space radiation environment surface radiation environment The natural radiation environment on or adjacent to the surface of a planet or moon, comprising: the free space radiation environment partially shielded by the planet or moon and modulated by interactions with the planet's or moon's crust, and atmosphere and magnetic field, if any, and radiation produced by naturally occurring radioactive elements in the planet's or moon's crust. A surface radiation environment can include both ionizing radiation and non-ionizing radiation such as UVA, UVB and visible light, but often is used to refer to biologically damaging ionizing radiation such as galactic cosmic radiation and solar particles.