When it comes to generating farm data, a drone is simply a tool to get a camera in the air. Drone platforms can carry a variety of cameras and imaging sensors, however most use off the shelf Canon digital cameras running a custom software load called CHDK. This custom software allows you to trigger the camera on a timer or via a trigger from the drone's navigation computer. After the flight is over the SD card is filled with hundreds of pictures taken straight down from above. At this point you stitch these files into a single large image. There are a variety of free of paid tools to accomplish this that are covered in our article on processing software, the resulting images can be imported into your choice of farm data managment software, or compared in powerful tools like Googles earth viewer.
Images can taken either as normal images, or by a camera with modifications made so it can capture light in the infrared spectrum. These images can be post processed into an NDVI (Normalized Difference Vegetation Index) that shows differences in a plants reflection of infrared light telling a farmer if plants under stress before changes can be seen by the naked eye.