Improvement of Data Precision and Spatial Resolution of cGNSS-R Altimetry Using Improved Device With External Atomic Clock

The applications of Global Navigation Satellite System Reflectometry (GNSS-R) altimetry will mainly rely on the precision of this remote-sensing system. Comparing with nadir measurement of satellite altimetry and water gauges, GNSS-R altimetry makes off-nadir measurements with high spatial and temporal resolution come true. To enhance the data precision and spatial resolution, an improved cGNSS-R altimetry system, including one uplooking geodetic GNSS receiver, one downward left-handed circularly polarized GNSS-R receiver, and one tamed atomic clock, was adopted. The objective of the introduced atomic clock is to provide an accurate and synchronous time frequency signal for both receivers, and receiver clock errors can be removed in the regular single difference geodetic processing. Therefore, the unknown parameters in the computation of cGNSS-R were reduced to only one, caused by the phase subtraction between two receivers. By this proposed method, water level height can be derived from one GNSS satellite's signals, and the spatial resolution will be improved greatly due to more observations. An experimental water level measurement over a smooth inland lake is presented with GNSS-R carrier-phase processing. Then, GNSS-R-derived local water level height is compared within situobservations. A high degree of agreement is found in these two independent data, and the standard deviation of the derived water level height is better than 1 cm at 1-Hz sample.