Modern Systems In Surveying

 

Modern Systems In Surveying

Modern surveying instruments provides faster and more precise surveying than conventional instruments. In conventional surveying, chain and tape are used for making linear measurements while compass and ordinary theodolites are used for making angular measurements. Levelling work is carried out using a dumpy level and a levelling staff with such surveying instruments, survey work will be slow.

Hence modern surveying instruments are becoming more popular and they are gradually replacing old surveying instruments such as compass and dumpy level. With modern surveying instruments, survey work will be precise & faster

Some of the modern surveying instruments are

1.     Electronic distance measurements (EDM)

2.     Infra-red instruments / Light wave instruments

3.     Micro wave instruments

4.     Digital Theodolite

5.     Total Station

6.     Digital Level

7.     Global positioning System (GPS)

1.Electronic Distance Measurement (EDM):

·       Direct measurement of distances and their directions can be obtained by using electronic instruments that rely on propagation, reflection and reception of either light waves (or) radio waves.

·       They are classified as

a.      Infrared wave instruments

b.     Light wave instruments

c.      Microwave instruments

2.Infra Red Instruments / Light Wave Instruments:

     Infrared Wave Instruments:

·       These instruments measure distances by using amplitude modulated infrared waves.

·       At the end of line, prisms mounted on target are used to reflect the waves.

·       These instruments are lite and economical .

·       The range of such an instrument will be 3 km and the accuracy achieved is +/- 10mm.

·       It is a very small, compact edm, particularly useful in building construction and other civil engineering works, where distance measurements are less than 500mm.

·       It is an EDM that makes to reduce the usage of tape.

·       To measure the distance, one has to simply point the instrument to the reflector ,touch  a key and read the result. 

 

Light Wave Instruments:

·       These are instruments which measures distances based on propagation of modulated light waves.

·       The accuracy of such an instrument varies from 0.5 to 5mm/km distance and has a range of nearly 3 km.

Example: Geode meter

Geode Meter:

·       Geode meter is an instrument which works based on the propagation of modulated light waves.

·       He instrument is more suitable for night time observations and requires a prism system at the end of the line for reflecting the waves.

3. Microwave Instruments:

·       These instruments make use of high frequency radio waves

·       These instruments were invented as early as 1950 in south Africa by Dr.T.L.Wadely.

·       The range of these instruments is up to 100 km and can be used both during day and night

Example: Telluro meter

Telluro Meter:

·       It is an EDM instrument which uses high frequency radio waves (micro waves) for measuring distances.

·       It is highly probable instrument and can be worked with 12 to 24volt battery.

·       For measuring distance two (2) tellurometers are required one to be stationed at each end of the line with two highly skilled persons to take observations.

·       One instrument is used as a master unit and the other as a remote unit.

·       Just by pressing a button a master can be converted in to remote unit and vice versa.

·       A speech facility (communication facility) is provided to each operator to interact during measurement.

4. Digital Theodolite:

·       There are two different kinds of theodolites

Ø  Digital Theodolites.

Ø  Non-digital Theodolites

·       Non-digital Theodolites are rarely used any more

·       Digital theodolites consist of a telescope that is mounted on a base, as well as an electronic read out screen that is used to display horizontal and vertical angles.

·       Digital theodolites are convenient because the digital readings take the place of traditional graduated circles and this creates more accurate readings.

5. Total Station:

·       Total station is a lite weight, compact and fully integrated electronic instrument combining the capacity of an EDM and an angular measuring instrument such as wild theodolite.

·       Total station can perform the following functions.

a.      Distance Measurement

b.     Angular Measurement

c.      Data Processing

d.     Digital display of point details

e.      Storing data is an electronic field book

The important features of Total Station are.

a.Key Board Control:

 All the functions are controlled by operating key board.

b.Digital Pannel:

The panel displays the values of distance, angles, height, and the co-ordinates of the observed point ,where the reflector ( Target) is kept.

c.Remote Height Object:

The heights of some inaccessible objects such as towers can be read directly. The microprocessor provided in the instrument applies the correction for earths curvature and mean refraction automatically.

d.Traversing Program:

The coordinates of the reflector and the angle (or) bearing on the reflector can be stored and can be recalled for next set up of instrument. Setting out for distance direction and height whenever a particular direction and horizontal distance is to be entered for the purpose of locating the point on the ground using a target, then the instrument displays the angle through which the theodolite has to be turned.

6 Digital Level

Digital levels use electronic image processing to evaluate the special bar-coded staff reading, this bar-coded pattern is converted into elevation and distance values using a digital image matching procedure within the instrument.

Automatic Level:

An automatic level is a special levelling instrument used in surveying which contains an optical compensator which maintains line of sight (or) line of collimation even though instrument is slightly tilted.

7. Global Positioning System (GPS):

·       Global positioning system (GPS) is developed by U.S Defense department and is called Navigational system with time and ranging global positioning system (NAVSTAR GPS) (or) simply GPS.

·       For this purpose U.S. Air Force has stationed 24 satellites at an altitude of 20,200 km above the earths surface.

·       The Satellites have been positioned in such a way at least four  (4 ) satellites will be visible from any point on earth.

·       The user needs a GPS receiver to locate the position of any point on ground. The receive process the signals received from the satellite and compute the position (latitude and longitude) and elevation of a point with reference to datum.