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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 8
Atmos. Meas. Tech., 8, 3163–3175, 2015
https://doi.org/10.5194/amt-8-3163-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 8, 3163–3175, 2015
https://doi.org/10.5194/amt-8-3163-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Aug 2015

Research article | 10 Aug 2015

Accounting for the effects of sastrugi in the CERES clear-sky Antarctic shortwave angular distribution models

J. Corbett1 and W. Su2 J. Corbett and W. Su
  • 1Science Systems and Applications, Inc., NASA Langley Research Center, Mail Stop 420, Hampton, Virginia 23681-2199, USA
  • 2NASA Langley Research Center, Mail Stop 420, Hampton, Virginia 23681-2199, USA

Abstract. The Cloud and the Earth's Radiant Energy System (CERES) instruments on NASA's Terra, Aqua and Soumi NPP satellites are used to provide a long-term measurement of Earth's energy budget. To accomplish this, the radiances measured by the instruments must be inverted to fluxes by the use of a scene-type-dependent angular distribution model (ADM). For permanent snow scenes over Antarctica, shortwave (SW) ADMs are created by compositing radiance measurements over the full viewing zenith and azimuth range. However, the presence of small-scale wind blown roughness features called sastrugi cause the BRDF (bidirectional reflectance distribution function) of the snow to vary significantly based upon the solar azimuth angle and location. This can result in monthly regional biases between −12 and 7.5 Wm−2 in the inverted TOA (top-of-atmosphere) SW flux. The bias is assessed by comparing the CERES shortwave fluxes derived from nadir observations with those from all viewing zenith angles, as the sastrugi affect fluxes inverted from the oblique viewing angles more than for the nadir viewing angles. In this paper we further describe the clear-sky Antarctic ADMs from Su et al. (2015). These ADMs account for the sastrugi effect by using measurements from the Multi-Angle Imaging Spectro-Radiometer (MISR) instrument to derive statistical relationships between radiance from different viewing angles. We show here that these ADMs reduce the bias and artifacts in the CERES SW flux caused by sastrugi, both locally and Antarctic-wide. The regional monthly biases from sastrugi are reduced to between −5 and 7 Wm−2, and the monthly-mean biases over Antarctica are reduced by up to 0.64 Wm−2, a decrease of 74 %. These improved ADMs are used as part of the Edition 4 CERES SSF (Single Scanner Footprint) data.

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Short summary
Sastrugi are surface roughness elements on Antarctica that modify the anisotropy of reflected shortwave solar radiation. This can create biases in the shortwave flux inverted from radiances measured by the satellite-borne Clouds and the Earths's Radiant Energy System instruments. Here we provide a detailed description of the methodology we use to account for their effect and examples of the reduction in bias from using our new method.
Sastrugi are surface roughness elements on Antarctica that modify the anisotropy of reflected...
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