MODERN SURVEYING TECHNIQUES

1. SURVEYING AND GEOMATICS
UNIT-V : Modern Survey Techniques
 Principle of Electronic Distance Measurement,
 Types of EDM instruments,
 Total Station – Parts of a Total Station – Accessories –Advantages and Applications,
 Field Procedure for total station survey,
 Errors in Total Station Survey;
 Global Positioning Systems- Segments,
 GPS measurements, errors and biases, Surveying with GPS

2. Electronic distance measurement (EDM) is a method of determining the length between
two points, using phase changes, that occur as electromagnetic energy waves travels from
one end of the line to the other end.
As a background, there are three methods of measuring distance between two points:
DDM or Direct distance measurement
This is mainly done by chaining or taping.
ODM or Optical distance measurement
This measurement is conducted by tacheometry, horizontal subtense method or telemetric
method. These are carried out with the help of optical attachments.
EDM or Electromagnetic distance measurement
The method of direct distance measurement cannot be implemented in difficult terrains.
When large amount of inconsistency in the terrain or large obstructions exist, this method is
avoided.

3. Types of Electronic Distance Measurement Instrument
EDM instruments are classified based on the type of carrier wave as
i. Microwave instruments
ii. Infrared wave instruments
iii. Light wave instruments.

7. TOTAL STATION

8. Total Station is an equipment used in surveying, designed for measuring horizontal and
vertical angles, inclusive of measuring sloping distance of object to the instrument. It is a
combination of electronic theodolite and electromagnetic distance measuring (EDM)
instrument. It also consists of a micro-processor with a memory unit which deals with
recordings, readings, and the fundamental calculation of measurements.

9. Components of a Total Station
TotalStation is a compact instrument which weighs around 5 kg to 5.5 kg. It consists of a
distance measuring instrument (EDM), an angle measuring instrument (Theodolite) and a
simple microprocessor. The components used in Total station surveying are as follows:
i. A tripod is used to hold the total station
ii. An electronic notebook used to record, calculate and even manipulate the field
data
iii. Prism and prism pole which can measure lengths up to 2 km and up to 5 km can
be measured with triple prism
iv. Battery
Currently there are approximately more than 40 different models available. Total-station
are currently the most used instrument in the surveying field. Leica is one of the most
famous total-station manufacturers.

10. TOTAL STATION TRIPOD AND REFLECTOR PRISM WITH STAND

11. Basic Steps involved in Totalstation surveying
Step-1: Setting up the of the instrument along with the tripod
Step-2: Levelling of the instrument approximately with the help of “bull’s eye bubble”
and then verifying the levelling electronically
Step-3: Adjustment of focus and image.
Step-4: Recording all the measurements
Step-5: Data Processing

12. Functions of Total-Station
Angle Measurement:
To measure horizontal and vertical angles, the electronic theodolite of device is used with
an accuracy of 2-6 seconds. For horizontal measurement of angles, any direction can be
taken as reference. In case of vertical measurement of angles, upward direction is taken as
reference.
Distance Measurement in Total Station:
To measure the distance, Electronic Distance Measuring (EDM) instrument of total station
is used with an accuracy of 5-10 mm per km. The range of EDM varies from 2.8-4.2 km.
Data Processing:
Computation of horizontal distances along with X, Y, Z coordinates is done by the
instrument called Microprocessor. Hence, if atmospheric temperature and pressure is
applied, the microprocessor applies suitable correction to the measurements.

13. Advantages of Total Station
i. The following are some of the major advantages of using total station over the
conventional surveying instruments:
ii. Field work is carried out very fast.
iii. Accuracy of measurement is high.
iv. Manual errors involved in reading and recording are eliminated.
v. Calculation of coordinates is very fast and accurate. Even corrections for temperature
and pressure are automatically made.
vi. Computers can be employed for map making and plotting contour and cross-sections.
Contour intervals and scales can be changed in no time.

14. Applications of Totalstation
i. General purpose of angle and distance measurements.
ii. Plotting of contours
iii. Illustration of detailed maps
iv. Carrying out controlled surveys
v. Archaeologists use total station to record excavations

15. Error in Electronic Distance Measurement Instruments
Personal Errors
Inaccuracy in initial setups of EDMs and the reflectors over the preferred stations
Instrument and reflector measurements going wrong
Atmospheric pressures and temperature determination errors
Instrumental Errors
Calibration errors
Chances of getting maladjusted time to time generating frequent errors
Errors shown by the reflectors
Natural Errors
Atmospheric variations in temperature, pressure as well as humidity. Micro wave EDM
instruments are more susceptible to these.
Multiple refraction of the signals.

16. Capability of a Total Station
Microprocessor unit in total station processes the data collected to compute:
i. Average of multiple angles measured.
ii. Average of multiple distance measured.
iii. Horizontal distance.
iv. Distance between any two points.
v. Elevation of objects and
vi. All the three coordinates of the observed points.
Data collected and processed in a Total Station can be downloaded to computers for further
processing.

17. GPS

18. To understand the GPS surveying process, you need to understand what GPS is.
In short, GPS, or the global positioning system, is a satellite-based navigation
system. GPS was first developed for military use starting in the 1970s and
became fully operational in 1993. Since then, it has expanded its use to
consumer and commercial applications.
GPS uses a network of satellites, which communicate with receivers on the
ground. When a receiver requests data to calculate its location, four or more GPS
satellites will communicate with the receiver, sending the position of the
satellite, the time the data was transmitted and the distance between the
satellite and the receiver. The information collected from these satellites then
calculates the latitude, longitude and height of the receiver. If the receiver is
moving, continuous data collection can be used to calculate the changing
position of the receiver over time, which can be used to calculate speed. No
matter the weather conditions or time, GPS can triangulate the signal and

21. SEGMENTS OF GPS
1. Space Segment
The GPS constellation consists of 24 satellites arranged in 6 orbital
planes of 55- degree inclination, 20,051 kilometers (12,532 miles)
above the Earth. Each satellite completes one orbit in one-half of a
sidereal day and, therefore, passes over the same location on earth
once every sidereal day, approximately 23 hours and 56 minutes. With
this orbital configuration and number of satellites, a user at any
location on Earth will have at least four satellites in view 24 hours per
day

22. 2. Operational Control Segment
The GPS OCS consists of the master control station (MCS), located at
Falcon Air Force Base in Colorado Springs, Colorado; remote monitoring
stations, located in Hawaii, Diego Garcia, Ascension Island, and
Kwajalein; and uplink antennas, located at three of the four remote
monitor stations and at the MCS. The four remote monitor stations
contribute to satellite control by tracking each GPS satellite in orbit,
monitoring its navigational signal, and relaying this information to the
MCS. The four stations can track and monitor the whereabouts of each
GPS satellite 20 to 21 hours per day. Land-based and space-based
communications connect the remote monitoring stations with the MCS.

23. 3. User Equipment
GPS user equipment varies widely in cost and complexity, depending on the
receiver design and application. Receiver sets, which currently vary in price from
approximately $135 or less to $30,000, can range from fairly simple devices that
provide only basic positioning information to complex multichannel units that track
all satellites in view and perform a variety of functions.
Most GPS receivers consist of three basic components:
(1) an antenna, which receives the signal and, in some cases, has anti-jamming
capabilities;
(2) a receiver-processor unit, which converts the radio signal to a useable
navigation solution; and
(3) a control/display unit, which displays the positioning information and provides
an interface for receiver control.