Презентация на тему GPS

/ Uses
Other GPS Systems
The Future of GPS

On
Users Discussion
GPS Operation and Tasks
GPS Data Collection
Mission planning
Data dictionaries
Data

accuracy
Importing GPS Data into ArcMap
GPS Accuracy
Limitations

scientist were able to track Sputnik observing the doplar

effect in radio signals
Using this technique they could effectively track the satellite - gps in reverse

TRANSIT – (Navy Navigation Satellite System)
6 satellite system
1100km polar orbits
1m accuracy w/ days of collection and post processing
90minute pass time
interpolate position
Low navigational accuracy
Retired in late 1996 (32 year service)

History

weather / Line of Site
The only Free Global Utility
Unlimited

Number of Simultaneous Users
Satellite / Receiver based system
Developed by the DoD and US Navy
Operated by:
Military: Air Force Joint program Office
Civil: U.S. Coast Guard Navigation Center

transmit radio signals (code)
GPS Receivers are always tuned to

that frequency
Receivers are producing the same code for each satellite
Each signal is then timed to determine the delay between both signals
distance between receiver and the satellite is equal to the delay
Sort of…
Process is repeated for each satellite in view

Principle Concepts of GPS Technology

atomic clocks each
Entire System is Synchronized
Receivers do not have

atomic clocks
Must have at least 4 different satellites
Receivers use Triangulation algorithm from 3 satellites for position / with timing error
Hence the pseudo range = range + timing error
1 additional satellite used to calculate receivers time error (Algebra Equation)

Principle Concepts of GPS Technology

atomic clocks each
Entire System is Synchronized
Receivers do not have

atomic clocks (but have atomic clock accuracy!)
Must have at least 4 different satellites
Receivers use Triangulation algorithm from 3 satellites for position / with timing error
Hence the pseudo range = range + timing error
1 additional satellite used to calculate receivers time error (Algebra Equation)

Principle Concepts of GPS Technology

Overlay Service
GPS: Global Positioning System
NDGPS: Nationwide Differential GPS

DGPS: Differential GPS
RTK: Real-Time Kinematic (Global Positioning System)
PRN: Pseudo Random Noise (Satellite Identification)
Pseudorange: range + range correction (time)
P-Code: Precise Code
PDOP: Position Dilution of Precision
DOP: Dilution of Precision
HDOP: Horizontal Dilution of Precision
GDOP: Geometric Dilution of Precision
C/A-code: Coarse/Acquisition-Code
C/No: Carrier to Noise Ratio
S/A: Selective Availability
TDOP: Time Dilution of Precision
VDOP: Vertical Dilution of Precision
NAVSTAR: NAVigational Satellite Timing And Ranging
Constellation: Group of Satellites working in one program
GNSS: Global Navigation Satellite System

Terminology / Abbreviations

(Rockwell Int.)
Powered by Solar Panels
800watts / ( Block IIF

2450 watts)
Designed to last for 7.5 – 11years
Weighs 3,600lbs – 4,480lbs
(2006 4 door Honda Accord is 3,400lbs)
In 12,000 Mile Orbits
12 hr orbit period (pass time)

General Satellite Information

hot spares
http://www.navcen.uscg.gov/ftp/GPS/status.txt
http://www.spaceandtech.com/spacedata/constellations/navstar-gps_consum.shtml
Four Generations of GPS Satellites
Block I
Block II/ IIA
Block

IIR
Block IIF

Constellation Information

Corporation - "GPS Primer"

System
Polar Orbits
Used to test Principals and Technologies of

GPS
Block II / IIA
First operational GPS constellation
(solely for military use in the beginning)
Block IIR, IIR-M (current satellites)
R-Replenishment (used to replace older Block II satellites)
M-Modernized (updated version of the GPS Satellite)
Block IIF
Satellites scheduled for launch 2008
Current Satellites of the System Being Replaced by Block IIF
Will include the L5 Carrier

Constellation Information

50 watt signal;1575.42MHz [UHF]
L2C Broadcasts - 1227.6 MHz [UHF]
L2

C (civil)
Signal Strength is approximately same strength as earths own natural background noise
Receivers that obtain both L1 and L2 signals are referred to as dual-frequency receivers
Multi-Channel refers to the actual satellite (one satellite frequency in each channel)
Tri-frequency –(new receivers?)

Satellites Signals – Pseudo random code

(precision code)
Y-Code (precision code encrypted)
Almanac Information
Signal Contains Satellite Location

Information for all satellites
Repeating Binary Code
This serves as a unique satellite ID

Pseudo Random Code
Also referred to PRN (Pseudo Random

Noise)
Repeating Binary Code
Serves as a unique satellite ID

Satellite Signal - Pseudo Random Code

(50th Space Wing of the USAF)
Tracks SVU Health (telemetry

data)
Tracks SVUs Position (Ephemeris Data)
Satellite Orbits are effected by gravity from the earth, moon and sun. Also effected by pressure of solar radiation
Maintains Clock Synchronization between SVUs
Transmits Flight Correction Commands
Almanac Data
Updates each satellite with it’s own corrected position and the corrected position of the constellation.

Ground Control

2008)
http://www.ags.gov.ab.ca/activities/Turtle_Mountain/gps.htm
Receiver Types

receivers are able to reject multipath
Receiver Errors
Clock differences and

SVU tracking
Satellite Positional Errors (Ephemeris)
Corrected for using DGPS

Error Sources

Standard GPS Differential GPS
Satellite

Clocks 1.5 0
Orbit Errors 2.5 0
Ionosphere 5.0 0.4
Troposphere 0.5 0.2
Receiver Noise 0.3 0.3
Multipath 0.6 0.6

Typical Error Budget

Operates a National System
Used for Navigation and Harbor Navigation
System

of 85 un-manned beacon transmitting sites
2 Manned Master Control Stations
Receives GPS Signal and re-transmitts atmosphere error clock error correction information
Must use a DGPS beacon receiver AND a GPS receiver
>3m accuracy

currently accurate enough for precision approach
Provides >3m accuracy
2 Geostationary

SVUs broadcast on L1
Transmits Location and Correction
Uses Ground Station Information for correction
24 + ground stations
2 master stations (one on each coast)

WAAS - Wide Area Augmentation System

Navigation
Navigation
Survey
Time Keeping
Network Synchronicity
Many Others


GPS Users

location
Corrects for atmospheric errors
Ephemeris errors / other
Centimeter Accuracy in

horizontal and vertical accuracy
Dual Frequency Receivers
Must have your own base station within close proximity to your collection site

five satellites. After that it can operate with four.

DGPS needs a minimum of three, though at least four are required for submeter accuracy.
For RTK, you need a dual frequency GPS receiver. Single frequency receivers are sufficient for DGPS.
For RTK, your GPS receiver must be capable of On-the-Fly initialization (obtaining centimeter accuracy while moving). For DGPS, this isn't necessary.
With RTK, it takes one minute to initialize. DGPS receivers initialize immediately.
You can expect accuracy of a few centimeters in all three dimensions using RTK. With DGPS, you can achieve sub-meter accuracy in horizontal position only.
To obtain GPS corrections for RTK, you need your own base station that is no more than ten kilometers from the field you are working in. For DGPS, you can use your own base station, a correction service provider, or make use of the free radio beacon broadcasts in many regions.

Difference between DGPS & RTK (Trimble Website)

June 2005
3 Orbital Planes

Galileo – Europe
30 Satellites
23 222 km

/ 75,459ft / 14.2miles
14 hour orbit
Better polar coverage
Search and Rescue function
transponds distress signals / reply
Anticipated fully operational 2008

Other GPS Systems