Geography Program (SNR)

 

Date of this Version

2-2013

Comments

A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Arts,Major: Geography, Under the Supervision of Professor Donald C. Rundquist. Lincoln, Nebraska: February, 2013

Copyright 2013 Travis Yeik

Abstract

Phragmites australis is an invasive wetland weed found throughout much of the United States. Documenting and mapping the growth and spread of this emergent macrophyte can be an important step in developing and implementing successful management strategies. Characterizing the phenology of a vegetation species with a sensor capable of hyperspectral resolution, positioned at close proximity to the canopy of interest, is often a first step necessary for understanding the basic species-specific reflectance patterns, and for quantifying the manner in which light interacts with the plants comprising particular communities. Spectral data over a P. australis canopy were collected during 22 field campaigns in 2011. Research was aimed at characterizing the spectral responses of a P. australis canopy throughout a growing season, and then relating the acquired reflectance data to individual stages in the life cycle, as well as changes in the vegetation fraction associated with the plant canopy. A deconvolution of primary constituents comprising the spectral signal upwelling from the canopy aided in understanding the temporal variations in reflectance. Analyses of both spectra and digital photographs of the canopy led to the development of a new transformation, termed the “Albedo Corrected Vegetation Index” (ACVI), aimed at increasing the accuracy in estimating vegetation fraction. Seed production and shoot density, both of which are closely linked with the invasive qualities of P. australis, were estimated using methods involving a simple digital camera as well as dual spectroradiometers. Additionally, considerations and procedures for collecting spectral data in the field were reviewed, and a procedure was developed, based upon concurrently acquired pyranometer data, to correct for incongruities that often occur due to the variable environmental conditions encountered during field campaigns. The findings of this research provide the necessary fundamental steps in the effort to monitor invasive species such as P. australis by means of remote sensing.