Assessing the Fitness of Satellite Albedo Products for Monitoring Snow Albedo Trends

Abstract

Accurate monitoring of albedo trends over snow is essential to evaluate the consequences of the global snow cover retreat on Earth’s energy budget. Satellite observations provide the best way to monitor these trends globally, but their uncertainty increases over snow. Besides, different products sometimes show diverging trends. A better assessment of the fitness of satellite products for monitoring snow albedo trends is needed. We analyze the consistency of black-sky albedo estimates from global long-term products over snow: AVHRR-based (CLARA-A2.1, GLASS-v4.2), MODIS-based (MCD43C3-v6.1/v6, GLASS-v4.2), MISR-based (MIL3MLSN-v4) and multi-sensor (C3S-v1/v2). We use MCD43C3-6.1 as the reference based on a previous comparison against in-situ measurements. CLARA-A2.1 is the one most consistent with MCD43C3, but has a low coverage in high latitudes and an artificial albedo decrease since 2015. The study shows the limitations of MIL3MLSN, GLASS, and C3S multi-sensor products over snow. MIL3MLSN has a too-low coverage of albedo over snow. GLASS-AVHRR overestimates albedo in regions with seasonal snow due to delayed snowmelt and underestimates it in permanently snow-covered regions. GLASS-MODIS is more consistent with MCD43C3 at mid-latitudes, but also underestimates albedo in regions with permanent snow and has an increase of missing values after 2011. Both GLASS datasets are temporally inconsistent with the other products. Despite the improvements from v1 to v2, C3S-v2 has the largest negative bias over snow and discontinuities in the transitions between sensors. The study evidences the difficulties of AVHRR products to provide stable snow albedo estimates in polar regions, particularly before 2000.