This paper is concerned with the application of ultrasonic thermometry for temperature profiling in the reactors of coal gasification plants. A temperature profiling sensor typically uses a thin rod with several notches to segregate the sensor length into various zones. An acoustic pulse transmitted through the multizone sensor is partially reflected back at each notch, and measurement of the time interval between each pair of the reflected signals provides an indication of the average temperature in the corresponding zone. The main contributions of this paper are (1) delineation of the reflection and transmission phenomenon of sound waves at a notch, (2) development of an improved method of attenuation measurement in single-zone and multizone sensors employing notches, and 3) determination of the acoustic properties, namely, velocity and attenuation of six candidate materials suitable to the gasifier environment in the temperature range from ambient to 1093/sup 0/C. Computer simulation was employed to analyze the reflected signals from the notches, and the simulation results were corroborated at each stage by experiments. 19 references, 6 figures, 2 tables.