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Global vegetation monitoring from active and passive microwave sensors (GVMAP)



Vegetation is a central component of the Earth’s system, governing surface water exchanges and constituting one of the largest terrestrial carbon reservoirs. Ongoing disturbances, whether natural or human-induced, combined with the impacts of changing climate, induce rapid alterations on a global scale. Accurate and consistent assessments of vegetation status are imperative to meet the needs of user communities, including earth system modeling and policymakers. Knowledge gaps persist regarding the dynamics of vegetation, spanning from biomass content to its response to fluctuations in water availability. Moreover, comprehensive, long-term evaluations of these critical parameters on a global scale have yet to be undertaken. While advancements have been made with high-resolution datasets and space borne LiDAR to accurately estimate vegetation structure and the associated biomass, their temporal coverage remains limited. Similarly, single-instrument retrievals of vegetation indices, such as vegetation optical depths, offer extended temporal scope but have limited inter instruments consistency. Microwave observations provide all-weather insights and penetrate surface vegetation cover for in-depth information. Active sensors can provide the highest resolution with Synthetic Aperture Radars (e.g., Sentinel-1 with approximately 10-meter resolution) but also coarse resolution with scatterometers (e.g. ASCAT).

Passive radiometers have coarser resolution (larger than 10 km) but ensure almost daily global coverage, with up to four decades of continuous observation. These distinct sources provide a fundamental set of observations to advance scientific knowledge of the hydrologic and carbon cycle from vegetation. Moreover, forthcoming missions, such as the passive radiometer CIMR and new radar missions like NISAR (L-band SAR, scheduled for 2024) and BIOMASS (P-band SAR anticipated for 2025), underscore the long term impact of this research. In this project, we will further develop the estimation of AGB as well as other vegetation parameters (hydrology or non-woody vegetation) as a product of satellite microwave observations. The methods will use the synergies between multiple frequencies onboard different instruments to obtain yearly AGB maps. The outcome of this project will consist of a global above ground biomass dataset spanning multiple decades that will improve understanding of long term vegetation dynamics. This study in addition sets out to also ensure consistency between above ground biomass maps from different epochs and at different scales (e.g, from the Climate Change Initiative Biomass project).


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