Question

1. uses sonar waves emitted from a ship to map the ocean floor

Explanation:

This process of using sonar waves from a ship to map the ocean floor is related to oceanography, which falls under the subfield of Geography (within Natural Science) as it involves studying the physical features of the ocean and its floor, or also could be related to Geology (another subfield of Natural Science) as it pertains to the structure of the Earth's crust under the ocean. However, more specifically, the use of sonar for ocean floor mapping is a technique used in marine geology and physical geography. The main concept here is that sonar (sound navigation and ranging) sends out sound waves that reflect off the ocean floor, and by measuring the time it takes for the waves to return, the depth and shape of the ocean floor can be determined. This is a method used in studying the ocean's topography, which is a part of Geography (or Geology) in Natural Science.

Answer:

The subfield that best applies is Geography (under Natural Science) (or Geology, but Geography is more focused on the physical features and mapping of the Earth's surface including the ocean floor).