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[1] The Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF)/albedo algorithm uses multiday, multiband MODIS surface reflectance products from Terra and Aqua to produce a global albedo product at a 500 m resolution (Collection 5). This paper evaluates the ability of the MODIS albedo product to represent albedos at all diurnal solar zenith angles through a comparison with field measurements from the Surface Radiation Budget Network (SURFRAD) and the Atmospheric Radiation Measurement Southern Great Plains (ARM/SGP) stations. The results show that, for most of the sites, the overall accuracy of the MODIS albedo is within 0.05 and shows an increasing negative bias and increased RMSE as zenith angle increases beyond 70°-75°as compared to the ground observations. The full inversion of the MODIS BRDF/albedo algorithm has a higher inversion quality than the backup algorithm. Site heterogeneity and spatial-scale mismatch between the MODIS and ground observations are the major factors contributing to the discrepancy between the MODIS albedo and the field measurements.

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Highlights:-We present a review and an expanded dataset of methane clumped isotope measurements.-Methane clumped isotope values often indicate equilibrium formation temperature.-Kinetic effects during or after methane production can affect clumped isotope values.-The wide variability in clumped isotope values suggests it will be a useful tracer. AbstractThe isotopic composition of methane is of longstanding geochemical interest, with important implications for understanding petroleum systems, atmospheric 3 greenhouse gas concentrations, the global carbon cycle, and life in extreme environments.Recent analytical developments focusing on multiply substituted isotopologues ('clumped isotopes') are opening a valuable new window into methane geochemistry.When methane forms in internal isotopic equilibrium, clumped isotopes can provide a direct record of formation temperature, making this property particularly valuable for identifying different methane origins. However, it has also become clear that in certain settings methane clumped isotope measurements record kinetic rather than equilibrium isotope effects. Here we present a substantially expanded dataset of methane clumped isotope analyses, and provide a synthesis of the current interpretive framework for this parameter. In general, clumped isotope measurements indicate plausible formation temperatures for abiotic, thermogenic, and microbial methane in many geological environments, which is encouraging for the further development of this measurement as a geothermometer, and as a tracer for the source of natural gas reservoirs and emissions.We also highlight, however, instances where clumped isotope derived temperatures are higher than expected, and discuss possible factors that could distort equilibrium formation temperature signals. In microbial methane from freshwater ecosystems, in particular, clumped isotope values appear to be controlled by kinetic effects, and may ultimately be useful to study methanogen metabolism.

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