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Remote sensing

From Wikipedia, the free encyclopedia

Jump to: navigation,searchFor the technique in archaeological surveying, see remote sensing (archaeology). Forthe claimed psychic ability, seeRemote viewing.

Synthetic aperture radarimage ofDeath Valleycolored usingpolarimetry

In the broadest sense, remote sensing is the small or large-scale acquisition ofinformation of an object or phenomenon, by the use of either recording or real-timesensing device(s) that is not in physical or intimate contact with the object (such as byway ofaircraft, spacecraft,satellite,buoy, orship). In practice, remote sensing is thestand-off collection through the use of a variety of devices for gathering information on agiven object or area. Thus, Earth observation orweather satellitecollection platforms,ocean and atmospheric observing weather buoyplatforms, monitoring of a pregnancy via

ultrasound, Magnetic Resonance Imaging (MRI),Positron Emission Tomography(PET),andspace probes are all examples of remote sensing. In modern usage, the term generallyrefers to the use of imaging sensor technologies including but not limited to the use ofinstruments aboard aircraft and spacecraft, and is distinct from other imaging-relatedfields such as medical imaging.

There are two kinds of remote sensing. Passive sensors detect natural energy (radiation)that is emitted or reflected by the object or surrounding area being observed. Reflected

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sunlight is the most common source of radiation measured by passive sensors. Examplesof passive remote sensors include film photography, infra-red, charge-coupled devicesand radiometers. Active collection, on the other hand, emits energy in order to scanobjects and areas whereupon a passive sensor then detects and measures the radiation thatis reflected or backscattered from the target. RADAR is an example of active remote

sensing where the time delay between emission and return is measured, establishing thelocation, height, speed and direction of an object.

Remote sensing makes it possible to collect data on dangerous or inaccessible areas.Remote sensing applications include monitoring deforestation in areas such as theAmazon Basin, the effects of climate change on glaciers and Arctic and Antarcticregions, and depth sounding of coastal and ocean depths. Military collection during thecold war made use of stand-off collection of data about dangerous border areas. Remotesensing also replaces costly and slow data collection on the ground, ensuring in theprocess that areas or objects are not disturbed.

Orbital platforms collect and transmit data from different parts of the electromagneticspectrum, which in conjunction with larger scale aerial or ground-based sensing andanalysis, provides researchers with enough information to monitor trends such as el nioand other natural long and short term phenomena. Other uses include different areas ofthe earth sciences such as natural resource management, agricultural fields such as landusage and conservation, and national security and overhead, ground-based and stand-offcollection on border areas.[1].

Contents

1 Data acquisition techniqueso 1.1 Applications of Remote Sensing datao 1.2 Geodetico 1.3 Acoustic and near-acoustic

2 Data processing 3 History 4 Remote Sensing software 5 Further reading 6 See also

7 External links

[edit] Data acquisition techniques

The basis for multi-spectral collection and analysis is that of examined areas or objectsthat reflect or emit radiation that stand out from surrounding areas.

[edit] Applications of Remote Sensing data

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RadarConventional radar is mostly associated with aerial traffic control, earlywarning, and certain large scale meteorological data. Doppler radar is used bylocal law enforcements' monitoring of speed limits and in enhancedmeteorological collection such as wind speed and direction within weathersystems. Other types of active collection includesplasmasin the ionosphere).

Interferometric synthetic aperture radaris used to produce precise digitalelevation models of large scale terrain (See RADARSAT, TerraSAR-X,Magellan).

Laser and radaraltimeters on satellites have provided a wide range of data. Bymeasuring the bulges of water caused by gravity, they map features on theseafloor to a resolution of a mile or so. By measuring the height and wave-lengthof ocean waves, the altimeters measure wind speeds and direction, and surfaceocean currents and directions.

LIDARLight Detection And Ranging - is well known in the examples of weaponranging, laser illuminated homing of projectiles. LIDAR is used to detect andmeasure the concentration of various chemicals in the atmosphere, while airborne

LIDAR can be used to measure heights of objects and features on the groundmore accurately than with radar technology. Radiometers andphotometersare the most common instrument in use, collecting

reflected and emitted radiation in a wide range of frequencies. The most commonare visible and infrared sensors, followed by microwave, gamma ray and rarely,ultraviolet. They may also be used to detect the emission spectra of variouschemicals, providing data on chemical concentrations in the atmosphere.

Stereographic pairs ofaerial photographs have often been used to makeTopographic maps by Imagery Analysts, Terrain Analysts in trafficability andhighway departments for potential routes.

Simultaneous multi-spectral platforms such as Landsat have been in use since the70's. These thematic mappers take images in multiple wavelengths of electro-magnetic radiation (multi-spectral) and are usually found on earth observationsatellites, including (for example) the Landsat programor the IKONOSsatellite.Maps of land cover and land use from thematic mapping can be used to prospectfor minerals, detect or monitor land usage, deforestation, and examine the healthof indigenous plants and crops, including entire farming regions or forests.

[edit] Geodetic

Overhead geodetic collection was first used in aerial submarine detection andgravitational data used in military maps. This data reveal minute perturbations in

the Earth'sgravitational field (geodesy) may be used to determine changes in themass distribution of the Earth, which in turn may be used for geological orhydrological studies.

[edit] Acoustic and near-acoustic

Passive;Sonaris used for detecting, ranging and measurements of underwaterobjects and terrain.

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Seismograms taken at different locations can locate and measureearthquakes(after they occur) by comparing the relative intensity and precise timing.

Active; pulses are used by geologists to detect oil fields.

To coordinate a series of large-scale observations, most sensing systems depend on the

following; platform location, what time it is, and the rotation and orientation of thesensor. High-end instruments now often use positional information fromsatellitenavigation systems. The rotation and orientation is often provided within a degree or twowith electronic compasses. Compasses can measure not just azimuth (i.e. degrees tomagnetic north), but also altitude (degrees above the horizon), since the magnetic fieldcurves into the Earth at different angles at different latitudes. More exact orientationsrequire gyroscopic-aided orientation, periodically realigned by different methodsincluding navigation from stars or known benchmarks.

Resolution impacts collection and is best explained with the following relationship; lessresolution=less detail & larger coverage, More resolution=more detail, less coverage. The

skilled management of collection results in cost-effective collection and avoid situationssuch as the use of multiple high resolution data which tends to clog transmission andstorage infrastructure.

[edit] Data processing

See also:Inverse problem

Generally speaking, remote sensing works on the principle of the inverse problem. Whilethe object or phenomenon of interest (the state) may not be directly measured, thereexists some other variable that can be detected and measured (the observation), which

may be related to the object of interest through the use of a data-derived computer model.The common analogy given to describe this is trying to determine the type of animalfrom its footprints. For example, while it is impossible to directly measure temperaturesin the upper atmosphere, it is possible to measure the spectral emissions from a knownchemical species (such as carbon dioxide) in that region. The frequency of the emissionmay then be related to the temperature in that region via variousthermodynamicrelations.

The quality of remote sensing data consists of its spatial, spectral, radiometric andtemporal resolutions. Spatial resolution refers to the size of apixel that is recorded in araster image - typically pixels may correspond to square areas ranging in side length from

1 to 1000 metres. Spectral resolution refers to the number of different frequency bandsrecorded - usually, this is equivalent to the number of sensors carried by the platform(s).Current Landsat collection is that of seven bands, including several in the infra-redspectrum. The MODIS satellites are the highest resolving at 31 bands. Radiometricresolution refers to the number of different intensities of radiation the sensor is able todistinguish. Typically, this ranges from 8 to 14 bits, corresponding to 256 levels of thegray scale and up to 16,384 intensities or "shades" of colour, in each band. The temporalresolution is simply the frequency of flyovers by the satellite or plane, and is only

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relevant in time-series studies or those requiring an averaged or mosaic image as indeforesting monitoring. This was first used by the intelligence community where repeatedcoverage revealed changes in infrastructure, the deployment of units or themodification/introduction of equipment . Cloud cover over a given area or object makes itnecessary to repeat the collection of said location. Finally, some people also refer to the

"economic resolution", that is, the cost-effective way to manage the collection of data.In order to create sensor-based maps, most remote sensing systems expect to extrapolatesensor data in relation to a reference point including distances between known points onthe ground. This depends on the type of sensor used. For example, in conventionalphotographs, distances are accurate in the center of the image, with the distortion ofmeasurements increasing the farther you get from the center. Another factor is that of theplaten against which the film is pressed can cause severe errors when photographs areused to measure ground distances. The step in which this problem is resolved is calledgeoreferencing, and involves computer-aided matching up of points in the image(typically 30 or more points per image) which is extrapolated with the use of an

established benchmark, "warping" the image to produce accurate spatial data. As of theearly 1990s, most satellite images are sold fully georeferenced.

In addition, images may need to be radiometrically and atmospherically corrected.Radiometric correction gives a scale to the pixel values, e.g. the monochromatic scaleof 0 to 255 will be converted to actual radiance values. Atmospheric correctioneliminates atmospheric haze by rescaling each frequency band so that its minimum value(usually realised in water bodies) corresponds to a pixel value of 0. The digitizing of dataalso make possible to manipulate the data by changing gray-scale values.

Interpretation is the critical process of making sense of the data. The first application was

that of aerial photographic collection which used the following process; spatialmeasurement through the use of a light table in both conventional single or stereographiccoverage, added skills such as the use of photogrammetry, the use of photomosaics,repeat coverage, Making use of objects' known dimensions in order to detectmodifications. Image Analysis is the recently developed automated computer-aidedapplication which is in increasing use.

Object-Based Image Analysis (OBIA) is a sub-discipline of GIScience devoted topartitioning remote sensing (RS) imagery into meaningful image-objects, and assessingtheir characteristics through spatial, spectral and temporal scale.

Old data from remote sensing is often valuable because it may provide the only long-termdata for a large extent of geography. At the same time, the data is often complex tointerpret, and bulky to store. Modern systems tend to store the data digitally, often withlossless compression. The difficulty with this approach is that the data is fragile, theformat may be archaic, and the data may be easy to falsify. One of the best systems forarchiving data series is as computer-generated machine-readable ultrafiche, usually intypefonts such as OCR-B, or as digitized half-tone images. Ultrafiches survive well instandard libraries, with lifetimes of several centuries. They can be created, copied, filed

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and retrieved by automated systems. They are about as compact as archival magneticmedia, and yet can be read by human beings with minimal, standardized equipment.

[edit] History

The TR-1 reconnaissance/surveillance aircraft.

The 2001 Mars Odyssey Spacecraftused spectrometers and imagers to hunt for evidenceof past or present water and volcanic activity on Mars.

Beyond the primitive methods of remote sensing our earliest ancestors used (ex.: standing

on a high cliff or tree to view the landscape), the modern discipline arose with thedevelopment of flight. The balloonist G. Tournachon (aliasNadar) made photographs ofParis from his balloon in 1858. The first tactical use was during the civil war. Messengerpigeons, kites, rockets and unmanned balloons were also used for early images. With theexception of balloons, these first, individual images were not particularly useful for mapmaking or for scientific purposes.

Systematic aerial photography was developed for military surveillance andreconnaissance purposes beginning inWorld War I and reaching a climax during theCold Warwith the use of modified combat aircraft such as the P-51, P-38, RB-66, F4-Cand the SR-71 or specifically designed collection platforms such as theU2/TR-1, A-5 and

the OV-1 series both in overhead and stand-off collection. A more recent development isthat of increasingly smaller sensor pods such as those used by law enforcement and themilitary, in both manned and unmanned platforms. The advantage of this approach is thatthis requires minimal modification to a given airframe. Later imaging technologies wouldinclude Infra-red, conventional, doppler and synthetic aperture radar.

The development of artificial satellites in the latter half of the 20th century allowedremote sensing to progress to a global scale as of the end of the cold war. Instrumentation

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aboard various Earth observing and weather satellites such asLandsat, theNimbusandmore recent missions such as RADARSAT and UARS provided global measurements ofvarious data for civil, research, and military purposes. Space probes to other planets havealso provided the opportunity to conduct remote sensing studies in extraterrestrialenvironments, synthetic aperture radar aboard the Magellanspacecraft provided detailed

topographic maps ofVenus, while instruments aboardSOHOallowed studies to beperformed on the Sun and thesolar wind, just to name a few examples.

Recent developments include, beginning in the 1960s and 1970s with the development ofimage processing ofsatellite imagery. Several research groups in Silicon ValleyincludingNASA Ames Research Center, GTEand ESL Inc.developedFourier transformtechniques leading to the first notable enhancement of imagery data.

The introduction of online web services for easy access to remote sensing data in the 21stcentury (mainly low/medium-resolution images), like Google Earth, has made remotesensing more familiar to the big public and has popularized the science.

[edit] Remote Sensing software

Remote Sensing data is processed and analyzed with computer software, known as aremote sensing application. A large number of commercial and open source applicationsexist to process remote sensing data. According to an NOAA Sponsored Research byGlobal Marketing Insights, Inc. the most used applications among Asian academic groupsinvolved in remote sensing are as follows: ESRI 30%; ERDAS IMAGINE25%; RSIENVI 17%; MapInfo 17%; ERMapper 11%. Among Western Academic respondents asfollows: ESRI 39%, ERDAS IMAGINE 27%, MapInfo 9%, AutoDesk 7%, RSI ENVI17%.

[edit] Further reading

Campbell, J.B. (2002).Introduction to remote sensing, 3rd ed., The GuilfordPress.ISBN 1-57230-640-8.

Jensen, J.R. (2007).Remote sensing of the environment: an Earth resourceperspective, 2nd ed., Prentice Hall. ISBN 0-13-188950-8.

Jensen, J.R. (2005).Digital Image Processing: a Remote Sensing Perspective, 3rded., Prentice Hall.

Lillesand, T.M.; R.W. Kiefer, and J.W. Chipman (2003).Remote sensing and

image interpretation, 5th ed., Wiley. ISBN 0-471-15227-7. Richards, J.A.; and X. Jia (2006).Remote sensing digital image analysis: anintroduction, 4th ed., Springer. ISBN 3-540-25128-6.

US Army FM series. US Army military intelligence museum, FT Huachuca, AZ

[edit] See also

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Remote sensing (archaeology) Aerial photography Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance Archaeological imagery Full Spectral Imaging

Geography Geographic information system (GIS) Geomatics Geophysical survey Hyperspectral Imagery Analysis Imaging Science Land cover List of Earth observation satellites National Center for Remote Sensing, Air, and Space Law Orthophoto

Pictometry Radar

Weather radar

Radiometry Satellite Space probe Vector Map

[edit] External links

Remote Sensing at theOpen Directory Project

Retrieved from "http://en.wikipedia.org/wiki/Remote_sensing"Categories: Applications of computer vision | Earth sciences |Satellite meteorology andremote sensing| Geographical technology | Remote sensing

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How Remote Sensing Works

The NMA has long been a proponent of remote sensing for air quality standards,preferring it over the "test-everyone" approach embodied in the BAR90, ASM or I/M-240 tests where all motorists must drive their vehicle to the testing station.

Remote sensing offers all of the advantages and none of the drawbacks of centralized,

drive-in tests.

The fact is that one out of every ten vehicles is responsible for the same amount ofpollution as the other nine combined. This pattern of "gross emitters" is consistentregardless of what form of testing program is in place.

Gross Emitters

are vehicles that can be 1 year old or 15 years old. Age isn't always a factor. are poorly tuned and have emission control systems that are defective or have

been tampered with. have poor performance and fuel economy, but otherwise appear like any other

vehicle. produce an even greater share of pollutants if they are high-use vehicles (taxis,

delivery trucks, etc.)

How do we identify gross emitters now? Most localities where emissions testing isrequired use some form of I/M (inspection and maintenance) drive-in test on a regular

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basis. However, there is a lot of room for improvement, and remote sensing provides theanswer.

How does a remote sensing system work?

Remote sensing was developed by Dr. Robert Stedman at the University of Denver,Colorado. This system uses one basic principle: certain gases absorb infrared light atdifferent rates. By placing an infrared (IR) light transmitter on one side of the road andaiming its beam into an IR receiver on the other side, when a vehicle drives through thebeam, the computer compares the wavelength of the light after it passed through theexhaust plume to the wavelength of the normal IR light. It then calculates the percentageof hydrocarbons (HC), oxides of nitrogen (NOx), carbon dioxide (CO2) and carbonmonoxide (CO). If, and only if, your vehicle is over the maximum limits, a camerarecords your license plate number and the state is notified. (Enforcement actions orpenalties depend on state laws.)

Remote sensing devices are being sold or rented commercially now. The average price ofa stationary setup is over $90,000, which includes training. If a mobile remote sensingstation is desired, the cost is over $140,000. Expensive? You bet. But it's far cheaper thanconstructing a slew of drive-in "test-everyone" stations.

Remote sensing system diagram

Specifications of the GM/Hughes RES-100 "Smog Dog"

Operation: System automatically triggers, acquires and records emissions data.Calibration: Push-button, used twice a day. Gas bottle normally will last one year.Discrimination: Carbon Monoxide (CO), Carbon Dioxide (CO2), and Hydrocarbons(HC).Temp. Range: -45 to +125 F.Accuracy/repeatability: 10%.Sensitivity: 100 parts per million,

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Power: 110 VAC.Max. test rate: 3,600 vehicles per hour.Data storage: Hard disk, floppy disk and magnetic tape.Violator data storage: Video image of rear license plate, with CO, CO2, HC, time/dateand sample number superimposed on image.

Operational features: Transmitter-to-receiver separation of up to 40 feet for camoflagedor hidden operation. Remote console with 100 foot cable.Other information: The infrared source is eye-safe. Emissions violation threshold isvariable. Print-outs available for a variety of information.

Comparison of remote sensing vs. I/M

Remote Sensing I/M

Cost less than 50 cents per car greater than $10 per car

Time 3600 cars per hour 10 cars per hour

Accuracy better than 10% better than 10%

Convenience unobtrusive, on-road testeveryone must makespecial trip

Tampering no way to cheatadvance notice helpscheating

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Cars and The Environment PageFrom the Reasonable Drivers Unanimous site.

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