000			03415 am a22002773u 4500
042			_adc
100	1	0	_aDöpper, Veronika _eauthor _91299
700	1	0	_aRocha, Alby Duarte _eauthor _91300
700	1	0	_aBerger, Katja _eauthor _91301
700	1	0	_aGränzig, Tobias _eauthor _91302
700	1	0	_aVerrelst, Jochem _eauthor
700	1	0	_aKleinschmit, Birgit _eauthor _91304
700	1	0	_aFörster, Michael _eauthor _91305
245	0	0	_aEstimating soil moisture content under grassland with hyperspectral data using radiative transfer modelling and machine learning
260			_c2022-05-18.
500			_a/pmc/articles/PMC7613374/
500			_a/pubmed/36093264
520			_aThe monitoring of soil moisture content (SMC) at very high spatial resolution (<10m) using unmanned aerial systems (UAS) is of high interest for precision agriculture and the validation of large scale SMC products. Data-driven approaches are the most common method to retrieve SMC with UAS-borne data at water limited sites over non-disturbed agricultural crops. A major disadvantage of data-driven algorithms is the limited transferability in space and time and the need of a high number of ground reference samples. Physically-based approaches are less dependent on the amount of samples and are transferable in space and time. This study explores the potential of (1) a hybrid method targeting the soil brightness factor of the PROSAIL model using a variational heteroscedastic Gaussian Processes regression (VHGPR) algorithm, and (2) a data-driven method employing VHGPR for the retrieval of SMC over three grassland sites based on UAS-borne VIS-NIR (399-1001 nm) hyperspectral data. The sites were managed by mowing (Fendt), grazing (Grosses Bruch) and irrigation (Marquardt). With these distinct local pre-conditions we aimed to identify factors that favor and limit the retrieval of SMC. The hybrid approach presented encouraging results in Marquardt (RMSE = 1.5 Vol_%, R(2) = 0.2). At the permanent grassland sites (Fendt, Grosses Bruch) the thatch layer jeopardized the application of the hybrid model. We identified the complex canopy structure of grassland as the main factor impacting the hybrid SMC retrieval. The data-driven approach showed high accuracy for Fendt (R(2) = 0.84, RMSE = 8.66) and Marquardt (R(2) = 0.4, RMSE = 10.52). All data-driven models build on the LAI-SMC relationship. However, this relationship was hampered by mowing (Fendt), leading to a lack of transferability in time. The alteration of plant traits by grazing prevents finding a relationship with SMC in Grosses Bruch. In Marquardt, we identified the timelag between changes in SMC and plant response as the main reason of decrease in model accuracy. Yet, the model performance is accurate in undisturbed and water-limited areas (Marquardt). The analysis points to challenges that need to be tackled in future research and opens the discussion for the development of robust models to retrieve high resolution SMC from UAS-borne remote sensing observations.
540			_a
540			_ahttps://creativecommons.org/licenses/by-nc-nd/4.0/This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/
546			_aen
690			_aArticle
655	7		_aText _2local
786	0		_nInt J Appl Earth Obs Geoinf
856	4	1	_uhttp://dx.doi.org/10.1016/j.jag.2022.102817 _zConnect to this object online.
999			_c1638 _d1638