GPS SBAS L1/L5 bistatic radar altimeter

GNSS bistatic radar offers a low cost alternative for ocean altimetry. It can also be used to measure wind speed, wind direction and modeling of the ocean surface state. A bistatic configuration, using one right-handed circular polarized and one left-handed circular polarized antenna, was built in 2012 and installed in the NOAA hurricane hunter in order to measure direct and reflected L1 and L5 signals. The direct and reflected signals were compared and the path difference between them calculated, leading to altitude measurements of the receiver using both SBAS L1 and L5 signals. Compared to publicly available signals on L1, the higher code rate of L5 provides higher measurement sensitivity. The estimated altitude of the airplane receiver was compared to a radar altimeter and an onboard GPS receiver was used as truth reference.