GPS helps us identify exact location of a place/feature in the globe. Now-a-days we can carry out survey, enter data and process data. GPS is very helpful in soil survey

1. Dr. M. Altaf Hossain
PSO
Survey Section

2.  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.
 A global navigation satellite system consisting of
positioning satellites and their associated ground
stations.
The system provides critical capabilities to military,
civil and commercial users around the world.
It is maintained by the US government and is freely
accessible to anyone with a GPS receiver.

3.  The GPS project was developed in 1973 to overcome the limitations of previous navigation
systems, integrating ideas from several predecessors, including a number of classified
engineering design studies from the 1960s.
 GPS was created and realized by the U.S. Department of Defense (DoD) and 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.
 Advances in technology and new demands on the existing system have now led to efforts to
modernize the GPS system and implement the next generation of GPS III satellites and Next
Generation Operational Control System (OCX).
 Announcements from Vice President Al Gore and the White House in 1998 initiated these
changes. In 2000, the U.S. Congress authorized the modernization effort, GPS III.
 In addition to GPS, other systems are in use or under development. The Russian Global
Navigation Satellite System (GLONASS) was developed contemporaneously with GPS, but
suffered from incomplete coverage of the globe until the mid-2000s.
 There are also the planned European Union Galileo positioning system, Chinese Compass
navigation system, and Indian Regional Navigational Satellite System.

4. Block
Launch
Period
Satellite launches
Currently in orbit
and healthySuccess Failure In preparation Planned
I 1978–1985 10 1 0 0 0
II 1989–1990 9 0 0 0 0
IIA 1990–1997 19 0 0 0 9
IIR 1997–2004 12 1 0 0 12
IIR-M 2005–2009 8 0 0 0 7
IIF From 2010 4 0 10 0 4
IIIA From 2014 0 0 0 12 0
IIIB — 0 0 0 8 0
IIIC — 0 0 0 16 0
Total 61 2 10 36 31
(Last update: November 30, 2013)

5. Satellites are placed in Medium Earth Orbit (MEO) at
an altitude of 12,552 miles
Orbital periods of MEO satellites range from 2 - 12
hrs.
Orbital period of GPS satellites is 12 hours (2
rotations/day)
GPS Satellites travel at a speed of 7,000 mph
Orbits are arranged so that at any time, anywhere on
Earth, at least four satellites are visible in the sky

6. A visual example of a 24 satellite GPS constellation in motion with
the Earth rotating. About nine satellites are visible from any point
on the ground at any one time, ensuring considerable redundancy
over the minimum four satellites needed for a position.

7. A GPS receiver calculates its position by
precisely timing the signals sent by GPS
satellites high above the Earth.
Each satellite continually transmits messages
that include-
 the time the message was transmitted
 satellite position at time of message
transmission
 Differential time of arrival and triangulation
are the methods used to determine location
in a GPS system.

8.  Differential Time of Arrival: Differential time of
arrival is the method used to determine how far
each satellite is from a GPS device. Although
each satellite transmits its position and the time
it was at that position, it takes time for that
signal to reach the Earth.
 The receiver contains a very accurate clock,
which can determine the difference in time
between the current time and when the satellite
sent the signal. With this differential time and
the speed of radio waves, the distance from each
of the three satellites can be determined using
the simple formula:
Rate x Time = Distance

9. Trilateration
 Trilateration is a method that is used to determine
position on Earth in three dimensions. GPS deals with
three-dimensions rather than two. Since the distance
from the Earth to a satellite results in a sphere
rather than a flat circle, the calculation is a bit
complex.
 Using trilateration, rather than draw circles to
determine position we need to draw spheres.
 For example, if the first acquired satellite is 25,000
miles from position one cannot simply draw a circle
around that satellite and determine a position 25,000
miles from it. A sphere must be plotted, extending
toward Earth and away from Earth.

10.  A second satellite is calculated to be 25,001 miles from
position, resulting in another sphere. The two spheres
intersect, creating a perfect circle. A circular plane now
exists, extending down through the earth and out into
space. A large number of potential positions have now
been eliminated, but there is not yet an exact location.
Many potential positions still exist and a third satellite is
needed to define a sphere that intersects with the two
current spheres resulting in two points that define
possible position. One point is in space and one is on
earth. Since the world is roughly a sphere, the point in
space can be eliminated and the approximate position of
the GPS receiver is located on Earth.
 A fourth satellite is necessary to account for altitude and
provide an exact fix of the location. The plotting of a
fourth sphere provides the exact location and altitude of
the receiver at the time the four measurements were
taken.

11.  The receiver uses the messages it receives to determine
the transit time of each message and computes the
distance to each satellite using the speed of light.
 Each of these distances and satellites' locations defines
a sphere.
 The receiver is on the surface of each of these spheres
when the distances and the satellites' locations are
correct.
 These distances and satellites' locations are used to
compute the location of the receiver using the
navigation equations.
 This location is then displayed, perhaps with a moving
map display or latitude and longitude; elevation or
altitude information may be included, based on height
above the geoid (e.g. EGM96).
 In typical GPS operation, four or more satellites must be
visible to obtain an accurate result.

12. Global Positioning System Operation - GPS
Diagram

13. The current GPS consists of three major
segments.
These are the space segment (SS), a control
segment (CS), and a user segment (US).
The U.S. Air Force develops, maintains, and
operates the space and control segments.
GPS satellites broadcast signals from space,
and each GPS receiver uses these signals to
calculate its three-dimensional location
(latitude, longitude, and altitude) and the
current time.

14.  The space segment is composed of 24 to 32 satellites in
medium Earth orbit and also includes the payload
adapters to the boosters required to launch them into
orbit.
 The control segment is composed of a master control
station, an alternate master control station, and a host
of dedicated and shared ground antennas and monitor
stations.
 The user segment is composed of hundreds of thousands
of U.S. and allied military users of the secure GPS
Precise Positioning Service, and tens of millions of civil,
commercial, and scientific users of the Standard
Positioning Service.

15. CONTROL SEGMENT: Ground monitor
station used from 1984 to 2007SPACE SEGMENT: Satellite
USER SEGMENT: GPS
Figure: Structure of GPS

16.  GPS receivers are composed of an antenna,
tuned to the frequencies transmitted by the
satellites, receiver-processors, and a highly
stable clock (often a crystal oscillator).
 They may also include a display for providing
location and speed information to the user.
 A receiver is often described by its number of
channels: this signifies how many satellites it
can monitor simultaneously.
 Originally limited to four or five, this has
progressively increased over the years so that,
as of 2007, receivers typically have between 12
and 20 channels.

17.  While originally a military project, GPS is
considered a dual-use technology, meaning it has
significant military and civilian applications.
 GPS has become a widely deployed and useful tool
for commerce, scientific uses, tracking, and
surveillance.
 GPS's accurate time facilitates everyday activities
such as banking, mobile phone operations, and even
the control of power grids by allowing well
synchronized hand-off switching.

18.  Astronomy: both positional and clock synchronization data is used in Astrometry and
Celestial mechanics calculations. It is also used in amateur astronomy using small
telescopes to professionals observatories, for example, while finding extrasolar
planets.
 Automated vehicle: applying location and routes for cars and trucks to function
without a human driver.
 Cartography: both civilian and military cartographers use GPS extensively.
 Cellular telephony: clock synchronization enables time transfer, which is critical for
synchronizing its spreading codes with other base stations to facilitate inter-cell
handoff and support hybrid GPS/cellular position detection for mobile emergency calls
and other applications. The first handsets with integrated GPS launched in the late
1990s. The U.S. Federal Communications Commission (FCC) mandated the feature in
either the handset or in the towers (for use in triangulation) in 2002 so emergency
services could locate 911 callers. Third-party software developers later gained access
to GPS APIs from Nextel upon launch, followed by Sprint in 2006, and Verizon soon
thereafter.
 Clock synchronization: the accuracy of GPS time signals (±10 ns) is second only to the
atomic clocks upon which they are based.

19.  Disaster relief/emergency services: depend upon GPS for location
and timing capabilities.
 Meteorology-Upper Airs: measure and calculate the atmospheric
pressure, wind speed and direction up to 27 km from the earth's
surface
 Fleet Tracking: the use of GPS technology to identify, locate and
maintain contact reports with one or more fleet vehicles in real-
time.
 Geofencing: vehicle tracking systems, person tracking systems, and
pet tracking systems use GPS to locate a vehicle, person, or pet.
These devices are attached to the vehicle, person, or the pet
collar. The application provides continuous tracking and mobile or
Internet updates should the target leave a designated area.[72]
 Geotagging: applying location coordinates to digital objects such as
photographs (in exif data) and other documents for purposes such
as creating map overlays with devices like Nikon GP-1

20.  GPS Aircraft Tracking
 GPS for Mining: the use of RTK GPS has significantly improved several
mining operations such as drilling, shoveling, vehicle tracking, and
surveying. RTK GPS provides centimeter-level positioning accuracy.
 GPS tours: location determines what content to display; for instance,
information about an approaching point of interest.
 Navigation: navigators value digitally precise velocity and orientation
measurements.
 Phasor measurements: GPS enables highly accurate timestamping of power
system measurements, making it possible to compute phasors.
 Recreation: for example, geocaching, geodashing, GPS drawing and
waymarking.
 Robotics: self-navigating, autonomous robots using a GPS sensors, which
calculate latitude, longitude, time, speed, and heading.
 Surveying: surveyors use absolute locations to make maps and determine
property boundaries.
 Tectonics: GPS enables direct fault motion measurement in earthquakes.
 Telematics: GPS technology integrated with computers and mobile
communications technology in automotive navigation systems

21.  Proceed to an outdoor location with a clear view of the sky from
horizon to horizon. You should stand well away from the building,
trees, etc., so that you have an unobstructed view of the sky.
 Hold the receiver at arm's length from your body so the built-in
antenna (the flat area above the display) is parallel to the
ground. Power-on the GPS receiver by pressing the red key. After
the Welcome Page, by default the receiver displays the Satellite
Status Page (sky view) and begins searching for satellite signals.
GPS receivers get their information from a system of 24 orbiting
satellites located approximately 18,300 kilometers (11,000 miles)
above the Earth's surface. To provide accurate position
information, the receiver must be able to "see" three or four
satellites.
 As satellites are acquired, you will see bars appear on the graph
at the bottom of the display; these bars indicate the strength of
the satellite signal. Once enough satellites have been acquired,
the Satellite Status Page will disappear automatically and be
replaced with the Position Page (graphic compass).

22.  Your GPS receiver has been pre-programmed (by
your instructor) with a mystery location. Now
let's explore how the GPS receiver can be used
to navigate to an unknown location.
 Randomly choose three-to-five different
locations on the grounds. These locations should
be fairly distant from each other (at least 500
feet apart). Remember to choose locations
where the GPS receiver will have a good view of
the sky.

23.  Proceed to Point No. 1. Record the following
information in the data table below:
 Use the Position Page (graphic compass) to acquire
your current position. Record your latitude and
longitude.
 Press the GOTO key. The Navigation Page (graphic
highway) will appear with the waypoint field
highlighted. Press the up or down arrow keys to
scroll through the available waypoints until
"MYSLOC" (short for "mystery location") is
displayed.
 Press the ENTER key to confirm that you want to
navigate to "MYSLOC". Record the bearing (in
degrees) and distance (in kilometers) to the
mystery location.
 Briefly describe the location.

24.  Repeat Steps 1-3 until you have visited at least
three different locations on the grounds. Do not
actually go to the mystery location!
Field Data
Point
No.
Latitude
(deg. N)
Longitude
(deg. W)
Bearing
(deg.)
Distance
(km)
Brief
Description
1
2
3
4
5

25.  Using your Field Data for Point No. 1
(latitude, longitude, and distance), draw
Circle 1. Technique Hint: Use latitude and
longitude to locate Point 1 on the map; use
the map scale to measure the radius of Circle
1; draw the circle.
 Using your Field Data for Point No. 2, draw
Circle 2.
 Using your Field Data for Point No. 3, draw
Circle 3.
 You would discover that there is one and only
one point where all three circles intersect.

26. Yield Monitoring Systems
 Yield monitoring systems typically utilize a mass flow sensor for
continuous measuring of the harvested weight of the crop. The
sensor is normally located at the top of the clean grain elevator.
As the grain is conveyed into the grain tank, it strikes the sensor
and the amount of force applied to the sensor represents the
recorded yield. While this is happening, the grain is being tested
for moisture to adjust the yield value accordingly.
 At the same time, a sensor is detecting header position to
determine whether yield data should be recorded. Header width
is normally entered manually into the monitor and a GPS, radar,
or a wheel rotation sensor is used to determine travel speed. The
data is displayed on a monitor located in the combine cab and
stored on a computer card for transfer to an office computer for
analysis.
 Yield monitors require regular calibration to account for varying
conditions, crops, and test weights. Yield monitoring systems cost
approximately $3,000 to $4,000, excluding the cost of the GPS
unit.

27.  GPS technology is used to locate and map
regions of fields, such as high weed, disease,
and pest infestations. Rocks, potholes, power
lines, tree rows, broken drain tile, poorly
drained regions, and other landmarks can
also be recorded for future reference.
 GPS is used to locate and map soil-sampling
locations, allowing growers to develop
contour maps showing fertility variations
throughout fields.
 The various datasets are added as map layers
in geographic information system (GIS)
computer programs. GIS programs are used
to analyze and correlate information
between GIS layers.

28.  GPS technology is used to vary crop inputs
throughout a field based on GIS maps or real-time
sensing of crop conditions. Variable rate technology
requires a GPS receiver, a computer controller, and
a regulated drive mechanism mounted on the
applicator. Crop input equipment, such as planters
or chemical applicators, can be equipped to vary
one or several products simultaneously.
 Variable rate technology (VRT) is used to vary
fertilizer, seed, herbicide, fungicide, and insecticide
rates and for adjusting irrigation applications. The
cost of all of the components necessary for variable
rate application of several products is
approximately $15,000, not including the cost of the
GPS receiver. Technology capable of varying just one
product costs approximately $4,000.

29.  The drawback to current GPS units is that
they cannot track positions inside of
buildings or other places that shield signals
coming from satellites.

30. Thanks for patience hearing