Conference Agenda

The X-band Synthetic Aperture Radar (SAR), with its short wavelength (~3 cm), offers exceptional spatial resolution and sensitivity to surface micro-structures—an attractive asset for precision agriculture. However, its limited penetration into vegetation and soil has historically constrained its utility for deeper biomass or subsurface retrievals.

Previous studies have demonstrated that X-band SAR data are particularly effective in distinguishing between surface roughness and tillage states over bare or sparsely vegetated soils (Baghdadi et al., 2002), owing to their enhanced sensitivity to micro-topographical variations. Nevertheless, several works have emphasized that this sensitivity decreases markedly in the presence of vegetation, as canopy volume scattering masks the soil contribution (Lopez-Sanchez & Ballester-Berman, 2009). More recently, multi-frequency comparative analyses have further confirmed that the X-band signal is predominantly sensitive to surface moisture and roughness, whereas deeper soil layers are better probed by lower-frequency systems (Zhou et al., 2025).

In this study, we explore two complementary aspects of repeat-pass PolInSAR data at X-band for agricultural applications: (1) the potential of repeat-pass interferometric phase coherence to reveal subsurface moisture and drainage features beneath cropped fields; and (2) the value of full polarimetry (orientation sensitivity, depolarisation metrics) to detect sowing ridges, tillage patterns, and crop growth stage via structural anisotropy of the soil–vegetation system.

Firstly, using TerraSAR-X Staring Spotlight acquisitions (single-polarisation, high resolution), we demonstrate that under specific seasonal and hydrological conditions, the interferometric phase (and coherence) signal exhibits sensitivity to subsurface moisture contrasts. In particular, we observe coherent phase-pattern anomalies aligned with known subsurface drainage networks beneath agricultural parcels—a surprising result, given the limited penetration of X-band. We interpret these signals as the result of dielectric contrasts in the shallow subsurface (wet vs dry soil), modulating the scattering phase behavior.

Secondly, employing an airborne, fully-polarimetric X-band sensor (SETHI), we investigate how polarimetric parameters (e.g., orientation angles and depolarization indices) vary with the presence or absence of sowing ridges and as a function of early crop growth stage. Our results show a clear correlation: fields with visible ridging manifest stronger anisotropy in orientation angle domains and lower depolarization, whereas mature crop covers produce more isotropic scattering and higher depolarization. Consequently, we find that the polarimetric signature can serve as a proxy for both soil preparation state (ridges vs flat) and early crop phenology.

Together, these findings illustrate the under‐exploited potential of X-band PolInSAR for precision agriculture: (i) as a sensor of subtle subsurface moisture heterogeneity via coherence/phase analytics, and (ii) as a structural probe of soil and crop architecture via polarimetry.

References

[1] Baghdadi, N., Holah, N., Dubois-Fernandez, P., Prévot, L., Hosford, S., Chanzy, A., ... & Zribi, M. (2004). Analysis of X-Band Polarimetric Sar Data for The Derivation of The Surface Roughness Over Bare Agricultural Fields. A A, 3, 2.

[2] Lopez-Sanchez, J. M., & Ballester-Berman, J. D. (2009). Potentials of polarimetric SAR interferometry for agriculture monitoring. Radio science, 44(02), 1-20.

[3] Zhou, X., Wang, J., Shan, B., He, Y., & Xing, M. (2025). Sensitivity of multi-frequency and multi-polarization SAR to soil moisture at different depths in agricultural regions. Journal of Hydrology, 133513.