An ultrasonic sensor includes a two-dimensional array of ultrasonic transducers, wherein the two-dimensional array of ultrasonic transducers is substantially flat, a contact layer having a non-uniform thickness overlying the two-dimensional array of ultrasonic transducers, and an array controller configured to control activation of ultrasonic transducers during an imaging operation for imaging a plurality of pixels at a plurality of positions within the two-dimensional array of ultrasonic transducers. For imaging a pixel of the plurality of pixels, the array controller is configured to activate a first subset of ultrasonic transducers of the two-dimensional array of ultrasonic transducers to generate an ultrasonic beam directed to a contact surface of the contact layer, and activate a second subset of ultrasonic transducers of the two-dimensional array of ultrasonic transducers to receive a reflected ultrasonic beam, wherein the second subset of ultrasonic transducers is at a location within the two-dimensional array of ultrasonic transducers to account for a local angle between the two-dimensional array of ultrasonic transducers and the contact surface where the ultrasonic beam interacts with the contact surface.