A line source, as opposed to a point source, area source, or volume source, is a source of air, noise, water contamination or electromagnetic radiation that emanates from a linear (one-dimensional) geometry. The most prominent linear sources are roadway air pollution, aircraft air emissions, roadway noise, certain types of water pollution sources that emanate over a range of river extent rather than from a discrete point, elongated light tubes, certain dose models in medical physics and electromagnetic antennas. While point sources of pollution were studied since the late nineteenth century, linear sources did not receive much attention from scientists until the late 1960s, when environmental regulations for highways and airports began to emerge. At the same time, computers with the processing power to accommodate the data processing needs of the computer models required to tackle these one-dimensional sources became more available. In addition, this era of the 1960s saw the first emergence of environmental scientists who spanned the disciplines required to accomplish these studies. For example, meteorologists, chemists, and computer scientists in the air pollution field were required to build complex models to address roadway air dispersion modeling. Prior to the 1960s, these specialities tended to work within their own disciplines, but with the advent of NEPA, the Clean Air Act, the Noise Control Act in the United States, and other seminal legislation, the era of multidisciplinary environmental science had begun. For electromagnetic linear sources, the principal early advances in computer modeling arose in the Soviet Union and USA when the end of World War II and the Cold War were fought partially by progress in electronic warfare, including the technologies of active antenna arrays.
