Question 816Navigation General

The correct answer is D) speed through the water. A Doppler log in the volume reverberation mode is used to measure the vessel's speed through the water. It does this by detecting the Doppler shift in the frequency of the reflected sound waves, which is proportional to the vessel's speed relative to the water. This provides a direct measurement of the speed through the water, rather than the speed made good over the ground, which can be affected by currents. The other answer choices are incorrect because a Doppler log does not directly indicate the set of the current (A), the depth of the water (C), or the speed being made good (B), which is affected by both the vessel's speed through the water and any current.