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In the Mediterranean areas there is an increase in the dependence of agriculture which leads to more competition on the use of water resources. Surveys conducted by the UMR EMMAH in the Ouvèze watershed in northern Vaucluse have shown a great variability in water management of orchards and in the agricultural practices. Some farmers start irrigation according to the phenological stages (after the flowering for example). Irrigation techniques can be : drip, underground irrigation, or micro-sprinklers... Restrictions are more and more frequent in summer.  In order to better preserve the available resources, it is important to develop methods to estimate the water needs of orchards, taking into account current agricultural practices, in order to provide the right quantity at the right time

Remote sensing, combined with field observations, can provide useful information on large areas, on the vegetation development and on agricultural practices. New products providing the soil surface moisture (S²MP) from the Sentinel 1 mission are now routinely delivered by the THEIA platform (https://www.theia-land.fr/product/humidite-du-sol-a-tres-haute-resolution-spatiale/) over the PACA region. Their spatial (field scale) and temporal resolutions (every 6 days) allow to have information well suitable for monitoring the hydric status of crops  declared to the CAP. Vines and orchards are not considered in these new products. It is therefore necessary to evaluate other data to characterize the water status of orchards.

Since 2021, UMR EMMAH with collaboration with Matthew McCabe's team from KAUST University in Saudi Arabia has installed various in situ sensors on several cherry trees in the northern Vaucluse area. Soil moisture measurements were recorded at different depths on the row and inter-row in 5 orchards with different irrigation practices. Observations on the phenological stages are  done in association with hemispherical photos to monitor the evolution of the canopy and to estimate the biophysical variables characterizing the vegetation strucure. Sentinel 1 and 2 images were downloaded over this area and various spectral indices were calculated at the scale of each plot.  Fine resolution images, Pleaides, Skysat and UAV images were also acquired at some dates on some sectors of the studied watershed.

The proposed work includes several stages:

- First, the THIEA S²MP products will be evaluated by comparing them with in situ soil moisture measurements made on different plots of the study sites. Grasslands, cereals and fallow lands have been monitored by TDR measurements since 2021. The expected outputs are to evaluate these products and give their application limit.

- In parallel, the average values of the radar signals from the Sentinel 1 images obtained on the orchard plots monitored by continuous moisture measurements will be analyzed according to the irrigation practices. A first simplified model has been developed based on a simple linear model combining Sentinel 2 NDVI and Sentinel 1 VV signals. This model will be analyzed with the recent 2022 measurements. A literature review will be conducted to assess whether another model can be proposed to monitor moisture variations of orchards.

- The second part of the work will focus on the analysis of spectral, spatial and temporal complementarities of the data acquired at very high resolution to access descriptive variables of agricultural practices in orchards.  PLEIADES, SKYSAT and UAV images will be used. Multi-resolution data fusion methods will be implemented to derive characteristics on tree density and inter-row management.

- The last step will be to compare different modeling approaches to reproduce the hydric functioning of orchards. Validation will be done at the plot scale where measurements are available. We plan to estimate the water needs at the watershed scale. The data provided by the ASA Ouvèze Ventoux (water manager at the basin scale), will be used to evaluate the simulated regional outputs.

The post-doctoral student will participate in the image processing and also in field experiments (installation of sensors, soil water measurements or plant parameters).

Skills required

- Skills and experiences in remote sensing (radar and optical) and modeling water transfer in the soil-plant-atmosphere continuum,

Ability to collaborate with a multidisciplinary team of scientists, and to write publications in English.

To postulate please send a cover letter, a complete CV, with a list of publications, the names and addresses (including phone and email) of two referees familiar with your professional qualifications and work experience, and relevant certificates.

The co-supervision will be ensured by Claude Doussan (CR) and Dominique Courault (DR2),  the SWIFT and DREAM teams of the UMR 1114 INRA-UAPV " EMMAH ", Site Agroparc, 84914 Avignon cedex 9 - 0432722386

Claude.doussan@inrae.fr; dominique.courault@inrae.fr (0432722385)

Duration: 12 months as soon as possible with possible extension of 6 months

Yearly salary: ~57600€