A flight in the Piedmont region for water surface detection and altimetry experimentation

As more and more attention is received by the underlying passive potential of Global Navigation Satellite Systems (GNSS) signals, reflectometry and scatterometry are visited in this paper in order to assess water surface identification and aircraft altimetry performance. This is possible thanks to the high reflectivity of Global Positioning System (GPS) signals in the L-Band frequency range on water as well as ice and snow covered surfaces which compensates for the otherwise low signal intensity. Indeed, GNSS reflectometry belongs to the class of bistatic radar systems where transmitter and receiver reside at different locations and signals pass through a reflecting surface. Code phase and carrier phase based time delay measurements between the direct path and reflected signals, are used to determine the small aircraft´s height with respect to the reflecting surface. On the other hand, specular reflection points are computed, and a comparison of the reflected power to the direct received power is shown to yield a good water surface identification performance. Code and carrier phase measurements are implemented in this paper to obtain cm level height estimates.