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| Home > Publications database > Quantitative evaluation of airborne maps of solar-induced fluorescence to determine the performance of different retrieval methods |
| Master Thesis | FZJ-2019-04120 |
; ;
2018
Please use a persistent id in citations: http://hdl.handle.net/2128/22594
Abstract: When plants absorb light, not all energy is converted by photosynthesis, but excessenergy is released as heat or emitted as Solar-induced chlorophyll Fluorescence ( F ).This signal, related to the photosynthetic efficiency of plants, has been intensivelystudied and measured from ground level up to global scale. However, retrieving ( F )from airborne data is challenging because scattering effects and other atmosphericinfluences must be taken into account here. A common method of testing thereliability of a F product (in this study airborne F maps) is the comparison to groundtruth data where the atmosphere can be neglected. In this work another possibilityof assessing the quality of the airborne F maps is tested, which does not requireground reference measurements. For this purpose we have developed so-called ’qualitycriteria’, which should help to find errors and artifacts that have arisen during Fretrieval. This method was used to test the quality of the airborne F maps of 2016campaign retrieved from iFLD and SFM.By applying the quality criteria, clear differences in the performance of two retrievalswere found. Although it was shown that both retrievals performed well in F 760retrieval, even at places with changes from vegetated to non-vegetated sites onpixel scale, iFLD was more robust for retrieving correct absolute values for F 760 andF 687 , while SFM performed less accurate in this term, over- and underestimating Fvalues. Furthermore, previously reported problems with image pre-processing (decon-volution for correcting PSF) of SFM became clear here. This was causing strongartifacts in F 687 retrievals from SFM. However, SFM proved to be the more suitablemethod for identifying small differences on pixel scale. Moreover, this algorithmdid not show systematic variations over entire flight lines as observed by the useof iFLD. The physically-based approach of atmospheric correction used with SFMthus provided more interference-free F maps than the semi-empirical correction usingnon-fluorescent surfaces used in iFLD retrieval. Testing F retrievals on vegetationunder different illumination conditions showed the necessity to calculate F yield forquantification of photosynthesis rates.The application of the proposed quality features proved to be a valuable tool forassessing the performance of F retrieval on airborne maps. This is why we propose touse the quality criteria even when sufficient ground references are available, becauseeven if they do not replace ground-truth data, they provide important additionalinformation about the quality of the F product of the respective retrieval method.
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