GSWA South Canning 1 Madley Herbert 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）数据依托航空地球物理勘测中采集并经处理的点位数据，记录地形高程的起伏变化。机载高度计数据记录飞机距地面的高度，而机载全球定位系统（Global Positioning System, GPS）则采集飞机相对于参考椭球的高度。将这两组数值相减，即可计算出飞机下方地形相对于参考椭球的高程。随后，针对参考椭球与大地水准面之间的差值（即n值改正）对该椭球面地形高程进行修正，最终得到相对于海平面的地形高程。