Global Positioning System Reference
In-Depth Information
FIGURE 1.11 .
Iceland on the move. A GPS site in Iceland records changes in latitude,
longitude, and height over a period of 8 years.
Adapted from a NASA graphic.
e√ect must be averaged out, and so must the more noticeable ocean tidal
movements. (One natural phenomenon that is not averaged, however, is
the rising and falling of sea levels, as ice ages come and go and air tem-
peratures cool and warm. Thus, the geoid changes slowly, on a geological
timescale.)
13
13. Many textbooks explain geoids and geodesy, and I will reference a few in chapter 2,
where we come to grips with geodesy and how it developed. For this chapter the reader
