Conditions of application of the Storey and Lefeuvre (Geophys. J. R. Astron. Soc. 56 (1979) 255–270; Geophys. J. R. Astron. Soc. 62 (1980) 173–194) wave distribution function concept (WDF) to the determination of the directions of arrival of the NETLANDER Ground Penetrating Radar echoes are examined. The hypotheses used to make a WDF analysis from wave field components measured in a space plasma are recalled. An example of application is given. Following Lagoutte (1981 Rapport de DEA, Université d'Orléans) the WDF concept is extended to the case of an isotropic and non-ionized medium. The application to the analysis of the radar echoes within the Mars subsurface is discussed. The main point is to have a thickness of the dry layer between the surface and the first reflector much larger than the wavelengths.