This airborne experiment studies GNSS-Reflectometry (GNSS-R) techniques for the detection of water body surfaces using a low-altitude airborne carrier with high rate (20ms) reflectivity observations. In the context of this work, it is important to detect and fastly reach the area of interest for which the waterbody surfaces are to be scanned. A GNSS-R setup onboard a gyrocopter with reduced size and weight has been developed for this application. The reflected GNSS signals are segmented into stationary parts representing areas with different reflectivities for the detection of water body surfaces. A real flight experimentation has taken place in the North of France obtaining reflections from different surfaces and landforms. We show that our radar technique differentiates different water body surfaces along the flight trajectory with temporal and spatial resol