The Phase I program demonstrated the efficacy of real-time of ultrasonic recession measurements on low density TPS materials. Measurements on internal echoes established the feasibility of non-intrusive temperature measurements. In the Phase II program we will continue to improve, optimize, and extend the technology. Sensors with better elevated temperature performance will be developed and configured for ablation measurements. Instrumentation with improved low frequency and more robust time-of flight algorithms will be incorporated into the system. Configurations with multiple sensors suitable for mapping recession profiles will be evaluated. The measurement technique will be applied and measurement results verified through a series of ablation tests where the real-time recession data will be quantitatively compared to that obtained from post-ablation analysis.