Sea Grant Project R/ET-4

"Advanced Remote Sensing Techniques for Coast-Effective Monitoring of the Environmental of Ecosystems in the Delaware Bay and Adjacent Coastal Ocean"

PI: Xiao-Hai Yan, Quanan Zheng,Vic Klemas

Results Animation OBJECTIVES: The general goal of the proposed research is to introduce the powerful satellite remote sensing technology to monitoring and assessment of hydrodynamic environmental variability of Delaware Bay and adjacent coastal ocean and to provide updated and dynamic data and information for development, utilization, management, planning and decision-making regarding environment and resources in the study area. The specific objectives are summarized as follows:

To develop SAR and SeaWiFS data processing methods which are suitable for the enhancement and extraction of spatial and temporal variability of the hydrodynamic environment in Delaware Bay and adjacent coastal ocean;
To anaylze current status of hydrodynamic environment in the study area which are derived from interpretation of SAR and SeaWiFS images and combined analysis with field observations including historical and light house measurements to be proposed by other groups of scientists in this college;
To generate chlorophyll distribution maps in the study area using SeaWiFs ocean color data, to analyze characteristics of this distribution, and to examine the relation of chlorophyll concentration to levels of nitrogen and phosphorus in the sea water.
To develop the applicability of models, which quantitatively relate the bathymetry to the radar backscatter, to Delaware Bay SAR observations;
To determine dynamic processes including sea surface waves and internal waves, and to determine tide-related parameters of Delaware Bay using high resolution Radarsat time series images;
To set up algorithms and models used for inversion of the SAR signature into geophysical parameters such as effects of variation in water quality in the bay to the radar cross section which will be used for coastal upwelling interpretation observed by SAR images and SeaWiFS ocean color images;
To publish final results in refereed journals and scientific conferences in the form of paper or report.

METHODOLOGY: Spaceborne synthetic aperture radar (SAR) and SeaWiFS ocean color data will be applied to monitoring hydrodynamic environment of ecosystem in Delaware Bay and adjacent coastal ocean. The SAR is especially suited to monitoring and assessment of dynamic processes in bays, estuaries, their adjacent coastal zone and coastal ocean due to its high performance, such as all weather and time abilities, high resolution and high sensitivity to the variation in the interface between the land and the waters, and high sensitivity to the water surface processes. The SeaWiFS sensor is designed to be sensitive to the variability of water quality and suspended components and able to penetrate water to a certain depth. In order to extract the required parameters and information, data processing, interpretation, calibration, and validation are necessary procedures. For a specific problem and a specific data product, specific techniques, algorithms, and suitable models will be developed.
RATIONALE: The Delaware Bay and adjacent coastal ocean are of great value to Delawarean and regional development. Recent reports indicate, however, that pollution inevitably damages the environment in Delaware Bay and adjacent coastal ocean. This has widely been concerned by the general public. Therefore, it is the time for taking legal and technical measures to stop further worsening of the situation. As one of technical measures, collecting the dynamical data of the variability of environment using advanced monitoring techniques is of vital importance.
The hydrodynamic environment is the most basic and the most important carrier of the marine ecosystem. Previous results have demonstrated that satellite remote sensing is suited for frequently, repeatedly, and synoptically observing various hydrodynamic processes in the coastal ocean area, and that it has the potential to serve as a complement or partial replacement for traditional techniques. In this proposal, we propose a research project to develop applications of spaceborne synthetic aperture radar (SAR) and SeaWiFS ocean color data to monitoring hydrodynamic environment of ecosystem in Delaware Bay and adjacent coastal ocean. The proposed research constitutes a unique constituent for environment technology development, which programatically fits University of Delaware Sea Grant Research Priority 2. Development of Environmental Technologies for Cost Effective Marine Ecosystems Assessment and Monitoring listed in University of Delaware Sea Grant College Strategic Plan 2000-2005. The proposed research also matches local government?s responsibility and growing public concerns in ecosystem health, rebuilding fisheries, marine environmental protection, and coastal ocean management.

PROJECT RESULTS

In the first ten months of the study period, a comparative analysis between ocean color, sea surface temperature and surface winds is performed. This part of investigation focuses on satellite derived Chlorophyll-A (Chl-A), Sea Surface Temperature (SST) and meteorological observations in the southern portion of the Middle Atlantic Bight (MAB) collected between October, 1997 and September 2001. The principle objectives of this part of project are to examine the spatial and temporal variability in concentrations of Chl-A, and to investigate the relationship between Chl-A, SST, and surface wind. A notable characteristics of this study is the near contemporaneous acquisition of ocean color data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on board the SeaStar satellite and SST derived measurements from the Advance Very High Resolution Radiometer on board the NOAA-14 satellite. Preliminary results indicate the existence of at least four distinct regions. (1) The nearshore region (shoreline to 30 m depth) dominated by land margin processes, Mid-Outer Shelf (from 30 m depth to shelf break), (3) Slope Sea region (north of the mean Gulf Stream position and east of the shelf break); (4) The Gulf Stream region. As anticipated, initial analysis of the data indicates that SST and CHL-A concentrations are highly correlated in the offshore regions with the principal agent acting on the two fields being the large-scale circulation (advective) processes. Local winds appear to have only a minor influence on surface CHL-A concentrations; nor are seasonal variations strong. In the Mid-Outer Shelf region, a complex association exists between SST, CHL-A and surface winds. Rapid changes are observed and initially appear to be driven by local winds. However, advection of warm surface water from Gulf Stream Warm Core Rings and seasonal warming dramatically influences CHL-A concentrations through enhanced phytoplankton production in the vicinity of the Shelf Break. In regards to the nearshore region, while the CHL-A algorithm breaks down in Case 2 waters rendering the actual CHL-A concentrations suspect, the actual data can act as a passive surface tracer of nearshore processes. Dynamically, the nearshore region is dominated by landscape processes and local winds. Imagery reveals a variety of processes that are independent of the surface concentration field including the formation of turbidity fronts and across-shelf mass exchange. Seasonal coastal upwelling in the Delaware and New Jersey coastal ocean normally occurs during the summer months because of generally alongshore southerly wind episodes. Southerly winds force an offshore surface Ekman flow over the inner continental shelf. Colder and nutrient-rich waters from below upwell toward the surface replacing offshore-flowing surface waters. Synthetic Aperture Radar (SAR) observations from the European Remote Sensing (ERS) satellite ERS-2 before and after upwelling-favorable wind episodes in early summer 2001 along the Delaware-New Jersey coast are conducted. Lower backscatter conditions appearing in the SAR imagery after the onset of upwelling demonstrate the influence of the upwelling regime on the sea surface roughness. Satellite sea surface temperature (SST) observations and in-situ sea temperature vertical profiles confirm upwelling conditions. Three key mechanisms are suggested to explain the lower radar returns observed under upwelling conditions, an increase in the atmospheric marine boundary layer stability, an increase in the viscosity of surface waters, and the presence of biogenic surfactants in the upwelling region.

ACCOMPLISHMENTS

During this period, two journal papers supported by this project were published (Nonlinear evolution of ocean internal solitons propagating along an inhomogeneous thermocline, J. Geophys. Res. 106, 14083-14094, 2001, and Analysis of coastal lee waves observed in advanced very high-resolution radiometer images, J. Geophys. Res., 106, 7017-7025, 2001) and two additional papers were submitted for publication. The new satellite data and research results were posted on the web site of the Center for Remote Sensing which linked to the web site of the Graduate College of Marine Studies, University of Delaware. The data and research results on the web are publicly accessible.

BENEFITS The results to be derived from the proposed research, including parameters, models, algorithms, maps, images, data, information, and conclusions will be essential for understanding the evolution of hydrodynamic environment of ecosystem in Delaware Bay and adjacent coastal ocean. They will constitute a very useful information source for planning, management, decision-making, and environmental protection agencies local or federal. The results will also provide a baseline to the navigation, coastal engineering, fishery, tourism, environmental engineering, and local poultry industries. The major results will be summarized by several papers and reports, which will be published in journals and conferences. These results will also be posted on the web site of Center for Remote Sensing, College of Marine Studies, University of Delaware. The web site will be up-dated four times a year in order to include the most recent results. The web site is publicly accessible, so that the results will be helpful to the public for learning the present background and evolution of ecosystem health in Delaware Bay and adjacent coastal ocean. The academic society may use the results as references for studies of related subjects in environmental remote sensing technology as well as coastal and ocean sciences. The results will benefit other Sea Grant projects for providing critical new satellite data and advanced cost-effective monitoring techniques to the studies.

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Last modified: September 10, 2001
Xuebin Zhang --- xbzhang@newark.cms.udel.edu