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Acoustic Shadow
An acoustic shadow or sound shadow is an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents, buildings, or sound barriers. Short-distance acoustic shadow A short-distance acoustic shadow occurs behind a building or a sound barrier. The sound from a source is shielded by the obstruction. Due to diffraction around the object, it will not be completely silent in the sound shadow. The amplitude of the sound can be reduced considerably, however, depending on the additional distance the sound has to travel between source and receiver. Long-distance acoustic shadow Anomalous sound propagation in the atmosphere can occur in certain conditions of wind, temperature and pressure. Such conditions enable sound to travel in refraction channels over long distances until returning to the earth's surface, and it thus may not be heard in intervening locations. As one website refers to it, "an acoustic sh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary science and is concerned with local detail in general, including not only relief, but also natural, artificial, and cultural features such as roads, land boundaries, and buildings. In the United States, topography often means specifically ''relief'', even though the USGS topographic maps record not just elevation contours, but also roads, populated places, structures, land boundaries, and so on. Topography in a narrow sense involves the recording of relief or terrain, the three-dimensional quality of the surface, and the identification of specific landforms; this is also known as geomorphometry. In modern usage, this involves generation of elevation data in digital form (DEM). It is often considered to include the graphic representation of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Civil War (TV Series)
''The Civil War'' is a 1990 American television documentary miniseries created by Ken Burns about the American Civil War. It was the first broadcast to air on PBS for five consecutive nights, from September 23 to 27, 1990. More than 39 million viewers tuned in to at least one episode, and viewership averaged more than 14 million viewers each evening, making it the most-watched program ever to air on PBS. It was awarded more than 40 major television and film honors. A companion book to the documentary was released shortly after the series aired. Its filmography was groundbreaking for the time, and spawned film techniques such as the Ken Burns effect. Its theme song, "Ashokan Farewell" is widely acclaimed. The series was extremely influential, and serves as the main source of knowledge about the Civil War to many Americans. However, some historians have criticized its historical accuracy, especially its lack of coverage of slavery as a cause of the war. The series was rebroadcast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
