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Characterizing the impact of vegetation -water interfaces as they affect composite spectral signals
Abstract
Wetlands are important to the environment because they perform many hydrologic and chemical “cleansing” functions and provide habitat for a variety of plant and animal lifeforms. It seems essential to measure and to monitor the variable proportions of open standing water versus emergent macrophyte vegetation, to more effectively monitor environmental change, to better model its contribution to greenhouse gas production and to improve the accuracy of landcover classifications of wetland communities involving digital aircraft or satellite data. The research focused on using both close-range spectral and satellite image data to innovate new methods to delineate emergent macrophyte vegetation within a water background. The close-range experiments investigated the relationship between close-range, hyperspectral and broad, multi-band reflectance patterns and their derivatives associated with varying densities of selected species of potted emergent macrophyte vegetation over a water surface. The magnitude of the near infrared reflectance in both the hyperspectral and multi-band data was found to be profoundly affected by the presence of water beneath the plant canopy. Hyperspectral derivative spectra near 720 nm and multi-band derivative spectra centered near 745 nm were both found to be highly correlated to changing percent cover. A hyperspectral reflectance ratio composed of a NIR band divided by a red light band and two, broad-band, NDVI-based models and a broad-band NIR/RED reflectance ratio were also compared to percent cover of plant canopies and were shown to be very useful in delineating sparse stands of emergent macrophyte vegetation in a water background. Satellite image data of a portion of the western Nebraska Sandhills (containing several freshwater wetland communities) were used in an unsupervised classification program (ISODATA) to determine how to best delineate emergent vegetation from a water background. In general, the unsupervised classification of first derivative bands best delineated emergent macrophyte vegetation from other aquatic and terrestrial classes, regardless of the values of selected user-defined program inputs. Using only reflectance data resulted in over-estimations of open water and possible over-estimations of certain emergent vegetation communities.
Subject Area
Physical geography|Environmental science|Geography
Recommended Citation
McFeeters, Stuart Kelly, "Characterizing the impact of vegetation -water interfaces as they affect composite spectral signals" (2000). ETD collection for University of Nebraska-Lincoln. AAI9997014.
https://digitalcommons.unl.edu/dissertations/AAI9997014