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| Titel |
Influence of local surface albedo variability and ice crystal shape on passive remote sensing of thin cirrus |
| VerfasserIn |
C. Fricke, A. Ehrlich, E. Jäkel, B. Bohn, M. Wirth, M. Wendisch |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 4 ; Nr. 14, no. 4 (2014-02-20), S.1943-1958 |
| Datensatznummer |
250118416
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| Publikation (Nr.) |
 copernicus.org/acp-14-1943-2014.pdf |
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| Zusammenfassung |
| Airborne measurements of solar spectral radiance reflected by cirrus are
performed with the HALO-Solar Radiation (HALO-SR) instrument onboard the High
Altitude and Long Range Research Aircraft (HALO) in November 2010. The data
are used to quantify the influence of surface albedo variability on the
retrieval of cirrus optical thickness and crystal effective radius. The
applied retrieval of cirrus optical properties is based on a standard two-wavelength approach utilizing measured and simulated reflected radiance in
the visible and near-infrared spectral region. Frequency distributions of the
surface albedos from Moderate resolution Imaging Spectroradiometer (MODIS)
satellite observations are used to compile surface-albedo-dependent lookup
tables of reflected radiance. For each assumed surface albedo the cirrus
optical thickness and effective crystal radius are retrieved as a function of
the assumed surface albedo. The results for the cirrus optical thickness are
compared to measurements from the High Spectral Resolution Lidar (HSRL). The
uncertainty in cirrus optical thickness due to local variability of surface
albedo in the specific case study investigated here is below 0.1 and thus
less than that caused by the measurement uncertainty of both instruments. It
is concluded that for the retrieval of cirrus optical thickness the surface
albedo variability is negligible. However, for the retrieval of crystal effective
radius, the surface albedo variability is of major importance,
introducing uncertainties up to 50%. Furthermore, the influence of the
bidirectional reflectance distribution function (BRDF) on the retrieval of
crystal effective radius was investigated and quantified with uncertainties
below 10%, which ranges below the uncertainty caused by the surface albedo
variability. The comparison with the independent lidar data allowed for
investigation of the role of the crystal shape in the retrieval. It is found that
if assuming aggregate ice crystals, the HSRL observations fit best with the
retrieved optical thickness from HALO-SR. |
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