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  • 1
    Publication Date: 2018-02-07
    Description: Beta diversity (β) is used in biogeography, ecology, and conservation to assess the heterogeneity of local communities. Ideally, researchers could include sensitivity to error in the list of reasons to choose a β index. However, only numerical undersampling has been rigorously studied. This study compared multiple β indices to determine which are most robust to geographic undersampling, numerical undersampling, and taxonomic error using simulated landscapes. For these landscapes, eight β indices were chosen to represent families of β and used to measure real and errant data. Six indices used both presence–absence and abundance data, while two more used only abundance data. Six of the abundance-based indices had adjusted versions for individual undersampling, and these versions were also evaluated (total = 14 indices). Presence–absence- and abundance-based indices were comparable in sensitivity to total method error. Numerical undersampling and taxonomic error generally caused more error in β than randomly distributed geographic undersampling. Among presence–absence-based indices, Jaccard's dissimilarity was the most robust to error overall, while β -3 was the most robust among narrow-sense measures. Among abundance-based indices, Bray-Curtis and BD TOTAL were the most robust to error. Some commonly used β indices (e.g., Sorensen, Simpson) are relatively unreliable given errors of taxonomy or numerical undersampling. Future studies of β should focus on using more robust indices (Jaccard, Bray-Curtis, BD TOTAL ), and past studies based on error-sensitive indices should be considered with caution. Studies of β should emphasize adequate numerical sampling and taxonomic accuracy to minimize errors in β.
    Electronic ISSN: 2150-8925
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 2
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    IEEE
    In:  EPIC3Geoscience and Remote Sensing, IEEE Transactions, IEEE, 99, pp. 1-13, ISSN: 0196-2892
    Publication Date: 2019-07-17
    Description: Considering the sea ice decline in the Arctic during the last decades, polynyas are of high research interest since these features are core areas of new ice formation. The determination of ice formation requires accurate retrieval of polynya area and thin-ice thickness (TIT) distribution within the polynya. We use an established energy balance model to derive TITs with MODIS ice surface temperatures $(T_{s})$ and NCEP/DOE Reanalysis II in the Laptev Sea for two winter seasons. Improvements of the algorithm mainly concern the implementation of an iterative approach to calculate the atmospheric flux components taking the atmospheric stratification into account. Furthermore, a sensitivity study is performed to analyze the errors of the ice thickness. The results are the following: 1) 2-m air temperatures $(T_{a})$ and $T_{s}$ have the highest impact on the retrieved ice thickness; 2) an overestimation of $T_{a}$ yields smaller ice thickness errors as an underestimation of $T_{a}$; 3) NCEP $T_{a}$ shows often a warm bias; and 4) the mean absolute error for ice thicknesses up to 20 cm is $pm$4.7 cm. Based on these results, we conclude that, despite the shortcomings of the NCEP data (coarse spatial resolution and no polynyas), this data set is appropriate in combination with MODIS $T_{s}$ for the retrieval of TITs up to 20 cm in the Laptev Sea region. The TIT algorithm can be applied to other polynya regions and to past and future time periods. Our TIT product is a valuable data set for verification of other model and remote sensing ice thickness data.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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