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Wouter Maes   Dr.  Institute, Department or Faculty Head 
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Wouter Maes published an article in February 2018.
Top co-authors See all
Kris Verheyen

254 shared publications

Alfredo R. Huete

142 shared publications

Hans Beeckman

92 shared publications

Hans Verbeeck

53 shared publications

Niko E. C. Verhoest

52 shared publications

Publication Record
Distribution of Articles published per year 
(2009 - 2018)
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Article 0 Reads 0 Citations Potential evaporation at eddy-covariance sites across the globe Wouter H. Maes, Pierre Gentine, Niko E. C. Verhoest, Diego G... Published: 12 February 2018
Hydrology and Earth System Sciences Discussions, doi: 10.5194/hess-2017-682
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Potential evaporation (Ep) is a crucial variable for hydrological forecast and in drought monitoring systems. However, multiple interpretations of Ep exist, and these reflect a diverse range of methods to calculate Ep. As such, a comparison of the performance of these methods against field observations in different global ecosystems is badly needed. In this study, we used eddy-covariance measurements from 107 sites of the FLUXNET2015 database, covering 11 different biomes, to parameterize and compare the main Ep methods and uncover their relative performance. For each site, we extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The evaporation measurements during these days were used as reference to validate the different methods to estimate Ep. Our results indicate that a simple radiation-driven method calibrated per biome consistently performed best, with a mean correlation of 0.93, an unbiased RMSE of 0.56 mm day−1, and a bias of −0.02 mm day−1 against in situ measurements of unstressed evaporation. A Priestley and Taylor method, calibrated per biome, performed just slightly worse, yet substantially and consistently better than more complex Penman, Penman-Monteith-based or temperature-based approaches. We show that the poor performance of Penman-Monteith based approaches relates largely to the fact that the unstressed stomatal conductance was assumed constant. Further analysis showed that the biome-specific parameters required for the simple radiation-driven methods are relatively constant per biome. This makes this simple radiation-driven method calibrated per biome a robust method that can be incorporated into models for improving our understanding of the impact of global warming on future global water use and demand, drought severity and ecosystem productivity.
CONFERENCE-ARTICLE 6 Reads 0 Citations Satellite observed solar induced fluorescence to monitor global plant stress Brianna Pagán, Brecht Martens, Wouter Maes, Diego Miralles Published: 10 November 2017
First International Electronic Conference on the Hydrological Cycle, doi: 10.3390/CHyCle-2017-04874
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Biophysical feedbacks on climate depend on plant responses to stress conditions. Yet current land surface models (LSMs) still treat plant stress rudimentarily, and typically assume the same sensitivity to soil moisture for all vegetation types. There is a need therefore to investigate the dynamics of vegetation stress at the global scale, both to further understand the effect of land feedbacks on climate, as well as to improve the representation of these processes in LSMs. Solar induced fluorescence (SIF) is a subtle glow of energy emitted by vegetation during photosynthesis. Recently, satellite observations of SIF have been shown to closely mimic the spatiotemporal variability of photosynthesis. Given the nexus between photosynthesis and transpiration through the opening and closing of stomata, a link between SIF observations and evaporation can be hypothesised. Here, we introduce a novel index of evaporative stress (i.e. the ratio of actual to potential evaporation) based on satellite SIF observations, and we compare it to the estimates of evaporative stress by various LSMs from the Earth2Observe database (i.e. JULES, HTESSEL, ORCHIDEE). Results of validations against in situ evaporative stress – calculated from the FLUXNET2015 eddy-covariance archive – indicate that our SIF-based stress index outperforms the estimates of the LSMs across the majority of sites, with the exception of regions with sparse vegetation in which bare soil evaporation dominates the flux of vapour from land to atmosphere. SIF derived stress greatly outperforms over densely forested regions, and shows a high skill to capture leaf-out periods. Overall, this novel SIF application provides improvements for large-scale estimates of transpiration and can be used to further understand vegetation–atmosphere feedbacks from different ecosystem types. Furthermore, the implications of this research are relevant to (a) the hydrology and climate modelling communities, given the opportunity to utilise our SIF-based evaporative stress to benchmark model representation of the land control over the atmospheric demand for water, and (b) the remote sensing community, that will see how an observation originally intended for the study of the carbon cycle is valorized through its application to study water cycle dynamics as well.

Article 0 Reads 0 Citations Optimizing the Processing of UAV-Based Thermal Imagery Wouter H. Maes, Alfredo R. Huete, Kathy Steppe Published: 12 May 2017
Remote Sensing, doi: 10.3390/rs9050476
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The current standard procedure for aligning thermal imagery with structure-from-motion (SfM) software uses GPS logger data for the initial image location. As input data, all thermal images of the flight are rescaled to cover the same dynamic scale range, but they are not corrected for changes in meteorological conditions during the flight. This standard procedure can give poor results, particularly in datasets with very low contrast between and within images or when mapping very complex 3D structures. To overcome this, three alignment procedures were introduced and tested: camera pre-calibration, correction of thermal imagery for small changes in air temperature, and improved estimation of the initial image position by making use of the alignment of RGB (visual) images. These improvements were tested and evaluated in an agricultural (low temperature contrast data) and an afforestation (complex 3D structure) dataset. In both datasets, the standard alignment procedure failed to align the images properly, either by resulting in point clouds with several gaps (images that were not aligned) or with unrealistic 3D structure. Using initial thermal camera positions derived from RGB image alignment significantly improved thermal image alignment in all datasets. Air temperature correction had a small yet positive impact on image alignment in the low-contrast agricultural dataset, but a minor effect in the afforestation area. The effect of camera calibration on the alignment was limited in both datasets. Still, in both datasets, the combination of all three procedures significantly improved the alignment, in terms of number of aligned images and of alignment quality.
Article 0 Reads 2 Citations Plant measurements on African tropical Maesopsis eminii seedlings contradict pioneering water use behaviour Jackie Epila, Wouter H. Maes, Hans Verbeeck, Janne Van Camp,... Published: 01 March 2017
Environmental and Experimental Botany, doi: 10.1016/j.envexpbot.2016.12.006
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Article 0 Reads 2 Citations Capacitive water release and internal leaf water relocation delay drought-induced cavitation in African Maesopsis eminii Jackie Epila, Niels J.F. De Baerdemaeker, Lidewei L. Vergeyn... Published: 05 January 2017
Tree Physiology, doi: 10.1093/treephys/tpw128
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Article 0 Reads 1 Citation A new wet reference target method for continuous infrared thermography of vegetations Wouter H. Maes, Annelies Baert, Alfredo R. Huete, Peter E.H.... Published: 01 October 2016
Agricultural and Forest Meteorology, doi: 10.1016/j.agrformet.2016.05.021
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