A method for estimating, from a platform, at least one parameter of an intruder. Consecutive frames of image data at different times of the intruder utilizing at least one passive sensor are generated. A direction from the platform to the intruder is determined based on the generated consecutive frames of image data. A time period remaining until a potential collision between the platform and the intruder is estimated. An angular extent of the intruder, as viewed by the passive sensor, is estimated based on the image data. At least one of a first relative location vector to a minimum intruder associated with the intruder or a second relative location vector to a maximum intruder associated with the intruder is estimated. An arrangement for generating input data to a sense-and-avoid system on-board a platform, a computer program, a computer program product and a platform carrying the arrangement are also provided.