What Are the Two Measurements Used in Measuring Elevation?

Sea-Level

• Zero sea level is considered the starting point for all elevation measurement. It is the point where the surface of the water is level to the surface of land. It is not a physically measurable point, but an internationally accepted standard. This is the first measurement required for all elevation calculation.

Distance

• The vertical distance of an object from zero sea level determines its altitude. Maps and blueprints use fixed survey points, or benchmarks, that mark an established elevation to provide additional local elevations in smaller increments. A building that is marked as 20 feet high in elevation is really 20 feet higher than the marked survey point, which may be several hundred feet above sea level. Using benchmarks makes local calculations easier to manage.

Radio Altimeter

• Radio altimeters measure the length of time it takes for a radio wave to bounce off an object on the ground and return to the altimeter to determine the height above the ground. These are most often found in airplanes. Calculations are then performed to add in the known height above sea level of the object on the ground to the distance measured by the radio wave to determine the flying height of the aircraft.

Aneroid Barometers

• Aneroid barometers measure the atmospheric pressure surrounding the object whose elevation is to be determined. Using established standards of the decrease in pressure compared to height above sea level and considering the influence of the nearness of landmass to air pressure the height of the object can be determined. Aneroid barometers are used in planes as well as fixed air devices such as weather balloons.