Contribution of L-band remote sensing to the study of the hydric state of the vegetation and biomass monitoring

Application deadline: 2021/6/8
Position: PhD fellowship
Duration : Three years
Location : Centre d’Etude Spatial de la BIOsphère, Toulouse.

Scientific background

Large-scale monitoring of vegetation properties is crucial to understand water, carbon and energy cycles. It is important to understand the vegetation response to climate and extreme events such as droughts, which are expected to become more frequent and more intense under climate change. In order to assess the evolution of the vegetation at global scale, several approaches can be used, among them optical indices or synthetic aperture radar (SAR) to estimate above ground biomass (AGB). However, optical indices are only sensitive to the green vegetation and only to the upper layer of the canopy in densely vegetated regions. In addition, they are not directly related to the vegetation water content. In contrast, the thermal emission arising from the Earth surface at microwave frequencies depends on soil characteristics such as soil temperature, soil roughness and soil moisture content which different relative contributions at different frequencies. It also depends on the vegetation water content (VWC) and structure, therefore, passive microwave radiometry is a promising tool for monitoring the vegetation hydric state and AGB on a global scale, in particular at L-band. The optical depth at this frequency, mainly due to the presence of water molecules within the vegetation and therefore known as L-band Vegetation Optical Depth (L-VOD), has been shown to be highly sensitivity to AGB (Rodriguez-Fernandez et al. 2018, Mialon et al. 2020). The frequent revisit of satellites such as European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS), 1-3 days, makes possible to monitor changes in the VWC and the evolution of large scale carbon stocks, adding a temporal dimension to higher spatial resolution AGB maps produced with SAR sensors. The objective of this PhD work is to twofold. First, L-band brightness temperatures and L-VOD will be analyzed in comparison to other vegetation indices (Normalized Difference Vegetation Index, Leaf Area Index, Solar Induced Fluorescence, …) and VOD at higher microwave frequencies. The study will be done at different temporal and spatial scales to understand the contribution of short-term variations of VWC and the long-term AGB evolution. Secondly, methods to retrieve the AGB from L-band observations will be investigated, in particular using data driven machine learning approaches trained on in situ plots estimations of AGB.

Expected profile of the applicants

The candidates should have have a Master degree and notions of geophysics and remote sensing and possibly applied mathematics (machine learning). They should be familiar with data analysis in Python/Matlab in a Unix environment. Good oral and writing skills in English.

Work Context

The PhD fellow will be based at the CESBIO facilities in Toulouse but he/she will work in collaboration with other international scientists and ESA. Short trips abroad are expected. The CESBIO (Centre d’Etudes Spatiales de la Biosphère) is a joint research unit of Université Toulouse 3 Paul Sabatier (UT3), the Centre National d’Etudes Spatiales (CNES), the Centre National de la Recherche Scientifique (CNRS), the Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE) and the Institut de Recherche pour le Développement (IRD). The laboratory aims at doing research in the domains of observation and modeling of the continental surfaces, addresses the interface between physical and biological sciences and participates in the specification of space missions and analysis of remotely sensed data to improve understanding of continental biosphere dynamics and functioning at various temporal and spatial scales. CESBIO hosts the PIs of two European Space Agency (ESA) satellite missions (SMOS and Biomass missions) and of the French-Israeli Venus satellite. The CESBIO is the lead «Expert Support Laboratory» for land applications with SMOS for ESA and «Expertise Center»for the SMOS French ground segment, the CATDS (Centre Aval de Traitement de Données SMOS).
The PhD candidate will join the SMOS and Biomass groups of the Observation Systems team at CESBIO and will work in close relation with the European Space Agency (ESA) and the Centre National d’Études Spatiales (CNES).


Inquires should be sent by e-mail to Nemesio Rodriguez  and Arnaud Mialon ( The application deadline at Toulouse 3 University is June 8th. More information at the University PhD program: here



•Fan, L., Wigneron, J. P., Ciais, P., Chave, J., Brandt, M., Fensholt, Mialon, A., Rodríguez-Fernández, N, Kerr Y, Tian F., Peñuelas, J. (2019). Satellite-observed pantropical carbon dynamics. Nature plants, 5(9), 944-951. https :// 019-0478-9

•Mialon, A. ; Rodríguez-Fernández, N.J. ; Santoro, M. ; Saatchi, S. ; Mermoz, S. ; Bousquet, E. ; Kerr, Y.H. Evaluation of the Sensitivity of SMOS L-VOD to Forest Above-Ground Biomass at Global Scale. Remote Sens. 2020, 12, 1450.

•Rodríguez-Fernández, N. J., Mialon, A., Mermoz, S., Bouvet, A., Richaume, P., Al Bitar, A., Al-Yaari, A., Brandt, M., Kaminski, T., Le Toan, T., Kerr, Y. H., and Wigneron, J.-P. : The high sensitivity of SMOS L-Band vegetation optical depth to biomass, (2018) Biogeosciences, 15, 4627-4645, https ://

•Scholze, M., Kaminski, T., Knorr, W.,Voßbeck, M., Wu, M., Ferrazzoli, P., Y. Kerr, Mialon, Richaume, Rodríguez-Fernández, Vittucci, Wigneron, Mecklenburg, Drusch (2019). Mean European carbonsink over 2010-2015 estimated by simultaneous assimi- lation of atmospheric CO2, soil moisture, and vegetation optical depth. Geophysical Research Letters,46, https ://