Geography 2122A/B Chapter Notes - Chapter 14: Declination, Latitude, Gps Satellite Blocks
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GPS and Maps
- LORAN – long range navigation, used all over the world for Marine
o Based on radio signals from multiple transmitters
o Limited accuracy, radio interference and signal problems depending
on geographic location
- Navstar GPS– Navigation System with Time and Ranging
- GPS – Global Positioning System
- Real name is Global Navigation Satellite System (GNSS)
- Space Trilateration – A method determining absolute ground positions
using satellite signal velocity and travel time to measure the distance
between the known locations of two or more satellites and GPS receiver
- GPS Components
o Consists of space segment, a control segment, and user segement
o Space Segment (SS)
Space segment is a constellation of GPS satellites positioned in
a medium earth orbit.
Placed in 6 orbital places evenly spaced 60 degrees apart so
that at any time 5 to 8 satellites are visible from any point o
Satellites placed in Posigrade orbit – moving in same
direction as Earths rotation
o Control Segment (CS)
Control Segment of the GPS is the set of ground monitoring
stations that track the location and health of each satellite,
which includes conditions such as clock error and satellite
Satellites are tracked by their own signals and an extrapolated
ephemeris – describes position of each of the satellites all
All of the info goes to Master Control Station
o User Segment (US)
User segment of the GPS is the receiver, which is tuned to the
frequencies transmitted by satellites.
- Selective Availability
o Selective Availability (SA) – intentional degradation of the GPS
signals. (done by military to prevent hostile forces)
o GPS Augmentation – improvement of GPS positioning using external
information, to improve the accuracy, availability, or reliability of the
- The Future of GPS
o Ubiquitous positioning – next gen GPS that would work everywhere,
at all times, and provide high-level precision, for cheap cost.
o GLONASS (Global Navigation Satellite System) – Russian. Started with
24 satellites, went to 14 operational satellites. India joined in to
o Galileo – being developed by European Union. A 30-satellite system.
Provide greater precision than is current and at higher altitudes.
o Beidou (China) – regional. Expanding to Compass, a global system.
o IRNSS (Indian Regional Navigational Satellite System) – in
o Quasi-Zenith Satellite System (QZSS) – Japans, in development
phase should provide better coverage for Japanese islands.
o GPS III – Selective Availability is not available in it. So cannot be
turned off EVER.
How GPS Works – The Big Picture
- Requires clear view of sky
- Does not work indoors, in mountain regions, under forest canopies, next to
tall buildings, etc.
- Each GPS transmits its location and time.
- Distance of GPS can be calculated by amount of time it takes for signals to
- GPS-determined position depends on the receive and the field conditions.
- Differential GPS (DGPS) – higher accuracy. Requires one fixed receiver and
one mobile receiver
- Satellite Positions
o Each satellite makes two revolutions in one sidereal day.
o Sidereal day – period it takes for the earth to complete one rotation
about its axis with respect to the stars.
o In terms of Solar Days (24 hours), satellites are in the same position
in the sky about 4 minutes earlier each day.
- Space Trilateration
o Basis of GPS positioning is 3-dimensional trilateration from satellites,
called Space trilateration.
o Trilateration is a method of determining relative positions using the
geometry of triangles
o Uses known locations of 2 or more satellites, and the measured
distance between the GPS receiver and each satellite to find an
absolute position, called a fix.
o Ranging – finding distance from one location to another.
- Elevation determination
Loran long range navigation, used all over the world for marine. Navigation: based on radio signals from multiple transmitters, limited accuracy, radio interference and signal problems depending on geographic location. Navstar gps navigation system with time and ranging. Real name is global navigation satellite system (gnss) Space trilateration a method determining absolute ground positions using satellite signal velocity and travel time to measure the distance between the known locations of two or more satellites and gps receiver. Gps components: consists of space segment, a control segment, and user segement, space segment (ss) Space segment is a constellation of gps satellites positioned in a medium earth orbit. Placed in 6 orbital places evenly spaced 60 degrees apart so that at any time 5 to 8 satellites are visible from any point o earth. Satellites placed in posigrade orbit moving in same direction as earths rotation: control segment (cs)