A "duck blind" was a term that originated from a method used by Human hunters to catch their prey, ducks, off guard. The expression was also used in the 24th century for the method of holographically masking a cultural observation post used by Federation cultural observers, since in cases where the Prime Directive applied, observations of the planet's inhabitants needed to be kept hidden.
A duck blind was employed on Mintaka III in 2366 by a three-man anthropology team. The power needed to maintain the duck blind required a fusion reactor with an output of 4.2 gigawatts. The duck blind failed when the reactor suffered a serious malfunction, and the observer team was discovered by the Mintakans. (TNG: "Who Watches The Watchers")
A similar technology was employed on the Ba'ku planet in the Briar Patch in 2375. This blind used three holographic emitters, and also provided the masking fields for the team's isolation suits. The duck blind was disabled by a malfunctioning Lieutenant Commander Data after he discovered the true nature of the mission - to displace the Ba'ku from their homes, and harvest the metaphasic radiation in the planet's rings. (Star Trek: Insurrection)
Background information Edit
The novelization and script for Star Trek: Insurrection stated that Admiral Matthew Dougherty had the duck blind on Ba'ku equipped with chromodynamic shields capable of withstanding the metaphasic radiation so that the Starfleet observers there would not feel the regenerative effects of the planet.