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@Article{TreuhaftLeGoKeSaNeAl:2017:TrStBi,
               author = "Treuhaft, Robert and Lei, Yang and Gon{\c{c}}alves, Fabio and 
                         Keller, Michael and Santos, Jo{\~a}o Roberto dos and Neumann, 
                         Maxim and Almeida, Andr{\'e}",
          affiliation = "Jet Propulsion Laboratory, California Institute of Technology and 
                         Jet Propulsion Laboratory, California Institute of Technology and 
                         {Canopy Remote Sensing Solutions} and Jet Propulsion Laboratory, 
                         California Institute of Technology and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and Amazon and {Universidade Federal 
                         de Sergipe (UFS)}",
                title = "Tropical-forest structure and biomass dynamics from TanDEM-X radar 
                         interferometry",
              journal = "Forests",
                 year = "2017",
               volume = "8",
               number = "8",
                pages = "Article number 277",
                month = "July",
             keywords = "tropical forest dynamics, aboveground biomass, interferometric 
                         SAR, TanDEM-X.",
             abstract = "Changes in tropical-forest structure and aboveground biomass (AGB) 
                         contribute directly to atmospheric changes in CO2, which, in turn, 
                         bear on global climate. This paper demonstrates the capability of 
                         radar-interferometric phase-height time series at X-band 
                         (wavelength = 3 cm) to monitor changes in vertical structure and 
                         AGB, with sub-hectare and monthly spatial and temporal resolution, 
                         respectively. The phase-height observation is described, with a 
                         focus on how it is related to vegetation-density, radar-power 
                         vertical profiles, and mean canopy heights, which are, in turn, 
                         related to AGB. The study site covers 18  60 km in the 
                         Tapaj{\'o}s National Forest in the Brazilian Amazon. 
                         Phase-heights over Tapaj{\'o}s were measured by DLR's TanDEM-X 
                         radar interferometer 32 times in a 3.2 year period from 2011-2014. 
                         Fieldwork was done on 78 secondary and primary forest plots. In 
                         the absence of disturbance, rates of change of phase-height for 
                         the 78 plots were estimated by fitting the phase-heights to time 
                         with a linear model. Phase-height time series for the disturbed 
                         plots were fit to the logistic function to track jumps in 
                         phase-height. The epochs of clearing for the disturbed plots were 
                         identified with \≈1-month accuracy. The size of the 
                         phase-height change due to disturbance was estimated with 
                         \≈2-m accuracy. The monthly time resolution will facilitate 
                         REDD+ monitoring. Phase-height rates of change were shown to 
                         correlate with LiDAR RH90 height rates taken over a subset of the 
                         TanDEM-X data's time span (2012-2013). The average rate of change 
                         of phase-height across all 78 plots was 0.5 m-yr-1 with a standard 
                         deviation of 0.6 m-yr-1. For 42 secondary forest plots, the 
                         average rate of change of phase-height was 0.8 m-yr-1 with a 
                         standard deviation of 0.6 m-yr-1. For 36 primary forest plots, the 
                         average phase-height rate was 0.1 m-yr-1 with a standard deviation 
                         of 0.5 m-yr-1. A method for converting phase-height rates to 
                         AGB-rates of change was developed using previously measured 
                         phase-heights and field-estimated AGB. For all 78 plots, the 
                         average AGB-rate was 1.7 Mg-ha-1-yr-1 with a standard deviation of 
                         4.0 Mg-ha-1-yr-1. The secondary-plot average AGB-rate was 2.1 
                         Mg-ha-1-yr-1, with a standard deviation of 2.4 Mg-ha-1-yr-1. For 
                         primary plots, the AGB average rate was 1.1 Mg-ha-1-yr-1 with a 
                         standard deviation of 5.2 Mg-ha-1-yr-1. Given the standard 
                         deviations and the number of plots in each category, rates in 
                         secondary forests and all forests were significantly different 
                         from zero; rates in primary forests were consistent with zero. 
                         AGB-rates were compared to change models for Tapaj{\'o}s and to 
                         LiDAR-based change measurements in other tropical forests. 
                         Strategies for improving AGB dynamical monitoring with X-band 
                         interferometry are discussed.",
                  doi = "10.3390/f8080277",
                  url = "http://dx.doi.org/10.3390/f8080277",
                 issn = "1999-4907",
             language = "en",
           targetfile = "forests-08-00277-v3.pdf",
        urlaccessdate = "24 nov. 2020"
}


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