@article {KNZ001024,
	title = {Indicators of plant species richness in AVIRIS spectra of a mesic grassland},
	journal = {Remote Sensing of Environment},
	volume = {98},
	year = {2005},
	pages = {304 -316},
	abstract = {Hyperspectral imagery of the Konza Prairie Biological Station in northeastern Kansas was used to evaluate upwelling spectral radiance, prairie spectral reflectance and band ratios of each as potential indicators of vascular plant species richness in a mesic grassland. The extent to which spatial variability in these parameters related to plant species richness also was investigated. A 224 channel hyperspectral data cube acquired in June 2000 by the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) provided complete coverage of the 400{\textendash}2500 nm range at approximately 10 nm per channel. After band deletions accounted for detector overlap and strong atmospheric attenuation features, 176 bands were retained for analysis and spanned the 404{\textendash}2400 nm range. Prairie reflectance was estimated via radiative transfer modeling and scaling to a library spectrum of highway construction material. Data were sampled from pixels having a 19 m ground sample distance (GSD) to represent each of 93 vegetation sampling transects. Reflectance and radiance at mid-infrared wavelengths (e.g., 1553 nm), and band ratios that were based on atmospheric windows in the red, near-infrared and mid-infrared spectra estimated species richness to within 6 to 7 species per transect. The 856 to 780 nm radiance or reflectance ratio yielded maximum adjusted coefficients of determination (r2) of approximately 0.4 in regressions with richness when data from bison-grazed and ungrazed areas were combined. These regressions remained significant (p <= 0.001) when only ungrazed areas were assessed although r2 reduced to approximately 0.2. Richness was related significantly also to the 433 to 674 nm reflectance ratio for grazed-plus-ungrazed and ungrazed-only areas. In contrast, the effectiveness of the 433 to 674 nm radiance ratio was reduced by atmospheric backscatter. Species richness did not correlate strongly or consistently with transect spatial variability (coefficient of variation or range) in radiance, reflectance or band ratio value, apparently as a consequence of the relatively small area sampled for each transect (approximately 0.5 ha). Relationships between richness and prairie spectral features were explained by the influence of soil exposure on both parameters. Richness and estimated soil exposure tended to increase from ungrazed lowlands, to ungrazed slopes, to ungrazed uplands to grazed areas. Remotely sensed estimates of soil exposure may be particularly useful in addressing plant species richness on grazed grasslands owing to an overall similarity in spectral reflectance among dominant plant species.},
	keywords = {LTER-KNZ, AVIRIS, Biodiversity, Bison grazing, grassland, Hyperspectral, Plant species richness, Radiance, Reflectance, Soil exposure, Spatial variability, Spectral mixing},
	doi = {10.1016/j.rse.2005.08.001},
	author = {Carter, G.A. and Alan K. Knapp and Anderson, J.E. and Hoch, G.A. and M.D. Smith}
}
@article {KNZ00759,
	title = {Leaf optical properties in higher plants: linking spectral characteristics to stress and chlorophyll concentration},
	journal = {American Journal of Botany},
	volume = {88},
	year = {2001},
	pages = {677 -684},
	keywords = {LTER-KNZ},
	author = {Carter, G.A. and Alan K. Knapp}
}
@article {KNZ00653,
	title = {Variability in leaf optical properties among 26 species from a broad range of habitats},
	journal = {American Journal of Botany},
	volume = {85},
	year = {1998},
	pages = {940 -946},
	abstract = {Leaves from 26 species with growth forms from annual herbs to trees were collected from open, intermediate, and shaded understory habitats in Mississippi and Kansas, USA. Leaf optical properties including reflectance, transmittance, and absorptance in visible and near infrared (NIR) wavelengths were measured along with leaf thickness and specific leaf mass (SLM). These leaf properties and internal light scattering have been reported to vary with light availability in studies that have focused on a limited number of species. Our objective was to determine whether these patterns in leaf optics and light availability were consistent when a greater number of species were evaluated. Leaf thickness and SLM varied by tenfold among species sampled, but within-habitat variance was high. Although there was a strong trend toward thicker leaves in open habitats, only SLM was significantly greater in open vs. understory habitats. In contrast, leaf optical properties were strikingly similar among habitats. Reflectance and reflectance/transmittance in the NIR were used to estimate internal light scattering and there were strong relationships (r1 \&gt; 0.65) between these optical properties and leaf thickness. We concluded that leaf thickness, which did not vary consistently among habitats, was the best predictor of NIR reflectance and internal light scattering. However, because carbon allocation to leaves was lower in understory species (low SLM) yet gross optical properties were similar among all habitats, the energy investment by shade leaves required to achieve optical equivalence with sun leaves was lower. Differences in leaf longevity and growth form within a habitat may help explain the lack of consistent patterns in leaf optics as the number of species sampled increases.},
	keywords = {LTER-KNZ},
	url = {http://www.amjbot.org/content/85/7/940.short},
	author = {Alan K. Knapp and Carter, G.A.}
}
