Timothy F. Donato

Automatic classification of land cover on Smith Island, VA, using HyMAP imagery

Automatic land cover classification maps were developed from Airborne Hyperspectral Scanner (HyMAP) imagery acquired May 8, 2000 over Smith Island, VA, a barrier island in the Virginia Coast Reserve. Both unsupervised and supervised classification approaches were used to create these products to evaluate relative merits and to develop models that would be useful to natural resource managers at higher spatial resolution than has been available previously. Ground surveys made by us in late October and early December 2000 and again in May, August, and October 2001 and May 2002 provided ground truth data for 20 land cover types. Locations of pure land cover types recorded with global positioning system (GPS) data from these surveys were used to extract spectral end-members for training and testing supervised land cover classification models. Unsupervised exploratory models were also developed using spatial-spectral windows and projection pursuit (PP), a class of algorithms suitable for extracting multimodal views of the data. PP projections were clustered by ISODATA to produce an unsupervised classification. Supervised models, which relied on the GPS data, used only spectral inputs because for some categories in particular areas, labeled data consisted of isolated single-pixel waypoints. Both approaches to the classification problem produced consistent results for some categories such as Spartina alterniflora, although there were differences for other categories. Initial models for supervised classification based on 112 HyMAP spectra, labeled in ground surveys, obtained reasonably consistent results for many of the dominant categories, with a few exceptions.

Cross-Scale Patterns in Shrub Thicket Dynamics in the Virginia Barrier Complex

A bstractTo interpret broad-scale erosion and accretion patterns and the expansion and contraction of shrub thickets in response to sea level rise for a coastal barrier system, we examined the fine-scale processes of shrub recruitment and mortality within the context of the influence of ocean current and sediment transport processes on variations in island size and location. We focused on Myrica cerifera shrub thickets, the dominant woody community on most barrier islands along the coastline of the southeastern USA. Observations suggest that M. cerifera, a salt-intolerant species, is increasing in cover throughout the Virginia barrier islands, yet rising sea level in response to climate change is increasing erosion and reducing island area. Our objective was to explain this apparent paradox using pattern–process relationships across a range of scales with a focus on ocean currents and sediment transport interacting with island characteristics at intermediate scales. Multi-decadal comparisons across scales showed a complex pattern. At the scale of the entire Virginia barrier complex, modest decreases in upland area were accompanied by large increases in shrub area. Responses were more variable for individual islands, reflecting inter-island variations in erosion and accretion due to differences in sediment transport via ocean currents. Several islands underwent dramatic shrub expansion. Only for within-island responses were there similarities in the pattern of change, with a lag-phase after initial shrub colonization followed by development of linear, closed canopy thickets. Understanding the fine-scale processes of shrub seedling establishment and thicket development, in conjunction with the influence of ocean currents and sediment transport, provides a framework for interpreting island accretion and erosion patterns and subsequent effects on shrub thicket expansion or contraction across scales of time and space.

Observations of an inshore front associated with the Chesapeake Bay outflow plume

Abstract Preliminary observations are reported of a recurring front located near Cape Henry, Virginia, USA. The front occurs on the right-hand side, looking seaward, of the buoyant plume discharging from the Chesapeake Bay and separates the plume from a band of relatively dense seawater confined against the Virginia coast. The front thus appears to be of a type similar to the inshore plume front reported by Sanders and Garvine for the Delaware Bay. Similar to an estuarine tidal intrusion front, the Cape Henry front evolves to a prominent V-shaped planform during flood tide and subduction of fluid along the front may provide a means for recirculation of near-surface material.

A credit assignment approach to fusing classifiers of multiseason hyperspectral imagery

A credit assignment approach to decision-based classifier fusion is developed and applied to the problem of land-cover classification from multiseason airborne hyperspectral imagery. For each input sample, the new method uses a smoothed estimated reliability measure (SERM) in the output domain of the classifiers. SERM requires no additional training beyond that needed to optimize the constituent classifiers in the pool, and its generalization (test) accuracy exceeds that of a number of other extant methods for classifier fusion. Hyperspectral imagery from HyMAP and PROBE2 acquired at three points in the growing season over Smith Island, VA, a barrier island in the Nature Conservancys Virginia Coast Reserve, serves as the basis for comparing SERM with other approaches.

Radar imaging of sand waves on the continental shelf east of Cape Hatteras, NC, U.S.A.

Abstract Imaging radars, under certain environmental conditions, can provide an extensive description of shallow submarine topography. In this investigation, sand waves were observed in shallow water and under light winds, weak flow, and highly stratified conditions with an L band synthetic aperture radar and X band real aperture radar. An analysis of the radar data reveals that regularly spaced modulations seen in the imagery are a result of bathymetric forcing. These modulations appear as a group of bright linear east-west trending features approximately 5 km in length and spaced 230 m apart with observed peak modulations exceeding predicted modulations by 7 dB. Bathymetric measurements extracted from shipboard ADCP data confirm the existence of sand waves in this region. Results from the ADCP data reveal an east-west orientation of the sand wave crest with lee slopes facing north. Mean wavelengths are 230 m and the heights are roughly 2.5 m. The radar modulations lead the sand wave crest, by approximately 135 m suggesting a possible upstream hydrodynamic effect, which is consistent with an observed Froude number less than one. This study shows that bathymetric effects are observed in radar imagery at low current speed, light winds, and strong stratification, demonstrating the critical nature that topographic and stratified hydrodynamic effects have on radar image interpretation in the littoral environment.

Convergence fronts in tidally forced rotating estuaries

In situ observation and remote sensing imagery reveal the presence of longitudinal velocity convergences over bathymetric channels in tidal estuaries. We present the results of numerical experiments designed to investigate the cause of these convergences for channels possessing shallow shoal regions and a deeper central region. The equations of motion for a homogeneous fluid on a rotating Earth are solved using a fully spectral code in the across-estuary (i.e., the vertical or x-z) plane, while no along-estuary flow variations (in the y direction) are permitted. A Gaussian-shaped bottom bathymetry is chosen. In the along-channel (y) direction we impose a pressure gradient which is the sum of constant and fluctuating parts to simulate the steady and tidally oscillating parts of the estuarine flow. The details of the transient response can be complicated, but we observe that for most (∼80%) of the tidal cycle there exists a cross-estuary recirculation cell colocated with a localized along-channel jet. Both of these are situated over the bottom bathymetric groove; the circulation is always clockwise when facing down current. This feature results from the generation of stream-wise vorticity through the tilting of planetary vorticity by the vertical shear of the along-estuary flow. A surface convergence-divergence pair is associated with the flow. The maximum value of each is seen to occur on the edge of the bathymetric feature but may migrate toward or away from the center as long as the current continues in the same direction. When the tide reverses, the feature reappears on the opposite shoal, and the migration of the convergence and divergence extrema begins again. We also find that the responses are qualitatively similar for all bathymetric grooves, even asymmetrically situated ones, provided that the estuary width-to-depth ratio is of order 100 or larger, the Rossby numbers are of order unity, and the Ekman layer thickness-to-channel-depth ratio is greater than ∼0.65.

The surface morphology of a coastal gravity current

The surface morphology of a coastal gravity current extending over 70 km from the mouth of the Chesapeake Bay (USA) is captured in a striking synthetic aperture radar (SAR) image, allowing comparisons to be made with recent field observations and with laboratory studies of rotating gravity currents.

A new data-driven approach to modeling coastal bathymetry from hyperspectral imagery using manifold coordinates

Recently a new approach to modeling nonlinear structure in hyperspectral imagery was introduced [Bachmann et al., 2005]. The new method is a data-driven approach which extracts a set of coordinates that directly parameterize nonlinearities present in hyperspectral imagery, both on land and in the water column. The motivation for such a parameterization and its applicability to coastal bathymetry is based on the physical expectation that in shallow waters in a region that is homogeneous in bottom type and dissolved constituents, the reflectance at any particular wavelength should decay exponentially as a function of depth. If the rate varies with wavelength, then the reflectance should best be described by a nonlinear sheet or manifold in spectral space. Other changes in the structure of the data manifold can be expected as inherent optical properties (IOP) and bottom type vary. The manifold coordinates can be used to extract information concerning the latter as well. In the present work, we compare a manifold coordinate based approach to extracting bathymetry with prior work [Maness et al., 2005] based on radiative transfer modeling; the latter defined a set of look-up tables produced by repeated execution of a radiative transfer software package known as EcoLight. Comparative results for the two approaches are presented for the same Portable Hyperspectral Imager for low-light spectroscopy (PHILLS) airborne hyperspectral scene, acquired over the Indian River Lagoon in Florida in July 2004 and described in [Maness et al., 2005].

Modeling Coastal Waters from Hyperspectral Imagery using Manifold Coordinates

In [1] [2], we introduced a direct data driven method of modeling nonlinear structure in hyperspectral imagery based on Isometric Mapping [15]. More recently, we have further improved the scaling of the approach [2], making it a practical method for large-scale hyperspectral scenes. The new method extracts a set of data manifold coordinates that directly parameterize nonlinearities present in hyperspectral imagery, both on land and in the water column. In the water column, this is particularly important because of the nonlinear, attenuating properties of the medium. In this paper, we model hyperspectral imagery acquired by the NRL PHILLS [5] at the Indian River Lagoon, Florida in July 2004. In our previous efforts [3] using a small subset of data derived from the surf zone outside of the lagoon, dominant manifold coordinates were shown to parameterize bathymetry directly with a high degree of correlation to a radiative transfer look-up table (LUT) approach. In the present work, we construct a full scene manifold coordinate representation and use this as the basis of a LUT for samples with known depths as determined by the SHOALS LIDAR. Sequestered test data presented to the manifold based LUT yield a mean estimated depth which differs from the LOAR retrieved depth by less than 0.44 m for depths between 0-10 m with a standard deviation less than 1.2 m.

Temporal analysis of synthetic aperture radar signatures in a back bay-barrier island system

We examine a 3-year sequence of SAR Imagery consisting of 30 RADARSAT frames and find a relationship between radar cross section and tide stage and bathymetry. Most notably, we observe that SAR signal intensity switches between banks within tidal channels on tide reversal.