- Related Research Areas
- Carbon Cycle & Ecosystems
Spatial structure of vegetation including plant height, vertical and horizontal heterogeneities, and biomass are important factors that influence the exchanges of matter and energy between the landscape and atmosphere, and the biodiversity of ecosystems. The NASA’s DESDynI mission will provide global systematic lidar point-sampling data and areal coverage of L-band InSAR data with polarimetric capabilities for 3-D structural studies of vegetation. The combined use of lidar’s direct sampling measurements and radar’s global areal mapping capabilities creates a real possibility and opportunity to map global ecosystem structures and functions that link to carbon dynamics. However, the relationship of the lidar point-sample data and corresponding areal InSAR data is yet to be established, much less the extrapolation of the relationship to location or area where only InSAR data are acquired. What the proper lidar sampling design is and how to expand the vegetation spatial structural parameters estimated at lidar footprints to areal coverage in high resolution using InSAR data are major objectives of this proposed project. Current configuration of DESDynI can also require lidar observations with variable looking angles, which creates a new challenge in the lidar data processing. Lidar samples the vegetation material within a cylindrical volume passed by its beam, and radar records the backscattering from a volume of vegetation which is not coincides with that sensed by lidar. How these signatures related to each other and in what scale remain questions. Lidar waveform and radar backscatter models that take the same 3D structure of a forest stand as inputs will be used to simulate data from various lidar/radar data acquisition modes and explore the possible parameters retrieval algorithms and uncertainties in the procedure. Lidar, radar and field data in test sites will be used to test and validate the algorithms and assess the accuracy derived from theoretical studies. We will thoroughly exam the potential and problems in vegetation 3-D structural and biomass measurements from combined use of lidar and SAR data to be acquired during the DESDynI mission. Specifically, we will: 1) Investigate the effects of lidar off-nadir looking on forest biomass estimation from lidar waveform and the required sampling rate of 25m-footprint lidar for specified accuracies of biomass estimation in certain scales through modeling and data analysis to yield early results that can be shared with DESDynI mission definition working group; 2) Test sensitivities of large footprint lidar and L-band polarimetric and InSAR data to forest spatial structure and biophysical parameters and identify the driving structural variables through modeling and data analysis; 3) Develop lidar-SAR data fusion techniques for extending lidar sample measurements to continuous areal coverage of SAR with high spatial resolution; and 4) Evaluate accuracies of data fusion algorithms and characterize product uncertainties. This proposal is a direct response to the NASA’s solicitation for the development of algorithms that combine radar and lidar data to estimate aboveground biomass and carbon stocks and is directly relevant to the DESDynI mission. During the first year of this project we will provide early results on lidar off-nadir looking, sampling rate and radar operation modes that can be shared with DESDynI mission definition working groups to inform overall mission planning.
Project PI: Guoqing Sun/University of Maryland
NASA Goddard Space Flight Center, Code 614.4, Bld. 33, Room G418
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