single positioning(absolute positioning, 1 point positioning) where position is measured by
only one receiver, so the single positioning method is being utilized mainly for navigation
such as vehicle, ship, aircraft, etc. or in GIS field where allowable error is relatively big
rather than for measurement.
Cause of Error Occurrence in GPS
Factors dropping accuracy in position measurement of GPS can be largely classified into
3 parts.
First, errors occurring due to structure factors include satellite time error, satellite position
error, refraction in ionosphere and troposphere, noise, multi-path, etc.; secondly, there is
geometrical error due to arrangement situation of satellite; and lastly, there is SA (Selective
Availability) that is the biggest error factor.
Potential combination of all these factors brings about very big error result, which is called
UERE(User Equivalent Range Error). Each error vary greatly depending on time and place.
Satellite time error 0-1.5 m
Satellite position error 1- 5 m
Refraction in ionosphere 0-30 m
Refraction in troposphere 0-30 m
Receiver noise 0-10 m
Multi-path 0-1 m
SA(Selective Availability) 0-70 m
In C/A code, horizontal error combined with all errors is 28m when SA does not activate
and 100m when SA activates.
SA code means enlargement of error range so that United States may limit use by non-
allowed GPS satellite users during military operation.
Basically, GPS is not much affected by weather. It cannot be said that there is no effect at
all, but there is no absolute effect. Depending on situation, as sunspot activity of sun
becomes active, if magnetic field change around earth becomes severe, GPS reception
cannot be well performed.
Cautions during Use of GPS
1 Do not dissemble, repair, or remodel it randomly.
2 Pay attention not to pour water or liquid.
3 Avoid use in environments with shock, high temperature, high humidity, etc.
4 Use it by avoiding the following conditions.