Round-Trip Time Gives Depth - Biophysical Ultrasound: Echo Timing and Acoustic Interfaces Step by Step

An ultrasound pulse travels out and back, so the reflector depth is half the round-trip path. With speed 4 m/s and echo time 6 s, the round-trip path is 4 times 6 = 24 m and the depth is 24/2 = 12 m exactly for the stated toy ranging model; real ultrasound depends on sound-speed estimate, timing resolution, beam geometry, tissue variation, attenuation and scattering, and measurement uncertainty.

An echo depth is half the sound-speed-times-time path. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Echo time measures an out-and-back path

The pulse travels at 4 meters per second for 6 seconds, so the checked path is 24 meters.

c t=4\cdot 6=24\ \text{m}

Depth is half of the round trip

The reflector depth is half of 24 meters, so the accepted depth is 12 meters.

d=\frac{24}{2}=12\ \text{m}