  A drop impacting on a solid surface deforms before the liquid makes contact
with the surface. We directly measure the time evolution of the air layer
profile under the droplet using high-speed color interferometry, obtaining the
air layer thickness before and during the wetting process. Based on the time
evolution of the extracted profiles obtained at multiple times, we measure the
velocity of air exiting from the gap between the liquid and the solid, and
account for the wetting mechanism and bubble entrapment. The present work
offers a tool to accurately measure the air layer profile and quantitatively
study the impact dynamics at a short time scale before impact.
