An aircraft collision alerting system comprising: one or more light projectors mountable at one or more projector locations on an aircraft and configured to project spatially-patterned light from the one or more light projectors onto a scene external to the aircraft, thereby illuminating a spatially-patterned portion of the scene; one or more cameras (36, 38) mountable at one or more camera locations on the aircraft, respectively, each of the one or more cameras (36, 38) configured to receive light reflected from the scene, and further configured to focus the received light onto a focal plane array comprising a plurality of light-sensitive pixels, thereby forming an image of the scene, and an image processor configured to identify pixel coordinates corresponding to a subset of the plurality of light-sensitive pixels upon which the spatially-patterned light projected by the one or more light projectors and reflected from the spatially-patterned portion of the scene is focused, the image processor further configured to use triangulation, based on the one or more projector locations of the one or more light projectors, the one or more camera locations of the one or more cameras (36, 38) and the identified pixel coordinates, to calculate position values and range data of object(s) in the scene from which the spatially-patterned light projected by the light projector is reflected, characterised in that: the one or more cameras (36, 38) are further configured to form a first image without spatially-patterned light from the one or more light projectors and a second image including spatially-patterned light from the one or more light projectors, the first and second images comprising pixel data generated by the plurality of light-sensitive pixels; and the image processor is configured to isolate reflections of the spatially-patterned light based upon a difference between the first and second images. one or more light projectors mountable at one or more projector locations on an aircraft and configured to project spatially-patterned light from the one or more light projectors onto a scene external to the aircraft, thereby illuminating a spatially-patterned portion of the scene; one or more cameras (36, 38) mountable at one or more camera locations on the aircraft, respectively, each of the one or more cameras (36, 38) configured to receive light reflected from the scene, and further configured to focus the received light onto a focal plane array comprising a plurality of light-sensitive pixels, thereby forming an image of the scene, and an image processor configured to identify pixel coordinates corresponding to a subset of the plurality of light-sensitive pixels upon which the spatially-patterned light projected by the one or more light projectors and reflected from the spatially-patterned portion of the scene is focused, the image processor further configured to use triangulation, based on the one or more projector locations of the one or more light projectors, the one or more camera locations of the one or more cameras (36, 38) and the identified pixel coordinates, to calculate position values and range data of object(s) in the scene from which the spatially-patterned light projected by the light projector is reflected, characterised in that: the one or more cameras (36, 38) are further configured to form a first image without spatially-patterned light from the one or more light projectors and a second image including spatially-patterned light from the one or more light projectors, the first and second images comprising pixel data generated by the plurality of light-sensitive pixels; and the image processor is configured to isolate reflections of the spatially-patterned light based upon a difference between the first and second images. the one or more cameras (36, 38) are further configured to form a first image without spatially-patterned light from the one or more light projectors and a second image including spatially-patterned light from the one or more light projectors, the first and second images comprising pixel data generated by the plurality of light-sensitive pixels; and the image processor is configured to isolate reflections of the spatially-patterned light based upon a difference between the first and second images.