3 results
Mapping Downy Brome (Bromus tectorum) Using Multidate AVIRIS Data
- Nina V. Noujdina, Susan L. Ustin
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- Journal:
- Weed Science / Volume 56 / Issue 1 / February 2008
- Published online by Cambridge University Press:
- 20 January 2017, pp. 173-179
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Invasive plants impose threats to both natural and managed ecosystems. Downy brome is among the most aggressive invasive weeds that has infested the shrub-steppe ecoregion of eastern Washington. Hyperspectral remote sensing has potential for early detection and for monitoring the spread of downy brome—information that is essential for developing effective management strategies. Two airborne hyperspectral Advanced Visible Infrared Imaging Spectrometer (AVIRIS) images (electromagnetic spectrum ranging from 400 to 2,500 nm) were acquired at a nominal 4-m ground resolution over a study area in south-central Washington on July 27, 2000 and May 5, 2003. We used a mixture-tuned matched filtering (MTMF) algorithm to classify downy brome and predict its percent cover in each dataset plus a merged multiseasonal dataset using the transformed bands from a minimum noise fraction (MNF) output. The correlation coefficient was 0.79, calculated for the multidate MTMF predicted downy brome abundance, compared to 0.41 and 0.51 derived from the July 2000 and May 2003 data, respectively. Although this study used high spatial resolution (∼3 to 4 m) hyperspectral imagery, this result shows that data acquired in different seasons is more effective for detection of downy brome invasion, compared to single-date datasets. These results support expanded use of multitemporal data for weed mapping to capitalize on spectral differences between seasons for weeds, in this case downy brome, and the surrounding environment.
Spectral and physiological uniqueness of perennial pepperweed (Lepidium latifolium)
- Margaret E. Andrew, Susan L. Ustin
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- Journal:
- Weed Science / Volume 54 / Issue 6 / December 2006
- Published online by Cambridge University Press:
- 20 January 2017, pp. 1051-1062
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Perennial pepperweed is an aggressive, exotic weed invading wetland and riparian areas in California, including the San Francisco Bay/Sacramento–San Joaquin Delta Estuary. Effective management will require detailed and accurate maps of its distribution. Remote sensing technologies offer the capability to map weed species over broad areas and with rapid return intervals. As a first step in assessing the potential to map perennial pepperweed with hyperspectral remote sensing data, this study determined its spectral uniqueness relative to co-occurring species. Spectral measurements were conducted during summer drought conditions in the Sacramento–San Joaquin Delta region. Reflectance spectra of perennial pepperweed and seven co-occurring species were collected with a portable spectrometer. Nineteen physiological indexes were calculated from the reflectance data. Physiological indexes are sensitive to narrow spectral features and encapsulate reflectance information in ecologically relevant ways. Classification trees generated from these indexes were able to discriminate both flowering and fruiting perennial pepperweed from co-occurring species with high levels of cross-validated accuracy when using the original spectrometer data and also when this data set was resampled to simulate the spectral resolution of two widely used airborne hyperspectral imagers. Perennial pepperweed's characteristic white flowers are the major component of the spectral uniqueness of this species. Phenological state influenced reflectance spectra more strongly than variation in intraseasonal maturity. Field spectrometer spectra were qualitatively and quantitatively similar to perennial pepperweed spectra extracted from airborne image data. These results suggest that hyperspectral remote sensing will be a powerful tool for the mapping and monitoring of perennial pepperweed. Future work will extend these analyses to image data encompassing the San Francisco Bay/Sacramento–San Joaquin Delta region.
Use of Hyperspectral Remote Sensing to Evaluate Efficacy of Aquatic Plant Management
- Maria J. Santos, Shruti Khanna, Erin L. Hestir, Margaret E. Andrew, Sepalika S. Rajapakse, Jonathan A. Greenberg, Lars W. J. Anderson, Susan L. Ustin
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- Journal:
- Invasive Plant Science and Management / Volume 2 / Issue 3 / July 2009
- Published online by Cambridge University Press:
- 20 January 2017, pp. 216-229
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Invasive aquatic weeds negatively affect biodiversity, fluvial dynamics, water quality, and water storage and conveyance for a variety of human resource demands. In California's Sacramento–San Joaquin River Delta, one submersed species—Brazilian egeria—and one floating species—waterhyacinth—are actively managed to maintain navigable waterways. We monitored the spatial and temporal dynamics of these species and their communities in the Sacramento-San Joaquin River Delta using airborne hyperspectral data and assessed the effect of herbicide treatments used to manage these species from 2003 to 2007. Each year, submersed aquatic plant species occupied about 12% of the surface area of the Delta in early summer and floating invasive plant species occupied 2 to 3%. Since 2003, the coverage of submersed aquatic plants expanded about 500 ha, whereas the coverage of waterhyacinth was reduced. Although local treatments have reduced the coverage of submersed aquatic plants, Delta-wide cover has not been significantly reduced. Locally, multiyear treatments could decrease submersed aquatic plants spread, given that no residual plants outside the treated area were present. In contrast, the spread of waterhyacinth either has been constant or has decreased over time. These results show that (1) the objectives of the Egeria densa Control Program (EDCP) have been hindered until 2007 by restrictions imposed on the timing of herbicide applications; (2) submersed aquatic plants appeared to function as ecosystem engineers by enabling spread to adjacent areas typically subject to scouring action; (3) repeated herbicide treatment of waterhyacinth has resulted in control of the spread of this species, which also appears to have facilitated the spread of waterprimrose and floating pennywort. These results suggest that management of the Delta aquatic macrophytes may benefit by an ecosystem-level implementation of an Integrated Delta Vegetation Management and Monitoring Program, rather than targeting only two problematic species.