At-Surface Reflectance and Albedo from Satellite for Operational Calculation of Land Surface Energy Balance

Abstract

Thispaper presents a rapid, operational method for estimating at-surface albedoapplicable to Landsat and MODIS satellite sensors for typical cloud-free,low-haze conditions and sensor view angles less than 20°. At-surfacealbedo estimates are required input to various surface energy balancemodels that are applied operationally. The albedo calculation method wasdeveloped using the SMARTS2 radiative transfer model and has beenapplied in recent versions of the University of Idaho METRICmodel as a component of the surface energy balance fordetermining evapotranspiration. The albedo procedure uses atmospheric correction functions developedto require only general humidity data and a digital elevationmodel. The atmospheric correction functions have a reduced structure toenhance their operational applicability in routine instantaneous surface energy balancesand to estimate evapotranspiration. The method does not require highlevels of knowledge in atmospheric physics and radiation transfer processes,common to traditional radiation transfer models, which enhances their useby a broad range of agricultural and hydrologic scientists andengineers. The atmospheric correction and surface albedo estimation procedures aredeveloped primarily for use with Landsat imagery, which does nothave an official albedo product. However, the procedure is alsoapplicable to MODIS imagery that has an official albedo productat the 1  km scale, for situations where full broadband albedohaving 500  m resolution is needed, where albedo is needed forselect days having small sensor view angles for reduction ofpixel blurring, or where image striping or reflectance data fallouthas occurred in the standard MODIS albedo product. Method resultshave been compared to literature values and independent data sets.Test applications against MODIS albedo products in New Mexico, Florida,and Idaho indicate that the expected error for actual albedofrom the developed method is within the interval of −0.035to +0.033 (95% confidence level), equivalent to a standard errorof 0.017, over broad ranges in land surface elevation, humidity,and sun angle. ©2008 ASCE