GSQ Central Bowen Basin Qld elevation grid geodetic

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.

数字高程模型（Digital Elevation Model, DEM）数据用于记录地形高程的起伏变化，其数据源为航空地球物理勘测中采集并经点位定位处理后的实测点数据。机载高度计可记录飞行器相对于地面的高度，机载GPS则可记录飞行器相对于参考椭球体（ellipsoid）的高度。将两组高度数值相减，即可计算出飞行器下方地形相对于参考椭球体的高程。随后对该基于参考椭球体的地形高程实施参考椭球体与大地水准面（geoid）间的差值改正（即n值改正），最终得到以海平面为基准的地形高程数据。