This paper describes a field campaign performed with a ground-based polarimetric tomographic imager designed to measure the vertical response of several forest plots in order to better understand the mechanisms contributing to the total radar response. The campaign took place in the Mende forest, an artificial forest of European black pines, in the south of France. The objective is to perform a sensitivity study on the radar observables based on biophysical parameters. This paper presents a description of the experiment hardware and procedure, the results obtained for all sites, and a discussion of the results in the light of the ground truth. The results show the vertical distribution of the backscattered intensity for several parameters like tree density, forest growth, presence of undergrowth, and ground slope. The evolution of the energy backscattered by the ground, the volume, and the whole forest structure is also displayed. These results have shown the interest of such a campaign to improve the understanding of the distribution of radar mechanisms along the vertical axis.