1. Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft

2. Overview
•Why GPS?
•History of GPS
•Satellites
•Ground control
•Measurements of distance
•Precision timing
•Satellite location
•Sources of error

3. Why GPS?
• Plane surveying has not changed for many years
• Measurement of distances and angles
• Use of ground control points
• Specialized training and understanding
• Careful & tedious work
• Plane surveying: daytime only
• You may use this in research or work

4. History of GPS
• Need for a more flexible tool
• Development of GPS & related systems from 1940s
through present
• Less user training
• Potentially very accurate
Location, navigation
• Faster tool (submarines)

5. Why was the GPS created?
• Cold War technology
• Fast locational fix
• Submarine surface, missile launch_
#
Moskva

6. Satellites
GPS SV
• Constellation of 24 satellites for full
GPS component
• The first satellite was placed in orbit on 22nd February
1978
• Expensive and advanced satellites
• New satellites deployed as older satellites fail
• Return interval 12 hours for each space vehicle (SV)

8. • 6 orbital planes (4 in each plane)
spaced 60° apart
• 5-8 SV visible at any time from
any point on Earth ellipsoid
• SPS( Standard Positioning Service) signal for general
public
• PPS( Precise Positioning Service) signal can only be
used by authorized government agencies

9. Ground control
• Control segment tracks satellites
• Send corrected ephemeris & time offsets to SVs
• SVs incorporate these updates in signals sent to
receivers

10. Measurements of distance: how it works
• Satellites broadcast radio signals (EM radiation)
• Simple distance calculation
d = r * t
• rate is known (speed of light)
• time is known (difference between send & receive)
• distance is calculated

11. Measurements of distance: how it works
• Distance measurement
end: 0.06 s
start: 0.00 s

12. Satellite location
• Given 1 satellite …

13. Satellite location
• We can locate our position on the surface of a sphere

14. Satellite location
• Given 2 satellites …

15. Satellite location
• Given 2 satellites …

16. Satellite location
• We can locate our position on the intersection of 2
spheres (a circle)

17. Satellite location
• Given 3 satellites …

18. Satellite location
• We can locate our position on the intersection of 3
spheres (2 points)

19. Satellite location
• Given 4 satellites we can locate our position on the
intersection of 4 spheres (1 point)

20. Satellite location
• The point should be located on the earth’s surface

21. Satellite location
• The precise location is determined
• Giving four variables Longitude, Altitude, Height and
Time.

22. Precision timing
• Distance calculation depends on accurate timing
• SVs contain atomic clocks, which are extremely
accurate
• However, receivers do not contain clocks as accurate
as SVs
• Receivers “calculate” correct time based on multiple
signals . . .

23. Sources of error: Atmospheric effects
• Ionospheric effects: ionizing radiation
• Tropospheric effects: water vapor
• Light is “bent” or reflected/refracted

24. Sources of error: Clock errors
• Receiver clock errors, mostly corrected by software in
receiver
• Satellite clock errors
• SV timing & clocks are constantly monitored and
corrected

25. Sources of error: Receiver errors
• Power interrupts
• On-board microprocessor failure
• Firmware
• Software
• Blunders (user error)

26. Sources of error: Landscape features
• Natural & artificial features can intercept signals
• Mountains, valleys, hills, buildings, tree canopies, etc.

27. Sources of error: Multipath errors
• Natural & artificial features can reflect signals
• Multiple “ghost” signals can confound timing

28. Sources of Signal Interference
Earth’s Atmosphere
Solid Structures
Metal Electro-magnetic Fields

29. DGPS Site
x+30, y+60
x+5, y-3
True coordinates =
x+0, y+0
Correction = x-5, y+3
DGPS correction = x+(30-5) and
y+(60+3)
True coordinates = x+25, y+63
x-5, y+3
Differential GPS
DGPS ReceiverReceiver

30. Tsunami

31. Tsunamis Detection
The Mission
Tsunamis Detection can help to minimize
loss of life and property from future
tsunamis.

32. Introduction
Tsunamis Detection:
• Tsunami disaster detection technologies
• Information dissemination technologies

33. Tsunamis Detection
• Tsunami disaster detection technologies
Earthquakes cannot be predicted, resulting
tsunamis can be detected by seabed monitors
and ocean buoys leaving adequate time for
evacuation.
• Information dissemination technologies
However, the technology is a minor part of the
solution. A mechanism needs to be in place to
interpret alerts, relay the warning to local
communities and enable them to undertake
quick action.

34. TSUNAMETER -- Architecture

35. TSUNAMETER -- Architecture
The system is composed of the following
main parts:
1. In underwater monitoring module (UM)
installed at the sea bed;
2. A surface buoy (SB) moored in the area of
the UM;
3. An “in water” communication segment
connecting the UM with SB;
4. An onshore centre (OC) hosting a standard
PC server;
5. A satellite communication segment
connecting SB and OC..

36. TSUNAMETER -- Underwater Monitoring Module (UM)

37. TSUNAMETER – Surface Buoy
The SB is composed by a metallic pole and a
foam body having a diameter of 1.45 m. The
main parts installed on the buoy are:
1. The electronic box containing the SB Data
Acquisition and Communication System (SB-
DACS) relied on the same type of electronics
of the UM;

38. 2. An autonomous power supply system composed of 3
photovoltaic panels (12V- 50W
each) and a gel battery pack (12V- 400Ah);
3. A magneto-inductive surface modem or the acoustic
modem for the data link with the underwater unit;
4. A satellite modem Inmarsat C for reliable data
connection with the Onshore Centre (OC).

39. TSUNAMETER – Surface Buoy

40. Tsunameter -- System Functionalities
It is provides the main basic functionalities
listed below:
1. Continuous measurement of the sea bottom
pressure with a rate of 15s, 30s, 1min, 2min,
5min selectable be the user in the OC.
Optional monitoring of earthquakes
occurrence.
2. On line processing of the pressure data filter
to detect a frequency component typical of a
tsunami: the thresholds for the detection of
tsunami waves can be configured by the OC
user.

41. Tsunameter -- System Functionalities
3. The beginning of a possible event is
automatically triggered by the pressure sensors
(able to detect earthquake waves) and also by
the hydrophone/seismometer if installed in UM.
4. The UM can start the tsunami detection
algorithm also on user request from the OC in
case of identification of seismic activity in the
interested area.
5. Daily synchronisation of the SB and UM clock
with the GPS.
6. Self-diagnostic and periodical notification to the
OC.

42. Tsunameter -- System Functionalities
7. Internal logging in UM and SB of all
acquired data, all detected events, all
diagnostic status and exchanged messages
(black box).
8. Remote configuration of the UM (change of
communication settings, filtering parameters,
on/off of sensors and devices, software
updating).
9. Reception of commands from OC and
notification of its execution;
10. Reception of data request from OC and reply
with the requested data.

43. Tsunameter -- Detection of an anomaly
The main scenario in case of detection of an
anomaly in the pressure signal is the following:
1. The UM-DACS in its standard operating mode
IDLE MODE detects an unexpected variation in
the pressure signal;
2. A notification message is sent to the OC and the
UM-MODULE changes in the new status
ALARM MODE;
3. In ALARM MODE the UM sends periodically
a message to the OC: on request the user in the
OC can transfer all pressure data acquired in
ALARM MODE.

44. Tsunameter -- Detection of an anomaly
4. In case of detection of a tsunami events
(frequency component in the range
0.01..0.0005Hz) an TSUNAMI DETECTION
message is sent to the OC.
5. The user in the OC can verify the pressure data
acquired during the ALARM MODE to
validate the alarm condition and to verify its
amplitude.

45. 6. After the decrease of the tsunami wave components under
some minimal threshold (parameter remotely configurable by
the OC user) and after a period of some hours (parameter
remotely configurable by the OC user), the UM chages from
ALARM MODE to IDLE MODE.

46. Information Dissemination
The Tsunami Alarm System
receives earthquake and
tsunami warning information
from a multiplicity of seismic
measuring stations and tsunami
warning stations from different
countries.
Alarm being sent to your
mobile telephone

47. Conclusion:
Key Components to an ideal Tsunami
Warning and Response System:
1. Risk Assessment
2. Detection
3. Warning
4. Response Plan
5. Ready Public
6. Situational Awareness
7. Lessons Learned

48. With the Tsunamis Detection,
no fear visiting the coast all over
the world !
Next

49. Some of the GPS Receivers

50. Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft