Line source - AbsoluteAstronomy.com

A line 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

Roadway air dispersion modeling

Roadway air dispersion modeling is the study of air pollutant transport from a roadway or other linear emitter. Computer models are required to conduct this analysis, because of the complex variables involved, including vehicle emissions, vehicle speed, meteorology, and terrain geometry...

, aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

air emissions

Emission standard

Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...

, roadway noise

Roadway noise

Roadway noise is the collective sound energy emanating from motor vehicles. In the USA it contributes more to environmental noise exposure than any other noise source, and is constituted chiefly of engine, tire, aerodynamic and braking elements...

, 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

Medical physics

Medical physics is the application of physics to medicine. It generally concerns physics as applied to medical imaging and radiotherapy, although a medical physicist may also work in many other areas of healthcare...

and electromagnetic antennas

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

. While point sources

Point source (pollution)

A point source of pollution is a single identifiable localized source of air, water, thermal, noise or light pollution. A point source has negligible extent, distinguishing it from other pollution source geometries. The sources are called point sources because in mathematical modeling, they can be...

of pollution

Pollution

Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

were studied since the late nineteenth century, linear sources did not receive much attention from scientists until the late 1960s, when environmental regulations for highway

Highway

A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

s and airport

Airport

An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...

s 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

Roadway air dispersion modeling

. Prior to the 1960s, these specialities tended to work within their own disciplines, but with the advent of NEPA

Nepa

Nepa is a village development committee in Dailekh District in the Bheri Zone of western-central Nepal. At the time of the 1991 Nepal census it had a population of 3621 people living in 739 individual households.-External links:*...

, the Clean Air Act

Clean Air Act

A Clean Air Act is one of a number of pieces of legislation relating to the reduction of airborne contaminants, smog and air pollution in general. The use by governments to enforce clean air standards has contributed to an improvement in human health and longer life spans...

, the Noise Control Act

Noise Control Act

The Noise Pollution and Abatement Act of 1972 is a statute of the United States initiating a federal program of regulating noise pollution with the intent of protecting human health and minimizing annoyance of noise to the general public....

in the USA, 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

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

and USA when the end of World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

and the Cold War

Cold War

The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

were fought partially by progress in electronic warfare

Electronic warfare

Electronic warfare refers to any action involving the use of the electromagnetic spectrum or directed energy to control the spectrum, attack an enemy, or impede enemy assaults via the spectrum. The purpose of electronic warfare is to deny the opponent the advantage of, and ensure friendly...

, including the technologies of active antenna arrays.

Linear air pollution source

Air pollution levels near major highways and urban arterials are in violation of U.S. National Ambient Air Quality Standards where millions of Americans live or work. Even the interior of a building does not really protect inhabitants from adverse exterior air quality, since the exterior air is the intake supply, and it is well known that indoor air quality

Indoor air quality

Indoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants....

is typically worse than exterior air.

A roadway travelled by motor vehicles can be idealized by a line source emitting air pollutants. This mathematical problem was first solved in 1970 by a collaboration of physics

Physics

Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

, mathematics

Mathematics

Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

and computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

. The original theory assumed steady-state traffic conditions and meteorology on a perfectly straight roadway. Currently the models have evolved to treat variable meteorology, time-variant traffic operations and complex roadbed geometries. Current technology allows highway designers and city planners to analyze alternative roadway development plans and assess air quality impacts. The same basic model theory can be applied to airport operations, since the linear source is merely an inclined line. In the early 1970s these ESL models were refined into area source models to account for the finite width of the roadway.

Linear noise source

Main article: Roadway noise

Roadway noise

Roadway noise is the most important example of a linear noise source, since it comprises about 80 percent of the environmental noise exposure for humans worldwide. In the 1960s, when computer modeling of this phenomenon was perfected, the first applications of linear source noise modeling became systematic. After passage of the National Environmental Policy Act

National Environmental Policy Act

The National Environmental Policy Act is a United States environmental law that established a U.S. national policy promoting the enhancement of the environment and also established the President's Council on Environmental Quality ....

and Noise Control Act, the demand for detailed analysis soared, and decision makers began to look to acoustical scientists for answers regarding the planning of new roadways and the design of noise mitigation

Noise mitigation

Noise mitigation is a set of strategies to reduce noise pollution. The main areas of noise mitigation or abatement are: transportation noise control, architectural design, and occupational noise control...

. The intensity of roadway noise is governed by the following variables: traffic

Traffic

Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

operations (speed, truck

Truck

A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

mix, age of vehicle

Vehicle

A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....

fleet), roadway surface type, tire types, roadway geometrics, terrain, micrometeorology and the geometry of area structures.

Due to the complexity of the variables, a line source acoustic model must be a computer model that can analyze sound levels in the vicinity of roadways. The first meaningful models arose in the late 1960s and early 1970s. Two of the leading research teams were BBN

BBN

BBN might refer to:* BBN Technologies, formerly Bolt, Beranek and Newman, a technology company in Cambridge, Massachusetts, best known for its work on packet switching technology and its construction of the Interface Message Processor - the first router...

in Boston

Boston

Boston is the capital of and largest city in Massachusetts, and is one of the oldest cities in the United States. The largest city in New England, Boston is regarded as the unofficial "Capital of New England" for its economic and cultural impact on the entire New England region. The city proper had...

and ESL Inc. of Sunnyvale, California. Both of these groups developed complex mathematical model

Mathematical model

A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...

s to allow the study of alternate roadway designs, traffic operations and noise mitigation

Noise mitigation

strategies in an arbitrary setting. Later model alterations have come into widespread use among state Departments of Transportation

Department of Transportation

The Department of Transportation is the most common name for a government agency in North America devoted to transportation. The largest is the United States Department of Transportation, which oversees interstate travel. All U.S. states, Canadian provinces, and many local agencies also have...

and city planners, but the accuracy of early models has had little change in 40 years.

Generally line source acoustic models trace sound ray bundles and calculate spreading loss along with ray bundle divergence (or convergence} from refractive phenomena. Diffraction

Diffraction

Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

is usually addressed by establishing secondary emitters at any points of topographic or anthropomorphic “sharpness” (such as noise barrier

Noise barrier

A noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...

s or building surfaces. Meteorology

Meteorology

Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

can be addressed in a statistical manner allowing for actual wind rose

Wind rose

A wind rose is a graphic tool used by meteorologists to give a succinct view of how wind speed and direction are typically distributed at a particular location. Historically, wind roses were predecessors of the compass rose , as there was no differentiation between a cardinal direction and the wind...

and wind speed

Wind speed

Wind speed, or wind velocity, is a fundamental atmospheric rate.Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications....

statistics (along with thermocline

Thermocline

A thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...

data).

Water pollution line source

Less common are line source applications in the field of water pollutant dispersal. This phenomenon generally arises when surface runoff

Surface runoff

Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

scours soil contaminants from upper soil layers and transports these pollutants to a linear receiving water, such as a river. The underlying land management practices which lead to such sources of water pollution are logging

Logging

Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...

, pesticide

Pesticide

Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

application, construction

Construction

In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

grading, slash-and-burn activity and urban stormwater

Stormwater

Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

runoff.

Again computer models are needed to address the complexity of such an extended linear discharge into a dynamic medium such as flowing water. The resulting surface runoff water carrying pollutants may be considered a line source discharging into a river or stream. The chemical composition of this surface runoff may be characterized by a surface runoff model such as the USGS runoff precipitation algorithm, while the instream transport may be analyzed by a dynamic river pollutant model such as DSSAM.

Light emission line source

In the study of illumination, a variety of sources are linear in nature, most commonly the fluorescent tube, During the process of interior lighting design it is important to calculate the light intensity at work stations or other user areas, not only to ensure sufficient light is present, but more importantly to avoid over-illumination

Over-illumination

Over-illumination is the presence of lighting intensity beyond that required for a specified activity. Over-illumination was commonly ignored between 1950 and 1995, especially in office and retail environments; only since then has the interior design community begun to reconsider this practice.The...

and its attendant energy wastage

Energy conservation

Energy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...

as well as adverse health effects. Thus the scientists involved in light transmission calculations employ computer models that recognize linear sources when fluorescent fixtures are used. In a typical setting there may be hundreds of finite length light sources that comprise the light output in an office environment. A related concept are the ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

tubes used in phototherapy, where output radiation from the tube can be accurately modeled by treating the tube as a line source . On a larger scale, an illuminated roadway may act as a line source of light pollution

Light pollution

Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Linear air pollution source

Linear noise source

Water pollution line source

Light emission line source

See also

External links