Modern surveying instruments provides faster and more precise surveying than conventional instruments. Their types and uses are discussed in this article.
In conventional surveying, chain and tape are used for making linear measurements while compass and ordinary theodolites are used for making angular measurements. Leveling work is carried out using a Dumpy level and a leveling staff. With such surveying instruments, survey work will be slow and tedious.
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 and less tedious. Some of the modern surveying instruments are discussed in this article.
Modern Surveying Instruments and Their Uses
Following are the modern surveying instruments which are used for surveying:
- Electronic Distance Measurement (EDM) Instruments
- Total Station
- Global Positioning System (GPS)
- Automatic Level
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 may be broadly classified into three types:
a. Infrared wave instruments
b. Light wave instruments
c. Microwave instruments
a. Infrared Wave Instruments
These instruments measure distances by using amplitude modulated infrared waves. At the end of the line, prisms mounted on target are used to reflect the waves. These instruments are light and economical and can be mounted on theodolites for angular measurements. The range of such an instrument will be 3 km and the accuracy achieved is ± 10 mm.
E.g. DISTOMAT DI 1000 and DISTOMAT DI 5
DISTOMAT DI 1000
It is a very small, compact EDM, particularly useful in building construction and other Civil Engineering works, where distance measurements are less than 500 m. It is an EDM that makes the meaning tape redundant. To measure the distance, one has to simply point the instrument to the reflector, touch a key and read the result.
b. Light Wave Instruments
These are the instruments which measures distances based on propagation of modulated light waves. The accuracy of such an instrument varies from 0.5 to 5 mm / km distance and has a range of nearly 3 km.
Geodimeter is an instrument which works based on the propagation of modulated light waves, was developed by E. Bergestand of the Swedish Geological Survey in collaboration with the manufacturer M/s AGA of Swedish. The instrument is more suitable for night time observations and requires a prism system at the end of the line for reflecting the waves.
c. 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. Wadley. The range of these instruments is up to 100 km and can be used both during day and might.
It is an EDM which uses high frequency radio waves (micro-waves) for measuring distances. It is a highly portable instrument and can be worked with 12 to 24-volt battery.
For measuring distance, two 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 into remote unit and vice-versa. A speech facility (communication facility) is provided to each operator to interact during measurement.
Total Station is a lightweight, compact and fully integrated electronic instrument combining the capability of an EDM and an angular measuring instrument such as wild theodolite.
Total Station can perform the following functions:
- Distance measurement
- Angular measurement
- Data processing
- Digital display of point details
- Storing data is an electronic field book
The important features of total station are,
- Keyboard-control – all the functions are controlled by operating key board.
- Digital panel – the panel displays the values of distance, angle, height and the coordinates of the observed point, where the reflector (target) is kept.
- 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 earth’s curvature and mean refraction, automatically.
- 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 and the distance by which the reflector should move.
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 20200 km above the earth’s surface. The satellites have been positioned in such a way, at least four 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 processes the signals received from the satellite and compute the position (latitude and longitude) and elevation of a point with reference to datum.
An automatic level is a special leveling instrument used in surveying which contains an optical compensator which maintains line of sight or line of collimation even though instrument is slightly tilted.
E.g.: Wild NAK2 Automatic level