Methods and ultrasonic sensor systems are presented for sensing distance in which an acoustic output signal is directed toward a target and acoustic input signals are received from the direction of the target, and the received signal is compared with a selected one of a plurality of different receiver threshold curves to identify the acoustic wave travel time to the target and back while differentiating between the target and acoustic waves reflected more than once and waves reflecting off obstructions between the sensor and the target, where the user selectable receiver threshold curves are tailored for different target and/or obstruction conditions.