Microwave Emission Models (EM) are used in retrieval algorithms to estimate geophysical state parameters such as soil Water Content (WC) and vegetation optical depth (tau), from brightness temperatures T-B(p,theta) measured at nadir angles theta at Horizontal and Vertical polarizations p = {H,V}. An EM adequate for implementation in a retrieval algorithm must capture the responses of T-B(p,theta) to the retrieval parameters, and the EM parameters must be experimentally accessible and representative of the measurement footprint. The objective of this study is to explore the benefits of the multiple-scattering Two-Stream (2S) EM over the "Tau-Omega" (TO) EM considered as the "reference" to retrieve WC and tau from L-band T-B(p,theta). For sparse and low-scattering vegetation T-B,EM(p,theta) simulated with EM = {TO, 2S} converge. This is not the case for dense and strongly scattering vegetation. Two-Parameter (2P) retrievals 2P(RC) = (WCRC, tau(RC)) are computed from elevation scans T-B(p,theta j) = T-B,TO(p,theta j) synthesized with TO EM and from T-B(p,theta j) measured from a tower within a deciduous forest. Retrieval Configurations (RC) employ either EM = TO or EM = 2S and assume fixed scattering albedos. WCRC achieved with the 2S RC is marginally lower (similar to 1 m(3)m(-3)) than if achieved with the "reference" TO RC, while tau(RC) is reduced considerably when using 2S EM instead of TO EM. Our study outlines a number of advantages of the 2S EM over the TO EM currently implemented in the operational SMOS and SMAP retrieval algorithms.
