Droid sensorscope
R2-D2's sensorscope rising from a Dagobah swamp
A standard piece of equipment for R-series astromech droids was a droid sensorscope, sometimes referred to as a periscope. This device came complete with a transceiver operating across the full spectrum, along with electro-photo receptors, dedicated energy receptors, a heat detector, and motion detectors. The data collected by the sensorscope was processed by the droid's internal Intellex IV computer. Functioning as an extendable visual aid, it emerged from a panel in the droid's dome, giving them a view that would typically be unavailable to shorter droids.
On multiple occasions, R2-D2 made use of his sensorscope. One instance was to navigate a swamp on Dagobah after he fell into the water soon after the Battle of Hoth. Later, he employed it for sight after sinking into the sands of Tatooine to get away from Jabba the Hutt's sail barge during the Rescue of Han Solo.
Behind the scenes
The sensor that R2-D2 used, first seen rising from the swamp in Star Wars: Episode V The Empire Strikes Back, was initially called a "periscope" in some of the early materials about the film. When Kenner released their second R2-D2 action figure in 1981, the device was officially named a "sensorscope." The packaging for the figure included a picture of the droid utilizing a different scanner on Hoth, but the toy's scanner looked more like the one seen on Dagobah. The Star Wars Customizable Card Game and Star Wars: Behind the Magic later identified this particular scanner as a "droid sensorscope".