GSWA P1177 Kojonup 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）数据记录了经处理的航空地球物理勘探机载点位观测数据所反映的地形高程变化。机载高度计采集飞机相对于地面的高度数据，机载全球定位系统（Global Positioning System, GPS）则记录飞机相对于参考椭球面的高程。将两组数值相减，即可计算得到飞机下方地形相对于参考椭球面的高程。随后，对该椭球面地形高程实施参考椭球面与大地水准面间的差值改正（即n值改正），最终得到相对于海平面的地形高程。