An apparatus, comprising: an ultrasonic sensor system ; a cover glass ; and a control system , at least part of which is coupled to the ultrasonic sensor system, the control system configured to: acquire first ultrasonic signals via the ultrasonic sensor system at a first time, the first ultrasonic signals including reference ultrasonic signals corresponding to reflections from at least one of a cover glass/air interface or a cover glass/target interface; acquire second ultrasonic signals via the ultrasonic sensor system at a second time; determine , based at least in part on a comparison of the first ultrasonic signals and the second ultrasonic signals, whether one or more layers reside on the cover glass at the second time; and, if it is determined that the one or more layers reside on the cover glass at the second time: i) determine one or more signal characteristics corresponding to one or more properties of the one or more layers, and ii) determine, based at least in part on the one or more properties, whether the one or more layers are compatible with the ultrasonic sensor system by determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers reside on the cover glass. an ultrasonic sensor system ; a cover glass ; and a control system , at least part of which is coupled to the ultrasonic sensor system, the control system configured to: acquire first ultrasonic signals via the ultrasonic sensor system at a first time, the first ultrasonic signals including reference ultrasonic signals corresponding to reflections from at least one of a cover glass/air interface or a cover glass/target interface; acquire second ultrasonic signals via the ultrasonic sensor system at a second time; determine , based at least in part on a comparison of the first ultrasonic signals and the second ultrasonic signals, whether one or more layers reside on the cover glass at the second time; and, if it is determined that the one or more layers reside on the cover glass at the second time: i) determine one or more signal characteristics corresponding to one or more properties of the one or more layers, and ii) determine, based at least in part on the one or more properties, whether the one or more layers are compatible with the ultrasonic sensor system by determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers reside on the cover glass. acquire first ultrasonic signals via the ultrasonic sensor system at a first time, the first ultrasonic signals including reference ultrasonic signals corresponding to reflections from at least one of a cover glass/air interface or a cover glass/target interface; acquire second ultrasonic signals via the ultrasonic sensor system at a second time; determine , based at least in part on a comparison of the first ultrasonic signals and the second ultrasonic signals, whether one or more layers reside on the cover glass at the second time; and, if it is determined that the one or more layers reside on the cover glass at the second time: i) determine one or more signal characteristics corresponding to one or more properties of the one or more layers, and ii) determine, based at least in part on the one or more properties, whether the one or more layers are compatible with the ultrasonic sensor system by determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers reside on the cover glass. i) determine one or more signal characteristics corresponding to one or more properties of the one or more layers, and ii) determine, based at least in part on the one or more properties, whether the one or more layers are compatible with the ultrasonic sensor system by determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers reside on the cover glass. <EOS>