- Tracks over the Mediterranean Sea with estimated sea surface heights from GNSS-R data of the GEOHALO mission. The thin black lines describe the flight trajectory.
- © GFZ
Different geoscientific instrumentation was set up
for the GEOHALO mission aboard the German research aircraft HALO 
(High Altitude and Long Range Aircraft). Four mission flights in June
2012 covered major parts of Italy and the adjacent Mediterranean
Sea. In addition to GNSS measurements for reflectometry (GNSS-R)
and positioning, measurements for laser altimetry, gravimetry and
magnetometry were accomplished during these flights. The recorded
reflectometry data was under analysis to finally retrieve the
topography of the sea surface.
The GEOHALO experiment allows for advancing ground-based altimetric GNSS-R methods for flight platforms. The main focus of the GFZ activities here lies on carrier phase observations. The carrier phase precision is significantly higher than for common code observations. A retrieval of carrier phase information, however, requires specularly reflected signals.
The airborne setup (in an altitude of about 3,500 m above sea level) is significantly higher than typical ground-based setups from lower altitudes. It yields a different ratio between specular reflection and diffuse reflection. At higher altitudes a large number of diffuse scatterers contributes to the reflected power and disturbs the specularly reflected signal.
The results of the GEOHALO experiment show that the GNSS-R carrier phase can be observed on flight platforms. The flight observations can be used to determine reflection tracks on the sea surface that follow the mean sea surface height with centimeter precision. Such tracks with the estimated sea surface heights from GEOHALO are shown in the figure.