A method of measuring and controlling a temperature distribution at a member is disclosed. A probe is placed proximate the member. The probe has a plurality of longitudinally-spaced reflective elements. An ultrasonic pulse is generated at a selected location of the probe so as to propagate along the probe. Reflected pulses are received at the selected location from the plurality of longitudinally-spaced reflective elements. The distribution of temperature at the member is determined from the reflected pulses. The determined distribution of temperature may be used in controlling the temperature of the member. The member may be a solid or fluid.