An experimental measurement and analytical modeling of latent heat during water droplet phase change were studied during this research. The aircraft icing phenomenon poses significant safety concerns to the global fleet of commercial aircrafts, helicopters, and unmanned aerial systems (UAS). To mitigate the concerns on the operation constraint, a real-time, in-situ monitoring of the phase-change latent heat transfer is developed and tested in this study. A sensor system has been setup and tested in both benchtop environment and inside an icing wind tunnel. Both temperature and heat flux at the base of the ice freezing surface are recorded during the test. Analytical model is used to solve the multi-layer transient heat transfer equations. This study shows the direct application of the sensor system to calculate the total mass of water that freezes on a surface based on the measurement of the latent heat flux generated during the phase transition process. Analytical equations for the heat flux are also provided. Based on the knowledge of liquid mass transformed into ice, estimations of phase transition stages, partially melting state of crystals and calculations of liquid water contents of clouds can be done with knowledge of environmental temperatures and other icing parameters.