Answer
$1.5\times10^{3}m$
Work Step by Step
Speed of sound in water = 1500m/s
Ultrasonic sound is received 2 secs after being emitted. The round trip is finished in 2 secs which means the ocean level is 1 sec away.
The signal will take 1 sec to reach the ocean bed and then 1 sec to return back to the ship.
Depth of ocean bed = v X t = $1500\times1m=1.5\times10^{3}m$
