Temporal Variability of Surface Reflectance Supersedes Spatial Resolution in Defining Greenland’s Bare-Ice Albedo

Abstract

Ice surface albedo is a primary modulator of melt and runoff, yet our understanding of how reflectance varies over time across the Greenland Ice Sheet remains poor. This is due to a disconnect between point or transect scale albedo sampling and the coarser spatial, spectral and/or temporal resolutions of available satellite products. Here, we present time-series of bare-ice surface reflectance data that span a range of length scales, from the 500 m for Moderate Resolution Imaging Spectrometer’s MOD10A1 product, to 10 m for Sentinel-2 imagery, 0.1 m spot measurements from ground-based field spectrometry, and 2.5 cm from uncrewed aerial drone imagery. Our results reveal broad similarities in seasonal patterns in bare-ice reflectance, but further analysis identifies short-term dynamics in reflectance distribution that are unique to each dataset. Using these distributions, we demonstrate that areal mean reflectance is the primary control on local ablation rates, and that the spatial distribution of specific ice types and impurities is secondary. Given the rapid changes in mean reflectance observed in the datasets presented, we propose that albedo parameterizations can be improved by (i) quantitative assessment of the representativeness of time-averaged reflectance data products, and, (ii) using temporally-resolved functions to describe the variability in impurity distribution at daily time-scales. We conclude that the regional melt model performance may not be optimally improved by increased spatial resolution and the incorporation of sub-pixel heterogeneity, but instead, should focus on the temporal dynamics of bare-ice albedo.

The Determination of the Snow Optical Grain Diameter and Snowmelt Area on the Greenland Ice Sheet Using Spaceborne Optical Observations

“…Regarding the detection of surface melt, no observation currently allows bridging between point estimations at AWS sites and microwave melt flags at 12-25 km resolution [12,54]. We consequently compare point observations to gridded retrievals and let to future work bridging these scale gaps such as recently done for surface albedo measurements [94,95].…”

Precast Concrete Pavements of High Albedo to Achieve the Net “Zero-Emissions” Commitments

“…According to the law of conservation of energy, radiation of wavelength λ incident upon a material has either been transmitted across the material, has been reflected from its external surface or has been absorbed. The proportions of transmitted, reflected and absorbed energy can be expressed as ratios of the incident energy [1]. Accordingly, transmissivity (Ψ λ ), reflectivity (α λ ) and absorptivity (ζ λ ) are defined as dimensionless numbers between zero and the unity, according to Equation (1).…”

“…The proportions of transmitted, reflected and absorbed energy can be expressed as ratios of the incident energy [1]. Accordingly, transmissivity (Ψ λ ), reflectivity (α λ ) and absorptivity (ζ λ ) are defined as dimensionless numbers between zero and the unity, according to Equation (1). They are radiative properties of the material.…”