A good example is that of the signal from the Global Positioning System (GPS) satellites. Their signals need to be extremely accurate and reliable. A small change in the height of the ionosphere (7-10 km) can give an error of up to 12 metres for the GPS measurement of a position on Earth.
This plot shows the measurements of a location
from a GPS receiver over a 24-hour period. All
the points should be close together, but see
how scattered they are? Some of the readings
give locations that are a few metres from the
true (or average) value. Rollover the image to
see how the satellite signal has been corrected
for the effects of the variable ionosphere and
now all the measures are much closer together. |
