Articles | Volume 11, issue 4
The Cryosphere, 11, 1575–1589, 2017
The Cryosphere, 11, 1575–1589, 2017

Research article 04 Jul 2017

Research article | 04 Jul 2017

Unmanned aerial system nadir reflectance and MODIS nadir BRDF-adjusted surface reflectances intercompared over Greenland

John Faulkner Burkhart1,2, Arve Kylling3, Crystal B. Schaaf4, Zhuosen Wang5,6, Wiley Bogren7, Rune Storvold8, Stian Solbø8, Christina A. Pedersen9, and Sebastian Gerland9 John Faulkner Burkhart et al.
  • 1Department of Geosciences, University of Oslo, Oslo, Norway
  • 2University of California, Merced, CA, USA
  • 3Norwegian Institute for Air Research, Kjeller, Norway
  • 4School for the Environment, University of Massachusetts Boston, Boston, MA, USA
  • 5NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 6Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA
  • 7U.S. Geological Survey, Flagstaff, AZ, USA
  • 8Norut-Northern Research Institute, Tromsø, Norway
  • 9Norwegian Polar Institute, Fram Centre, Tromsø, Norway

Abstract. Albedo is a fundamental parameter in earth sciences, and many analyses utilize the Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF)/albedo (MCD43) algorithms. While derivative albedo products have been evaluated over Greenland, we present a novel, direct comparison with nadir surface reflectance collected from an unmanned aerial system (UAS). The UAS was flown from Summit, Greenland, on 210 km transects coincident with the MODIS sensor overpass on board the Aqua and Terra satellites on 5 and 6 August 2010. Clear-sky acquisitions were available from the overpasses within 2 h of the UAS flights. The UAS was equipped with upward- and downward-looking spectrometers (300–920 nm) with a spectral resolution of 10 nm, allowing for direct integration into the MODIS bands 1, 3, and 4. The data provide a unique opportunity to directly compare UAS nadir reflectance with the MODIS nadir BRDF-adjusted surface reflectance (NBAR) products. The data show UAS measurements are slightly higher than the MODIS NBARs for all bands but agree within their stated uncertainties. Differences in variability are observed as expected due to different footprints of the platforms. The UAS data demonstrate potentially large sub-pixel variability of MODIS reflectance products and the potential to explore this variability using the UAS as a platform. It is also found that, even at the low elevations flown typically by a UAS, reflectance measurements may be influenced by haze if present at and/or below the flight altitude of the UAS. This impact could explain some differences between data from the two platforms and should be considered in any use of airborne platforms.

Short summary
We present the first use of spectrometer measurements from a drone to assess reflectance and albedo over the Greenland Ice Sheet. In order to measure albedo – a critical parameter in the earth's energy balance – a drone was flown along 200 km transects coincident with Terra and Aqua satellites flying MODIS. We present a direct comparison of UAV-measured reflectance with satellite data over Greenland and provide a new method to study cryospheric surfaces using UAV with spectral instruments.