The present invention is directed to an improved method and apparatus for determining ultrasonically the quantity of liquid in a tank having multiple inventive aspects. One aspect includes an ultrasonic transducer having three layers, the top two each having a thickness of approximately one-quarter wavelength and having materials with corresponding acoustic impedances which together are chosen to match the acoustic impedance of the bottom layer to the acoustic impedance of the tank liquid about the operational frequency passband of the ultrasonic pulse transmitted from the transducer. Another aspect involves a system and method for discriminating between echo sources of an ultrasonic burst echo signal resulting from an incipient ultrasonic burst signal transmitted from the ultrasonic transducer. A further aspect involves the method of determining ultrasonically the height of a thermally stratified liquid in a tank using at least one ultrasonic transducer disposed at the bottom of the tank for transmitting an ultrasonic pulse towards the height surface of the tank liquid and for receiving ultrasonic reflections therefrom. A still further aspect involves a circuit for generating an electrical excitation signal for the ultrasonic transducer including a step-up transformer which affords DC isolation between the excitation signal generator and the transducer and which conveys the excitation signal differentially to the transducer in an electrically balanced configuration.