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Doppler Radar
A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar. The term applies to radar systems in many domains like aviation, police radar detectors, navigation, meteorology, etc. Concept Doppler effect The Doppler effect (or Doppler shift), named after Austrian physicist Christian Doppler who proposed it in 1842, is the difference between the observed frequency and the emitted frequency of a wave for an observer moving relative to the source of the waves. It is commonly heard when a vehicle sounding a siren approaches, passes and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radar Gun
A radar speed gun, also known as a radar gun, speed gun, or speed trap gun, is a device used to measure the speed of moving objects. It is commonly used by police to check the speed of moving vehicles while conducting Traffic police, traffic enforcement, and in professional sports to measure speeds such as those of baseball Pitch (baseball), pitches, tennis Serve (tennis), serves, and cricket Bowling (cricket), bowls. A radar speed gun is a Doppler radar unit that may be handheld, vehicle-mounted, or static. It measures the speed of the objects at which it is pointed by detecting a change in frequency of the returned radar signal caused by the Doppler effect, whereby the frequency of the returned signal is increased in proportion to the object's speed of approach if the object is approaching, and lowered if the object is receding. Such devices are frequently used for speed limit enforcement, although more modern LIDAR speed gun instruments, which use pulsed laser light instead of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radial Velocity
The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity onto the relative direction or line-of-sight (LOS) connecting the two points. The radial speed or range rate is the temporal rate of the distance or range between the two points. It is a signed scalar quantity, formulated as the scalar projection of the relative velocity vector onto the LOS direction. Equivalently, radial speed equals the norm of the radial velocity, modulo the sign. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from the Earth (or approaches it, for a negative radial velocity). Formulation Given a differentiable vector \mathbf r \in \mathbb^3 defining the instantaneous relative position of a target with respe ... [...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] |
Chaff (countermeasure)
Chaff, originally called Window or Düppel, is a radar countermeasure involving the dispersal of thin strips of aluminium, metallized glass fiber, or plastic. Dispersed chaff produces a large radar cross section intended to blind or disrupt radar systems. Modern military forces use chaff to distract active radar homing missiles from their targets. Military aircraft and warships can be equipped with chaff dispensing systems for self-defense. During its midcourse phase, an intercontinental ballistic missile may release chaff along with its other penetration aids. Contemporary radar systems can distinguish chaff from legitimate targets by measuring the Doppler effect; chaff quickly loses speed after leaving an aircraft, and the resulting shift in wavelength of the radar return can be measured. To counter this, a chaff cloud can be illuminated by the defending vehicle with a doppler-corrected frequency. This is known as JAFF (jammer plus chaff) or CHILL (chaff-illuminated). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Matched Filter
In signal processing, the output of the matched filter is given by correlating a known delayed signal, or ''template'', with an unknown signal to detect the presence of the template in the unknown signal. This is equivalent to convolving the unknown signal with a conjugated time-reversed version of the template. The matched filter is the optimal linear filter for maximizing the signal-to-noise ratio (SNR) in the presence of additive stochastic noise. Matched filters are commonly used in radar, in which a known signal is sent out, and the reflected signal is examined for common elements of the out-going signal. Pulse compression is an example of matched filtering. It is so called because the impulse response is matched to input pulse signals. Two-dimensional matched filters are commonly used in image processing, e.g., to improve the SNR of X-ray observations. Additional applications of note are in seismology and gravitational-wave astronomy. Matched filtering is a demodulation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
United States Army Research Laboratory
The U.S. Army Combat Capabilities Development Command Army Research Laboratory (DEVCOM ARL) is the foundational research laboratory for the United States Army under the United States Army Futures Command (AFC). DEVCOM ARL conducts intramural and extramural research guided by 11 Army competencies: Biological and Biotechnology Sciences; Humans in Complex Systems; Photonics, Electronics, and Quantum Sciences; Electromagnetic Spectrum Sciences; Mechanical Sciences; Sciences of Extreme Materials; Energy Sciences; Military Information Sciences; Terminal Effects; Network, Cyber, and Computational Sciences; and Weapons Sciences. The laboratory was established in 1992 to unify the activities of the seven corporate laboratories of the U.S. Army Laboratory Command (LABCOM) as well as consolidate other Army research elements to form a centralized laboratory. The seven corporate laboratories that merged were the Atmospheric Sciences Laboratory (ASL), the Ballistic Research Laboratory (BRL), ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultra-wideband
Ultra-wideband (UWB, ultra wideband, ultra-wide band and ultraband) is a radio technology that can use a very low energy level for short-range, high-bandwidth communications over a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging. Most recent applications target sensor data collection, precise locating, and tracking. UWB support started to appear in high-end smartphones in 2019. Characteristics Ultra-wideband is a technology for transmitting information across a wide bandwidth (>500 MHz). This allows for the transmission of a large amount of signal energy without interfering with conventional narrowband and carrier wave transmission in the same frequency band. Regulatory limits in many countries allow for this efficient use of radio bandwidth, and enable high-data-rate personal area network (PAN) wireless connectivity, longer-range low-data-rate applications, and the transparent co-existence of radar and imaging systems ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflectivity
The reflectance of the surface of a material is its effectiveness in Reflection (physics), 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 (optics), 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Range Rate
The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity onto the relative direction or line-of-sight (LOS) connecting the two points. The radial speed or range rate is the temporal rate of the distance or range between the two points. It is a signed scalar quantity, formulated as the scalar projection of the relative velocity vector onto the LOS direction. Equivalently, radial speed equals the norm of the radial velocity, modulo the sign. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from the Earth (or approaches it, for a negative radial velocity). Formulation Given a differentiable vector \mathbf r \in \mathbb^3 defining the instantaneous relative position of a target with respect to a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Look-down/shoot-down
A radar system has look-down/shoot-down capability if it can detect, track and guide a weapon to an air target that (as seen by the radar) is silhouetted against the ground. Problem and naming Airborne intercept radar relying exclusively on time domain radar techniques is effectively blind any time the radar's antenna is aimed towards the Earth's surface. That is because pointing the radar at the ground produces a large reflection. That reflection and the ensuing "cluttered" display overwhelms human operators and computing systems (see ground clutter). Radar systems of this type are essentially useless when pointed ‘down’ at the surface, with the zone of weakness near and below the horizon. This zone can be actively utilized by enemy combatants wishing to hide from radar tracking. Frequency domain signal processing combined with time domain signal processing, as in pulse-Doppler radar, is a way to eliminate that vulnerability. Look down Militaries require performance of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pocket Radar
Pocket Radar products are handheld K‐band Doppler speed radar guns developed and manufactured by Pocket Radar, Inc, a company based in Santa Rosa, California. It was intended for those wishing to measure the speed of everyday objects (such as cars and people). Functionality Pocket Radar utilizes very similar microwave signal emission and detection methods found in the Doppler speed radar guns used by law enforcement agencies. The device measures and weighs when equipped with two AAA batteries. It operates at the 24.125 GHz K-Band frequency and can measure speeds ranging from {{convert, 7, to, 375, mph, abbr=on with an accuracy of ±1 mph (±1.6 km/h) and can also measure feet/second and meters/second. Pocket Radar, Inc Pocket Radar was developed and manufactured by Pocket Radar, Inc. of Santa Rosa, California. The company’s founders, Chris Stewart, Steve Goody, and Grant Moulton were developers in wireless and communication technology companies Hewlett Pac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency Modulation
Frequency modulation (FM) is a signal modulation technique used in electronic communication, originally for transmitting messages with a radio wave. In frequency modulation a carrier wave is varied in its instantaneous frequency in proportion to a property, primarily the instantaneous amplitude, of a message signal, such as an audio signal. The technology is used in telecommunications, radio broadcasting, signal processing, and Run-length limited#FM: .280.2C1.29 RLL, computing. In Analog signal, analog frequency modulation, such as radio broadcasting of voice and music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude. Digital data can be encoded and transmitted with a type of frequency modulation known as frequency-shift keying (FSK), in which the instantaneous frequency of the carrier is shifted among a set of frequencies. The frequencies m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
