Module 5

• Global Positioning Systems-Components and principles, satellite

ranging-calculating position, signal structure, application of GPS,
GPS Surveying methods-Static, Rapid static, Kinematic methods –
DGPS

• Remote Sensing : Definition- Electromagnetic spectrum-Energy

interactions with atmosphere and earth surface features-spectral
reflectance of vegetation, soil and water- Classification of
sensorsActive and Passive, Resolution-spatial, spectral radiometric
and Temporal resolution, Multi spectral scanning-Along track and
across track scanning

• Geographical Information System - components of GIS, GIS

operations, Map projectionsmethods, Coordinate systems-
Geographic and Projected coordinate systems, Data Types- Spatial
and attribute data, Raster and vector data representation
GPS SURVEYING
Where on earth am I ?
Global Positioning System (GPS)
• Global Positioning System or GPS is a Global Navigation Satellite
System (GNSS) that provides positioning, navigation, and timing
system (PNT).

• The GPS can provide accurate measurements of the latitude,

longitude and elevation of a survey point by means of geometric
trilateration (a method for determining the intersections of three
sphere surfaces given their centres and radii) of
a constellation of geostationary satellites
• Global Positioning System or GPS or GNSS was developed by the
United States’ Department of Defense (U.S. DoD) in the early 1970s.
• Before the development of GPS Technology, the main
aid for navigation (in sea, land or water) are maps and
compass.

• With the introduction of GPS, the navigation and

location positioning became very easy with a position
accuracy of two meters or less.
• GPS is the shortened form of NAVSTAR

• NAVSTAR - acronym for NAVigation System with Time

And Ranging Global Positioning System.
• Using a GNSS system the following values can
accurately be determined anywhere on the globe.

➢ Exact position (longitude, latitude and altitude co-

ordinates) accurate to within 20 m to approximately
1 mm.
➢Exact time (Universal Time Coordinated, UTC)
accurate to within 60ns to approximately 0. 5ns
GNSS
Current global navigation systems
• GPS - US
• GLONASS - RUSSIA
• COMPASS - CHINA
• DORIS - FRANCE
• Galileo – EUROPE
• IRNSS – Indian Regional Navigation Satellite
System
• QZSS - JAPAN
• United States’ Global Positioning System (GPS) and
Russian Global Navigation Satellite System (GLONASS)
are the fully functional Satellite based Navigation
system with 32 satellite constellation and 27 satellite
constellation respectively.
Components of a GPS

• Space Segment – All Operational satellites

• Control Segment – All ground stations involved in the

monitoring of the system : Master Control Stations,
Monitor Stations & Ground Control Stations

• User Segment – All civilian and military users

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• The fundamental technique of the satellite based navigation system
Global Positioning System (GPS) is to measure the distances
between the receiver and a few satellites that are simultaneously
observed.

• The positions of these satellites are already known and hence by

measuring the distance between four of these satellites and the
receiver, the three coordinates of the GPS receiver’s position i.e.
latitude, longitude and altitude can be established.

• Since the change in position of the receiver can be determined very

accurately, the velocity of the receiver can also be determined.
 GPS
• GPS-United States' Global Positioning System (GPS), is
the fully functional, fully available global navigation
satellite system.

• 32 medium Earth orbit satellites in six different orbital

planes, with the exact number of satellites varying as
older satellites are retired and replaced.

• Operational since 1978 and globally available since

1994, GPS is currently the world's most utilized
satellite navigation system.
13
Advantages of GPS
• Relatively high positioning accuracies
• Capability of determining velocity and time
• Signal availability to users
• No user charges and low cost hardware
• All–weather system
• Three dimensions

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Components of a GPS

• Space Segment – All Operational satellites

• Control Segment – All ground stations involved in the

monitoring of the system : Master Control Stations,
Monitor Stations & Ground Control Stations

• User Segment – All civilian and military users

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Three GNSS Segments

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Components of a GPS

• Space Segment – All Operational satellites

• Control Segment – All ground stations involved in the

monitoring of the system : Master Control Stations,
Monitor Stations & Ground Control Stations

• User Segment – All civilian and military users

1
Three GNSS Segments

2
 Space Segment
• Consists of upto 32 operational satellites orbiting the
earth

• They orbit at a height of 20,180 km above the Earth’s

surface and are inclined at 55° to the equator.

• Any one satellite completes its orbit in around 12 hours

• Due to the rotation of the Earth, a satellite will be its

initial starting position above the earth’s surface after
approx. 24 hours(23 hours 56 minutes)

3
GPS satellites orbiting the earth in 6 orbital planes
4
Basic Functions of the Space Segment
• To receive and store data transmitted from control segment stations
• To maintain accurate time by means of several on-board atomic
clocks
• To transmit information and radio signals to users on two L- band
frequencies
• To maintain a stable platform and orbit for the L- band transmitters

5
Signals from GPS Satellites
• Each GPS Satellite transmit signals – L1 & L2 of 2 different frequencies
• L1 carrier
19 cm wavelength
1227 MHz frequency
• L2 carrier
24 cm wavelength
1775 MHz

6
Signals from GPS Satellites
• GPS codes :

Following are the two types of GPS codes.

1. Coarse / Acquisition Code (C/A Code ) used by public
2. Precise Code ( P- Code) used in military positioning systems
C/A Code – Rougher Positioning

Generally P Code is transmitted in an encrypted format and it is called

Y code.
- unusable by civilians with one receiver but is usable when
performing differential corrections between 2 or more receivers;
used by military

7
• The P code gives better measurement accuracy when compared to
C/A code, since the bit rate of P code is greater than the bit rate of
C/A code.
GPS Message
• Continuous stream of data transmitted at 50 bits per sec
ond.
Each satellite relays the following information to Earth:

▪ System time and clock correction values

▪ Its own highly accurate orbital data (ephemeris)
▪ Approximate orbital data for all other satellites (al
manac)
▪ System health, etc.
▪ The navigation message is needed to calculate the cur
rent position of the satellites and to determine signal
travel times.

9
 The Control Segment
Functions of the Control Segment

• Observing the movement of the satellites and computi

ng orbital data (ephemeris)
• Monitoring the satellite clocks and predicting their b
ehavior
• Synchronizing onboard satellite time
• Relaying precise orbital data received from satellites

10
• Relaying the approximate orbital data of all satellit
es (almanac)
• Relaying further information, including satellite health,
clock errors etc.
• Oversees the artificial distortion of signals (SA, Selectiv
e Availability), in order to degrade the system’s positi
onal accuracy for civil use.

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Ground Control Stations

(1) Schriever Air Force Base

(2) Hawaii
(3) Cape Canaveral
(4) Ascension Island
(5) Deigo Garcia
(6) Kwajalein.
12
The User Segment
• GPS receivers used to receive the GPS signal for
determination of position and time.
• Consists of an antenna and preamplifier, radio signal
microprocessor, control and display device, data
recording unit and power supply
• Decodes the timing signals from the ‘visible’ satellites
and having calculated their distances, computes its
own latitude, longitude, elevation and time.

13
User Segment

14
Levels of Accuracy
• Working Mode Accuracy

• Autonomous 15-100 metres

• Differential GPS 0.5- 5m
• Real Time Kinematic Float 20 cm – 1m
• Real Time Kinematic Fixed 1cm – 5 cm

15
GPS Receivers
• The basic split of receivers is based on the number of satellites the
receiver can track at a time.
• Each tracked satellite requires a channel.
• Receivers usually have between one and twelve channels.

16
GPS Receivers
• Since four satellites are required for an accurate
position, any receiver with less than four channels
must necessarily be a sequencing receiver.
• A sequencing receiver tracks one satellite, drops that
one and goes to the next in sequence, and so on until
at least four satellites have been tracked.
• The whole process then begins again.

17
GPS Receivers
• Single-channel receivers are the cheapest and smallest.
• Two-channel receivers process the signal from one satellite while
tracking the next satellite.
• Receivers with four or more channels are continuous receivers. Each
channel tracks one satellite. No gaps or delays in tracking occur.

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GPS Receivers
• Six channels are better than four, since another satellite or two is a
benefit, but eight channels is a only a small step better than six.
• Five or six satellites within easy "viewing" distance are common.
• The seventh and eighth satellites are further afield and require a
larger antenna to capture.

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GPS Receivers
• Obstructions low on the horizon may block the farthest satellites and
negate the advantage of eight or more channels.

• Ten- and 12-channel receivers are usually reserved for benchmark

locations and other activities requiring similar accuracy

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Principle of measuring signal transit time
• One calculates position by establishing the distance relative to
reference satellites with a known position.

• The distance is calculated from the travel time of radio waves

transmitted from the satellites.

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Basic Principles of Satellite Navigation
• Satellites with a known position transmit a regular
time signal.

• Based on the measured travel time of the radio waves

(electromagnetic signals travel through space at the
speed of light c = 3,00,000km/s) the position of the
receiver is calculated.

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Basic Principles of Satellite Navigation

The distance D is calculated by multiplying the travel time by ΔT by

velocity of light c.
D= ΔT × c
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Basic Principles of Satellite Navigation

24
Basic Principles of Satellite Navigation

Satellite Navigation Systems use satellites as time signal transmitters.

Contact to at least four satellites is necessary in order to determine the three
desired coordinates (Longitude, Latitude, Altitude) as well as the exact time.
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Signals from GPS Satellites
Satellite signal structure consists of 3 components:

1. Carrier Wave:
• Each GPS Satellite transmit signals – L1 & L2 of 2 different
frequencies
• L1 carrier
19 cm wavelength
1227 MHz frequency
• L2 carrier
24 cm wavelength
1775 MHz
1
2. Ranging codes or pseudo-Random codes( GPS codes) :

Following are the two types of GPS codes.

1. Coarse / Acquisition Code (C/A Code ) used by public
2. Precise Code ( P- Code) used in military positioning systems
C/A Code – Rougher Positioning

Generally P Code is transmitted in an encrypted format and it is

called Y code.
- unusable by civilians with one receiver but is usable when
performing differential corrections between 2 or more
receivers; used by military

2
• The P code gives better measurement accuracy when
compared to C/A code, since the bit rate of P code is
greater than the bit rate of C/A code.

3. Navigation Codes:
• This contains the satellite orbital position ephemeris data
and clock information, general system status messages,
satellite health status, satellite clock corrections,
ionospheric and atmospheric data.
• The Navigation codes have a low frequency of 50 MHz and
are modulated over both L1 and L2 Carrier.
• It communicates the data in a message called “Navigation
Message” or “GPS message”.
GPS Message
• Continuous stream of data transmitted at 50 bits per sec
ond.
Each satellite relays the following information to Earth:

▪ System time and clock correction values

▪ Its own highly accurate orbital data (ephemeris)
▪ Approximate orbital data for all other satellites (al
manac)
▪ System health, etc.
▪ The navigation message is needed to calculate the cur
rent position of the satellites and to determine signal
travel times.

4
Working principle of GPS
• GPS works on the principle of trilateration.
• Determining absolute or relative location of points based on the distance to at-
least 3 known positions.

Satellite ranging

• If the distance of a satellite from a GPS receiver on earth is determined, then it

can be known that the position of the receiver must be at some point on the
surface of an imaginary sphere of radius equal to that distance and with the
satellite as center.
• By intersecting 3 such imaginary spheres, the receiver position can be
determined accurately
Determining position

6
Determining position

The position is determined at the point where all three spheres

intersect 7
• In-order to calculate the distance to each satellite the following
equation is used. ie, Distance = velocity x time

• The GPS signal travel with a velocity approximately equal to that of

light (3 x 10^8 m/s).
• The time is the time taken by the radio signal to travel from satellite
to the GPS receiver.
• The distance of satellite from the GPS receiver calculated using the
above equation is called as the “Satellite range”.
• The satellite range can be measured by:
1. Code phase measurements
2. Carrier phase measurements
1. CODE PHASE MEASUREMENTS

• A GPS signal consists of codes and carriers. When the codes are used
to measure the distance between the satellite and receiver (satellite
range), it is called code phase measurements.
• When a pseudorandom code generated by a satellite reaches a
receiver, it generates the same code and tries to match it with the
satellite code.
• The receiver then compares the two signal to determine how much
delay (shift) is required in its code to match the satellite code.
• This delay time (shift) when multiplied with the velocity of signal
(velocity = velocity of light) will gives the distance between satellite
and receiver.
• This distance is called satellite range or pseudo range or code phase
measurements
2. CARRIER PHASE MEASUREMENTS
• It is the measurements of distance between satellite and
receiver expressed in units of cycles of the carrier waves.
• Suppose a GPS signal is transmitted from satellite. When a GPS
receiver locks on to that signal, it records the carrier phase
signal and measures the fraction of wave length after the lock
on.
Comparison between code phase and carrier phase
measurements
code phase measurements carrier phase measurements

Uses the codes in the signal to determine Uses the carrier waves in the signal to
the satellite range determine the distance between satellite
and receiver
Data is noisy More precise
No problem of ambiguity Primary drawback is its range ambiguity
Precise to meter level High precision in the order of millimeter
Distance = velocity X time Distance = Nλ + φ
Velocity = speed of light N – number of full wave
Time = delay or shift in the code λ- wavelength of carrier wave
generated by satellite and receiver φ- phase measurements after lock on
Time calculation:

• The GPS receiver needs to determine the accurate time taken

by the radio signal to travel from the satellite to the GPS
receiver.
• This is done using the coded (pseudo random code) signal
transmitted by the satellite.
• When a pseudo random code generated by a satellite reaches
the receiver, it generate the same code and tries to match it
with the satellite’s code.
• The receiver then compares the 2 codes to determine how
much delay (or shift) is required in its code to match the
satellite code.
• This delay time (shift) is multiplied by speed of light to get the
distance
GPS SURVEYING
GPS POSITIONING METHODS GPS- SURVEYING PHASES

• Principle • Planning
• Number of receivers • Preparation
• The movement of receiver • Field control H and V
• The mode of processing • Data Sheet
• Visibility Diagram
• Processing
• Report preparation
GPS Surveying/Positioning Approaches

• GPS Positioning methods

• Based on number of receivers
• Single point positioning
• Relative positioning
• Based on the movement of receiver
• Static
• Kinematic
• Based on the mode of processing
• Post-Mission processing
• Real time processing
GPS Positions and Methods
GPS Surveying/Positioning Approaches

• GPS Positioning methods

• Based on number of receivers
• Single point positioning
• Relative positioning
• Based on the movement of receiver
• Static
• Kinematic
• Based on the mode of processing
• Post-Mission processing
• Real time processing
GPS Positions and Methods
• Receivers get positioned for collection of GPS measurements/Data
• Different ways of receiver positioning leads to different surveying
methods
• Methods depend on different criteria
• Type of receiver
• Number of receiver
• Type of movement
• Processing strategy
• Field condition
• Accuracy requirement
GPS Positions and Methods
GPS Positioning- Based on number of receivers

• Positioning with GPS can be performed by either of two ways:

• Single Point (Absolute) positioning
• Relative (Differential) positioning

Based on number of receivers

GPS methods - Based on number of receivers

1. Point positioning or absolute positioning: When the position of an

object is determined with respect to a well-defined coordinate by
using a single GPS receiver and by making observations to four or
more satellites.

2 Relative positioning: If the coordinates are determined with respect

to a known point, by observations to four or more satellites by two
receivers placed at the points simultaneously
 Based on number of receivers

1. Single Point (Absolute) positioning

• GPS point positioning employs one GPS receiver (stationary or
in movement) that measures the code pseudo ranges to
determine the user’s position instantaneously, as long as four
or more satellites are visible at the receiver.
• Absolute static surveying
• Single Point Positioning (SPP)
• Precise Point Positioning (PPP)
• Autonomous GPS surveying (navigation)
• GPS point positioning is used mainly when a relatively low
accuracy is required. This includes recreation applications and
low-accuracy navigation
Single Point (Absolute) positioning
• Single Point Positioning (SPP)
• uses code measurements to perform absolute positioning, in real time or in post
processing, in kinematic or static mode
• Accuracy range of about 50-100 meters.
• Uses: the c/a code only for SPP and carrier phase for PPP
• Requires : only one receiver.
• Data from at least 4 satellites are required for getting the observation

Based on number of receivers

Single Point (Absolute) positioning
• Precise Point Positioning (PPP) is based in the same principle as
SPP except that carrier phase pseudoranges are used instead of
code pseudoranges.
• As compared to SPP, the use of ambiguous phase measurements
brings additional unknowns (1 unknown per observed satellite)..
• long initialization phase (ambiguity resolution) : about 1 hour
• Accuracy: few cm (static) – dm (kinematic)

Based on number of receivers

Relative(Differential) Positioning

Based on number of receivers

Relative(Differential) Positioning
• In differential or relative positioning where the coordinates are in relation to
some fixed point. In GPS surveying this is referred to as baseline determination.
• Reference or base receiver
• Rover or remote Receiver
Condition:
• Both should receive signal from atleast 4 identical satellites
• epoch of observation for the rover receiver should be equal to that of reference
receiver or more than it
• Epoch is the time interval in which signal is received

Based on number of receivers

Relative Positioning
• Repositioning: error can be calculated for receiver, same error removed from
rover
• More accurate
• Accuracy 3to 12m range

Based on number of receivers

GPS Positioning- Based on number of
receivers
• Single Point (Absolute) positioning
• Absolute static surveying (static)
• Single Point Positioning (SPP) (code) (simplest low cost )(1-
10s) (50-100m)
• Precise Point Positioning (PPP) (carrier) ( expensive) (
1hr)(cm)
• Autonomous GPS surveying (moving)(code) (15m)

• Relative (Differential) positioning

(code)( simple and low cost)( 1-50s) (3-12m range)
GPS Position Based on Movement of receiver
Based on the movement of receiver:
Static
Kinematic
• Receiver is kept stationary ✓Single
• Data gets post processed, higher kinematic
accuracy through precise ephemeries ✓Relative
• Adopted for precise or accurate kinematic
estimation of parameters
✓Absolute
✓Relative static
✓Rapid static

Based on movement of receivers

 Static Positioning

• Absolute Positioning, Relative static, Rapid static

• Single point static positioning method

• For establishment of control points in stand alone condition
• Duration of observation depends on quality of control point to be established
• Epoch of observation is usually high 15-20 seconds

Based on movement of receivers

Static Positioning
• Absolute Positioning, Relative static, Rapid static

• Receivers are stationary centered above the stations

• Any number of rover receivers connected to a single reference
receiver
• Capable of providing most accurate position(1cm to 0.1cm )
• Used for long bases 10 to 20km (1-2 hr observation)
• Duration of observation depends on accuracy requirement,
base line length, Number and geometry of satellites, field
condition, type of receiver, type of processing s/w
• Most preferred method for establishment of control points
• Monitoring tectonic movement, High accuracy survey
Based on movement of receivers
Static Positioning
• Absolute Positioning, Relative static, Rapid static

• Also Known as Fast static

• Fundamentally same as that relative static positioning
• A reference receiver and one or more rover
• Difference lies in shorter occupation time at the rover station(5-20minutes)
• Consequently reduced epoch interval of 5 seconds
• Use to establish lower level control points, detailing the network, glacier surface
velocity determination
• For small base lines (< 10 Km)

Based on movement of receivers

• To measure short baselines (up to 15 km) and determine positions up to
centimeter level with short observation time of about 5-20 min

• A reference point is chosen and one or more rovers operate with respect to
it

• Reference receiver is set up at a known point

• Rover receivers are moved to each of the required points

• Used for detailing the existing network, establishing control points etc..

• When working with more than one rover, it is essential to ensure that all
rovers operate at each occupied point simultaneously

• Rapid static technique provide the same accuracy available from 1-2 hour
session of static positioning with observations of 5-20 min
Rapid static in field

Based on movement of receivers

Kinematic Positioning
• Single kinematic
A single receiver will be used and that will be in movement condition

• Relative kinematic
One of the receivers will be in a reference station in a static condition and the
other ie, a rover and will be in a kinematic condition.

Based on movement of receivers

Kinematic

Based on movement of receivers

GPS of Position Based on GPS data Processing

• Post Processing (PP) and Real time Processing(RT)

• Post Processing (PP)
• Gets processed well after field observation
• For high accuracy works
• Precise ephemeris are used
• Three types
• Stop and Go surveying
• Kinematic surveying
• Kinematic on fly

Based on GPS data Processing

Post Processing (PP)
Stop and go, kinematic, kinematic on fly
• A base receiver that remains stationary over the known point
and one or more rover receivers which are kinematic.
• Semi Kinematic surveying
• The rover receiver travels between the unknown points, and
makes a brief stop at each point to collect the GPS data.
• Initialization

Based on GPS data Processing

Intializaton
GPS receiver initialization is the process of capturing initial parameters
that are used by the satellite receiver to capture information from
the satellite system.
For GPS systems, receiver initialization can be used to gather and
correct some of the errors created by the GPS system
The received GPS correction values can be updated and stored using
the known location information. When the GPS receiver is then
moved to a nearby position, the updated correction parameters can
be used to improve the accuracy of the measurements.
Post Processing (PP)
Stop and go, kinematic, kinematic on fly
• The data is usually collected at a 1- to 2-second recording rate
for a period of about 30 seconds per each stop.
• Similar to the previous methods, the base receiver can support
any number of rovers.
• This method is suitable when the survey involves a large
number of unknown points located in the vicinity (i.e., within
up to 10-15 km) of a known point.
• It is of utmost importance that at least four satellites are
tracked, even during the move; otherwise the initialization
process must be repeated again

Based on GPS data Processing

Post Processing (PP)
Stop and go, kinematic, kinematic on fly

• Good GDOP and favorable ionosphere condition required

❖Used for detailed and engineering survey in open area

❖Used where points are close together
+Fast and economical
-Need to do initialisation
-If loss of satellite lock occurs new fix is needed( lock with 4
satellite)

Based on GPS data Processing

 Post Processing (PP)
Stop and go, kinematic, kinematic on fly

• True Kinematic or dynamic surveying

• We have to do that initialization process as we did in stop and go method
• Reference and rover is switched on and stationary for 5-20 minutes
• Reference remains fixed on known control point
• After initialization the rover will be in continues kinematic mode. ( on a moving
platform)
• Collects observations at a pre-set recording rate- 1/2 /5 sec interval
• Generally for locating linear type of objects like the corner of the roads or
seashore , road profiles.

Based on GPS data Processing

 Post Processing (PP)
Stop and go, kinematic, kinematic on fly
+large no of data collection in a given time
+ short sessions and continuous measurements
-slight degradation in the accuracy of work
-reciever resolves phase ambiguity only once at the beginning of the project
-If loss of satellite occurs , a new period of static intialisation must take place
-Route must be clear

❖Measuring trajectory of moving objects

❖In hydrographic surveys, surveying center of road
❖Preparing topographic maps

Based on GPS data Processing

Post Processing (PP)
Stop and go, kinematic, kinematic on fly

• No initialization
• Rover receiver always in kinematic condition
• Uses Dual frequency L1/L2 , hence can handle loss of satellite clock
• Used for hydrographic survey

Based on GPS data Processing

Pseudo Kinematic
• Pseudo-kinematic (PK) positioning with GPS is a survey technique employed by the
National Geodetic Survey.
• This technique, which could also be called broken static surveying (or intermittent static
surveying), must not be confused with kinematic surveying.
• This is a combination of both static and kinematic methods.
• There is a reference (base) receiver and a roving receiver, the former remains at the
reference point during the entire survey while the later visits the unknown points.
• It has the speed of kinematic method but there is no need to maintain lock on 4
satellites.
• There is no initialization as in ‘stop and go’ method.
Pseudo Kinematic
• Each point is occupied for 5-10 min for baselines of 10 km or less.
• Each point must be revisited ( 1hr). Multiple observations at the same
site at different times capture different epochs along the satellite's
orbit and allow the satellite configuration to change and to resolve
the integer ambiguity
+PK promises substantial productivity gains over classical static surveys
and can be employed where the regular kinematic method is
impractical.
+ This technique is suitable for areas where there are obstructions to
signal or the receivers are not equipped with the kinematic software.
+ no 4 common satellite, no initialisation
-Prior mission planning is required.( 4 satellite common during intial
and reoccupation)
Pseudo Kinematic - Stop and Go
Pseudo and stop and go are ideal for GPS measurement technique for
large scale surveying

Psuedo is not very widespread s the difficulty in ocuupying same

position again after 1 hr
Pseudo-kinematic is the least precise of all methods but is more
productive than static “Stop-and-Go” and suitable for lower order
control such as photogrammetric control etc.

Pseudo is preferred when there is fear of signal shading due to

buildings and vegetation

Stop and go advantageous in open areas.

SUMMARY
 GPS of Position Based on GPS data
Processing
• Real time processing
• Errors are sent from reference to rover
• Rover makes corrections in real time
• Provides position in real time.
• Three Types
• DGPS (Differential GPS)
• Real time Kinematic
• Real time networking

Based on GPS data Processing

Real time processing
DGPS (Differential GPS), Real time Kinematic, Real time networking

Based on GPS data Processing

Real time processing
DGPS (differential GPS), real time kinematic, real time networking

• DGPS or DGNSS
• Reference receiver is placed on a point whose position is known
• Rover receiver is at unknown position
• Radio communication between reference and rover
• Tracking of at least 4 same satellites (propagation path is also
same)
• Errors computed from code phase (error correction factor)
• More accurate
• Base station takes some time to calculate the error and transmit
them to rover through the radio link .This lag is called ‘latency of
the communication’

Based on GPS data Processing

Real time processing
DGPS (Differential GPS), Real time Kinematic, Real time networking

• Can be done in real time or done later (post processing)

• Baseline 10-15 Km
• Location of Reference station - By surveying, or GPS recording for 24x7
for few months and avg the value
• Since the reference has no way of knowing which of the many available
satellite a roving receiver is communicating, the reference quickly runs
through all the visible satellites and computes the error for each visible
satellites
• The references encodes this information in a standard format and
transmits it to receiver
• Rover gets complete list of errors and the rover applies the correction to
satellite which it is looking
• DGPS or DGNSS is presently less expensive

Based on GPS data Processing

Real time processing
DGPS (Differential GPS), Real time Kinematic, Real time networking

• is a carrier phase-based relative positioning technique similar to DGPS

(cm level accuracy)
• This method is suitable when:
• the survey involves a large number of unknown points located in
the vicinity (i.e., within up to about 10-15 km) of a known point
• the coordinates of the unknown points are required in real time
• In Real Base communicates to rover or to a geostationary satellite
• the line of sight, the propagation path, is relatively unobstructed

Based on GPS data Processing

Real time processing
DGPS (Differential GPS), Real time Kinematic, Real time networking

• Provides cm level accuracy within 10 km radial distance from

reference station
• Accuracy reduces as distance between rover and receiver increases
• Because of its ease of use as well as its capability to determine the
coordinates in real time, this method is the preferred method by many
users.

Based on GPS data Processing

Real time processing
DGPS (differential GPS), real time kinematic, real time networking RTN
• After initialization, the survey proceeds in exactly the same manner as
an RTK survey.
• The rover sends its position to the central server
• There will be permanent network of reference stations. The reference
station network continuously streams data (using lan, internet, or
radio links) to a central location (server).
• The server then performs several functions including storage of data,
performance of quality assurance checks on the raw data, network
modeling and estimation of systematic errors, calculation of and
conversion of correction data to a user format and communication of
the data to the users.
• The user then receives the corrections (using lan, internet, radio links,
or a cellular modem) in real time.
Based on GPS data Processing
Real time processing
DGPS (differential GPS), real time kinematic, real time networking RTN
+The need for a user to establish a permanent/semi-permanent base
station is eliminated
+Since the reference stations are part of a network, a loss of one station
does not result in failure of the entire network or the resulting survey
+A sufficiently dense reference station network can result in shorter
baselines
-a high cost of setting up and maintaining the RTN
-Subscription fee
-RTN can be limited by cell phone coverage and system down times

Based on GPS data Processing

Real time processing
DGPS (differential GPS), real time kinematic, real time networking RTN

Based on GPS data Processing

APPLICATION OF GPS
• Road transport – public transport monitoring and passenger
information, taxi services, emergency vehicle location
• Aviation – en-route navigation
• Shipping – Vessel Traffic Services (VTS)
• Rail transport – passenger information, preventing door
opening until the carriage is alongside the platform, cargo
tracking signalling, etc
• Used for navigation by mariners and fishermen
• Survey operations
• Telecommunications
• Vehicle tracking
• Social activities – in-car navigation, GPS based social
networking, geo tagging photographs etc
Remote Sensing

11/10/2020 1
Syllabus
• Remote Sensing : Definition- Electromagnetic spectrum
• Energy interactions with atmosphere and earth surface features
• Spectral reflectance of vegetation, soil and water
• Classification of sensors- Active and Passive
• Resolution-spatial, spectral radiometric and Temporal resolution
• Multi spectral scanning-Along track and across track scanning

11/10/2020 2
Remote Sensing - Introduction
• Remote sensing is an art and science of obtaining information
about an object or feature without physically coming in contact
with that object or feature .
• Sonar Sensor
• Natural wave sensors in our body
• Eye detects electromagnetic waves
• Ear detects sound or pressure variation

11/10/2020 3
 Remote sensing - Definitions
• F.F. Sabins in his book "Remote sensing: principles and
interpretation" defines it as follows:
• "Remote Sensing is the science of acquiring, processing and
interpreting images that record the interaction between
electromagnetic energy and matter.“

• ESRI Defines:
• Collecting and interpreting information about the environment and
the surface of the earth from a distance, primarily by sensing
radiation that is naturally emitted or reflected by the earth's surface
or from the atmosphere, or by sensing signals transmitted from a
device and reflected back to it.
• Aerial Photography, radar, satellite image
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Remote sensing

11/10/2020 5
Remote sensing - Definitions
[American Society of Photogrammetry, 1975]. “Remote sensing is
▪ detecting and measuring electromagnetic (EM) energy
▪ emanating or reflected from distant objects made of various
materials,
▪ so that we can identify and categorize these objects by class or
type, substance and spatial distribution

11/10/2020 6
Basic principle of remote sensing
• Uses electromagnetic energy and interaction of electromagnetic
energy with the object.

• Sensing of electromagnetic radiation, which is reflected, scattered or

emitted from the object.
Electromagnetic energy
• It is a form of energy that moves with the velocity of light (3 x 10^8
m/sec) in a harmonic pattern consisting of sinusoidal waves, equally
and repeatedly spaced in time.

• It has two fields:

• Electric field and magnetic field, both are perpendicular to each other
• Electrical components are vertical and magnetic components are horizontal
• Electromagnetic energy is composed of many discrete units called photons or
quanta.
• It is characterized by velocity (c), wavelength (λ) and frequency (f)

E = hf
E = h c/λ [since c = f λ]

Where,
E = energy of quantum
h = Plank’s constant (6.6262 × 10-34 Js)
c = speed of light (3 x 108 m/sec) , λ = in micro meter 10-6
Electro magnetic waves characteristics
• The wavelength is the length of one wave cycle, which can be measured as the
distance between successive wave crests. Wavelength is usually represented by
(λ). Wavelength is measured in metres (m) or some factor of metres (nm,10-9
metres),(μm, 10-6 metre s), (cm, 10-2 metres).
• Frequency refers to the number of cycles of a wave passing a fixed point per unit
of time. Frequency is normally measured in (Hz), equivalent to one cycle per
second, and various multiples of hertz.

11/10/2020 11
Basic radiation laws
Wave Theory
It describes electromagnetic energy as travelling in a harmonic, sinusoidal fashion
at the velocity of light(c)
c=fλ

Where λ = Wavelength is measured in metres (m)

f = Frequency, normally measured in hertz (Hz)
c = speed of light (2.99792458 x 108 m/s)

11/10/2020 12
 Particle Theory
It suggests that electromagnetic radiation is composed of many
discrete units called photons or quanta.
E = hf
E = h c/λ [since c = f λ]

Where,
E = energy of quantum
h = Plank’s constant (6.6262 × 10-34 Js)
c = speed of light (3 x 108 m/sec) , λ = in micro meter 10-6

11/10/2020 13
 Stefan–Boltzmann law

It states that the total radiant heat energy emitted from a surface is
proportional to the fourth power of its absolute temperature.
M = σT4
Where,

M = Total emitted radiation from the surface of the material (watt per
metre2)
σ = Stefan–Boltzmann constant (5.6704 × 10-8 watt per metre2 ∙K-4 )
T = absolute Temperature in K

11/10/2020 14
 Black body theory
A black body is an ideal body which
allows the whole of the incident
radiation to pass into itself (without
reflecting the energy ) and absorbs
within itself this whole incident
radiation (without passing on the
energy).
This property is valid for radiation
corresponding to all wavelengths
and to all angles of incidence.
Therefore, the black body is an ideal
absorber of incident radiation.
A black body in thermal
equilibrium(that is, at a constant
temperature) emits electromagnetic
radiation called black body
radiation.

11/10/2020 15
Energy source and radiation principles

Solar radiation (insolation)

6000K
Amount of energy is not uniform across all wavelength
(99% in the range of 0.28-4.96micrometer)(max at 0.48μm)

Terrestrial radiation
Temp above absolute zero(0K)
(Earth temp 300K)
emits maximum radiation at 9.7 micro meter
Thermal IR radiation

11/10/2020 16
EMR Spectrum
• Electromagnetic radiation can be produced at a range of
wavelengths and can be categorised according to its position
into discrete regions which is called electromagnetic
spectrum.

• EM spectrum is the distribution of the continuum of energy

that ranges from meters to nano meters in wavelength and
travels at a speed of light and propagates through vaccum like
the outer space.

• All matter radiates a range of electromagnetic energy with the

maximum intensity for shorter wavelengths at an increasing
temperature of the matter.

11/10/2020 17
EMR Spectrum

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EMR Spectrum

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EMR Spectrum

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Remote sensing - Principle
• Different objects reflect or emit different amounts of energy in
different bands of the electromagnetic spectrum.

• The amount of energy reflected or emitted depends on the

properties of both the material and the incident energy (angle of
incidence, intensity and wavelength).

• Detection and discrimination of objects or surface features is done

through the uniqueness of the reflected or emitted electromagnetic
radiation from the object.

• A device to detect this reflected or emitted electro-magnetic

radiation from an object is called a “sensor” (e.g., cameras and
scanners).

• A vehicle used to carry the sensor is called a “platform” (e.g.,

aircrafts and satellites).
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Remote sensing - Components

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Remote sensing - stages
• Energy Source or Illumination (A)– the First requirement for remote sensing is to
have an energy source which illuminates or provides electromagnetic energy to
the target of interest.
• Radiation and the Atmosphere (B,D)– as the energy travels from its source to
the target, it will come in contact with and interact with the atmosphere it passes
through. This interaction may take place a second time as the energy travels from
the target to the sensor.
• Interaction with the Target (C)– once the energy makes its way to the target
through the atmosphere, it interacts with the target depending on the properties
of both the target and the radiation.

11/10/2020 23
Remote sensing - stages
• Recording of Energy by the Sensor (E) – after the energy has been scattered by
or emitted from the target, we require sensor (remote – not in contact with the
target) to collect and record the electromagnetic radiation.
• Transmission, Reception, and Processing (F)– the energy recorded by the sensor
has to be transmitted, often in electronic form, to a receiving and processing
station where the data are processed into an image (hardcopy and/or digital).
• Interpretation and Analysis (G)– the processed image is interpreted, visually
and/or digitally or electronically, to extract information about the target which
was illuminated.

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Remote sensing - stages
Application (H)– the Final element of the remote sensing process is achieved when
we apply the information we have been able to extract from the imagery about
the target in order to better understand it, reveal some new information, or assist
in solving a particular problem.

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Advantages
• Advantages of remote sensing are:

• Provides data of large areas

• Provides data of very remote and inaccessible regions
• Able to obtain imagery of any area over a continuous period of time through
which the any anthropogenic or natural changes in the landscape can be
analyzed
• Relatively inexpensive when compared to employing a team of surveyors
• Easy and rapid collection of data
• Rapid production of maps for interpretation
11/10/2020 26
Disadvantages

Disadvantages of remote sensing are:

• The interpretation of imagery requires a certain skill level

• Needs cross verification with ground (field) survey data
• Data from multiple sources may create confusion
• Objects can be misclassified or confused
• Distortions may occur in an image due to the relative motion of sensor and source

11/10/2020 27
Electromagnetic energy interactions with the
atmosphere
Electromagnetic energy interactions
with the atmosphere
Scattering
Surface phenomena
Spatial distribution of energy changes
No energy change
Absorption
Volume phenomena
Loss of energy (CO2,O3, H2O)

Effect of atmospheric interaction depends on

Properties of radiation (magnitude and wavelength)
Atmospheric condition
Path length
Electromagnetic interaction - Scattering
Scattering occurs when particles or large gas molecules present
in the atmosphere interact with and cause the electromagnetic
radiation to be redirected from its original path. How much
scattering takes place depends on several factors including the
• Magnitude and wavelength of the radiation,
• the abundance of particles or gases,
• the distance the radiation travels through the atmosphere.
Types of Scattering
(a) Selective (b) Non selective
Rayleigh scattering(< 0.1 μm)
Mie scattering(0.1 to 10 μm)
Rayleigh scattering
• It occurs when particles are very small (less than one tenth)
compared to the wavelength of the radiation.
Eg: small specks of dust or nitrogen and oxygen molecules.
• causes shorter wavelengths of energy to be scattered much
more than longer wavelengths. (scattering intensity is inversely
proportional to 4th power of wavelength)
• dominant scattering mechanism in the upper atmosphere.
Rayleigh scattering
• Rayleigh scattering is also known as selective scattering or molecular scattering
• O2 and N2 causes
• Blue sky at noon
• Red /orange sky at sunrise and sunset
Mie Scattering
• It occurs when the particles are just about the same size as the
wavelength of the radiation.
• Dust, smoke and water vapour are common causes
• Tends to affect longer wavelengths than those affected by Rayleigh
scattering.(scattering intensity is inversely proportional to
wavelength)
• Occurs mostly in the lower portions of the atmosphere where larger
particles are more abundant
• dominates when cloud conditions are overcast
• Mie Scattering Radiation is used commonly in Remote sensing
Non selective scattering
• This occurs when the particles are much larger (approx 10 times) than the
wavelength of the radiation.
• Water droplets and large dust particles, pollen, ice crystals

• Nonselective scattering gets its name from the fact that all wavelengths are
scattered about equally.

• This type of scattering causes fog and clouds to appear white to our eyes because
blue, green, and red light are all scattered in approximately equal
Electromagnetic interaction - Absorption
• Certain regions of the EM spectrum are completely absorbed by the various gases
that make up the atmosphere so that wavelengths in these regions cannot be
used for remote sensing of the Earth’s surface.
• Ozone, carbon dioxide, and water vapour are the three main atmospheric
constituents which absorb radiation.
• Ozone serves to absorb the harmful (to most living things) ultraviolet radiation
from the sun.
• Carbon dioxide referred to as a greenhouse gas. It tends to absorb radiation
strongly in the far-infrared portion of the spectrum.
• Water vapour in the atmosphere absorbs much of the incoming longwave
infrared and shortwave microwave radiation (between 22μm and 1m).
Atmospheric window
• The ranges of wavelength that are partially or wholly
transmitted through the atmosphere are known as
"atmospheric windows." Remote sensing data acquisition is
limited through these atmospheric windows
Atmospheric window
Atmospheric window
Atmospheric window
 recap
Interaction with atmosphere
Properties of radiation Atmospheric condition Path length
✓ Scattering
Surface phenomena Spatial distribution of energy changes No energy change
(a) Selective (b) Non selective
Rayleigh scattering(< 0.1 μm)
Mie scattering(0.1 to 10 μm)

✓Absorption
Volume phenomena Loss of energy (CO2,O3, H2O)

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Electromagnetic energy interactions with the
surface objects
There are three forms of interaction that can take place when energy strikes or is
incident upon a surface object.
absorption; transmission; and reflection.
The total incident energy will interact with the surface depending on the
• Wavelength of the energy
• Angle of intersection of radiation
• The material
• Condition of the feature
Electromagnetic energy interactions with the
surface objects
Absorbed energy will get emitted in the longer wave length
Transmitted energy get scattered or absorbed by the medium

Reflected energy/scattered energy in the visible and NIR and SWIR

Emitted energy in the thermal IR(MWIR,LWIR,VLWIR)

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11/13/2020 4
Reflection and scattering
• If roughness of surface < λ of radiation reflection occurs
Roughness to λ of radiation is less than 1
• If roughness of surface >λ of radiation scattering occurs
Roughness to λ of radiation is more than 1
 Type of Reflection

1. Specular reflection: It occurs when the surface is smooth and flat. λmore
• A mirror-like or smooth reflection is obtained where complete or nearly
complete incident energy is reflected in one direction.
• The angle of reflection is equal to the angle of incidence.
• Reflection from the surface is the maximum along the angle of reflection,
whereas in any other direction it is negligible.
.
Type of Reflection
2. Diffuse (Lambertian) reflection: It occurs when the surface is
rough. λless
• The energy is reflected uniformly in all directions.
• Since all the wavelengths are reflected uniformly in all
directions, diffuse reflection contains spectral
information on the "colour" of the reflecting surface.
• Hence, in remote sensing diffuse reflectance properties
of terrain features are measured.
• Since the reflection is uniform in all direction, sensors
located at any direction record the same reflectance and
hence it is easy to differentiate the features
Spectral Reflectance
• For any given material, the amount of solar radiation that reflects, absorbs,
or transmits varies with wavelength.
• This important property of matter makes it possible to identify different
substances or classes and separate them by their spectral signatures
(spectral curves).

• EI(λ) ER(λ) EA(λ) ET(λ)

• ER(λ)/ EI(λ) EA(λ)/ EI(λ) ET(λ)/ EI(λ)

• Reflectance Absorbance Transmittance

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Spectral reflectance
• How much electromagnetic energy is reflected from the
surface is reflectance. Reflectance range from 0 to 1.
Spectrometer is used to measure the reflectance.
• This reflected energy represented as the function of
wavelength is called spectral reflectance.
• Rl is spectral reflectance or Albedo

• Spectral reflectance as a function of wavelength is called

spectral reflectance curve
Spectral reflectance

• The energy that is reflected by a feature on the earth surface

over a variety of different wavelength will give their spectral
responses.
Spectral reflectance curve
• A basic assumption made in remote sensing is that a specific target has an
individual and characteristic manner of interacting with the incident radiation.
That is spectral response
• The graphical representation of the spectral response of an object over different
wavelength of EMR spectrum is called spectral reflectance curve.
• The difference in the reflectance/emittance characteristics with respect to
incident wavelengths (i.e.,reflectance/emittance as a function of wavelength) is
called as the spectral signature.
11/13/2020 12
Spectral reflectance curve
 Spectral reflectance curve
• Objects having different surface features reflect or absorb the
sun's radiation in different ways.
• The most important surface features are colour, structure
and surface texture.

• The reflectance properties of an object depend on :

• the particular material and its physical and chemical state
(e.g. moisture, health of vegitation),
• the surface roughness
• the geometric circumstances (e.g. orientation of
sun,incidence angle of the sunlight, look angle).
Spectral reflectance curve
These differences make it possible to identify different earth
surface features or materials by analysing their spectral
reflectance patterns or spectral signatures.
These signatures can be visualised in so called spectral
reflectance curves as a function of wavelengths.
The figure below shows typical spectral reflectance curves of
three basic types of Earth features: green vegetation, dry
bare soil and clear water.
Spectral reflectance of vegetation
• A chemical compound in leaves called chlorophyll strongly absorbs radiation in the red
and blue wavelengths but reflects green wavelengths. Leaves appear “greenest” when
chlorophyll content is at its maximum. When there is less chlorophyll in the leaves, there
is less absorption and proportionately more reflection of the red wavelengths, making
the leaves appear red or yellow (yellow is a combination of red and green wavelengths).
• The internal structure of healthy leaves acts as excellent diffuse reflectors of near-
infrared wavelengths. If our eyes were sensitive to near-infrared, trees would appear
extremely bright to us at these wavelengths. In fact, measuring and monitoring the near-
IR reflectance is one way that scientists can determine how healthy (or unhealthy)
vegetation may be.
Spectral reflectance of vegetation
Spectral reflectance of vegetation
• Spectral curve of healthy vegetation
• Spectral curve varies with leaf structure
Spectral reflectance of vegetation
• In stressed vegetation IR bands
are less reflected by mesophyll cells
• Spectral reflectance varies with canopy
density
Spectral reflectance of vegetation

• Healthy vegetation are good absorber in visible band and good Reflectance ( 50%)
in IR band.
• 0.4 to 0.7 μm – chlorophyl
• 0.7 to 1.3 μm uniform reflectance –mesophyll
• 1.4,1.9,2.7 μm dips due to water presence
• 1.6,2.2 μm peaks

11/13/2020 20
Spectral reflectance of vegetation

• Reflectance in IR band varies with leaf structure, canopy density and vegetation
health hence can be used to distinguish between species.
• Coniferous trees and deciduous trees behave similar in visible band, however coniferous
trees show high reflectance in IR band.
• A dense canopy gives higher reflectance in IR band, due to mutli layer reflection
• Distinguish between stressed and healthy vegetation in visible and IR band due to less
absorbance in blue red band (visible) and more absorption by the mesophyll cells(IR)

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 Spectral reflectance of Soil
The spectral reflectance curve of bare soil is considerably less
variable.
The spectral reflectance of soil is controlled, for the most part, by
six variables:
a) Moisture content
b) Organic matter content
c) Particle size distribution
d) Iron oxide content
e) Soil mineralogy
f) Soil structure
Of these variables, moisture content is the most important due to
its dynamic nature and large overall impact on soil reflectance.
Spectral reflectance of Soil
• Presence of moisture in soil decreases its reflectance
• Clay soil and vegetation shows water absorption bands at 1.4,
1.9, 2.7 um
• Coarse and sandy soil are well drained and high reflectance
due to low moisture content. Poorly drained fine grained soil
shows low reflectance
• Presence of iron oxide in the soil decreases the reflectance at
visible region
Spectral reflectance of Soil
• Effects of Organic Matter in Soils - Organic matter is a strong
absorber of EMR, so more organic matter leads to darker soils
(lower reflectance curves).
• In the absence of water coarse textured soil reflects less and
appear darker
Spectral reflectance of Water
The water curve is characterised by a high absorption at near infrared
wavelengths range and beyond and high reflectance in visible region
between 0.4 um and 0.6 um. Reflectance in NIR range is generally used for
delineation water bodies.
Spectral Characteristics of Water
There are three types of possible reflectance from a water body
a) Surface (specular) reflectance
b) Bottom reflectance
c) Volume reflectance

Only volume reflectance contains information relating to water quality. For

deep (> 2 m) clear water bodies, volume reflectance is very low (6-8 percent)
and is confined to the visible wavelengths.
Spectral reflectance of Water
• Clear and turbid water
• Clear water absorbs less energy in λ< 0.6 μm with maximum in
blue green portion of spectrum. As turbidity of water changes
due to presence of organic or in organic materials the
reflectance increases.
• Eg: increase in chlorophyll tends to decrease reflectance in
blue and increase reflectance in green
• Turbid water has a higher reflectance in the visible region than
clear water. This is also true for waters containing high
chlorophyll concentrations. These reflectance patterns are
used to detect algae colonies as well as contaminations such
as oil spills or industrial waste water
Spectral reflectance of Water
Spectral reflectance of Water
• Snow and ice

cont.snow (contaminated snow)

Spectral reflectance of Water
• Shallow and deep waters
• Comparison of mean spectral reflectance between shallow-
water (in green) and deep-water (in black) in Hawai. Error bars
represent standard deviation from the mean .
Platforms
Vehicle or carrier for remote sensors.
Ground-based platforms
Aerial Platforms/Air-borne platforms
Satellite Platforms

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Platforms

11/13/2020 32
Satellites
• Geostationary 36000km INSAT,GOES,METEOSTAT
• Near earth, Polar orbiting and sun synchronous 1000km Landsat, IRS, SPOT
• Circular and near polar

Sun
synchronous
satellite
11/13/2020 33
 Sensors
• It is a device that record EMR reflected or emitted from Earth
features.
• Consists of mechanisms usually sophisticated lenses with
filters. It is designed to operate specifically to study and
produce outputs for a specific region of the EM spectrum, i.e,
it is made sensitive to a particular region of the spectrum.

11/16/2020 1
 Sensor Requirement

• While selecting a sensor the following factors should

be considered:

i. The spectral sensitivity of the available sensors.

ii. The available atmospheric windows in the spectral range(s)
considered. The spectral range of the sensor is selected by
considering the energy interactions with the features under
investigation.
iii. The source, magnitude, and spectral composition of the
energy available in the particular range.
iv. Multi Spectral Sensors sense simultaneously through
multiple, narrow wavelength ranges that can be located at
various points in visible through the thermal spectral
11/16/2020
regions. 2
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 Sensor types
Different types of Sensors:
1. Passive sensors: Detect the reflected or emitted EMR from
natural resources.
2. Active sensors: Detect the reflected responses from objects
which are radiated from artificially generated energy sources
Eg: Radar (radio detection and ranging)
Lidar(Light detection and ranging)

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11/16/2020 7
 Resolution
• In remote sensing the term resolution is used to represent
the resolving power, which includes not only the capability
to identify the presence of two objects, but also their
properties.
• In qualitative terms the resolution is the amount of details
that can be observed in an image.
• Four types of resolutions are defined for the remote sensing
systems.
• Spatial resolution
• Spectral resolution
• Temporal resolution
• Radiometric resolution

11/16/2020 8
 Spatial resolution

• A digital image consists of an array of pixels. Each pixel

contains information about a small area on the land surface,
which is considered as a single object.
• Spatial resolution is a measure of the area or size of the
smallest dimension on the Earth’s surface over which an
independent measurement can be made by the sensor.
• It is expressed by the size of the pixel on the ground in meters

11/16/2020 9
Spatial resolution
• A measure of size of pixel is given by the Instantaneous Field of View
(IFOV). IFOV is the angular cone of visibility
• The size of the area viewed on the ground can be obtained by
multiplying the IFOV (in radians) by the distance from the ground to
the sensor.
• This area on the ground is called the ground resolution or ground
resolution cell. It is also referred as the
spatial resolution of the remote sensing system.

11/16/2020 10
 Spatial resolution
• For a homogeneous feature to be detected, its size generally
has to be equal to or larger than the resolution cell.

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 Spatial resolution
• Based on the spatial resolution, satellite systems can be
classified as follows.
• Low resolution systems
• MODIS AVHRR >1km or more
• Medium resolution systems
• 100m- 1km IRS WiFS (188m), Landsat TM (120)
• High resolution systems
• 5-100m Landsat ETM,
• Very high resolution systems
• <5m GeoEye, IKONOS
large scale maps/images provide finer spatial resolution
compared to small scale maps/images.

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11/16/2020 13
 Spectral Resolution
• This represents the width of the spectral band and the number of
spectral bands in which the image is taken.
• For example, a true colour photography will consist of 3 spectral
bands, each sensitive to the blue, green and red region of the EM
spectrum.
• For studying vegetation, we would go for a combination of 4 bands,
i.e., 3 bands of the visible light and IR band.
• Thus, spectral resolution describes the ability of a sensor to define
fine wavelengths intervals. The finer the spectral resolution, the
narrower the wavelengths range for a particular band.
• To improve the better potential of the system to discriminate
between features, it is better to increase the spectral resolution or
increase the number of bands. This would lead to more narrower
wavelength bands and finer the spectral resolution.
• Features, which may have a reflectance over a broadband, may differ
in detail if the spectral interval of sensing is narrowed.

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 Spectral Resolution

11/16/2020 15
 Spectral Resolution
• Present-day sensor systems can detect hundreds of very narrow
spectral bands throughout the different regions of the EM
spectrum.
• Their very high spectral resolution facilitates fine discrimination
between different targets.
High spectral resolution: - 220 bands
Medium spectral resolution: 3 - 15 bands
Low spectral resolution: - 3 bands
• Advantage of narrow band over broadband
• Narrow bands give more spectral detail
• More bands = more information to store, transmit and
process
• BUT more bands enables discrimination of more spectral
detail
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 Radiometric Resolution
• Radiometric resolution of a sensor is a measure of how many
grey levels are measured between pure black (no reflectance) to
pure white. In other words, radiometric resolution represents
the sensitivity of the sensor to the magnitude of the
electromagnetic energy.
• The finer the radiometric resolution of a sensor the more
sensitive it is to detecting small differences in reflected or
emitted energy or in other words the system can measure more
number of grey levels.
• It is expressed as the number of binary digits, i.e, bits, recorded
as exponents of power 2.
• If a sensor used 8 bits to record the data, there would be 28 =
256 digital values available ranging from 0 – 255, representing
different colours.
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 Radiometric Resolution
• Image data are generally displayed in a range of grey tones, with
black representing a digital number (DN) of 0 and white
representing the maximum value (255 in 8-bit data).

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 Radiometric Resolution

11/16/2020 19
 Temporal Resolution
• Temporal resolution describes the number of times an object is
sampled or how often data are obtained for the same area
• The absolute temporal resolution of a remote sensing system to
image the same area at the same viewing angle a second time is
equal to the repeat cycle of a satellite
• The actual temporal resolution of a sensor therefore depends on
a variety of factors, including the satellite/sensor capabilities,
the swath overlap, and latitude.

11/16/2020 20
 Temporal Resolution
• During each successive overpass, changes or variations in
reflectivity or emissivity of objects are expected, and this can be
detected.
• The use of repeat coverage becomes necessary when the
phenomena of interest undergo significant changes with the
passage of time.
• Very useful in identification of agricultural crops.
• This is important when studying
• Short-lived phenomena /dynamic events need to be imaged
(Floods, oil slicks, cyclone, volcano, earthquake)
• Spread of a forest disease from one year to the next.
• Changing appearance of a feature over time can be used to
distinguish it from near-similar features (Wheat/Maize)
• Temporal variation in land use/landcover

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 Temporal Resolution

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 Temporal Resolution

11/16/2020 23
 Scanners
• Multi spectral scanner
• Visible , Near IR , mid IR , Thermal infrared
• Thermal Scanner
• Hyperspectral scanner

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 Multi spectral Scanners
• Multispectral scanner (MSS) simultaneously acquires images
in multiple bands of the EMR spectrum.

• MSS onboard the first five Landsat missions were operational

in 4 bands: 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-1.1 μm

• Spectral reflectance of the features differs in different

wavelength bands. Features are identified from the image by
comparing their responses over different distinct spectral
bands.

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 Multi spectral Scanners

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 Multi spectral scanning
Two different approaches are adopted for this:

Across-track (whiskbroom) scanning

Along-track (push broom) scanning

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 Across track Scanners

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 Across track Scanner
• The scanner thus continuously measures the energy from one side
to the other side of the platform and thus a two-dimensional
image is generated.

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 Along track Scanners
• Use the forward motion of the platform to record successive
scan line.
• Use no scanning mirrors, instead a linear array of detectors to
simultaneously record the energy received from multiple
ground resolution cells along the scan line.
• This linear array typically consists of numerous charged
coupled devices (CCDs).
• A single array may contain more than 10,000 individual
detectors. Each detector element is dedicated to record the
energy in a single column

11/16/2020 30
 Along track Scanners
• The arrays of detectors are arranged in the focal plane of the
scanner in such a way that the each scan line is viewed
simultaneously by all the arrays.
• The array of detectors are pushed along the flight direction to
scan the successive scan lines, and hence the name
push-broom scanner.
• A two dimensional image is created by recording successive
scan lines as the aircraft moves forward.

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 Along track Scanners

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11/16/2020 33
 Indian Remote Sensing
• Aryabhata (Launch Date: April 19, 1975)
• Bhaskara I (Launch Date: June 7, 1979
• IRS -1A, 1B,1C, 1D 1988-1997
• IRS –P2, IRS-P4,IRS –P5 (Cartostat series)
• RESOURCESAT 2A –(Launched on December 7, 2016.)
• INSAT3DR (Launched on Sep 08, 2016)

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11/16/2020 38
Geographic Information Systems

1
Syllabus
➢Geographical Information System-components of GIS, GIS
operations,
➢Map projections- methods
➢Coordinate systems-Geographic and Projected coordinate
systems
➢ Data Types- Spatial and attribute data,
➢Raster and vector data representation

2
Introduction

➢Geographic relates to the surface of the earth.

➢ Information is a knowledge derived from study, experience, or
instruction.
➢System is a group of interacting, interrelated, or
interdependent elements forming a complex whole

➢GIS is a tool for working with geographic information.

3
GIS
➢GIS stands for Geographical Information System.
➢It is defined as an integrated tool, capable of mapping,
analysing, manipulating and storing geographical data in order
to provide solutions to real world problems and help in
planning for the future.
➢A GIS is a computer based system that provides the following
four sets of capabilities to handle georeferenced data:
➢Data Capture and preparation
➢Data management ,including storage and maintenance
➢Data manipulation and analysis
➢Data Presentation

4
GIS - Functions
➢Data collection
➢ Capture data
➢ using Surveying, Photogrammetry, GPS & RS
➢ paper maps are also sources of data
➢Data storing, processing & analysis
➢ Store data
➢Query data
➢ Analyze data
➢ Output production
➢Display data
➢Produce output

5
GIS Definitions

➢a system which uses a spatial database to provide answers to

queries to a geographical nature.
➢a computer assisted system for the capture, storage, retrieval,
analysis and the display of spatial data within a particular
organization’
➢a powerful set of tools for collecting, storing, retrieval and
displaying spatial distribution with the real world
➢a GIS is a system of hardware, software and procedures to
facilitate the management, manipulation, analysis, modelling,
representation and display of georeferenced data to solve
complex problems regarding planning and management of
resources (NCGIA, 1990)

6
GIS Definitions

➢An organized collection of computer hardware, software,

geographical data and personnel design to efficiently capture,

store, update, manipulate, analyze and display all forms of

geographically referenced information”(ESRI)

7
GIS Components

➢People
➢Data
➢Software
➢Hardware
➢Procedures/Methods

8
GIS components
➢ People: Viewers, general user, GIS specialist
➢This component of GIS includes all those individuals (such as
programmer, database manager, GIS researcher etc.) who are
making the GIS work, and also the individuals who are at the
user end using the GIS services, applications and tools.
➢Are the most important part of a GIS
➢Define and develop the procedures
used by a GIS
➢Can overcome shortcoming of the
other 4 elements (data, software,
Hardware, procedure), but not vice-versa

9
GIS components
➢Data
➢The data is captured or collected from various sources (such as
maps, field observations, photography, satellite imagery etc)
and is processed for analysis and presentation.
➢Data is the information used within a GIS
➢Since a GIS often incorporates data
from multiple sources, its accuracy
defines the quality of the GIS.
➢GIS quality determines the types
of questions and
problems that may be
asked of the GIS
10
Data:

• It includes geographic data and tabular data

(Geospatial data)
• Geospatial data consist of
1. Spatial data: describe the location, shape and
orientation of geographical features
2. Attribute data: describe the characteristics of
spatial feature
GIS components
➢GIS software ➢The software used must
➢It encompasses not only to match the needs and
the GIS package, but all the skills of the end user.
software used for ➢Popular GIS Software
databases, drawings,
➢ Vector-based GIS
statistics, and imaging. ➢ ArcGIS (ESRI)
➢ The functionality of the ➢ ArcView
software used to manage ➢ MapInfo
the GIS determines the type ➢Raster-based GIS
of problems that the GIS ➢ Erdas Imagine (Leica)
may be used to solve. ➢ ENVI (RSI)
➢ ILWIS (ITC)
➢ IDRISI (Clark Univ.)

12
GIS components
➢Software
➢Software is the heart of a GIS system.
➢The GIS software must have the basic capabilities of data
input, storage, transformation, analysis and providing desired
outputs.

➢proprietary
➢ArcGIS by ESRI is the widely used proprietary GIS software.
MapInfo, Microstation, Geomedia

➢open source.
➢Quantum, uDIG, GRASS, MapWindow GIS etc.

13
GIS components
➢Hardware
➢It consists of the equipments and support devices that are
required to capture, store process and visualize the geographic
information. These include computer with hard disk, digitizers,
scanners, printers and plotters etc.
➢The type of hardware determines, to an extent, the speed at
which a GIS will operate.
➢ Additionally, it may influence the
type of software used.
➢ To a small degree, it may influence
the types/ personalities of the people
working with the GIS.

14
GIS components
➢Procedures/ Methods
➢The procedures used to input, analyze, and query data
determine the quality and validity of the final product.
➢The procedures used are simple the steps taken in a well
defined and consistent method to produce correct and
reproducible results from the GIS system.
➢These include the methods or ways by which data has to be
input in the system, retrieved, processed, transformed and
presented.

15
GIS OPERATIONS
• The various GIS operations are
1. Spatial data input
2. Attribute data input and management
3. Data display
4. Data exploration
5. Data analysis
6. GIS modeling
1. Spatial data input

• Spatial data acquired from existing data or by creating new data

• Existing data includes paper maps or digital maps
• New data is created from satellite images, GPS data or from filed
survey
• Spatial data is entered into the GIS by the following methods
• 1. Digitizing
• 2. Scanning
• 3. Co-ordinate entry
• 4. Conversion of existing data
Digitizing:

• Digitizer consist of an electronic device with a hand held

magnetic pen and a table up on which map is placed.

• The features on the map is traced by the magnetic pen

and sent to the computer and stored
Tracing is done in two modes.

• Point mode: single points are traced one at a time. Eg:

tracing the location of well, school etc.
• Stream mode: many points are traced on regular intervals
of time. Eg: tracing of roads, boundaries etc.
Error in digitizing
• Gaps
• Overshoot
• Spikes
• Duplicate
• Disconnection
Advantages of digitizing
• Easy to learn
• No skilled labour required
• Attribute data can be added during digitizing
• High accuracy
Disadvantages of digitizing
• Tedious activity
• Require post processing
• Slow process
Scanning
• Scan the paper map using scanner
• Automatically capture spatial data
• Rapid rate of input
• But it require manual editing after scanning
Co-ordinate entry
• Spatial data can be created by entering co-ordinate of each points
• It is very costly but it is very precise

Conversion of existing data

• Converting available digital map into GIS format maps
2. Attribute data input and management

Enter attribute data into GIS by:

1. Manual typing
2. Uploading excel sheets
• Attribute data reside as rows and columns
• Row represents spatial feature and column represents
corresponding attribute data

3. Data display
• Data (both spatial and attribute data) entered into the GIS
is displayed for checking corrections
• Data is visualized by maps with different legends and
index based on the attribute data
4. Data exploration
• Based on the data entered, explore general trend in
data, focusing on relationship between data.
• Exploration like data classification, data aggregation
and map comparison.
5. Data analysis

Different kinds of data analysis can be done in GIS

depending upon our needs.

The different analysis are as follows:

1. Vector data analysis
2. Raster data analysis
3. Terrain mapping and analysis
4. View shed and watershed analysis
5. Spatial interpolation
6. Path analysis and network application
6. GIS modeling

• Models are used to represents process, phenomena or a

system.
• GIS models are used to visualize the result of analysis
done in GIS.

Types of GIS models:

1. Binary models: shows some index values to indicate.
2. Regression models: it shows the statistical relations
between different variables
3. Process models: it shows environmental process
CO-ORDINATE SYSTEM IN GIS

• Different co-ordinate systems used are:

1. Geographical co-ordinate system
2. Projected co-ordinate system
Geographical co-ordinate system
• It is used to locate objects on a curved surface of earth
• It is a three dimensional co-ordinate system
• Position of an object on earth surface is determined using two angles called
latitude and longitude
• Latitude: it is the vertical angle between plane of equator and radius drawn
to the point measured at the center of earth
• The reference plane is equator
• Latitude is measured as positive along North Pole up to +90 degree and
negative along South Pole up to -90 degree
• Lines of equal latitudes are called parallels
• Longitude: horizontal angle measured in plane of equator between plane of
meridian through the point and plane of prime meridian
• The reference plane is plane meridian (Greenwich meridian)
• Longitude is measured positive along east up to +180 degree and negative
along west up to – 180 degree
• Lines of equal longitude is called meridian
Projected co-ordinate system

• It is used to locate objects on a flat surface (on paper maps or digital

map).
• Object is located using (x,y) coordinates.
• Reference line is horizontal and vertical line passing through the
origin.
• Center of map is selected as origin (0,0).
MAP PROJECTIONS
• Map projection is the transformation of spherical earth into a
plane surface. (Transforming spherical earth to a map).

8
• When transforming a spherical earth into a map, the following
distortion occurs:

1. Distortion in area
2. Distortion in shape
3. Distortion in distance
4. Distortion in direction
Type of map projection
• Map projection is classified based on:
• quantity preserved without distortion and
• surface used for developing map.

Based on Preserved quantity

1. Conformal projection
2. Equivalent projection
3. Equidistant projection
4. Azimuthal projection
Conformal projection
• It preserves shape and direction, but area and distance will be
distorted
• It is used for topographic mapping and navigation purpose
Example: Mercator projection, Lambert conformal conic projection
Equivalent projection
• It preserves area. But shape, distance and direction may be distorted
• It is used for spatial distribution like population map, land use map
etc.
• Example: Albers equal area projection, Lamberts equal area
projection, sinusoidal equal area projection
Equidistant projection
• It preserves distance, but shape, direction and area may be distorted
• It is used for airline distance map and seismic map
• Example: Atlas map, equidistance conic projection map
Azimuthal projection
• It preserves direction, but area, shape and distance may be distorted
• It is used for air and sea navigation
• Example: azimuthal projection, Mercator projection
• Map projection based on Developable surface

1. Cylindrical projection
2. Conical projection
3. Planar or azimuthal projection
 Cylindrical projection

• Earth projected on to a cylinder which is then cut length wise and laid
flat
• It will be accurate at equator zone
• Poles cannot be shown in this projection
• Parallels become horizontal lines and meridians become vertical lines
• Example: Mercator projection
Conical projection
• Earth projected on to a cone which is then cut length wise and laid
flat
• It will be accurate at mid latitude region
• Parallels become concentric circular arcs and meridians become radial
lines
• Example: Lambert conformal conic projection
Planar or azimuthal projection
• Earth projected on to a plane which is placed at the North or South
pole
• Map will be circular in shape
• Parallels become complete concentric circles and meridians become
radial lines
DATA REPRESENTATION IN GIS

Data in GIS is represented in two forms

1. Vector data
2. Raster data
Vector data

• It is a co-ordinate based representation

• Vector represents geographic features as points, lines and polygons
• Points: Location of well, school etc.
• Lines: Road, river etc.
• Polygon: Boundary of cities, forests etc.
Raster data
• Geographic space is divided into a grid cells and data is represented
using these cells
• Each cell contains a value
• Point feature: represented by a single cell
• Line: represented by a series of cells
• Polygon: represented by a group of cells
Vector versus Raster
DATA TYPES
➢ Introduction
➢ GIS data types

➢ Spatial data
➢ Discrete and continuous
➢ Attribute data

➢ Storing data
➢ Spatial data representation
➢ Data Model
➢ Vector
➢ Raster

30
DATA TYPES
➢ Collection of thematic layers
➢ Spatial data and attribute data
➢ Spatial data: Describes the absolute and relative position of
geographic features.
➢ Discrete data
➢ Continuous data

➢Says where the feature is

➢Coordinate based
➢ Spatial data is stored in graphic file
and managed by file management system.

31
DATA TYPES
➢ Attribute data (Non spatial data)
➢ The non spatial data or the attribute data on the other hand
describes the characteristics of the spatial features.
➢ These characteristics can be quantitative or qualitative.
➢ Referred as tabular data

➢Says what the feature is Like : statistics, text, image, sound etc
➢Stored in tables and managed by RDBMS

➢Tables are inter connected by unique identification code

32
DATA TYPES

33
DATA TYPES- DISCRETE SPATIAL DATA
➢ Discrete data are distinct features that have definite
boundaries and identities
➢ The space could be seen as occupied with entities that are
described by their properties and can be located on earth using
coordinate systems.
➢ The entities have a clear boundary.
Buildings, roads, land parcels etc. are the example of discrete
entities
➢ A district, houses, towns, agricultural fields, rivers,
highways, …

34
DATA TYPES- CONTINUOUS SPATIAL DATA
➢ Continuous data has no defined borders or distinctive values,
instead, a transition from one value to another.
➢ The variation of an attribute over the space as a continuous
field.
➢ No physical boundary can ever be observed in such case.
➢ Temperature, precipitation, elevation, ...

35
DATA TYPES – Storing Data
➢Geo relational model: Many GIS package stores attribute data
separate from spatial data in a split data system
➢Spatial data – location of features ie “Geo”. Stored them in
a split file ie graphic file
➢Attribute data- description of the feature ie “Relational”.
Stored in relational data base

➢Object oriented data model:stores spatial and attribute data

in a single data base

36
DATA TYPES- Spatial data representation

• Data Model - An abstraction of the real world which

incorporates only those properties thought to be relevant to
the application at hand, define specific groups of entities, and
their attributes and the relationships between these entities.
• Data models describe how geographic data will be represented
in the GIS.
• Spatial data is traditionally represents in the form of a map.
• To store geographic data digitally there are 3 basic type of data
model.
• Vector, Raster, Image

37
DIGITAL SPATIAL DATA

Raster

Vector

Real world

Source: Defense Mapping School

38
National Imagery and Mapping Agency
SPATIAL DATA REPRESENTATION
➢The spatial features can be represented in four types in GIS.

➢Point : well, bench mark etc

➢Line: road , stream, contour lines
➢Area: land parcels water bodies
➢Surfaces

39
SPATIAL DATA REPRESENTATION
Different geographical features are best expressed by different
types of geometry ➢ Points
Discrete ➢ Lines
features ➢ Areas
➢ Networks
➢ A series of interconnecting
lines
➢ Road network
➢ River network
➢ Sewage network
Continuous ➢ Surfaces
features ➢ Elevation surface
➢ Temperature surface
40
POINTS
➢ A point is a 0 dimensional object and has only the
property of location (x,y)

➢ Points can be used to Model features such as a well,

building, power, pole, sample location etc.

➢ Other name for a point are vertex, node

Point

41
LINES
➢ A line is a one-dimensional object that has the property of
length
➢ Lines can be used to represent road, streams, faults, dikes,
maker beds, boundary, contacts etc.
➢ Lines are also called an edge, link, chain, arc
➢ In an ArcInfo coverage an arc starts with a node, has zero or
more vertices, and ends with a node

Line
42
AREAS (POLYGONS)
➢ A polygon is a two-dimensional object with properties of area
and perimeter

➢ A polygon can represent a city, geologic formation, dike, lake,

river, etc.

➢ Other name for polygons face, zone

Area
43
VECTOR SPATIAL DATA MODEL

44