GPS Flashcards
GPS stands for
global positioning system
GPS
technology that broadcasts satellite signals for navigation and position determination on earth
examples of how are GPS receivers used
- in car navigation
- cell phones
- smart watches
is GPS free
yes
when and what was the first use of GPS
1964 with the NAVSAT system
what was NAVSAT used for
tracking the locations of commercial and military sea vessels
what was the origin of the GPS we use
the NAVSTAR system developed by USA
what was the first use of GPS outside of the USA
Soviet Union shoots down Korean Airline in 1983
what administration allowed worldwide access to the GPS
Reagan administration
GNSS
the overall term for technology that uses signals to find locations on Earth
what does GNSS stand for
global navigation satellite system
what are the three segments of GPS
- space segment
- control segment
- user segment
what segment(s) does the space segment send data to
control and user segment
how many satellites does GPS require
24
how many orbital planes are there for the satellites for GPS
six orbital planes
what is the orbit altitude of the satellites for GPS
20 200 km
how many degrees are the six orbital planes for the GPS satellites separated
60 degrees
how many satellites are visible from any point on earth
5 to 8
describe the data from the space segment of GPS
ephemeris
ephemeris data
information about the satellite’s status, orbit and precise location
what type of GPS data is sent to users from a satellite
ephemeris data
how is the data from the satellite sent to the control stations and users
done through digital pseudo-random codes
C/A code in satellite data
information accessible by ALL GPS Receivers
what is a frequency in C/A codes
L1 - navigation information (time and position)
what are P-codes
information from satellites that is accessible by MILITARY receivers
what L level data is received by P-code data
L1 and L2
what does L2 measure
atmospheric interference
Y -codes
encrypted version of P-code intended for MILITARY use
what is the control segment of GPS
series of worldwide ground stations that monitor signals from GPS satellites
where is the master control center for GPS satellites
Colorado
what type of corrections are sent from the control station to a GPS satellite
- orbit correction
- time corrections
- atmospheric condition corrections
what is the user segment of GPS
GPS receivers on the ground that pick up satellite signals
what controls the number of satellites a GPS receiver will connect to
the number of channels (12 channels = 12 satellites)
what are single frequency GPS receivers
receivers that only use the L1 frequency
what type of data do single frequency GPS receivers have access to
time and position of satellite
what type of data do dual frequency GPS receivers have access to
L1 and L2 (military recievers)
what are dual frequency GPS receivers
receivers that use L1 and L2
what is needed with GPS receivers for accurate readings
direct line of sight of the satellite
what is trilateration
a method to find your position based on the distance from at least THREE known points
how does 3D trilateration differ from regular trilateration
finding your position on earth’s surface, which is not flat but an ellipsoid
what speed does the signal from the satellite travel at
speed of light
what is pseudo-range
the distance between a GPS satellite and a GPS receiver
how to calculate pseudo-range
speed of light * transmission time
where is your location if two satellites are used
the location is somewhere along the boundary
what happens when trilateration is done with 3 instead of 2 satellites
the location narrows to two points
of the two points found with three satellites in trilateration, where are they
one is in space and the other is on earth
what causes trilateration to NOT be accurate
time the signal takes to reach the receiver (if time is a little off from speed of light = huge distance on earth that’s off)
what type of clocks do satellites use to reduce time errors
atomic clocks
what type of clocks do receivers use to reduce time errors
quartz clock
what is used in trilateration to account for time errors
a fourth satellite
what are 5 sources of errors in GPS
- time dilution of precision
- position dilution of precision
- atmospheric interference
- multipath signals
- selective availability
what is position dilution of precision
error introduced due to geometric position of satellite
what results in higher position accuracy
a wider distribution of satellites
where are two instances of atmospheric interference
- ionosphere (density and stratification variation)
- troposphere
(atmosphere pressure and moisture)
does the ionosphere cause larger error or the troposphere
ionosphere
what is multipath signal error
an error caused by the reflection of GPS signals from surrounding surfaces
what can be used to have the clearest signal to the satellite
antennas that raise the receiver so it has access to clear sky
what is differential GPS
a method of using ground based corrections in addition to satellite signals
where are base stations placed in DGPS
locations with known coordinates
how do base stations work best
when built close to receivers
what is real time kinematics
combination of GPS signals and a base station to provide real time corrections
what is post processed kinematics
combination of GPS signals and a base station to correct location information POST data collection
what is WAAS
a network of ground stations that measure variation in GPS signal
importance of WAAS
reduces the error to 3 meters or less
