surveillance vs police work

surveillance and police work both are nouns.

Word	Noun	Adjective	Verb	Adverb
surveillance	Yes	No	No	No
police work	Yes	No	No	No

As nouns, police work is a hypernym of surveillance; that is, police work is a word with a broader meaning than surveillance:

surveillance: close observation of a person or group (usually by the police)
police work: the investigation of criminal activities

Other hypernyms of surveillance include police investigation.

surveillance (noun)	police work (noun)
close observation of a person or group (usually by the police)	the investigation of criminal activities