1) If an echo sounder emits a pulse of 100 cycles at a frequency of 500 kHz what is the pulse length and the minimum water depth it can operate in? 2) If a source emits 10W of sound power in an unbounded medium what is the Sound Intensity Level in dB re 10-2 watts/m at a distance of 10m, 20m and 40m from the source? What are the corresponding SPL levels in air re 20 Pa and in water re 1 Pa.