Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
The Cryosphere, 11, 1575-1589, 2017
https://doi.org/10.5194/tc-11-1575-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
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 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.

Citation: Burkhart, J. F., Kylling, A., Schaaf, C. B., Wang, Z., Bogren, W., Storvold, R., Solbø, S., Pedersen, C. A., and Gerland, S.: Unmanned aerial system nadir reflectance and MODIS nadir BRDF-adjusted surface reflectances intercompared over Greenland, The Cryosphere, 11, 1575-1589, https://doi.org/10.5194/tc-11-1575-2017, 2017.
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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.
We present the first use of spectrometer measurements from a drone to assess reflectance and...
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