GSQ Croydon elevation line data

Digital Elevation Model data record the terrain height variations from the processed point-located data recorded on an airborne geophysical survey.� The aircraft altimeter data records the height of the aircraft above the ground and the aircraft GPS records the height of the aircraft above the ellipsoid.� Subtracting the two values enables the height of the terrain beneath the aircraft relative to the ellipsoid to be calculated.� This ellipsoidal terrain height is corrected for the variation between the ellipsoid and the geoid (the n-value correction) to produce terrain heights relative to sea level.