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Radar Cross-section
Radar cross-section (RCS), also called radar signature, is a measure of how detectable an object is by radar. A larger RCS indicates that an object is more easily detected. An object reflects a limited amount of radar energy back to the source. The factors that influence this include: *the material with which the target is made; *the size of the target relative to the wavelength of the illuminating radar signal; *the absolute size of the target; *the incident angle (angle at which the radar beam hits a particular portion of the target, which depends upon the shape of the target and its orientation to the radar source); *the reflected angle (angle at which the reflected beam leaves the part of the target hit; it depends upon incident angle); *the polarization of the transmitted and the received radiation with respect to the orientation of the target. While important in detecting targets, strength of emitter and distance are not factors that affect the calculation of an RCS becaus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigma Invader RCS
Sigma (; uppercase Σ, lowercase σ, lowercase in word-final position ς; grc-gre, σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used as an operator for summation. When used at the end of a letter-case word (one that does not use all caps), the final form (ς) is used. In ' (Odysseus), for example, the two lowercase sigmas (σ) in the center of the name are distinct from the word-final sigma (ς) at the end. The Latin letter S derives from sigma while the Cyrillic letter Es derives from a lunate form of this letter. History The shape (Σς) and alphabetic position of sigma is derived from the Phoenician letter ( ''shin''). Sigma's original name may have been ''san'', but due to the complicated early history of the Greek epichoric alphabets, ''san'' came to be identified as a separate letter in the Greek alphabet, represented as Ϻ. Herodotus reports that "san" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The ''law of reflection'' says that for specular reflection (for example at a mirror) the angle at which the wave is incident on the surface equals the angle at which it is reflected. In acoustics, reflection causes echoes and is used in sonar. In geology, it is important in the study of seismic waves. Reflection is observed with surface waves in bodies of water. Reflection is observed with many types of electromagnetic wave, besides visible light. Reflection of VHF and higher frequencies is important for radio transmission and for radar. Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors. Reflection of light Reflection of light is either '' specular'' (mirror-like) or '' diffuse'' (retaining ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Container Ship
A container ship (also called boxship or spelled containership) is a cargo ship that carries all of its load in truck-size intermodal containers, in a technique called containerization. Container ships are a common means of commercial intermodal freight transport and now carry most seagoing non-bulk cargo. Container ship capacity is measured in twenty-foot equivalent units (TEU). Typical loads are a mix of 20-foot (1-TEU) and 40-foot (2-TEU) ISO-standard containers, with the latter predominant. Today, about 90% of non-bulk cargo worldwide is transported by container ships, and the largest modern container ships can carry up to 24,000 TEU (e.g., '' Ever Ace''). Container ships now rival crude oil tankers and bulk carriers as the largest commercial seaborne vessels. History There are two main types of dry cargo: bulk cargo and break bulk cargo. Bulk cargoes, like grain or coal, are transported unpackaged in the hull of the ship, generally in large volume. Break-bulk ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frigate
A frigate () is a type of warship. In different eras, the roles and capabilities of ships classified as frigates have varied somewhat. The name frigate in the 17th to early 18th centuries was given to any full-rigged ship built for speed and maneuverability, intended to be used in scouting, escort and patrol roles. The term was applied loosely to ships varying greatly in design. In the second quarter of the 18th century, the 'true frigate' was developed in France. This type of vessel was characterised by possessing only one armed deck, with an unarmed deck below it used for berthing the crew. Late in the 19th century (British and French prototypes were constructed in 1858), armoured frigates were developed as powerful ironclad warships, the term frigate was used because of their single gun deck. Later developments in ironclad ships rendered the frigate designation obsolete and the term fell out of favour. During the Second World War the name 'frigate' was reintroduced to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corner Reflector
A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects waves directly towards the source, but translated. The three intersecting surfaces often have square shapes. Radar corner reflectors made of metal are used to reflect radio waves from radar sets. Optical corner reflectors, called corner cubes or cube corners, made of three-sided glass prisms, are used in surveying and laser ranging. Principle The incoming ray is reflected three times, once by each surface, which results in a reversal of direction. To see this, the three corresponding normal vectors of the corner's perpendicular sides can be considered to form a basis (a rectangular coordinate system) (''x'', ''y'', ''z'') in which to represent the direction of an arbitrary incoming ray, . When the ray reflects from the first side, say ''x'', the ray's ''x'' component, ''a'', is reversed to −''a'' while the ''y'' and ''z'' components are unchan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coastal Trading Vessel
Coastal trading vessels, also known as coasters or skoots, are shallow-hulled ships used for trade between locations on the same island or continent. Their shallow hulls mean that they can get through reefs where deeper-hulled seagoing ships usually cannot. Coasters can load and unload cargo in shallow ports. World War II During World War II there was a demand for coasters to support troops around the world. Type N3 ship and Type C1 ship was the designation for small cargo ships built for the United States Maritime Commission before and during World War II. Both were use for close to shore and short cargo runs. Government of the United Kingdom used Empire ships type Empire F as a merchant ship A merchant ship, merchant vessel, trading vessel, or merchantman is a watercraft that transports cargo or carries passengers for hire. This is in contrast to pleasure craft, which are used for personal recreation, and naval ships, which are ... for coastal shipping. UK sea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface-to-air-missile
A surface-to-air missile (SAM), also known as a ground-to-air missile (GTAM) or surface-to-air guided weapon (SAGW), is a missile designed to be launched from the ground to destroy aircraft or other missiles. It is one type of anti-aircraft system; in modern armed forces, missiles have replaced most other forms of dedicated anti-aircraft weapons, with anti-aircraft guns pushed into specialized roles. The first attempt at SAM development took place during World War II, but no operational systems were introduced. Further development in the 1940s and 1950s led to operational systems being introduced by most major forces during the second half of the 1950s. Smaller systems, suitable for close-range work, evolved through the 1960s and 1970s, to modern systems that are man-portable. Shipborne systems followed the evolution of land-based models, starting with long-range weapons and steadily evolving toward smaller designs to provide a layered defence. This evolution of design increasin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lockheed F-117 Nighthawk
The Lockheed F-117 Nighthawk is a retired American single-seat, twin-engine stealth attack aircraft developed by Lockheed's secretive Skunk Works division and operated by the United States Air Force (USAF). It was the first operational aircraft to be designed with stealth technology. The F-117 was based on the ''Have Blue'' technology demonstrator. The Nighthawk's maiden flight took place in 1981 at Groom Lake, Nevada, and the aircraft achieved initial operating capability status in 1983. The aircraft was shrouded in secrecy until it was revealed to the public in 1988. Of the 64 F-117s built, 59 were production versions, with the other five being prototypes. The F-117 was widely publicized for its role in the Gulf War of 1991. Although it was commonly referred to as the "Stealth Fighter", it was strictly an attack aircraft. F-117s took part in the conflict in Yugoslavia, where one was shot down by a surface-to-air missile (SAM) in 1999. The U.S. Air Force retired the F-117 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stealth Aircraft
Stealth aircraft are designed to avoid detection using a variety of technologies that reduce reflection/emission of radar, infrared, visible light, radio frequency (RF) spectrum, and audio, collectively known as stealth technology. The F-117 Nighthawk was the first operational aircraft specifically designed around stealth technology. Other examples of stealth aircraft include the B-2 Spirit, the B-21 Raider, the F-22 Raptor, the F-35 Lightning II, the Chengdu J-20, and the Sukhoi Su-57. While no aircraft is totally invisible to radar, stealth aircraft make it more difficult for conventional radar to detect or track the aircraft effectively, increasing the odds of an aircraft successfully avoiding detection by enemy radar and/or avoiding being successfully targeted by radar guided weapons. Stealth is the combination of passive low observable (LO) features and active emitters such as low-probability-of-intercept radars, radios and laser designators. These are usually com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anechoic Chamber
An anechoic chamber (''an-echoic'' meaning "non-reflective") is a room designed to stop reflections of either sound or electromagnetic waves. They are also often isolated from energy entering from their surroundings. This combination means that a person or detector exclusively hears direct sounds (no reflected sounds), in effect simulating being outside in a free field. Anechoic chambers, a term coined by American acoustics expert Leo Beranek, were initially exclusively used to refer to acoustic anechoic chambers. Recently, the term has been extended to other RF and Sonar anechoic chambers, which eliminate reflection and external noise caused by electromagnetic waves. Anechoic chambers range from small compartments the size of household microwave ovens to ones as large as aircraft hangars. The size of the chamber depends on the size of the objects and frequency ranges being tested. Acoustic anechoic chambers The requirement for what was subsequently called an anechoic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scattering Range
Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiation) in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. Reflections of radiation that undergo scattering are often called ''diffuse reflections'' and unscattered reflections are called ''specular'' (mirror-like) reflections. Originally, the term was confined to light scattering (going back at least as far as Isaac Newton in the 17th century). As more "ray"-like phenomena were discovered, the idea of scattering was extended to them, so that William Herschel could refer to the scattering of "heat rays" (not then recognized as electromagnetic in nature) in 1800. John Tyndall, a pioneer in light scattering resear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflectivity Range
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic structure of the material to the electromagnetic field of light, and is in general a function of the frequency, or wavelength, of the light, its polarization, and the angle of incidence. The dependence of reflectance on the wavelength is called a ''reflectance spectrum'' or ''spectral reflectance curve''. Mathematical definitions Hemispherical reflectance The ''hemispherical reflectance'' of a surface, denoted , is defined as R = \frac, where is the radiant flux ''reflected'' by that surface and is the radiant flux ''received'' by that surface. Spectral hemispherical reflectance The ''spectral hemispherical reflectance in frequency'' and ''spectral hemispherical reflectance in wavelength'' of a surface, denoted and respectively, are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
