A sensor processing unit comprising: a sonic transducer configured to transmit sonic signals toward a surface and receive corresponding returned signals reflected from the surface , wherein the surface is within a ringdown distance associated with the sonic transducer ; and a sensor processor coupled with the sonic transducer and configured to: following cessation of active transmission of the sonic signals, sample a plurality of points of a ringdown signal generated by the sonic transducer , wherein the sampling occurs during an early portion of the ringdown signal before the corresponding returned signals from the surface have reflected back to be received by the sonic transducer and the sampling also occurs during a later portion of the ringdown signal which includes the corresponding returned signals ; estimate , using the early portion of the plurality of sampled points, a void ringdown signal of the sonic transducer , wherein the estimated void ringdown signal represents performance of the sonic transducer in absence of any returned signals being received; compare the estimated void ringdown signal to the later portion of the ringdown signal ; generate a metric based on the comparison ; and utilize the metric to determine a type of the surface , out of a plurality of surface types. a sonic transducer configured to transmit sonic signals toward a surface and receive corresponding returned signals reflected from the surface , wherein the surface is within a ringdown distance associated with the sonic transducer ; and a sensor processor coupled with the sonic transducer and configured to: following cessation of active transmission of the sonic signals, sample a plurality of points of a ringdown signal generated by the sonic transducer , wherein the sampling occurs during an early portion of the ringdown signal before the corresponding returned signals from the surface have reflected back to be received by the sonic transducer and the sampling also occurs during a later portion of the ringdown signal which includes the corresponding returned signals ; estimate , using the early portion of the plurality of sampled points, a void ringdown signal of the sonic transducer , wherein the estimated void ringdown signal represents performance of the sonic transducer in absence of any returned signals being received; compare the estimated void ringdown signal to the later portion of the ringdown signal ; generate a metric based on the comparison ; and utilize the metric to determine a type of the surface , out of a plurality of surface types. following cessation of active transmission of the sonic signals, sample a plurality of points of a ringdown signal generated by the sonic transducer , wherein the sampling occurs during an early portion of the ringdown signal before the corresponding returned signals from the surface have reflected back to be received by the sonic transducer and the sampling also occurs during a later portion of the ringdown signal which includes the corresponding returned signals ; estimate , using the early portion of the plurality of sampled points, a void ringdown signal of the sonic transducer , wherein the estimated void ringdown signal represents performance of the sonic transducer in absence of any returned signals being received; compare the estimated void ringdown signal to the later portion of the ringdown signal ; generate a metric based on the comparison ; and utilize the metric to determine a type of the surface , out of a plurality of surface types. <EOS>