Building spectral libraries for wetlands land cover classification and hyperspectral remote sensing.

Recent advances in remote sensing provide opportunities to map plant species and vegetation within wetlands at management relevant scales and resolutions. Hyperspectral imagers, currently available on airborne platforms, provide increased spectral resolution over existing space-based sensors that can document detailed information on the distribution of vegetation community types, and sometimes species. Development of spectral libraries of wetland species is a key component needed to facilitate advanced analytical techniques to monitor wetlands. Canopy and leaf spectra at five sites in California, Texas, and Mississippi were sampled to create a common spectral library for mapping wetlands from remotely sensed data. An extensive library of spectra (n=1336) for coastal wetland communities, across a range of bioclimatic, edaphic, and disturbance conditions were measured. The wetland spectral libraries were used to classify and delineate vegetation at a separate location, the Pacheco Creek wetland in the Sacramento Delta, California, using a PROBE-1 airborne hyperspectral data set (5m pixel resolution, 128 bands). This study discusses sampling and collection methodologies for building libraries, and illustrates the potential of advanced sensors to map wetland composition. The importance of developing comprehensive wetland spectral libraries, across diverse ecosystems is highlighted. In tandem with improved analytical tools these libraries provide a physical basis for interpretation that is less subject to conditions of specific data sets. To facilitate a global approach to the application of hyperspectral imagers to mapping wetlands, we suggest that criteria for and compilation of wetland spectral libraries should proceed today in anticipation of the wider availability and eventual space-based deployment of advanced hyperspectral high spatial resolution sensors.

Mapping invasive aquatic vegetation in the Sacramento-San Joaquin Delta using hyperspectral imagery.

The ecological and economic impacts associated with invasive species are of critical concern to land managers. The ability to map the extent and severity of invasions would be a valuable contribution to management decisions relating to control and monitoring efforts. We investigated the use of hyperspectral imagery for mapping invasive aquatic plant species in the Sacramento-San Joaquin Delta in the Central Valley of California, at two spatial scales. Sixty-four flightlines of HyMap hyperspectral imagery were acquired over the study region covering an area of 2,139 km(2) and field work was conducted to acquire GPS locations of target invasive species. We used spectral mixture analysis to classify two target invasive species; Brazilian waterweed (Egeria densa), a submerged invasive, and water hyacinth (Eichhornia crassipes), a floating emergent invasive. At the relatively fine spatial scale for five sites within the Delta (average size 51 ha) average classification accuracies were 93% for Brazilian waterweed and 73% for water hyacinth. However, at the coarser, Delta-wide scale (177,000 ha) these accuracy results were 29% for Brazilian waterweed and 65% for water hyacinth. The difference in accuracy is likely accounted for by the broad range in water turbidity and tide heights encountered across the Delta. These findings illustrate that hyperspectral imagery is a promising tool for discriminating target invasive species within the Sacramento-San Joaquin Delta waterways although more work is needed to develop classification tools that function under changing environmental conditions.

Three-dimensional radiation transfer modeling in a dicotyledon leaf.

The propagation of light in a typical dicotyledon leaf is investigated with a new Monte Carlo ray-tracing model. The three-dimensional internal cellular structure of the various leaf tissues, including the epidermis, the palisade parenchyma, and the spongy mesophyll, is explicitly described. Cells of different tissues are assigned appropriate morphologies and contain realistic amounts of water and chlorophyll. Each cell constituent is characterized by an index of refraction and an absorption coefficient. The objective of this study is to investigate how the internal three-dimensional structure of the tissues and the optical properties of cell constituents control the reflectance and transmittance of the leaf. Model results compare favorably with laboratory observations. The influence of the roughness of the epidermis on the reflection and absorption of light is investigated, and simulation results confirm that convex cells in the epidermis focus light on the palisade parenchyma and increase the absorption of radiation.

Boron toxicity in the rare serpentine plant, Streptanthus morrisonii.

The release of boron-laden mist from the cooling towers of some geothermal power stations in northern California potentially threatens nearby populations of the rare serpentine plant, Streptanthus morrisonii F. W. Hoffm. To assess the tolerance of S. morrisonii to high levels of boron, the effect of boron on leaf condition, life history, germination rate, growth rate, allocation and photosynthesis was measured on plants grown in a greenhouse. Relative to other species, S. morrisonii was tolerant of excess boron. On serpentine soil, mild to moderate toxicity symptoms (older leaves exhibiting chlorosis and necrosis, but few leaves killed) were apparent when the boron concentration in applied nutrient solutions was 240-650 microm. Severe toxicity symptoms (significant leaf loss, young leaves with toxicity symptoms) were apparent when the applied solution was over 1000 microm boron. Above 1000 microm boron, S. morrisonii appeared unable to complete its life cycle. On a tissue basis, boron toxicity was first observed when leaf boron content was 40-90 micromol g(-1) dry weight. In leaves with severe boron toxicity (> 35% injury), the boron content was generally above 130 micromol g(-1) dry weight. These levels were an order of magnitude above the tissue boron content of plants in the field. Prior to the onset of pronounced boron toxicity symptoms, growth rate, allocation patterns, and photosynthesis were unaffected by high boron. These results indicate that inhibition of growth and photosynthesis occurred because of a loss of viable tissue due to boron injury, rather than a progressive decline as leaf boron levels increased.