FINNISH METEOROLOGICAL INSTITUTE (FI)
Surface albedo controls the absorption of sunlight and its reflection back to the atmosphere and space. The bright, highly reflecting surfaces such as seasonal snow cover and sea ice cover that expand to cover large areas during winter and shrink in coverage during summer have high impact on the surface energy balance of the Earth. Surface albedo estimates with global coverage can be quantified from satellite-based reflectance via complex algorithms. In-situ measurements are needed to develop the albedo retrieval algorithms and validate satellite-derived albedo estimates. In-situ measurements of spectral albedo and, in particular, of the bi-directional reflectance distribution function (BRDF) for satellite validation are rare. In cases where such measurements are available, direct comparison is hampered by scale differences. This challenge is amplified over heterogeneous environments where surface types with high contrast in albedo exist at a spatial resolution higher than that of the satellite sensor. Arctic sea ice during summer months and melt/freeze-up periods, snow-covered and snow-free patterns of Antarctic sea ice, and snow-covered boreal landscape all represent heterogeneous environments. These environments also cover vast areas that are often inaccessible by in-situ measurements. This project aims to fill current gaps in the ground truth albedo and BRDF measurements over heterogeneous polar environments. This will be implemented by state-of-the-art unmanned aerial vehicle (UAV) equipment that enable measurements of spectral and broadband albedo as well as BRDF of the surface and characterization of the different surface types and their spatial proportions with co-located photo-mosaics. UAVs allow us to cover both scales of typical point-scale ground measurements and scales represented by a satellite sensor (10-300 m). With these novel observations, collected by the applicant and her collaborators during recent and upcoming field campaigns, the project aims to characterize the spatial heterogeneity of surface spectral and broadband albedo as well as surface BRDF over Arctic sea ice, Antarctic sea ice and boreal snow-covered landscape (mixture of snow-covered open areas and sparse coniferous forests). These UAV-based measurements of albedo and BRDF will be used to validate and improve surface albedo estimates from Sentinel-2/3 and Landsat-8/9 satellite observations. The proposed project enables the candidate to focus on the BRDF and albedo scale and heterogeneity effects over sea ice and boreal snowy landscape – the critical aspects of research otherwise unfulfilled within current project activities.