AUTHOR=Ryan Jonathan C. , Hubbard Alun , Box Jason E. , Brough Stephen , Cameron Karen , Cook Joseph M. , Cooper Matthew , Doyle Samuel H. , Edwards Arwyn , Holt Tom , Irvine-Fynn Tristram , Jones Christine , Pitcher Lincoln H. , Rennermalm Asa K. , Smith Laurence C. , Stibal Marek , Snooke Neal 

TITLE=Derivation of High Spatial Resolution Albedo from UAV Digital Imagery: Application over the Greenland Ice Sheet

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 5 - 2017

YEAR=2017

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2017.00040

DOI=10.3389/feart.2017.00040

ISSN=2296-6463

ABSTRACT=Measurements of albedo are a prerequisite for modelling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimetre resolution albedo products with accuracies of 5% using consumer-grade digital camera and unmanned aerial vehicle (UAV) technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique will likely become increasingly attractive in field studies and used in a wide range of applications for high temporal and spatial resolution surface mapping of debris, dust, cryoconite and bioalbedo and for directly constraining surface energy balance models.