NASA Facts Planet Earth Through Eyes of LANDSAT 4

8/8/2019 NASA Facts Planet Earth Through Eyes of LANDSAT 4

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r\l/NSA FactsAn Educational Publicationof theNational Aeronautics an dSpace AdministrationNF-138/3-83

Planet EarthThrough theEyes ofLandsat 4

For more than 10years, NASALandsat satellites have beenrecording pictures of the Earth'ssurface. Landsat 1, the first satel-lite in this series, was launched in1972 and it literally changed theway we looked at our planet.Instead of returning exposed filmit transmitted an astoundingstream of numbers. Through itscomplex optical system, theEarth's surface was broken intonarrow slices or scan lines. Whilemoving roughly north to southover the sunlit side of Earth amirror directed Earth's reflectedlight from the east/west sendingscan lines into detectors. Beforereaching the dectectors, the lightwas broken down into spectral

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bands and four weremeasured for bright-ness. Furthermore eachscan line wassubdividedinto individual segments79 by 79meters insize so thatthe reflectedlight levelsofacre-sizedplots of landcould berecorded.

Back on Earth,the streamsof num-bers received fromLandsat 1 were assembled by acomputer into black and white orcolored images 185 by 185kilo-meters in size. To make just onecolored view, more than six mil-lion pieces of Landsat 1 data hadto be assembled. Once assembled,the data could be manipulated.Unusual or unique combinationsof reflected light levels could beintensified by computers to reveal

features and trends on the Earth'surface not readily apparent tothe human eye alone. When combined with observations made onthe ground itself, Landsat 1datacould be processed into land-useclassification maps. For example,a particular hardwood forest, fol-lowing its identification, could belocated on the Landsat scene.The light intensity levels of thevarious spectral bands measuredof that forest by Landsat 1couldbe as unique as a human finger-print. Other areas, of the samescene, that exhibit the samereflected characteristics, could beinterpreted as consisting of thesame surface materialin thiscase, another hardwood forest. Itwas not necessary for theresearcher to hunt for the rightreflectance combinations. Thatjob was done by a computer injust seconds.

The pictures of the Earth's sur-face from Landsat 1 and laterfrom Landsats 2 and 3, launchedin 1975 and 1978, gave scientistsin many disciplines new oppor-tunities to understand the com-plex systems of Earth. Wherenormally 100aerial photographsand many months or years wouldbe necessary to assemble andanalyze a scene 185 by 185kilometers in size, Landsat could


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cover the same area in just a sin-gle picture. The analysis of thepicture could be accomplished injust days or weeks. Furthermore,Landsat data was t imelyespecially useful for agriculturaland environmental studies.Since the first Landsat launch,scientists and technicians frommore than 130countries haveused Landsat data to know andunderstand the resources andenvironment of their portions ofthe Earth.In 1982, a new Landsat,Landsat 4, was launched. Thefourth Landsat carried the sameoptical scanning system as thefirst three, but it also carried anew scanner, the ThematicMapper, for high resolutionstudies. Those square segmentsofscan lines, looked at by the firstLandsats, became much smaller30 by 30 meters in size. TheThematic Mapper also increasedthe number of spectral bands oflight measured in each segmentfrom four to seven. A singlescene from the Thematic Mapperof Landsat 4 contains six timesmore data than a similar-sizedarea from the first Landsats. Thescientific payoff from thisimprovement can be found onthe next pages.

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Washington DC/Baltimore,MarylandFrom Landsai 4 s 960kilometeraltitude, the nation's capital, Balti-more, MD, and large segments ofMa ryland, V irginia, and the Chesa-peake Bay are easily captured in asingle image. Because data fromLandsa i satellites is transmitted toEarth in digital form , images can begiven any combinations of colors toaccent groundfeatures of interest. Inthis particular combination, vegeta-

tion appears red. Hea\'ily forestedan d agricultural areas reveal thestrongest reds. Suburban areas sur-rounding Washington (left center ofimage) appear a dull pink to greycolor because of the blending oftrees, lawns, and residential build-ings. Urban areas appear a light bluebecause of a relative lack ofvegeta-tion and a high percentage of buildingsan d parking lots. With this particularcolor combination, water appearsdeep blue. Water with pollution andsuspended sedim ents, however, shows

a lighter color as is visible in some othe reaches of the Potomac River(running downward in the picturefrom Washington). Baltimore, Mdappears in the upper center of thisscene. Date: No vem ber 2, 1982.


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Boston, MassachusettsIn these two scenes of the Bostonarea, Tttematic Mapper data wasprocessed differently to produce afalse color image (right) and a naturalcolor image (left). Boston appearsat the top and Providence, RI is

found at the center. The land in thisarea was hea\'ily modified by glaciaadvances and the direction of icemovement is presented in the elon-gated, north-south lakes foundthroughout much of the area. Date:September 10, 1982.

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New Orleans, LouisianaLake Pontchartrain and the city ofNew Orleans are the central featuresof this false color image of thesoutheastern end of Louisiana. Thesediment-rich Mississippi Rivermeanders from left to right, south ofthe city, toward the Gulf of Mexico(not seen). Along the Mississippi,and other nearby rivers, a peculiararrangement offarm land isvisible.This is the "long lot" system of landsubdivision that was carried overfrom the French Colonial days. Withthis system, land was parceled insuch a way as to give estatessome river frontage. Date:September 16, 1982.

Death V alley, CaliforniaThe arid, vegetation-sparse terrainof Death Valley appears in a varietyof dark and light tones in this falsecolor scene. V egetation (red) appearsonly in a few scattered regions wherethe land is irrigated an d near the topof snow-covered mountains. Scenes,such as this one, are especially usefulfo r differentiating betw een rock typeswhen exploringfo r mineral deposits.V ariations in the color tones canindicate zones of mineralization.Light colored areas on valley floorsindicate clay and salt deposits. In theenlarged subscene to the right, takenfrom the northwest corner of thelarger view, sediment washed downfrom higher land streaks into valleysforming alluvialfa n deposits. Date:November 17, 1982.

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Jamestown, New YorkThe region of southwestern NewYork, northwestern Pennsylvania,and southeastern Lake Erie areshown in this false color image of theAllegheny Plateau. Jamestown, NYis found at the southeastern end ofChautauqua Lake (upper left). Flat-lying sedimentary rock underlies thisarea. Long years of erosion ha\'eproduced the typical dendritic drain-age (tree branch-like) patternassociated with this type of rockstructure. A lthough m uch of the areais sparsely populated and heavilyforested (deep red), much land south-

eastward from Lake Erie has beenpartially cleared and devoted to longstrips of meadows andfields forcattle raising and farm ing (light redand pink). Date: August 28, 1982.

Medicine Hat, AIberta, CanadaThe Canadian province of Albertaoccupies the western one third of thisfalse color scene just north of theU.S. border. Saskatchewan occupiesthe eastern tw o thirds of this picture.Running southwest to northeast isthe Saskatchewan River. The town ofMedicine Hat appears on the bend ofthe river near the southwest corner ofthe scene. The southe astern portionof the scene is cloud-covered. Colorsha\'e been com pute r- assigned to high-light agricu ltural pa tterns of theregion. In the Medicine Hat subsceneindividua l fields and alternating crops

are easily seen and several circularirrigation fields can be picked out.The land in this area is relatively flatlying and scars of the meanderingSaskatchewan River are visible.Date: November, 10, 1982.


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NASA Facts Planet Earth Through Eyes of LANDSAT 4

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