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Title: Use of in situ and airborne multiangle data to assess MODIS-and landsat-based estimates of directional reflectance and albedo

Author
item ROMAN, MIGUEL - National Aeronautics And Space Administration (NASA)
item GATEBE, CHARLES - National Aeronautics And Space Administration (NASA)
item SHUAI, YANMIN - National Aeronautics And Space Administration (NASA)
item WANG, ZHUOSEN - University Of Massachusetts
item Gao, Feng
item MASEK, JEFFREY - National Aeronautics And Space Administration (NASA)
item HE, TAO - University Of Maryland
item SCHAAF, CRYSTAL - University Of Massachusetts

Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2013
Publication Date: 3/1/2013
Publication URL: http://handle.nal.usda.gov/10113/59910
Citation: Roman, M., Gatebe, C., Shuai, Y., Wang, Z., Gao, F.N., Masek, J., He, T., Schaaf, C. 2013. Use of in situ and airborne multiangle data to assess MODIS-and landsat-based estimates of directional reflectance and albedo. IEEE Transactions on Geoscience and Remote Sensing. 51(3):1393-1404.

Interpretive Summary: Land surface albedo, a ratio of the light flux reflected from a surface area to the total incoming incident flux is an important parameter characterizing the Earth’s radiative regime. Land surface albedo can be derived from satellite data. A challenge in validating albedo measurements acquired from space is the ability to overcome the spatial scaling errors. In this paper, we present the results from an accuracy assessment of the Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat Thematic Mapper (TM) albedo retrievals, based on collocated comparisons with tower and airborne Cloud Absorption Radiometer (CAR) measurements collected during the 2007 Cloud and Land Surface Interaction Campaign (CLASIC). The initial focus was on evaluating inter-sensor consistency through comparisons of intrinsic bidirectional reflectance estimates. In general, the satellite-derived estimates met the accuracy requirements established for the high quality MODIS operational albedos. An accurate estimate of surface albedo at the MODIS and Landsat scale is critical for the understanding of carbon and water cycles for regional and global climate models. The bidirectional reflectance data product provides a consistent measurement for crop condition monitoring for the National Agricultural Statistics Service and Foreign Agricultural Service.

Technical Abstract: The quantification of uncertainty in satellite-derived global surface albedo products is a critical aspect in producing complete, physically consistent, and decadal land property data records for studying ecosystem change. A challenge in validating albedo measurements acquired from space is the ability to overcome the spatial scaling errors that can produce disagreements between satellite and field-measured values. Here, we present the results from an accuracy assessment of MODIS and Landsat-TM albedo retrievals, based on collocated comparisons with tower and airborne Cloud Absorption Radiometer (CAR) measurements collected during the 2007 Cloud and Land Surface Interaction Campaign (CLASIC). The initial focus was on evaluating inter-sensor consistency through comparisons of intrinsic bidirectional reflectance estimates. Local and regional assessments were then performed to obtain estimates of the resulting scaling uncertainties, and to establish the accuracy of albedo reconstructions during extended periods of precipitation. In general, the satellite-derived estimates met the accuracy requirements established for the high quality MODIS operational albedos at 500 m (the greater of 0.02 units or ±10% of surface measured values). However, results reveal a high degree of variability in the root-mean-square error (RMSE) and bias of MODIS visible (0.3- 0.7µm) and Landsat-TM shortwave (0.3- 5.0µm) albedos; where, in some cases, retrieval uncertainties were found to be in excess of 15%. Results suggest that an overall improvement in MODIS shortwave albedo retrieval accuracy of 7.8%, based on comparisons between MODIS and CAR albedos, resulted from the removal of sub-grid scale mismatch errors when directly scaling-up the tower measurements to the MODIS satellite footprint.