High-resolution spectroscopy using the Portable Hyperspectral Imager for Low-Light Spectroscopy (PHILLS) was applied to the problem of detecting potentially harmful algae blooms in the coastal environment. Data were collected on two aircraft passes, 30-min apart, over the tidally influenced part of the Potomac River. Use of two wavelengths, 0.676 and 0.700 µm, permitted the detection of surface algae accumulations while avoiding the need for atmospheric corrections, which are problematic in Case-2 water. The analysis identified algal accumulations derived from frontal processes, and narrow, linearly coherent streaks, derived from Langmuir circulation. The streaks increased markedly in number between the two passes and formed a two-dimensional pattern across the river, consistent with the advection time of surface material into windrows. The effect of wind on the patches is primarily a local reorganization of the algal material into new streaks. Spectra from within the streaks compared to those from ambient water showed absorption characteristics consistent with the presence of cyanobacteria. This interpretation is reinforced by available in-situ data. This study illustrates the value of high spectral and temporal resolutions in observing the spatial distribution of the algae, in identifying dominant functional groups, and in understanding the response of the algae to physical forcing.
This paper demonstrates the characterization of the water properties, bathymetry, and bottom type of the Indian River Lagoon (IRL) on the eastern coast of Florida using hyperspectral imagery. Images of this region were collected from an aircraft in July 2004 using the Portable Hyperspectral Imager for Low Light Spectroscopy (PHILLS). PHILLS is a Visible Near InfraRed (VNIR) spectrometer that was operated at an altitude of 3000 m providing 4 m resolution with 128 bands from 400 to 1000 nm. The IRL is a well studied water body that receives fresh water drainage from the Florida Everglades and also tidal driven flushing of ocean water through several outlets in the barrier islands. Ground truth measurements of the bathymetry of IRL were acquired from recent sonar and LIDAR bathymetry maps as well as water quality studies concurrent to the hyperspectral data collections. From these measurements, bottom types are known to include sea grass, various algae, and a gray mud with water depths less than 6 m over most of the lagoon. Suspended sediments are significant (~35 mg/m3) with chlorophyll levels less than 10 mg/m3 while the absorption due to Colored Dissolved Organic Matter (CDOM) is less than 1 m-1 at 440 nm. Hyperspectral data were atmospherically corrected using an NRL software package called Tafkaa and then subjected to a Look-Up Table (LUT) approach which matches hyperspectral data to calculated spectra with known values for bathymetry, suspended sediments, chlorophyll, CDOM, and bottom type.
Charles Bachmann, Timothy Donato, Robert Fusina, Richard Lathrop, Joseph Geib, Andrew Russ, Joseph Burke, Michael Bettenhausen, Jeffrey Bowles, Gia Lamela, W Rhea, Barry Truitt, John Porter
This study focuses on Coastal land cover classification from airborne hyperspectral at two sites. Our primary study area, is a chain of barrier islands, collectively known as the Virginia Coast Reserve (VCR); the second site is located in and around Barnegat Bay, NJ. At the Barnegat Bay site, hyperspectral imagery was acquired by PHILLS during a two week campaign in late July and early August. The present work examines land-cover models for PHILLS imagery subsets acquired on August 2, 2001. At the VCR site, we
have acquired an extensive time-series of PROBE2 imagery over six of the barrier islands, as well as one HyMAP scene. Multi-season models
have been developed that take advantage of seasonal differences in land-cover to improve classification accuracy. Automatic classification experiments consider roughly 20-25 categories
of land-cover at the two different sites. Categories include a variety of wetland plant species (brackish and freshwater), beach, dune, and upland plant species and plant communities. We also examine in detail detectability and accuracy of mapping invasive plant species such as Phragmites australis, which pose a particular challenge to natural resource managers.
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