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Terrain Return
The terrain return is the signal returned from the ground surface when sensed by various remote sensing systems, e.g., radars. One may distinguish two components of terrain return: the wanted signal (e.g., when generating a radar map of the terrain or when used for terrain avoidance and collision detection) and ground clutter, an unwanted signal that interferes with sensing of various objects other than terrain. The ground-to-air terrain return at vertical or near-vertical incidence angles may be decomposed into two components: a mirror-like specular component and the scatter component produced by reradiation from the individual scatterers in the terrain (large isolated scatterers and area scatter). The image record of the radar terrain return depends on the frequency, angle of incidence, and polarization of the signal. This dependence varies with the nature of the terrain surface; for example, if the terrain is covered by vegetation, a 35GHz K band signal will record vegetatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Remote Sensing
Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth and other planets. Remote sensing is used in numerous fields, including geophysics, geography, land surveying and most Earth science disciplines (e.g. exploration geophysics, hydrology, ecology, meteorology, oceanography, glaciology, geology). It also has military, intelligence, commercial, economic, planning, and humanitarian applications, among others. In current usage, the term ''remote sensing'' generally refers to the use of satellite- or airborne-based sensor technologies to detect and classify objects on Earth. It includes the surface and the atmosphere and oceans, based on wave propagation, propagated signals (e.g. electromagnetic radiation). It may be split into "active" remote sensing (when a signal is emitted b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radar
Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain. The term ''RADAR'' was coined in 1940 by the United States Navy as an acronym for "radio detection and ranging". The term ''radar'' has since entered English and other languages as an anacronym, a common noun, losing all capitalization. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwave domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the objects. Radio waves (pulsed or continuous) from the transmitter reflect off the objects and return to the receiver, giving ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radar Map
Imaging radar is an application of radar which is used to create two-dimensional images, typically of landscapes. Imaging radar provides its light to illuminate an area on the ground and take a picture at radio wavelengths. It uses an antenna and digital computer storage to record its images. In a radar image, one can see only the energy that was reflected back towards the radar antenna. The radar moves along a flight path and the area illuminated by the radar, or footprint, is moved along the surface in a swath, building the image as it does so. Digital radar images are composed of many dots. Each pixel in the radar image represents the radar backscatter for that area on the ground (terrain return): brighter areas represent high backscatter, darker areas represents low backscatter. The traditional application of radar is to display the position and motion of typically highly reflective objects (such as aircraft or ships) by sending out a radiowave signal, and then detecting th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terrain Awareness And Warning System
In aviation, a terrain awareness and warning system (TAWS) is generally an on-board system aimed at preventing unintentional impacts with the ground, termed "controlled flight into terrain" accidents, or CFIT.Federal Aviation AdministrationInstallation of Terrain Awareness and Warning System (TAWS) Approved for Part 23 Airplanes, 14 June 2000 The specific systems currently in use are the ground proximity warning system (GPWS) and the enhanced ground proximity warning system (EGPWS). The U.S. Federal Aviation Administration (FAA) introduced the generic term ''TAWS'' to encompass all terrain-avoidance systems that meet the relevant FAA standards, which include GPWS, EGPWS and any future system that might replace them. As of 2007, 5% of the world's commercial airlines still lacked a TAWS. A study by the International Air Transport Association examined 51 accidents and incidents and found that pilots did not adequately respond to a TAWS warning in 47% of cases. Several factors can s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground Clutter
Clutter is the unwanted return (echoes) in electronic systems, particularly in reference to radars. Such echoes are typically returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences, and can cause serious performance issues with radar systems. What one person considers to be unwanted clutter, another may consider to be a wanted target. However, targets usually refer to point scatterers and clutter to extended scatterers (covering many range, angle, and Doppler cells). The clutter may fill a volume (such as rain) or be confined to a surface (like land). A knowledge of the volume or surface area illuminated is required to estimated the echo per unit volume, η, or echo per unit surface area, σ° (the radar backscatter coefficient). Causes Clutter may be caused by man-made objects such as buildings and — intentionally — by radar countermeasures such as chaff. Other causes include natural objects such as terrain features, sea, precipitation, hail sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
K Band (NATO)
The NATO K band is the obsolete designation given to the radio frequencies from 20 to 40 GHz (equivalent to wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...s between 1.5 and 0.75 cm) during the cold war period. Since 1992 frequency allocations, allotment and assignments are in line to NATO Joint Civil/Military Frequency Agreement (NJFA). However, in order to identify military radio spectrum requirements, e.g. for crises management planning, training, electronic warfare activities, or in military operations, this system is still in use. References {{EMSpectrum Microwave bands Satellite broadcasting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P Band
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and 300 GHz, broadly construed. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz (wavelengths between 30 cm and 3 mm), or between 1 and 3000 GHz (30 cm and 0.1 mm). In all cases, microwaves include the entire super high frequency (SHF) band (3 to 30 GHz, or 10 to 1 cm) at minimum. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency (UHF) are fairly arbitrary and differ between different fields of study. The prefix ' in ''microwave'' indicates that microwaves are small (having shorter wavelengths), compared to the radio waves used in prior radio technology. Frequencies in the microwave range are often referred ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
