Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

Abstract

Abstract:Albedo is a key variable in the response of glaciers to climate. In Iceland, large albedo variations in the ice caps may be caused by the deposition of volcanic ash (tephra). Sparse in situ field measurements are insufficient to characterize the spatial variation of albedo over the ice caps. Here we evaluate the latest MCD43 MODIS albedo product (collection 6) to monitor albedo over the Icelandic ice caps using albedo from ten automatic weather stations in Vatnajökull and Langjökull as ground truth. We examine the influence of the albedo variability within MODIS pixels by comparing the results with a collection of Landsat scenes. The results indicate a good ability of the MODIS product to characterize the seasonal and interannual albedo changes with correlation coefficients ranging from 0.47 to 0.90 (median 0.84) and a small bias ranging from -0.07 to 0.09. The root-mean square errors (RMSE) ranging from 0.08 and 0.21, is larger than that from previous studies, but we did not discard the retrievals flagged as bad quality to maximize the amount of observations given the frequent cloud obstruction in Iceland. We find a positive but non-significant relationship between the RMSE and the subpixel variability as indicated by the standard deviation of the Landsat albedo within the MODIS pixel (R=0.48). The summer albedo maps and time series computed from the MODIS product show that the albedo decreased significantly after the Eyjafjallajökull and Grímsvötn eruptions in 2010 and 2011 in all the main ice caps (except the northernmost Drangajökull), with albedo reduction up to 0.6 over large regions of the accumulation areas. Following this validation, these data will be assimilated in an energy and mass balance model of to better understand the relative influence of the volcanic and climate forcing to the ongoing mass losses of Icelandic ice caps.

Assessment of NPP VIIRS Albedo Over Heterogeneous Crop Land in Northern China

“…The MCD43A3 (V006) is the latest version of MODIS albedo with the same temporal resolution as that of VIIRS albedo. However, the MCD43A3 (V005), with a temporal resolution of 8 days, is still the most extensively used and widely evaluated product now (Gascoin et al, ). In this paper, the V005 product was also used at a spatial resolution of 1 km for comparison with VIIRS 16 day mean albedo to demonstrate their characteristics.…”

North Atlantic Cooling is Slowing Down Mass Loss of Icelandic Glaciers

“…In line with Gascoin et al. (2017) and Gunnarsson et al. (2021), the minimum albedo in MODIS imageries for tephra‐covered snow in the accumulation zone is set to 0.30, while for tephra‐covered bare ice in the ablation zone, the minimum is set to 0.15.…”

“…As contemporary precipitation has remained mostly unchanged in Iceland, changes in glacier SMB are primarily driven by trends in atmospheric temperature, resulting in fluctuations of meltwater runoff (Björnsson et al., 2013). Superimposed on this, major volcanic eruptions cause high incidental SMB variability as a result of large‐scale deposition of dark tephra (ashes) on the brighter snow and ice that amplifies surface melt through a strong albedo effect (Björnsson et al., 2013; Box et al., 2012; Gascoin et al., 2017; Gunnarsson et al., 2021; Schmidt et al., 2017). Icelandic glaciers have been losing mass since their peak extent at the end of the Little Ice Age in the mid‐to‐late 1800s (Aðalgeirsdóttir et al., 2020), with accelerated mass loss following the recent rapid Arctic warming (Meredith et al., 2019).…”