Abstract
Microwave vegetation index (MVI) is a vegetation index defined in microwave bands. It has been developed based on observations from AMSR-E and widely used to monitor global vegetation. Recently, our study found that MVI was influenced by the atmosphere, although it was calculated from microwave bands. Ignoring the atmospheric influence might bring obvious uncertainty to the study of global vegetation. In this study, an atmospheric effect sensitivity analysis for MVI was carried out, and an atmospheric correction algorithm was developed to reduce the influence of the atmosphere. The sensitivity analysis showed that water vapor, clouds and precipitation were main parameters that had an influence on MVI. The result of the atmospheric correction on MVI was validated at both temporal and spatial scales. The validation showed that the atmospheric correction algorithm developed in this study could obviously improve the underestimation of MVI on most land surfaces. Seasonal patterns in the uncorrected MVI were obviously related to atmospheric water content besides vegetation changes. In addition, global maps of MVI showed significant differences before and after atmospheric correction in the northern hemisphere in the northern summer. The atmospheric correction will make the MVI more reliable and improve its performance in calculating vegetation biomass.
Highlights
Vegetation is an important land surface cover in the Earth’s ecosystems
The Microwave vegetation index (MVI) is calculated from dual-frequency and dual-polarization of AMSR-E measurements
The atmospheric correction will obviously improve the ability of MVI to monitor vegetation information at regional or global scales, and further extend the application of microwaves in the study of global carbon cycles and the Earth’s ecosystem
Summary
Vegetation is an important land surface cover in the Earth’s ecosystems. Improving the ability to monitor global vegetation and obtaining accurate measurements of vegetation parameters are of great importance to the study of the global carbon cycle, net primary productivity, and security of grain production in agriculture. Vegetation indices built from band combinations of passive microwave observations were used in these studies. These vegetation indices include microwave polarization difference temperatures (MPDT) at 37 GHz [7,8], the normalized. The long wavelength of microwaves is much larger than the diameter of cloud particles and makes it possible to acquire vegetation information in all weather conditions This is why few of these vegetation indices from passive microwave sensors consider the influence of the atmosphere when acquiring vegetation information. The atmospheric correction will obviously improve the ability of MVI to monitor vegetation information at regional or global scales, and further extend the application of microwaves in the study of global carbon cycles and the Earth’s ecosystem.
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