In the subsea engineering, protective structures made from thick metallic plates are often used to house and protect fragile equipment against potential damage due to impact by debris. The ability to quickly localize impacts on the protective structure will help mitigate damage to equipment and lower the likelihood of system failure. This paper presents an innovative in-situ impact localization system with a sparse array of lead zirconate titanate (PZT) sensors. The impact localization method uses linear regression, which is adaptive to expected environmental changes, such as immersion in water. Furthermore, the proposed impact localization system is not sensitive to the amplitude of the detected signal, which enables the system to bypass the interference introduced by signal saturation/clipping and be robust against sensor degradation. Results from an impact experiment on an aluminum plate verified the predictive accuracy of the linear regression models, as well as the accuracy and precision of impact localization.