SURVEYING METHODS

                                 

PAPER ON  
 SURVEYING METHODS

                      

                                                                                        

                                                                                                                                            

  

                               

           PRESENTED BY,

                          K.E.K.RAVI

                   

CONTENTS

Ø  INTRODUCTION

Ø  SURVEYING METHODS

Ø  DISTANCE MEASUREMENT DEVICES

Ø  ELEVATON DIFFERENCES IN LEVELLING

Ø  ADVANCED SURVEYING

Ø  HISTORY OF GPS

Ø  APPLICATION OF GPS

Ø  TRACING SYSTEM

Ø  NAVIGATION SYSTEM

Ø  TOTAL STATION

Ø  CO-ORDINATE MEASUREMENT

Ø  ANGLE MEASUREMENT

Ø  DISTANCE MEASUREMENT

Ø  DATA PROCESSING

Ø  APPLICATION OF TOTAL STATION

Ø  MINING  

Ø  CONCULSION         

introduction

                Surveying, a means of making relatively large-scale, accurate measurements of the Earth’s surfaces. It includes the determination of the measurement data, the reduction and interpretation of the data to usable form, and, conversely, the establishment of relative position and size according to given measurement requirements. Thus, surveying has two similar but opposite functions:  the determination of existing relative horizontal and vertical position, such as that used for the process of mapping, and the establishment of marks to control construction or to indicate land boundaries. The measurement ofy dimensional relationships among points, lines, and physical features on or near the Earth's surface. Basically, surveying determines horizontal distances, elevation differences, directions, and angles. These basic determinations are applied further to the computation of areas and volumes and to the establishment of locations with respect to some coordinate system. Surveying is typically used to locate and measure property lines; to lay out buildings, bridges, channels, highways, sewers, and pipelines for construction; to locate stations for launching and tracking satellites; and to obtain topographic information for mapping and charting. Horizontal distances are usually assumed to be parallel to a common plane. Each measurement has both length and direction. Length is expressed in feet or in meters. Direction is expressed as a bearing of the azimuthal angle relationship to a reference meridian, which is the north-south direction. It can be the true meridian, a grid meridian, or some other assumed meridian. The degree-minute-second system of angular expression is standard in the United States.

Aerial surveying

                 Aviation and photography have revolutionized detailed mapping of features visible from the air. An aerial photograph, however, is not a map. In the case of the House of Parliament and Westminster Bridge, London, for example, the tops of the towers would coincide with the corners of the foundations when mapped. In an aerial photograph, however, they would not, being displaced radially from the centre. An important property of vertical aerial photography is that angles are correctly represented at their centres, but only there. Similar distortions are present in photographs of hilly ground.

Detail surveying

                The actual depiction of the features to be shown on the map can be performed either on the ground or, since the invention of photography, aviation, and rocketry, by interpretation of aerial photographs and satellite images. On the ground the framework is dissected into even smaller areas as the surveyor moves from one point to another, fixing further points on the features from each position by combinations of angle and distance measurement and finally sketching the features between them freehand.

 

Gravity method

            The gravity field of the Earth can be measured by timing the free fall of an object in a vacuum, by measuring the period of a pendulum, or in various other ways. Today almost all gravity surveying is done with gravimeters. Such an instrument typically consists of a weight attached to a spring that stretches or contracts corresponding to an increase or decrease in gravity. It is designed to measure differences in gravity accelerations rather than absolute magnitudes.

Seismographic methods

                  The survey methods described above can show the presence of large geologic anomalies such as anticlines (arch-shaped folds in subterranean layers of rock), fault blocks (sections of rock layers separated by a fracture or break), and salt domes, even though there may not be surface indications of their presence. However, they cannot be relied upon to find smaller and less obvious traps and unconformities in the stratigraphic arrangement of rock layers that may harbour petroleum reservoirs. These can be detected and located by seismic surveying, which makes use of the sound-transmitting and sound-reflecting properties of underground rock formations

            

 

Magnetic methods

             Measurements can be made of the Earth’s total magnetic field or of components of the field in various directions. The oldest magnetic prospecting instrument is the magnetic compass, which measures the field direction. Other instruments include magnetic balances and fluxgate magnetometers. Most magnetic surveys are made with precession or optical-pumping magnetometers, which are appreciably more accurate. The proton magnetometer measures a radio-frequency voltage induced in a coil by the reorientation (precession) of magnetically polarized protons in a container of ordinary water. The optical-pumping magnetometer makes use of the principles of nuclear resonance and cesium or rubidium vapour.

Distance measurement

Traverse distances are usually measured with a surveyor's tape or by EDM, but also may sometimes be measured by stadia, sub tense, or trig-traverse. Whether on sloping or level ground, it is horizontal distances that must be measured. In taping, horizontal components of hillside distances are measured by raising the downhill end of the tape to the level of the uphill end. On steep ground this technique is used with shorter sections of the tape. The raised end is positioned over the ground point with the aid of a plumb bob. Where slope distances are taped along the ground, the slope angle can be measured with the clinometers. The desired horizontal distance can then be computed. In EDM the time a signal requires to travel from an emitter to a receiver or reflector and back to the sender is converted to a distance readout. The great advantage of electronic distance measuring is its unprecedented precision, speed, and convenience. Further, if mounted directly onto a theodolite, and especially if incorporated into it and electronically coupled to it, the EDM instrument with an internal computer can in seconds measure distance (even slope distance) and direction, then compute the coordinates of the sighted point with all the accuracy required for high-order surveying. In the stadia technique, a graduated stadia rod is held upright on a point and sighted through a transit telescope set up over another point. The distance between the two points is determined from the length of rod intercepted between two horizontal wires in the telescope.

In the subtense technique the transit angle subtended by a horizontal bar of fixed length enables computation of the transit-to-bar distance. In trig-traverse the subtense bar is replaced by a measured baseline extending at a right angle from the survey line whose distance is desired. The distance calculated in either subtense or trig-traverse is automatically the horizontal distance and needs no correction.

Elevation differences

                            Elevations may be measured trigonometrically in conjunction with reduction of slope measurements to horizontal distances, but the resulting elevation differences are of low precision. Most third-order and all second- and first-order measurements are made by differential leveling, wherein a horizontal line of sight of known elevation is sighted on a graduated rod held vertically on the point being checked ( Fig. 2). The transit telescope, leveled, may establish the sight line, but more often a specialized leveling instrument is used. For approximate results a hand level may be used.

                                 Theory of differential leveling.

             Other methods of measuring elevation include trigonometric leveling which involves calculating height from measurements of horizontal, distance and vertical angle; barometric leveling, a method of determining approximate elevation difference with aid of a barometer; and airborne profiling, in which a radar altimeter on an aircraft is used to obtain ground elevations.

ADVANCED SURVEYING

Advanced surveying is nothing but the manner of inducing a precision in the surveying methods by the which one easily save a lot of time and at the same time a lot of manpower is saved and also money too is saved in the long term run which saves a lot of money in terms of salary given for the employers in the surveying during leveling where a lot of workers are needed for the work. So the advanced surveying makes a lot of changes in the surveying field in fact a dramatic change. The instruments used in the advanced surveying are as follows

1.     GLOBAL POSITIONG SYSTEM

2.     GEOGRAPHICAL INFORMATION SYSTEM

3.      TOTAL STATION

History of gps

                        The design of GPS is based partly on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. In 1956, Friedwardt Winterberg proposed a test of general relativity (for time slowing in a strong gravitational field) using accurate atomic clocks placed in orbit inside artificial satellites. (To achieve accuracy requirements, GPS uses principles of general relativity to correct the satellites' atomic clocks.^[4]) Additional inspiration for GPS came when the Union launched the first man-made satellite, Sputnik in 1957. Two American physicists, William Guier and George Weiffenbach, at Johns Hopkins's Applied Physics Laboratory (APL), decided on their own to monitor Sputnik's radio transmissions. They soon realized that, because of the Doppler, they could pinpoint where the satellite was along its orbit from the Doppler shift. The Director of the APL gave them access to their brand new UNIVAC II to do the heavy calculations required. When they released the orbit of Sputnik to the media the Russians were dumbfounded to learn how powerful American computers had become, as they would not have been able to calculate the orbit themselves. The following spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to look at the inverse problem where you know the location of the satellite and you want to find your own location. (The Navy was developing the submarine launched Polaris missile, which required them to know the submarine's location.) This led them and APL to develop the Transit system.^[5]

The first satellite navigation system, Transit (satellite), used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timationsatellite that proved the ability to place accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy.

While there were wide needs for accurate navigation in military and civilian sectors, almost none of those were seen as justification for the billions of dollars it would cost in research, development, deployment, and operation for a constellation of navigation satellites. During the Cold arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded. It is also the reason for the ultra secrecy at that time. The triad consisted of the United States Navy's submarine-launched ballistic missiles (SLBMs) along with United (USAF) strategic bombers and intercontinental ballistic missiles (ICBMs). Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier.

Precise navigation would enable United States submarines to get an accurate fix of their positions prior to launching their SLBMs. The USAF with two-thirds of the nuclear triad also had requirements for a more accurate and reliable navigation system. The Navy and Air Force were developing their own technologies in parallel to solve what was essentially the same problem. To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms (such as Russian SS-24 and SS-25) and so the need to fix the launch position had similarity to the SLBM situation. In 1960, the Air Force proposed a radio-navigation system called MOSAIC (Mobile System for Accurate ICBM Control) that was essentially a 3-D LORAN. A follow-on study called Project 57 was worked in 1963 and it was "in this study that the GPS concept was born."That same year the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS and promised increased accuracy for Air Force bombers as well as ICBMs. Updates from the Navy Transit system were too slow for the high speeds of Air Force operation. The Navy Research Laboratory continued advancements with their Timation (Time Navigation) satellites, first launched in 1967, and with the third one in 1974 carrying the first atomic clock into orbit. With these parallel developments in the 1960s, it was realized that a superior system could be developed by synthesizing the best technologies from 621B, Transit, Timation, and SECOR in a multi-service program.

Application of gps

Tracking Devices

One of the easiest applications to consider is the simple GPS tracking device; which combines the possibility to locate itself with associated technologies such as radio transmission and telephony. Tracking is useful because it enables a central point to monitor the position of several vehicles or people, in real time, without them needing to relay that information explicitly. This can include children, criminals, police and emergency vehicles or military applications. The tracing devices themselves come in various different flavors. They will always contain a GPS receiver, and some GPS software, along with some way of transmitting the resulting coordinates. GPS watches, for example, tend to use radio waves to transmit their location to a tracking center, while GPS phones use existing cell phone technology. The tracking center can then use that information for co-ordination or alert services. One application in the field is to allow anxious parents to locate their children by calling the tracking station – mainly for their peace of mind.

GPS vehicle tracking is also used to locate stolen cars, or provide services to the driver such as locating the nearest gas station. Police can also benefit from using GPS tracing devices to ensure that parolees do not violate curfew, and to locate them if they do.

Navigation Systems

Once we know our location, we can, of course, find out where we are on a map, and GPS mapping and navigation is perhaps the most well-known of all the applications of GPS. Using the GPS coordinates, appropriate software can perform all manner of tasks, from locating the unit, to finding a route from A to B, or dynamically selecting the best route in real time. These systems need to work with map data, which does not form part of the GPS system, but is one of the associated technologies that we spoke of in the introduction to this article. The availability of high powered computers in small, portable packages has lead to a variety of solutions which combines maps with location information to enable the user to navigate The first such application was the car navigation system, which allows drivers to receive navigation instructions without taking their eyes off the road, via voice commands. Usually, these systems take their map data from a CD which can be replaced when the driver moves from one geographical location to another. Then there are handheld GPS units, such as those from Garmin, which are commonly used by those involved in outdoor pursuits, and only relay very limited information such as the location, and possibly store GPS waypoints. A waypoint being a location that is kept in memory so that the unit can retrace the path at a later time.More advanced versions include aviation GPS systems, which offer specific features for those flying aircraft, and marine GPS systems which offer information pertaining to marine channels, and tide times. These last two require maps and mapping software which differ vastly from traditional GPS solutions, and as such can often be augmented with other packages designed to allow the user to import paper maps or charts. The map source software is one such industry standard package. There are even GPS solutions for use on the golf course. Golf GPS systems help the player to calculate the distance from the tee to the pin, or to know exactly where they are with relation to features such as hidden bunkers, water hazards or greens. Again, specific maps are needed for such applications.

Total station

               A total station is an electronic/optical instrument used in modern surveying. The total station is an electronic theodolite (transit) integrated with an electronic distance meter (EDM) to read slope distances from the instrument to a particular point. Robotic total stations allow the operator to control the instrument from a distance via remote control. This eliminates the need for an assistant staff member as the operator holds the reflector and controls the total station from the observed point.

         

Coordinate Measurement

Coordinates of an unknown point relative to a known coordinate can be determined using the total station as long as a direct line of sight can be established between the two points. Angles and distances are measured from the total station to points under survey, and the coordinates (X, Y, and Z or northing, easting and elevation) of surveyed points relative to the total station position are calculated using trigonometry and triangulation. To determine an absolute location a Total Station requires line of sight observations and must be set up over a known point or with line of sight to 2 or more points with known location. For this reason, some total stations also have a Global Navigation Satellite System interface which do not require a direct line of sight to determine coordinates. However, GNSS measurements may require longer occupation periods and offer relatively poor accuracy in the vertical axis.

Angle measurement

Most modern total station instruments measure angles by means of electro-optical scanning of extremely precise digital bar-codes etched on rotating glass cylinders or discs within the instrument. The best quality total stations are capable of measuring angles to 0.5 arc-second. Inexpensive "construction grade" total stations can generally measure angles to 5 or 10 arc-second

Distance Measurement

Measurement of distance is accomplished with modulated microwave or infrared carrier signal, generated by a small solid-state emitter within the instrument's optical path, and reflected by a prism reflector or the object under survey. The modulation pattern in the returning signal is read and interpreted by the computer in the total station. The distance is determined by emitting and receiving multiple frequencies, and determining the integer number of wavelengths to the target for each frequency. Most total stations use purpose-built glass corner cube prism reflectors for the EDM signal. A typical total station can measure distances with an accuracy of about 1.5 millimeters (0.0049 ft) + 2 parts per million over a distance of up to 1,500 meters (4,900 ft).        Reflector less total stations can measure distances to any object that is reasonably light in color, to a few hundred meters.

 

Data processing

Some models include internal electronic data storage to record distance, horizontal angle, and vertical angle measured, while other models are equipped to write these measurements to an external data collector, such as a hand-held computer. When data is downloaded from a total station onto a computer, application software can be used to compute results and generate a map of the surveyed area.

Total station Applications

Total stations are mainly used by land surveyors and Civil Engineers. Either to record features as in Topographic Surveying or to set out features (such as roads, houses or boundaries). They are also used by archaeologists to record excavations and by police, crime scene investigators, private accident Reconstructionists and insurance companies to take measurements of scenes.

Mining

Total stations are the primary survey instrument used in mining surveying. A total station is used to record the absolute location of the tunnel walls (stopes), ceilings (backs), and floors as the drifts of an underground mine are driven. The recorded data is then downloaded into a CAD program, and compared to the designed layout of the tunnel. The survey party installs control stations at regular intervals. These are small steel plugs installed in pairs in holes drilled into walls or the back. For wall stations, two plugs are installed in opposite walls, forming a line perpendicular to the drift. For back stations, two plugs are installed in the back, forming a line parallel to the drift. A set of plugs can be used to locate the total station set up in a drift or tunnel by processing measurements to the plugs by intersection and resection.

CONCULSION

           By this abstract I submit a general report over the   surveying for which we have collecetd a lot of information over surveying techniques. This is very usefull for us.  Surveying Techniques Is Going To Be Future In The Civil Engineering.