Question

what is the study and measurement of underwater depth?
bathymetry
sonography
hydrology
radiology

Explanation:

Bathymetry is the study and measurement of underwater depth. Sonography is mainly used in medical imaging (like ultrasound for fetus etc.). Hydrology is the study of water in general (its distribution, properties etc. on Earth). Radiology is related to medical imaging using radiation (like X - rays).

Answer:

bathyemetry