The development of this ultrasonic method for determining the modulus of thin adhesive layers was motivated by the recent development of a nonintrusive ultrasonic Liquid Level Sensor (LLS) which meets military specifications for space launch [1,2]. The sensor is designed to signal when the surface of the fuel in a liquid propellant tank has receded to the level of the sensor during flight. As depicted in Fig. 1, the sensor is bonded to the outer tank wall with Versilok 202 (V202) adhesive [3]. To detect the fuel level, the sensor is stimulated to propagate an ultrasonic pulse into the wall of the tank and then used to monitor the height of echoes which return from the inner wall. More details on the basic operation of the sensor are given in references 1 and 2.