Spectral Reflectance Features Related to Foliar Nitrogen in Forests and their Implications for Broad-Scale Nitrogen Mapping

Scott V. Ollinger, University of New Hampshire, scott.ollinger@unh.edu (Presenter)
Lucie C. Lepine, University of New Hamphire, lucie.lepine@unh.edu
Andrew P. Ouimette, University of New Hampshire, andrew.ouimette@unh.edu
Mary E. Martin, University of New Hamsphire, mary.martin@unh.edu

The ability to estimate foliar nitrogen concentration (%N) over a range of scales would substantially improve our understanding of terrestrial carbon and nitrogen cycles. At fine scales, %N estimation has been achieved using data from high spectral resolution remote sensing instruments, or imaging spectrometers. Recently, observations of strong correlations between field-measured %N in closed-canopy forests and reflectance across broad portions of the near infrared (NIR) region have raised the possibility that some level of N estimation may be possible with broad-band data.

Here, we present results from an analysis that combines remote sensing and field measurements from 155 forested plots across North America to explore the effects of spectral resolution, spatial resolution and sensor fidelity on relationships between %N and reflectance from airborne imaging spectrometer and satellite data. Consistent with our earlier findings, observed relationships between %N and reflectance were driven primarily by reflectance in the near infrared region, with little contribution from the visible or mid infrared regions. In addition, the strength of the relationship between NIR reflectance and %N was influenced more by sensor fidelity (signal-to-noise ratio, radiometric resolution) than spatial or spectral resolution. Together, these results indicate promise for broad scale canopy N estimation from existing sensors, such as Landsat 8 and MODIS.

We also demonstrate that the %N-NIR relationship is significant within pure broad-leaf deciduous forests and pure needle-leaf evergreen forests, as well as mixed forest stands, dispelling the notion that the relationship is driven only by the relative abundance of the two groups. Although our understanding of why foliar %N is related to canopy NIR reflectance remains incomplete, evidence points to functional associations among plant traits related to photosynthesis, carbon allocation and structural properties at leaf to canopy scales. Expanding the utility of the %N-NIR relationship will require a better understanding of these underlying associations and how they vary across a range of environmental conditions.

Presentation Type:  Poster

Session:  Theme 3: Future research direction and priorities: perspectives relevant to the next decadal survey   (Mon 4:30 PM)

Associated Project(s): 

• Ollinger, Scott: Effects of Disturbance and N Deposition on Nitrogen-Albedo Relations in Forests ...details

Poster Location ID: 100