Decadal Changes in Salt Marsh Succession and Assessing Salt Marsh Vulnerability using High-Resolution Hyperspectral Imagery

Change in the coastal zone is accelerating with external forcing by sea-level rise, nutrient loading, drought and over-harvest is impacting salt marshes. Understanding marsh resilience, including recovery from coastal storms and detection of stress, is essential for conservation and prediction of ecosystem services. The ‘chronosequence approach’ of predicting future state change by examining ecosystem structure and function in existing ecosystems of different ages is a powerful tool, but assumes that the past mimics the future, and time is the dominant driver of change. This approach was evaluated by replicating a 1995 salt marsh chronosequence study in back-barrier marshes ranging from 4 to \u3e170 yr old on Hog Island, Virginia. Physico-chemical properties, such as porewater redox potential and sediment organic matter and nutrients, followed predictable age-related patterns. However, invertebrate abundance, plant biomass, and sediment grain size instead seemed to respond to sea level rise and stochastic die-off and sand deposition. Thus, while time drives the intrinsic evolution of some physico-chemical components, extrinsic drivers exert a strong influence on key biotic-abiotic feedbacks. Exacerbation of external forcing may push the trajectory of marsh succession away from a predictable trajectory, limiting ecosystem services. This rapid evolution of marsh state makes the ability to detect stressors prior to marsh collapse important. Hyperspectral imagery of plants was collected in marshes of varying age/stressor characteristics, including salinity, sediment redox potential and nitrogen availability, and in the greenhouse, where environmental conditions were manipulated. Models developed to stressors based on plant spectral response were useful for salinity and nitrogen within the greenhouse or within the field, but were not transferable from lab to field. This study is an important step towards development of a remote sensing tool for tracking of ecosystem development, marsh health, and future ecosystem services

A Low-Rate Video Approach to Hyperspectral Imaging of Dynamic Scenes

The increased sensitivity of modern hyperspectral line-scanning systems has led to the development of imaging systems that can acquire each line of hyperspectral pixels at very high data rates (in the 200–400 Hz range). These data acquisition rates present an opportunity to acquire full hyperspectral scenes at rapid rates, enabling the use of traditional push-broom imaging systems as low-rate video hyperspectral imaging systems. This paper provides an overview of the design of an integrated system that produces low-rate video hyperspectral image sequences by merging a hyperspectral line scanner, operating in the visible and near infra-red, with a high-speed pan-tilt system and an integrated IMU-GPS that provides system pointing. The integrated unit is operated from atop a telescopic mast, which also allows imaging of the same surface area or objects from multiple view zenith directions, useful for bi-directional reflectance data acquisition and analysis. The telescopic mast platform also enables stereo hyperspectral image acquisition, and therefore, the ability to construct a digital elevation model of the surface. Imaging near the shoreline in a coastal setting, we provide an example of hyperspectral imagery time series acquired during a field experiment in July 2017 with our integrated system, which produced hyperspectral image sequences with 371 spectral bands, spatial dimensions of 1600 × 212, and 16 bits per pixel, every 0.67 s. A second example times series acquired during a rooftop experiment conducted on the Rochester Institute of Technology campus in August 2017 illustrates a second application, moving vehicle imaging, with 371 spectral bands, 16 bit dynamic range, and 1600 × 300 spatial dimensions every second