🔍 Key Concepts

• Doppler speed log operating modes (bottom track vs. water track / volume reverberation) • Difference between speed through the water and speed over the ground • Effect of current on what the instrument is actually measuring

💭 Think About

• Which operating mode of a Doppler log uses echoes from the seabed, and which one uses echoes from particles in the water column? • If current is present, does the instrument see that as motion of the ship or motion of the water? How would that change whether you get speed over ground or speed through the water? • Under what depth or bottom conditions can the log actually detect the seabed reliably?

✅ Before You Answer

• Identify which mode gives bottom track (returns from the seabed) and which gives water track (volume reverberation). • Decide in which mode the reading is independent of current and therefore represents speed over ground. • Confirm whether the log can truly show speed over ground all the time, or only when a certain mode/condition is available.