One of the first common applications of surface plasmon resonance spectroscopy was the measurement of the thickness (and refractive index) of adsorbed self-assembled nanofilms on gold substrates. The resonance curves shift to higher angles as the thickness of the adsorbed film increases. This example is a static SPR measurement.
When higher speed observation is desired, one can select an angle right below
the resonance point (the angle of minimum reflectance), and measure the reflectivity changes at that point.
This is the so-called dynamic SPR measurement. The interpretation of the data assumes that the structure of the film does not change significantly during the measurement.