The unknown inter number of cycls of the reconstructed carrier phase between the satellites and the sensor at the beginning of the observation
Anti-Spoofing (A.S.)
When P-codes becomes encrypted and no longer availabe to the civil users
Baseline
Consists of a pair of stations for which simultaneous GPS data has been collected
C/A Code
The coarse/acquisition GPS code- a pseudo random (PRN) code transmitted at 1.023 MHz that repeats every milli-second. Each satellite has its own C/A code so that it can be uniquely identified and recieved seperately from other satellites transmitting on the same frequency
Ephemeris
A list of positions or locations of a celestial object as a function of time
Epoch
A particular fixed instant of time used as a reference point on a time scale
Alerts
Indicates the positions of the satellites in view to an observer on the earths surface at a designated time and location
Cut-off angle
The minimum elevation angle used by the sensor to track GPS satellites
Geomagnetic Activity
Occurs when solar flares cause irregular ionization of the ionosphere which in turn causes irregular refraction delays of a radiowave passing through the non-homogeneous medium
GDOP
Geometric dilution of precision
GPS Window
Th period during the 24-hour day when there are a sufficient number of satellites in view to meet the positioning requirement
Mission
The manner in which the GPS will be used in the field
Multipath
Refers to a reflected signal that combines with the true signal resulting in a weaker position
PDOP-Position of Dilution of Precsion
A numerical indicator of the geometric strength of the satellite constellation in relation to positioning at a certain location
Point Positioning
The indpendent reduction of observations made by a particular recieer using the pseudorange with information broadcast from satellites
Post Processing
Computer processing of data ater the observation session
Project
Description of a survey job. There is no limit to the number of stations
P-Code
Precise GPS code - usually encrypted and reserved for military applications
What frequency does the P-code run at and what is its repeating interval?
P-Code is a 10.23 MHz PRN code that repeats every week
PRN (Pseudorandom Noise) Number
A number assigned by the GPS system designers to a given set of pseudorandom codes. Typically a satellite will keep its PRN indefinitely. Used as a way of labeling satellites.
Pseudorange Measurements
Measurements made using one of the pseudorange codes on the GPS signal. They provide an unambiguous measure of the range to the satellite including the effects of the satellite and user clock biases.
Selective Availability (S.A.)
Used to describe the situation when the operators of the GPS system degrade the broadcast GPS message by dithering the clock or orbital information.
UTC Time
Coordinated Universal Time is a high precision atomic clock standard, with unifirn and "leap" seconds. It is aligned with GMT
Three major componets of the GPS system are:
The satellite system
The control segment
The user
The GPS reciever can compute the transmit time by knowing the _____ time a message was recieved.
The GPS reciever can compute the transmit time by knowing the exact time a message was recieved.
A GPS is message is assumed to travel at what speed?
The speed of light
Based on the GPS system for USA, answer the following questions:
A) What is the minimum number or Satellites?
B) What is distance from the satellites to Earth?
A) 24
B) 20200 km
Based on the GPS system for USA how many orbital planes are there, how many satellites follow each plane and at what degree are the satellites inclined with respect to the equator?
6 orbital planes with 4 satellites each @ 55 degrees inclincation to the equator
What is the expected life of a satellite?
7.5 years
How many satellites are currently in orbit and healthy?
30
How many microwave signals are typically emitted from a GPS satellite? What are the names?
Two microwave signals, L1 and L2
What are the five primary signals from which observations are and used by surveyors and engineers?
L1
L2
L1 C/A
L1 P
L2 P
Precise Position Systems (PPS) use the ______ signal to measure the ______ delay.
Precise Position Systems (PPS) use the L2 signal to measure the ionosphere delay.
Which code is unique to each satellite?
PRN Code
Which code is the basis for civilian GPS?
C/A Code
Ground stations around the world are used to...
Monitor the health of satellites
Upload orbital paratmeters to the satellite
Master control stations for the USA GPS are located where?