Estimating the mass balance of Vatnajökull, Iceland, from NOAA AVHRR imagery

Abstract

We investigate the possibility of obtaining the mass balance of Vatnajö kull, Iceland, from US National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) albedo images for the years 1991–2002. De Ruyter de Wildt and others (2002) demonstrated that the mean potential absorbed radiation (<Qpot,net>) averaged over the melting season correlates well with the mean specific mass balance and that (<Qpot,net>) can be estimated from the evolution of the surface albedo. Here, we improve the retrieval method of de Ruyter deWildt and others (2002) by introducing the more realistic 6S atmospheric transfer model and by adding the latest narrowto- broadband (NTB) albedo conversion equations. Bidirectional reflectance distribution functions for both ice and snow are used where appropriate. We show that the choice of the NTB conversion equations greatly influences the calculated (<Qpot,net>) . Measured mass balance correlates well with (<Qpot,net>) if enough cloud-free images can be found through the year and if the spatial variation in measured mass balances is high enough. The correlation coefficient for all drainage basins combined is 0.92, with a residual standard deviation of 0.18mw.e. We present an estimated mass-balance series for the whole of Vatnajö kull based on our findings. Switching between different AVHRR instruments over time may cause serious errors in the calculated mass balance.