Two Echoes Sort by Depth - Biophysical Ultrasound: Echo Timing and Acoustic Interfaces Step by Step

Echo ordering only compares depths after a shared speed is cited. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

The earlier echo gives the shallower reflector

With shared speed 4, the 4 second echo maps to depth 8 meters.

d_{\text{early}}=\frac{4\cdot 4}{2}=8\ \text{m}

The later echo gives the deeper reflector

The 10 second echo maps to depth 20 meters, so it is deeper.

d_{\text{late}}=\frac{4\cdot 10}{2}=20\ \text{m}