the fuel air interface and the echo e1 is reflected from the fuel water interface if echo e2 is not detected then the echo e1 is from the fuel air interface at this time the system will attempt to operate in a high resolution mode the system may not be able to switch to the high resolution mode if for example the surface of the fuel air interface is moving during high resolution initialization as it would if the tank is being filled initially when operating in the high resolution mode the signal level of pulse generator 260 determined in the low resolution mode is utilized as well as the echo validation time window determined in the low resolution mode for the fuel air interface and the fuel water interface the waveform for the fuel air interface is now profiled to choose a specific echo ring to trigger on for the fuel air echo the submerged reflectors are then profiled to profile the reflector echoes the threshold of the receiver is set to a minimum value and a signal is transmitted from the transducer the times of all echoes received which are less than the time for the fuel air interface to be received are stored these times will be the echo times for each submerged reflector the system will then profile each of the reflector echo waveforms if at least two reflectors are identified then the system will operate in the high resolution mode as a result of profiling the pulse generator signal levels are set the.