2012 AGU Chapman Conference on Remote Sensing of the ...

vapor pressure, and a 20% reduction in 2m wind speed overan evaporating surface as compared to the original ‘desert’condition. These differences were confirmed by datameasurements over an irrigated alfalfa field. Theconditioned data reduced estimated reference ET by 20%which has significant, negative consequences for ETestimates used in irrigation water management, in waterbalance studies and water rights transfers, that, in thefuture, may be based on gridded weather data from theWRF-Noah and similar models. Partially funded by NSFEPSCoR.Allen, Richard G.Ground-based Energy Balance, Scintillometer andEvapotranspiration Studies in Natural Systems toSupport Remote Sensing ModelsAllen, Richard G. 1 ; Zhao, Wenguang 1 ; deBruin, Henk 2 ;Germino, Matt 3 ; Sridhar, Venkat 4 ; Robison, Clarence 1 ;Greth, Jeremy 11. Civil Engineering, University of Idaho, Kimberly, ID, USA2. Retired, Wageningen University, Wageningen,Netherlands3. Biology, Idaho State University, Pocatello, ID, USA4. Civil Engineering, Boise State University, Boise, ID, USAMany river basins contain complex combinations andgradients of vegetation and gradients in elevation,precipitation, soils, aspect and slope. These complexitiesmake it difficult to estimate evapotranspiration (ET) for thebasins, thereby complicating the establishment of waterbalances and the parameterization of hydrologic models.Satellite-based energy balance computation systems havebecome widely used during the past decade; however, thesesystems have some uncertainty and themselves need someindependent calibration. In Idaho, we have strong interest indeveloping a better understanding of the time-based releaseof precipitation, in the form of evaporation andtranspiration, from extensive systems of sagebrush andinvasive cheatgrass in order to better predict impacts toground-water and ecosystem health under land-use andclimate change and tendencies for cheatgrass invastions tospread. Sensible heat fluxes over a sagebrush and an invasivecheat grass have been measured since late 2009 usingmultiple eddy covariance stations and large aperaturescintillometers (LAS). We have used combinations of CSAT3and RM Young 81000 3D sonic anemometers with LI-7500CO2/H2O analyzers placed along transects of ScintecBLS900 LAS systems to independently derive H at each site.Optical large aperture scintillometers (LAS) have beendeployed over sagebrush and invasive cheatgrass systems indesert and above a 1600 m transect over lodgepole pineforest near Yellowstone National Park to estimate H andultimately ET. Results show the H derived by thescintillometry method to closely agree with that derived bythe eddy covariance over both sagebrush and cheatgrassecosystems during fall, winter, spring and summer,including during nighttime, when boundary layer conditionsare sometimes highly stable. Four different computationschemes have been used with the LAS that use varyingamounts of measurements from the sonic anemometer,including friction velocity and the Monin-Obukhov stabilitylength. We have also used multiple linear regression with themore than 10 soil heat flux subsights to determine aweighted combination of soil heat flux data to explain themeasured energy balance data. Uses of the data are describedincluding improving our understanding of surfaceconductance behavior of vegetation during soil waterdepletion, projection of energy balance behavior underfuture climates and improved parameterization of remotesensing models. The challenges with deriving H fromscintillometry include uncertainties in effective path heightover mixed vegetation/terrain systems and uncertainties inspecifying an effective friction velocity for these samecomplex systems. The need for many replicates of netradiometers and soil heat flux sensors (we use 16 at eachlocation) is emphasized and illustrated. Funding is by theNSF EPSCoR.Allen, Richard G.Impact of Aerodynamic Algorithms in Mountainswhen Applying Landsat-scale Energy BalancesAllen, Richard G. 1 ; Trezza, Ricardo 1 ; Irmak, Ayse 2 ; Healey,Nathan 2 ; Tasumi, Masahiro 31. Civil Engineering, University of Idaho, Kimberly, ID, USA2. School of Natural Resources, University of Nebraska,Lincoln, NE, USA3. University of Miyazaki, Miyazaki, JapanThermal satellite-based energy balance models havebecome common for producing images of ET over largeareas. Applications are typically made using Landsat imageryto produce 30 m resolution data for obtaining field-scale ETinformation. This same resolution is useful for describingsurface energy balance and partitioning on mountain slopes.In mountains and complex terrain, solar radiation is astrong function of slope and aspect. We describe a recentlyrefined technique to estimate beam, diffuse and terraincomponents of solar radiation independently and thepositive impact this has on reflectance retrievals at 30 mresolution. We describe an adjustment in terraintemperature for cross-valley thermal emission of long-wave.In addition to radiation effects, we describe the sensitivity ofsensible heat flux estimation to wind speed and terrainroughness in mountainous areas. To conduct the sensitivityanalysis, we increase wind speed in proportion to a relativeelevation parameter computed for a 3 km locality of eachpixel and we increase aerodynamic roughness to assimilateimpacts of relative terrain roughness, estimated inproportion to standard deviation of elevation within a 3 kmlocality. These aerodynamic modifications increaseconvective heat transfer in complex terrain and reduceestimated ET. In some applications we reduce estimatedwind speed on leeward slopes of mountains when winddirection is judged to be consistent within the image.Illustrations of estimated ET with and without thesealgorithms is demonstrated in mountainous areas of Idaho,32