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- Alikas, Krista, et al.
(författare)
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Robust remote sensing algorithms to derive the diffuse attenuation coefficient for lakes and coastal waters
- 2015
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Ingår i: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 13:8, s. 402-415
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Tidskriftsartikel (refereegranskat)abstract
- In this study, empirical and semianalytical algorithms are developed and compared for optically complex waters to retrieve the diffuse attenuation coefficient of downwelling irradiance (Kd(lambda)) from satellite data. In the first approach, a band ratio algorithm was used. Various sets of MERIS band ratios were tested to achieve the best estimates for K-d(490) based on the in situ dataset which was measured in Nordic lakes (oligotrophic to eutrophic conditions). In the second approach, K-d(490) was expressed as a function of inherent optical properties which were retrieved from MERIS standard products. The algorithms from both approaches were tested against an independent data set and validated in optically complex coastal waters in the Baltic Sea and in Nordic lakes with high concentrations of coloured dissolved organic matter (0.3 < a(cdom)(442) m(-1) < 4.5), chlorophyll a (Chl a) (0.7< C-Chl a(mg m(-3))< 67.5) and total suspended matter (TSM) (0.5 < C-TSM(g m(-3)) < 26.4). MERIS-derived K-d(490) values showed reliable estimates in case of both methods. The results indicate that for band ratio algorithms, the root mean square error (RMSE) decreases and the coefficient of determination (R-2) increases when using longer wavelengths in the visible spectrum as a reference band. It was found that the best estimates were retrieved from MERIS data when using the ratio of R-rs(490)/R-rs(709) for coastal waters (K-d(490) < 2.5 m(-1)) and the ratio R-rs(560)/R-rs(709) for more turbid inland waters (Kd(490) > 2.5 m(-1)). As a result, a combined band ratio algorithm was developed, which provides a promising approach R-2 = 0.98, RMSE= 17%, N = 34, p < 0.05) for estimating K-d(490) over a wide range of values (0.3-6.1 m(-1)).
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| 4. |
- van Swaay, Chris A.M., et al.
(författare)
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The European Butterfly Indicator for Grassland species: 1990-2015
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents the sixth version of the European Grassland Butterfly Indicator, one of the EU biodiversity indicators of the European Environment Agency.The indicator is based on more than 9200 transects in national Butterfly Monitoring Schemes covering 22 countries across Europe, most of them active in the European Union. In 2015, counts were made in more than 4500 transects.Butterflies represent the largest animal group (insects), highly included in food webs, having a high impact on ecosystem services and stability. This report does not represent only the patrimonial conservation of some species, but indicates the changes in biodiversity on grasslands and discusses underlying causes.Fluctuations in numbers between years are typical features of butterfly populations. The assessment of change istherefore made on an analysis of the underlying trend.Indicators were produced on EU, European (EU plus Norway and Switzerland) and pan-European level (including Ukraine, Russia and Armenia).The underlying analysis of the indicator shows that since 1990, grassland butterfly abundance has declined by 30%.The rate of loss has slowed in the last 5-10 years. Part of this slowing down might be caused by climate warming, as this favours cold-blooded animals like butterflies, thus masking the effects of intensification. In parts of Western Europe butterfly numbers outside nature reserves have come to an absolute minimum, meaning it is unlikely for the indicator to further drop.The priority now is to halt further losses and support recovery. This can only come about with greater protection and more sustainable management of semi-natural grassland.
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