1. Monitoring of wheat crops using the backscattering coefficient and the interferometric coherence derived from Sentinel-1 in semi-arid areas
- Author
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Jamal Ezzahar, El houssaine Bouras, Said Khabba, Safa Bousbih, Mehrez Zribi, Pierre-Louis Frison, Nadia Ouaadi, Lionel Jarlan, Laboratoire de Mécanique des Fluides et Energétique (LMFE), Faculté des Sciences Semlalia Marrakech, Centre d'études spatiales de la biosphère (CESBIO), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Université Cadi Ayyad [Marrakech] (UCA), Mohammed VI Polytechnic University [Marocco] (UM6P), Institut National Agronomique de Tunisie (INAT), Laboratoire des Sciences et Technologies de l'Information Géographique (LaSTIG), École nationale des sciences géographiques (ENSG), Institut National de l'Information Géographique et Forestière [IGN] (IGN)-Institut National de l'Information Géographique et Forestière [IGN] (IGN), Faculté des Sciences Semlalia [Marrakech], Université Cadi Ayyad [Marrakech] (UCA)-Université Cadi Ayyad [Marrakech] (UCA), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), and Université Mohammed VI Polytechnique [Ben Guerir] (UM6P)
- Subjects
Canopy ,Interferometric coherence ,010504 meteorology & atmospheric sciences ,0208 environmental biotechnology ,Soil Science ,Growing season ,Soil science ,02 engineering and technology ,01 natural sciences ,Backscattering coefficient ,law.invention ,law ,Semi-arid region ,Computers in Earth Sciences ,Leaf area index ,Radar ,C-band ,Water content ,0105 earth and related environmental sciences ,Remote sensing ,2. Zero hunger ,Geology ,15. Life on land ,Surface soil moisture ,Arid ,020801 environmental engineering ,Winter wheat ,Hydric soil ,[SDE]Environmental Sciences ,Sentinel-1 ,Environmental science - Abstract
Radar data at C-band has shown great potential for the monitoring of soil and canopy hydric conditions of wheat crops. In this study, the C-band Sentinel-1 time series including the backscattering coefficients u(0) at VV and VH polarization, the polarization ratio (PR) and the interferometric coherence p are first analyzed with the support of experimental data gathered on three plots of irrigated winter wheat located in the Haouz plain in the center of Morocco covering five growing seasons. The results showed that p and PR are tightly related to the canopy development. p is also sensitive to soil preparation. By contrast, u(0) was found to be widely linked to changes in surface soil moisture (SSM) during the first growth stages when Leaf Area Index remains moderate (< 1.5 m(2)/m(2)). In addition, drastic changes in the crop geometry associated to heading had a strong impact on the C-band u(0), in particular for VH polarization. The coupled water cloud and Oh models (WCM) were then calibrated and validated on the study sites. The comparison between the predicted and observed u0 yielded a root mean square error (RMSE) values ranging from 1.50 dB to 2.02 dB for VV and between 1.74 dB to 2.52 dB for VH with significant differences occurring in the second part of the season after heading. Finally, new approaches based on the inversion of the WCM for SSM retrieval over wheat fields were proposed using Sentinel-1 radar data only. To this objective, the dry above-ground biomass (AGB) and the vegetation water content (VWC) were retrieved from the interferometric coherence and the PR. The relationships were then used as the vegetation descriptor in the WCM. The best retrieval results were obtained using the relationship between pVV and the AGB (R and RMSE of 0.82, 0.05 m3/m3 respectively and no bias). The new retrieval approaches were then applied to a large database covering a rainfed field in Morocco and 18 plots of rainfed and irrigated wheat of the Kairouan plain (Tunisia) and compared to other classical techniques of SSM retrieval including simple linear relationships between SSM and u0. The method based on the WCM and the pVV-AGB relationships also provided with slightly better results than the others on the validation database (r = 0.75, RMSE = 0.06 m(3)/m(3) and bias = 0.01 m(3)/m(3) over the 18 plots of Tunisia) but the simple linear relationships performed also reasonably well (r = 0.62, RMSE = 0.07, bias = -0.01 in Tunisia for instance). This study opens perspectives for high resolution soil moisture mapping from Sentinel-1 data over south Mediterranean wheat crops and in fine, for irrigation scheduling and retrieval through the assimilation of these new products in an evapotranspiration model.
- Published
- 2020