Project Funding: 2008 - 2011

NRA: 2007 NASA: Terrestrial Ecology   

Funded by NASA

Abstract:
We propose to quantify the potential of L-band polarimetric and interferometric synthetic aperture radar (PolinSAR) and lidar to characterize the 3D structure of vegetation. In particular, this proposal addresses issues related to the application of the DESDynI (Deformation, Ecosystem Structure and Dynamics of Ice) mission to characterize 3D vegetation structure. This mission combines the ability of lidar to measure localized canopy height profiles (CHP) and of radar to provide wide area estimates of canopy height. The overall objective of this proposal is to study the most likely scenarios for DESDynI and quantify their performance and the remaining uncertainty in the retrieval of vegetation structure parameters (i.e. height, density, biomass, and canopy/biomass dynamics). Most importantly, we will find the best compromise between long (greater lidar spatial coverage and lower interferometric correlation) and short repeat cycle (lower lidar coverage but higher interferometric correlation). Our approach uses existing data from spaceborne (ICEsat/GLAS) and airborne lidar data (LVIS) in addition to spaceborne (ALOS/PALSAR) and airborne (UAVSAR) L-band polarimetric inSAR data. Our team already possesses the available ICEsat/GLAS waveforms, LVIS and ALOS/PALSAR data covering all 10 proposed test sites. Much of this data has been processed as part of previous NASA projects by the investigators and we are ready to perform the proposed tasks. UAVSAR is a new airborne L-band polarimetric repeat pass interferometer. To achieve the overall objective, we propose to collect new data with UAVSAR to study temporal interferometric decorrelation over a wide range of vegetation types at six time intervals: 1hour, 2-days, 5-days, 8-days, 12-days and 16-days. To sample a variety of important vegetation types, we will collect UAVSAR data over 6 of the 10 sites in California, New England and Central America. Using the ALOS/PALSAR and UAVSAR data, we also propose to assess and compare the accuracy of two SAR-based techniques to estimate 3D vegetation structure and in particular canopy height, density and biomass. The techniques are: 1) SAR interferometry (inSAR); 2) SAR polarimetric interferometry (PolinSAR). Finally, we propose to combine lidar data to the SAR techniques to improve characterization of 3D vegetation structure. For the InSAR technique, we will combine lidar and inSAR data to estimate ground topography in addition to vegetation height. On the other hand, the PolinSAR technique does not require knowledge of ground topography and exploits the full potential of a mission like DESDynI. Thus, PolinSAR is the most promising technique to characterize canopy structure and is based on the fact that ground and vegetation scattering mechanisms are different and so are polarimetric signatures. In order to retrieve heights, a simple polarimetric scattering model is fitted to the data which depends on several parameters, including canopy extinction and vegetation height. We will use lidar height estimates to constrain the polarimetric scattering model and derive canopy extinction. This analysis will also enable us to characterize the relationship between canopy closure and extinction in the canopy. This proposal directly responds to Sub-element 1 of this NRA (Vegetation 3-D Structure, Biomass and Disturbance), which states that of "particular interest are: (1) studies to develop and evaluate algorithms and analysis strategies that address the merger of lidar and radar measurements".

2011 NASA Carbon Cycle & Ecosystems Joint Science Workshop Poster(s)

• Measuring canopy height with UAVSAR   --   (Marc Simard, Scott Hensley, Marco Lavalle, Ralph Dubayah, Naiara Pinto)   [abstract]

2010 NASA Terrestrial Ecology Science Team Meeting Poster(s)

• Field and Aircraft Observations in Support of DESDynI   --   (Ralph Dubayah, Kathleen Bergen, Bryan Blair, Bruce Cook, Peter Griffith, Forrest Hall, Megan McGroddy, Paul Montesano, Amy Morrell, Ross Nelson, Wenge Ni-Meister, Michael O'Connell, Jon Ranson, Chelsea Robinson, Jeremy Rubio, Sassan Saatchi, Marc Simard, Paul Siqueira, Alan Strahler, Guoqing Sue, Anuradha Swatantran)   [abstract]   [poster]
• UAVSAR airborne L-band radar campaign over boreal, temperate and tropical forests   --   (Marc Simard, Naiara Pinto, Ralph Dubayah, Scott Hensley)   [abstract]   [poster]
• 3-D Mapping Of Africa’s Mangrove Forests   --   (Temilola Fatoyinbo, Marc Simard)   [abstract]

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

• NASA Terrestrial Ecology (TE) Project Profile