## 5 Conclusions  
Based on a dense dataset collected on a specific experimental device, the present study aimed at evaluating the possibilities of modeling backscattering coefficients at the intra-plot spatial scale on bare agricultural soils. The estimations of the backscattering coefficient were performed using a statistical approach, at spatial scales ranging from 80 to 2800 m\({}^{2}\), and compared to satellite signals acquired by TerraSAR-X and Radarsat-2. A high level of accuracy was observed in the X-band (with a correlation of 0.91 and RMSE of 0.83 dB for the 2800 m\({}^{2}\) area), while the explained variance was lower in the C-band (best values of correlation between 0.74 and 0.80, and RMSE between 1.65 and 1.85 dB, depending on the considered polarization state). Whatever the considered wavelength, the best performances obtained at the intra-plot spatial scale overpass the level of accuracy observed at the plot scale in the literature. By applying the modeling approach at the intra-plot scale, the spatial variability of soil surface descriptors (averaged in plot-scale approaches) is better considered. This qualification of the possibility of using radar images on an intra-plot scale opens the way to new approaches for monitoring variables of interest in an agricultural context. Nevertheless, the dataset will have to be extended with in situ measurements taken on soils with extreme conditions of roughness (smooth and very rough) and moisture (dry and saturated). In addition, the approach implemented during the bare soil period should be tested during the vegetation growing cycles. The accuracy of the intra-plot approach is strongly linked to the specificities of the microwave signals (i.e., NESZ and RRAD), which condition the possibility to get closer to the pixel size. The same approach could therefore be applied to other satellite missions (e.g., COSMO-SkyMed, TanDEM-X, Radarsat Constellation, and Sentinel-1) to study whether images can be used at different spatial scales. It could also be extended to data acquired at higher wavelengths provided by the L and P-band sensors onboard the current ALOS-2 and ALOS-4 missions, or forthcoming Biomass satellite. The performances associated with the estimation of the backscattering coefficients finally make it possible to define an area of interest specific to the considered signal (~700 m\({}^{2}\) and ~2000 m\({}^{2}\) for the tested images, respectively, acquired in the X- and C-band), useful for future approaches to estimating surface moisture or roughness at intra-plot spatial scales.  
Conceptualization, R.F. and F.B.; methodology, R.F. and F.B.; formal analysis, R.F. and F.B.; writing--original draft preparation, review and editing, R.F. and F.B. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors wish to thank the DLR (German Space Agency), SOAR Project and CNES (Centre National des Etudes Spatiales) for their support, funding, and satellite images (proposal HYD0611 and SOAR-EU and Categorie-1 ESA project no. 6843). In addition, the authors wish to thank the farmers ([PERSON], [PERSON], [PERSON], [PERSON], and [PERSON]) for their time and precious discussion and the people who helped to collect the ground data.  
**Conflicts of Interest:** The authors declare no conflicts of interest.