Traditional sonar 83hz

(1) According to the principle of echolocation, scientists invented sonar. The frequency of ultrasonic wave is higher than 2000Hz, and the time for ultrasonic wave to travel from the sea surface to the seabed is t= 12×4s=2s.

Then the seawater depth is s=vt=2s× 1500m/s=3000m.

(2) Ultrasonic waves need to propagate in a medium, and sound cannot propagate in a vacuum without a medium, so ultrasonic sonar cannot be used to measure the distance in space.

So the answer is: 20000; 3000; Vacuum can't transmit sound.