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实习一指导书
Lab.01:
IntroductiontoENVI4.5(ENVI简介)
NotethatthereisaworksheetattheendofthisLabwrite-upthatyoumustturninattheendofthelabperiod.(实验后有一些问题,完成这些问题,并于实习结束后上交)
ENVIisapowerfulsoftwarepackagethatisarguablythemostcommonlyused(althoughtherearemanyothergoodpackages)byremotesensingscientistsformanipulatingandanalyzingdata.Inthisexerciseyouwillfamiliarizeyourselveswithitscapabilities.Probablythebestwaytogetstartedwithanycomplexsoftwareistoexplorethevariousmenusandbuttonstoseewhatkindsoftasksthesoftwarecando.
ENVIInstallation(安装)
Clickfile‘envi45winx86_32.exe’,afterfinishinstallingthisfile,copy“idl.dll”incracktodirector“C:
\ProgramFiles\ITT\IDL70\bin\bin.x86”,thancopyfolder“licence”todirector“C:
\ProgramFiles\ITT”
UsingENVIHelpDocuments(帮助文档)
Clickmenu:
Themostusefulforthisclassisaccessedbyclickingonthelittlequestionmark(?
)ontheupperrightsideoftheENVIinterface.
OpeningImages(打开影像)
1)StartENVI.
2)Let’sopenaLandsatThematicMapper(TM)imageinfolder“TM20080802”.Clickasthisfollowingfigureshow.
3)Inthisfolderisafoldercalled“SCENE01”,inthisfolder,choose“header.dat”andclickOK.Itshouldopen.
4)Openanimageingrayscale(灰度影像).
Inthe“availablebandlists”,chooseanyoneband,click“grayscale”whichisadefaultoption,andclick“loadband”,thenthisimageisshowinginthreewindows,oneisforimage,oneisforscroll,oneisforzoom.
Nowlet’sopenasecondwindowsothatyoucandisplaytwoimagessidebyside.Chooseanotheroneband,andclick“NoDisplay”,choose“NewDisplay”,click“LoadBand”,thenthisimageisshowinginanotherthreewindows
5)openanimageinRGBColor(彩色影像).
Chooseoption“RGBColor”whichisnexttooption“GrayScale”.ThenchooseonebandforchannelR,anotheronebandforChannelG,andanotheroneforChannelB,thenclick“loadband”
6)ChangingtheColorScheme(改变配色方案,即选择不同的波段分别赋给R、G、B三个通道,查看合成结果)
Theappearanceofanimagedependsonhowyouchoosetoassignthethreeadditiveprimarycolors(red,greenandblue)tosatelliteimagebands(alsocalledspectralbandsorchannels).Theconventionistoassignwhicheverspectralbandcorrespondstonearinfrared(NIR)tothecolorred.
TheTMimagethatyouareusinghas7spectralbands,numbered1–7,eachofwhichhascapturedadifferentpartoftheelectromagneticspectrum.Nowyouwilltrytochangethebandsthatareassignedtotheprimarycolorstomaketheimagelooklikewhatyouwouldseewithyoureye(orwithaconventionalcamera).Noticethattherearevariouscontrolsforchangingtheappearanceofimages.Experimentwithvariousbandcombinationswiththegoalofmakinganimagelooklikeitwouldlooktoyoureye.Notethatanystandingwaterwillbedark,vegetationwillbegreenish.Ontheworksheet,recordthebandtoprimarycolorcombinationsthatresultin“truecolor.”
GettingInformationaboutanImage(获取影像信息)
Oftenyouneedtogatherbasicinformationaboutimagefiles.First,someterminology:
“Raster”isthetechnicaltermforimageorGISdatathatarecomposedofpixelsarrangedinrows(orlinesorrecords)andcolumns(orsamples).Eachx,y(row,column)gridcelliscalleda“pixel”(justlikeinyourdigitalcamera).(栅格数据)
“Vector”isthetechnicaltermforGISpoint,line,andpolygondataincomputer(digital)format.Vectordataarecomposedofthex,ycoordinatesofpointsandinformationaboutifandhowthepointsareconnectedintolinesorareas(polygons).(矢量数据)
AlayerinENVIiseitherasinglerastersatellitebandoravectordataset.(ENVI中图层可以是栅格也可以是矢量)
Afile(e.g.animagefile)canhaveoneorseverallayers.(一个影像文件中可有一个或多个图层)
Getthemapinformation:
Click⊕infrontof“mapinfo”in“availablebandlist”,thenyouwillseethemapinformationforthisimage.Readcarefullysothatyoucananswertheworksheetquestions.(获取地图信息)
RightClickontheLayerInfoiconatthetopofyour“availablebandlists”andchoose“EditHeader”.Awindowwillopenthatincludessomebasicinformationaboutthisfile,includingthenumberoflayers(bands),thenumberofcolumns(width)androws(height),thetypeofdata.(查看文件的基本信息)
RightClickontheLayerInfoiconatthetopofyour“availablebandlists”andchoose“QuickStats”.Afterafewminutes,awindowwillopenthatincludessomebasicinformationaboutthisfile,includingtheminimum,maximumandmeanpixelvaluesandotherinformationforeachband.Exploresomeofthetabsonthisinformationwindow(andanswertheworksheetquestions).(查看文件的统计信息)
LinkingandUnlinkingImagesinSeparateGraphicsWindows(影像关联及解除影像关联)
Itisoftenusefulto“Link”viewerstogethersothatyoucanidentifythesamelocationintwoormoreimages.Gobacktoyour“Availablebandlist”,clicktwodifferentbandsonebyoneanddisplaythemintwodifferentwindows.Inanyoneimage,clickasthefollowingfigureshow:
(基于像素的关联)
Awindowdisplayedas:
ClickOK,thenthosetwoimageslinked.
ClickCursorlocations/valueasthefollowingfigureshow:
Ifyourimagesarelinked,redrectangleswillappearinbothimages(iftheyaren’tlinkedthewhitecrosswillonlyappearintheactiveimage)andawindowwillpopupthatcontainsinformationabouttheexactpixelattheintersectionoftherectangles.Movetherectanglearoundwithyourmouseandnotethatitmovesinbothimages.
Theabovemethodisalinkbasedonimagepixel.Pleasetrytolinktoimagebasedongeographicallocations.(基于地理位置的关联)
Worksheet:
Lab01:
IntroductionToENVI
(作业,要求每个题在必要的地方要截图,对结果仔细分析后回答问题)
1.Whataretherolesofthethreedifferentwindowsforoneimage?
(影像显示时,三个不同窗口的作用是什么?
)
2.Whatistheprojectionofthisimage?
whatisthepixelspatialresolution?
(给定影像的投影方式是什么?
空间分辨率是多少?
)
3.DescribetheTMimagethatyouoriginallyopenedusingthestandardfalsecolorcomposition(标准假彩色合成)(inanRGBimage,Band4(近红外波段)forchannelR(红通道),Band3(红波段)forchannelG(绿通道),Band2(绿波段)forchannelB)(蓝通道).(影像的彩色合成)
a.Whatcoloristhevegetationsurroundingtown?
Why?
(城区外围植被是什么颜色,为什么?
)
b.Whatcoloristhewaterbody?
Why?
(水体是什么颜色,为什么?
)
4.DescribetheTMimagethatyouoriginallyopenedusinganotherfalsecolorcomposition(另一种假彩色合成)(inanRGBimage,Band5forchannelR,Band4forchannelG,Band3forchannelB).(影像的彩色合成)
a.Whatcoloristhevegetationsurroundingtown?
Why?
(城区外围植被是什么颜色,为什么?
)
b.Whatcoloriswaterbody?
Why?
(水体是什么颜色,为什么?
)
5.Whatbandandcolorcombinationsarerequiredtomaketheimagelooklikewhatyoureyewouldsee(“truecolor”)?
(如何合成一景真彩色影像?
)
a.Whatcoloristhevegetationsurroundingtown?
Why?
(城区外围植被是什么颜色,为什么?
)
b.Whatcoloriswaterbody?
Why?
(水体是什么颜色,为什么?
)
c.Pleasemakeacomparisonofthevegetationcolor,waterbodycolorbasedontheresultsfromquestions3,4and5.(对3,4,5中植被、水体的颜色作一个对比.)
6.BasedontheLayerInformationwindowprovidethefollowinginformationabouttheTMimagefile:
(TM影像的相关信息)
a.Howmanybandsdoestheimagehave?
(影像有几个波段?
)
b.WhatisthemeanpixelvalueforBand4?
(第4个波段像素DN值的平均值是多少?
)
c.WhatistheminimumpixelvalueforBand2?
(第2个波段像素DN值的最小值是多少?
)
d.Whatisthehistogramforallbandslikeinthisimage?
(显示该影像所有波段的直方图。
)
7.Linkband2andband6basedongeographicallocations:
(基于地理位置对波段2和波段6进行关联)
a.WhataretheDNvaluesofwaterbodysurroundingforbiddencityinband2andband6?
(波段2和波段6中紫禁城外水体的DN值各是什么?
)
b.WhataretheDNvaluesofvegetationinTiantanParkinband2andband6?
(波段2和波段6中天坛公园植被的DN值各是什么?
)
Lab02:
ConvertingRadiancetoReflectance
(辐射率到反射率的转换)
Notethatthereisaworksheetattheendofthislabwrite-upthatyoumustturninattheendofthelabperiod.(实验后有一些问题,完成这些问题,并于是实习结束后上交)
TodaywewillusesomeENVItoolstoconvertwhatthesatellitemeasures,calledradiance,tothecharacteristicabilityofmaterialsonthegroundtoreflectlight(reflectance).Therearemanyconceptsintoday’slabthatwehavediscussedinmuchmoredetailinthepastfewweeks,rememberingthatreflectanceisNOTdirectlymeasuredbysatellitesandmustinsteadbecalculated.
First,somedefinitions:
DigitalNumber(DN)–theunitlessintegerthatasatelliteusestorecordradiance(e.g.0–255where0=noradianceand255=somemaximumamountofradiancethatthesensorissensitiveto).EachimagepixelhasoneDNforeachband.(DN值)
Radiance(L)–theamountoflightreceivedataparticularplace,inthiscaseasatellite(watts/m2/sr).(辐射率)
Irradiance(E)–theamountofincominglightfromthesun(eitheratthegroundoratthetopoftheatmosphere(TOA)(watts/m2).(入射辐射)
Reflectance(r)–theamountoflightthatreflectsoffofsomethingdividedbytheamountofincominglight(oftengivenasafractionorapercent).(反射率)
Transmittance(t)–theproportionoflightthatistransmittedthroughsomething(e.g.,throughtheearth’satmosphere),usuallygivenasafraction.(透过率)
Thefundamentaltaskinremotesensingisdistinguishingobjects(e.g.,plants,rocks)orproperties(e.g.,plantleafnutrientcontent)onearth,basedontheamountoflightthattheobjectsreflectacrossthevariouswavelengthsthatsatellitesmeasure(capturedinbands).Theproblemisthatsatellitesdon’tmeasurereflectance,theymeasureradiance.Thepatternofradianceacrossthesatellitebandsisoftensimilartothepatternofreflectanceacrossthesamebands,butitisalteredbythingslikeatmosphericeffects.Anotherissueisthatweoftenneedtodirectlycomparethereflectanceofobjectsonthegroundwithreflectancecalculatedfromsatellitedata.Todothis,wemustconvertsatellitedigitalnumbers(DNs)orpi