What is the Difference between geopotential altitude and geometric altitude?

Answer 1

Altitude in an aircraft is generally measured by the hydrostatic equation: p=rho*g*h, where p is the pressure at the point of measurement, rho is the density at the point of measurement, g is the acceleration due to gravity at the point and h is the height from a reference to that point (the reference is generally taken as sea level).

Aircrafts use the hydrostatic equation to determine the height/ altitude because pressure can be easily measured with a pitot tube that planes have. So using a pitot tube the airplanes measure the pressure and with that they can put it into the equation and solve for the height.

However, gravity is not the same at different altitudes and changes with respect to the altitude. It is very difficult for an airplane to measure gravity in the air. Therefore airplanes generally measure geopotential altitude. The geopotential altitude uses gravity at sea level and takes it to be constant. Whereas geometric altitude uses gravity at the point of measurement.

Therefore P = rho*g0*h(geopotential)

where g0 is the gravity at sea-level and h(geopotential) is the geopotential altitude

and

P=rho*g*h(geometric)

where g is the gravity at the point of measurement and h(geometric) is the geometric altitude or the actual height above sea-level

Notice that the pressure and rho are common in both equations

-by floyd617

Answer 2

It is a correction/adjustment to Geometric Altitude using

variation of gravity with latitude and elevation and hence it is also known as ‘Gravity

Adjusted Height’.