Application of GPS as a satellite altimeter
 
 
 The multipath effect is a kind of noise in GPS positioning, which is a very unresolved “interference” in high-precision GPS positioning. In the past, the use of the atmosphere on the GPS signal delay noise development of GPS atmospheric, is also being used to develop GPS positioning in the multipath effect GPS altimetry technology, that is, the use of airborne GPS as an altimeter for altimetry. It is used to determine sea or ice topography, wave patterns, current speed and direction by using GPS signals reflected from the sea or ice surface. Usually, satellite altimetry or airborne altimetry measures a single point, and the result of continuous measurements is a cross-section on the reversed surface, whereas GPS altimetry measures a band of a certain width, so that the undulation (topography) of the reflected surface can be determined. It was reported that two GPS receivers were installed on the airborne plane during the test, one with the antenna upward for positioning the carrier and one with the antenna downward for receiving the GPS signal on the reflecting surface.