Imaging radar

radar imagingradar imageryimaging
Current radar imaging techniques rely mainly on synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) imaging. Emerging technology utilizes monopulse radar 3-D imaging. Real aperture radar(RAR) is a form of radar that transmits a narrow angle beam of pulse radio wave in the range direction at right angles to the flight direction and receives the backscattering from the targets which will be transformed to a radar image from the received signals. Usually the reflected pulse will be arranged in the order of return time from the targets, which corresponds to the range direction scanning. The resolution in the range direction depends on the pulse width.

Aperture synthesis

aperture synthesis imagingsynthetic apertureinterferometric imaging
Interferometric synthetic aperture radar (IfSAR or InSAR). Synthetic aperture radar (SAR) and Inverse synthetic aperture radar (ISAR). Synthetic aperture sonar. Beamforming. Synthetic aperture magnetometry. Light field. Development of radio interferometry, from Astronomical Optical Interferometry, A Literature Review by Bob Tubbs, Cambridge, 2002. Cambridge Optical Aperture Synthesis Telescope. APerture SYNthesis SIMulator (an interactive tool to learn the concepts of Aperture Synthesis).

Phased array

phased array radarphased-arrayphased-array radar
Interferometric synthetic-aperture radar. Inverse synthetic-aperture radar. Multi-user MIMO. Optical heterodyne detection. Phased array ultrasonics. Phased-array optics. Radar MASINT. Side-scan sonar. Single-frequency network. Smart antenna. Synthetic-aperture radar. Synthetic aperture sonar. Synthetically thinned aperture radar. Thinned-array curse. Wave field synthesis. History of smart antennas. Radar Research and Development - Phased Array Radar—National Severe Storms Laboratory. Shipboard Phased Array Radars. NASA Report: MMICs For Multiple Scanning Beam Antennas for Space Applications. Principle of Phased Array @ www.radartutorial.eu. 'Phased Array' microphone system of Tony Faulkner.

Digital elevation model

digital terrain modelDEMdigital elevation map
One powerful technique for generating digital elevation models is interferometric synthetic aperture radar where two passes of a radar satellite (such as RADARSAT-1 or TerraSAR-X or Cosmo SkyMed), or a single pass if the satellite is equipped with two antennas (like the SRTM instrumentation), collect sufficient data to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.

European Remote-Sensing Satellite

ERSERS-1ERS-2
RA (Radar Altimeter) is a single frequency nadir-pointing radar altimeter operating in the K u band. ATSR-1 (Along-Track Scanning Radiometer) is a 4 channel infrared radiometer and microwave sounder for measuring temperatures at the sea-surface and the top of clouds. SAR (synthetic aperture radar) operating in C band can detect changes in surface heights with sub-millimeter precision. Wind Scatterometer used to calculate information on wind speed and direction. MWR is a Microwave Radiometer used in measuring atmospheric water, as well as providing a correction for the atmospheric water for the altimeter.

TerraSAR-X

OPS 3762: The very first SAR radar in space, 1964. Seasat: The SAR radar in space in 1978. SAR Lupe: Germany's military radar satellites. SAR technology(Synthetic Aperture Radar). Earth observation technology. Earth observation satellite. Digital elevation model. SIR-A (Shuttle Imaging Radar) aboard STS-2 in 1981. SIR-B aboard STS-41-G in 1984. SRL-1 (Shuttle Radar Laboratory): SIR-C (Spaceborne Imaging Radar) and X-SAR (X-Band Synthetic Aperture Radar) on STS-59 in 1994. SRL-2: SIR-C/X-SAR on STS-68 in 1994. SRTM (Shuttle Radar Topography Mission) on STS-99 in 2000. Astrium Geo. TerraSAR-X at DLR website. TerraSAR-X for risk management. TanDEM-X at DLR website.

Interferometry

interferometerinterferometricoptical interferometry
Interferometric synthetic aperture radar (InSAR) is a radar technique used in geodesy and remote sensing. Satellite synthetic aperture radar images of a geographic feature are taken on separate days, and changes that have taken place between radar images taken on the separate days are recorded as fringes similar to those obtained in holographic interferometry. The technique can monitor centimeter- to millimeter-scale deformation resulting from earthquakes, volcanoes and landslides, and also has uses in structural engineering, in particular for the monitoring of subsidence and structural stability. Fig 20 shows Kilauea, an active volcano in Hawaii.

Remote sensing (geology)

remote sensing
Microwave radar can also take part in landslide recognition in synthetic aperture radar (SAR) images and monitoring through the InSAR technique which effectively shows small scale deformation. The hazard risk management could be further discussed using geographical information system (GIS). In the context of economic geology, the surficial data help locate possible reserves of natural resources. The occurrence of nature reserves that are exploitable is in close association with the surrounding geology. Feasible resources explorations should be backed up by accurate geological models to locate prospect ore and petroleum deposits from a preliminary regional overview.

Remote sensing (archaeology)

remote sensingmulti-spectral aerial photographyremote-sensing
Microwave Radar. Satellite Imaging. Laser altimeters or light detection and ranging (LIDAR). Synthetic Aperture Radar (SAR). INSAR - Interferometric SAR.

Space-based radar

military orbital radarSatellite radarSpace Radar
German SAR-Lupe. Russian Kondor. Japanese Information Gathering Satellite. a synthetic aperture radar (SAR) for high-resolution imaging. a radar altimeter, to measure the ocean topography. a wind scatterometer to measure wind speed and direction. RISAT-1 (SAR,ISRO India, 2012). RORSAT (SAR, Soviet Union, 1967-1988). Seasat (SAR, altimeter, scatterometer, US, 1978). RADARSAT-1 (SAR, Canadian, 1995). RADARSAT-2 (SAR, Canadian, 2007). SAR Lupe 1-5 (SAR satellites of the German Air Force). TerraSAR-X (SAR Germany, 2007). TanDEM-X (SAR Germany, 2010). COSMO-SkyMed (SAR, Italy, 2007). SAOCOM (L band SAR constellation, Argentina). TecSAR (SAR, Israeli, 2008). TOPEX/Poseidon (altimeter).

Mapping of Venus

During the mapping cycle 1 (left-looking) radar surface mapping on Venus (September 15, 1990 to May 15, 1991), around 70% of the Venusian surface was mapped by synthetic aperture radar. In cycle 2 (right-looking), 54.5% of the surface was mapped, mainly the south pole regions and gaps from cycle 1 during May 15, 1991 to January 14, 1992. Combining cycle 1 and 2 results in a total coverage of 96% of Venusian surface mapped. Cycle 3 (left looking) filled remaining gaps and collected stereo imagery of approximately 21.3% of the surface, increasing the total coverage to 98%. The use of Interferometric synthetic aperture radar (InSAR) for mapping Venus has been proposed.

Fast Fourier Transform Telescope

This technique is already being used in radar applications. This paper refers to an earlier telescope design from 1993 which took direct images of the Crab nebula at radio wavelengths using an eight-by-eight-pixel two-dimensional spatial FFT processor. Aperture synthesis. Interferometric synthetic aperture radar. Inverse synthetic aperture radar. List of telescope types. Synthetic aperture radar. Jan Hamann, Steen Hannestad, Martin S. Sloth, Yvonne Y. Y. Wong (2008), "Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes", Journal of Cosmology and Astroparticle Physics, arxiv 0807.4528. Jonathan R.

Pulse-Doppler radar

Dopplerpulse-Dopplerpulse doppler
Pulse-Doppler techniques also find widespread use in meteorological radars, allowing the radar to determine wind speed from the velocity of any precipitation in the air. Pulse-Doppler radar is also the basis of synthetic aperture radar used in radar astronomy, remote sensing and mapping. In air traffic control, they are used for discriminating aircraft from clutter. Besides the above conventional surveillance applications, pulse-Doppler radar has been successfully applied in healthcare, such as fall risk assessment and fall detection, for nursing or clinical purposes. The earliest radar systems failed to operate as expected.

Radio wave

radio wavesradioradio signal
Remaining uses are by military over-the-horizon (OTH) radar systems, by some automated systems, by radio amateurs, and by shortwave broadcasting stations to broadcast to other countries. Radio astronomy. Television transmitter.

Microwave

microwavesmicrowave radiationmicrowave tube
The letter system had its origin in World War 2 in a top secret U.S. classification of bands used in radar sets; this is the origin of the oldest letter system, the IEEE radar bands. One set of microwave frequency bands designations by the Radio Society of Great Britain (RSGB), is tabulated below: P band is sometimes used for K u Band. "P" for "previous" was a radar band used in the UK ranging from 250 to 500 MHz and now obsolete per IEEE Std 521. When radars were first developed at K band during World War II, it was not known that there was a nearby absorption band (due to water vapor and oxygen in the atmosphere).

Antenna (radio)

antennaantennasradio antenna
These can be used to give the antenna a different behavior on receiving than it has on transmitting, which can be useful in applications like radar. The majority of antenna designs are based on the resonance principle. This relies on the behaviour of moving electrons, which reflect off surfaces where the dielectric constant changes, in a fashion similar to the way light reflects when optical properties change. In these designs, the reflective surface is created by the end of a conductor, normally a thin metal wire or rod, which in the simplest case has a feed point at one end where it is connected to a transmission line.

Reflection (physics)

reflectionreflectedreflective
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 is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface. In specular reflection the phase of the reflected waves depends on the choice of the origin of coordinates, but the relative phase between s and p (TE and TM) polarizations is fixed by the properties of the media and of the interface between them.

Pulse repetition frequency

PRFpulse repetition frequenciesmedium pulse repetition frequency
Unlike lower radio signal frequencies, light does not bend around the curve of the earth or reflect off the ionosphere like C-band search radar signals, and so lidar is useful only in line of sight applications like higher frequency radar systems. Radar. Laser range finder. Sonar. Radar. Pulse-Doppler radar. Weather radar.

Polarization (waves)

polarizationpolarizedpolarized light
Polarization is also important in the transmission of radar pulses and reception of radar reflections by the same or a different antenna. For instance, back scattering of radar pulses by rain drops can be avoided by using circular polarization. Just as specular reflection of circularly polarized light reverses the handedness of the polarization, as discussed above, the same principle applies to scattering by objects much smaller than a wavelength such as rain drops. On the other hand, reflection of that wave by an irregular metal object (such as an airplane) will typically introduce a change in polarization and (partial) reception of the return wave by the same antenna.

Matched filter

matched filteringmatched-filteringNorth filters
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 impulse response is matched to input pulse signals. Two-dimensional matched filters are commonly used in image processing, e.g., to improve SNR for X-ray. Matched filtering is a demodulation technique with LTI (linear time invariant) filters to maximize SNR. It was originally also known as a North filter. The following section derives the matched filter for a discrete-time system.

Doppler radar

DopplerDoppler navigationDoppler navigation radar
. * Description of Doppler shift used in Continuous wave Doppler radar Coherent pulsed (CP). Pulse-Doppler radar. Continuous wave (CW), or. Frequency modulation (FM). Radar gun. Continuous-wave radar. Semi-active radar homing.

Doppler effect

Dopplerdoppler shiftDoppler shifts
The Doppler effect is used in some types of radar, to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source. Each successive radar wave has to travel farther to reach the car, before being reflected and re-detected near the source. As each wave has to move farther, the gap between each wave increases, increasing the wavelength. In some situations, the radar beam is fired at the moving car as it approaches, in which case each successive wave travels a lesser distance, decreasing the wavelength.

Speed of light

clight speedvelocity of light
Radar systems measure the distance to a target by the time it takes a radio-wave pulse to return to the radar antenna after being reflected by the target: the distance to the target is half the round-trip transit time multiplied by the speed of light. A Global Positioning System (GPS) receiver measures its distance to GPS satellites based on how long it takes for a radio signal to arrive from each satellite, and from these distances calculates the receiver's position. Because light travels about 300000 kilometres (186000 miles) in one second, these measurements of small fractions of a second must be very precise.

Radio astronomy

radio astronomerradioradioastronomy
Surprisingly the first use of a radio interferometer for an astronomical observation was carried out by Payne-Scott, Pawsey and Lindsay McCready on 26 January 1946 using a SINGLE converted radar antenna (broadside array) at 200 MHz near Sydney, Australia. This group used the principle of a sea-cliff interferometer in which the antenna (formerly a World War II radar) observed the sun at sunrise with interference arising from the direct radiation from the sun and the reflected radiation from the sea.

Remote sensing

remote-sensingremotely sensedremote sensor
Conventional radar is mostly associated with aerial traffic control, early warning, and certain large scale meteorological data. Doppler radar is used by local law enforcements’ monitoring of speed limits and in enhanced meteorological collection such as wind speed and direction within weather systems in addition to precipitation location and intensity. Other types of active collection includes plasmas in the ionosphere. Interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain (See RADARSAT, TerraSAR-X, Magellan). Laser and radar altimeters on satellites have provided a wide range of data.