Ecological-assessment-of-phragmites-abstract-wetland-using-multi-season-spot-5-scenes

distinguishedwholestemswithflowerheads(one-yearreed)fromflowerlessorbrokenstalks.Wholestemswithorwithoutflowerswereaggregatedduringthe2006fieldsurvey,henceweusedhalfthe2005dataforvalidationonthe2005scenes.Reedheightanddiameterweremeasuredontwogreenandfourdry‘average’stemsinsidethequadratsonbothyears.2.4.SPOT-5dataSPOT-5scenescentredontheRhonedeltawereacquiredon30December2004,17March,19May,18June,31Julyand21September2005throughtheSPOTImageProgrammingService(CopyrightCNES).Theseperiodswereselectedbasedonkeyeventsinthephenologyandwatermanagementofreedbeds(Davrancheetal.,2010).Formodelvalidation,weusedimagesfrom18December2005,16March,29May,23June,24Julyand15October2006,asnoscenewasavailableinSeptember.SPOT-5sceneshave10-mpixelresolutionandfourspectralbands:B1(green:0.50–0.59μm),B2(red:0.61–0.68μm),B3(nearinfraredNIR:0.79–0.89μm)andB4(short-waveinfraredSWIR:1.58–1.75μm).Radiometriccorrectionswereper-formedusingtheSecondSimulationoftheSatelliteSignalintheSolarSpectrum(6S)developedbyVermoteetal.(1997).Thisatmosphericmodelpredictsthesensorsignalassumingcloudlessatmosphere,takingintoaccountthemainatmosphericeffects(gaseousabsorptionbywatervapour,carbondioxide,oxygenandozone;scatteringbymoleculesandaerosols)andleadtoameanerrorof0.7%perband(Davrancheetal.,2009).ThecorrectedsceneswereprojectedtoLambertconformalconicprojectiondatumNTF(NouvelleTriangula-tionFrançaise)usingasecond-ordertransformationandnearest-neighbourre-sampling(Davrancheetal.,2009),andgeoreferencedtoatopographicmapat1:25000scaleusinggroundcontrolpoints(RMSEb1pixel).Meanreflectancevaluesatthelocationsofthefieldplotswereextractedforeachbandusingthe‘SpatialAnalyst’ofArcGISversion9.2(EnvironmentalSystemsResearchInstitute).Elevenmultispectralindicesamongthemostcommonlyfoundintheliterature(Table2)werecalculatedforeachscene,aswellasFig.1.ReedbeddistributionintheCamarguewiththelocationofthetraining(2005)andvalidation(2006)fieldplots.Table1Selectedindicatorsofreedconditionsandtheirrelationship(+or−)withreedbedhealth,req