In the near future, spaceborne low-resolution measurements of the L-band brightness temperature will be available from areas covered by all sorts of vegetation. Several studies have addressed the problem of estimating soil moisture at L-band for bare soil and crops, where a simple radiative approach with little need for ancillary information (tau-omega model) proved to be suitable. The possibility to obtain information about forests needs to be studied. The formulation of the tau-omega model can be maintained to simulate the microwave emission if tau and omega are defined as effective parameters. However, knowing the sensitivity of tau and omega to configuration parameters (angle and polarization) is required in the inversion process. As a first step of the study, we investigate the dependence of the model parameters on angle, polarization and understory layer.