GPS and GNSS

Week Seven Flash Cards

What is GNSS

Global Navigation Satellite Systems

Satellite systems that provide positioning, navigation, and timing anywhere on Earth.

Responsible for GPS

Portage Traxx - Snow Removal in Portage

Snow plows use GPS

Links to snowplows to systems within the plow

39,000 miles driven

300 cul-de-sacs (a street, lane, closed at one end)

What is GPS?

Global Positioning Systems

Satellite-based location/navigation system

Provides location and time information anywhere on Earth at any given time

Who was Dr. Gladys West?

Mathematician hired by the U.S. Naval Weapons Laboratory

Developed mathematical models (geoid shape of Earth) and computer programs needed for GPS

Who created GPS?

U.S. Department of Defense

When was the first satellite launched? What happened in 1993?

1978

1993: system complete with 24 satellites

GPS System #1: Space / Satellite segment

Consists of satellites: Two orbits a day, 12,500 mi Alt

Constellation: Fixed positions for optimal/ full coverage, 24 required

Satellites broadcast signals to Earth: position/time sent; L1 = 1575.42 MHz and L2 = 1227.60 MHz are the radio frequencies used to send information; MUST BE OUTSIDE

GPS System #2: Control Segment

Series of ground stations that monitor GPS signals

Relay to master control: Schriever Air Force Base

Monitored; corrections uploaded to satellites

GPS System #3: User Segment

GPS Receivers: Passively receive signals; display location

Receivers: Channels (# of satellites a receiver can communicate with)

Single-frequency GPS

Relies on one radio signal

typically L1 band

Dual-frequency GPS

two simultaneous signals from each satellite to cross-reference and correct positioning errors

L1 and L5 bands

Why did Iran bomb Bahrain?

Targeting the US Navy’s 5th Fleet

Targeting American military installations

The Three Segments of GPS (IMAGE)

What is GPSIII?

Third generation of navigational satellites

Developed by Lockheed Martin for the U.S. Space Force

10 launched, 33 is the goal

Orbital Altitudes of many significant satellites of earth (IMAGE)

Space Junk - 2023

Federal Communications Commission (FCC) issued its first fine for space debris

US TV provider Dish: $150,000 for failing to move satellite into a safe orbit

Why was OCX axed?

Officials believed it put current military and civilian GPS capabilities at risk.

Trilateration

Uses three points of reference to determine where you are

What signals do satellites send?

Almanac: status, orbit, and location

Radio Waves: speed of light

Pseudorange: distance between receiver and satellites

How does the Earth’s atmosphere caused errors in GPS and GNSS satellite signals?

System based on the assumption of unaltered signal transmission to calculate pseudorange (distance between receiver and satellites)

Clock in comparison

SAIT (layer order)

Other GPS-like Systems

GLONASS - Russia; worldwide

Galileo - EU; worldwide (2019)

BeiDou - China, worldwide (2020)

IRNSS - India, regional

QZSS - Japan, regional

GPS: Data Accuracy

What factors impact GPS accuracy?

Atmospheric effects

Sky Blockage

Receiver quality

Higher accuracy is attainable by using GPS in combination with __________

Augmentation systems

Enable real-time positioning to within a few cm, post-mission measurements at the mill level

What is Selective Availability (SA)?

Intentional degradation of GPS signal (time, orbit position)

Discontinued on May 2000 by Pres Clinton

With SA vs Without SA

With: 100 m accuracy

Without: 15 m accuracy

WAAS

Wide Area Augmentation System

Improves GPS position accuracy to under 1 meter!

PDOP

Position Dilution of Precision

Error due to undesirable satellite geometry

The lower the PDOP, the better

Atmospheric interferences causes:

Delays

Ionosphere

ionization (neutral atom or molecule turns into a charged particle = ion)

alter speed (5+m error)

Troposphere

water vapor (0.5m error)

What other issues affect GPS accuracy?

Poor view of the sky

Tree canopy, buildings

Multipath effect

How do I improve accuracy? Differential GPS (DGPS)

Ground-based correction: transmitted to mobile receivers to adjust in real time

Fixed base station: permanent location

Error Detection

How do I improve accuracy? Real-time (direct connection)

NDGPS broadcast: broadcast differential correction signals for accuracy; discontinued

Real-Time Kinematic positioning (RTK): receive signals while in the field

How do I improve accuracy? Post-processing (no direct connection)

Download files from the local base station

Continuously Operating Reference Station (CORS): receives satellite signals and calculates error corrections

How do I improve accuracy? Continuously Operating Reference Stations (CORS)

Constant collection of GPS data for free download

Request the day/hours of data to correct your field data

How do I improve accuracy? Wide Area Augmentation System (WAAS)

USA-only; consists of ground, space, and user segments (stas in geosych orbit)

GPS satellites augmented with WAAS satellites

WAAS-enabled GPS receivers

WAAS system

NDGPS

Nationwide Differential Global Positioning System

Ground-based navigation and positioning network

U.S. Coast Guard / U.S. Department of Transportation

Improved standard GPS accuracy

GPS Receivers

Recreational Grade

Mapping Grade

Survey Grade

Recreational Grade: 5-20m

No differential; most WAAS-enabled

$100-$400

Mapping Grade 1-5m

Usually post-processing differential

Smartphone accuracy is usually here

$400-$5,000

Survey Grade- under 5cm

Usually real-time differential

$5,000 - $75,000

GPS App: USGS Fault Surveys

• GPS stations observe the same satellites to measure positions very accurately.

• Distances between stations can be measured within a few millimeters.

• Comparing positions over time shows fault movement and strain buildup

GPS App: NOAA: 'Micro-Satellites' will use GPS signals to study hurricanes

measure inner core winds, tracks the transfer of energy

produce more accurate measurements of wind speeds over the ocean

Better storm surge estimates, as the height of the ocean changes with pressure

Time - THE 4TH DIMENSION

GPS satellites contain multiple atomic clocks

100 billionths of a second

Precise time is CRUCIAL for economic activity, like communication systems or power grids

GPS Time: Wireless telephone and data networks

GPS for base station sync

Mobile handsets share limited radio spectrum more efficiently

Digital broadcast radio services use GPS time to ensure radio stations arrive

GPS Time: Business

Time-stamp transactions for records

Major financial institutions use it to set internal clocks for transaction timestamps

Automated systems that track transactions made by a global network

GPS Time: Flight information

The U.S. Federal Aviation Administration (FAA) uses GPS to sync reporting

flight time and location

hazardous weather

GPS Time: Instrumentation

Precise timing for devices over wide geographic areas

GPS timing in seismic monitoring networks enables researchers to quickly locate the epicenters of earthquakes and other seismic events.

GPS Time: Power

By analyzing the precise timing of an electrical anomaly as it propagates through a grid, engineers can trace back the exact location of a power line break.