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Global Positioning System
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Overview
•Why GPS?•History of GPS•Satellites•Ground control•Measurements of distance•Precision timing •Satellite location•Sources of error
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
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)
Why was the GPS created?
• Cold War technology• Fast locational fix• Submarine surface, missile launch_
#Moskva
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)
• 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
Ground control
• Control segment tracks satellites• Send corrected ephemeris & time offsets to SVs• SVs incorporate these updates in signals sent to
receivers
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
Measurements of distance: how it works
• Distance measurement
end: 0.06 s
12,000 mi
start: 0.00 s
Satellite location
• Given 1 satellite …
Satellite location
• We can locate our position on the surface of a sphere
Satellite location
• Given 2 satellites …
Satellite location
• Given 2 satellites …
Satellite location
• We can locate our position on the intersection of 2 spheres (a circle)
Satellite location
• Given 3 satellites …
Satellite location
• We can locate our position on the intersection of 3 spheres (2 points)
Satellite location
• Given 4 satellites we can locate our position on the intersection of 4 spheres (1 point)
Satellite location
• The point should be located on the earth’s surface
Satellite location
• The precise location is determined• Giving four variables Longitude, Altitude, Height and
Time.
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 . . .
Sources of error: Atmospheric effects
• Ionospheric effects: ionizing radiation• Tropospheric effects: water vapor• Light is “bent” or reflected/refracted
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
Sources of error: Receiver errors
• Power interrupts• On-board microprocessor failure• Firmware • Software• Blunders (user error)
Sources of error: Landscape features
• Natural & artificial features can intercept signals• Mountains, valleys, hills, buildings, tree canopies, etc.
Sources of error: Multipath errors
• Natural & artificial features can reflect signals• Multiple “ghost” signals can confound timing
Sources of Signal InterferenceSources of Signal Interference
Earth’s Atmosphere
Solid Structures
Metal Electro-magnetic Fields
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 GPSDifferential GPS
DGPS ReceiverReceiver
Tsunami
Tsunamis Detection
The Mission
Tsunamis Detection can help to minimize loss of life and property from future tsunamis.
Introduction
Tsunamis Detection:
• Tsunami disaster detection technologies
• Information dissemination technologies
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.
TSUNAMETER -- Architecture
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..
*
TSUNAMETER -- Underwater Monitoring Module (UM)
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;
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).
TSUNAMETER – Surface Buoy
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.
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.
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.
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.
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.
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.
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
Conclusion:
Key Components to an ideal Tsunami Warning and Response System:
1. Risk Assessment2. Detection3. Warning4. Response Plan5. Ready Public6. Situational Awareness7. Lessons Learned
With the Tsunamis Detection,
no fear visiting the coast all over
the world !
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Some of the GPS Receivers
