A counter measure apparatus and method for modifying a path of an electromagnetic detector signal (204) so as to prevent incidence thereof on a platform (200), the apparatus comprising an electromagnetic radiation source, communicably coupled to a control system. The control system is configured to create an atmospheric element (202) operative to simulate a physical electromagnetic radiation path modifying device within an atmospheric volume located in said electromagnetic detector signal path (204) by causing electromagnetic radiation from the source to be applied to a selected plurality of three-dimensional portions of said atmospheric volume so as to heat and/or ionise the air within said portions, wherein said selected portions are spatially located together in a substantially unbroken, three-dimensional configuration.