Scaling issues are always playing a critical role in most studies based on remote sensing data. The process of getting quantitative scaling information from raw multi-resolution images is not trivial, and many aspects must be taken very carefully into consideration. To get a better picture about the role of spatial resolution, we conducted a series of flights in summer 1997, in several test sites over Spain and Portugal. In order to minimize the time of acquisition (to get minimal changes in atmospheric status and solar illumination) we used three flight altitude levels, that produced images with 1.25 m, 3 m and 12 m resolutions. The main steps in our methodology are: a) Geometrical registration of the multi-resolution dataset; b) Compensation of atmospheric effects; c) Compensation of angular view changes; d) Multi-resolution analysis. This work evaluates the importance of applying all steps thoroughly in order to achieve a fully comparable multi-resolution data set. Particularly BRDF effects have been commonly disregarded despite the big influence of these effects in apparent reflectance. Results obtained from two different test sites (La Mancha, in Spain, and Evora Natural Park, Portugal), with very different spatial characteristics, indicate the robustness of the approach, but also point out the importance of perturbing effects in getting actual multi-resolution information.