Global long-term passive microwave satellite-based retrievals of vegetation optical depth

• Published in: Geophysical research letters Vol. 38; no. 18
• Main Authors: Liu, Yi Y., de Jeu, Richard A. M., McCabe, Matthew F., Evans, Jason P., van Dijk, Albert I. J. M.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 28-09-2011; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Annual variations; Drought; Earth sciences; Earth, ocean, space; Exact sciences and technology; global vegetation; Hydrology; Leaves; long-term trend; NDVI; Optical analysis; passive microwave; Precipitation; Remote sensing; Time series; Vegetation; vegetation optical depth; Water content; microwaves; trend-surface analysis; Vegetation index; abundance; vegetation; global; Long term variation; instruments; fluctuations; Planetary scale; water content; wood; Optical thickness; satellites; biomass; atmospheric precipitation; Space remote sensing; chlorophyll; Satellite observation; Vegetation dynamics; indicators; Long term; Interannual variation; optical properties; seasonal variations
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL048684

Vegetation optical depth (VOD) retrievals from three satellite‐based passive microwave instruments were merged to produce the first long‐term global microwave‐based vegetation product. The resulting VOD product spans more than two decades and shows seasonal cycles and inter‐annual variations that generally correspond with those observed in the Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI). Some notable differences exist in the long‐term trends: the NDVI, operating in the optical regime, is sensitive to chlorophyll abundance and photosynthetically active biomass of the leaves, whereas the microwave‐based VOD is an indicator of the vegetation water content in total above‐ground biomass, i.e., including wood and leaf components. Preliminary analyses indicate that the fluctuations in VOD typically correlated to precipitation variations, and that the mutually independent VOD and NDVI do not necessarily respond in identical manners. Considering both products together provides a more robust structural characterization and assessment of long‐term vegetation dynamics at the global scale.
Key Points
First long‐term global microwave‐based vegetation product (VOD) was developed
Notable similarities and differences exist between VOD and NDVI product
Mutually independent products will provide a more comprehensive analysis