synthetic radar

8/7/2019 synthetic radar

1/12

What is Synthetic aperture radar (SAR)?

Synthetic aperture radar (SAR) is a form ofradar in which sophisticated post-processing

of radar data is used to produce a very narrow effective beam. It can only be usedby moving instruments over relatively immobile targets, but it has seen wide

applications in remote sensing and mapping.

(A) Basic operation

In a typical SAR application, a single radar antenna will be attached to the side of an

aircraft. A single pulse from the antenna will be rather broad (several degrees) because

diffraction requires a large antenna to produce a narrow beam. The pulse will also be

broad in the vertical direction; often it will illuminate the terrain from directly beneath the

aircraft out to the horizon. However, if the terrain is approximately flat, the time at whichechoes return allows points at different distances from the flight track to be distinguished.

Distinguishing points along the track of the aircraft is difficult with a small antenna.However, if the amplitude and phase of the signal returning from a given piece of ground

are recorded, and if the aircraft emits a series of pulses as it travels, then the results from

these pulses can be combined. Effectively, the series of observations can be combinedjust as if they had all been made simultaneously from a very large antenna; this process

creates a synthetic aperture much larger than the length of the antenna (and in fact much

longer than the aircraft itself).

Combining the series of observations is done using Fast Fourier Transform techniques; it

requires significant computational resources, and is normally done at a ground stationafter the observation is complete. The result is a map of radar reflectivity (including both

amplitude and phase) on the ground. The phase information is, in the simplestapplications, discarded. The amplitude information, however, contains information about

ground cover, in much the same way that a black-and-white picture does. Interpretation is

not simple, but a large body of experimental results has been accumulated by flying test

flights over known terrain.

Before rapid computers were available the processing stage was done using holographic

techniques in what was one of the first effective analogue optic computer systems. A

scale hologram interference pattern was produced directly from the analogue radar data

(for example 1:1000000 for 0.6 meters radar) and a laser light with the same scale (in theexample 0.6 micrometers) passing through the hologram would produce a terrain

projection. This works because SAR is fundamentally very similar to holography with

microwaves instead of light.
http://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Remote_sensinghttp://en.wikipedia.org/wiki/Mappinghttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Fast_Fourier_Transformhttp://en.wikipedia.org/wiki/Holographyhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Remote_sensinghttp://en.wikipedia.org/wiki/Mappinghttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Fast_Fourier_Transformhttp://en.wikipedia.org/wiki/Holography


2/12

(B) More complex operation

1) Polarimetry - Radar waves have apolarization. Different materials reflect radarwaves with different intensities, butanisotropic materials such as grass often reflectdifferent polarizations with different intensities. Some materials will also convert one

polarization into another. By emitting a mixture of polarizations and using receiving

antennas with a specific polarization, several different images can be collected from thesame series of pulses. Frequently three such images are used as the three color channels

in a synthesized image. This is what has been done in the picture above. Interpretation of

the resulting colors requires significant testing of known materials.

New developments in polarimetry also include utilizing the changes in the randompolarization returns of some surfaces (such as grass or sand), between two images of the

same location at different points in time to determine where changes not visible to optical

systems occured. Examples include subterranean tunneling, or paths of vehicles drivingthrough the area being imaged.
http://en.wikipedia.org/wiki/Polarizationhttp://en.wikipedia.org/wiki/Polarizationhttp://en.wikipedia.org/wiki/Anisotropichttp://en.wikipedia.org/wiki/Anisotropichttp://en.wikipedia.org/wiki/Polarizationhttp://en.wikipedia.org/wiki/Anisotropic


3/12

SAR image ofDeath Valleycolored using polarimetry

2) Interferometry- Rather than discarding the phase information, information canbe extracted from it. If two observations of the same terrain from very similar positions

are available, a great deal of interesting information can be extracted. This technique iscalled interferometricSARorInSAR.

If the two samples are obtained simultaneously (perhaps by placing two antennas on the

same aircraft, some distance apart), then any phase difference will contain information

about the angle from which the radar echo returned. Combining this with the distanceinformation, one can determine the position in three dimensions of the image pixel. In

other words, one can extract terrain altitude as well as radar reflectivity, producing a

digital elevation model with a single airplane pass. One aircraft application at theCanadaCenter for Remote Sensingproduced digital elevation maps with a resolution of 5 m andaltitude errors also on the order of 5 m.

If the two samples are separated in time, perhaps from two different flights over the same

terrain, then there are two possible sources of phase shift. The first is terrain altitude, asdiscussed above. The second is terrain motion: if the terrain has shifted between

obervations, it will return a different phase. The amount of shift required to cause a
http://en.wikipedia.org/wiki/Death_Valleyhttp://en.wikipedia.org/wiki/Death_Valleyhttp://en.wikipedia.org/wiki/Interferometryhttp://en.wikipedia.org/wiki/Interferometryhttp://en.wikipedia.org/wiki/Digital_elevation_modelhttp://en.wikipedia.org/w/index.php?title=Canada_Center_for_Remote_Sensing&action=edithttp://en.wikipedia.org/w/index.php?title=Canada_Center_for_Remote_Sensing&action=edithttp://en.wikipedia.org/w/index.php?title=Canada_Center_for_Remote_Sensing&action=edithttp://en.wikipedia.org/w/index.php?title=Canada_Center_for_Remote_Sensing&action=edithttp://en.wikipedia.org/wiki/Death_Valleyhttp://en.wikipedia.org/wiki/Interferometryhttp://en.wikipedia.org/wiki/Digital_elevation_modelhttp://en.wikipedia.org/w/index.php?title=Canada_Center_for_Remote_Sensing&action=edithttp://en.wikipedia.org/w/index.php?title=Canada_Center_for_Remote_Sensing&action=edit


4/12

significant phase difference is on the order of the wavelength used. This means that if the

terrain shifts by centimeters, it can be seen in the resulting image (Adigital elevation map

must be available in order to separate the two kinds of phase difference; a third pass maybe necessary in order to produce one).

This second method offers a powerful tool in geology and geography. Glacierflow canbe mapped with two passes. Maps showing the land deformation after a minorearthquake

or after a volcanic eruption (showing the shrinkage of the whole volcano by severalcentimeters) have been published.

3) Ultra-wideband SAR

Normal radar emits pulses with a very narrow range of frequencies. This places a lower

limit on the pulse length (and therefore the resolution in the distance direction) butgreatly simplifes the electronics. Interpretation of the results is also eased by the fact that

the material response must be known only in a narrow range of frequencies.

Ultra-wideband radar emits very short pulses consisting of a very wide range offrequencies, from zero up to the radar's normal operating frequency. Such pulses allow

high distance resolution but much of the information is concentrated in relatively low

frequencies (with long wavelengths). Thus such systems require very large receiving

apertures to obtain correspondingly high resolution along the track. This can be achievedwith synthetic aperture techniques.

The fact that the information is captured in low frequencies means that the most relevant

material properties are those at lower frequencies than for most radar systems. In

particular, such radar can penetrate some distance into foliage and soil.

4) Multistatic operation

SAR requires that echo captures be taken at multiple antenna positions. The more

captures taken (at different antenna locations) the more reliable the target

characterization.

Multiple captures can be obtained by moving a single antenna to different locations, by

placing multiple stationary antennae at different locations, or combinations thereof.

The advantage of a single moving antenna is that it can be easily placed in any number of

positions to provide any number of monostatic waveforms. For example, an antennamounted on an airplane takes many captures per second as the plane travels.

The principal advantages of multiple static antennae are that a moving target can be

characterized (assuming the capture electronics are fast enough), that no vehicle or

motion machinery is necessary, and that antenna positions need not be derived fromother, sometimes unreliable, information. (One problem with SAR aboard an airplane is

knowing precise antenna positions as the plane travels).
http://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Geographyhttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Volcanic_eruptionhttp://en.wikipedia.org/w/index.php?title=Ultra-wideband_SAR&action=edithttp://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Geographyhttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Volcanic_eruptionhttp://en.wikipedia.org/w/index.php?title=Ultra-wideband_SAR&action=edit


5/12

For multiple static antennae, all combinations of monostatic and multistatic radar

waveform captures are possible. Note, however, that it is not advantageous to capture a

waveform for each of both transmission directions for a given pair of antennae, becausethose waveforms will be identical. When multiple static antennae are used, the total

number of unique echo waveforms that can be captured is

where Nis the number of unique antenna positions.

5) Differential interferometry

Differential interferometry (D-InSAR) requires taking at least two images with addition

of a DEM. The DEM can be either produced by GPS measurements or could begenerated by interferometry as long as the time between acquisition of the image pairs is

short, which guarantees minimal distortion of the image of the target surface. In principle,3 images of the ground area with similar image acquisition geometry is often adequate for

D-InSar. The principle for detecting ground movement is quite simple. One interferogram

is created from the first two images; this is also called the reference interferogram ortopographical interferogram. A second interferogram is created that captures topography

+ distortion. Subtracting the latter from the reference interferogram can reveal differential

fringes, indicating movement. The described 3 image D-InSAR generation technique iscalled 3-pass or double-difference method.

Differential fringes which remain as fringes in the differential interferogram are a resultof SAR range changes of any displaced point on the ground from one interferogram to

the next. In the differential interferogram, each fringe is directly proportional to the SARwavelength, which is about 5.6 cm for ERS and RADARSAT single phase cycle. Surface

displacement away from the satellite look direction causes an increase in path (translating

to phase) difference. Since the signal travels from the SAR antenna to target and back

again, the measured displacement is twice the unit of wavelength. This means indifferential interferometry one fringe cycle -pi to +pi or one wavelength corresponds to a

displacement relative to SAR antenna of only half wavelength (2.8 cm). There are

various publications on measuring subsidence movement, slope stability analysis,landslide, glacier movement, etc tooling D-InSAR. Further advancement to this technique

whereby differential interferometry from satellite SAR ascending pass and descendingpass can be used to estimate 3-D ground movement. Research in this area has shownaccurate measurements of 3-D ground movement with accuracies comparable to GPS

based measurements can be achieved.
http://en.wikipedia.org/wiki/Multistatic_radarhttp://en.wikipedia.org/wiki/Multistatic_radar


6/12

( C ) Doppler Beam Sharpening

A commonly used technique for SAR systems is called Doppler BeamSharpening. Because the real aperture of the RADAR antenna is sosmall (compared to the wavelength in use), the RADAR energyspreads over a wide area (usually many degrees wide in a directionortho-normal (right angle) to the direction of the platform (aircraft).Doppler Beam Sharpening takes advantage of the motion of theplatform in that targets ahead of the platform return a Doppler up-shifted signal (slightly higher in frequency) and targets behind theplatform return a Doppler down-shifted signal (slightly lower infrequency). The amount of shift varies with the angle forward orbackward from the ortho-normal direction. By knowing the speed ofthe platform, target signal return is placed in a specific angle "bin"that changes over time. Signals are integrated over time and thus

the RADAR "beam" is synthetically reduced to a much smalleraperture - or more accurately (and based on the ability to distinguishsmaller doppler shifts) the system can have hundreds of very "tight"beams concurrently. This technique dramatically improves angularresolution; however, it is far more difficult to take advantage of thistechnique for range resolution.

( D) Chirped (Pulse Compressed) Radars

A common techniqe for many RADAR systems (sometimes found in SAR systems) is to"chirp" the signal. In a "chirped" radar, the pulse is allowed to be much longer. A longer

pulse allows more energy to be emitted, and hence received, but usually hinders range

resolution. But in a chirped radar, this longer pulse also has a frequency shift during thepulse (hence the chirp or frequency shift). When the "chirped" signal is returned, it is

passed to a dispersive delay line (often a SAW device (Surface Acoustic Wave) that has

the property of varying velocity of propogation based on frequency. This technique"compresses" the pulse in time - thus having the effect of a much shorter pulse (improved

range resolution) while having the benefit of longer pulse length (much more signalreturned).

( E) Data collection

Highly accurate data can be collected by aircraft overflying the terrain in question. In the

1980s, as a prototype for instruments to be flown on the NASA Space shuttles, NASA


7/12

operated a synthetic aperture radar on a NASA CV-990. However, in 1986, this plane

crashed on takeoff. In 1988, NASA rebuilt a C, L, and P-band SAR to fly on the NASA

DC-8 aircraft. CalledAIRSAR, it flew missions at sites around the world until 2004.Another such aircraft was flown by the Canada Center for Remote Sensing until about

1996 when it was decommissioned for cost reasons. Most land-surveying applications are

now carried out by satellite observation. Satellites such asERS-1/2, JERS-1,EnvisatASAR, andRADARSAT-1 were launched explicitly to carry out this sort of observation.

Their capabilities differ, particularly in their support for interferometry, but all have

collected tremendous amounts of valuable data. The Space Shuttle has also carriedsynthetic aperture radar equipment during the SIR-AandSIR-Bmissions during the

1980s, as well as the Shuttle Radar Laboratory (SRL) missions in 1994 and the Shuttle

Radar Topography Mission in 2000.

The Magellan space probe mapped the surface of Venus over several years usingsynthetic aperture radar.

Synthetic aperture radar was first used by NASA on JPL'sSeasat oceanographic satellitein 1978 (this mission also carried an altimeterand a scatterometer); it was later developed

more extensively on the Spaceborne Imaging Radar (SIR) missions on the space shuttlein 1981, 1984 and 1994. The Cassini mission to Saturn is currently using SAR to map the

surface of the planet's major moon Titan, whose surface is partially hidden from direct

optical inspection by atmospheric haze.

The Mineseeker Project ([1]) is designing a system for determining whether regionscontain landmines based on a blimpcarrying ultra-wideband synthetic aperture radar.

Initial trials show promise; the radar is able to detect even buried plastic mines.

SAR has been used in radio astronomy for many years to simulate a large radio telescopeby combining observations taken from multiple locations using a mobile antenna.
http://en.wikipedia.org/w/index.php?title=NASA_DC-8&action=edithttp://en.wikipedia.org/w/index.php?title=NASA_DC-8&action=edithttp://en.wikipedia.org/w/index.php?title=AIRSAR&action=edithttp://en.wikipedia.org/w/index.php?title=AIRSAR&action=edithttp://en.wikipedia.org/wiki/1996http://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/ERS-1http://en.wikipedia.org/wiki/ERS-1http://en.wikipedia.org/wiki/JERS-1http://en.wikipedia.org/wiki/Envisathttp://en.wikipedia.org/wiki/Envisathttp://en.wikipedia.org/wiki/RADARSAT-1http://en.wikipedia.org/wiki/RADARSAT-1http://en.wikipedia.org/wiki/Space_Shuttlehttp://en.wikipedia.org/w/index.php?title=SIR-A&action=edithttp://en.wikipedia.org/w/index.php?title=SIR-A&action=edithttp://en.wikipedia.org/w/index.php?title=SIR-B&action=edithttp://en.wikipedia.org/w/index.php?title=SIR-B&action=edithttp://en.wikipedia.org/w/index.php?title=SIR-B&action=edithttp://en.wikipedia.org/w/index.php?title=Shuttle_Radar_Laboratory&action=edithttp://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Missionhttp://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Missionhttp://en.wikipedia.org/wiki/Magellan_probehttp://en.wikipedia.org/wiki/Seasathttp://en.wikipedia.org/wiki/Seasathttp://en.wikipedia.org/wiki/Altimeterhttp://en.wikipedia.org/wiki/Scatterometerhttp://en.wikipedia.org/wiki/Cassini-Huygenshttp://en.wikipedia.org/wiki/Saturn_(planet)http://en.wikipedia.org/wiki/Titan_(moon)http://en.wikipedia.org/w/index.php?title=Mineseeker_Project&action=edithttp://www.mineseeker.com/http://en.wikipedia.org/wiki/Landminehttp://en.wikipedia.org/wiki/Blimphttp://en.wikipedia.org/wiki/Blimphttp://en.wikipedia.org/wiki/Radio_astronomyhttp://en.wikipedia.org/w/index.php?title=NASA_DC-8&action=edithttp://en.wikipedia.org/w/index.php?title=NASA_DC-8&action=edithttp://en.wikipedia.org/w/index.php?title=AIRSAR&action=edithttp://en.wikipedia.org/wiki/1996http://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/ERS-1http://en.wikipedia.org/wiki/JERS-1http://en.wikipedia.org/wiki/Envisathttp://en.wikipedia.org/wiki/RADARSAT-1http://en.wikipedia.org/wiki/Space_Shuttlehttp://en.wikipedia.org/w/index.php?title=SIR-A&action=edithttp://en.wikipedia.org/w/index.php?title=SIR-B&action=edithttp://en.wikipedia.org/w/index.php?title=Shuttle_Radar_Laboratory&action=edithttp://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Missionhttp://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Missionhttp://en.wikipedia.org/wiki/Magellan_probehttp://en.wikipedia.org/wiki/Seasathttp://en.wikipedia.org/wiki/Altimeterhttp://en.wikipedia.org/wiki/Scatterometerhttp://en.wikipedia.org/wiki/Cassini-Huygenshttp://en.wikipedia.org/wiki/Saturn_(planet)http://en.wikipedia.org/wiki/Titan_(moon)http://en.wikipedia.org/w/index.php?title=Mineseeker_Project&action=edithttp://www.mineseeker.com/http://en.wikipedia.org/wiki/Landminehttp://en.wikipedia.org/wiki/Blimphttp://en.wikipedia.org/wiki/Radio_astronomy


8/12

A model of a German SAR-Lupe reconnaissance satellite inside a Cosmos-3M rocket.

SAR-Lupe is Germany's firstreconnaissance satellite system. SAR is an abbreviation forSynthetic Aperture Radarand "Lupe" is German formagnifying glass. The SAR-Lupe

program consists of five identical (770kg)satellites, developed by the Germanaeronautics companyOHB-Systemwhich are controlled by a ground station[1]which is

responsible for controlling the system and analysing the retrieved data. A large dataarchive of images will be kept in a formerCold Warbunkerbelonging to the KommandoStrategische Aufklrung(Strategic Reconnaissance Command) of the Bundeswehr.

SAR-Lupe's "high-resolution" images can be acquired day or night through all weatherconditions. The first satellite was launched fromPlesetskin Russiaon 19 December

2006, about a year after the intended launch date; four more satellites were launched at

roughly six-month intervals, and the entire system achieved full operational readiness on

22 July 2008.[2]

The five satellites operate in three 500-kilometre orbits in planes roughly sixty degrees

apart. They use an X-band radar with a three-metre dish, providing a resolution of about

50 centimetres over a frame size of 5.5km on a side ('spotlight mode', in which the

satellite rotates to keep the dish pointed at a single target) or about one metre over aframe size of 8km x 60km ('stripmap mode', in which the satellite maintains a fixed

orientation over the earth and the radar image is formed simply by the satellite's motion
http://en.wikipedia.org/wiki/SAR-Lupehttp://en.wikipedia.org/wiki/Germanyhttp://en.wikipedia.org/wiki/Germanyhttp://en.wikipedia.org/wiki/Reconnaissance_satellitehttp://en.wikipedia.org/wiki/Reconnaissance_satellitehttp://en.wikipedia.org/wiki/Synthetic_Aperture_Radarhttp://en.wikipedia.org/wiki/Magnifying_glasshttp://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/OHB-Systemhttp://en.wikipedia.org/wiki/OHB-Systemhttp://en.wikipedia.org/wiki/OHB-Systemhttp://en.wikipedia.org/wiki/SAR_Lupe#cite_note-groundstation-0http://en.wikipedia.org/wiki/SAR_Lupe#cite_note-groundstation-0http://en.wikipedia.org/wiki/Cold_Warhttp://en.wikipedia.org/wiki/Cold_Warhttp://en.wikipedia.org/wiki/Bunkerhttp://en.wikipedia.org/wiki/Bundeswehrhttp://en.wikipedia.org/wiki/Bundeswehrhttp://en.wikipedia.org/wiki/Plesetsk_Cosmodromehttp://en.wikipedia.org/wiki/Plesetsk_Cosmodromehttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/SAR_Lupe#cite_note-1http://en.wikipedia.org/wiki/Radar#Frequency_bandshttp://en.wikipedia.org/wiki/SAR-Lupehttp://en.wikipedia.org/wiki/Germanyhttp://en.wikipedia.org/wiki/Reconnaissance_satellitehttp://en.wikipedia.org/wiki/Synthetic_Aperture_Radarhttp://en.wikipedia.org/wiki/Magnifying_glasshttp://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/OHB-Systemhttp://en.wikipedia.org/wiki/SAR_Lupe#cite_note-groundstation-0http://en.wikipedia.org/wiki/Cold_Warhttp://en.wikipedia.org/wiki/Bunkerhttp://en.wikipedia.org/wiki/Bundeswehrhttp://en.wikipedia.org/wiki/Plesetsk_Cosmodromehttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/SAR_Lupe#cite_note-1http://en.wikipedia.org/wiki/Radar#Frequency_bands


9/12


10/12

The Airborne Synthetic Aperture Radar (AIRSAR) was an all-weather imaging tool able

to penetrate through clouds and collect data at night. The longer wavelengths could also

penetrate into the forest canopy and in extremely dry areas, through thin sand cover anddry snow pack. AIRSAR was designed and built by the Jet Propulsion Laboratory (JPL)

which also manages the AIRSAR project. AIRSAR served as a NASA radar technology

testbed for demonstrating new radar technology and acquiring data for the developmentof radar processing techniques and applications. As part of NASAs Earth Science

Enterprise, AIRSAR first flew in 1988, and flew its last mission in 2004.

UAVSAR

UAVSAR, a reconfigurable, polarimetricL-band synthetic aperture radar (SAR), isspecifically designed to acquire airborne repeat track SAR data for differential

interferometric measurements.

Differential interferometrycan provide key deformation measurements, and is important

for studies of earthquakes, volcanoes and other dynamically changing phenomena.
http://www.ccrs.nrcan.gc.ca/resource/tutor/polarim/index_e.phphttp://www.ccrs.nrcan.gc.ca/resource/tutor/polarim/index_e.phphttp://en.wikipedia.org/wiki/Synthetic_aperture_radarhttp://en.wikipedia.org/wiki/Synthetic_aperture_radarhttp://www.ccrs.nrcan.gc.ca/resource/tutor/polarim/index_e.phphttp://en.wikipedia.org/wiki/Synthetic_aperture_radar


11/12

Using precision real-time GPS and a sensor controlled flight management system, the

system will be able to fly predefined paths with great precision. The expected

performance of the flight control system require the flight path to be within a 10 mdiameter tube about the desired flight track.

The radar will be designed to be operable on a UAV (Uninhabited Aerial Vehicle), butwill initially be demonstrated on a on aNASA Gulfstream III. The radar will be fully

polarimetric, with a range bandwidth of 80 MHz (2 m range resolution), and will supporta 16 km range swath.

The antenna will be electronically steeredalong track to assure that the antenna beam can

be directed independently, regardless of speed and wind direction.

Other features supported by the antenna include elevation monopulse and pulse-to-pulsere-steering capabilities that will enable some novel modes of operation. The system will

nominally operate at 45,000 ft (13800 m).

The program began as an Instrument Incubator Project (IIP) funded by NASA Earth

Science Technology Office (ESTO)

GEOSAR

GeoSAR is Fugro's unique commercial airborne remote sensing solution for mapping

over large, rugged and remote regions. As the world's only dual-band, single-pass

interferometric synthetic aperture radar (IFSAR) mapping system, GeoSAR concurrentlycollects both surface features and bare-earth elevation data using X-band and P-band

radar. The system's profiling LiDAR simultaneously collects dynamic ground and quality

control data to reduce the need for people on the ground. Acquiring high-resolutiongeospatial information with unprecedented speed and accuracy, Fugro's GeoSARmapping system solves the age-old problem of imaging and modeling geographic regions

obscured by clouds or dense vegetation.

Interferometric synthetic aperture radar, also abbreviated InSARorIfSAR, is a radartechnique used in geodesyandremote sensing. This geodetic method uses two or more

synthetic aperture radar(SAR) images to generate maps of surface deformation ordigital

elevation, using differences in the phase of the waves returning to the satellite[1][2][3], or

aircraft. The technique can potentially measure centimetre-scale changes in deformationover timespans of days to years. It has applications for geophysical monitoring of natural

hazards, for example earthquakes, volcanoes and landslides, and also in structural

engineering, in particular monitoring of subsidence and structural stability.
http://www.nasa.gov/centers/dryden/business/UAV_BU/index.htmlhttp://www.nasa.gov/centers/dryden/research/G-III/index.htmlhttp://www.nasa.gov/centers/dryden/research/G-III/index.htmlhttp://www.nasa.gov/centers/dryden/research/G-III/index.htmlhttp://en.wikipedia.org/wiki/Active_Electronically_Scanned_Arrayhttp://en.wikipedia.org/wiki/Active_Electronically_Scanned_Arrayhttp://esto.nasa.gov/obs_technologies_iip.htmlhttp://esto.nasa.gov/index.htmlhttp://esto.nasa.gov/index.htmlhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Geodesyhttp://en.wikipedia.org/wiki/Geodesyhttp://en.wikipedia.org/wiki/Remote_sensinghttp://en.wikipedia.org/wiki/Remote_sensinghttp://en.wikipedia.org/wiki/Synthetic_aperture_radarhttp://en.wikipedia.org/wiki/Synthetic_aperture_radarhttp://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-0http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-0http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-1http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-2http://www.nasa.gov/centers/dryden/business/UAV_BU/index.htmlhttp://www.nasa.gov/centers/dryden/research/G-III/index.htmlhttp://en.wikipedia.org/wiki/Active_Electronically_Scanned_Arrayhttp://esto.nasa.gov/obs_technologies_iip.htmlhttp://esto.nasa.gov/index.htmlhttp://esto.nasa.gov/index.htmlhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Geodesyhttp://en.wikipedia.org/wiki/Remote_sensinghttp://en.wikipedia.org/wiki/Synthetic_aperture_radarhttp://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Digital_elevation_maphttp://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-0http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-1http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar#cite_note-2


12/12

Most SAR applications make use of theamplitude of the return signal, and ignore the

phasedata. However interferometry uses the phase of the reflected radiation. Since the

outgoing wave is produced by the satellite, the phase is known, and can be compared tothe phase of the return signal. The phase of the return wave depends on the distance to the

ground, since the path length to the ground and back will consist of a number of whole

wavelengths plus some fraction of a wavelength. This is observable as a phase differenceor phase shift in the returning wave. The total distance to the satellite (i.e. the number of

whole wavelengths) is not known, but the extra fraction of a wavelength can be measured

extremely accurately.

In practice, the phase is also affected by several other factors, which together make theraw phase return in any one SAR image essentially arbitrary, with no correlation from

pixel to pixel. To get any useful information from the phase, some of these effects must

be isolated and removed. Interferometry uses two images of the same area taken from thesame position (or for topographic applications slightly different positions) and finds the

difference in phase between them, producing an image known as an interferogram. This

is measured in radians of phase difference and, due to the cyclic nature of phase, isrecorded as repeating fringes which each represent a full 2 cycle.
http://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Wavelengthshttp://en.wikipedia.org/wiki/Phase_(waves)#Phase_differencehttp://en.wikipedia.org/wiki/Radianshttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Wavelengthshttp://en.wikipedia.org/wiki/Phase_(waves)#Phase_differencehttp://en.wikipedia.org/wiki/Radians

synthetic radar

Documents