Uncertainties in the Relationship Between Hyperspectral Data and Leaf Nitrogen Content

Yuri Knyazikhin, Boston University, jknjazi@bu.edu (Presenter)
Mitchell Schull, Boston University, schull@bu.edu
Ranga Babu Myneni, Boston University, rmyneni@bu.edu
Robert Kaufmann, Boston University, kaufmann@bu.edu

NASA's Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and ground based data on canopy structure and foliage nitrogen concentration acquired over six sites in Maine, New England, Florida, North Carolina and Washington was analyzed to assess the role of canopy structure, leaf optics and its biochemical constituents in the spectral variation of radiation reflected by the forest. Our results suggest: (1) Impact of canopy structure is so strong that it can significantly suppress the sensitivity of hyperspectral data to leaf optics; (2) Forest reflectance spectra in the interval [710, 790 nm] are required to obtain the fraction of the total leaf area that a “sensor sees” in a given direction. For closed canopy forests its retrieval does not require canopy reflectance models, suggesting that canopy reflectance spectra in this interval provide a direct estimate of the leaf area fraction. (3) The leaf area fraction fully explains variation in measured reflectance spectra due to variation in canopy structure. This variable is used to estimate the mean leaf scattering over foliage that the “sensor sees.” For example the nadir-viewing AVIRIS sensor accumulates foliage optical properties over 25% of the total foliage area in needle leaf forest and about 50% in broadleaf forest. (4) Leaf surface properties have an impact on forest reflectivity, lowering its sensitivity to leaf absorbing pigments. (5) Variation in foliar nitrogen concentration can explain up to 55% of variation in AVIRIS spectra in the interval between 400 and 900 nm. The remaining factors could be due to (a) impact of leaf surface properties and/or (b) under-sampling of leaf optical properties due to the single view of the AVIRIS sensor.

Presentation: 2011_Poster_Knyazikhin_221_20.pdf (1008k)

Presentation Type:  Poster

Session:  Other   (Tue 11:30 AM)

Associated Project(s): 

• Knyazikhin, Yuri: Biophysical Parameters From MISR Sensor ...details
• Knyazikhin, Yuri: Remote Sensing of Forest Structure Across Multiple Scales From Leaves to Canopies and Stands ...details
• Knyazikhin, Yuri: Vegetation Biophysical Parameter Suite from MISR for Ecological Applications ...details
• Myneni, Ranga: A Synergistic Study for LIDAR and Passive Optical Remote Sensing of Forest Horizontal Structure in Support of DESDynI Mission ...details
• Myneni, Ranga: Remote Sensing of Forest Canopy Structure Across Multiple Scales from Synergistic Analysis of Lidar, Hyperspectral and Multiangle Data With Time-Dependent Stochastic Radiative Transfer Based Algorithm ...details

Poster Location ID: 221