We discuss an airborne experiment aimed to establish the potential of the PARIS concept (PAssive Reflectometry and Interferometry System) to retrieve small features in the sea surface topography. The date and location were chosen to coincide with a TOPEX/POSEIDON (T/P) overflight. The signals of the Global Positioning System (GPS) reflected off the sea surface are tracked and compared to the directly received ones, to compute the relative delays. The features detected in the peak tracking are likely caused by topographic and sea roughness variations. While very promising, these results open the challenge to use additional information to appropriately separate both contributions.