Assessment of Fully Polarimetric Biomass Data for Soil Moisture Retrieval

Kurzfassung

Water management for irrigation is an essential activity especially in agricultural areas or where water is scarce. Water storage in the soil affects the vapour transpiration but also its heat storage capacity, its thermal conductivity and the energy separation between latent and sensible heat fluxes. From a hydrological perspective, soil moisture links the partitioning of rainfall into runoff and infiltration and therefore it has an important role in several ecological applications as flood forecasting, crop yield expectation, meteorological prediction, erosion and slope failure forecasting, water reservoir management, etc. Most of the soil moisture models describe only the bare soil response. In a real scenario, the presence of bare soil is not common as most of the time some kind of vegetation may be found on top. In order to reduce the amount of vegetation responses in addition to the soil moisture estimation longer wavelength can be used. In this study we like to explore the polarimetric and interferometric response of the BIOMASS mission, which operates in P band wavelength. Polarimetry can be used to define the scattering mechanisms and is able, when using decomposition methods to separate the ground and vegetation contribution. To perform this separation a physical model is employed and fully polarimetric data is needed in order to invert for the different involved parameters. It is worth mentioning that for extracting the ground response and the corresponding soil moisture, a significant degree of penetration into vegetation is required. For this reason, SAR soil moisture inversion has traditionally been investigated with L-band. In this study we use quad polarimetry in P band to investigate the sensitivity to bare soil and vegetated soil for soil moisture estimation [R1]. Differential SAR interferometry, a popular technique for measuring displacements of the Earth's surface, is potentially influenced by changes in soil moisture. Different mechanisms for this impact have been proposed, but its magnitude, sign and even presence remain poorly understood. In this study the dependence of the phase, the coherence magnitude as well as the phase triplets at different polarisation on soil moisture is investigated. In addition, the impact of vegetation is analysed [R2]. The main test site is located in Argentina, where massive ground measurements exists and a comparison with the SAOCOM derived soil moisture can be performed.

[R1] Hajnsek, I., Pottier, E., & Cloude, S. R. (2003). Inversion of surface parameters from polarimetric SAR. IEEE Transactions on Geoscience and Remote Sensing, 41(4), 727-744. [R2] Zwieback, S., Hensley, S., & Hajnsek, I. (2015). Assessment of soil moisture effects on L-band radar interferometry. Remote Sensing of Environment, 164, 77-89.