METRIC: High Resolution Satellite Quantificationof EvapotranspirationBackground on the ET mapping procedureEvapotranspiration “mapping” with SEBAL and METRICtmSurface Energy Balance:Landsat – Polar OrbitingLandsat – Polar OrbitingWhat Landsat seesMODIS – Polar OrbitingMODIS – Polar OrbitingWhy we selected the SEBAL Modeland evolved the METRICtm ModelWhy we selected the SEBAL Modeland evolved the METRICtm ModelMETRIC: High Resolution Satellite Quantificationof EvapotranspirationUniversity of Idaho, Kimberly, IdahoCo-developers and Collaborators:R. Allen, M. Tasumi, R. Trezza, W. Bastiaanssen, T. Morse, W. Kramber, J. WrightPart One Part One ––IntroductionIntroductionCopyright, R.G.Allen, University of Idaho, 2005Major Irrigatedareas in Idaho and areas of METRIC applicationIdaho from LandsatSeasonal ET for SE IdahoImperial Valley, CAvia Landsat 7ET (mm)0100200300400433Imperial ValleyET during January – March, 2003Imperial Valley, CAvia Landsat 7ETrFET (mm/yr)050010001500200025000.000.250.500.751.001.25Albuquerque Intl. AirportSanta Fe AirportEspanola NWS293031San AcaciaBoys RanchJaralesLosLunasAlbuquerqueCandelaria FarmsAngosturaPena BlacaJemezAlcaldePath 34Path 35Middle Rio Grande of New Mexico3 million acres with 30 m resolution200 milesResults of METRICtmfor Southeastern IdahoSeasonal ET from Irrigated Areas for S. Idahohttp://maps.idwr.state.id.us/etAnnual ET for all of Californiahttp://www.sebal.usCreated by SEBAL-North America for 2002 using MODIS satellite imagery (resolution = 1 km)Background on the ET mapping procedureEvapotranspiration “mapping” with SEBAL and METRICtmSurface Energy Balance Algorithm for LandMapping EvapoTranspiration with high Resolution and Internalized CalibrationDr. Wim Bastiaanssen, WaterWatch, The Netherlands– beginning in 1990– SEBAL is commercially applied in the U.S.A. by SEBAL-North AmericaAllen and Tasumi, University of Idaho, Kimberly– beginning in 2000– rooted in SEBAL2000METRICtmis energy-balance-based ET mapping tied down and partly calibrated using ground-based reference ET (from weather data)METRICtmworks well in advectiveconditions of the western U.S.Energy balance gives us “actual” ETSurface Energy Balance:ET is calculated as a “residual” of the energy balanceRnET = R - G - HnG (heat to ground)H (heat to air)ETThe energy balance includes all major sources (Rn) and consumers (ET, G, H) of energy(radiation from sun and sky)Basic Truth: Evaporation consumes EnergyEnergy balance gives us “actual” ETTherefore, we can account for impacts on ET caused by:water shortagediseasecrop varietyplanting densitycropping datessalinitymanagement(these effects can be converted directly into a crop coefficient)8/14/00Why use High Resolution Imagery?ET from individualFields is Critical for Water Rights, Water Transfers, Farm Water ManagementMinidoka County, IdahoWhy use High Resolution Imagery?Daily ET (8/26/2002)Monthly ET (Aug. 2002)Annual ET(2002)Landsat False Color (8/26/2002)Landsat False Color Daily ET (8/26/2002)Monthly ET (Aug. 2002)Annual ET(2002)ETrFET (mm/yr)050010001500200025000.000.250.500.751.001.25(8/26/2002)Minidoka County, IdahoRiparian vegetation and small fields along theMiddle Rio Grande, New MexicoLandsat vs MODISWhy use High Resolution Imagery?Landsat False Color (MRG)8/26/2002 10:33amMODIS False Color (MRG)8/26/2002 11:02amNeed for ET Maps in IdahoQuantify Net Depletion from Ground-water Pumping (unmeasured)Compare actual ET with Water RightCalculate Natural and Irrigation-Induced Recharge to Aquifers (via water balance to calibrate MODFLOW)Determine “Actual” ET for Developing better Crop Coefficient Curves4 million acres with 30 m resolution200 milesCalculation of the Energy BalanceRnGHETNet Radiation (Rn) = function of: date and timereflectance(brightness) of surfacesurface temperature humidity (minor effect)Heat to Air (H) = function of:surface temperature wind speedvegetationtype and “roughness” surface to air temperature difference: H at the “cold” pixel = Rn–G –ETreference H at the “hot” pixel = Rn–G –0Heat to Ground (G) = function of:amount of vegetationNet radiationsurface temperature, reflectanceRnGHETunderlined terms are measurable by satelliteLandsat – Polar OrbitingA new image each 16 daysfor a specific locationLandsat – Polar OrbitingWhat Landsat seesTransmissivity of atmosphereVarious amounts of reflectionWavelength in Microns:0 0.4 0.6 0.8 1.2 1.6 2.0 2.4Visible Near Infrared(Band 6 is the surface temperature band (not shown))Land Surface12 3 4 5 7MODIS – Polar OrbitingA new image each day for a region705 km, 10:30 a.m. (Terra) and 1:30 p.m. (Aqua)36 bands-- most at 1 km resolutionMODIS – Polar OrbitingMany “products” at 1 km (0.62 mile) resolutionSurface Temperature, Southern California, Record Weather, May 2, 2004BIOMASS Net Primary Productivity for North AmericaLandsat vs MODISLandsat False Color (path 34, row 36 (MRG))8/26/2002 10:33amMODIS False Color (equiv path 34/36 area)8/26/2002 11:02amLandsat vs MODISLandsat False Color (MRG)8/26/2002 10:33amMODIS False Color (MRG)8/26/2002 11:02amLandsat vs MODISLandsat False Color (MRG)8/26/2002 10:33amMODIS False Color (MRG)8/26/2002 11:02amAccuracy of ET by Satellite Energy BalanceWhat can we expect?Satellite is 705 km above the earthBesides energy “seen” by satellite, ET is impacted by aerodynamics invisibleto the satelliteNeed to key aerodynamic characterizations off imageDesign of SEBAL and METRIC make process relatively insensitiveto the parameterization of aerodynamics“Magic” of the temperature difference (dT) vs. surface temperature function of SEBAL (Bastiaanssen1995, 1998) provides internal and relatively automatic calibrationAccuracy of ET by Satellite Energy BalanceWhat can we expect?METRIC is an “engineer’s tool”Focus is on a ‘small’ region of interest (100 miles x 100 miles) (i.e, not the world, not 17 western states)METRIC combines the strengths of energy balance from satellite and accuracy of ground-based reference ET calculation: satellite-based energy balance provides the spatial information and distribution for a large area (and does most of the “heavy lifting”) reference ET calculation “anchors” the energy balance surface and provides “reality” to the product.What is the Alternative to Satellite Energy Balance?Crop Coefficient x Reference ET(Kcx ETr)Sugar
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