Head to the marked location to start the mission. A NERO helicopter will land nearby and you have to sneak in the landing zone and avoid getting seen by NERO operatives at all cost. Start by approaching the chopper and following the stream to the left.
After passing through the canal, move from bush to bush while tailing them. Once you reach the point shown below, one of the guards will stay behind so circle around to the left and make sure that you’re not in his line of sight. Hug the rock wall and continue tailing the researcher and his last escort.
Finally, wait for the guard to leave the researcher alone so you can sneak in and approach him. A cutscene will trigger as soon as you get near. After the cutscene, the mission is complete.