The Hanle effect is the only tool available for measuring turbulent (i.e., spatially unresolved) magnetic fields at the surface of the quiet Sun. The Hanle-effect diagnostics relies on the discrepancy between the linear polarization calculated in the absence of a magnetic field and the observed polarization. We interpreted the linear polarization of the Sr I 4607 Å line, observed at THEMIS (December 7-9, 2002) and Pic-du-Midi (May 14, 2004), in terms of the Hanle effect. We present here the main results of this study. In particular, we stress the importance of a proper adjustment of the theoretical intensity profile to the observed one, through the application of a zero-field model, the magnetic field being determined in a second step from the line-center polarization degree. With the spatial resolution and coverage of the Pic-du-Midi data (1 arcsec resolution, 132 distances from the limb), we can also attain depth probing of the turbulent magnetic strength, and we discuss whether this can vary within the range of heights of formation for the line center.