The document provides information on the Global Positioning System (GPS) and remote sensing. It discusses the three main parts of GPS - the space segment consisting of satellites, the control segment of ground stations, and the user segment of receivers. It describes how GPS uses trilateration of satellite signals to determine position. Sources of error and applications including surveying, navigation, and remote sensing are also summarized. Remote sensing is defined and the basic components and types including optical, thermal, microwave, active and passive are outlined.

2. PRESENTED BY:
2012-CE-46
2012-CE-47
2012-CE-48
2012-CE-49

3. GLOBAL POSITIONING SYSTEM
AND
REMOTE SENSING

4. • The Global Positioning System (GPS) is a space-based satellite
navigation system that provides location and time information in all
weather conditions, anywhere on or near the Earth where there is an
unobstructed line of sight to four or more GPS satellites.
• Official name of GPS is Navigational Satellite Timing And Ranging
Global Positioning System (NAVSTAR GPS)
• First developed by the United States Department of Defense
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5. • GPS provides specially coded satellite signals that can be processed
with a GPS receiver, enabling the receiver to compute position,
velocity and time.
• A minimum of four GPS satellite signals are required to compute
positions in three dimensions and the time offset in the receiver clock.
• Accuracy and precision of data increases with more satellites.

6. • The design of GPS is based partly on similar ground-based radio-navigation
systems, such as LORAN and the Decca Navigator, developed in the early
1940s and used by the British Royal Navy during World War II.
• The GPS project was developed in 1973 to overcome the limitations of
previous navigation systems.
• GPS was created and realized by the U.S. Department of Defense (DOD)
• was originally run with 24 satellites.
• It became fully operational in 1995.
• Bradford Parkinson, Roger L. Easton, and Ivan A. Getting are credited with
inventing it.

7. PARTS OF GPS
There are three main parts of global positioning system:
• Space segment
• Control segment
• User segment

8. • The GPS space segment consists of a constellation of 24 satellites
transmitting radio signals to users. The United States is committed to
maintaining the availability of at least 24 operational GPS satellites, 95% of
the time. To ensure this commitment, the Air Force has been flying 31
operational GPS satellites for the past few years.
• GPS satellites fly in medium Earth orbit (MEO) at an altitude of
approximately 20,200 km (12,550 miles). Each satellite circles the Earth
twice a day.
• The satellites in the GPS constellation are arranged into six equally-spaced
orbital planes surrounding the Earth. Each plane contains four "slots"
occupied by baseline satellites.
• This 24-slot arrangement ensures users can view at least four satellites from
virtually any point on the planet.

9. • Because the GPS receiver calculates its location by trilateration, the task of
the receiver is to determine its distance from multiple satellites.
• The GPS system uses two types of signals to calculate distance.
• Code-phase ranging
• Carrier-phase ranging

10. Code-Phasing Ranging
• Each satellite has a unique signal.
• It continuously broadcasts its signal and also sends out a time
stamp every time it starts.
• The receiver has a copy of each satellite signal and determines
the distance by recording the time between when the satellite
says it starts its signal and when the signal reaches the receiver.
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11. CODE-PHASING RANGING – CONT.
• Distance is calculated using the velocity equation.
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

Velocity =
Distance
Time
• Rearranging the equation for distance:

Distance =VelocityxTime
• If the system knows the velocity of a signal and the time it
takes for the signal to travel from the sender to the receiver,
the distance between the sender and the receiver can be
determined.

12. SPACE SEGMENT—CARRIER-PHASE RANGING
• Surveying quality receivers
use the underlying carrier
frequency.
• Easy to determine number of
cycles.
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• The proportion of a partial cycle is difficult to
determine.
• This is called phase ambiguity.
• Phase ambiguity error is resolved by comparing
multiple signals from multiple receivers.
• More precise system.

13. CONTROL SEGMENT
• The CS consists of 3 parts:
• Master Control System
• Monitor Stations
• Ground Antennas

14. MASTER CONTROL STATION
• The master control station, located at Falcon Air Force Base in
Colorado Springs, Colorado, is responsible for overall management of
the remote monitoring and transmission sites.
• The MCS generates and uploads navigation messages and ensures the
health and accuracy of the satellite constellation. It receives
navigation information from the monitor stations, utilizes this
information to compute the precise locations of the GPS satellites in
space, and then uploads this data to the satellites.

15. MONITOR STATION
• Monitor stations track the GPS satellites as they pass overhead and
channel their observations back to the master control station. Monitor
stations collect atmospheric data, range/carrier measurements, and
navigation signals. The sites utilize sophisticated GPS receivers and
are operated by the MCS.
• There are 16 monitoring stations located throughout the world,
including six from the Air Force and 10 from the National Geospatial-
Intelligence Agency (NGA).

16. GROUND ANTENNAS
• Ground antennas are used to communicate with the GPS satellites for
command and control purposes. These antennas support S-band
communications links that send/transmit navigation data uploads and
processor program loads, and collect telemetry. The ground antennas
are also responsible for normal command transmissions to the
satellites.
• There are four dedicated GPS ground antenna sites co-located with the
monitor stations at Kwajalein Atoll, Ascension Island, Diego Garcia,
and Cape Canaveral.

17. USER SEGMENT
• The GPS User Segment consists of the GPS receivers and the user
community.
• GPS receivers convert SV signals into position, velocity, and time
estimates.
• The receiver determines its location by trilateration.

18. GPS Trilateration
• Each satellite knows its
position and its distance from
the center of the earth.
• Each satellite constantly
broadcasts this information.
• With this information and the
calculated distance, the
receiver calculates its position.
• Just knowing the distance to
one satellite doesn’t provide
enough information.
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19. GPS Trilateration--cont.
• When the receiver knows
its distance from only one
satellite, its location could
be anywhere on the earths
surface that is an equal
distance from the satellite.
• Represented by the circle in
the illustration.
• The receiver must have
additional information.
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20. GPS Trilateration--cont.
With signals from two satellites, the
receiver can narrow down its location
to just two points on the earths
surface.
Were the two circles intersect.
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21. GPS Trilateration--cont.
• Knowing its distance from
three satellites, the
receiver can determine its
location because there is
only two possible
combinations and one of
them is out in space.
• In this example, the
receiver is located at b.
• The more satellite that are
used, the greater the
potential accuracy of the
position location.
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22. Factors Influencing Position Accuracy
 The number of satellites (channels) the receiver can track.
 The number of satellites that are available at the time.
 The number of different systems that the receiver can track.
 The system errors that are occurring during the time the receiver is
operating
 Differential GPS uses one unit at a known location and a rover.
The stationary unit compares its calculated GPS location with the actual
location and computes the error.
The rover data is adjusted for the error.
• Real Time Kinematic (RTK)
• Post processing
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23. GPS ERRORS
• Satellite geometry
• Satellite orbits
• Multipath
• Atmospheric effects
• Clock
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24. ERROR-SATELLITE GEOMETRY
• Describes the position of the satellites with each other.
• The best geometry, and least error, occurs when the satellites are
equally distributed.
• Satellite geometry error occurs when the satellites are concentrated in
on quadrant or in a line.
• The Positional Dilution of Precision (PDOP) is an indication of the
quality of the 3D coordinate satellite geometry.
• General surveys PDOP’s should be less than 3.
• Satellite geometry error is not measureable, it tends to enhance other
errors.
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25. ERROR-ORBITS
• Even though the satellites are positioned in very precise orbits,
slight shifts are possible do to the gravitational influences of the
sun and moon.
• Orbit errors can be as high as 2 meters.
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26. ERROR-MULTIPATH
• Multipath errors are caused by satellite signals reflecting off of
objects.
• Increase chance of occurrence when around tall buildings.
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27. ERROR-ATMOSPHERIC
• Radio signals travel at the speed of light in space, but are slowed
down by the atmosphere.
• The majority of this effect can be eliminated by the receiver.
• Lower frequency signals are slowed down more that high
frequencies.
• The receiver can determine the difference in the arrival time of
high and low frequency signals and calculate a correction.
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28. ERROR-CLOCK
• In spite of the synchronization of the satellite and receiver clocks,
and small amount of inaccuracy in timing remains.
• This can result in errors up to 1 meter.
• To keep clock errors to 1 meter or less, the time error must be be
limited to 20-30 nanoseconds.
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29. APPLICATIONS OF GPS
• Military GPS user equipment has been integrated into fighters,
bombers, tankers, helicopters, ships, submarines, tanks, jeeps, and
soldiers' equipment.
• In addition to basic navigation activities, military applications of GPS
include target designation of cruise missiles and precision-guided
weapons and close air support.
• To prevent GPS interception by the enemy, the government controls
GPS receiver exports
• GPS satellites also can contain nuclear detonation detectors.

30. • Automobiles are often equipped GPS receivers.
• They show moving maps and information about your position on the map,
speed you are traveling, buildings, highways, exits etc.
• For aircraft, GPS provides
• Continuous, reliable, and accurate positioning information for all phases of
flight on a global basis, freely available to all.
• Safe, flexible, and fuel-efficient routes for airspace service providers and
airspace users.
• Potential decommissioning and reduction of expensive ground based
navigation facilities, systems, and services.
• Increased safety for surface movement operations made possible by situational
awareness.

31. • Marine applications
• GPS allows access to fast and accurate position, course, and speed
information, saving navigators time and fuel through more efficient traffic
routing.
• Provides precise navigation information to boaters.
• Enhances efficiency and economy for container management in port facilities.

32. GPS IN SURVEYING
The combination of real time positioning , mobile data communication, data
processing and application software, all contribute to a new era in surveying.
• Today GPS is a vital part of surveying and mapping activities around the world.
• Global applications of GPS provides a powerful geodetic tool.
• GPS can be applied to programs for topography , and for correction to sea level ,
curvature and refraction.
• GPS techniques permits the collection of data on specified profile , cross section
and boundary location.
• Contours may be readily plotted from the plotted data.
• GPS is also useful for layout works.
• The accurate positioning through GPS enables the development of precise seismic
maps and location of drill site w.r.t geological structures.

34. GPS SURVEYING TECHNIQUES
• GPS surveying implies the precise measurements of the vector between two GPS
instruments.
• Mainly 3 techniques are used in GPS surveying:
i. Static survey.
ii. Re-occupation technique.
iii. Kinematic technique.

35. STATIC SURVEYS
a) Traditional static surveying:
• First high-precision method for GPS requiring atleast two recievers.
• Accuracy obtained is 5-10 mm + 1-2 ppm of the baseline length.
• One base receiver is placed over a point of known coordinates.
• Other is placed over new permanent stations to be positioned.
• This technique is useful for long line in geodetic control ,
photogrametic control for arial survey.
• Limitation of this method is the need of hours of observation required.

36. b) Rapid surveying techniques:
• this technique ideally requires one receiver to be positioned on a station of
known coordinates.
• Other moves from station to station.
• No need to maintain a lock on satellites while moving rover receiver.
• Accuracy of a few millimeter (10-30) is possible
• Used over short (15 km) lines.

37. RE-OCCUPATION TECHNIQUE
• Also known as pseudo static / pseudo kinematics techniques.
• In this technique a pair of receiver occupies a pair of points for two brief periods
(2-5 min ) that are separated in time by 60-30 min.
• This technique is used when less than 4 satellites are used or GDOP is weak.
• the processing software will combine the satellite observations to provide a
solution.
• Accuracy is 10-30 mm .

38. KINEMATIC TECHNIQUE
• Both the base unit and rover unit occupies a base line and start from a point of
known coordinates.
• Roving station then moves to new location. While satellite signals are locked.
• If lock is lost , the receiver is held stationary until initial ambiguities are resolved
then survy can continue.
 A similar technique real time kinematics (RTK) is also used.
• In RTK rover does not occupy the base line.
• Base station transmits code and carrier phase data to roving receiver.
• Rover use this data to help resolve ambiguities and to solve for change in
coordinates difference between reference and roving station.
• This is also known as on-the-fly ambiguity resolution techniques.

40. REMOTE SENSING

41. REMOTE SENSING
• Remote sensing is defined as the technique of obtaining information about objects
through the analysis of data collected by special instruments that are not in
physical contact with the objects of investigation.
OR
• Collection of information about an object without coming into physical contact

42. Energy Source or Illumination (A)
Radiation and the Atmosphere (B)
Interaction with the Target (C)
Recording of Energy by the Sensor (D)
Transmission, Reception, and Processing
(E)
Interpretation and Analysis (F)
Application (G)
Remote Sensing Process Components

43. TYPES
• Based on Range of Electromagnetic Spectrum:-
1. Optical Remote Sensing.
2. Thermal Remote Sensing.
3. Microwave Remote Sensing.
• Based on the source of the energy:-
1. Active remote sensing.
2. Passive remote sensing.

44. OPTICAL REMOTE SENSING
• The optical remote sensing devices operate in the visible, near infrared, middle
infrared and short wave infrared portion of the electromagnetic spectrum.
• These devices are sensitive to the wavelengths ranging from 300 nm to 3000
nm.

45. THERMAL REMOTE SENSING
• The sensors, which operate in thermal range of electromagnetic spectrum record,
the energy emitted from the earth features inthe wavelength range of 3000 nm to
5000 nm and 8000 nm to 14000 nm.

46. ACTIVE REMOTE SENSING
• Active remote sensing uses an artificial source for energy.
• For example the satellite itself can send a pulse of energy which can interact with
the target.
• In active remote sensing, humans can control the nature (wavelength, power,
duration) of the sourceenergy.
• Active remote sensing can be carried out during day and night and in all weather
conditions.
• Example-
RADAR

47. PASSIVE REMOTE SENSING
• Passive remote sensing depends on a natural source to provide energy.
• The sun is the most powerful and commonly used source of energy for passive
remote sensing.
• The satellite sensor in this case records primarily the radiation that is reflected
from the target.
• Examles:
radiometer

48. RESOLUTION
All remote sensing systems have four types of resolution:
• Spatial
• Spectral
• Temporal
• Radiometric

49. SPATIAL RESOLUTION
• Spatial resolution is the smallest area on Earth that a satellite can observe.
• Depends on the type of instrument

50. • Low spatial resolution (1
km):
– Major regional features are
visible (rivers, urban areas,
clouds)
– Detailed features are NOT
visible!

51. • High spatial resolution (10 m):
– Detailed features are visible!
– Usually high spatial resolution
images are expensive!!

52. TEMPORAL RESOLUTION
• Temporal resolution is how frequently a satellite observes the same
area on Earth.
• Depends primarily on the orbit of the satellite
• High temporal resolution (e.g., 30 minutes):
nearly continuous observations
• Low temporal resolution (e.g., 1 day):
only one observation per day

53. RADIOMETRIC RESOLUTION
• This is the smallest difference in radiant energy that can be detected by
a sensor.
• It is applicable to both photographs and digital images

54. 2-BIT IMAGE 8-BIT IMAGE

55. SPECTRAL RESOLUTION
• This refers to the electromagnetic radiation wavelengths to which a remote sensing
system is sensitive.
• There are two main characteristics.
a) the no of wavelength bands.
b) the width of each wave band.
• A larger no of bands and narrower band
Width for each band will give
rise to a high spectral resolution.

56. APPLICATIONS OF REMOTE SENSING
 Meteorology
 Profiling of atmospheric temp. and water vapor
 Measuring wind velocity
 Oceanography
 Measurements of sea surface temperature
 Mapping ocean currents
 Glaciology
 Mapping motion of sea ice and ice sheets
 Determining the navigability of the sea
 Geology
 Identification of rock types
 Location of geological faults and anomalies
 Agriculture
 Monitoring the extend and type of vegetation
 Mapping soil types
 Hydrology
 Assessing water resources
 Forecasting melt water run-off from snow
 Disaster control
 Warning of sand and dust storms, flooding
 Monitoring of pollution

57. ADVANTAGES OF REMOTE SENSING
• Provides a regional view (large areas).
• Provides repetitive looks at the same area.
• Remote sensors "see" over a broader portion of the spectrum than the human eye.
• Provides geo-referenced, digital, data.
• Some remote sensors operate in all seasons, at night, and in bad weather.
• Give information of inaccessible area.

58. DISADVANTAGES
• Expensive to build and operate.
• Measurement uncertainty can be large.
• Data interpretation can be difficult