Liquid jet in crossflow (LJIC) is a process in which a high-speed gas crossflow deforms and shears a
continuous liquid flow into tiny droplets. This study quantifies the liquid surface motion of LJIC during
the primary breakup process, which has not been quantified due to the optical limitation close to the
nozzle exit. The interfacial velocity of a breaking liquid jet indicates the local interaction of the gas and
liquid flows and determines the initial velocity of the stripped droplets. The local interfacial liquid
velocities of LJIC have only been estimated from theoretical and computational studies, which have not
been evaluated from measurements. Optical Connectivity (OC) introduces a laser beam through an
atomiser nozzle and relies on total internal reflection at the liquid interface to propagate the laser light
inside the continuous liquid to record the instantaneous features of the interface of the continuous liquid
during the primary atomisation at the near nozzle region through imaging of the emitted fluorescent
intensity from the liquid flow. The current study combines Optical Connectivity with Optical Flow
Velocimetry (OFV) to quantify the time-dependent, local interfacial velocity of the liquid interface
structures of the LJIC for gas Weber numbers between 14.9 - 112.6 and liquid-to-gas momentum ratios
between 2.1 - 36.4. The combined OC-OFV measurements of the spatial distribution of the mean and
fluctuating values of the different components of the liquid interfacial velocity of LJIC demonstrate
how the gaseous shear and liquid jet geometry interact to influence the atomisation process.