Abstract: The present disclosure relates to an object detection unit for detecting the presence of foreign object debris, FOD, on a runway, taxiway or apron surface, the object detection unit comprising a processor, the object detection unit configured to: receive an image taken by a camera, the image comprising at least part of the runway surface, taxiway surface or apron surface, input the image to a zero-shot object detection model, wherein the zero-shot object detection model is configured to output co-ordinates of a bounding box around a candidate FOD in the image and determine a likelihood that FOD is present in the bounding box; obtain, from the zero-shot object detection model, co-ordinates of a bounding box around a candidate FOD in the image and a likelihood that the candidate FOD is foreign object debris; and determine if the likelihood exceeds a threshold value.