ABoVE Standard Projection and Reference Grid v2 20170621
Transcript of ABoVE Standard Projection and Reference Grid v2 20170621
ABoVE Standard Projection and Reference Grid Justification The ABoVE field campaign will provide the opportunity to expand and coordinate a set of focused,interdisciplinary research activities designed to further understand the causes and consequences ofchangeinthesocial-ecologicalsystemsoftheArcticandborealregionsofwesternNorthAmerica.Thecampaign is expected to result in thedevelopmentofmultiple geospatial datasets. To facilitatedatainteroperability,astandardprojectionandreferencegridhavebeenproposedtocovertheABoVEstudydomain.
Thedomainforthestudyareaisover6.3x106km2asshownintheredandpurpleoutlinesinFigure1.Thematic data products will be generated from field measurements, flux towers, airborne remotesensorsandsatellite remotesensingdata. Thedatasetswill rangeconsiderably in resolution, format,geographic extent, projection and/or reference system. This variability in ABoVE datasets is likely toplace a considerable burden on individual researchers as theywill need to standardize the incomingdatasetstosupportgeospatialanalysis,thusleadingtoduplicatedeffortacrossresearchgroupsutilizingtheseproducts.Thisduplicationofeffortwill continue topropagateasoutcomesof scientificanalysisfrom individual research groups will require subsequent standardization to support their furtherinclusion in ABoVE science projects. Implementing a standard projection and grid would enable theproducersofthedatatoalignandsubdividedataproductsinordertoeasearchivinganddistributionofdatasets (both for long-term archiving of the data and near-term use throughout the campaign’sduration), and would simplify data standardization for scientific analysis within ABoVE. Thiscompatibilityacrossmultipledatasetswillfacilitateinteroperabilityofthedatasetsinscientificanalysis,andisanimportantbenefitofthestandardizedprojectionandreferencegrid.
Additionally, it isexpectedthatmanydataproductswillbegeneratedwithmediumto fineresolution(30mspatial resolutionor less) imageryandhencewouldbe too large todistribute tousersas singlefilescoveringtheentirestudyregion. Wheretheprojectionprovidesamechanismtoensurethattheproductsaregeometricallycompatible,thereferencegridprovidesastandardizedwaytobreakthefilesupintounitsthatareeasytodownloadandmanipulatebytheresearchers.
TheapproachtakenhereismodeledaftertheMODISstandardproducts.Belowisalistofassumptionsthatwereusedwhendeterminingtheprojectionandgrid:
1. While the projectionwould be applicable tomultiple data types, the gridwould primarily beusedforrasterproductsproducedoverthestudydomain(notincludingcircumpolardatasets).
2. Toprovidearealcalculationsfromthedataproductsweneedtohavethedatainanequalareaprojection.
3. Theproductscouldrangefromfinespatialresolution(1–5m)tocoarsespatialresolution(250mormore).
4. 30mwillbeacentralspatialresolution.5. Usersofrasterdatacaneasilydownloadfilesthatare300MBinsize.
Standard Projection The projection for use and archiving of geospatial data products for the ABoVE study domain is theCanadaAlbersEqualAreaprojection.Thisprojectionhasbeenselectedbecauseitisequalarea,iswidelysupported in geospatial software (ESRI, ENVI, gdal, etc), is commonly used for data products in thisregion,andhascentralmeridianandparallelswithinthehighnorthernlatitudeareasthatarethefocusoftheABoVEcampaign.
Projection Specifications: Canada_Albers_Equal_Area_ConicWKID(EPSG):102001Authority:ESRIProjection: AlbersFalse_Easting:0.0False_Northing:0.0Central_Meridian:-96.0Standard_Parallel_1:50.0Standard_Parallel_2:70.0Latitude_Of_Origin:40.0LinearUnit:Meter(1.0)GeographicCoordinateSystem:GCS_North_American_1983AngularUnit:Degree(0.0174532925199433)PrimeMeridian:Greenwich(0.0)Datum:North_American_1983Spheroid:GRS_1980SemimajorAxis:6378137.0SemiminorAxis:6356752.314140356InverseFlattening:298.257222101
Reference Grid Theproposedgridisapplicablemainlyforraster-basedproductsderivedforthestudydomain(butwouldnotapplytocircumpolardatasets).Thegridhasbeendesignedtocovertheentirestudydomain,andextendstotheeasternportionsofNorthAmerica(seeFigure1below)toaccommodateanyproductsthatarelookingatcontinentalscaleprocesses.ThisgridissimilartotheMODIStilingschemeandisanestedsetofgridsprovidedatscalesof240,30,and5meterspatialresolution,suchthatproductsfromMODIS,Landsat,andveryhighspatialresolution(VHR)datawouldbecompatiblewithinthegrid.Itiseasilyscalableforproductsof1meterto10kilometersbyswitchingfromonegridresolutiontoanotherastheresolutiongetscoarser.Thethreegrids(Table1)coverthesamespatialextentandnestwithineachother(seeReferencegridnestingschemeandbetweengridconversion)
Table1.SummarydescriptionofthethreenestedgridsystemfortheABoVEdataproducts.
GridName Resolution
Gridcell(m)
#ofhorizontal(h)tiles htilesrange
#ofvertical(v)tiles vtilesrange
A coarse 240 6 h000-h005 4 v000-v003B moderate 30 36 h000-h035 24 v000-v023
C fine 5 216 h000-h215 144 v000-v143
Figure1TheABoVEreferencegridandstudydomain.a)The240mreferencegrid(4500X4500gridcellspertile)withassociatedAhandAvvaluesandb)The30mreferencegrid(6000X6000gridcellspertile)superimposedonthe“A”grid.
GriddedABoVEdatasetsoftheextentlargerthan100X100km2aretobeproducedinthisgridandprojection(thisisroughlyaLandsattile).Also,werecognizethatatveryhighresolution,reprojectionof
originaldatacanresultinsubstantialspatialshiftsinorientation,location,andshapeofsmallobjects;therefore,scienceteammembersareencouragedtosubmittheirfine-scaledatasetsintheoriginalprojectioninadditiontotheABoVEgridformat(iftheextentoftheirdatasetisgreaterorequalto10,000km2)oronlyintheoriginalprojectionifitissmallerthanthatsize.
Reference Grid Naming Convention Thereferencegridnamingconventionis,again,modeledaftertheMODISgridusinghorizontal(h)andvertical(v)offsetsfromtheupperleftcornertodescribethetile.ForexampleinFigure1a(showingthelargegrid) thetile intheupper leftcorner is referredtoas“h000v000”andthetile inthe lowerrightcornerisreferredtoas“h005v003”.Figure1bshowsthesmallergridnestedinsidethelargergrid.Foreachofthelargetilesthereisaseriesofsmalltilesnestedinside.Thelargegridisreferredtoas“A”,themedium grid is referred to as “B”, and the small grid is referred to as “C”. This yields a namingconventionsuchas:
FortheA–grid:
ABoVE.water.2001001.Ah000v000.001.2014075120101.hdf
Where:
ABoVE–referstothecampaign
Water–referstotheproductIDortype
2001001–referstothedatareferencedate
Ah000v000–referstotheupperlefttileinthe“A”orlargergrid
001–referstotheversionoftheproduct
2014075120101–isaproductiondatefortheproduct
FortheB–grid:
ABoVE.water.2001001.Bh002v003.001.2014075120101.hdf
Where:
ABoVE–referstothecampaign
Water–referstotheproductIDortype
2001001–referstothedatareferencedate
Bh002v003–referstothepurpletileinthe“B”ormediumgrid(figure2a)
001–referstotheversionoftheproduct
2014075120101–isaproductiondatefortheproduct
FortheC–grid:
ABoVE.water.2001001.Ch014v020.001.2014075120101.hdf
Where:
ABoVE–referstothecampaign
Water–referstotheproductIDortype
2001001–referstothedatareferencedate
Ch014v020–referstothegreentileinthe“C”orfinegrid(figure2b)
001–referstotheversionoftheproduct
2014075120101–isaproductiondatefortheproduct
Figure2A)ThelocationofsampletileBh002v003(inpurple)withinboththelarger“A”grid(inbold)andthesmaller“B”grid.B)thelocationofsampletileCh014v020withinthelargertwogridsisshown.
Tosimplifydownstreamprocessingitisrecommendedthatallproductsusethreedigitidentifiersforallgridtileidentifiers(i.e.Ch014v020insteadofh14v20)tofacilitatescriptinginanalyseslateron.
Reference grid nesting scheme and between grid conversion Thenestingschemeprovidesastandardizedandstraightforwardtilingpatternwhereeachofthelargertilesiscomposedfrom6X6(36)smallertilesofthesmallergridsystem.Forexample,asingletileforthecoarseresolutionA-gridiscontains6X6(36)tilesofB-grid.Similarly,eachsingletileofB-gridcontains6X6(36)tilesofC-grid.Simplecalculationscanbeusedtotranslatebetweenresolutions.Forexample:
TofindthelocationofagiventheC-gridtileCh036v012withinB-grid,thehorizontal(h036)andvertical(v012)componentsofthetilenumberingshouldbedividedby6:
floor(36/6)=6andfloor(12/6=2) (“floor”isamathfunctionthattruncatesfloatingpointvaluestointegerswithoutrounding)
HenceCh036v012isfoundinBh006v002.ThepositionofaC-gridtilewithintheA-gridcanbedeterminedinasimilarwaybydividinghandvcomponentsby36:
floor(36/36)=1andfloor(12/36)=0
HenceCh036v012isinAh001v000.TranslatingfromtheB-gridtotheA-gridisthesameastranslatingfromC-gridtoB-grid,simplydividehandvby6.
GivenBh010v008:
floor(10/6)=1andfloor(8/6)=1
HenceBh010v008isinAh001v001.Thissimpletranslationmethodcanfacilitateanalysisthatrequiresusingmultipleproductsatvaryingspatialresolutions.AusercanalsosimplyquerytheassociatedshapefilesusingGISsoftwaretofindwhereafinerresolutiontilenestswithinthecoarserresolutiongrids.AshapefileforeachofthethreegridsisavailablefromtheOakRidgeNationalLaboratoryDAACorfromtheABoVEwebsite.Forfurtherinformationorquestionsregardingtheprojectionorgridpleasecontactsupport@cce.nasa.gov.