Refinement of microwave vegetation indices

Previous investigations have established the basis for a new type of vegetation index, Microwave Vegetation Indices (MVIs), based on passive microwave satellite observations. In this technique, the quantitative basis of the MVIs can be derived from the zeroth-order radiative transfer solution. However, the zeroth-order solution is only applicable when the scattering contributions within the vegetation are negligible. As a result, the first-order radiative transfer solution is superior to the zeroth-order solution due the fact that it considers volume scattering. In this paper, we evaluated the applicability of the zeroth-order solution at different microwave frequencies and for vegetation with different densities. Next, a parameterized vegetation microwave emission model for the first-order solution was developed that was used to improve the MVIs. The superiority of MVIs derived from the parameterized model was demonstrated by comparison to the original approach. The refinement of MVIs presented in this study will be helpful in improving their accuracies and expanding their applications, and will contribute to improved information on vegetation coverage, biomass, and water content.