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.
A recent study established the theoretical basis for a new type of index based on passive microwave vegetation indices
(MVIs). The approach was then calibrated for use with data from the Advanced Microwave Scanning Radiometer
(AMSR-E) on the Aqua satellite under the assumption that there is no significant polarization dependence of the
vegetation emission and attenuation properties. To demonstrate the potential of the new microwave vegetation indices,
these were compared with the Normalized Difference of Vegetation Index (NDVI) derived using MODIS at continental
and global scales. These results verified that the microwave vegetation indices can provide new and complementary
information on vegetation to NDVI for the global monitoring of vegetation and ecosystem properties from space. The
next phase of analysis has focused on quantifiable vegetation parameters, specifically vegetation water content that is a
valuable parameter in soil moisture retrievals using microwave data. Data sets collected in several recent large scale field
campaigns included vegetation water content over domains in addition to conventional indices. Comparisons to date
indicate that the MVI does provide vegetation water content information, however, further analysis of vegetation type
effects are needed.
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