L-Band Passive and Active Signatures of Vegetated Soil: Simulations With a Unified Model

The synergistic exploitation of L-band active and passive measurements has received increasing interest. In this paper, both theoretical simulations and experimental data are employed to get a deeper insight into the relations between the backscattering coefficient and the emissivity. An active/passive discrete model is used to simulate the backscattering coefficient and the emissivity of bare soil, maize crop of various heights, and deciduous forests of various biomass values. Volumetric soil moisture is varied in a 5–40% range. Simulations confirm the already known effects of soil moisture (whose increase produces a decrease in emissivity e and an increase in backscattering coefficient ${\sigma ^0}$ ) and the effects of vegetation growth that yields an increase in both ${\sigma ^0}$ and e . Experimental data collected by four airborne campaigns and spaceborne active/passive instruments, together with ground measurements, are also reported. Simulated data are used to investigate the sensitivity of active and passive measurements to soil moisture variations under different vegetation covers, and to estimate the coefficient of a linear relation between backscattering coefficient and emissivity.