Which field of anthropology uses ethnography to record the observations of a participant observer in a study?

Answer: Cultural Anthropology.

Explanation:

It is an aspect of anthropology that studies the variation in human culture, beliefs, values, ideas, economy, etc adopting the technique, concept and data in ethnography, archeology, folklore, ethnology in analyzing and describing the people in the world.

Cultural anthropology is a study that is based on understanding the culture of a population, living humans, acquired via experience and observation.