GPS

Navigation Satellite Time and Ranging Global Positioning System

full name of NAVSTAR GPS

US Department of Defense

developed NAVSTAR GPS for very precise navigation

1973

when NAVSTAR GPS was proposed

8-Dec-93

when NAVSTAR GPS was ready for initial operational capability

17-Jul-95

when NAVSTAR GPS was ready for full operational capability

1. space segment

2. control segment

3. user segment

GPS segments

space segment

segment involving the constellation of satellites

control segment

segment that controls the satellites themselves

user segment

segment involving the users with receivers

32

number of satellites in the space segment in operational mode

31 in use; 1 reserve

among the number of satellites in the space semgent, how many are used and in reserve?

8

how many spares of satelites are there?

10

number of satellites that have yet to be launched

US$ 25,000,000

how much is a satellite?

2000 kg

weight of a satellite

Hydrogen Maser Atomic Clocks

satellite clocks

6

number of orbital planes

4-6

number of satellites per orbital plane

20,200 km

altitude of satelites

55-degrees

inclination of satellites

control segment

segment that tracks satellite orbits, does time synchronization, uploads navigation message, and manages denial of accuracy

Consolidated Space Operations Center (CSOC) at Falcon Air Force Station, near Colorado Springs

location of the master control station

1. L1 frequency

2. L2 frequency

microwave carrier signals transmitted by GPS satellites

1575.42 MHz

frequency of L1 frequency

L1 frequency

signal that carries the navigation message and the SPS code signals

1227.60 MHz

frequency of L2 frequency

L2 frequency

signal that is used by PPS receivers

1. C/A Code (Coarse/Acquisition Code)

2. P-Code (Precise Code)

3. Navigation Message

binary codes that shift the L1 and/or L2 carrier phase

C/A Code (Coarse/Acquisition Code)

modulates the L1 carrier phase and provides the basis for the civilian SPS

P-Code (Precise Code)

modulates both L1 and L2 carrier phases and provides basis for PPS

Navigation Message

modulates the L1-C/A code signal

50 Hz

frequency of signal provided by navigation message

4

minimum number of satellites for GPS observation

3 for 3D coordinates and 1 to correct clock errors

distribution of roles of the 4 satellites of GPS

denial of accuracy (DOA)

prohibition of the US military from civilians using full resolution of the system

1. selective availability (S/A)

2. anti-spoofing (AS)

denial of accuracy methods

selective availability (S/A)

when noise is added to the clock signal and the navigation message has lies in it

anti-spoofing

when P-code is encrypted with Y-code

1. satellite clock

2. receiver clock

3. satellite orbit error

4. atmospheric errors

5. multipath

6. geometric dilution of precision

7. satellite mask angle

8. selective availability

sources of error in GPS surveys

1 billionth of a second of error every 3 hours

amount of error satellite clocks produce

30 cm

consequence of 1 billionth of a second in error to the distance measurement

make simultaneous measurements to 4 satellites

remedy to receiver clock errors

satellite orbit error

accuracy of orbital prediction is in the order of a few meters of error in position

atmospheric error

variation of speed of light due to atmospheric conditions; delay of GPS signals as they pass through the atmosphere

>10 m

effects of ionosphere in refraction (as in the number)

dual frequency receivers

remedy for atmospheric errors

multipath

occurs when GPS signals are reflected and the receiver detects 2 signals instead of 1

geometric dilution of precision

how forming a more spread-out shape with the satellites results in a more accurate outcome

more; less

______ satellites, _____ GDOP

atmospheric refraction

greater for satellites at angles that are low to receiver because signal must pass through more atmosphere

decrease possibility of tracking the necessary 4 satellites

setting high angles will decrease atmospheric refraction but will also ___

selective availability (S/A)

man-made intentional errors to GPS results by the US Department of Defense to limit the high level of precision of GPS to the general public

100 meters

by how much S/A degrades position accuracy of GPS

May 2000

when S/A was removed

differential GPS

effective way to correct various inaccuracies in GPS system

stationary

is differential GPS better when moving or stationary?

base

GPS receiver that is placed at a known point of reference that collects GPS signals and compares the results to the actual known coordinate of the base

rover

GPS receiver that collects autonomous information in the field

at least 2

how many GPS receivers are used in DGPS

yes

Do the rover and base receivers observe the same satellites simultaneously?

1. post processing differential GPS

2. real time differential GPS

general types of DGPS

1. static

2. kinematic

positioning modes of DGPS

post-processing DGPS

no real-time connection between base and rover; independent collection of data; rover data be brought back to the office for processing

real-time processing DGPS

usually used when highly accurate real-time GPS data is critical; processed on the spot

post-processing DGPS

which is more accurate, post-processing or real-time processing DGPS?

1. post-processing

2. real-time

3. real-time

4. post-processing

5. real-time

6. post-processing

which is better among post-processing and real-time processing in the following:
1. accuracy

2. time

3. navigation

4. cost

5. remote locations

6. portability

1. recreation-grade receivers

2. navigating receiver

3. mapping-grade receivers

4. survey-grade receivers

types of GPS receivers from least to most accurate

multi-GNSS

receiver system that can calculate position, time ,and velocity from multiple GNSS

GLONASS

Russia's GNSS

24

number of satellites of GLONASS

BeiDou

China's GNSS

20

number of satellites of BeiDou

GALILEO

Europe's GNSS

12

number of satellites of GALILEO

Quasi-Zenith Satellite System

Japan's GNSS

4

number of satellites in QZSS

12 to 30

number of visible satellite increases from ___ to ___ if we use all navigation satellites

Coast and Geodetic Survey control point

found beneath the base station antenna of the GPS community base station in UP