NavList:

I can’t remember hearing the term terrestrial navigation before, certainly not in the context that it would warrant capital letters to describe it as something special like Air Navigation for example.  I wonder if this is because the term wasn’t really required in the past.  For years people were perfectly happy with Navigation and Pilotage.  Air Navigation on the other hand was sufficiently new and different to warrant its own name.  I have a row of books on my bookshelves written in the 20s and 30s by several different authors all with the title ‘Air Navigation’. 

I can imagine the term ‘terrestrial’ being used to differentiate a position line or other navigational feature from one from a different source.  E.g. Weems compares the ‘Terrestrial Triangle’ with the ‘Celestial Triangle’ (Air Navigation ChXI p274).   Perhaps closer to the point, dear Captain Lecky talks of combining a ‘celestial bearing’ with a ‘terrestrial bearing’ (“Wrinkles” see index for page).

To me, terrestrial is not a good word to use, because people today interpret its meaning differently.  Does it mean ‘on land’ or just in relation to what you see on land?  Alternatively, does it mean with respect to the entire Earth, land and sea, and if that, how high or deep should you go?  Does the boundary extend to GNSS height or the bottom of the oceans, or are you restricted to the Earth’s surface?  I suspect the answer is closely tied to what the Author or Organisation had in mind when introducing the expression.  For example, an astronaut might use the expression quite differently from a river pilot.  DaveP