Some disclosed methods involve acquiring first ultrasonic signals corresponding to reflections from a cover/air interface of an apparatus that includes an ultrasonic sensor system, and determining one or more first ultrasonic signal parameters of the first ultrasonic signals. Some methods involve acquiring second ultrasonic signals corresponding to reflections from a cover/target interface, and determining one or more second ultrasonic signal parameters of the second ultrasonic signals. Some methods involve estimating, based at least in part on the one or more first ultrasonic signal parameters, the one or more second ultrasonic signal parameters and the ultrasonic sensor system temperature, a target object temperature. Some disclosed methods involve receiving ultrasonic sensor system temperature data indicating a temperature of an ultrasonic sensor system and calibrating the ultrasonic sensor system according to the temperature.