There plausibly exist situations in which a researcher undertaking fieldwork would have to conceal their own identity from non-researchers they encounter in the field, in order to protect themselves or the research project. Here are some possible scenarios:
Previous research has shown that the community under study deviates from its normal behaviour when it knows a researcher is present.
The researcher would be in danger if their profession or identity were known to people in the field.
The researcher plans to publish anonymously or pseudonymously, and would otherwise risk being "outed" by people encountered in the field.
What are some good sources on research ethics that discuss protocols for handling such cases?
Can you provide any published examples describing such fieldwork?