Project Funding: 2012 - 2015

NRA: 2011 NASA: Terrestrial Ecology   

Funded by NASA

Abstract:
Because tropical forests contain about 50% of the Earth's forested biomass and because they are very poorly surveyed on the ground, this proposal investigates the global measurement of tropical forest structure and biomass with remote sensing. It will advance the development and utilization of a multisensor approach to structure and biomass estimation from interferometric synthetic aperture radar (InSAR)/polarimetric InSAR (PolInSAR) and lidar. The proposal uses data from the German satellite system TanDEM-X, which consists of two spacecraft carrying X-band (wavelength 3.1 cm) radar and flying in tandem, with separations (baselines) of 100 m to more than 1000 m. TanDEM-X will take data from June 2011 through 2014, between 10 and 30 baselines for this project per year. The proposal also uses data from airborne lidar in areas where field measurements have been taken in the time period 2009-2011, and further uses spaceborne ICESat historical data. Our proposed work will emphasize development of new methods and comparison among sensors, which prompts our selection of a very well characterized site, the Tapajos National Forest in Brazil that has been studied in great detail. Of particular relevance are large data sets of small-spot lidar, and infrastructure for extensive field acquisition via the Brazilian Co-I's. The objectives of the proposal are to 1) Develop methods for height and profile estimation from multibaseline X-band InSAR and PolInSAR; 2) Determine the structural metrics for biomass estimation from optimal vertical and horizontal vegetation relative density scales, thereby producing local, state-of-the-art biomass estimates by regression of InSAR and lidar to field data; and 3) Make regional, mission-simulated structure and biomass maps of Tapajós from TanDEM-X and lidar. The approach to developing methods for height and profile estimation from TanDEM-X will involve using uniform-volume models, as has been done in the literature. We will also look at field data in hand, taken from 2009 to the present to compare InSAR-estimate heights to field-measured heights. We will experiment with modifications to the uniform-volume model based on small-spot lidar measurements, which are a part of this proposal. The approach to identifying structural metrics which best correlate with stand biomass will be based on identifying vertical and horizontal scales over which vegetation density is changing, primarily with lidar. As has been done frequently in the literature, we will try various height metrics in regression of field biomass estimates. We will also try the Fourier transform of the lidar vertical profile at a few vertical frequencies as a correlate to stand biomass. Horizontal Fourier transforms of lidar metrics will also be done. State-of-the-art structure and biomass maps will be generated over the 20-30 km^2 area of field sites from TanDEM-X and small-spot lidar, using field acquisitions as "truth" measurements. The approach to the regional (15 x 66 km) structure and biomass maps will be to aggregate small-spot lidar to the anticipated size of ICESat-2 spots and demonstrate fusion, mission-relevant methods of combining InSAR and lidar. GLAS historic lidar may be used as well, if we can show sufficient structure and biomass accuracy comparing GLAS, forward-propagated with growth models, and ICESat-2-like spots from contemporaneous, aggregated small-spot lidar. 30 additional field sites will be measured in this work, either within planned lidar acquisitions or in more remote parts of Tapajos for validating the regional map. InSAR, whether multibaseline and/or polarimetric, will be an important component of any global strategy for forest structure and consequent biomass monitoring. The performance of biomass estimation strategies in tropical moist forests will bear heavily on the design of NASA space-based monitoring systems.

Publications:

Goncalves, F., Treuhaft, R., Law, B., Almeida, A., Walker, W., Baccini, A., dos Santos, J., Graca, P. 2017. Estimating Aboveground Biomass in Tropical Forests: Field Methods and Error Analysis for the Calibration of Remote Sensing Observations. Remote Sensing. 9(1), 47. DOI: 10.3390/rs9010047

Treuhaft, R., Gonzalves, F., dos Santos, J. R., Keller, M., Palace, M., Madsen, S. N., Sullivan, F., Graca, P. M. L. A. 2015. Tropical-Forest Biomass Estimation at X-Band From the Spaceborne TanDEM-X Interferometer. IEEE Geoscience and Remote Sensing Letters. 12(2), 239-243. DOI: 10.1109/LGRS.2014.2334140

2015 NASA Carbon Cycle & Ecosystems Joint Science Workshop Poster(s)

• Tropical-Forest Profiles and Biomass from TanDEM-X, Single-Baseline Interferometric SAR: InSAR Performance at Higher Frequencies and Bandwidths   --   (Robert Neil Treuhaft, Fabio G. Goncalves, Michael Keller, João Roberto Santos, Maxim Neumann, Michael Palace)   [abstract]   [poster]

2013 NASA Terrestrial Ecology Science Team Meeting Poster(s)

• Tropical Forest Structure and Biomass Estimation from Bistatic InSAR at X-band (TanDEM-X), Small-Spot Lidar, and Field Measurements in the Amazonian Basin   --   (Robert Neil Treuhaft, Fabio G. Goncalves, Joao Roberto dos Santos, Soren Madsen, Michael Palace, Michael Keller, Scott Hensley)   [abstract]

More details may be found in the following project profile(s):

• NASA Terrestrial Ecology (TE) Project Profile