Unmanned aerial system nadir reflectance and MODIS nadir BRDF-adjusted surface reflectances intercompared over Greenland
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 presen...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-07-01
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| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/11/1575/2017/tc-11-1575-2017.pdf |
| Summary: | 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. |
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| ISSN: | 1994-0416 1994-0424 |