|| Starpath online classroom || Celestial Navigation Glossary || Glossary Index || Home ||

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

mean sea level The average depth of the water exposed to the ocean. It can be approximated as the half way point between mean high water and mean low water, ie MSL = (MHW+MLW)/2, although there are more sophisticated definitions that account for the effect of atmospheric pressure. See The Barometer Handbook, under Inverse Barometer Effect. This is the level (MSL) that is slowly increasing with time as the ice caps melt due to global warming. Topo maps and other land based maps reference elevations to MSL. Nautical charts reference elevation contours and spot elevations to MSL, but light heights and bridge clearances are referenced to MHW. Abbreviation:  MSL

[close window]