Baseline

Boundary line between the drop contour and the surface of the solid in the two-dimensional projection of a sessile drop when measuring the contact angle using drop shape analysis (DSA).

Background

The points of intersection between the fitted drop shape and the baseline are determined in all drop shape analysis methods for measuring the contact angle. These points of intersection correspond to the three-phase contact points of the system.
KRÜSS DSA programs determine the baseline from the video image of the drop with the help of discontinuities in the contour. These occur either due to the termination of the contour line itself or - in the case of reflecting solids - due to the transition between the drop image and its reflection.

Drop with baseline and reflection below the baseline

The baseline can also be set manually however.
The mathematical description of the baseline depends on its shape: a linear equation for flat surfaces and a trigonometric function for rounded substrates.

Shape analysis on flat and curved sample surface