example, stations A and B are exactly eight half-wavelengths apart : hence, the phase change is zero. When a line is not exactly an even meltiple of the halfwavelength (the usual case) , the fractional part is measured by the instrument as a nonzero phase angle or phase change. If the precise length of a wave is known, the fractional part can be converted to distance.

EDMIs directly resolve the fractional wavelength bu do not count the full cycles undergone by the returned energy in traveling its double path. This ambiguity is resolved, however, by transmetting additional signals of lower frequency and longer wavelengths.

中文翻译

水准尺和水准仪

有许多类型的有价值的水准尺，一些是一体的，另一些（为了运输的安全）要么是需安装望远镜，要么是得安装绞链，水准尺通常是由木材制成的，并且在底端刻度从零开始，他们可以通过望远镜或者通过司尺员在尺上设置的觇标来直接读数。大多数水准尺既可以自读又可以作为觇标水准尺。

在使用的几种水准尺中有费拉德尔菲亚水准尺，芝加哥水准尺和佛罗里达水准尺，费拉德尔菲亚水准尺由两部分组成，是最普通的一种。它有一个后续部分，其前面部分上可以滑动。读数在7-13英尺之间时，后面部分不必延伸出来；读数在7-13英尺之间，则要延伸水准尺。当水准尺被延伸时，则被称为高标尺。菲亚水准尺被分为英尺、十分之英尺、百分之读尺（被尺子上黑白相间的交换的条节划分开）。

芝加哥水准尺是12英尺，其刻度划分与菲亚尺相同，但它由三个滑动的部分组成。佛罗里达有10英尺长，刻度由红、白条带划分，每一条带有0.1英尺宽。另外为了运输方便也采用防水织物作的带尺，这种带尺的分划与普通水准尺的分划方法是相同的，而且可以贴在普通木条上。一但工作完成，带尺便可以重新移动或若卷起，而木条则可以扔掉。测量员可以在200-300英尺之外通过望远镜用战标清晰地读出各种水准尺的读数。战标是附加在标尺上很小的、红白相间的金属卡。战标上的游标可以让司尺员读到近0.001英尺。

如果司尺员使用战标读数，且望远镜超过7英尺，显然，司尺员这时无法进行正常的读数。因此，水准尺背面是从低端开始7-13英尺。战标被安置在水准尺前面，并且后面部分被拉起来以后，战标移动一个刻度，以便让司尺员在水准尺前面读数。

在安置水准仪前，观测员应该想到他应该站在什么地方观测。换句话说，他应该考虑到如何安置三角架的腿，以便他能舒服的站在腿的中间，测他所想的工作。

三脚架应安置在坚硬的、仪器不下沉的地面上，当然大多数都安置在松软时而下沉的地方。给仪器提供一些特殊的支持如林庄或平台是必要的。三角架的腿应该合适地展开并调节以便使水平脚，螺旋下的底座能够接近水平。观册员绕着仪器将三脚架每条腿伸长固定在地面上。在山上时，通常将一条腿安上山坡上，两条腿安在山坡下，更便于观测。

通往调节三条腿尺可能使仪器整平。如果使用的是四个脚螺旋，望远镜要转到一对向相反方向转动的脚螺旋上。通过向相反方向转动两个脚螺旋，水准气泡粗略对中，气泡将向左手大拇指方向移动。接着，望远镜转向另一对相对的脚螺旋，水准气泡又一次粗略的对中。这个过程要小心的重复几次，直到望远镜转到

任意一对脚螺旋的方向气泡都对中。如果水准仪整平了，那么望远镜转到任一方向时，气泡应保持对中。我们期望仪器轻微移动时，气泡也轻微的移动。无论如何，如果每次读数时气泡都居中，观测的精度不应该有不利的影响。

在整平三角架脚螺旋时，第一步转动望远镜，向相反方向调节两个脚螺旋。 接下来转动望远镜，以使水准管垂直于脚螺旋1和2，调节使其居中，重复这些步骤，直到望远镜来回转动时气泡保持居中。

电子测距仪

近年来，测量中的主要进步是电子测距仪的发展，当已知波长的电波能从一条边的一端传播一另一端并返回时就发生了相变，这些装置就是根据这些来测定长度的。

最早介绍电子测距仪的确1984年瑞典的物理学家Erik Bergstrand,他的装置，命名为光电测距仪（gecdetic distance meter的首字母缩写），结果导致从实验到改进测量光速的方法。在晚上，仪器传送可见，并且可精确40km的距离。1957年，第二代EDM仪器产生，微波测距仪由D.K博士发明并介绍到南非，传送不可见的微波可全天观测，距离在80km以上。

这些早期的EDM模型对测量专业的潜在价值立即被人们认可，尽管他们是昂贵的，甚至在里子外操作是不轻便的，并且测量的过程是冗长的，而且从数据中获取有用价值是困难的。另外，在宽广区域，第一代测距仪在白天的使用有限，持续的研究和发展攻破了所以的疑难问题。

电子测量最大的优势是提高了测量的速度和精度，如果视线是有限的，那么长波或是短波都可以通过水体或是不可能到达的地势而测的，现代EDM距离在仪器上可以以英尺或者米自动显示，并且许多给出的水平和垂直上的数字都已建立在微机上，他们许多重要的合优势已经改变了测量的进程并且得到世界蝗认可，在实践中，使用EDM距离测量使无线电信号变得非常有必要。

EDMIS的分类系统是从传递电子磁能的波长来分类的，可分为： 光学电子仪器，它传递调制的红外线，红外线光在可见光范围内或稍微越出范围外存在。

微波仪器，它传送微波的频率为3000-35000HZ，相当于1.0到2.1mm的波长。

另一种分类按使用范围分的。它是相当主观的，但通常两种方法都适用这种系统：短波和长波。短波范围包括最大测量能力不超过大约5km的装置。这种装置大多是电子光学类型的而且使用红外线，这种仪器很小、轻便、易于操作，适合于广泛的各种野外测量，并且被许多实践者所适用。

中波范围组的测量仪器延伸到100km，并且使用电磁波或者微波。尽管他们经常被用在精确大地测量中，也适用于土木工程和工程测量。更长的波长范围的仪器装置也能精确测量边长超过100km，但是他们不经常用在普通测量工作中，许多仪器的工作是靠传送长无线电波，但是一些是使用短波。他们主要被用在海洋或水路测量中，以及导航中大体上，EDM测量距离是通过比较一条未知长度的边到一条已知边，调制电磁波波长实现的。

这类似于一个需要的距离和测量钢R的校正。

电磁能通过大气依下列方式传播：v=fλ（1）其中v是电磁波的速度，单位是m/s ,f是电磁波的频率，单位是赫兹；λ是波长，单位是米。

使用EDM仪器频率可以被除数精确控制，但是速度是随着大气压力，温度和温度而变化的，这样，波长和频率必须遵从（1）式。为了精确的电子测距仪，大气压必须要按照上述情形测定校正。

EDM的装置，在A点通过铅垂线或光学器中。任选一个带有信号的电磁波，并且已经附加上一个参考频率或是可调制的。信号通过返回接收者，这样它的传播途径是AB距离的两倍。调制电磁波是通过一系列的不确定波长的波来表示的。在绘出的一些位置是通过象限角表示的起点是0o，中是180o，，终点是360o。

EDM装置在测量中，是通过测量相位变化来工作的，在这个过程中，反射波经历了一个360o的相变。即使是正好分割一个测量边的两端为半个边长的倍数，如果距离正好为半个波长的整数倍，则相变为0，AB间相距8个半波长，此时相变为0，当边长不恰好是半个边长的整计算数倍时，通常情况下，通过仪器测量的小数部分为一个非0的相角或相变，如果一个已知精确的波长，小数部分可以转变成距离。

EDM直接能算出非整数波长，但是不能通过反射波的双倍路径计算元波经历的几个周期，这个不确定性被解决了，总之，通过传递低频和长波的附合信号来实现的。