the other of the aforementioned mechanisms of geometrical damping and with reference to fig3 damping due to reflections results primarily because as the ultrasound propagates across an interface a portion of it is reflected as shown in the schematic representation of fig3 the object 40 it is desired to image is separated from the transducer 16 by a first coupling medium which might be the water coupling path mentioned earlier two contiguous layers 44 and 46 and a portion of a third layer 48 which surrounds the object 40 which represent three distinct interfaces across which the ultrasound must propagate before reaching the front surface of the object 40 moreover the layers 44 46 and 48 may have different impedances z 1 z 2 and z 3 respectively and the reflection from each of the interfaces is in turn a function of these impedances as well as the incident energy at each interface the reflected and transmitted intensities i r and i t are algebraically related i t i i i r where i i is the incident ultrasound intensity for imaging of subsequent interfaces therefore only a smaller portion of the energy i i is available more particularly in the illustrated example if the pulse from the transducer 16 has an intensity i 1 the echo reflected from the front surface of layer 44 has an intensity i 2 which is proportional to the impedance z 1 of layer 44 and of the incident intensity i 1 leaving an intensity for transmission through layer 46 of i sub 1 i 2 a portion of this energy designated i 3 is reflected from the interface of layers 44 and 46 and so.