A method of detecting a target in a scene is described that comprises the step of taking one or more data sets, each data set comprising a plurality of normalized data elements, each normalized data element corresponding to the return from a part of the scene normalized to a reference return for the same part of the scene. The method then involves thresholding (16) at least one of the normalized data elements of each of said one or more data sets. The thresholding step (16) comprises comparing each of the normalized data elements to at least first and second thresholds, wherein the first threshold is greater than the second threshold. The use of one or more confirmation scans (18) in combination with the thresholding step is also described. A radar system is also described that uses the method to detect foreign object debris (FOD) on a surface such as an airport runway.